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Home My WebLink AboutIndianhead_Arrowhead_UAA_July2006_Draft Arrowhead and Indianhead Lakes Use Attainability Analysis Prepared for Nine Mile Creek Watershed District July 2006 DRAFT 4700 West 77th Street Minneapolis, MN 55435-4803 Phone: (952) 832-2600 Fax: (952) 832-2601 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC i Executive Summary Overview This report describes the results of the Use Attainability Analysis (UAA) for Arrowhead and Indianhead Lakes in Edina, MN. The UAA provides the scientific foundation for a lake-specific best management plan that will permit maintenance or attainment of the intended beneficial uses of these lakes. The UAA is a scientific assessment of a water body’s physical, chemical, and biological condition. This study includes both a water quality assessment and prescription of protective and/or remedial measures for Arrowhead and Indianhead Lakes and their tributary watersheds. The conclusions and recommendations are based the results of intensive lake water quality monitoring in 2004, and computer simulations of land use impacts on water quality in each lake using watershed and lake models calibrated to the 2004 data set. In addition, best management practices (BMPs) were evaluated to compare their relative effect on total phosphorus concentrations and Secchi disc transparencies (i.e., water clarity). Management options were then assessed to determine attainment or non-attainment with the lake’s beneficial uses. Nine Mile Creek Watershed District Water Quality Goals The approved Nine Mile Creek Watershed District Water Management Plan (Barr, 1996) did not articulate goals for Arrowhead and Indianhead Lake. Part of this analysis process was to propose preliminary goals for each lake based on water quantity, water quality, aquatic communities, recreational-use, and wildlife. Where possible this assessment was quantified using the standardized lake rating system termed the Carlson’s Trophic State Index (TSI). This index considers the lake’s total phosphorus (TP), Chlorophyll a (Chl a) , and Secchi disc transparencies to assign a water quality index number reflecting the lake’s general fertility level. The rating system results in index values between 0 and 100, with the index value increasing with increased lake fertility. Total phosphorus, Chlorophyll a, and Secchi disc transparency are key water quality indicators for the following reasons. • Phosphorus generally controls the growth of algae in lake systems. Of all the substances needed for biological growth, phosphorus is typically the limiting nutrient. • Chlorophyll a is the main photosynthetic pigment in algae. Therefore, the amount of Chlorophyll a in the water indicates the abundance of algae present in the lake. • Secchi disc transparency is a measure of water clarity, and is inversely related to the abundance of algae. Water clarity typically determines recreational-use impairment. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC ii All three of the parameters can be used to determine a TSI. However, water transparency is typically used to develop the TSISD (trophic state index based on Secchi disc transparency) because people’s perceptions of water clarity are often directly related to recreational-use impairment. The TSI rating system results in the placement of a lake with medium fertility in the mesotrophic trophic status category. Water quality trophic status categories include oligotrophic (i.e., excellent water quality), mesotrophic (i.e., good water quality), eutrophic (i.e., poor water quality), and hypereutrophic (i.e., very poor water quality). Water quality characteristics of lakes in the various trophic status categories are listed below with their respective TSI ranges: 1. Oligotrophic – [20 < TSISD < 38] clear, low productive lakes, with total phosphorus concentrations less than or equal to 10 µg/L, Chlorophyll a concentrations of less than or equal to 2 µg/L, and Secchi disc transparencies greater than or equal to 4.6 meters (15 feet). 2. Mesotrophic – [38 < TSISD < 50] intermediately productive lakes, with total phosphorus concentrations between 10 and 25 µg/L, Chlorophyll a concentrations between 2 and 8 µg/L, and Secchi disc transparencies between 2 and 4.6 meters (6 to 15 feet). 3. Eutrophic – [50 < TSISD < 62] high productive lakes relative to a neutral level, with 25 to 57 µg/L total phosphorus, Chlorophyll a concentrations between 8 and 26 µg/L, and Secchi disc measurements between 0.85 and 2 meters (2.7 to 6 feet). 4. Hypereutrophic – [62 < TSISD < 80] extremely productive lakes which are highly eutrophic and unstable (i.e., their water quality can fluctuate on daily and seasonal basis, experience periodic anoxia and fish kills, possibly produce toxic substances, etc.) with total phosphorus concentrations greater than 57 µg/L, Chlorophyll a concentrations of greater than 26 µg/L, and Secchi disc transparencies less than 0.85 meters (2.7 feet). The NMCWD’s proposed management strategy is to “protect” both Arrowhead and Indianhead Lakes. According to the NMCWD Water Management Plan, “protect” means “to avoid significant degradation from point and nonpoint pollution sources and from wetland alterations, in order to maintain existing beneficial uses, aquatic and wetland habitats, and the level of water quality necessary to protect these uses in receiving waters.” The proposed NMCWD goals for both Arrowhead and Indianhead Lakes include the following: The Water Quantity Goal for Arrowhead and Indianhead Lakes is to provide sufficient water storage of surface runoff during a regional flood, the critical 100-year frequency storm event. This goal is attainable with no action. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC iii The recommended Water Quality Goal for both lakes is a NMCWD Level II management classification and would meet the NMCWD nondegradation policy. This level indicates that the water body fully supports water-based recreational activities, including sailboating, canoeing, hiking and picnicking, among others. This classification level does not support full body contact activity such as swimming and scuba diving. The specific NMCWD goal for Level II lakes is to achieve and maintain a TSISD between 50 and 60. This recommended goal is currently being attained by both lakes. The Aquatic Communities Goal for Arrowhead and Indianhead Lakes is to achieve a balanced ecosystem which includes a diverse growth of native aquatic macrophytes and a balanced fishery. With a NMCWD Level II classification, these lakes should fully support water-based activities including canoeing, fishing, wildlife and aesthetic viewing, and runoff management. However, primary users are limited to residents living around the lakes as there is no public access for boating or swimming uses. Therefore, the Recreational Use Goal for both Arrowhead and Indianhead Lakes is to achieve water quality that supports these functions as well as to maintain a balanced ecosystem. The Wildlife Goal for both Arrowhead and Indianhead Lakes is to protect existing beneficial wildlife uses. Lake Characteristics Arrowhead and Indianhead Lakes are located in the western portion of Edina, south of Highway 62 and east of Highway 169. Both are land-locked basins with no surface outlets and are therefore dependent on evaporation and discharge to the groundwater as outflow. Arrowhead Lake Arrowhead Lake has a water surface of approximately 22 acres, a maximum depth of approximately 7 feet, and a mean depth of 4.6 feet at an average water surface elevation of 873.9 feet. At this elevation the lake volume is approximately 96 acre-feet. The estimated natural overflow elevation is 882.5 feet. The lake is shallow and the entire lake has been classified as a littoral zone by the MDNR. In addition, it is also a polymictic lake (mixing many times per year). Indianhead Lake Indianhead Lake has a water surface of approximately 14 acres, a maximum depth of approximately 6.5 feet, and a mean depth of 4.3 feet at an average water surface elevation of 863.2 feet. At this P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC iv elevation the lake volume is approximately 61.3 acre-feet. The estimated natural overflow elevation is 882.5. The lake is shallow and is also a polymictic lake (mixing many times per year). Water Quality Problem Assessment Baseline Lake Water Quality Status The Minnesota Lake Eutrophication Analysis Procedure (MINLEAP) is intended to be used as a screening tool for estimating lake conditions and for identifying “problem” lakes. MINLEAP is particularly useful for identifying lakes requiring “protection” versus those requiring “restoration” (Heiskary and Wilson, 1990). In addition, MINLEAP modeling has been done in the past to identify Minnesota lakes which may be in better or worse condition than they “should be” based on their location, watershed area and lake basin morphometry (Heiskary and Wilson, 1990). Vighi and Chiaudani (1985) developed another method to determine the phosphorus concentration in lakes that are not affected by anthropogenic (human) inputs. As a result, the phosphorus concentration in a lake resulting from natural, background phosphorus loadings can be calculated from information about the lake’s mean depth and alkalinity or conductivity. Baseline Lake Water Quality Status for Arrowhead Lake MINLEAP modeling predicted a total phosphorus concentration of 57 μg/L for Arrowhead Lake, with a standard error of 19 μg/L. Comparison of the predicted MINLEAP concentration and observed annual average phosphorus concentration (67 µg/L) indicates that the water quality of Arrowhead Lake falls within the expected range based on its location, watershed area and lake basin morphometry. The Vighi and Chiaudani analysis predicted total phosphorus concentration from natural, background loadings should be around 30 μg/L which is more than half of the observed 2004 summer average concentration in Arrowhead Lake. Baseline Lake Water Quality Status for Indianhead Lake MINLEAP modeling suggests that the water quality in Indianhead Lake is better than expected for a lake in a developed watershed. MINLEAP predicted a total phosphorus concentration of 56 μg/L for Indianhead Lake, with a standard error of 19 μg/L. Comparison of the predicted MINLEAP concentration and observed annual average phosphorus concentration (42 µg/L) indicates that the water quality of Indianhead Lake falls within the expected range based on its location. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC v The Vighi and Chiaudani analysis predicted total phosphorus concentration from natural, background loadings should be around 23 μg/L. Observed TP concentrations in Indianhead Lake are approximately double what would be expected in a similar lake in a natural setting. Current (2004) Water Quality Arrowhead Lake Current (2004) Water Quality Looking at the water quality data collected for Arrowhead Lake during the summer of 2004, the summer average TP concentration was 72 µg/L while for Chl a, the concentration was 19 µg/L. The summer average Secchi disc transparency was 1.0 meters. Figure EX-1 summarizes the seasonal changes in concentration of TP, Chl a, and Secchi disc transparencies for Arrowhead Lake in 2004. The data are shown compared to the trophic status categories. As Figure EX-1 illustrates, the epilimnetic (surface water, i.e., 0-2 meter depth) phosphorus concentration increased from the lake’s steady-state spring concentration, assumed to be 41 µg/L observed in late-April, to the lake’s summer average concentration (72 µg/L). The increase was likely due to accumulation of phosphorus from surface runoff and internal loads to the lack of a surface outlet from the lake. The summer average values correspond to the following Carlson Trophic State Index (TSI) values of 66, 59, and 60 for TP, Chl a, and Secchi disc, respectively. This classifies Arrowhead Lake as a eutrophic/hypereutrophic lake. It should be noted that aerators in Arrowhead Lake were running during the 2004 sampling period. Indianhead Lake Current (2004) Water Quality Looking at the water quality data collected for Indianhead Lake during the summer of 2004, the summer average TP concentration was 46 µg/L while for Chl a, the concentration was 9 µg/L. The summer average Secchi disc transparency was 1.1 meters. Figure EX-2 summarizes the seasonal changes in concentration of TP, Chl a, and Secchi disc transparencies for Indianhead Lake in 2004. The data are shown compared to the trophic status categories. As Figure EX-2 illustrates, the epilimnetic (surface water, i.e., 0-2 meter depth) TP concentration increased from the lake’s steady- state spring concentration, assumed to be 24 µg/L observed in late-April, to the lake’s summer average concentration (45.8 µg/L). The increase was likely due to the accumulation of phosphorus from surface runoff. The observed summer averages translate to the following TSI values of 59, 52, and 58 for TP, Chl a, and transparency, respectively. This classifies Indianhead Lake as a eutrophic lake. It should be noted that aerators were operating in Indianhead Lake during all sampling periods. In addition, Indianhead Lake was treated with copper sulfate in May and August of 2004. Arrowhead Lake Secchi Disc Transparency 0 1 2 3 4 5 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Se c c h i D i s c ( m ) Summer Average = 0.98 m Oligotrophic Mesotrophic Eutrophic Hypereutrophic Arrowhead Lake Total Phosphorus Concentration 0 25 50 75 100 125 150 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 To t a l P h o s p h o r u s ( µµµµg/ L ) Summer Average = 72.2 µµµµg/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic Arrowhead Lake Chlorophyll-a Concentration 0 10 20 30 40 50 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Ch l o r o p h y l l - a ( µµµµg/ L ) Summer Average = 18.5 µµµµg/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic Figure EX-1 Arrowhead Lake 2004 Seasonal Changes in Total Phosphorus and Chlorophyll a Concentrations and Secchi Disc Transparency P:\23\27\634\Indianhead_Arrowhead_UAA\Data\WQData\WQ\Arrowhead Lake WQ04 Data.xls Indianhead Lake Total Phosphorus Concentrations 0 25 50 75 100 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 To t a l P h o s p h o r u s ( u g / L ) Summer Average = 45.8 ug/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic Indianhead Lake Chlorophyll-a Concentrations 0 10 20 30 40 50 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Ch l o r o p h y l l - a ( µg/ L ) Summer Average = 8.7 µµµµg/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic Indianhead Lake Secchi Disc Transparency 0 1 2 3 4 5 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Se c c h i D i s c ( m ) Summer Average = 1.1 m Oligotrophic Mesotrophic Eutrophic Hypereutrophic Figure EX-2 Indianhead Lake 2004 Seasonal Changes in Total Phosphorus and Chlorophyll a Concentrations and Secchi Disc Transparency P:\23\27\634\Indianhead_Arrowhead_UAA\Data\WQData\WQ\Indianhead Lake WQ04 Data.xls P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC viii Trend Analysis Trend analysis is a process by which changes in measured water quality indices can be evaluated as to their statistical significance; it is a way to determine whether apparent trends constitute a real decline or improvement in lake water quality. Since only one year of water quality data has been collected, a trend analysis was not able to be performed for either Arrowhead or Indianhead Lakes . Watershed Runoff Pollution Existing land use conditions were determined using land use information provided by the city of Edina. It is the same land use information that was used in the City of Edina Comprehensive Water Resources Management (Barr, 2003). During the development of the Water Resources Management Plan, this information was reclassified to incorporate right-of-way land use into the standard land use classes for modeling purposes. Because the city of Edina is fully urbanized, with less than one percent of the remaining land being developable, it was assumed that existing land use conditions in the Arrowhead and Indianhead Lakes watersheds are also representative of future conditions. Existing/future land use conditions for the Arrowhead and Indianhead Lakes watersheds can be seen in Figure EX-3. Residential land use is the major land use in both watersheds. See Figure EX-4 for a summary of the land uses within each watershed. Both of the watersheds of Arrowhead and Indianhead Lakes are part of the larger watershed to the South Fork of Nine Mile Creek. However, because both Arrowhead and Indianhead Lakes are land- locked lakes, they are only tributary to the South Fork during extreme storm events greater than the 100-year frequency storm. Natural conveyance features are limited in both watersheds as there are no perennial streams within either of the watersheds, and there are few identified wetlands. The majority of the storm water conveyance in both Arrowhead and Indianhead watersheds is through underground storm sewer pipes, sections of open channel, and a few wet and dry detention ponds. Arrowhead Lake Indianhead Lake AH_1 AH_1 AH_6 AH_6 AH_32 AH_6 AH_4AH_1 IH_1 IH_14 !;N Ba r r F o o t e r : D a t e : 7 / 1 3 / 2 0 0 6 5 : 4 9 : 3 6 P M F i l e : I : \ C l i e n t \ N m c w d \ L a k e s \ U A A \ A r r o w h e a d _ I n d i a n h e a d \ G I S \ M a p s \ F i g u r e s \ F i g u r e _ E X _ 3 . m x d U s e r : j a k 2 Figure EX-3 Arrowhead and Indianhead LakesSubwatersheds and Land Use Arrowhead and Indianhead UAA Nine Mile Creek Watershed District 750 0 750Feet Legend Land Use Natural/Park/Open Developed Parkland Agricultural High Density Residential Very Low Density Residential Low Density Residential Medium Density Residential Institutional XWXWXWXWXWXWXWXWXWXWXWXWXWXWXWGolf Course Institutional - High Imperviousness Airport Highway Commercial Industrial/Office Other Open Water Wetland Indianhead Subwatersheds Arrowhead Subwatersheds Arrowhead Lake Watershed Land Uses 178 Acres Including Lake Surface Area Institutional 0.0% Medium Density Residential 0.0% Natural/Park/Open 0.8% Very Low Density Residential 22.5% Developed Park 2.4% Highway 18.6% Institutional - High Imperviousness 3.5% Low Density Residential 38.3% Open Water 13.8% Indianhead Lake Watershed Land Uses 107 Acres Including Lake Surface Area Institutional 1.1% Low Density Residential 46.1% Very Low Density Residential 37.3% Wetland 0.9% Open Water 14.6% Figure EX-4 Watershed Current/Future Land Use Summary Arrowhead and Indianhead Lakes UAA Nine Mile Creek Watershed District P:\23\27\634\Indianhead_Arrowhead_UAA\Data\LandUse\LU_Summary.xls P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xi Arrowhead Lake Pollutant Loading For existing/future land use conditions in the Arrowhead Lake watershed, modeling simulations indicate an annual (May 2003 through April 2004) watershed total phosphorus load to Arrowhead Lake of 54 lbs, and a watershed stormwater runoff volume of 124.4 acre-feet. The water and phosphorus loads are equivalent to 6.5 inches and 0.35 lb/acre, respectively (assuming an area of 156 acres, excluding the surface area of Arrowhead Lake (22 acres)). Watershed analysis suggests that under existing conditions, watershed loading is the largest external phosphorus loading source to Arrowhead Lake, contributing approximately 74.8 percent of the lake annual phosphorus load and 67.6 percent of the annual water load (see Figure EX-5). In addition to watershed loading, the other external source of phosphorus and water loading to Arrowhead Lake is atmospheric deposition and direct precipitation. This loading source accounts for 6.8 and 32.4 percent of the annual phosphorus loading and water loading, respectively. Computer simulations and observed water quality data indicate internal phosphorus loading (likely due to die-back of Curlyleaf pondweed) is a major component of the lake’s annual phosphorus budget. Using the mass balance equation, the net internal phosphorus loading in Arrowhead Lake for 2004 was calculated to be approximately 13.3 lbs; 13 lbs likely due to Curlyleaf die-back and the remaining 0.3 lbs due to release of phosphorus from the sediment. This internal loading comprises 18.5 percent of the annual phosphorus loading to Arrowhead Lake (see Figures EX-5). Indianhead Lake Pollutant Loading For existing/future land use conditions in the Indianhead Lake watershed, modeling simulations indicate an annual (May 2003 through April 2004) watershed total phosphorus load to Indianhead Lake of 22.1 lbs, and a watershed stormwater runoff volume of 33.2 acre-feet. The water and phosphorus loads are equivalent to 4.3 inches and 0.24 lb/acre, respectively (assuming an area of 93 acres, excluding the surface area of Indianhead Lake (14 acres)). Watershed analysis suggests that under existing conditions, watershed loading is the largest external phosphorus loading source to Indianhead Lake, contributing approximately 88.2 percent of the lake annual phosphorus load and 55 percent of the annual water load (see Figure EX-6). In addition to watershed loading, the other external source of phosphorus and water loading to Arrowhead Lake is atmospheric deposition and direct precipitation. This external loading sources account for 11.4 and 45 percent of the annual phosphorus loading and water loading, respectively. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xii Computer simulations and observed water quality data indicate internal phosphorus loading is not a major component of the lake’s annual phosphorus budget. Using the mass balance equation, the net internal phosphorus loading in Indianhead Lake for 2004 was calculated to be approximately 0.1 lbs. This internal loading comprises 0.3 percent of the annual phosphorus loading to Indianhead Lake (see Figures EX-6). Arrowhead Lake Annual Water Budget (124.4 acre-ft) Model Calibration Year (May 1, 2003 to April 30, 2004) Watershed Runoff, 67.6% Direct Precipitation, 32.4% Arrowhead Lake Phophorus Budget (72.2 lbs) Model Calibration Year (May 1, 2003 to April 30, 2004) Watershed Runoff 74.8% Atmospheric Deposition 6.8% Internal Load 18.5% Figure EX-5 Arrowhead Lake Watershed Water and Phosphorus Budgets P:\23\27\634\Indianhead_Arrowhead_UAA\InLakeModel\AH\In-LakeModel_Partition6_AH_7706_Final.xls Indianhead Lake Annual Water Budget (60.4 acre-ft) Model Calibration Year (May 1, 2003 to April 30, 2004) Direct Precipitation, 45.0% Watershed Runoff 55.0% Indianhead Lake Annual Phophorus Budget (25.1 lbs) Model Calibration Year (May 1, 2003 to April 30, 2004) Watershed Runoff 88.2% Atmospheric Deposition 11.4% Internal Load 0.3% Figure EX-6 Indianhead Lake Water and Phosphorus Budgets P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xv Aquatic Macrophytes and Lake Fisheries Arrowhead Lake Macrophyte Surveys and Fisheries Information Arrowhead Lake surveys showed that macrophyte growth was limited to areas of the lake with water depths less than 5 to 6 feet, with much of the central, deeper portion of the lake containing no aquatic vegetation. Curlyleaf pondweed (Potamogeton crispus) turions were present in the lake and there was evidence that the lake was treated to kill the Curlyleaf pondweed prior to the June 2004 survey. Coontail (Ceratophyllum demersum) was observed in the lake as well, though its presence was sporadic in low densities. Other submerged macrophytes present included Eurasian watermilfoil, stonewort, white waterlily and little yellow water lily, cattail, bullrush, and blue flag iris. The pattern of macrophyte coverage seen in June was similar in August of 2004. According to MDNR’s most recent (1995) Lake Survey Report for Arrowhead Lake, a limited variety of fish were sampled during the survey. Black bullhead and green sunfish dominate the fishery in Arrowhead Lake. The report also suggests that the lake was stocked with bluegills and large mouth bass by the city of Edina in the year prior to the survey. However, review of MDNR stocking reports for the past decade suggests that Arrowhead Lake has not been stocked with any species during this period. Additionally, it was noted that Arrowhead Lake has experienced winterkill. Indianhead Lake Macrophyte Surveys and Fisheries Information Indianhead Lake macrophyte surveys showed that macrophytes were found throughout the lake, though they were less dense near the center of the lake. Many species were present in Indianhead Lake during the summer of 2004 including slender riccia, stonewort, and narrowleaf pondweed, yellow iris, cattail, bullrush, sweetflag, and arrowhead. The pattern of macrophyte coverage seen in June was similar in August of 2004 with the same species present in Indianhead Lake. It should be noted that neither Curlyleaf pondweed nor coontail were present in Indianhead Lake during the summer of 2004. There is also no MDNR fishery survey data available for Indianhead Lake. Recommended Lake and Watershed Management Practices Three types of BMPs were considered for recommendation in this plan including structural, nonstructural, and in-lake practice, though most focus was placed on structural and in-lake practices. Identifying opportunities for structural BMPs in both Indianhead and Arrowhead Lakes’ watersheds was limited as both lakes have relatively small watersheds that are almost entirely developed. Additionally, there are several existing stormwater ponds in each watershed and residential land uses P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xvi are the predominant land uses in the watersheds. There are very few undeveloped, open space/natural areas that would allow for the construction of additional water quality ponds. With regards to in-lake BMPs to address internal loading sources, the only identified internal load in either lake was the presence of Curlyleaf pondweed in Arrowhead Lake. The evaluation of 2004 water quality data for both Arrowhead and Indianhead Lakes suggests that both lakes are in fairly good condition, meeting the NMCWD Level II management class criteria for nearly all climatic conditions. Therefore, the implementation of the BMPs discussed below is necessary to protect these resources. However, if the NMCWD feels that the improvement of water quality within these two lakes is of high priority, there are several management options discussed that will improve the water quality in each lake. Additionally, it should be emphasized that the promotion of source control through the implementation of nonstructural BMPs throughout the watershed is crucial to protecting the water quality of the lakes and helps maintain the performance of the structural and in-lake practices that are currently in place or will be implemented in the future. The following is a discussion of the BMPs and recommendations for Arrowhead and Indianhead Lakes. Invasive Species Monitoring & Management We recommend that NMCWD continue to perform periodic macrophyte surveys in both Arrowhead and Indianhead Lakes to monitor the presence/growth of undesirable non-native species such as Eurasian watermilfoil and Curlyleaf pondweed. Macrophyte surveys typically cost $2000 per lake. If the NMCWD feels that management of the non-native macrophyte species (Eurasian watermilfoil and Curlyleaf pondweed) present in Arrowhead Lake is of high priority, these macrophytes can be successfully managed by herbicides, mechanical harvesting, a winter drawdown of lake levels, or a combination of these methods. Modeling suggests that about 20 percent of the phosphorus load in Arrowhead Lake is the result of phosphorus release from the die-back of Curlyleaf pondweed, so a reduction in the coverage and density of Curlyleaf pondweed will help improve the water quality of Arrowhead Lake (See Table EX-1; Figure EX-8). Results show that a reduction in the Curlyleaf pondweed coverage would reduce summer average total phosphorus concentrations to levels that would meet the proposed MPCA shallow lake criteria ([TP] < 60 µg/L) in all climatic scenarios except during wet conditions. Estimated costs for the Curlyleaf pondweed management options varies and are summarized in Table EX-1 and Figure EX-8. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xvii Copper Sulfate Treatments in Indianhead Lake Copper sulfate is typically not considered a means of as a means of controlling phosphorus in lakes because it is a temporary solution that does not reduce the source of the nutrient loading to the lake. However, during the summer of 2004, there were two applications of copper sulfate to Indianhead Lake per the request of the lake homeowners’ association. Water quality data and modeling suggest that there was an improvement in lake water quality due to these treatments. However, there is only one year of water quality data so the impact directly related to the copper sulfate treatments was not quantified exactly. The estimated cost per application of copper sulfate is $550. Aeration There are several submerged aerators operating continuously throughout the year in both Arrowhead and Indianhead Lakes. These were installed more than a decade ago for the lake homeowners’ association. These were operating during the 2004 water quality sampling period and may have influenced the observed water quality. However, because only one year of data is available for both lakes, we are unable to determine the impact the aerators have on the overall water quality of each lake. Additional Recommendations The in-lake models developed for Arrowhead and Indianhead Lakes are based on calibration of the of water quality data collected in 2004. However, models were unable to be verified due to having only one year of water quality data. If the NMCWD should decide to continue with a water quality monitoring program in these lakes, it is recommended that the aerators in both lakes be turned off during the sampling season. Additionally, any sort of chemical treatment should not be used during this monitoring period. The use of aerators and chemical treatments appears to alter the water quality of the lake and does not provide insight to the actual baseline water quality status of the water body. The monitoring should follow the same protocol as the 2004 sampling period, monitoring various water quality parameters as well as phytoplankton and zooplankton communities. A fishery survey would also be recommended for Indianhead Lake as there is currently no information available for the fishery. Public Participation It is a general NMCWD goal to encourage public participation in all NMCWD activities and decisions that may affect the public. In accordance with this goal, the NMCWD seeks to involve the public in the discussion of this UAA. This goal is expected to be achieved through a public meeting to obtain comments on the Arrowhead and Indianhead UAA. TP C H L a SD T P C H L a SD T P C H L a SD T P C H L a SD (µµµµg/ L ) (µµµµg/ L ) (m ) (µµµµg/ L ) (µµµµg/ L ) (m ) (µµµµg/ L ) (µµµµg/ L ) (m ) (µµµµg/ L ) (µµµµg/ L ) (m) 1 Ex i s t i n g ( 2 0 0 4 ) C o n d i t i o n s 2 - N o B M P s 68 . 8 2 0 . 4 1 . 0 6 0 6 6 . 6 2 1 . 1 1 . 0 6 0 9 1 . 2 2 8 . 6 0 . 9 6 2 7 2 . 2 1 8 . 5 1 . 0 60 -- 2 In s t a l l a t i o n o f N U R P P o n d A H _ 1 a 68 . 4 2 0 . 2 1 . 0 6 0 6 6 . 1 2 1 . 0 1 . 0 6 0 9 0 . 9 2 8 . 5 0 . 9 6 2 7 1 . 8 1 8 . 5 1 . 0 60 $106,930 3a Cu r l y l e a f P o n d w e e d M a n a g e m e n t - 1 5 % o f L i t t o r a l A r e a Tr e a t e d w i t h H e r b i c i d e 60 . 0 1 8 . 2 1 . 0 6 0 5 9 . 8 1 8 . 1 1 . 0 5 9 8 4 . 2 2 6 . 3 0 . 9 6 1 6 5 . 6 2 0 . 1 1 . 0 60 $1,300 3b Cu r l y l e a f P o n d w e e d M a n a g e m e n t - 5 0 % o f L i t t o r a l A r e a Tr e a t e d w i t h H e r b i c i d e 39 . 8 1 1 . 7 1 . 1 5 8 4 3 . 8 1 3 . 0 1 . 1 5 8 6 7 . 8 2 0 . 8 1 . 0 6 0 5 0 . 0 1 5 . 0 1 . 1 59 $4,200 3c Cu r l y l e a f P o n d w e e d M a n a g e m e n t - 5 0 % o f L i t t o r a l A r e a Tr e a t e d w i t h M e c h a n i c a l H a r v e s t i n g 50 . 6 1 5 . 2 1 . 1 5 9 5 2 . 4 1 5 . 7 1 . 1 5 9 7 6 . 6 2 3 . 7 1 . 0 6 1 5 8 . 4 1 7 . 7 1 . 0 59 $6,700 3d Cu r l y l e a f P o n d w e e d M a n a g e m e n t - W i n t e r D r a w d o w n 39 . 8 11 . 7 1. 1 58 43 . 8 13 . 0 1. 1 58 67 . 8 20 . 8 1. 0 60 50 . 0 15 . 0 1.1 59 $4,500 1 N o B M P s 44 . 9 8 . 1 1 . 1 5 8 5 5 . 0 1 0 . 1 1 . 0 6 0 9 8 . 6 1 9 . 3 0 . 7 6 6 7 7 . 1 1 4 . 7 0 . 8 63 -- 2 Ex i s t i n g ( 2 0 0 4 ) C o n d i t i o n s - C o p p e r S u l f a t e T r e a t m e n t s in M a y a n d A u g u s t 2 , 3 14 . 5 2 . 3 1 . 8 5 2 2 3 . 5 4 . 0 1 . 5 5 4 6 7 . 3 1 2 . 7 0 . 9 6 2 4 5 . 8 8 . 7 1 . 1 58 $1,100 Ta b l e E X - 1 Be n e f i t s a n d C o s t s o f A s s e s s e d B M P S c e n a r i o s f o r A r r o w h e a d a n d I n d i a n h e a d L a k e s 2 - F o r b o t h A r r o w h e a d a n d I n d i a n h e a d L a k e s , m o d e l c a l i b r a t i o n i n c l u d e s t h e i m p a c t o f t h e a e r a t o r s o n t h e i n - l a k e w a t e r q u a l i t y t h a t w e r e o p e r a t i n g d u r i n g t h e 2 0 0 4 s a m p l i n g s e a s o n . 1 - F o r D r y C l i m a t i c C o n d i t i o n s , t h e 1 0 - i n c h s u p e r s t o r m o n 7 / 2 3 / 1 9 8 7 w a s r e m o v e d d u e t o t h e r a r i t y o f t h e e v e n t Su m m e r A v e r a g e Su m m e r A v e r a g e Su m m e r A v e r a g e Su m m e r A v e r a g e Be s t M a n a g e m e n t P r a c t i c e ( B M P ) S t r a t e g y Ar r o w h e a d L a k e TS I SD TSI SD 3 - T h e r e w e r e 2 a p p l i c a t i o n s o f C o p p e r S u l f a t e t o I n d i a n h e a d L a k e d u r i n g 2 0 0 4 . M o d e l s w e r e c a l i b r a t e d t o t h e a c t u a l w a t e r q u a l i t y d a t a w h i c h i s f o u n d i n S c e n a r i o 2 f o r I n d i a n h e a d L a k e . S c e n a r i o 1 - E x i s t i n g c o n d i t i o n w a t e r q u a i l t y v a l u e s w e r e e s t i m a t e d f r o m t h e m o d e l c a l i b r a t e d t o t h e c o p p e r s u l f a t e i m p a c t e d w a t e r q u a l i t y d a t a . In d i a n h e a d L a k e Dr y C l i m a t i c C o n d i t i o n s ( 1 9 8 7 - 8 8 ) 1 Av e r a g e C l i m a t i c C o n d i t i o n s ( 1 9 9 4 - 9 5 ) Sc e n a r i o Nu m b e r TS I SD TS I SD We t C l i m a t i c C o n d i t i o n s ( 2 0 0 1 - 2 0 0 2 ) C a l i b r a t i o n C l i m a t i c C o n d i t i o n s ( 2 0 0 3 - 0 4 ) Estimated Cost ($) P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ I n L a k e S u m m a r y . x l s IH_1 IH_14 AH_1 AH_1 AH_6 AH_6 AH_32 AH_4 AH_6 AH_1a AH_1 !;N Ba r r F o o t e r : D a t e : 7 / 1 3 / 2 0 0 6 7 : 0 2 : 5 6 P M F i l e : I : \ C l i e n t \ N m c w d \ L a k e s \ U A A \ A r r o w h e a d _ I n d i a n h e a d \ G I S \ M a p s \ F i g u r e s \ F i g u r e _ E X _ 7 . m x d U s e r : j a k 2 625 0 625Feet Legend Arrowhead Lake Watersheds Indianhead Lake Watersheds ^_Structural BMPs In-Lake BMPs Figure EX-7 Arrowhead and Indianhead Lakes Potential BMP Locations Arrowhead and Indianhead Lakes UAANine Mile Creek Watershed District In-Lake BMP: Curlyleaf Pondweed Management In-Lake BMP: Copper Sulfate Treatments Structural BMP: Addition of NURP Pond AH_1a Indianhead Lake Arrowhead Lake P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ I n L a k e S u m m a r y . x l s Fi g u r e E X - 8 Ar r o w h e a d L a k e : E s t i m a t e d S u m m e r A v e r a g e T o t a l P h o s p h o r u s C o n c e n t r a t i o n Fo l l o w i n g B M P I m p l e m e n t a t i o n 020406080 10 0 12 0 1 2 3a 3b 3c 3d BM P S c e n a r i o T o t a l P h o s p h o r u s C o n c e n t r a t i o n ( µ µ µ µ g / L ) $0$20,000$40,000$60,000$80,000$100,000$120,000 Estimated Cost ($) BM P C o s t 19 8 7 - 8 8 D r y C o n d i t i o n 19 9 4 - 9 5 A v e r a g e C o n d i t i o n 20 0 1 - 0 2 W e t C o n d i t i o n 20 0 3 - 0 4 C a l i b r a t i o n C o n d i t i o n BM P L e g e n d Op t i o n 1 E x i s t i n g ( 2 0 0 4 ) C o n d i t i o n s - N o B M P s Op t i o n 2 A d d i t i o n o f N U R P P o n d A H _ 1 a Op t i o n 3 a Cu r l y l e a f P o n d w e e d M a n a g e m e n t - He r b i c i d e T r e a t m e n t ( 1 5 % L i t t o r a l A r e a ) Op t i o n 3 b Cu r l y l e a f P o n d w e e d M a n a g e m e n t - He r b i c i d e T r e a t m e n t ( 5 0 % L i t t o r a l A r e a ) Op t i o n 3 c Cu r l y l e a f P o n d w e e d M a n a g e m e n t - Me c h a n i c a l H a r v e s t i n g ( 5 0 % L i t t o r a l A r e a ) Op t i o n 3 d Cu r l y l e a f P o n d w e e d M a n a g e m e n t - W i n t e r Dr a w d o w n MP C A P r o p o s e d S h a l l o w L a k e C r i t e r i a [T P ] < 6 0 µg/ L NM C W D ' s P r o p o s e d W a t e r Q u a l i t y G o a l U p p e r L i m i t o f L e v e l I I C l a s s i f i c a t i o n [T P ] < 7 5 µg/L 20 0 4 O b s e r v e d S u m m e r A v e r a g e P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ I n L a k e S u m m a r y . x l s Fi g u r e E X - 9 In d i a n h e a d L a k e : E s t i m a t e d S u m m e r A v e r a g e T o t a l P h o s p h o r u s C o n c e n t r a t i o n Fo l l o w i n g B M P I m p l e m e n t a t i o n 020406080 10 0 12 0 1 2 BM P S c e n a r i o T o t a l P h o s p h o r u s C o n c e n t r a t i o n ( µ µ µ µ g / L ) $0$200$400$600$800$1,000$1,200 Estimated Cost ($) BM P C o s t 19 8 7 - 8 8 D r y C o n d i t i o n 19 9 4 - 9 5 A v e r a g e C o n d i t i o n 20 0 1 - 0 2 W e t C o n d i t i o n 20 0 3 - 0 4 C a l i b r a t i o n C o n d i t i o n MP C A P r o p o s e d S h a l l o w L a k e C r i t e r i a [T P ] < 6 0 µg/ L NM C W D ' s P r o p o s e d W a t e r Q u a l i t y G o a l U p p e r L i m i t o f L e v e l I I C l a s s i f i c a t i o n [T P ] < 7 5 µg/ L 20 0 4 O b s e r v e d S u m m e r A v e r a g e BM P L e g e n d Op t i o n 1 N o B M P s Op t i o n 2 Ex i s t i n g ( 2 0 0 4 ) C o n d i t i o n s - C o p p e r S u l f a t e Tr e a t m e n t s i n M a y a n d A u g u s t P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxii Arrowhead and Indianhead Lakes Use Attainability Analyses Table of Contents Executive Summary ....................................................................................................................................... i Overview ................................................................................................................................................ i Nine Mile Creek Watershed District Water Quality Goals .................................................................... i Lake Characteristics ............................................................................................................................. iii Arrowhead Lake ........................................................................................................................ iii Indianhead Lake......................................................................................................................... iii Water Quality Problem Assessment ..................................................................................................... iv Baseline Lake Water Quality Status .......................................................................................... iv Baseline Lake Water Quality Status for Arrowhead Lake ........................................... iv Baseline Lake Water Quality Status for Indianhead Lake ............................................ iv Current (2004) Water Quality ..................................................................................................... v Arrowhead Lake Current (2004) Water Quality ............................................................ v Indianhead Lake Current (2004) Water Quality ............................................................ v Trend Analysis ......................................................................................................................... viii Watershed Runoff Pollution .................................................................................................... viii Arrowhead Lake Pollutant Loading .............................................................................. xi Indianhead Lake Pollutant Loading .............................................................................. xi Aquatic Macrophytes and Lake Fisheries ........................................................................................... xv Arrowhead Lake Macrophyte Surveys and Fisheries Information .............................. xv Indianhead Lake Macrophyte Surveys and Fisheries Information .............................. xv Recommended Lake and Watershed Management Practices .............................................................. xv Invasive Species Monitoring & Management ......................................................................... xvi Copper Sulfate Treatments in Indianhead Lake ..................................................................... xvii Aeration .................................................................................................................................. xvii Additional Recommendations ................................................................................................ xvii Public Participation ................................................................................................................. xvii 1.0 Introduction ............................................................................................................................................ 1 1.1 Purpose and Process of the UAA ................................................................................................ 1 1.2 Watershed and Lake Water Quality Modeling Tools ................................................................. 1 1.3 Joint Consideration of Arrowhead and Indianhead Lakes .......................................................... 3 1.4 Scope ........................................................................................................................................... 3 1.5 General Framework of the UAA ................................................................................................. 3 1.5.1 Identification of Goals and Expectations ....................................................................... 3 1.5.2 Assessment of Current Conditions ................................................................................. 6 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxiii 1.5.3 Assessment of Future Conditions .................................................................................. 6 1.5.4 Evaluation of Management Strategies ........................................................................... 6 2.0 General Concepts in Lake Water Quality .............................................................................................. 7 2.1 Eutrophication ............................................................................................................................. 7 2.2 Trophic States ............................................................................................................................. 7 2.3 Limiting Nutrients ....................................................................................................................... 8 2.4 Stratification ................................................................................................................................ 9 2.5 Nutrient Recycling and Internal Loading .................................................................................. 10 3.0 Identification of Goals and Expectations ............................................................................................. 12 3.1 NMCWD Goals for Arrowhead and Indianhead Lakes ............................................................ 12 3.1.1 Water Quantity Goal .................................................................................................... 12 3.1.2 Water Quality Goal ...................................................................................................... 12 3.1.3 Aquatic Communities Goal .......................................................................................... 12 3.1.4 Recreational-Use Goal ................................................................................................. 13 3.1.5 Wildlife Goal ............................................................................................................... 13 3.2 Expected Benefits of Water Quality Improvements ................................................................. 13 3.2.1 Enhancement of Recreational Use ............................................................................... 13 3.2.2 Improvements in Aquatic Habitat ................................................................................ 14 4.0 Lake Basin and Watershed Characteristics .......................................................................................... 15 4.1 Lake Basin Characteristics ........................................................................................................ 15 4.1.1 Arrowhead Lake ........................................................................................................... 15 4.1.2 Indianhead Lake ........................................................................................................... 18 4.2 Watershed Characteristics ......................................................................................................... 21 4.2.1 Present Land Use ........................................................................................................ 21 4.2.1.1 Arrowhead Lake Land Use .......................................................................... 21 4.2.1.2 Indianhead Lake Land Use ........................................................................... 22 4.2.2 Future Land Use .......................................................................................................... 22 4.3 Lake Inflows and Drainage Areas ............................................................................................. 22 4.3.1 Natural Conveyance Systems....................................................................................... 22 4.3.2 Stormwater Conveyance Systems ................................................................................ 23 5.0 Existing Water Quality ........................................................................................................................ 27 5.1 Water Quality ............................................................................................................................ 27 5.1.1 Data Collection ............................................................................................................ 27 5.1.1.1 Arrowhead Lake Water Quality Data ........................................................... 27 5.1.1.2 Indianhead Lake Water Quality Data ........................................................... 28 5.1.2 Baseline/Current Water Quality ................................................................................... 32 5.1.2.1 Baseline Lake Water Quality Status for Arrowhead Lake ........................... 33 5.1.2.2 Baseline Lake Water Quality Status for Indianhead Lake ........................... 33 5.1.2.3 Arrowhead Lake Current (2004) Water Quality .......................................... 34 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxiv 5.1.2.4 Indianhead Lake Current (2004) Water Quality ........................................... 35 5.2 Nutrient Loading ....................................................................................................................... 36 5.2.1 External Loads ............................................................................................................. 37 5.2.1.1 Arrowhead Lake External Loads .................................................................. 37 5.2.1.2 Indianhead Lake External Loads .................................................................. 37 5.2.2 Internal Loads .............................................................................................................. 40 5.2.2.1 Arrowhead Lake Internal Load .................................................................... 40 5.2.2.2 Indianhead Lake Internal Load..................................................................... 40 5.3 Aquatic Communities ............................................................................................................... 41 5.3.1 Phytoplankton .............................................................................................................. 41 5.3.1.1 Arrowhead Lake Phytoplankton Surveys ..................................................... 41 5.3.1.2 Indianhead Lake Phytoplankton Surveys ..................................................... 42 5.3.2 Zooplankton ................................................................................................................. 45 5.3.2.1 Arrowhead Lake Zooplankton Surveys ........................................................ 45 5.3.2.2 Indianhead Lake Zooplankton Surveys ........................................................... 46 5.3.3 Macrophytes ................................................................................................................. 49 5.3.3.1 Arrowhead Lake Macrophyte Surveys ......................................................... 49 5.3.3.2 Indianhead Lake Macrophyte Surveys ......................................................... 50 5.3.4 Fish and Wildlife.......................................................................................................... 51 5.3.4.1 Arrowhead Lake Fish and Wildlife Surveys ................................................ 51 5.3.4.2 Indianhead Lake Fish and Wildlife Surveys ................................................ 51 6.0 Water Quality Modeling for the UAA ................................................................................................. 53 6.1 Use of the P8 Model ................................................................................................................. 53 6.2 Water Quality Model (P8) Calibration ...................................................................................... 54 6.2.1 Stormwater Volume Calibration .................................................................................. 54 6.2.1.1 Arrowhead Lake Stormwater Volume Calibration ...................................... 54 6.2.1.2 Indianhead Lake Stormwater Volume Calibration ....................................... 54 6.2.2 Phosphorus Loading ..................................................................................................... 55 6.2.3 Atmospheric Deposition .............................................................................................. 55 6.3 In-Lake Modeling ..................................................................................................................... 60 6.3.1 Balance Modeling to Existing Water Quality .............................................................. 60 6.3.2 Accounting for Internal Loading.................................................................................. 61 6.3.3 In-Lake Modeling Results ............................................................................................ 62 6.3.4 Existing (2004) Land Use Conditions (Model Calibration) ......................................... 62 6.4 Use of the P8/In-lake Model ..................................................................................................... 65 6.5 Modeling Chlorophyll a and Secchi Disc Transparency .......................................................... 65 7.0 Climatic Condition Analysis ................................................................................................................ 70 7.1 Future Conditions Modeling Assumptions ............................................................................... 70 7.2 Modeling Results ...................................................................................................................... 70 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxv 7.2.1 Water Quality Model Results for Arrowhead Lake ..................................................... 70 7.2.2 Water Quality Model Results for Indianhead Lake ..................................................... 71 8.0 Evaluation of Possible Management Options ......................................................................................... 74 8.1 General Discussion of Improvement Options ........................................................................... 74 8.1.1 Structural BMPs ........................................................................................................... 74 8.1.1.1 Wet Detention Ponds .................................................................................... 76 8.1.1.2 Infiltration .................................................................................................... 77 8.1.1.3 Vegetated Buffer Strips ................................................................................ 78 8.1.1.4 Oil and Grit Separators ................................................................................. 78 8.1.2 Nonstructural BMPs ..................................................................................................... 79 8.1.2.1 Public Education .......................................................................................... 79 8.1.2.2 Ordinances .................................................................................................... 79 8.1.2.3 Street Sweeping ............................................................................................ 80 8.1.2.4 Deterrence of Waterfowl .............................................................................. 80 8.1.3 In-Lake BMPs .............................................................................................................. 81 8.1.3.1 Winter Drawdown ........................................................................................ 81 8.1.3.2 Mechanical Harvesting ................................................................................. 81 8.1.3.3 Application of Herbicides ............................................................................ 82 8.1.3.4 Application of Copper Sulfate ...................................................................... 83 8.1.3.5 Diffused Aeration ......................................................................................... 83 8.2 Feasibility Analysis ................................................................................................................... 84 8.2.1 Statement of Problem for Arrowhead Lake ................................................................. 84 8.2.2 Statement of Problem for Indianhead Lake ................................................................. 85 8.2.3 Selection and Effectiveness of Alternatives ................................................................. 87 8.2.3.1 Site-Specific Structural BMPs ..................................................................... 87 8.2.3.1.1 Construction of Wet Detention Pond AH_1a in the Arrowhead Lake Watershed (AH_1a) to treat Parking Lot Runoff ................................. 87 8.2.3.2 In-Lake Treatments ...................................................................................... 90 8.2.3.2.1 Copper Sulfate Treatment in Indianhead Lake .......................... 90 8.2.3.2.2 Aquatic Plant Management in Arrowhead Lake ........................ 91 8.2.3.2.3 Aeration in Arrowhead and Indianhead Lakes .......................... 93 9.0 Discussion and Recommendations....................................................................................................... 94 9.1 Attainment of Stated Goals ....................................................................................................... 94 9.1.1 Water Quantity Goal .................................................................................................... 94 9.1.2 Water Quality Goal ...................................................................................................... 94 9.1.2.1 Arrowhead Water Quality Goal ................................................................... 94 9.1.2.2 Indianhead Water Quality Goal .................................................................... 95 9.1.3 Aquatic Communities Goal .......................................................................................... 97 9.1.4 Recreational-Use Goal ................................................................................................. 98 9.1.5 Wildlife Goal ............................................................................................................... 98 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxvi 9.2 Recommendations ................................................................................................................... 101 9.2.1 Invasive Species Monitoring & Management ............................................................ 101 9.2.2 Copper Sulfate Treatments in Indianhead Lake ......................................................... 101 9.2.3 Aeration ..................................................................................................................... 102 9.2.4 Additional Recommendations .................................................................................... 102 9.2.5 Public Participation .................................................................................................... 102 References ................................................................................................................................................. 103 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxvii List of Tables Table EX-1 Benefits and Costs of Assessed BMP Options for Arrowhead and Indianhead Lakesxviii Table 1-1 Arrowhead and Indianhead Lakes Management Table. Water quality conditions and goals, recreational-uses and management strategy, referencing Carlson’s Trophic State index (TSI) values (Secchi disc transparency basis) .......................................... 5 Table 4-1 Stage-Storage-Discharge Relationship for Arrowhead Lake ..................................... 16 Table 4-2 Stage-Storage-Discharge Relationship for Indianhead Lake ..................................... 19 Table 5-1 Arrowhead Lake 2004 Water Quality Data .............................................................. 28 Table 5-2 Indianhead Lake Water Quality Data ....................................................................... 28 Table 6-1 Precipitation Amounts and Hydrologic Residence Time for Various Climatic Conditions used for Modeling Water and TP Loading to Arrowhead and Indianhead Lakes ...................................................................................................................... 65 Table 7-1 Watershed Total Phosphorus Loading to Arrowhead and Indianhead Lakes for Various Climatic Conditions .................................................................................... 71 Table 8-1 General Effectiveness of Stormwater BMPs at Removing Common Pollutants from Runoff ..................................................................................................................... 75 Table 8-2 Arrowhead and Indianhead Lakes Predicted Total Phosphorus and Chlorophyll a Concentrations, Secchi Disc Transparency, and TSISD for All Management Alternatives Analyzed ............................................................................................. 86 Table 8-3 Arrowhead Lake UAA MPCA/NURP Wet Detention Volume (Required per MPCA/NURP) for Pond AH_1a .............................................................................. 89 Table 8-4 Arrowhead Lake External Total Phosphorus Loading Reduction with the Construction of Pond AH-1a ........................................................................................................ 90 Table 9-1 Arrowhead and Indianhead Lakes Management Table. Water quality, recreational- use and ecological classifications of, and management philosophies for Arrowhead and Indianhead Lakes, referencing Carlson’s Trophic State index (TSI) values (Secchi disc transparency basis) .............................................................................. 96 Table 9-2 NMCWD Water Quality Management Goals ........................................................... 97 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxviii List of Figures Figure EX-1 Arrowhead Lake 2004 Seasonal Changes in Total Phosphorus and Chlorophyll a Concentration and Secchi Disc Transparency ............................................................vi Figure EX-2 Indianhead 2004 Seasonal Changes in Total Phosphorus and Chlorophyll a Concentration and Secchi Disc Transparency .......................................................... vii Figure EX-3 Arrowhead and Indianhead UAA Subwatersheds and Existing Land Use—Nine Mile Creek Watershed District ..........................................................................................ix Figure EX-4 Arrowhead and Indianhead Lakes Watershed Land Uses............................................ x Figure EX-5 Arrowhead Lake Watershed Phosphorus and Water Budgets .................................. xiii Figure EX-6 Indianhead Lake Watershed Phosphorus and Water Budgets ................................... xiv Figure EX-7 Arrowhead and Indianhead Lakes UAA Location of Potential BMPs - Nine Mile Creek Watershed District ........................................................................................ xix Figure EX-8 Arrowhead Lake: Estimated Summer Average Total Phosphorus Concentration Following BMP Implementation and BMP Cost ...................................................... xx Figure EX-9 Indianhead Lake: Estimated Summer Average Total Phosphorus Concentration Following BMP Implementation and BMP Cost ..................................................... xxi Figure 4-1 Arrowhead Lake Approximate Bathymetry .............................................................. 17 Figure 4-2 Indianhead Lake Approximate Bathymetry .............................................................. 20 Figure 4-3 Arrowhead and Indianhead Lakes – Watershed Land Uses ....................................... 24 Figure 4-4 Arrowhead and Indianhead Summary of Land Uses ................................................. 25 Figure 4-5 Arrowhead and Indianhead Drainage and Stormsewer Systems ................................ 26 Figure 5-1 Arrowhead Lake 2004 Seasonal Changes in Concentration of Total Phosphorus, Chlorophyll a and Secchi Disc Transparencies ........................................................ 30 Figure 5-2 Indianhead Lake 2004 Seasonal Changes in Concentration of Total Phosphorus, Chlorophyll a and Secchi Disc Transparencies ........................................................ 31 Figure 5-3 Arrowhead Lake Watershed Water and Phosphorus Budgets .................................... 38 Figure 5-4 Indianhead Lake Watershed Water and Phosphorus Budgets .................................... 39 Figure 5-5 Arrowhead Lake Phytoplankton Surveys, Data Summary by Division ...................... 43 Figure 5-6 Indianhead Lake Phytoplankton Surveys, Data Summary by Division ...................... 44 Figure 5-7 Arrowhead 2004 Zooplankton Surveys, Data Summary by Division ........................ 47 Figure 5-8 Indianhead 2004 Zooplankton Surveys, Data Summary by Division ........................ 48 Figure 6-1 Arrowhead Lake Water Balance Modeling Results .................................................. 56 Figure 6-2 Arrowhead Lake Water Balance Modeling Results, Predicted versus Observed Lake Levels ..................................................................................................................... 57 Figure 6-3 Indianhead Lake Water Balance Modeling Results .................................................. 58 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC xxix Figure 6-4 Indianhead Lake Water Balance Modeling Results, Predicted versus Observed Lake Levels ..................................................................................................................... 59 Figure 6-5 Arrowhead Lake UAA. In-Lake Model Calibration Results for 2004 Climatic Conditions ............................................................................................................... 63 Figure 6-6 Indianhead Lake UAA. In-Lake Model Calibration Results for 2004 Climatic Conditions ............................................................................................................... 64 Figure 6-7 Arrowhead Lake Relationship between Total Phosphorus Concentration, Chlorophyll a Concentration, and Secchi Disc Transparency ................................... 68 Figure 6-8 Indianhead Lake Relationship between Total Phosphorus Concentration, Chlorophyll a Concentration, and Secchi Disc Transparency ................................... 69 Figure 7-1 Arrowhead Lake Estimated Average Summer Total Phosphorus and Chlorophyll a Concentrations and Transparency for Existing Conditions under Varying Climatic Scenarios ................................................................................................................. 72 Figure 7-2 Indianhead Lake Estimated Average Summer Total Phosphorus and Chlorophyll a Concentrations and Transparency for Existing Conditions under Varying Climatic Scenarios ................................................................................................................. 73 Figure 8-1 Location of Potential BMP Options for Arrowhead and Indianhead Lakes ............... 88 Figure 9-1 Arrowhead Lake: Estimated Summer Average Total Phosphorus Concentration Following BMP Implementation and BMP Cost ...................................................... 99 Figure 9-2 Indianhead Lake: Estimated Summer Average Total Phosphorus Concentration Following BMP Implementation and BMP Cost .................................................... 100 List of Appendices Appendix A Data Collection Methods Appendix B Arrowhead and Indianhead Lakes 2004 Macrophyte Surveys Appendix C Pond Data Appendix D Arrowhead and Indianhead Lakes 2004 Water Quality Data Appendix E Arrowhead and Indianhead Lakes Biological and Fisheries Data Appendix F BMP Cost Estimates 1.0 Introduction This report details the results of a Use Attainability Analysis (UAA) of Arrowhead and Indianhead Lakes. The UAA is a structured scientific assessment of the chemical, physical, and biological conditions in a water body. The analysis includes diagnosis of the causes of observed problems and prescription of alternative remedial measures intended to result in the attainment of intended beneficial uses of Arrowhead and Indianhead Lakes. The analysis is based on the results of a 2004 lake water quality monitoring program and computer simulations of watershed runoff calibrated to those 2004 data sets. NMCWD water quality goals have not been established yet for these lakes based on their beneficial uses (e.g., swimming and fishing). Therefore, part of this study was to determine reasonable and attainable water quality goals for each of these lakes as well as evaluate management options to determine attainment or non-attainment of the lake’s beneficial uses. 1.1 Purpose and Process of the UAA The intent of the UAA is to provide a means by which the effects of various watershed and lake management strategies can be evaluated. To evaluate management strategies, it is first necessary to identify the intended uses of the lake in question. With these uses in mind, appropriate water quality goals for the lake can be established and reviewed. Once the intended uses and corresponding goals for the lake have been identified, it becomes possible to evaluate lake and watershed management strategies. The UAA uses a watershed runoff model and a lake water quality model; the lake water quality model predicts changes in lake water quality based on the results of the watershed runoff model. Using these models, various watershed and lake management strategies can be evaluated to determine their likely effects on the lake. The resulting lake water quality can then be compared with the water quality goals for the lake to see if the management strategies are able to produce the desired changes in the lake. Using the tools of the UAA, the cost-effectiveness of the management strategies can also be evaluated. 1.2 Watershed and Lake Water Quality Modeling Tools Central to the water quality analysis is the use of a water quality model that predicts the amount of pollutants that reach a lake via stormwater runoff. During development of the Nine Mile Creek Watershed District’s Water Management Plan (Barr, 1996), a simplified model using literature-based export rate coefficients was used to estimate the annual water and phosphorus loads to the lake. The P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 2 1996 Plan recommended using the water quality model XP-SWMM (the EPA’s Stormwater and Wastewater Management Model with a graphical interface by XP Software) in the UAA to provide a more precise estimate of water and phosphorus loads. Since the P8 model (Program for Predicting Polluting Particle Passage through Pits, Puddles and Ponds; IEP, Inc., 1990) is less data intense and provides similar predictions of phosphorus loads to a lake as XP-SWMM, this UAA uses the P8 model instead. The P8 model requires hourly precipitation and daily temperature data; long-term climatic data can be used so that watersheds and BMPs can be evaluated for varying hydrologic conditions. To properly develop and calibrate the model also requires an accurate assessment of land use and impervious percentages, pond system morphology, flow routing, and lake water quality. After supplying the required input data, the P8 model was used to estimate both the water and phosphorus loads introduced from the entire watershed. The phosphorus and water loads estimated with P8 for 2003-04 were entered into a separate in-lake mass balance model so that the phosphorus concentrations in both Arrowhead and Indianhead Lakes could be estimated. These modeled 2004 phosphorus concentrations were compared to 2004 monitoring data to calibrate the in-lake model and ensure that it was producing reasonable results. The calibrated model was then used to estimate phosphorus loads and concentrations with varying climatic regimes and BMP options. Details of the modeling results and a discussion of management opportunities are presented later in this report. When evaluating the results of the modeling, it is important to consider that the results provided can be assumed to be more accurate in terms of relative differences than in absolute results. The model will predict the percent difference in phosphorus reduction between various BMP options in the watershed fairly accurately. It also provides a realistic estimate of the relative differences in phosphorus and water loadings from the various subwatersheds and major inflow points to the lake. However, since runoff quality is highly variable with time and location, the phosphorus loadings estimated by the model for a specific watershed may not necessarily reflect the actual loadings, in absolute terms. Various site-specific factors, such as lawn care practices, illicit point source discharges and erosion due to construction are not accounted for in the model. The model provides values that are considered to be typical of the region, given the land uses identified for the watershed in question. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 3 1.3 Joint Consideration of Arrowhead and Indianhead Lakes A combined UAA was performed for Arrowhead and Indianhead Lakes because of the Lakes’ proximity to each other within the NMCWD, their relatively small watershed areas, and their similar outlet characteristics. Both Arrowhead and Indianhead Lakes are closed-basin lakes with high level natural surface outlets; thus, they are entirely dependent on evaporation and seepage as water removal mechanisms. 1.4 Scope This UAA evaluates current and future conditions for Arrowhead and Indianhead Lakes. As a result, the watershed analysis intrinsic to the UAA focuses on the local watersheds of each lake. 1.5 General Framework of the UAA Several steps were necessary for the evaluation of the watershed, lake, and management initiatives conducted for this UAA. Those steps are outlined in the sections that follow. 1.5.1 Identification of Goals and Expectations To evaluate lake management strategies, it is first necessary to establish the criteria against which outcomes can be measured. To identify those criteria, past NMCWD documents were consulted, as well as the City of Edina Comprehensive Water Resource Management Plan (Barr, 2003). The Nine Mile Creek District Water Management Plan (Barr, 1996; Barr, update draft, 2006) currently has no specific goals for Arrowhead and Indianhead Lakes. Thus, the existing water quality, recreational- use, aquatic communities, water quantity, and wildlife were evaluated to find establish the current situation. Then a goal was determined to improve water quality to those levels needed to maintain current recreational uses. Since the completion of the NMCWD Water Management Plan, the MPCA has developed assessment methodologies, conducted extensive sampling of lakes, and ultimately derived ecoregion-based lake eutrophication guidelines, beginning with guidelines for total phosphorus (MPCA, 2004). In turn, the total phosphorus guidelines have been used as the basis for assessing swimmable-use support for lakes. The MPCA has proposed a shallow lake total phosphorus guideline of 60 μg/L, which serves as the upper threshold for full-support of swimmable use (or primary-contact recreation and aesthetics) for the North Central Hardwood Forests (NCHF) ecoregion (which includes the watersheds of Arrowhead and Indianhead Lakes). This concentration corresponds to a Carlson’s trophic state index (TSI) values P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 4 of 57. Total phosphorus concentrations above full-support guideline levels would result in greater frequencies of nuisance algal blooms and increased frequencies of “impaired swimming.” The MPCA has used the ecoregion-based total phosphorus guidelines in conjunction with Carlson’s Trophic State Index (TSI) (Carlson, 1977) as a means to classify lakes relative to support of swimmable use in 305(b) assessments. Separate indices are calculated from measurements of total phosphorus, Chlorophyll a or Secchi disc depth using formulas that normalize the measurements such that each computed TSI value translates to comparable use support. Using these formulas, the Chlorophyll a concentration and Secchi disc depth that corresponds to a Carlson’s trophic state index (TSI) value of 57 (that serves as the upper threshold for full-support of swimmable use) is 15 µg/L and 1.2 meters, respectively. The MPCA has also reconstructed water quality from analysis of fossil diatoms contained in sediment cores obtained from some Minnesota lakes (Heiskary and Swain, 2004). As part of this study, the MPCA found that there was good agreement between the phosphorus contained in diatom fossils and the Vighi and Chiaudani (MEI) model (1985) for lakes with background phosphorus concentrations of 30 μg/L or less. The Vighi and Chiaudani MEI model provides reasonable accurate estimates of pre-European settlement total phosphorus concentrations for lakes, based on current alkalinity or conductivity water quality measurements. Vighi and Chiaudani (1985) recommend using current measurements of alkalinity over conductivity measurements from lakes that are affected by anthropogenic (human) sources of phosphorus. In addition to the Vighi and Chiaudani model that predicts pre-settlement phosphorus concentrations in lakes, Minnesota Lake Eutrophication Analysis (MINLEAP) was developed by Heiskary and Wilson (1990) to estimate where water quality in lakes “should be” based on their location, watershed area, and lake basin morphometry. MINLEAP is intended to be used as a screening tool for estimating lake conditions and for identifying “problem” lakes. MINLEAP is particularly useful for identifying lakes requiring “protection” versus those requiring “restoration”. Table 1-1 lists the current water quality conditions, the recommended NMCWD water quality goals and management strategy, the proposed MPCA shallow lakes criteria, and recreational-uses for both Arrowhead and Indianhead Lakes. The table lists total phosphorus (TP) and Chlorophyll a (Chl a) concentrations, Secchi disc (SD) transparencies, and Carlson’s Trophic State Index (TSI) based on Secchi disc. Cu r r e n t S u m m e r A v e r a g e W a t e r Qu a l i t y C o n d i t i o n s ( T S I SD )1 Ex p e c t e d R a n g e s , U l t i m a t e Wa t e r s h e d L a n d U s e W i t h BM P s Ex p e c t e d R a n g e s , U l t i m a t e Wa t e r s h e d L a n d U s e Wi t h o u t B M P s Pr o p o s e d D i s t r i c t W a t e r Qu a l i t y G o a l 2 MP C A S w i m m a b l e Us e C l a s s Me t r o C o u n c i l Pr i o r i t y W a t e r s Cl a s s M u n i c i p a l U s e 3MDNR* Ecological Class 4District Management Strategy Ar r o w h e a d Ye a r o f R e c o r d = 2 0 0 4 II Pa r i a l b o d y - c o n t a c t Sh a l l o w L a k e s C r i t e r i a N/ A N/A N/A Protect re c r e a t i o n a l [T P ] = 7 2 . 2 µg/ L 39 . 8 < [ T P ] < 8 2 . 6 µg/ L 68 . 8 < [ T P ] < 9 1 . 2 µg/ L 45 < [ T P ] < 7 5 µg/ L [T P ] < 6 0 µg/ L [C h l a ] = 1 8 . 5 µg/ L 11 . 7 < [ C h l a ] < 2 5 . 7 µg/ L 18 . 5 < [ C h l a ] < 2 8 . 6 µg/ L 20 < [ C h l a ] < 4 0 µg/ L [C h l a ] < 2 0 µg/ L SD = 1 . 0 m 0. 9 < S D < 1 . 1 m 0. 9 < S D < 1 . 0 m 1. 0 < S D < 2 . 0 m SD > 1 . 0 m TS I SD = 6 0 58 < T S I SD < 6 0 60 < T S I SD < 6 2 50 < T S I SD < 6 0 In d i a n h e a d Y e a r o f R e c o r d = 2 0 0 4 II Pa r i a l b o d y - c o n t a c t S h a l l o w L a k e s C r i t e r i a N / A N / A N / A P r o t e c t re c r e a t i o n a l [T P ] = 4 5 . 8 µg/ L 14 . 5 < [ T P ] < 6 7 . 3 µg/ L 44 . 9 < [ T P ] < 9 8 . 6 µg/ L 45 < [ T P ] < 7 5 µg/ L [ T P ] < 6 0 µg/ L [C h l a ] = 8 . 7 µg/ L 2. 3 < [ C h l a ] < 1 2 . 7 µg/ L 8. 1 < [ C h l a ] < 1 9 . 3 µg/ L 2 0 < [ C h l a ] < 4 0 µg/ L [ C h l a ] < 2 0 µg/ L SD = 1 . 1 m 0. 9 < S D < 1 . 8 m 0. 7 < S D < 1 . 1 m 1. 0 < S D < 2 . 0 m SD > 1 . 0 m TS I SD = 5 8 52 < T S I SD < 6 2 58 < T S I SD < 6 6 50 < T S I SD < 6 0 1 T S I SD Ca r l s o n ' s T r o p h i c S t a t e I n d e x s c o r e . T h i s i n d e x w a s d e v e l o p e d f r o m t h e i n t e r r e l a t i o n s h i p s b e t w e e n s u m m e r a v e r a g e S e c c h i d i s c t r a n s p a r e n c i e s a n d e p i l i m n e t i c c o n c e n t r a t i o n s o f c h l o r o p h y l l a a n d t o t a l p h o s p h o r u s . T h e i n d e x re s u l t s i n s c o r i n g g e n e r a l l y i n t h e r a n g e b e t w e e n z e r o a n d o n e h u n d r e d . [ D i s t r i c t v a l u e s c a l c u l a t e d b y B a r r E n g i n e e r i n g C o m p a n y ( f r o m f i e l d d a t a a n d w a t e r q u a l i t y m o d e l p r e d i c t i o n s ) . M P C A v a l u e s t a k e n f r o m t h e 1994 Clean Water Act Re p o r t t o t h e U . S . C o n g r e s s ; a n d M D N R v a l u e s t a k e n f r o m S c h u p p ( 1 9 9 2 ) M i n n e s o t a D e p a r t m e n t o f N a t u r a l R e s o u r c e s I n v e s t i g a t i o n a l R e p o r t N o . 4 1 7 . An e c o l o g i c a l c l a s s i f i c a t i o n o f M i n n e s o t a l a k e s w i t h a s s o c i a t e d f i s h c o m m u n i t i e s .] 2 D i s t r i c t I = F u l l y s u p p o r t s a l l w a t e r - b a s e d r e c r e a t i o n a l a c t i v i t i e s i n c l u d i n g s w i m m i n g , s c u b a d i v i n g a n d s n o r k e l i n g . I I = A p p r o p r i a t e f o r a l l r e c r e a t i o n a l u s e s e x c e p t f u l l b o d y c o n t a c t a c t i v i t i e s : s a i l b o a t i n g , w a t e r s k i i n g , c a n o e i n g , w i n d s u r f i n g , j e t s k i i n g . I I I = S u p p o r t s f i s h i n g , a e s t h e t i c v i e w i n g a c t i v i t i e s a n d w i l d l i f e o b s e r v a t i o n I V = G e n e r a l l y i n t e n d e d f o r r u n o f f m a n a g e m e n t a n d h a v e n o s i g n i f i c a n t r e c r e a t i o n a l u s e v a l u e s V = W e t l a n d s s u i t a b l e f o r a e s t h e t i c v i e w i n g a c t i v i t i e s , w i l d l i f e o b s e r v a t i o n a n d o t h e r p u b l i c u s e s . 3 M u n i c i p a l U s e S W I M = P u b l i c s w i m m i n g b e a c h F I S H = D e s i g n a t e d f i s h i n g r e s o u r c e 4 M D N R E x a m i n a t i o n o f t h e M D N R e c o l o g i c a l c l a s s i f i c a t i o n s y s t e m r e v e a l e d t h e T S I SD v a l u e f o r a g i v e n l a k e c l a s s c o u l d v a r y d r a m a t i c a l l y . T h e a b o v e m e a n T S I SD v a l u e w a s p r e s e n t e d i n t h e 19 9 6 N M C W D W a t e r M a n a g e m e n t P l a n . L a k e C l a s s 4 4 m a y b e s u b j e c t t o o c c a s i o n a l w i n t e r k i l l . N P = N o r t h e r n P i k e C A = C a r p B L B = B l a c k B u l l h e a d La k e La k e C l a s s i f i c a t i o n , B y R e g u l a t o r y A g e n c y ( S e c c h i D i s c T r a n s p a r e n c y B a s i s ) Ta b l e 1 - 1 Ar r o w h e a d a n d I n d i a n h e a d L a k e s M a n a g e m e n t T a b l e Wa t e r Q u a l i t y , R e c r e a t i o n a l U s e a n d E c o l o g i c a l C l a s s i f i c a t i o n o f , a n d M a n a g e m e n t Ph i l o s o p h i e s , R e f e r e n c i n g C a r l s o n ’ s T r o p h i c S t a t e I n d e x ( T S I ) V a l u e s P: \ 2 3 \ 2 7 \ 0 0 3 \ U A A \ S A S \ A n d e r s o n L a k e s \ R e p o r t \ A n d e r s o n G o a l s T a b l e . x l s 7/17/2006 7:47 AM P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 6 1.5.2 Assessment of Current Conditions The condition of the lake’s watershed, biological communities, and water quality within Arrowhead and Indianhead Lakes was evaluated for this study. The watershed analysis involved assessment of soil type, land use and residential density, and the impervious fraction of the land in the watershed. Land use assumptions were made based on the Metropolitan Council land use coverage GIS database. For this UAA, the division of the lakes’ watersheds into subwatersheds was identified through consultation of previous reports; the subwatershed delineation was confirmed by field investigations (which were also used to confirm land-use patterns and stormwater routing). Originally, the subwatersheds were delineated using two- foot topographic data from the city of Edina and field verified where necessary. The storm sewer routing was determined using storm sewer information provided by the city of Edina, and was also field verified. The pond storage data was taken from bathymetry data from the city of Edina as well as the MDNR to allow correct evaluation of the ponds’ current water treatment performance. Based on the wetland inventories for the surrounding area, pond characteristics were estimated for the ponds that did not have survey information. Biological communities were evaluated through consideration of past sampling of the lakes’ phytoplankton, zooplankton, and macrophyte communities. Further information with respect to the aquatic communities was gathered through reviewing MDNR fishery surveys. Current lake water quality was assessed through examination of recent water sampling data. In particular, the evaluation of current in-lake water quality was based on the results of an intensive 2004 data collection program. These data were also used in calibration of the current water quality model used in the UAA. 1.5.3 Assessment of Future Conditions The city of Edina is fully urbanized, with less than one percent of the remaining land being developable. Because of this, it was assumed that existing land use conditions in the Arrowhead and Indianhead Lakes watersheds are also representative of future conditions. 1.5.4 Evaluation of Management Strategies Having modeled the watershed loading and lake response under the assumed existing/future conditions, it is possible to evaluate the potential impacts of various watershed and lake management strategies. Several likely approaches to watershed and lake management were selected and evaluated under various climatic conditions. Costs of the strategies were estimated so that those costs could be compared to the in-lake benefits that the management initiatives are expected to provide. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 7 2.0 General Concepts in Lake Water Quality There are a number of concepts and terminology that are necessary to describe and evaluate a lake’s water quality. This section is a brief discussion of those concepts, divided into the following topics: • Eutrophication • Trophic states • Limiting nutrients • Stratification • Nutrient recycling and internal loading To learn more about these five topics, one can refer to any text on limnology (the science of lakes and streams). 2.1 Eutrophication Eutrophication, or lake degradation, is the accumulation of sediments and nutrients in lakes. As a lake naturally becomes more fertile, algae and weed growth increases. The increasing biological production and sediment inflow from a lake’s watershed eventually fill the lake’s basin. Over a period of many years, the lake successively becomes a pond, a marsh and, ultimately, a terrestrial site. This process of eutrophication is natural and results from the normal environmental forces that influence a lake. Cultural eutrophication, however, is an acceleration of the natural process caused by human activities. Nutrient and sediment inputs (i.e., loadings) from wastewater treatment plants, septic tanks, and stormwater runoff can far exceed the natural inputs to the lake. The accelerated rate of water quality degradation caused by these pollutants does result in unpleasant consequences. These include profuse and unsightly growths of algae (algal blooms) and/or the proliferation of rooted aquatic weeds (macrophytes). 2.2 Trophic States Not all lakes are at the same stage of eutrophication; therefore, criteria have been established to evaluate the nutrient status of lakes. Trophic state indices (TSIs) are calculated for lakes on the basis of total phosphorus, Chlorophyll a concentrations, and Secchi disc transparencies. TSI values range upward from 0, describing the condition of the lake in terms of its trophic status (i.e., its degree of fertility). All three of the parameters can be used to determine a TSI. However, water transparency is P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 8 typically used to develop the TSISD (trophic state index based on Secchi disc transparency) because people’s perceptions of water clarity are often directly related to recreational-use impairment. The TSI rating system results in the placement of a lake with high fertility in the hypereutrophic status category. Water quality trophic status categories include oligotrophic (i.e., excellent water quality), mesotrophic (i.e., good water quality), eutrophic (i.e., poor water quality), and hypereutrophic (i.e., very poor water quality). Water quality characteristics of lakes in the various trophic status categories are listed below with their respective TSI ranges: 1. Oligotrophic – [20 < TSISD < 38] clear, low productive lakes, with total phosphorus concentrations less than or equal to 10 µg/L, Chlorophyll a concentrations of less than or equal to 2 µg/L, and Secchi disc transparencies greater than or equal to 4.6 meters (15 feet). 2. Mesotrophic – [38 < TSISD < 50] intermediately productive lakes, with total phosphorus concentrations between 10 and 25 µg/L, Chlorophyll a concentrations between 2 and 8 µg/L, and Secchi disc transparencies between 2 and 4.6 meters (6 to 15 feet). 3. Eutrophic – [50 < TSISD < 62] high productive lakes relative to a neutral level, with 25 to 57 µg/L total phosphorus, Chlorophyll a concentrations between 8 and 26 µg/L, and Secchi disc measurements between 0.85 and 2 meters (2.7 to 6 feet). 4. Hypereutrophic – [62 < TSISD < 80] extremely productive lakes which are highly eutrophic and unstable (i.e., their water quality can fluctuate on daily and seasonal basis, experience periodic anoxia and fish kills, possibly produce toxic substances, etc.) with total phosphorus concentrations greater than 57 µg/L, Chlorophyll a concentrations of greater than 26 µg/L, and Secchi disc transparencies less than 0.85 meters (2.7 feet). Determining the trophic status of a lake is an important step in diagnosing water quality problems. Trophic status indicates the severity of a lake’s algal growth problems and the degree of change needed to meet its recreational-use goals. Additional information, however, is needed to determine the cause of algal growth and a means of reducing it. 2.3 Limiting Nutrients The quantity or biomass of algae in a lake is usually limited by the water’s concentration of an essential element or nutrient “the limiting nutrient”. (For rooted aquatic plants, the nutrients are derived from the sediments.) The limiting nutrient concept is a widely applied principle in ecology and in the study of eutrophication. It is based on the idea that plants require many nutrients to grow, but the nutrient with the lowest availability, relative to the amount needed by the plant, will limit plant growth. It follows then, that identifying the limiting nutrient will point the way to controlling algal growth. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 9 Nitrogen (N) and phosphorus (P) are generally the two growth-limiting nutrients for algae in most natural waters. Analysis of the nutrient content of lake water and algae provides ratios of N:P. By comparing the ratio in water to the ratio in the algae, one can estimate whether a particular nutrient may be limiting. Algal growth is generally phosphorus-limited in waters with N:P ratios greater than 12. Laboratory experiments (bioassays) can demonstrate which nutrient is limiting by growing the algae in lake water with various concentrations of nutrients added. Bioassays, as well as fertilization of in-situ enclosures and whole-lake experiments, have repeatedly demonstrated that phosphorus is usually the nutrient that limits algal growth in freshwaters. Reducing phosphorus in a lake, therefore, is required to reduce algal abundance and improve water transparency. Failure to reduce phosphorus concentrations will allow the process of eutrophication to continue at an accelerated rate. 2.4 Stratification The process of internal loading is dependent on the amount of organic material in the sediments and the depth-temperature pattern, or “thermal stratification,” of a lake. Thermal stratification profoundly influences a lake’s chemistry and biology. When the ice melts and air temperature warms in spring, lakes generally progress from being completely mixed to stratified with only an upper warm well- mixed layer of water (epilimnion), and cold temperatures in a bottom layer (hypolimnion). Because of the density differences between the lighter warm water and the heavier cold water, stratification in a lake can become very resistant to mixing. When this occurs, generally in mid-summer, oxygen from the air cannot reach the bottom lake water and, if the lake sediments have sufficient organic matter, biological activity can deplete the remaining oxygen in the hypolimnion. The epilimnion can remain well-oxygenated, while the water above the sediments in the hypolimnion becomes completely devoid of dissolved oxygen (anoxic). Complete loss of oxygen changes the chemical conditions in the water and allows phosphorus that had remained bound to the sediments to reenter the lake water. As the summer progresses, phosphorus concentrations in the hypolimnion can continue to rise until oxygen is again introduced (recycled). Dissolved oxygen concentration will increase if the lake sufficiently mixes to disrupt the thermal stratification. Phosphorus in the hypolimnion is generally not available for plant uptake because there is not sufficient light penetration to the hypolimnion to allow for growth of algae. The phosphorus, therefore, remains trapped and unavailable to the plants until the lake is completely mixed. In shallow lakes this can occur throughout the summer, with sufficient wind energy (polymixis). In deeper lakes, however, only extremely high wind energy is P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 10 sufficient to destratify a lake during the summer and complete mixing only occurs in the spring and fall (dimixis). Cooling air temperature in the fall reduces the epilimnion water temperature, and consequently increases the density of water in the epilimnion. As the epilimnion water density approaches the density of the hypolimnion water very little energy is needed to cause complete mixing of the lake. When this fall mixing occurs, phosphorus that has built up in the hypolimnion is mixed with the epilimnion water and becomes available for plant and algal growth. 2.5 Nutrient Recycling and Internal Loading The significance of thermal stratification in lakes is that the density change in the metalimnion (i.e., middle transitional water temperature stratum) provides a physical barrier to mixing between the epilimnion and the hypolimnion. While water above the metalimnion may circulate as a result of wind action, hypolimnetic waters at the bottom generally remain isolated. Consequently, very little transfer of oxygen occurs from the atmosphere to the hypolimnion during the summer. Shallow water bodies may circulate many times during the summer as a result of wind mixing. Lakes possessing these wind mixing characteristics are referred to as polymictic lakes. In contrast, deeper lakes generally become well-mixed only twice each year. This usually occurs in the spring and fall. Lakes possessing these mixing characteristics are referred to as dimictic lakes. During these periods, the lack of strong temperature/density differences allows wind-driven circulation to mix the water column throughout. During these mixing events, oxygen may be transported to the deeper portions of the lake, while dissolved phosphorus is brought up to the surface. Phosphorus enters a lake from either watershed runoff or direct atmospheric deposition. It would, therefore, seem reasonable that phosphorus in a lake can decrease by reducing these external loads of phosphorus to the lake. All lakes, however, accumulate phosphorus (and other nutrients) in the sediments from the settling of particles and dead organisms. In some lakes this reservoir of phosphorus can be reintroduced in the lake water and become available again for plant uptake. This resuspension or dissolution of nutrients from the sediments to the lake water is known as “internal loading”. As long as the lake’s sediment surface remains sufficiently oxidized (i.e., dissolved oxygen remains present in the water above the sediment), its phosphorus will remain bound to sediment particles as ferric hydroxy phosphate. When dissolved oxygen levels become extremely low at the water-sediment interface (as a result of microbial activity using the oxygen), the chemical reduction of ferric iron to its ferrous form causes the release of dissolved phosphorus, which is readily available for algal growth, into the water column. The amount of phosphorus released from internal loading can be estimated from depth profiles (measurements from surface to bottom) of dissolved P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 11 oxygen and phosphorus concentrations. Even if the water samples indicate the water column is well oxidized, the oxygen consumption by the sediment during decomposition can restrict the thickness of the oxic sediment layer to only a few millimeters. Therefore, the sediment cannot retain the phosphorus released from decomposition or deeper sediments, which result in an internal phosphorus release to the water column. Low-oxygen conditions at the sediments, with resulting phosphorus release, are to be expected in eutrophic lakes where relatively large quantities of organic material (decaying algae and macrophytes) are deposited on the lake bottom. If the low-lying phosphorus-rich waters near the sediments remain isolated from the upper portions of the lake, algal growth at the lake’s surface will not be stimulated. Shallow lakes and ponds can be expected to periodically stratify during calm summer periods, so that the upper warmer portion of the water body is effectively isolated from the cooler, deeper (and potentially phosphorus-rich) portions. Deep lakes typically retain their stratification until cooler fall air temperatures allow the water layers to become isothermal and mix again. Deep lakes are, therefore, frequently dimictic, typically mixing only twice a year. However, relatively shallow lakes are less thermally stable and may mix frequently during the summer periods. The pH of the water column can also play a vital role in affecting the phosphorus release rate under oxic conditions. Photosynthesis by macrophytes and algae during the day tend to raise the pH in the water column, which can enhance the phosphorus release rate from the oxic sediment. Enhancement of the phosphorus release at elevated pH (pH > 7.5) is thought to occur through replacement of the phosphate ion (PO4-3) with the excess hydroxyl ion (OH-) on the oxidized iron compound (James, et al., 2001). Another potential source of internal phosphorus loading is the die-off of Curlyleaf pondweed. Curlyleaf pondweed, an exotic (i.e., non-native) lake weed is present in Arrowhead Lake but not in Indianhead Lake. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 12 3.0 Identification of Goals and Expectations 3.1 NMCWD Goals for Arrowhead and Indianhead Lakes The 1996 NMCWD Plan does not list current water quality conditions, corresponding TSI indices, recreational use classes, MDNR ecological classes, or the District Management goals for Arrowhead and Indianhead Lakes. Also, the Plan has not established goals for Arrowhead and Indianhead Lakes include requirements for water quantity, water quality, aquatic communities, recreational-use, and wildlife and habitat. Therefore the development of this UAA should assist in establishing goals in each of these categories. The five specific goals criteria to be developed for Arrowhead and Indianhead Lakes are outlined and discussed here and in Table 1-1. 3.1.1 Water Quantity Goal The water quantity goal for Arrowhead and Indianhead Lakes is to provide sufficient water storage during a regional flood. This goal is attainable with no action. 3.1.2 Water Quality Goal The water quality goals for both Arrowhead and Indianhead Lakes are not specified by the NMCWD in the 1996 NMCWD Water Management Plan or the draft of the 2006 update. Current water quality levels (TSISD = 60) places Arrowhead Lake on the border of the Level II and Level III lake management category. For Level II management classification, the lake is intended for partial body-contact recreational use/fishing and aesthetic viewing with a goal to achieve and maintain a TSISD between 51 to 60. The proposed NMCWD goal for Arrowhead Lake is to achieve and maintain a Level II classification. For Indianhead Lake, the current water quality (TSISD = 58) places it within the Level II lake management category, which supports partial body-contact recreational uses. The proposed NMCWD goal for this lake classification is to achieve and maintain a TSISD between 51 to 60. 3.1.3 Aquatic Communities Goal In 1992, the MDNR categorized many Minnesota lakes according to the type of fishery each lake might reasonably be expected to support (An Ecological Classification of Minnesota Lakes with Associated Fish Communities; Schupp, 1992). The MDNR’s ecological classification system takes P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 13 into account factors such as the lake area, percentage of the lake surface area that is littoral, maximum depth, degree of shoreline development, Secchi disc transparency, and total alkalinity. However, the MDNR did not classify either Arrowhead or Indianhead Lakes as part of its 1992 study. Since the MDNR did not specify the ecological classification for these lakes, there is no specific fisheries related TSI goal. However, it is the goal of the NMCWD to achieve water quality that will result in a diverse and balanced native ecosystem dominated by native species. 3.1.4 Recreational-Use Goal With a NMCWD Level II classification, these lakes should fully support water-based activities including canoeing, fishing, wildlife and aesthetic viewing, and runoff management. However, primary users are limited to residents living around the lakes as there is no public access for boating or swimming uses. Therefore, the recreational use goal for both Arrowhead and Indianhead Lakes is to achieve water quality that supports these functions as well as to maintain a balanced ecosystem. In accordance with the NMCWD’s non degradation policy, the lake shall be protected from significant degradation from point and nonpoint pollution sources and shall maintain existing water uses, aquatic habits, and the necessary water quality to protect these uses. 3.1.5 Wildlife Goal The wildlife goal for both Arrowhead and Indianhead Lakes is to protect existing beneficial wildlife uses. 3.2 Expected Benefits of Water Quality Improvements Arrowhead and Indianhead Lakes are important aquatic resource for those living around the lakes. The NMCWD has indicated that the management strategy for these lakes should be to protect the resources and prevent further degradation. If the lakes’ water quality is protected, all recreational and aquatic habitat uses for the lake should be maintained. 3.2.1 Enhancement of Recreational Use Neither Arrowhead nor Indianhead Lake is typically used for swimming or boating as there is not public access to either of these lakes. Recreational users are predominantly limited to residents around that lake and include fishing, canoeing, and wildlife and aesthetic viewing. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 14 Decreases in phosphorus concentrations and resulting transparency improvements for both lakes will likely improve the lake’s aesthetic appeal, make fish kills less likely, and reduce the frequency of odor-producing algal blooms that thrive on over-fertilization of the waters. Such improvements will make the lakes more pleasant for the surrounding residents and others who enjoy the lakes. 3.2.2 Improvements in Aquatic Habitat Improving the eutrophic status of both Arrowhead and Indianhead Lakes is expected to benefit the aquatic communities of the lakes. Reduction in the eutrophication process typically results in reduced algal concentrations (esp. blue-green algae) and increased transparency. These changes allow for greater plant and animal diversity, as species with less tolerance for low light and low oxygen are once again able to populate the lake and its littoral regions. Higher diversity and improved habitat for the communities lowest on the food chain (algae, zooplankton, etc.) are reflected in benefits to higher-order species—from benthic invertebrates through birds and mammals. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 15 4.0 Lake Basin and Watershed Characteristics The following sections describe the unique characteristics of the Arrowhead and Indianhead Lake basins. General features of the land use in the lakes’ watersheds are discussed. The network of water storage and treatment ponds is also described, as well as the flows in and out of the lake. 4.1 Lake Basin Characteristics 4.1.1 Arrowhead Lake Arrowhead Lake is located in western portion of Edina, south of Highway 62 and east of Highway 169. The lake has a water surface of approximately 22 acres, a maximum depth of approximately 7 feet, and a mean depth of 4.6 feet at an average water surface elevation of 873.9 feet. At this elevation, the lake volume is approximately 96 acre-feet (see Figure 4-1 for approximate lake bathymetry information). The lake is shallow enough for aquatic plants to grow over much of the lake bed and the entire lake has been classified as a littoral zone by the MDNR. Arrowhead Lake is also a land locked basin as there is no surface outlet. As a result, the water level in the lake is controlled mainly by weather conditions (snowmelt, rainfall, and evaporation) and groundwater interaction. A water balance of Arrowhead Lake generally discharges to the groundwater. The estimated natural overflow elevation is 882.5 feet. The stage-storage-discharge relationship that was used in this study for Arrowhead Lake is shown in Table 4-1. Since Arrowhead Lake is shallow, the lake would be expected to be prone to frequent wind-driven mixing of the lake’s water during the summer. One would therefore expect Arrowhead Lake to be polymictic (mixing many times per year) as opposed to lakes with deep, steep-sided basins that are usually dimictic (mixing only twice per year). Daily monitoring of the lake would be necessary to precisely characterize the mixing dynamics of a lake, but the limited data gathered from Arrowhead Lake suggests that the lake is indeed polymictic. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 16 Table 4-1 Stage-Storage-Discharge Relationship for Arrowhead Lake Elevation Area (ac) Cumulative Storage (ac-ft) Discharge (cfs) 866.4 0.04 0.000 0 867.4 3.34 1.7 0 868.4 7.5 7.1 0 869.4 12.2 17.0 0 870.4 15.5 30.8 0 871.4 17.6 47.4 0 873.9 21.0 96.2 0 875.4 21.9 127. 8 0 876.0 22.3 141.1 0 877.0 23.0 163.7 0 878.0 23.6 187.0 0 879.0 24.4 211.0 0 880.0 25.1 235.7 0 881.0 25.8 261.2 0 882.0 26.6 287.4 0 882.5 27.0 300.8 !;N Ba r r F o o t e r : D a t e : 6 / 2 5 / 2 0 0 6 2 : 1 1 : 1 1 P M F i l e : I : \ C l i e n t \ N m c w d \ L a k e s \ U A A \ A r r o w h e a d _ I n d i a n h e a d \ G I S \ M a p s \ F i g u r e s \ F i g u r e _ 4 _ 1 _ A H _ B a t h y m e t r y . m x d U s e r : j a k 2 Figure 4-1 Arrowhead Lake Approximate Bathymetry Arrowhead and Indianhead Lakes UAANine Mile Creek Watershed District 150 0 150Feet Legend Bathymetry Elevation (msl - ft) 872.4 871.4 870.4 869.4 868.4 867.4 866.4 NWL = 873.9 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 18 4.1.2 Indianhead Lake Indianhead Lake is also located in the western portion of Edina, south of Highway 62 and east of Highway 169, to the southeast of Arrowhead Lake. The lake has a water surface of approximately 14 acres, a maximum depth of approximately 6.5 feet, and a mean depth of 4.3 feet at an average water surface elevation of 863.2 feet. At this elevation the lake volume is approximately 61.3 acre- feet (see Figure 4-3 for approximate lake bathymetry information). The lake is shallow enough for aquatic plants to grow over the majority of the lake bed. Like Arrowhead Lake, there is no surface outlet from Indianhead Lake, and as a result, the water level in the lake is controlled mainly by weather conditions (snowmelt, rainfall, and evaporation) and groundwater interaction. A water balance of Indianhead Lake suggests that the lake discharges to the groundwater. The estimated natural overflow elevation is 882.5. The stage-storage-discharge relationship that was used in this study for Indianhead Lake is shown in Table 4-2. Since Indianhead Lake is shallow, the lake would be expected to be prone to frequent wind-driven mixing of the lake’s water during the summer. One would therefore expect Indianhead Lake to be polymictic (mixing many times per year) as opposed to lakes with deep, steep-sided basins that are usually dimictic (mixing only twice per year). Daily monitoring of the lake would be necessary to precisely characterize the mixing dynamics of a lake, but the limited data gathered from Indianhead Lake suggests that the lake is indeed polymictic. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 19 Table 4-2 Stage-Storage-Discharge Relationship for Indianhead Lake Elevation Area (ac) Cumulative Storage (ac-ft) Discharge (cfs) 856.7 0.00 0.00 0.0 858.2 7.6 5.0 0.0 860.2 11.0 23.6 0.0 863.2 14.2 61.3 0.0 865.0 15.5 88.1 0.0 868.0 17.2 138.6 0.0 871.0 19.1 193.1 0.0 874.0 20.8 252.9 0.0 877.0 22.9 318.3 0.0 880.0 25.1 390.4 0.0 !;N Ba r r F o o t e r : D a t e : 6 / 2 5 / 2 0 0 6 2 : 1 5 : 1 6 P M F i l e : I : \ C l i e n t \ N m c w d \ L a k e s \ U A A \ A r r o w h e a d _ I n d i a n h e a d \ G I S \ M a p s \ F i g u r e s \ F i g u r e _ 4 _ 2 _ I H _ B a t h y m e t r y . m x d U s e r : j a k 2 Figure 4-2 Indianhead Lake Approximate Bathymetry Arrowhead and Indianhead Lakes UAA Nine Mile Creek Watershed District 200 0 200Feet Legend Bathymetry Elevation (msl - ft) 863.2 861.2 860.7 860.2 858.2 857.23 856.7 NWL = 863.2 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 21 4.2 Watershed Characteristics All land use practices within a lake’s watershed influence the lake and its water quality. The impacts result from sediment and nutrient transfer, primarily phosphorus, from the lake’s watershed to the lake. Each land use contributes a different quantity of phosphorus to the lake, thereby impacting the lake’s water quality differently. As land use changes over time, changes can be expected in downstream water bodies as a result. Historically, the region surrounding Arrowhead and Indianhead Lakes’ watersheds was primarily comprised of basswood, sugar maple, and oak forests. There were also numerous lakes, wetlands, and ponds located throughout the region with the terrain varyi ng from rolling to steeply rolling. The 178-acre watershed (including the lake surface area) for Arrowhead Lake and the 107-acres (including the lake surface area) for Indianhead Lake are both within the city limits of Edina. Runoff from both watersheds enters each lake via overland flow and storm sewer outfalls at various points along the lakeshore. Existing land use patterns within the watersheds were identified for the purpose of predicting runoff volumes and annual phosphorus loads under these development conditions. 4.2.1 Present Land Use Existing land use conditions were determined using land use information provided by the City of Edina. It is the same land use information used in the City of Edina Comprehensive Water Resources Management Plan (Barr, 2003). During the development of the Water Resources Management Plan, this information was reclassified to incorporate right-of-way land use into the standard land use classes for modeling purposes. 4.2.1.1 Arrowhead Lake Land Use The entire contributing watershed is developed, with the majority of the land use being low-density residential (38.3 percent), with some roadway right-of-way (ROW) (18.6 percent), high-impervious institutional (3.5 percent), park/open space (3.2 percent), and very low-density residential (22.5 percent) uses. The remaining 14 percent is classified as open water. Figures 4-3 and 4-4 detail the primary existing land uses within the Arrowhead Lake watershed. Analyses of these data indicate that, under existing land use conditions, Arrowhead Lake’s contributing watershed consists of: • High Impervious Institutional: ................... ………………….0.1 acres • Highways/Transport .............................................................. 33.1 acres • Low-Density Residential (1 to 4 housing units per acre) ..... 68.3 acres P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 22 • Very Low-Density Residential (<1 housing unit per acre) .. 40.0 acres • Natural/Park/Open .................................................................. 1.5 acres • Developed Park ....................................................................... 4.3 acres • Open Water ............................................................................ 24.6 acres 4.2.1.2 Indianhead Lake Land Use The entire contributing watershed is developed, with the majority of the land use being low-density residential (46.1 percent), with some very low-density residential (37.3 percent), institutional (1.1 percent), and wetland (0.9 percent). The remaining 14.6 percent is classified as open water. Figures 4-3 and 4-4 detail the primary existing land uses within the Indianhead Lake watershed. Analyses of these data indicate that, under existing land use conditions, Indianhead Lake’s 107-acre contributing watershed consists of: • Institutional ............................................................................. 1.1 acres • Low-Density Residential (1 to 4 housing units per acre) .... 49.5 acres • Very Low-Density Residential (<1 housing unit per acre) ... 40.1 acres • Wetland ................................................................................... 1.0 acres • Open Water ............................................................................ 15.7 acres 4.2.2 Future Land Use The city of Edina is fully urbanized, with less than one percent of the remaining land being developable. Because of this, it was assumed that existing land use conditions in the Arrowhead and Indianhead Lakes watersheds are also representative of future conditions for the modeling done in this UAA. 4.3 Lake Inflows and Drainage Areas Because the watershed modeling depends on the evaluation of the watershed conditions as they relate to stormwater runoff, the hydrology of the watersheds for both Arrowhead and Indianhead Lakes is discussed in the following sections. 4.3.1 Natural Conveyance Systems Both watersheds of Arrowhead and Indianhead Lakes are part of the larger watershed to the South Fork of Nine Mile Creek. However, as previously mentioned, both Arrowhead and Indianhead Lakes P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 23 are land-locked lakes with no surface outlets. As a result, they are only tributary to the South Fork during extreme storm events greater than the 100-year frequency storm. Natural conveyance features are limited in both the Arrowhead and Indianhead Lake watersheds. There are no perennial streams within either of the watersheds, and there are few identified wetlands. Most areas that have been classified as wetland under the National Wetland Inventory (NWI) have been incorporated into the storm sewer system as detention ponds and storage areas. 4.3.2 Stormwater Conveyance Systems The majority of the storm water conveyance in both Arrowhead and Indianhead watersheds is through underground storm sewer pipes, sections of open channel, and wet and dry detention ponds. To determine the watershed pollutant loads, three stormwater detention basins were modeled for Arrowhead Lake while in the Indianhead Lake watershed, there were two stormwater detention basins. Details on these ponds can be found in Appendix C. Arrowhead Lake Indianhead Lake AH_1 AH_1 AH_6 AH_6 AH_32 AH_6 AH_4AH_1 IH_1 IH_14 !;N Ba r r F o o t e r : D a t e : 6 / 2 5 / 2 0 0 6 2 : 1 8 : 2 9 P M F i l e : I : \ C l i e n t \ N m c w d \ L a k e s \ U A A \ A r r o w h e a d _ I n d i a n h e a d \ G I S \ M a p s \ F i g u r e s \ F i g u r e _ 4 _ 3 _ A H I H _ L U . m x d U s e r : j a k 2 Figure 4-3 Arrowhead and Indianhead LakesSubwatersheds and Land Use Arrowhead and Indianhead UAA Nine Mile Creek Watershed District 750 0 750Feet Legend Land Use Natural/Park/Open Developed Parkland Agricultural High Density Residential Very Low Density Residential Low Density Residential Medium Density Residential Institutional XWXWXWXWXWXWXWXWXWXWXWXWXWXWXWGolf Course Institutional - High Imperviousness Airport Highway Commercial Industrial/Office Other Open Water Wetland Indianhead Subwatersheds Arrowhead Subwatersheds Arrowhead Lake Watershed Land Uses 178 Acres Including Lake Surface Area Institutional 0.0% Medium Density Residential 0.0% Natural/Park/Open 0.8% Very Low Density Residential 22.5% Developed Park 2.4% Highway 18.6% Institutional - High Imperviousness 3.5% Low Density Residential 38.3% Open Water 13.8% Indianhead Lake Watershed Land Uses 107 Acres Including Lake Surface Area Institutional 1.1% Low Density Residential 46.1% Very Low Density Residential 37.3% Wetland 0.9% Open Water 14.6% Figure 4-4 Watershed Current/Future Land Use Summary Arrowhead and Indianhead Lakes UAA Nine Mile Creek Watershed District P:\23\27\634\Indianhead_Arrowhead_UAA\Data\LandUse\LU_Summary.xls Arrowhead Lake Indianhead Lake AH_1 AH_1 AH_6 AH_6 AH_32 AH_6 AH_4AH_1 IH_1 IH_14 !;N Ba r r F o o t e r : D a t e : 7 / 1 4 / 2 0 0 6 2 : 5 6 : 3 3 P M F i l e : I : \ C l i e n t \ N m c w d \ L a k e s \ U A A \ A r r o w h e a d _ I n d i a n h e a d \ G I S \ M a p s \ A H _ I H _ D r a i n a g e _ S t o r m S e w e r . m x d U s e r : j a k 2 Figure 4-5 Arrowhead and Indianhead Lakes Drainage and Stormsewer System Arrowhead and Indianhead UAANine Mile Creek Watershed District 750 0 750Feet Legend Arrowhead Subwatersheds Indianhead Subwatersheds Flow Direction Storm Sewer P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 27 5.0 Existing Water Quality 5.1 Water Quality 5.1.1 Data Collection The NMCWD collected water quality data during 2004 for both Arrowhead and Indianhead Lakes. For each lake, six samples were collected and analyzed in 2004 from the months of April through September. The summer averages were calculated from the data collected from June through September. It is important to note that during the collection of the samples in both Arrowhead and Indianhead Lakes, several aerators were operating in each lake. Additionally, in Indianhead Lake, it was confirmed that two copper sulfate treatments were applied to the lake during May and August of 2004. The intense data collection program was completed in 2004 to evaluate current water quality conditions and to calibrate the water quality models used in the UAA. Several water quality indices were evaluated, including temperature, dissolved oxygen (DO), pH, specific conductivity (conductivity), total phosphorus (TP), orthophosphate, total Kjeldahl Nitrogen (TKN), Nitrate + Nitrite Nitrogen, Chlorophyll a (Chl a), and Secchi disc transparency (transparency). Temperature, DO, and conductivity were all measured at regular intervals (typically 1 meter) throughout the water column to allow characterization of the lakes’ stratification profiles. TP and pH were measured near the water surface and at the lake bottom for each sampling event. Among the water quality parameters sampled, TP, Chl a, and transparency are the key determinants of water quality and eutrophic state for the lakes (see Section 2.0 for further discussion). Because recreational-use is greatest during the summer (June, July, and August) months, and because it is during these times that algal blooms and diminished transparency are most common, attention is usually focused on summer water quality in the upper (epilimnetic) portions of the lakes. 5.1.1.1 Arrowhead Lake Water Quality Data For Arrowhead Lake, the 2004 sampling results for TP, Chl a, and Secchi disc transparency are summarized in Table 5-1. The 2004 sampling results for these three water quality parameters are presented graphically on Figure 5-1. The 2004 epilimnetic summer averages for TP, Chl a, and transparency were 72.2 μg/L, 18.5 μg/L, and 1.0 meters, respectively. The 2004 summer average Chl a concentration and Secchi disc transparency would place Arrowhead Lake in the eutrophic category. The total phosphorus concentrations would categorize the lake as hypereutrophic. This P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 28 characterization means that by comparison to other lakes, Arrowhead Lake is rich in algal nutrients, susceptible to dense algal blooms, and exhibits fair water clarity. Table 5-1 Arrowhead Lake 2004 Water Quality Data Sample Date Epilimnetic Total Phosphorus (µg/L) Epilimnetic Chlorophyll a (µg/L) Secchi Disc (m) Epilimnetic Summer Average Total Phosphorus (µg/L) Epilimnetic Summer Average Chlorophyll a (µg/L) Summer Average Secchi Disc (m) 4/21/2004 41 8.7 1.1 72.2 18.5 1.0 6/10/2004 110 6.7 0.8 7/7/2004 84 11 0.9 8/11/2004 56 17 1.2 8/24/2004 56 27 1 9/10/2004 55 31 1 5.1.1.2 Indianhead Lake Water Quality Data For Indianhead Lake, the 2004 sampling results for TP, Chl a, and transparency are summarized in Table 5-2. The 2004 sampling results for these three water quality parameters are presented graphically on Figure 5-2. The 2004 epilimnetic summer averages for TP, Chl a, and transparency were 45.8 μg/L, 8.7 μg/L, and 1.1 meters, respectively. The 2004 summer averages of total phosphorus, Chl a, and Secchi disc transparency would place Indianhead Lake in the eutrophic category. This characterization means that by comparison to other lakes, Indianhead Lake is rich in algal nutrients, susceptible to dense algal blooms, and exhibits fair water clarity. Table 5-2 Indianhead Lake Water Quality Data Sample Date Epilimnetic Total Phosphorus (µg/L) Epilimnetic Chlorophyll a (µg/L) Secchi Disc (m) Epilimnetic Summer Average Total Phosphorus (µg/L) Epilimnetic Summer Average Chlorophyll a (µg/L) Summer Average Secchi Disc (m) 4/21/2004 24 3.6 1.4 45.8 8.7 1.1 6/10/2004 44 6.7 1.1 7/7/2004 47 8.9 1.2 P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 29 Sample Date Epilimnetic Total Phosphorus (µg/L) Epilimnetic Chlorophyll a (µg/L) Secchi Disc (m) Epilimnetic Summer Average Total Phosphorus (µg/L) Epilimnetic Summer Average Chlorophyll a (µg/L) Summer Average Secchi Disc (m) 8/11/2004 60 9.4 0.8 8/24/2004 40 13 1.4 9/10/2004 38 5.3 1.2 Arrowhead Lake Total Phosphorus Concentration 0 25 50 75 100 125 150 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 To t a l P h o s p h o r u s ( µµµµg/ L ) Summer Average = 72.2 µµµµg/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic Arrowhead Lake Chlorophyll-a Concentration 0 10 20 30 40 50 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Ch l o r o p h y l l - a ( µµµµg/ L ) Summer Average = 18.5 µµµµg/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic Arrowhead Lake Secchi Disc Transparency 0 1 2 3 4 5 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Se c c h i D i s c ( m ) Summer Average = 0.98 m Oligotrophic Mesotrophic Eutrophic Hypereutrophic Figure 5-1 Arrowhead Lake 2004 Seasonal Changes in Total Phosphorus and Chlorophyll a Concentrations and Secchi Disc Transparency P:\23\27\634\Indianhead_Arrowhead_UAA\Data\WQData\WQ\Arrowhead Lake WQ04 Data.xls Indianhead Lake Chlorophyll-a Concentrations 0 10 20 30 40 50 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Ch l o r o p h y l l - a ( µg/ L ) Summer Average = 8.7 µµµµg/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic Indianhead Lake Secchi Disc Transparency 0 1 2 3 4 5 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 Se c c h i D i s c ( m ) Summer Average = 1.1 m Oligotrophic Mesotrophic Eutrophic Hypereutrophic Figure 5-2 Indianhead Lake 2004 Seasonal Changes in Total Phosphorus and Chlorophyll a Concentrations and Secchi Disc Transparency Indianhead Lake Total Phosphorus Concentrations 0 25 50 75 100 4/1/04 5/1/04 6/1/04 7/1/04 8/1/04 9/1/04 10/1/04 To t a l P h o s p h o r u s ( u g / L ) Summer Average = 45.8 ug/L Oligotrophic Mesotrophic Eutrophic Hypereutrophic P:\23\27\634\Indianhead_Arrowhead_UAA\Data\WQData\WQ\Indianhead Lake WQ04 Data.xls P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 32 5.1.2 Baseline/Current Water Quality Water quality data (2004 data) were evaluated according to the trophic status categories for both Arrowhead and Indianhead Lakes. The trophic status categories use the lakes’ total phosphorus concentration, Chlorophyll a concentration, and Secchi disc transparency measurements to assign a water quality category to the lake that best describes its water quality. Water quality categories include oligotrophic (i.e., excellent water quality), mesotrophic (i.e., good water quality), eutrophic (i.e., poor water quality), and hypereutrophic (i.e., very poor water quality). Total phosphorus, Chlorophyll a, and Secchi disc transparency are key water quality indicators for the following reasons: • Phosphorus generally controls the growth of algae in lake systems. Of all the substances needed for biological growth, phosphorus is typically the limiting nutrient. • Chlorophyll a is the main photosynthetic pigment in algae. Therefore, the amount of Chlorophyll a in the water indicates the abundance of algae present in the lake • Secchi disc transparency is a measure of water clarity, and is inversely related to the abundance of algae. Water clarity determines recreational-use impairment. There are several tools used to evaluate expected water quality in a lake. This analysis utilizes the Minnesota Lake Eutrophication Analysis (MINLEAP) developed by Heiskary and Wilson (1990) as well as the relationship developed by Vighi and Chiaudani (1985). MINLEAP is intended to be used as a screening tool for estimating lake conditions and for identifying “problem” lakes. MINLEAP is particularly useful for identifying lakes requiring “protection” versus those requiring “restoration” (Heiskary and Wilson, 1990). In addition, MINLEAP modeling has been done in the past to identify Minnesota lakes which may be in better or worse condition than they “should be” based on their location, watershed area and lake basin morphometry (Heiskary and Wilson, 1990). Vighi and Chiaudani (1985) developed another method to determine the phosphorus concentration in lakes that are not affected by anthropogenic (human) inputs. As a result, the phosphorus concentration in a lake resulting from natural, background phosphorus loadings can be calculated from information about the lake’s mean depth and alkalinity or conductivity. Alkalinity is considered more useful for this analysis because it is less influenced by development of the watershed. However, in lakes where alkalinity data is not available, specific conductivity can be used. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 33 5.1.2.1 Baseline Lake Water Quality Status for Arrowhead Lake MINLEAP modeling predicted a total phosphorus concentration of 57 μg/L for Arrowhead Lake, with a standard error of 19 μg/L. Comparison of the predicted MINLEAP concentration and observed annual average phosphorus concentration (67 µg/L) indicates that the water quality of Arrowhead Lake falls within the expected range based on its location, watershed area and lake basin morphometry. However, since the concentration is on the upper end of the range, it could be suggested that Arrowhead Lake either maintain or improve its water quality. The relationship developed by Vighi and Chiaudani was used to determine what a typical phosphorus concentration would be in Arrowhead Lake under natural, undeveloped conditions within the watershed. The phosphorus concentration was determined using the epilimnetic specific conductivity data collected throughout the summer of 2004. The predicted total phosphorus concentration from natural, background loadings should be around 30 μg/L. This predicted concentration is about half of the value as determined by the MINLEAP analysis. 5.1.2.2 Baseline Lake Water Quality Status for Indianhead Lake MINLEAP modeling suggests that the water quality in Indianhead Lake is better than expected for a lake in a developed watershed. MINLEAP predicted a total phosphorus concentration of 56 μg/L for Indianhead Lake, with a standard error of 19 μg/L. Comparison of the predicted MINLEAP concentration and observed annual average phosphorus concentration (42 µg/L) indicates that while the water quality of Indianhead Lake falls within the expected range based on its location, watershed area and lake basin morphometry, it is on the low end of the range. Since the concentration of total phosphorus is on the lower end of the expected range, it could be suggested that Indianhead Lake maintain its current level of water quality. The relationship developed by Vighi and Chiaudani was used to determine what a typical phosphorus concentration would be in Indianhead Lake under natural, undeveloped conditions within the watershed. The phosphorus concentration was determined using the epilimnetic specific conductivity data collected throughout the summer of 2004. The predicted total phosphorus concentration from natural, background loadings should be around 23 μg/L. This predicted concentration is less than half of the value as determined by the MINLEAP analysis. Observed TP concentrations in Indianhead Lake are approximately double what would be expected in a similar lake in a natural setting. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 34 5.1.2.3 Arrowhead Lake Current (2004) Water Quality Looking at the water quality data collected for Arrowhead Lake during the summer of 2004, the summer average TP concentration was 72.2 µg/L while for Chl a, the concentration was 18.5 µg/L. The summer average Secchi disc transparency was 1.0 m. The 2004 surface water quality data have been summarized and are presented in Table 5-1. This year of data indicates that the water quality in Arrowhead Lake is better than would by expected for most water quality parameters for a “minimally” impacted water body per the MINLEAP model. Figure 5-1 summarizes the seasonal changes in concentration of TP, Chl a, and SD transparencies for Arrowhead Lake in 2004. The data are shown compared to the trophic status categories. During the spring and fall, the total phosphorus data collected were in the eutrophic (i.e., poor water quality) category. The data collected from mid-summer through early-fall 2004 placed the lake in the hypereutrophic category. As Figure 5-1a illustrates, the epilimnetic (surface water, i.e., 0-2 meter depth) phosphorus concentration increased from the lake’s steady-state spring concentration, assumed to be 41 µg/L observed in late-April, to the lake’s summer average concentration (72.2 µg/L). The increase was likely due to the lack of a surface outlet from the lake and accumulation of phosphorus from surface runoff. Because phosphorus has been shown to most often be the limiting nutrient for algal growth, the phosphorus-rich waters indicate the lake had the potential for abundant algal growth throughout the monitoring period. According to previous studies (Heiskary and Wilson, 1990), phosphorus concentrations of 60 µg/L typically result in the frequency of nuisance algal blooms (greater than 20 µg/L Chl a) to be about 70 percent of the summer. Since Arrowhead Lake’s summer average TP concentration was higher than the 60 mg/L, it is likely to experience nuisance algal blooms greater than 70 percent of the summer. Surface Chl a concentrations during 2004 ranged from 6.7 µg/L to 31 µg/L, with the summer average being 18.5 µg/L. This is indicative of a eutrophic system. The mid-September sampling date had the highest Chl a concentration observed during the sampling period suggesting that the lake may have been hypereutrophic and an algal bloom could have occurred in late August and early September. Secchi disc measurements for 2004 were primarily placed Arrowhead Lake in the eutrophic, borderline hypereutrophic, (i.e., very poor water quality) category. The summer average Secchi disc transparency (1.0 m) of the lake is also considered eutrophic. The Secchi disc measurements ranged between 0.8 and 1.2 meters, with the lowest Secchi disc transparencies occurring during mid to late P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 35 June. The low Secchi disc transparencies occurred during months of high TP concentrations. However, neither the poor Secchi disc measurements or high TP concentrations coincides with the high Chl a concentrations that occurred at the end of August and beginning of September. The summer average values correspond to the following Carlson Trophic State Index (TSI) of 66, 59, and 60 for TP, Chl a, and Secchi disc, respectively. This classifies Arrowhead Lake as a eutrophic/hypereutrophic lake. It should be noted that aerators in Arrowhead Lake were running during all sample collections and is likely to have impacted the water quality in Arrowhead Lake during the summer of 2004. 5.1.2.4 Indianhead Lake Current (2004) Water Quality Looking at the water quality data collected for Indianhead Lake during the summer of 2004, the summer average TP concentration was 45.8 µg/L while for Chl a, the concentration was 8.7 µg/L. The summer average Secchi disc transparency was 1.14 m. The 2004 surface water quality data have been summarized and are presented in Table 5-1. This year of data indicates that the water quality in Indianhead Lake is significantly better than would by expected for a “minimally” impacted water body per the MINLEAP model results. Figure 5-2 summarizes the seasonal changes in concentration of TP, Chl a, and SD transparencies for Indianhead Lake in 2004. The data are shown compared to the trophic status categories. During the spring and fall, the total phosphorus data collected were typically in the eutrophic (i.e., poor water quality) category. The data collected from mid-summer through early-fall placed the lake in the eutrophic/hypereutrophic category. As Figure 5-2 illustrates, the epilimnetic (surface water, i.e., 0- 2 meter depth) TP concentration increased from the lake’s steady-state spring concentration, assumed to be 24 µg/L observed in late-April, to the lake’s summer average concentration (45.8 µg/L). The increase was likely due to the lack of a surface outlet from the lake and accumulation of phosphorus from surface runoff. Because phosphorus has been shown to most often be the limiting nutrient for algal growth, the phosphorus-rich waters indicate the lake had the potential for abundant algal growth throughout the monitoring period. According to previous studies (Heiskary and Wilson, 1990), phosphorus concentrations of 60 µg/L typically result in the frequency of nuisance algal blooms (greater than 20 µg/L Chlorophyll a) to be about 70 percent of the summer. Since Indianhead Lake’s summer P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 36 average TP concentration was less than the 60 mg/L, it is unlikely to have experienced nuisance algal blooms for a majority of the summer. Surface Chl a concentrations during 2004 ranged from 3.6 µg/L to 13 µg/L, with the summer average being 8.7 µg/L. This is indicative of a eutrophic system that could be considered borderline mesotrophic. The highest Chl a concentration observed during the late August sampling period which may have been the result of a large algal bloom. Secchi disc measurements for 2004 were primarily placed Indianhead Lake in the eutrophic (i.e., poor water quality) category. The summer average Secchi disc transparency (1.14 m) of the lake is also considered eutrophic. The Secchi disc measurements ranged between 0.8 and 1.4 meters, with the lowest Secchi disc transparencies occurring during late August. The low Secchi disc transparencies occurred during the month with the highest TP and Chl a concentrations. This demonstrates the relationship typically seen between TP and Chl a and Chl a’s impact on SD transparencies. The observed summer averages translates to the following TSI values of 59, 52, and 58 for TP, Chl a, and transparency, respectively. This classifies Indianhead Lake as a eutrophic lake. Aerators were operating in Indianhead Lake during all sample collections. In addition, Indianhead Lake was treated with copper sulfate in May and August of 2004, most likely to control excessive algal growth in the lake. The aeration and copper sulfate treatment are likely to have influenced the water quality in Indianhead Lake during the summer of 2004. 5.2 Nutrient Loading Arrowhead and Indianhead Lakes receive the majority of their phosphorus loads from external sources, contained in the runoff from the lakes’ immediate and tributary watersheds and through atmospheric deposition. In addition, the data suggest that the lakes also receive phosphorus loads from internal sources. These sources of phosphorus are discussed in the following sections. Most of the phosphorus that runs off a watershed is in particulate form (i.e., is associated with soil or debris particles). However, it is assumed in the P8 model that 30 percent of the phosphorus that accumulates on a watershed is soluble (i.e., not associated with particles). While BMPs that rely on particle settlement, such as detention ponds and grit chambers, are effective at removing phosphorus associated with particles in stormwater runoff, they are ineffective at removing soluble phosphorus. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 37 5.2.1 External Loads 5.2.1.1 Arrowhead Lake External Loads For existing land use conditions in the Arrowhead Lake watershed, modeling simulations indicate an annual total phosphorus load to Arrowhead Lake from its watershed of 54 lbs and a watershed stormwater runoff volume of 124.4 acre-feet, calculated from model results for the period of May 1, 2003 through April 30, 2004. The water and phosphorus loads are equivalent to 6.5 inches/acre/year and 0.35 lb/acre/year, respectively (assuming an area of 156 acres, excluding the surface area of Arrowhead Lake (22 acres)). Watershed analysis suggests that under existing conditions, watershed loading is the largest phosphorus loading source to Arrowhead Lake, contributing approximately 74.8 percent of the lake annual phosphorus load and 67.6 percent of the annual water load (see Figure 5-3). In addition to watershed loading, the other external source of phosphorus and water loading to Arrowhead Lake is atmospheric deposition and direct precipitation. This loading source accounts for 6.8 and 32.4 percent of the annual phosphorus and water loading, respectively. The remainder of the phosphorus loading to Arrowhead Lake comes from internal sources, which will be discussed in Section 5.2.2. 5.2.1.2 Indianhead Lake External Loads Average annual loads predicted for Indianhead Lake under existing land use conditions were 22.1 lbs of TP and 33.2 acre-ft of stormwater runoff, calculated from the model calibration year (May 1, 2003 to April 30, 2004). This translates to water and phosphorus loads of 4.3 inches of runoff/acre/year and 0.24 lbs TP/acre/year, respectively (assuming an area of 93 acres (excluding the surface area of Indianhead Lake (14 acres)). Watershed analysis suggests that under existing conditions, watershed loading is the largest external phosphorus loading source to Indianhead Lake, contributing approximately 88.2 percent of the lake annual phosphorus load and 55 percent of the annual water load (see Figure 5-4). In addition to watershed loading, the other external source of phosphorus and water loading to Indianhead Lake is atmospheric deposition and direct precipitation. These external loading sources account for 11.4 and 45.0 percent of the annual phosphorus loading and water loading, respectively. The remainder of the phosphorus loading in Indianhead Lake comes from internal sources, which will be discussed in the following section. Arrowhead Lake Annual Water Budget (124.4 acre-ft) Model Calibration Year (May 1, 2003 to April 30, 2004) Watershed Runoff, 67.6% Direct Precipitation, 32.4% Arrowhead Lake Phophorus Budget (72.2 lbs) Model Calibration Year (May 1, 2003 to April 30, 2004) Watershed Runoff 74.8% Atmospheric Deposition 6.8% Internal Load 18.5% Figure 5-3 Arrowhead Lake Watershed Water and Phosphorus Budgets P:\23\27\634\Indianhead_Arrowhead_UAA\InLakeModel\AH\In-LakeModel_Partition6_AH_7706_Final.xls Indianhead Lake Annual Water Budget (60.4 acre-ft) Model Calibration Year (May 1, 2003 to April 30, 2004) Direct Precipitation, 45.0% Watershed Runoff 55.0% Indianhead Lake Annual Phophorus Budget (25.1 lbs) Model Calibration Year (May 1, 2003 to April 30, 2004) Watershed Runoff 88.2% Atmospheric Deposition 11.4% Internal Load 0.3% Figure 5-4 Indianhead Lake Water and Phosphorus Budgets P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 40 5.2.2 Internal Loads In addition to being affected by the runoff from the watershed and atmospheric deposition, the water quality of many lakes is impacted by internal phosphorus loads. Computer simulations and observed water quality data were used to determine the extent of internal phosphorus loading for Arrowhead and Indianhead Lakes as well as identifying the sources of their internal load. The magnitude of internal phosphorus loading in each lake varies. Internal loading will delay each lake’s response to phosphorus loading reduction efforts in the watershed. Large reductions in phosphorus loading from the watershed would eventually lead to reduced internal loading of phosphorus, although internal loading can be treated in the interim to achieve water quality goals. 5.2.2.1 Arrowhead Lake Internal Load Using the mass balance equation, the net internal phosphorus loading in Arrowhead Lake for 2004 was calculated to be approximately 13.3 lbs; 13 lbs likely due to Curlyleaf die-back and the remaining 0.3 lbs due to release of phosphorus from the sediment. This internal loading comprises only 18.5 percent of the annual phosphorus loading to Arrowhead Lake (see Figures 5-3). Modeling suggests that the largest portion of the internal load is due to the die back of Curlyleaf pondweed and not sediment release. However, because there is only one year of water quality data available for the lake and aerators were running during the entire season, we are unable to determine if there would be an anoxic sediment release of phosphorus if aerators were not operating. 5.2.2.2 Indianhead Lake Internal Load Analysis of the data collected for 2004 indicates that Indianhead Lake does not thermally stratify or become anoxic as it is a polymictic, or well-mixed, system. However, it is important to note that several aerators were operating in the lake throughout the summer that may have influenced the oxygen, temperature, and internal phosphorus loading to the lake. Two copper sulfate treatments were also done in the lake during the summer of 2004, most likely for the treatment of algal blooms, and may have resulted in the removal of some phosphorus in the lake after the treatment. According to the analysis of the watershed and the 2004 water quality data, internal loads contribute very little phosphorus to the lake. The mass balance estimated the net internal phosphorus loading to be approximately 0.1 lbs, which comprises 0.3 percent of the annual phosphorus load to the lake. Like Arrowhead Lake, aerators were operating in Indianhead Lake throughout the summer of 2004. Additionally, the two copper sulfate treatments are likely to have influenced the overall phosphorus P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 41 load and budget of the lake. See Figure 5-4 for a more detailed summary of the water and phosphorus budgets for Indianhead Lake. 5.3 Aquatic Communities In addition to the physical and chemical indices of lake water quality, an evaluation of the plant and animal species that inhabit the water provides valuable information as to the health of the lake. An assessment of the current situation with respect to the aquatic communities in the lake is given in the following sections. 5.3.1 Phytoplankton The phytoplankton communities in lakes form the base of the food web and affect recreational-use of the lake. Phytoplankton, also called algae, is small aquatic plants naturally present in all lakes. They derive energy from sunlight (through photosynthesis) and from dissolved nutrients found in lake water. They provide food for several types of animals, including zooplankton, which are in turn eaten by fish. An inadequate phytoplankton population limits the lake’s zooplankton population and can, thereby, limit the fish production in a lake. Conversely, excess phytoplankton can alter the structure of the zooplankton community and interfere with sight-based fish predation, thereby also having an adverse effect on the lake’s fishery. In addition, excess phytoplankton reduces water clarity; reduced water clarity can in itself make recreational-usage of a lake less desirable. Green algae are considered beneficial as they are edible to zooplankton and serve as a valuable food source. Blue-green algae are considered nuisance algae because they: • are generally inedible for fish, waterfowl, and most zooplankton, • float at the lake surface in expansive algal blooms, • may be toxic to animals when occurring in large blooms, and • can interfere with recreational uses of the lake 5.3.1.1 Arrowhead Lake Phytoplankton Surveys Figure 5-5 shows that the overall phytoplankton levels in Arrowhead Lake varies during 2004 as does the distribution of the type of species present. The cryptomonads were the dominant phytoplankton group sampled early in the season (April, May, and early June) while Chlorophyta, or green algae, P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 42 were the dominant phytoplankton group in Arrowhead Lake during the peak of the growing season. There were very low numbers of blue-green algae seen in Arrowhead Lake throughout the season which is atypical of lakes impacted by excess phosphorus and poor water quality. Also, it should be noted that the species Anabaenopsis raciborski was present in low numbers, and it is species known to produce a hepatatoxin, which poses a potential for human health risk as it can affect liver function if enough water is ingested. 5.3.1.2 Indianhead Lake Phytoplankton Surveys Figure 5-6 shows that the overall phytoplankton levels in Indianhead Lake varied throughout the 2004 season with the peak levels occurring in June and again in the beginning of September. The distribution of the types of species present also varied. Green algae were dominant in Indianhead Lake during most sampling events (see Figure 5-6) and were present in all samples. Diatom, or bacillariophyta, concentrations were highest during June and were comparable to green algae concentrations at that time as well. There were also very low numbers of blue-green algae during the growing season in Indianhead Lake, suggesting relatively good water quality with lower total phosphorus concentrations. Indianhead Lake was treated with copper sulfate in May and August of 2004 which most likely impacted the phytoplankton populations within the lake. P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ D a t a \ W Q D a t a \ P h y t o p l a n k t o n \ 0 4 A r r o w h e a d L a k e P h y t o p l a n k t o n . x l s Fi g u r e 5 - 5 Ar r o w h e a d L a k e 20 0 4 P h y t o p l a n k t o n D a t a Su m m a r y b y D i v i s i o n 0 5, 0 0 0 10 , 0 0 0 15 , 0 0 0 20 , 0 0 0 25 , 0 0 0 30 , 0 0 0 35 , 0 0 0 4/ 2 2 / 2 0 0 4 6/ 1 0 / 2 0 0 4 7/ 8 / 2 0 0 4 8/ 1 1 / 2 0 0 4 8/ 2 5 / 2 0 0 4 9/8/2004 Sa m p l e D a t e # o f o r g a n i s m s / m 2 Ot h e r Cr y p t o p h y t a ( C r y p t o m o n a d s ) Ba c i l l a r i o p h y t a ( D i a t o m s ) Cy a n o p h y t a ( B l u e - G r e e n A l g a e ) Ch r y s o p h y t a ( Y e l l o w - B r o w n A l g a e ) Ch l o r o p h y t a ( G r e e n A l g a e ) P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ D a t a \ W Q D a t a \ P h y t o p l a n k t o n \ 0 4 I n d i a n h e a d L a k e P h y t o p l a n k t o n . x l s Fi g u r e 5 - 6 In d i a n h e a d L a k e 20 0 4 P h y t o p l a n k t o n D a t a Su m m a r y b y D i v i s i o n 0 5, 0 0 0 10 , 0 0 0 15 , 0 0 0 20 , 0 0 0 25 , 0 0 0 4/ 2 2 / 2 0 0 4 6/ 1 1 / 2 0 0 4 7/ 8 / 2 0 0 4 8/ 1 1 / 2 0 0 4 8/ 2 5 / 2 0 0 4 9/8/2004 Sa m p l e D a t e # o f o r g a n i s m s / m 2 Ot h e r Cr y p t o p h y t a ( C r y p t o m o n a d s ) Ba c i l l a r i o p h y t a ( D i a t o m s ) Cy a n o p h y t a ( B l u e - G r e e n A l g a e ) Ch r y s o p h y t a ( Y e l l o w - B r o w n A l g a e ) Ch l o r o p h y t a ( G r e e n A l g a e ) P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 45 5.3.2 Zooplankton Zooplankton—microscopic crustaceans—are vital to the health of a lake ecosystem because they feed upon the phytoplankton and are food themselves for many fish species. Protection of the lake’s zooplankton community through proper water quality management practices protects the lake’s fishery. Zooplankton is also important to lake water quality. The zooplankton community is generally comprised of three groups: cladocera, copepoda, and rotifera. The rotifers and copepods in lakes graze primarily on extremely small particles of plant matter and, therefore, do not significantly affect lake water transparency by removing algae. By contrast, cladocera graze primarily on algae and can increase transparency if they are present in abundance. Daphnia spp. is among the larger cladocera species and is considered especially desirable in lakes because of their ability to consume large quantities of algae. There is not a surrogate measurement of zooplankton biomass similar to Chl a concentration for phytoplankton biomass. Therefore, zooplankton must be identified and counted to get an estimate of zooplankton biomass. 5.3.2.1 Arrowhead Lake Zooplankton Surveys Figure 5-7 shows the zooplankton totals (expressed as the number of organisms per square meter of lake surface) for Arrowhead Lake on each of the sampling dates throughout the summer of 2004. The zooplankton data are present in Appendix E. Each total shown is divided into the three main divisions of zooplankton to give an indication of their relative abundance. The overall amount and distribution of the type of zooplankton in Arrowhead Lake varied throughout the season. However, there was a good balance of the three major groups of zooplankton present in the lake. In the early part of the season, copepods and clodocera were the dominant groups of zooplankton. Later in the season, the smaller-bodied rotifers were the dominant group most likely as the result of the decline in the number of copepods and clodocera due the predation by fish. In Arrowhead Lake, a very low numbers of the Daphnia species were observed in 2004. Planktivorous fish (such as sunfish and bluegills) eat zooplankton and will preferentially select the large Daphnia. Therefore, to thrive, the Daphnia require either a refuge from predators (i.e., deep, well-oxygenated water) or a smaller predator population. The MDNR fishery data shows that both green sunfish and bluegills are present in Arrowhead Lake (see Section 5.3.4.1 – Arrowhead Lake P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 46 Fish and Wildlife Surveys). It is also a shallow lake. The combination of these factors could likely contribute to the low Daphnia populations this lake. 5.3.2.2 Indianhead Lake Zooplankton Surveys Figure 5-8 shows the zooplankton totals (expressed as the number of organisms per square meter of lake surface area) for Indianhead Lake on each of the sampling dates throughout the summer of 2004. The zooplankton data are present in Appendix E. Each total shown is divided into the three main divisions of zooplankton to give an indication of their relative abundance. The overall amount and distribution of the type of zooplankton in Indianhead Lake varied throughout the season. In the early part of the season, overall zooplankton levels were very low. The peak number of zooplankton in the lake occurred in the end of August. Copepods were the dominant group of zooplankton April through June. However, by July, the number of copepods declined to almost zero, most likely as the result of predation by fish. The rotifers were the dominant zooplankton group throughout the rest of the season. Clodocera was nearly nonexistent in Indianhead Lake throughout the entire sampling season. Indianhead Lake is a small and shallow lake and this might impact the clodocera population. Because the rotifers are the dominant group of zooplankton in Indianhead Lake and have very little or no impact on algae concentrations, biological control of algae within this system is very unlikely. P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ D a t a \ W Q D a t a \ Z o o p l a n k t o n \ Z o o p l a n k t o n _ A r r o w h e a d _ 2 0 0 4 . x l s Fi g u r e 5 - 7 Ar r o w h e a d L a k e 20 0 4 Z o o p l a n k t o n D a t a Su m m a r y b y D i v i s i o n 0 2 00 , 0 0 0 40 0 , 0 0 0 60 0 , 0 0 0 80 0 , 0 0 0 1, 0 0 0 , 0 0 0 1, 2 0 0 , 0 0 0 1, 4 0 0 , 0 0 0 1, 6 0 0 , 0 0 0 1, 8 0 0 , 0 0 0 4/ 2 1 / 2 0 0 4 6/ 1 0 / 2 0 0 4 7/ 7 / 2 0 0 4 8/ 1 1 / 2 0 0 4 8/ 2 4 / 2 0 0 4 9/10/2004 Sa m p l e D a t e # o f o r g a n i s m s / m 2 Rotifera Copepoda Cladocera P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ D a t a \ W Q D a t a \ Z o o p l a n k t o n \ Z o o p l a n k t o n _ I n d i a n h e a d _ 2 0 0 4 . x l s Fi g u r e 5 - 8 In d i a n h e a d L a k e 20 0 4 Z o o p l a n k t o n D a t a Su m m a r y b y D i v i s i o n 0 1 ,0 0 0 , 0 0 0 2, 0 0 0 , 0 0 0 3, 0 0 0 , 0 0 0 4, 0 0 0 , 0 0 0 5, 0 0 0 , 0 0 0 6, 0 0 0 , 0 0 0 7, 0 0 0 , 0 0 0 4/ 2 1 / 2 0 0 4 6/ 1 0 / 2 0 0 4 7/ 7 / 2 0 0 4 8/ 1 1 / 2 0 0 4 8/ 2 4 / 2 0 0 4 9/10/2004 Sa m p l e D a t e # o f o r g a n i s m s / m 2 Ro t i f e r a Co p e p o d a Cl a d o c e r a P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 49 5.3.3 Macrophytes Aquatic plants—macrophytes—are a natural and integral part of most lake communities, providing valuable refuge, habitat and forage for many animal species. The lake’s aquatic plants, generally located in the shallow areas near the shoreline of the lake: • Provide habitat for fish, insects, and small invertebrates • Provide food for waterfowl, fish, and wildlife • Produce oxygen • Provide spawning areas for fish in early-spring/provide cover for early-life stages of fish • Help stabilize marshy borders and protect shorelines from wave erosion • Provide nesting sites for waterfowl and marsh birds Surveys of the aquatic plant communities in Arrowhead and Indianhead Lakes were completed in June and August of 2004. Survey results are presented in Appendix B and are summarized below. 5.3.3.1 Arrowhead Lake Macrophyte Surveys The June 2004 macrophyte survey of Arrowhead Lake showed that macrophyte growth was limited to areas of the lake with water depths less than 5 to 6 feet, with much of the central, deeper portion of the lake containing no aquatic vegetation. Curlyleaf pondweed (Potamogeton crispus) turions were present in the lake and there was evidence that the lake was treated to control the Curlyleaf pondweed prior to the June survey. It should be noted that Curlyleaf pondweed is an undesirable non-native species. It frequently replaces native species in lakes and exhibits a dense growth that may interfere with the recreational use of a lake. A dense growth also creates a convenient refuge for small fish, making it difficult for larger fish, such as bass, to locate and prey upon the small fish they need for food. As such, Curlyleaf pondweed can hinder gamefish production. Furthermore, the mid-season die-off that is a natural part of the life cycle of Curlyleaf pondweed can contribute (through plant matter decay) to increases in the lake’s late-summer epilimnetic phosphorus concentration. This non-native species is thus often held partially responsible for late-summer algal blooms. Coontail (Ceratophyllum demersum) was observed in the lake as well, though its presence was sporadic in low densities. Since coontail absorbs its nutrients from the water column, its presence likely impacted the TP concentration observed in Arrowhead Lake. Other submerged macrophytes P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 50 present in June included Eurasian watermilfoil in a very low density and stonewort (Myriophyllum spicatum and Nitella sp.), found in high density in the northwest lobe of the lake. Sporadic white waterlily and little yellow water lily (Nymphaea tuberosa and Nuphar microphyllum) were seen on top of the submerged species covering the littoral zone along the northern shore of the lake while the white water lily was also found in the littoral zone along the southern shore of Arrowhead Lake. Sporadic emergent stands of cattail, bullrush, and blue flag iris (Typha sp., Scirpus sp., and Iris vericolor) were located predominantly along the north shore of the Lake. The pattern of macrophyte coverage seen in June was similar in August of 2004. However, much of the Curlyleaf pondweed (Potamogeton crispus) had died off by the August sampling as is typically the case for that species. Coontail, Eurasian milfoil, and stonewort were still present along with bushy pondweed and naiad, water star grass, muskgrass, and narrow pondweed (Najas sp., Zostrella dubia, Chara sp., and Potamogeton sp.). Both white waterlily and little yellow waterlily were still present in August, although white waterlily was sporadically present along the entire perimeter of the lake. The same emergent species were also found in a similar pattern along the shore of the lake. There were also algal mats present in the southeast lobe of Arrowhead Lake. 5.3.3.2 Indianhead Lake Macrophyte Surveys The June 2004 macrophyte survey of Indianhead Lake showed that macrophytes were found throughout the lake, though they were less dense near the center of the lake. Three species of submerged macrophytes were present during the June survey. These species included slender riccia, stonewort, and narrowleaf pondweed (Riccia fluitans, Nitella sp., and Potamogeton sp.). Narrowleaf pondweed was found in the northwest lobe of the lake while stonewort was located throughout, most densely in the southeast lobe. No species of floating leaf macrophytes were present. However, there were several species of emergent vegetation sporadically located along the perimeter of the lake, including yellow iris, cattail, bullrush, sweetflag, and arrowhead (Iris sp., Typha sp., Scirpus sp., Acorus calamus, and Sagittaria sp.). A large area of cattail and slender riccia was located on the northside of the southeast lobe of Indianhead Lake. The pattern of macrophyte coverage seen in June was similar in August of 2004 with the same species present in Indianhead Lake. Macrophyte densities did increase in some areas of the lake. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 51 Survey notes indicated that a water colorant may have been used. According to the MDNR, it is illegal to use water colorants that claim to inhibit macrophyte growth within the state of Minnesota, with Aqua Shade being the only water colorant registered with the USEPA claiming the control of macrophyte growth. Currently, MDNR permits only allow a maximum of herbicide treatment area of 15 percent of the littoral area. Application of a colorant for macrophyte growth is considered a full- lake treatment and therefore is not legal within the State. 5.3.4 Fish and Wildlife 5.3.4.1 Arrowhead Lake Fish and Wildlife Surveys According to MDNR’s most recent (1995) Lake Survey Report for Arrowhead Lake, a limited variety of fish were sampled during the survey. Black bullhead and green sunfish dominate the fishery in Arrowhead Lake (see Appendix E). The numbers of these species were well above the average for similar lakes, though the sizes of the fish sampled were slightly below average. In addition to the black bullhead and the green sunfish, a few bluegill were also sampled. The report also suggests that the lake was stocked with bluegills and large mouth bass by the City of Edina in the year prior to the survey. However, review of MDNR stocking reports for the past decade suggests that Arrowhead Lake has not been stocked with any species during this period. According to the MDNR survey, Arrowhead Lake has experienced winterkill. Frequent winterkills are related to poor water quality. Eutrophic lakes (such as Arrowhead Lake) produce relatively large quantities of algae during summer months. After the algae die and settle to the bottom of the lake, their decomposition uses oxygen that would otherwise be available to the fish population. The problem becomes especially severe in the winter when ice cover on the lake prevents transfer of oxygen from the atmosphere to the water. However, during the 2004 sampling year, there were several aerators operating in Arrowhead Lake. In addition to supporting its fish populations, Arrowhead Lake provides habitat for seasonal waterfowl, such as ducks and geese, which find refuge and forage in the lake’s diverse macrophyte communities in the lake’s large littoral area. 5.3.4.2 Indianhead Lake Fish and Wildlife Surveys There are no MDNR fishery survey data available for Indianhead Lake. Additionally, review of MDNR stocking reports for the past decade suggests that Indianhead Lake has not been stocked with any species during this period. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 52 Indianhead Lake provides habitat for seasonal waterfowl, such as ducks and geese, which find refuge and forage in the lake’s diverse macrophyte communities in the lake’s large littoral zone. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 53 6.0 Water Quality Modeling for the UAA For this study, a detailed analysis was completed to determine phosphorus sources and management opportunities that would reduce the amount of phosphorus reaching both Arrowhead and Indianhead Lakes. Phosphorus typically is transported as soluble phosphorus (dissolved in the water) or attached to sediments carried by water. Therefore, the determination of the volume of water discharged annually to each lake is integral to defining the amount of phosphorus loading. 6.1 Use of the P8 Model The P8 model was used (see Section 1.2) to estimate both the water and phosphorus loads introduced to each lake from their respective watersheds. The model requires hourly precipitation and daily temperature data; long-term climatic data can be used so that watersheds and BMPs can be evaluated for varying hydrologic conditions. Hourly precipitation data was obtained from the Eden Prairie and Hopkins precipitation gages operated by the Nine Mile Creek Watershed District during from 1998 through the model calibration year with the exception of the period of June 2000 though April of 2001, which, according to the water balance models, appeared to underestimate the actual precipitation in these watersheds. Minneapolis-St. Paul International Airport gage data was used for this period as well as for years prior to 1998. The 2003-04 simulation period (May 1, 2003 through September 30, 2004) precipitation total was 44.8 inches. Daily temperature data was obtained from the NWS site at the Minneapolis-St. Paul International Airport. When evaluating the results of P8 modeling, it is important to consider that the results provided are more accurate in terms of relative differences than in terms of absolute results. The model will help predict the percent difference in phosphorus reduction between various BMP options in the watershed fairly accurately. It also provides a realistic estimate of the relative differences in phosphorus and water loadings from the various subwatersheds and major inflow points to the lake. However, since runoff quality is highly variable with time and location, the phosphorus loadings estimated by the model for a specific watershed may not necessarily reflect the actual loadings, in absolute terms. Various site-specific factors, such as lawn care practices, illicit point discharges and erosion due to construction are not accounted for in the model. The model provides values that can be expected to be typical of the region, given the watershed’s respective land uses. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 54 6.2 Water Quality Model (P8) Calibration 6.2.1 Stormwater Volume Calibration Both Arrowhead and Indianhead Lakes were initially modeled as part of the larger Normandale Lake UAA and the City of Edina Comprehensive Water Resources Plan. These larger runoff models were calibrated to the observed runoff at two monitoring sites on Nine Mile Creek just upstream of where the North and South Forks of Nine-Mile Creek merge. Though modeled as part of a larger area, attention was not focused specifically on the Arrowhead or Indianhead Lakes’ watersheds. Because the original models were not specifically calibrated to Arrowhead and Indianhead Lakes, the models used in this study were calibrated to the observed water surface elevation of each lake using the water balance model, WATBUD, developed by MDNR. The model uses a lake-specific stage- storage-discharge relationship as well as estimated daily inflows (i.e., predicted by the P8 model), daily precipitation, daily evaporation, and observed lake levels to estimate total annual outflows. Because there are no surface outlets in either Arrowhead Lake or Indianhead Lake, surface discharge was assumed to be zero. WATBUD was then used to determine the daily volume of groundwater exchange for each lake. 6.2.1.1 Arrowhead Lake Stormwater Volume Calibration Lake level data was available for Arrowhead Lake from 1964 through 2005 for all months of the year. The WATBUD model was calibrated using the period from January 1998 through September 2002. The stage-storage-discharge relationships provided in Table 4-1 was used in WATBUD and was developed based on basin bathymetry data and topographic information from the city of Edina. The groundwater exchange parameters determined by WATBUD for this calibration period were then used to determine the groundwater exchange for the period of May 2003 through September 2004 which was used for water quality modeling. Figure 6-1 illustrates the results of the water balance modeling using these calibrated groundwater exchange parameters for Arrowhead Lake. The predicted water levels shown by the pink line on the plot closely matched the observed water levels (dark blue points). A plot of predicted versus observed lake levels illustrates the close relationship (r2 = 0.79, see Figure 6-2). 6.2.1.2 Indianhead Lake Stormwater Volume Calibration Lake level data was available for Indianhead Lake from 1993 through 2005 for non-winter months. The WATBUD model was calibrated using the period from April 1998 through September 2002. The stage-storage -discharge relationships provided in Table 4-2 was used in WATBUD and was P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 55 developed based on basin bathymetry data and topographic information from the city of Edina. The groundwater exchange parameters determined by WATBUD for this calibration period were then used to determine the groundwater exchange for the period of May 2003 through September 2004 which was used for water quality modeling. Figure 6-3 illustrates the results of the water balance modeling using the groundwater exchange parameters calibrated to Indianhead Lake levels. The predicted water levels shown by the pink line on the plot closely matched the observed water levels (dark blue points). A plot of predicted versus observed lake levels illustrates the close relationship (r2 = 0.90, see Figure 6-4). 6.2.2 Phosphorus Loading The phosphorus loads predicted by the P8 model were determined using runoff particle parameters taken from the Nationwide Urban Runoff Program (NURP 50). 6.2.3 Atmospheric Deposition An atmospheric deposition rate of 0.2615 kg/ha/yr (Barr, 2005) was applied to the surface area of each lake to determine annual phosphorus loading. An annual total phosphorus load from atmospheric deposition of 4.9 lbs (2.2 kg) was estimated for Arrowhead Lake during 2004. For Indianhead Lake, the total phosphorus load due to atmospheric deposition was 2.9 lbs (6.3 kg). P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ W A T B U D \ R e s u l t s \ A H \ M E P 4 9 0 2 _ P P T \ A H _ W A T B U D _ 4 1 3 0 6 . x l s Fi g u r e 6 - 1 Ar r o w h e a d L a k e Wa t e r B a l a n c e M o d e l i n g R e s u l t s 87 2 . 0 0 87 3 . 0 0 87 4 . 0 0 87 5 . 0 0 87 6 . 0 0 87 7 . 0 0 87 8 . 0 0 1/1 4/199 8 7/1 4/199 8 1/1 4/199 9 7/1 4/199 9 1/1 4/200 0 7/1 4/200 0 1/1 4/200 1 7/1 4/200 1 1/1 4/200 2 7/1 4/200 2 1/1 4/200 3 7/1 4/200 3 1/1 4/200 4 7/1 4/200 4 Da t e W a t e r S u r f a c e E l e v a t i o n ( f e e t M S L ) Ob s e r v e d L a k e L e v e l Pr e d i c t e d L a k e L e v e l Gr o u n d w a t e r P a r a m e t e r C a l i b r a t i o n P e r i o d Water Quality Calibration Period P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ W A T B U D \ R e s u l t s \ A H \ M E P 4 9 0 2 _ P P T \ A H _ W A T B U D _ 4 1 3 0 6 . x l s Fi g u r e 6 - 2 Ar r o w h e a d L a k e Wa t e r B a l a n c e M o d e l i n g R e s u l t s Pr e d i c t e d v s O b s e r v e d L a k e L e v e l s ( 7 / 3 1 / 0 3 - 9 / 2 9 / 0 4 ) y = 0 . 9 9 9 7 x R 2 = 0 . 7 8 6 9 87 1 . 5 87 2 87 2 . 5 87 3 87 3 . 5 87 4 87 4 . 5 87 5 87 5 . 5 87 2 . 0 0 87 2 . 5 0 87 3 . 0 0 87 3 . 5 0 87 4 . 0 0 87 4 . 5 0 875.00 875.50 Ob e r v e d L a k e L e v e l s ( f e e t M S L ) P r e d i c t e d L a k e L e v e l s ( f e e t M S L ) P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ W A T B U D \ R e s u l t s \ I H \ I H _ W A T B U D . x l s Fi g u r e 6 - 3 In d i a n h e a d L a k e Wa t e r B a l a n c e M o d e l i n g R e s u l t s 86 1 . 0 0 8 61 . 5 0 86 2 . 0 0 86 2 . 5 0 86 3 . 0 0 86 3 . 5 0 86 4 . 0 0 4/1 8/1998 10/18/1998 4/1 8/1999 10/18/1999 4/1 8/2000 10/18/2000 4/1 8/2001 10/18/2001 4/1 8/2002 10/18/2002 4/1 8/2003 10/18/2003 4/1 8/2004 Da t e W a t e r S u r f a c e E l e v a t i o n ( f e e t M S L ) Ob s e r v e d L a k e L e v e l Pr e d i c t e d L a k e L e v e l Gr o u n d w a t e r P a r a m e t e r C a l i b r a t i o n P e r i o d Water Quality Calibration Period P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ W A T B U D \ R e s u l t s \ I H \ I H _ W A T B U D . x l s Fi g u r e 6 - 4 In d i a n h e a d L a k e Wa t e r B a l a n c e M o d e l i n g R e s u l t s Pr e d i c t e d V s O b s e r v e d L a k e L e v e l s ( 4 / 7 / 0 4 - 9 / 2 7 / 0 4 ) y = 0.9998x R 2 = 0.8966 86 1 86 1 . 5 86 2 86 2 . 5 86 3 86 3 . 5 86 4 86 1 . 0 0 86 1 . 5 0 86 2 . 0 0 86 2 . 5 0 86 3 . 0 0 86 3 . 5 0 864.00 Ob s e r v e d L a k e L e v e l ( f e e t M S L ) P r e d i c t e d L a k e L e v e l ( f e e t M S L ) P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 60 6.3 In-Lake Modeling While the P8 model is a useful tool for evaluating runoff volumes and pollutant concentrations from a watershed, another method is needed to predict the in-lake phosphorus concentrations that are likely to result from the various phosphorus loads. For evaluating the resultant in-lake concentrations in Arrowhead and Indianhead Lakes, a spreadsheet model based on the empirical equation set forth by Dillion and Rigler (1974) was used. To calibrate the mass balance water quality model for existing land use conditions, phosphorus loads for 2004 were predicted using the P8 model and then used with the 2004 in-lake water quality data to calculate the internal phosphorus load (described in more detail in Section 6.3.2). 6.3.1 Balance Modeling to Existing Water Quality Water quality sample data for both Arrowhead and Indianhead Lakes, which consisted of total phosphorus data from 2004, were used to calibrate and verify the lake water quality mass balance model for each lake. The model was calibrated using data from a 2004 intensive water quality sampling effort. Because there was only one year of water quality data available for both Arrowhead and Indianhead Lakes, the models were not able to be verified. To improve the model verification, it is recommended that additional water quality data be collected for both of these lakes. The water quality data were used to determine the best in-lake water quality model to use for this analysis. The best fit proved to be the Vollenweider equation. Therefore, this model was used for predicting the spring total phosphorus concentrations of both Arrowhead and Indianhead Lakes. The following steady-state mass balance equation was used for modeling the springtime total phosphorus concentrations of Arrowhead and Indianhead Lakes: V)K(Q WP s SPRING += P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 61 where: PSPRING = spring total phosphorus concentration (μg/L) W = total phosphorus loading rate (mg/yr) Q = outflow (m3/yr) Ks = first order settling loss rate per year V = lake volume (m3) While this model, supplied with the May 1, 2003 to April 30, 2004 total phosphorus loading predicted by P8 for existing land use conditions, adequately predicted the spring steady-state concentration of phosphorus in lake, early-summer, summer average and fall overturn concentrations were not accounted for in the above model. It was determined after analyzing historical water quality data that the phosphorus concentrations varied significantly during the summer time. These variations were the result of additional watershed runoff and internal loading (see Section 6.3.3 for the in-lake calibration results). 6.3.2 Accounting for Internal Loading Most of the empirical phosphorus models assume that the lake to be modeled is well-mixed, meaning that the phosphorus concentrations within the lake are uniform. This assumption is useful in providing a general prediction of lake conditions, but it does not account for the seasonal changes in phosphorus concentrations that can occur in a lake. Such changes occur in dimictic lakes when phosphorus is removed by settling from the epilimnion. As has been discussed, these changes can also occur seasonally as a result of internal loading. Therefore, mass balance models are needed to allow the use of the P8-generated TP loads to provide reasonable predictions of summer average epilimnetic lake phosphorus concentrations. During periods of stratification the bottom waters can become anoxic (devoid of oxygen), even for short periods, and internal phosphorus load from the lake sediments may occur. The phosphorus released from the sediments can build up in the hypolimnion during periods of stratification, especially during periods of high temperatures and low wind. This internal load of phosphorus can be transported to the entire water column as wind increases and causes lake circulation or as fall approaches and mixing typically begins to occur. However, based on observed temperature and dissolved oxygen profiles in Arrowhead Lake throughout the summer months of 2004, it appears to P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 62 be “polymictic” (normally well-mixed) with only slight stratification occurring in June. Indianhead Lake also appears to be polymictic during 2004. The internal loading of phosphorus was calculated from the following mass balance equation: Internal P = Observed P + Outflow P - Runoff P - Atmospheric P The phosphorus mass balance was calculated for each lake basin based on existing land use conditions and phosphorus concentrations measured in 2004. Because both Arrowhead and Indianhead Lakes are land locked basins, the only outflow from the basins were assumed to be losses to the groundwater which were quantified using the WATBUD water balance model. 6.3.3 In-Lake Modeling Results The estimated atmospheric, internal and watershed runoff phosphorus loads were applied to the in-lake water quality model to predict the associated phosphorus concentrations in the lake. The annual internal phosphorus load discussed in the previous section, and additional watershed runoff loads were used to calibrate the model to the in-lake phosphorus concentration during the 2004 monitoring period. 6.3.4 Existing (2004) Land Use Conditions (Model Calibration) The in-lake phosphorus model simulation was essentially used to validate the estimated watershed and internal loads, since actual in-lake data were collected during 2004. Figure 6-5and 6-6 compares the simulated and the actual in-lake phosphorus concentrations for spring steady-state, early-summer peak, summer average for Arrowhead and Indianhead Lakes. The modeling results are accurately predicting the observed total phosphorus concentrations for the individual basins for the time periods of interest. There was an insignificant difference between the observed and modeled spring steady- state phosphorus concentration. P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ A H \ I n - L a k e M o d e l _ P a r t i t i o n 6 _ A H _ 7 7 0 6 _ F i n a l . x l s : F I G U R E 6 _ 5 7/13/2006 7:27 PM Fi g u r e 6 - 5 Ar r o w h e a d L a k e U A A In - L a k e M o d e l C a l i b r a t i o n R e s u l t s f o r 2 0 0 4 C l i m a t i c C o n d i t i o n s wi t h W a t e r s h e d a n d S p r i n g D e c a y 41 40 26 15 14 13 2 2 2 3 3 34 29 22 23 26 33 28 17 16 1 4 11 0 8 4 56 56 5572.2 23 . 1 6 1 0. 5 9 2. 8 4 3. 0 1 0. 6 7 1.5 020406080 10 0 12 0 4/ 3 0 / 0 4 6/ 1 0 / 0 4 7/ 7 / 0 4 8/ 1 1 / 0 4 8/ 2 4 / 0 4 9/10/04 Da t e I n - L a k e [ T P ] ( µ µ µ µ g / L ) 0 5 10 15 20 25Precipitation (inches) St e a d y S t a t e [ T P ] At m o s p h e r i c D e p o s i t i o n [ T P ] W a t e r s h e d R u n o f f [ T P ] Cu r l y L e a f P o n d w e e d [ T P ] Ob s e r v e d [ T P ] Su m m e r A v e r a g e [ T P ] Pe r i o d P r e c i p i t a t i o n P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ I H \ I n - L a k e M o d e l _ P a r t i t i o n 6 _ I H _ 7 6 0 6 _ F I N A L _ 2 0 0 4 _ C A L I B R A T I O N _ C u S O 4 . x l s : F i g u r e 6 - 6 7/13/2006 7:28 PM Fi g u r e 6 - 6 In d i a n h e a d L a k e U A A In - L a k e M o d e l C a l i b r a t i o n R e s u l t s f o r 2 0 0 4 C l i m a t i c C o n d i t i o n s wi t h W a t e r s h e d a n d S p r i n g D e c a y 24 15 13 12 8 6 3 4 7 5 6 26 30 39 27 26 0 0 1 0 0 44 4 7 60 40 3845.8 23 . 2 1 0. 6 2. 8 3. 0 0. 7 4.5 010203040506070 4/ 3 0 / 0 4 6/ 1 0 / 0 4 7/ 7 / 0 4 8/ 1 1 / 0 4 8/ 2 4 / 0 4 9/10/04 I n - L a k e [ T P ] ( µ µ µ µ g / L ) 0.0 5.0 10.0 15.0 20.0 25.0Precipitation (inches) Sp r i n g S t e a d y S t a t e At m o s p h e r i c D e p o s i t i o n W a t e r s h e d R u n o f f In t e r n a l Ob s e r v e d Su m m e r A v e r a g e Pe r i o d P r e c i p i t a t i o n Co p p e r S u l f a t e T r e a t m e n t s P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 65 6.4 Use of the P8/In-lake Model The in-lake model, adjusted to account for internal loading and calibrated to measured 2004 in-lake TP concentrations, was subsequently used to estimate phosphorus loads and concentrations under varying climatic conditions and BMP options. The annual water and watershed phosphorus loadings to Arrowhead and Indianhead Lakes under existing land use conditions were estimated for three different years, each representing a distinct climatic. The varying climatic conditions affect the lake’s volume and hydrologic residence time, and thereby affect the phosphorus concentrations in the lake. The precipitation totals during the 3 climatic conditions modeled are summarized in Table 6-1along with the estimated hydrologic residence time (in years). Table 6-1 Precipitation Amounts and Hydrologic Residence Time for Various Climatic Conditions used for Modeling Water and TP Loading to Arrowhead and Indianhead Lakes Lake Climatic Condition May 1 through April 30 Precipitation (inches) May 1 through September 30 Precipitation (inches) Estimated May Though April Hydrologic Residence Time (years) Arrowhead Dry (1987-88)* 26.03 8.47 1.19 Average (1994-95) 28.25 15.33 1.18 Wet (2001-02) 25.66 26.79 1.56 Calibration (2003-04) 22.24 18.18 1.51 Indianhead Dry (1987-88)* 26.03 8.47 1.22 Average (1994-95) 28.25 15.33 1.22 Wet (2001-02) 25.66 26.79 1.96 Calibration (2003-04) 22.24 18.18 1.76 *The May 1, 1987 through April 30, 1988 precipitation total excludes the 10-inch 1987 (7/23/87) superstorm because of the rarity of this event. In -lake modeling was used to evaluate the lake’s response to the P8-predicted loadings resulting from several BMP options. Details of the modeling results and a discussion of management opportunities follow. 6.5 Modeling Chlorophyll a and Secchi Disc Transparency The P8 model used for the analysis predicts phosphorus loads to the lakes, and the in-lake model used to determine water quality in the lake itself only estimates phosphorus loads and concentrations. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 66 To estimate Chl a concentrations and SD transparencies, it was necessary to develop additional models (i.e., regression relationships). Several authors have published equations giving general relationships between TP, Chl a, and transparency. These published equations are generally best-fit regression equations developed as general descriptions of the results of water quality analysis for many lakes. The published regression equations give reasonable indications of the algal growth and transparency dynamics for lakes of a particular class or region, but they may or may not be well-suited for application to a specific lake. In most cases, the comparison of the published equations with data for Arrowhead and Indianhead Lakes showed that the published equations were not suitable for representing the dynamics of these lakes. The exception was the equation used for the estimation of Secchi disc transparency in Arrowhead Lake. Because only one year of observed water quality data were available for both lakes, developing reliable lake-specific relationships between summer average TP and Chl a and Secchi disc transparency was not able to be preformed. Instead, all surface water quality data collected from each lake for 2004 were used to estimate Chl a concentrations and Secchi disc transparencies from modeled TP concentrations. Figure 6-7 and 6-8 depicts the numerical water quality models used to estimate Chl a and SD values for Arrowhead and Indianhead Lakes. Because the original regressions to the actual water quality data available for Arrowhead Lake linking Chl a concentrations to both TP and Secchi disc values resulted in very poor correlation and illogical predictions, the relationship developed by the MPCA for shallow lakes in the West-central lakes study was used to predict the Chl a concentrations in Arrowhead Lake (MPCA, 2005). For Arrowhead Lake, the equations are: Log[Chl a] = 1.08*Log[TP] – 0.66 R2 = 0.8 SD = -0.0047*[TP] + 1.3164 R2 = 0.71 And for Indianhead Lake, the equations are: [Chl a] = 0.12*[TP]1.1069 R2 = 0.54 SD = -0.5842Ln[TP] + 3.3519 R2 = 0.65 Where: [TP] = measured or estimated epilimnetic (mixed surface layer) mean summer P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 67 total phosphorus concentration (µg/L) [Chl a] = estimated epilimnetic mean summer Chlorophyll a concentration (µg/L) Secchi (SD) = estimated mean summer Secchi disc transparency (m) TSISD = was estimated from Carlson (1977): TSISD = 10(6- ln(SD)/ln(2)) These equations were subsequently used to give indications of what may be expected with respect to Chl a and transparency, given the P8/in-lake model results for TP. It should be noted that the response of Chl a and Secchi disc to TP is highly variable. Due to the high variability, the regression equations therefore can be expected only to allow a general indication of the lake response to changing TP, and the predicted Chl a and transparency values should not be interpreted as absolute. Arrowhead Lake Secchi Disc Tranparency as a Function of Total Phosphorus SD = -0.0047*TP + 1.3164 R2 = 0.7133 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 20 40 60 80 100 120 Total Phosphorus Concentration (µµµµg/L) Se c c h i D i s c T r a n s p a r e n c y ( m ) Individual Samples Summer Average Figure 6-7 Arrowhead Lake Relationships between Total Phosphorus, Chlorophyll a , and Secchi Disc Transparency Arrowhead Lake Chlorophyll a as a Function of Total Phosphorus 0 5 10 15 20 25 30 35 0 20 40 60 80 100 120 Total Phosphorus Concentration (µµµµg/L) Ch l o r o p h y l l - a C o n c e n t r a t i o n ( µµµµg/ L ) Individual Samples Summer Average From MPCA, 2005: Log[Chla ] = 1.08*Log[TP] - 0.66 P:\23\27\634\Indianhead_Arrowhead_UAA\Data\WQData\WQ\Arrowhead Lake WQ04 Data.xls Indianhead Lake Chlorophyll-a as a Function of Total Phosphorus Chl a = 0.12*TP1.1069 R2 = 0.5401 0 2 4 6 8 10 12 14 20 25 30 35 40 45 50 55 60 65 Total Phosphorus Concentration (µµµµg/L) Ch l o r o p h y l l - a C o n c e n t r a t i o n ( µµµµg/ L ) Individual Samples Summer Average Indianhead Lake Secchi Disc Transparency as a Funtion of Total Phosphorus SD = -0.5842Ln(TP) + 3.3519 R2 = 0.6466 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 20 25 30 35 40 45 50 55 60 65 TP Concentration (µµµµg/L) Se c c h i D i s c T r a n p a r e n c y ( m ) Individual Samples Summer Average Figure 6-8 Indianhead Lake Relationships between Total Phosphorus, Chlorophyll a , and Secchi Disc Transparency P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 70 7.0 Climatic Condition Analysis The likely responses of Arrowhead and Indianhead Lakes to watershed conditions under the three modeled climate scenarios (described in Section 6.4) was evaluated using the P8 model in conjunction with the calibrated in-lake model. The purpose of this portion of the UAA is to provide a means of evaluating the condition of the lakes if no management initiatives (apart from those the NMCWD already requires for newly urbanized areas) are taken. Modeling assumptions and results are presented in the following sections. 7.1 Future Conditions Modeling Assumptions The land use used in the modeling for the ultimate watershed conditions was as described in Section 4.2 of this report. In general, it was assumed that the land uses within the Arrowhead and Indianhead Lakes’ watersheds are not expected to change in future years. As a result, the modeling results of existing land use were also considered to be representative of future land use in each watershed. 7.2 Modeling Results As was discussed in Section 6.4, three climate conditions were used in evaluating the likely water quality of Arrowhead and Indianhead Lakes for the current/future land use conditions. The modeling results for the climate condition scenarios for each watershed are presented below. 7.2.1 Water Quality Model Results for Arrowhead Lake Water quality simulations using the P8 and in-lake water quality models indicate that wet weather conditions will produce the greatest strain upon water quality in Arrowhead Lake. This is the result of a higher total load of phosphorus to the lakes during wet weather. Although wetter weather results in larger volumes of relatively less concentrated water reaching the lake, Arrowhead is a land-locked basin with no surface outlet. For that reason, no flushing occurs and phosphorus accumulates in the lake, especially during periods of high watershed loading. The modeling analysis indicated that the lake currently has water quality conditions ranging from poor to very poor under all climatic conditions. The estimated average summer total phosphorus concentrations for all the climatic conditions were in the hypereutrophic category (i.e., very poor water quality; see Figure 7-1). Under average, dry, and wet conditions, the modeled average summer P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 71 Chl a concentrations and Secchi disc transparencies were all in the eutrophic category (i.e., poor water quality; see Figure 7-1). 7.2.2 Water Quality Model Results for Indianhead Lake Like in Arrowhead Lake, water quality simulations using the P8 and in-lake water quality models indicate that wet weather conditions will produce the greatest strain upon water quality in Indianhead Lake. This is the result of a higher total load of phosphorus to the lakes during wet weather. Although wetter weather results in larger volumes of relatively less concentrated water reaching the lake, Arrowhead is a land-locked basin with no surface outlet. For that reason, no flushing occurs and total phosphorus accumulates in the lake, especially during periods of high watershed loading. The modeling analysis indicated that under existing water quality conditions, the lake currently has poor to very poor water quality under all climatic conditions. The estimated average summer total phosphorus and Chl a concentrations and Secchi disc transparencies for the wet and calibration climatic conditions were in the hypereutrophic category (i.e., very poor water quality; see Figure 7- 2). Under average and dry conditions, the modeled summer averages were all within the eutrophic range (i.e., poor water quality; see Figure 7-2). Table 7-1 Watershed Total Phosphorus Loading to Arrowhead and Indianhead Lakes for Various Climatic Conditions Watershed Climatic Condition 17 Month Modeled Total Phosphorus Load (lbs) Arrowhead Lake Wet (2001-02) 127.39 Average (1994-95) 97.95 Dry (1987-88)* 91.32 Calibration (2003-04) 102.68 Indianhead Lake Wet (2001-02) 51.50 Average (1994-95) 40.34 Dry (1987-88)* 38.43 Calibration (2003-04) 41.82 *The May 1, 1987 through April 30, 1988 precipitation total excludes the 10-inch 1987 superstorm because of the rarity of this event. 72.2 91.2 68.8 66.6 0 10 20 30 40 50 60 70 80 90 100 Calibration Wet Dry Average Climatic Conditions To t a l P h o s p h o r u s ( µµµµg/ L ) 18.5 28.6 21.1 20.4 0 5 10 15 20 25 30 35 40 Calibration Wet Dry Average Climatic Conditions Ch l o r o p h y l l a ( µµµµg/ L ) 1.0 0.9 1.0 1.0 0 0.2 0.4 0.6 0.8 1 1.2 Calibration Wet Dry Average Se c c h i D i s c T r a n s p a r e n c y ( m ) Figure 7-1 Arrowhead Lake Estimated Average Summer Total Phosphorus and Chlorophyll a Concentrations and Secchi Disc Transparency under Varying Climatic Conditions Hypereutrophic = Very Poor Eutrophic = Poor Mesotrophic = Good Eutrophic = Poor Mesotrophic = Good Eutrophic = Poor Hypereutrophic = Very Poor Upper Threshold NMCWD Level II Upper Threshold NMCWD Level II Lower Threshold NMCWD Level II P:\23\27\634\Indianhead_Arrowhead_UAA\InLakeModel\InLakeSummary.xls 0 10 20 30 40 50 60 70 80 Calibration Wet Dry Average Climatic Conditions To t a l P h o s p h o r u s ( µµµµg/ L ) 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 Calibration Wet Dry Average Climatic Conditions Ch l o r o p h y l l a ( µµµµg/ L ) 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 Calibration Wet Dry Average Se c c h i D i s c T r a n s p a r e n c y ( m ) Figure 7-2 Indianhead Lake Estimated Average Summer Total Phosphorus and Chlorophyll a Concentrations and SecchiDisc Transparency For Existing Conditions* Under Varying Climatic Scenarios Hypereutrophic = Very Poor Eutrophic = Poor Mesotrophic = Good Eutrophic = Poor Mesotrophic = Good Eutrophic = Poor Hypereutrophic = Very Poor Upper Threshold NMCWD Level II Lower Threshold NMCWD Level II Lower Threshold NMCWD Level II * Existing conditions for Indianhead Lake includes two copper sulfate treatments during the growing season P:\23\27\634\Indianhead_Arrowhead_UAA\InLakeModel\InLakeSummary.xls P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 74 8.0 Evaluation of Possible Management Options Analysis of the modeling done to evaluate the likely water quality for Arrowhead and Indianhead Lakes indicates that improvements could be made within the lakes and their watershed. The modifications necessary to achieve these improvements were evaluated under the calibration and three additional climatic conditions to determine what effect they might have on lake water quality. The management options, costs, and benefits are presented in Section 8.2. 8.1 General Discussion of Improvement Options This section discusses improvement options and general BMPs considered for the Arrowhead and Indianhead Lakes and watersheds to remove phosphorus and/or reduce sediment loads entering a lake. Three types of BMPs were considered during the preparation of this report: structural, nonstructural, and in-lake. However, it is important to note that this is not a complete list but rather a select list of BMPs most applicable to the conditions specific to the watersheds and lakes of this study. 1. Structural BMPs remove a fraction of the pollutants and sediment loads contained in stormwater runoff prior to discharge into receiving waters. 2. Nonstructural BMPs (source control) eliminate pollutants at the source and prevent pollutants from entering stormwater flows. 3. In -Lake BMPs reduce phosphorus already present in a lake, and/or prevent the release of phosphorus from anoxic lake sediments. 8.1.1 Structural BMPs Structural BMPs temporarily store and treat urban stormwater runoff to reduce flooding, remove pollutants, and provide other amenities (Schueler, 1987). Water quality BMPs are specifically designed for pollutant removal. The effectiveness of the various BMPs is summarized in Table 8-1. Structural BMPs control total suspended solids and total phosphorus loadings by slowing stormwater and allowing particles to settle in areas before they reach the stream. Settling areas can be ponds, storm sewer sediment traps, or vegetative buffer strips. Settling can be enhanced by treatment with a flocculent prior to entering the settling basin (see alum treatment plants below). P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 75 When choosing a structural BMP, the ultimate objective must be well understood. The BMP should accomplish the following (Schueler 1987): 1. Reproduce, as nearly as possible, the stream flow before development. 2. Remove at least a moderate amount of most urban pollutants. 3. Require reasonable maintenance. 4. Have a neutral impact on the natural and human environments. 5. Be reasonably cost-effective compared with other BMPs. Table 8-1 General Effectiveness of Stormwater BMPs at Removing Common Pollutants from Runoff Best Management Practice (BMP) Suspended Sediment Total Phosphorus Total Nitrogen Oxygen Demand Trace Metals Bacteria Overall Removal Wet Pond 5 3 2 3 4 ? 4 Infiltration Trench or Basin 5 3 3 4 5 4 4 Porous Pavement 4 4 4 4 4 5 4 Water Quality Inlet (Grit Chamber) 1 ? ? ? ? ? ? Filter Strip 2 1 1 1 1 ? 1 Percent Removal Score 80 to 100 5 60 to 80 4 40 to 60 3 20 to 40 2 0 to 20 1 Insufficient Knowledge ? Source: Schueler 1987 Examples of structural BMPs commonly installed to improve water quality include: • Wet detention ponds • Infiltration • Vegetative buffer strips • Oil and grit separators Each of the BMPs is described below and their general effectiveness is summarized in Table 8-1. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 76 8.1.1.1 Wet Detention Ponds Wet detention ponds (sometimes called “NURP” ponds after the Nationwide Urban Runoff Program) are impoundments that have a permanent pool of water and also have the capacity to hold runoff and release it at slower rates than incoming flows. Wet detention ponds are one of the most effective methods available for treatment of stormwater runoff. Wet detention ponds are used to interrupt the transport phase of sediment and pollutants associated with it, such as trace metals, hydrocarbons, nutrients, and pesticides. When designed properly, wet detention ponds can also provide some removal of dissolved nutrients. Detention ponds have also been credited with reducing the amount of bacteria and oxygen-demanding substances as runoff flows through the pond. During a storm, polluted runoff enters the detention basin and displaces “clean” water until the plume of polluted runoff reaches the basin’s outlet structure. When the polluted runoff does reach the outlet, it has been diluted by the water previously held in the basin. This dilution further reduces the pollutant concentration of the outflow. In addition, much of the total suspended solids and total phosphorus being transported by the polluted runoff and the pollutants associated with these sediments are trapped in the detention basin. A well-designed wet detention pond could remove approximately 80 to 95 percent of total suspended solids and 40 to 60 percent of total phosphorus entering the pond (MPCA, 1989). As storm flows subside, finer sediments suspended in the pond’s pool will have a relatively longer period of time to settle out of suspension during the intervals between storm events. These finer sediments eventually trapped in the pond’s permanent pool will continue to settle until the next storm flow occurs. In addition to efficient settling, this long detention time allows some removal of dissolved nutrients through biological activity (Walker, 1987). These dissolved nutrients are mainly removed by algae and aquatic plants. After the algae die, the dead algae can settle to the bottom of the pond, carrying with them the dissolved nutrients that were consumed, to become part of the bottom sediments. The wet detention process results in good pollutant removal from small storm events. Runoff from larger storms will experience pollutant removal, but not with the same high efficiency levels as the runoff from smaller storms. Studies have shown that because of the frequency distribution of storm events, good control for more frequent small storms (wet detention’s strength) is very important to long-term pollutant removal. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 77 8.1.1.2 Infiltration Infiltration is the movement of water into the soil surface. For a given storm event, the infiltration rate will tend to vary with time. At the beginning of the storm, the initial infiltration rate is the maximum infiltration that can occur because the soil surface is typically dry and full of air spaces. The infiltration rate will tend to gradually decrease as the storm event continues because the soil air spaces fill with water. For long duration storms the infiltration rate will eventually reach a constant value, the minimum infiltration rate (the design infiltration rate). The infiltrated runoff helps recharge the groundwater and mitigate the impacts of development. Stormwater flows in, ponds on the surface, and gradually infiltrates into the soil bed. Pollutants are removed by adsorption, filtration, volatilization, ion exchange, and decomposition. Therefore, infiltration is one of a few BMPs that can reduce the amount of dissolved pollutant in stormwater. Infiltration BMP devices, such as porous pavements, infiltration trenches and basins, and rainwater gardens, can be utilized to promote a variety of water management objectives, including: • Reduced downstream flooding • Increased groundwater recharge • Reduced peak stormwater discharges and volumes • Improved stormwater quality An infiltration basin collects and stores stormwater until it infiltrates to the surrounding soil and evaporates to the atmosphere. Infiltration basins remove fine sediment, nutrients (including dissolved nutrients), trace metals, and organics through filtration by surface vegetation, and through infiltration through the subsurface soil. Deep-rooted vegetation can increase infiltration capacity by creating small conduits for water flow. Infiltration basins are designed as a grass-covered depression underlaid with geotextile fabric and coarse gravel. A layer of topsoil is usually placed between the gravel layer and the grassed surface. Pretreatment is often required to remove any coarse particulates (leaves and debris), oil and grease, and soluble organics to reduce the potential of groundwater contamination and the likelihood of the soil pores being plugged. Infiltration can also be promoted in existing detention ponds by excavating excess sediments (typically the fines that have seal the bottom of the pond) and exposing a granular sub-base (assuming one was present prior to the original construction of the detention pond). Rainwater gardens (a form of bio-retention) are shallow, landscaped depressions that channel and collect runoff. To increase infiltration, the soil bed is sometimes amended, such as with mulch. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 78 Vegetation takes up nutrients, and stored runoff is reduced through evapotranspiration. Bio-retention is commonly located in parking lot islands, or within small pockets in residential areas. Bio-retention is primarily designed to remove sediment, nutrients, metals, and oil and grease. Secondary benefits include flow attenuation, volume reduction, and removal of floatables, fecal coliform, and BOD. 8.1.1.3 Vegetated Buffer Strips Vegetative buffer strips are low sloping areas that are designed to accommodate stormwater runoff traveling by overland sheet flow. Vegetated buffer strips perform several pollutant attenuation functions, mitigating the impact of development. Urban watershed development often involves disturbing natural vegetated buffers for the construction of homes, parking lots, and lawns. When natural vegetation is removed, pollutants are given a direct path to the lake -- sediments cannot settle out; nutrients and other pollutants cannot be removed. Additional problems resulting from removal of natural vegetation include streambank erosion and loss of valuable wildlife habitat (Rhode Island Department of Environmental Management, 1990). The effectiveness of buffer strips is dependent on the width of the buffer, the slope of the site, and the type of vegetation present. Buffer strips should be 20-feet wide at a minimum, however 50- to 75-feet is recommended. Many attractive native plant species can be planted in buffer strips to create aesthetically pleasing landscapes, as well as havens for wildlife and birds. When properly designed, buffer strips can remove 30 to 50 percent of total suspended solids from lawn runoff. In addition, well-designed buffer strips will discourage waterfowl from nesting and feeding on shoreland lawns. Such waterfowl can be a significant source of phosphorus to the pond, by grazing turfed areas adjacent to the water and defecating in or near the water’s edge where washoff into the pond is probable. 8.1.1.4 Oil and Grit Separators Oil-grit separators (e.g., StormCeptors) are concrete chambers designed to remove oil, sediments, and floatable debris from runoff, and are typically used in areas with heavy traffic or high potential for petroleum spills such as parking lots, gas stations, roads, and holding areas. A three-chamber design is common; the first chamber traps sediment, the second chamber separates oil, and a third chamber holds the overflow pipe. The three-chambered unit is enclosed in reinforced concrete. They are good at removing coarse particulates, but soluble pollutants probably pass through. In order to operate properly, they must be cleaned out regularly (at least twice a year). The major benefit of a P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 79 water oil-grit separator is as a pre-treatment for an infiltration basin or pond. They can also be incorporated into existing stormwater system or included in an underground vault detention system when no available land exists for a surface detention basin. Only moderate removals of total suspended solids can be expected; however, oil and floatable debris are effectively removed from properly designed oil and grit separators. 8.1.2 Nonstructural BMPs Nonstructural (“Good Housekeeping”) BMPs discussed below include: 1. Public Education 2. City Ordinances 3, Street Sweeping 4. Deterrence of Waterfowl Good housekeeping practices help reduce the pollutant at its source. 8.1.2.1 Public Education Public education regarding proper lawn care practices, such as fertilizer use and disposal of lawn debris, would result in reduced organic matter and phosphorus loadings to the lake. A public information and education program may be implemented to teach residents within the watershed how to protect and improve the quality of the lake. The program would include distribution of fliers to all residents in the watershed and placement of advertisements and articles in the city’s newsletters and the local newspapers. Information could also be distributed through organizations such as local schools, Girl Scouts and Boy Scouts and other local service clubs, or lake associations. Initiation of a stenciling program to educate the public would help reduce loadings to the storm sewer system. Volunteers could place stenciled messages (i.e., “Dump No Waste, Drains to Lake Cornelia”) on all storm sewer catch basins within the watershed to promote environmental stewardship. 8.1.2.2 Ordinances Water quality problems can be addressed through legislative methods, such as a watershed-wide ban on the use of phosphorus fertilizers or a commercial lawn care ordinance to control content of mixture and ensure that no phosphorus is present in the case of a complete phosphorus ban. A new legislated fertilizer phosphorus limitation has become effective in 2004, which bans the use of P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 80 fertilizers containing phosphorus on lawns in the Twin Cities metro area (Anoka, Carver, Dakota, Hennepin, Ramsey, Scott and Washington counties). Exceptions to such a ban would be granted in cases where a resident was able to demonstrate, by means of soil analyses, that phosphorus was required. Other ordinances pertaining to littering, pet feces, and buffer strips adjacent to lakes and other water bodies could be strengthened or created. 8.1.2.3 Street Sweeping Most often, street sweeping is performed only in the spring, after the snow has melted and in the fall, after the leaves have fallen, to reduce this potential source of phosphorus from entering the storm sewer. For most urban areas, street sweeping has relatively low effectiveness from late-spring (after the streets are cleaned of accumulated loads) until early-fall (prior to the onset of leaf fall) (Bannerman, 1983). In addition, the use of vacuum sweepers is preferred over the use of mechanical, brush sweepers. The vacuum sweepers are more efficient at removing small phosphorus-bearing particles from impervious surfaces within the watershed. Fall street sweeping is particularly important in the watershed directly tributary to the lake, where treatment of stormwater is not available. 8.1.2.4 Deterrence of Waterfowl The role of waterfowl in the transport of phosphorus to lakes is often not considered. However, when the waterfowl population of a lake is large relative to the lake size, a substantial portion of the total phosphorus load to the lake may be caused by the waterfowl. Waterfowl tend to feed primarily on plant material in or near a lake; the digestive processes alters the form of phosphorus in the food from particulate to dissolved. Waterfowl feces deposited in or near a lake may result in an elevated load of dissolved phosphorus to the lake. One recent study estimated that one Canada goose might produce 82 grams of feces per day (dry weight) while a mallard may produce 27 grams of feces per day (dry weight) (Scherer et al., 1995). Waterfowl prefer to feed and rest on areas of short grass adjacent to a lake or pond. Therefore, shoreline lawns that extend to the water’s edge will attract waterfowl. The practice of feeding bread and scraps to waterfowl at the lakeshore not only adds nutrients to the lake, but attracts more waterfowl to the lake and encourages migratory waterfowl to remain at the lake longer in the fall. Two practices often recommended to deter waterfowl are construction of vegetated buffer strips, and prohibiting the feeding of waterfowl on public shoreline property. As stated above, vegetated strips P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 81 along a shoreline will discourage geese and ducks from feeding and nesting on lawns adjacent to the lake, and may decrease the waterfowl population. 8.1.3 In-Lake BMPs In -lake BMPs reduce phosphorus already present in a lake or prevent the release of phosphorus from the lake sediments and macrophyte die-off. However, based on the one year of water data available for both Arrowhead and Indianhead Lakes, internal loads from sediment release have not been identified as a large part of the phosphorus budget in either lake. Therefore, several in-lake BMPs are discussed below, focusing mainly on internal loads due to macrophyte growth and die-off. 8.1.3.1 Winter Drawdown Lake level control has been shown to be an effective means of controlling growth of certain macrophyte species and reducing the spatial distribution of these plants over the lake area. By reducing water levels in the winter, the sediments and plants are exposed to freezing and drying conditions which can impact the growth of the plant the following spring (Helsel et al., 2003a; Helsel et al., 2003b). Drawdown has been successfully coupled with chemical treatment in some lakes in southeast Wisconsin and resulted in the establishment of a more native plant community (Helsel et al., 2003a; Helsel et al., 2003b). Additionally, lake drawdowns have been used for the control of sediment resuspension as well as the eradication of rough fish populations. With drawdowns, loose bottom sediments are consolidated and resuspension is less likely (Helsel et al., 2003a; Helsel et al., 2003b). Studies have shown that during these periods of low water levels, rough fish populations have effectively been removed with the use of a rotenone solution (Helsel et al., 2003a; Helsel et al., 2003b). Because lake level drawdown may potentially impact the fishery within a lake, restocking may be necessary after lake levels have returned to normal conditions. However, drawdown is most economical and feasible in lakes with surface outlets and control structures that allow for increased discharge. Land-locked basins would require the use of pumps to lower lake levels, which may be a costly option. 8.1.3.2 Mechanical Harvesting Harvesting of lake macrophytes is typically used to remove plants that are interfering with uses such as boating, fishing, swimming, or aesthetic viewing. Mechanical control involves macrophyte removal via harvesting, hand pulling, hand digging, rotovation/cultivation, or diver-operated suction P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 82 dredging. Small-scale harvesting may involve the use of the hand or hand-operated equipment such as rakes, cutting blades, or motorized trimmers. Individual residents frequently clear swimming areas via small-scale harvesting or hand pulling or hand digging. Large-scale mechanical control often uses floating, motorized harvesting machines that cut the plants and remove them from the water onto land, where they can be disposed. Mechanical harvesters consist of a barge, a reciprocating mower in front of the barge that can cut up to a depth of roughly 8 feet, and an inclined porous conveyer system to collect the cuttings and bring them to the surface. Removal of aquatic vegetation through mechanical harvesting has not been shown to be an effective nutrient control method (Cooke et al, 1993). However, none of this research was focused on the internal phosphorus load reduction due to mechanical harvesting of Curlyleaf pondweed. Blue water Science’s 2000 Orchard Lake Management Plan suggests that there is up to 5.5 pounds of phosphorus per acre of Curlyleaf pondweed. Additional research mentions that harvesting can reduce the extent of nuisance Curlyleaf pondweed growth if harvesting occurs for several years and reduce stem densities by up to 80 percent (McComas and Stuckert, 2000). Therefore, harvesting of Curlyleaf pondweed may significantly reduce the phosphorus in the water column of a lake assuming enough biomass can be removed from the lake. This assumes that enough time and equipment would be available to harvest the Curlyleaf prior to die-back in early-July. While mechanical harvesting is more acceptable to the MDNR than chemical methods it would still require an MDNR permit and provide only temporary benefits and must be repeated annually. The MDNR regulations state that the maximum area that can be harvested is 50 percent of the littoral zone. 8.1.3.3 Application of Herbicides Controlling Curlyleaf pondweed can be done by herbicide treatments applied from a barge or boat or by mechanical harvesting, or by a combination of these methods. Early to mid-springtime herbicide treatments are most effective at eradicating the plant by reducing the shoot and root biomass as well as suppressing turion production (Poovey, Skogerboe, and Owens, 2002). MDNR regulations limit the extent of the lake that can be treated in any year. Aquatic herbicides are among the most closely scrutinized compounds known, and must be registered for use by both the U.S. EPA and the State of Minnesota. Registration of an aquatic herbicide requires extensive testing. Consequently, all of the aquatic herbicides currently registered for use are characterized by excellent toxicology packages, are only bio-active for short periods of time, have relatively short-lived P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 83 residuals, and are not bioconcentrated (The Lake Association Leader’s Aquatic Vegetation Management Guidance Manual, Pullmann, 1992). Examples of two aquatic herbicides appropriate for use in controlling the Curlyleaf pondweed growth in Arrowhead Lake are Reward (active ingredient = Diquat) and Aquathol-K (active ingredient = Endothall). The use of low-level Sonar application has recently been found to selectively control exotic weed species such as Eurasian watermilfoil and Curlyleaf pondweed (Whole-Lake Applications of Sonar for Selective Control of Eurasian Watermilfoil, Getsinger et al, 2001). Due to past history of Sonar applications and the limited research on the new low level applications, the use of Sonar is not feasible at this time. It is also important to note that the MDNR will currently only permit 15 percent of the littoral zone of a given lake to be treated with herbicides. 8.1.3.4 Application of Copper Sulfate Application of copper sulfate can be a highly effective algaecide in some cases, but the application is always temporary (days) and can have high annual costs. In addition, care must be taken to limit the impacts on none target organisms, such as invertebrates, and possible sediment contamination with copper. The primary effects on algae include inhibition of photosynthesis and cell division as a result of the additional cupric ion, the form of copper toxic to algae, present in the water column (Cooke et al, 1993). Blue-green algae are particularly sensitive to copper sulfate treatments. As a result, after a copper sulfate treatment is made the blue-green algae concentration is knocked back. However, after a few days the green algae (fast growers) take control and within a few weeks the Chlorophyll a concentration is back to pretreatment levels (Swain, et al., 1986). As the algae die and settle out of the water column they take with them the nutrients they used for growth. Therefore, copper sulfate application may temporarily reduce the total phosphorus concentration in a water body by removing the phosphorus that is associated with algal biomass. Once the algae have settle out of the water column and start to decompose, soluble phosphorus is released back into the water column that can be used for future algal growth. As a result, copper sulfate treatments are typically not considered a long-term solution to nutrient loading problems. 8.1.3.5 Diffused Aeration The mobile P sediment fraction consists of iron bound and loosely sorbed phosphorus. If enough iron is present and the sediment remains oxic, the iron bound and loosely sorbed phosphorus sediment fractions will remain stable and bound to the sediment. However, phosphorus release, from the mobile phosphorus sediment fraction, occurs when sediments become anoxic. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 84 Diffused aeration is intended to destratify the lake and is used as a means of maintaining oxic conditions in the sediment. Diffused aeration/destratification works by injecting compressed air into the water from a diffuser on the lake bottom resulting in circulation of the lake and increased oxygenation. This option can reduce or eliminate the release of phosphorus from sediments during anoxic periods in the hypoliminion. Additionally, aeration would likely result in improved habitat for fish and zooplankton in the bottom waters of the lake, since it would increase the dissolved oxygen concentrations. The development of scum-forming algal species is highly dependent on the stability of the water column (World Health Organization, 1999). In water without vertical mixing, blue-green algae can migrate up and down by changing their buoyancy. Interrupting this vertical migration of blue-greens by artificial mixing can prevent rapid development of surface scums (World Health Organization, 1999). This will also reduce the growth rate of blue-green algae by limiting optimum light conditions, enabling other phytoplankton species that can’t regulate their buoyancy to better compete under fully mixed conditions. The species that would likely benefit from these conditions include green algae and diatoms, which do not form surface scums and are preferred food sources for zooplankton. Holdren et al. (2001) noted that the results of destratification have varied. Some of the results include the following: • Problems with low dissolved oxygen have typically been solved • Where small water column temperature differences have been maintained all summer, algae blooms seem to decline • Phosphorus and turbidity have increased, and in some cases, transparency has decreased • Surface scums have been prevented, although total biomass may not decline • Systems that bring deep water to the surface must move enough water to prevent anoxia at the sediment-water interface, or the quality of the bottom water may cause the surface water conditions to deteriorate 8.2 Feasibility Analysis 8.2.1 Statement of Problem for Arrowhead Lake Although it has not yet been classified by NMCWD, analysis of the 2004 water quality data for Arrowhead Lake suggests that it falls on the border between the Level II and Level III District Management Categories, with a TSISD of 60. This indicates that the lake is generally intended for uses such as canoeing, hiking and picnicking, fishing, and aesthetic viewing and potentially uses that require partial body-contact. This classification level does not support full body-contact activities P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 85 such as swimming. Based on this classification, water quality modeling simulations show that the phosphorus load to Arrowhead Lake under current/future land use conditions will typically result in Chlorophyll a concentrations and Secchi disc transparencies that meet the NMCWD’s Level II goals for the lake (see Table 8-2). However, in-lake total phosphorus concentrations for wet climatic conditions are likely to exceed the NMCWD’s Level II goal (45µg/L<[TP]<75µg/L). In addition to not meeting the NMCWD’s total phosphorus goal under wet climatic conditions, model simulations suggest that the lake’s total phosphorus concentrations will not meet the MPCA’s proposed shallow lake criteria (TP<60µg/L) under any of the climatic scenarios. Additionally, MPCA’s Chl a and Secchi disc transparency standards (Chl a<20µg/L; SD>1m) will not be achieved under all climatic conditions. Various management options to maintain and/or improve the water quality of Arrowhead Lake were explored. Table 8-2 details the predicted summer average total phosphorus and Chl a concentrations, Secchi disc transparency, and TSISD for existing/future conditions and all management alternatives. T he lake management scenarios considered for Arrowhead Lake are discussed below. 8.2.2 Statement of Problem for Indianhead Lake Based on the existing water quality data collected for Indianhead Lake, it would be classified by the NMCWD as a Level II lake, meaning the lake is generally intended for water-based recreational activities, including sailboating, canoeing, hiking and picnicking, among others. This classification level does not support full body-contact activities such as swimming and scuba diving. Based on this classification, water quality modeling simulations for existing conditions shows that the expected phosphorus and Chlorophyll a concentrations and Secchi disc transparencies typically meet the NMCWD’s Level II goals (see Table 8-2). However, during wet climatic conditions, the predicted Secchi disc transparency does not meet the Level II goals. In addition, the predicted total phosphorus and Secchi disc transparencies for wet climatic conditions will not meet the MPCA’s proposed shallow lake criteria (TP<60µg/L; SD>1.0m). Table 8-2 details the predicted summer average total phosphorus concentration, Chl a concentration, Secchi disc transparency, and TSISD for existing conditions and all management alternatives analyzed. The Indianhead Lake management scenarios are discussed below. The estimated water quality under varying climatic conditions are based on 2004 water quality data that has been influenced by two copper sulfate treatments. Therefore, water quality in Indianhead Lake without the use of copper sulfate would be expected to be worse that the observed water quality. TP C H L a SD T P C H L a SD T P C H L a SD T P C H L a SD (µµµµg/ L ) (µµµµg/ L ) (m ) (µµµµg/ L ) (µµµµg/ L ) (m ) (µµµµg/ L ) (µµµµg/ L ) (m ) (µµµµg/L)(µµµµg/L)(m) 1 E x i s t i n g ( 2 0 0 4 ) C o n d i t i o n s 2 - N o B M P s 68 . 8 2 0 . 4 1 . 0 6 0 6 6 . 6 2 1 . 1 1 . 0 6 0 9 1 . 2 2 8 . 6 0 . 9 6 2 7 2 . 2 1 8 . 5 1 . 0 60 2 I n s t a l l a t i o n o f N U R P P o n d A H _ 1 a 68 . 4 2 0 . 2 1 . 0 6 0 6 6 . 1 2 1 . 0 1 . 0 6 0 9 0 . 9 2 8 . 5 0 . 9 6 2 7 1 . 8 1 8 . 5 1 . 0 60 3a Cu r l y l e a f P o n d w e e d M a n a g e m e n t - 1 5 % o f L i t t o r a l A r e a Tr e a t e d w i t h H e r b i c i d e 60 . 0 1 8 . 2 1 . 0 6 0 5 9 . 8 1 8 . 1 1 . 0 5 9 8 4 . 2 2 6 . 3 0 . 9 6 1 6 5 . 6 2 0 . 1 1 . 0 60 3b Cu r l y l e a f P o n d w e e d M a n a g e m e n t - 5 0 % o f L i t t o r a l A r e a Tr e a t e d w i t h H e r b i c i d e 39 . 8 1 1 . 7 1 . 1 5 8 4 3 . 8 1 3 . 0 1 . 1 5 8 6 7 . 8 2 0 . 8 1 . 0 6 0 5 0 . 0 1 5 . 0 1 . 1 59 3c Cu r l y l e a f P o n d w e e d M a n a g e m e n t - 5 0 % o f L i t t o r a l A r e a Tr e a t e d w i t h M e c h a n i c a l H a r v e s t i n g 50 . 6 1 5 . 2 1 . 1 5 9 5 2 . 4 1 5 . 7 1 . 1 5 9 7 6 . 6 2 3 . 7 1 . 0 6 1 5 8 . 4 1 7 . 7 1 . 0 59 3d Cu r l y l e a f P o n d w e e d M a n a g e m e n t - W i n t e r D r a w d o w n 39 . 8 1 1 . 7 1 . 1 5 8 4 3 . 8 1 3 . 0 1 . 1 5 8 6 7 . 8 2 0 . 8 1 . 0 6 0 5 0 . 0 1 5 . 0 1 . 1 59 1 N o B M P s 44 . 9 8 . 1 1 . 1 5 8 5 5 . 0 1 0 . 1 1 . 0 6 0 9 8 . 6 1 9 . 3 0 . 7 6 6 7 7 . 1 1 4 . 7 0 . 8 63 2 Ex i s t i n g ( 2 0 0 4 ) C o n d i t i o n s - C o p p e r S u l f a t e T r e a t m e n t s i n Ma y a n d A u g u s t 2, 3 14 . 5 2 . 3 1 . 8 5 2 2 3 . 5 4 . 0 1 . 5 5 4 6 7 . 3 1 2 . 7 0 . 9 6 2 4 5 . 8 8 . 7 1 . 1 58 Ar r o w h e a d a n d I n d i a n h e a d L a k e s P r e d i c t e d T o t a l P h o s p h o r u s a n d C h l o r o p h y l l a C o n c e n t r a t i o n s , S e c c h i D i s c T r a n s p a r e n c i e s , a n d T S I SD f o r a l l M a n a g e m e n t S c e n a r i o s 3 - T h e r e w e r e 2 a p p l i c a t i o n s o f C o p p e r S u l f a t e t o I n d i a n h e a d L a k e d u r i n g 2 0 0 4 . M o d e l s w e r e c a l i b r a t e d t o t h e a c t u a l w a t e r q u a l i t y d a t a w h i c h i s f o u n d i n S c e n a r i o 2 f o r I n d i a n h e a d L a k e . S c e n a r i o 1 - N o B M P w a t e r q u a i l t y v a l u e s w e r e e s t i m a t e d f r o m t h e m o d e l c a l i b r a t e d t o t h e c o p p e r s u l f a t e i m p a c t e d w a t e r q u a l i t y da t a . In d i a n h e a d L a k e Dr y C l i m a t i c C o n d i t i o n s ( 1 9 8 7 - 8 8 ) 1 Av e r a g e C l i m a t i c C o n d i t i o n s ( 1 9 9 4 - 9 5 ) Sc e n a r i o Nu m b e r TS I SD TS I SD Ar r o w h e a d L a k e TS I SD TSI SD Ta b l e 8 - 2 2 - F o r b o t h A r r o w h e a d a n d I n d i a n h e a d L a k e s , m o d e l c a l i b r a t i o n i n c l u d e s t h e i m p a c t o f t h e a e r a t o r s o n t h e i n - l a k e w a t e r q u a l i t y t h a t w e r e o p e r a t i n g d u r i n g t h e 2 0 0 4 s a m p l i n g s e a s o n . 1 - F o r D r y C l i m a t i c C o n d i t i o n s , t h e 1 0 - i n c h s u p e r s t o r m o n 7 / 2 3 / 1 9 8 7 w a s r e m o v e d d u e t o t h e r a r i t y o f t h e e v e n t Su m m e r A v e r a g e Su m m e r A v e r a g e Su m m e r A v e r a g e Summer Average Be s t M a n a g e m e n t P r a c t i c e ( B M P ) S t r a t e g y We t C l i m a t i c C o n d i t i o n s ( 2 0 0 1 - 2 0 0 2 ) C a l i b r a t i o n C l i m a t i c C o n d i t i o n s ( 2 0 0 3 - 0 4 ) P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ I n L a k e S u m m a r y . x l s P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 87 8.2.3 Selection and Effectiveness of Alternatives Three types of BMPs were considered for recommendation in this plan including structural, nonstructural, and in-lake practices. Each of these types are defined and discussed in Section 8.1. Specific BMP alternatives that were considered for the Arrowhead and Indianhead Lakes and watersheds are discussed below although not all of the BMP alternatives discussed below are recommended for implementation in each watershed. Figure 8-1 shows the location of these potential options. Estimated “budgeting” costs reflect 2006 dollars and do not include costs to acquire land or easements, obtain permits, or to mitigate wetland loss (concept level cost estimates are provided in Appendix F). 8.2.3.1 Site-Specific Structural BMPs 8.2.3.1.1 Construction of Wet Detention Pond AH_1a in the Arrowhead Lake Watershed (AH_1a) to treat Parking Lot Runoff Both Indianhead and Arrowhead Lakes have relatively small watersheds that are almost entirely developed. Additionally, there are several existing stormwater ponds in each watershed (a summary of the existing stormwater ponds can be found in Appendix C). Residential land uses are the predominant land uses in the watersheds and there are very few open spaces/natural areas that would provide the space for the construction of additional water quality ponds. However, in the Arrowhead Lake watershed, there is a large, untreated impervious surface (the parking lot of Cross View Lutheran Church) south of US Highway 212. This lot drains southeast directly to the stormsewer system that discharges to Arrowhead Lake. However, there is space available for the construction of a water quality treatment pond (AH_1a) in this area that could allow for treatment of the runoff from the impervious lot. A summary of the storage necessary for this pond to meet MPCA/NURP criteria is found in Table 8-3. Construction of Pond AH_1a would reduce the external watershed loads to Arrowhead Lake by 4 to 5 lbs over the 17 month modeling period depending on the climatic condition (See Table 8-4 for the results of the watershed load modeling). This reduction in phosphorus load to Arrowhead Lake translates into a minimal reduction in the summer average total phosphorus and Chlorophyll a concentrations and improvement in the water clarity of the lake (See Option 2, Table 8-2). This BMP option is estimated to have a capitol cost of $106,930 including engineering, design, and contingencies. IH_1 IH_14 AH_1 AH_1 AH_6 AH_6 AH_32 AH_4 AH_6 AH_1a AH_1 !;N Ba r r F o o t e r : D a t e : 7 / 1 1 / 2 0 0 6 1 2 : 3 7 : 4 1 P M F i l e : I : \ C l i e n t \ N m c w d \ L a k e s \ U A A \ A r r o w h e a d _ I n d i a n h e a d \ G I S \ M a p s \ F i g u r e s \ F i g u r e _ 8 _ 1 _ B M P _ L o c a t i o n s . m x d U s e r : j a k 2 625 0 625Feet Legend Arrowhead Lake Watersheds Indianhead Lake Watersheds ^_Structural BMPs In-Lake BMPs Figure 8-1 Arrowhead and Indianhead Lakes Potential BMP Locations Arrowhead and Indianhead Lakes UAANine Mile Creek Watershed District In-Lake BMP: Curlyleaf Pondweed Management In-Lake BMP: Copper Sulfate Treatments Structural BMP: Addition of NURP Pond AH_1a Indianhead Lake Arrowhead Lake Im p e r v i o u s P e r v i o u s P e r v i o u s W a t e r s h e d P o t e n t i a l W a t e r s h e d R u n o f f W a t e r s h e d S e d i m e n t R e q u i r e d N U R P E x i s t i n g Volume of Deficient Wa t e r s h e d F r a c t i o n F r a c t i o n C u r v e # C o m p o s i t e A b s t r a c t i o n 2 . 0 " S t o r m A r e a S t o r a g e D e a d S t o r a g e D e a d S t o r a g e D e f i c i e n t ? D e a d S t o r a g e C o m m e n t Cu r v e # * (O n e - y e a r e v e n t ) ( a c r e s ) ( a c r e - f t ) V o l u m e ( a c r e - f t ) V o l u m e ( a c - f t ) (ac-ft) AH _ 1 a 0. 4 3 4 8 0 . 5 7 8 2 . 2 8 9 1 . 2 1. 0 5. 0 5 0 . 0 4 0. 4 7 0 YE S 0.47 No Existing Pond *C N pe r v i n c l u d e s i n d i r e c t l y c o n n e c t e d i m p e r v i o u s s u r f a c e s ( e . g . , r o o f t o p s ) Se d i m e n t S t o r a g e , V = [ ( E ) ( D R ) ( T E ) ( A ) ( Y ) ] / [ ( 2 1 7 8 0 0 ) ( G ) ] E = 1 t o n / a c r e / y r ( T a b l e 4 . 2 - 1 ) DR = 60 % ( F i g u r e 4 . 2 - 5 ) TE = 77 % ( F i g u r e 4 . 2 - 1 , a s s u m i n g 2 4 - h o u r d e t e n t i o n t i m e ) Y= 25 y e a r s G= 75 l b / c u . f t ( T a b l e 4 . 2 - 2 ) Ta b l e 8 - 3 A r r o w h e a d L a k e U A A M P C A / N U R P W e t D e t e n t i o n V o l u m e s ( R e q u i r e d p e r M P C A / N U R P ) P: \ 2 3 \ 2 7 \ 6 3 4 \ N O R M A N D A L E U A A \ R e p o r t \ N r m a n d a l e _ N U R P _ M P C A _ 1 9 8 9 _ D i r e c t _ S t r e a m _ H o p k i n s . x l s 7/14/2006 2:29 PM P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 90 Table 8-4 Arrowhead Lake External Total Phosphorus Loading Reduction with the Construction of Pond AH-1a Climatic Condition 17 Month Modeled Total Phosphorus Load (lbs) 17 Month Modeled Total Phosphorus Load with Pond AH_1a (lbs) Percent Reduction (%) Calibration (2003-2004) 103 98 4.4 Average (1994-95) 98 93 3.9 Dry (1987-88)* 91 87 4.3 Wet (2001-02) 127 122 4.8 *The May 1, 1987 through April 30, 1988 precipitation total excludes the 10-inch 1987 superstorm because of the rarity of this event. 8.2.3.2 In-Lake Treatments 8.2.3.2.1 Copper Sulfate Treatment in Indianhead Lake The application of copper sulfate can be a highly effective algaecide and can temporarily reduce the total phosphorus concentration in a water body by removing the phosphorus that is associated with algal biomass. However, once the algae that have settled out of the water column decompose, soluble phosphorus is released back into the water column. Thus, the application is always temporary and can have high annual costs because of the need for multiple applications throughout the season. As a result, copper sulfate treatments are typically not considered a long-term solution to nutrient loading problems. However, this scenario was analyzed for Indianhead Lake as the lake currently is treated with copper sulfate per the lake homeowner’s association. During the 2004 water quality sampling in Indianhead Lake, there were 2 applications of copper sulfate. The first application was on May 24, 2004 and the second was on August 4, 2004. Development and calibration of the in-lake water quality model is based on data impacted by copper sulfate applications. Modifications to the calibrated model allowed for the prediction of total phosphorus concentrations in Indianhead Lake without the application of copper sulfate in late May and early August for the various climatic conditions. The model estimated that the double application of copper sulfate during the growing season resulted in a 32 to 68 percent reduction in the overall in-lake total phosphorus concentration depending on the climatic condition. It should be noted that the estimated impact of the copper sulfate on lake water quality is very approximate. Only one year of data was available for calibration of the water quality model and that data included the effect of the copper sulfate. Because there is only one year of water quality data (2004) for Indianhead Lake, there are no baseline water quality data that do not include the effect of copper sulfate treatments. Therefore, there were no data available to quantify the actual effect of copper P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 91 sulfate on the lake water quality. The predicted baseline water quality of the lake could only be estimated from the model calibrated to the 2004 data. The estimated cost per application of copper sulfate to Indianhead Lake is $550. 8.2.3.2.2 Aquatic Plant Management in Arrowhead Lake A few of non-native macrophyte species (Eurasian watermilfoil and Curlyleaf pondweed) were sampled during the June and August surveys in 2004. The presence of Eurasian watermilfoil (Myriophyllum spicatum) is undesirable, as it out-competes native plants and can eventually replace the native species, thereby reducing the quality of habitat and interfering with the wildlife use of the lake. The presence of Curlyleaf pondweed (Potamogeton crispus) was also observed during the June 2004 macrophyte survey, and because of the undesirable effects of Curlyleaf pondweed in the lake, it would be useful to develop a macrophyte management plan to reduce the growth of this exotic weed in Arrowhead Lake. The survey suggests that about 50 percent of the lake is covered with low- density Curlyleaf pondweed. Reductions in summer in-lake TP concentrations would be expected if the coverage and density of Curlyleaf pondweed were managed in Arrowhead Lake. Modeling scenarios evaluated the treatment of 15 percent of the lake littoral area (area typically permitted by MDNR for herbicide treatment in a given year at 80 percent removal efficiency), 50 percent of the lake littoral area (at 80 percent removal efficiency, representing the results of herbicide and lake drawdown scenarios), and 50 percent of the lake littoral area (area typically permitted by MDNR for mechanical harvesting at 50 percent removal efficiency). Results indicate that treatment of 15 percent of the littoral area would results in a 7.7 to 12.8 percent reduction in in-lake TP concentrations during the various climatic conditions, with a maximum reduction of 9 µg/L occurring during dry climatic conditions. When treating 50 percent of the littoral area with herbicides or a lake level drawdown, the reductions in internal loading would translate into a decrease in the summer average total phosphorus concentration in the lake by 22 µg/L to 29 µg/L, with the most significant reduction occurring during dry climatic conditions. Treatment using mechanical harvesting would reduce summer average TP concentrations by 15.1 to 26.5 percent. For a summary of all modeling scenarios, see Options 3a through 3d, Table 8-2. There are several options for the control of Curlyleaf pondweed (and Eurasian watermilfoil) including mechanical harvesting, application of aquatic herbicides, and winter drawdown of the lake or any combination of these treatments. Herbicide treatments are more effective at eradicating the plant but MDNR regulations limit the extent of the lake that can be treated in any year. Mechanical P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 92 harvesting is more acceptable to the MDNR but provides only temporary benefits and must be repeated annually. Winter drawdown exposes the Curlyleaf turions to freezing and drying conditions which can affect their ability to grow in the spring. However, a winter drawdown may result in fishkills and require restocking of the lake. Additionally, drawdowns can be more difficult and costly in lakes with no surface outlet or flow control structures. Using herbicides containing diquat or endothall have been shown to be effective controlling Curlyleaf pondweed. Therefore, treatment of Arrowhead Lake will likely help eradicate the Curlyleaf pondweed present in the lake. Because of possible objections by the MDNR, it is recommended that plans to attempt Curlyleaf pondweed control be developed in close coordination with that agency. It is also important to note that the MDNR will currently only permit 15 percent of the littoral zone of a given lake to be treated with herbicides in any given year. As a result, multiple treatments over several years may be required. However, special permits may be obtained from the MDNR that allows for experimental application of products that can include treatment of 100 percent of the lake area. The estimated cost of an individual herbicide treatment covering 15 percent of the littoral area of Arrowhead Lake is $1,300. Because the lifecycle of Curlyleaf pondweed occurs earlier in the growing season, mechanical harvesting of the plant would need to occur before the plant’s dieback which typically happens in early to mid-July. Mechanical harvesting is a temporary solution and does not reduce the growth of the plant the following growing season, thus it will need to per performed annually. Access to Arrowhead Lake is limited for getting a mechanical harvester into the lake. Currently the MDNR permits up to 50 percent of the lake littoral area to be treated by mechanical harvesting at one time. Estimated costs for mechanical harvesting of Curlyleaf pondweed is $6,700. A winter drawdown would be a final option for the control of both Curlyleaf pondweed and Eurasian watermilfoil in Arrowhead Lake. The drawdown would expose the Curlyleaf turions and watermilfoil root crowns to freezing and drying which limits the future growth of these species and can help reestablish native plant communities. The drawdown of Arrowhead Lake would be entirely dependent on the use of pumps as there is no surface outlet. However, Arrowhead Lake is a relatively small, shallow lake with no major groundwater inflows. It is important to keep in mind that storm and flood events can reduce the effectiveness of a drawdown so typically it is most efficient to perform lake drawdowns during periods of low precipitation and runoff. The estimated cost of a drawdown of Arrowhead Lake is $4,500. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 93 Macrophyte surveys should continue on this lake to monitor the growth of undesirable non-native species. Two species that are of special concern are Eurasian watermilfoil (Myriophyllum spicatum) and Curlyleaf pondweed (Potamogeton crispus) to manage their proliferation. A decline in native aquatic plant species reduces available habitat for wildlife, invertebrates, and other food organisms for small fish. A typical macrophyte survey costs approximately $2000 per lake. 8.2.3.2.3 Aeration in Arrowhead and Indianhead Lakes Currently there are several submerged aerators operating in both Arrowhead and Indianhead Lakes throughout the growing season and during the winter months as well. These were purchased by the lake homeowner association more than a decade ago, although the city is responsible for the administration related to the aeration. It was observed that these aerators were in operation throughout each lake during the 2004 water quality sampling period and most likely influenced the observed water quality in each lake. For example, current data and modeling suggests that neither Arrowhead nor Indianhead Lakes experiences periods of stratification, hypoliminetic anoxia, or internal phosphorus loading from anoxic sediment release. However, because there is only one year of water quality data for each lake during which the aerators were operating, it is difficult to estimate what the water quality within each lake would be without aeration. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 94 9.0 Discussion and Recommendations 9.1 Attainment of Stated Goals The approved Nine Mile Creek Water Management Plan (Barr, 1996) has not assessed Arrowhead and Indianhead Lakes’ water quality for ultimate land use conditions nor has it outlined the five specific goals for these lakes. This UAA has evaluated the current/ultimate situations of both Arrowhead and Indianhead Lakes and has proposed goals for each of the following: water quantity, water quality, aquatic communities, recreational-use, and wildlife. Table 9-1 lists the proposed goals for water quality, recreational-use, and ecological classifications for Arrowhead and Indianhead Lakes. The table also lists total phosphorus and Chlorophyll a concentrations, Secchi disc transparencies, and Carlson’s Trophic State Index (TSI) based on Secchi disc depth. The recommended management strategy for Arrowhead and Indianhead Lakes is to “protect” these resources. According to the Plan, “protect” means “to avoid significant degradation from point and nonpoint sources and wetland alterations to maintain existing beneficial uses, aquatic and wetland habitats, and the level of water quality necessary to protect these uses in receiving waters.” A discussion of the recommended goals follows. 9.1.1 Water Quantity Goal The water quantity goal for Arrowhead and Indianhead Lakes is to provide sufficient water storage during a regional flood. Both lakes are land-locked basins with no surface outlets. 9.1.2 Water Quality Goal The lake classification system, established in the approved Nine Mile Creek Watershed District Water Management Plan (Barr, 1996), established water quality goals for the majority of lakes in NMCWD based on the current or desired recreational use of the lake. Table 9-2 gives the recreational use criteria used in defining the water quality classifications, and gives their associated water quality goals as indicated in the 2006 draft plan. As can be inferred from the listed water quality parameter goals, Level I water bodies are managed for the highest water quality. Level II, III, and IV water bodies require successively lower water quality to support their intended use. 9.1.2.1 Arrowhead Water Quality Goal Although there is currently no water quality goal specified for Arrowhead Lake in the 2006 NMCWD Water Management Plan (Barr, 2006 Draft), the proposed NMCWD management class would be for a Level II classification. This level fully supports water-based recreational activities, including sailboating, P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 95 canoeing, hiking and picnicking, among others. This classification level does not support full body contact activities such as swimming and scuba diving. The proposed NMCWD goal for Arrowhead Lake is to achieve and maintain a TSISD between 50 and 60. 9.1.2.2 Indianhead Water Quality Goal The proposed water quality management level and goal for Indianhead Lake is for Level II classification with a TSISD between 50 and 60. Cu r r e n t S u m m e r A v e r a g e W a t e r Qu a l i t y C o n d i t i o n s ( T S I SD )1 Ex p e c t e d R a n g e s , U l t i m a t e Wa t e r s h e d L a n d U s e W i t h BM P s Ex p e c t e d R a n g e s , U l t i m a t e Wa t e r s h e d L a n d U s e Wi t h o u t B M P s Pr o p o s e d D i s t r i c t W a t e r Qu a l i t y G o a l 2 MP C A S w i m m a b l e Us e C l a s s Me t r o C o u n c i l Pr i o r i t y W a t e r s Cl a s s M u n i c i p a l U s e 3MDNR* Ecological Class 4District Management Strategy Ar r o w h e a d Ye a r o f R e c o r d = 2 0 0 4 II Pa r i a l b o d y - c o n t a c t Sh a l l o w L a k e s C r i t e r i a N/ A N/ A N/A Protect re c r e a t i o n a l [T P ] = 7 2 . 2 µg/ L 39 . 8 < [ T P ] < 8 2 . 6 µg/ L 68 . 8 < [ T P ] < 9 1 . 2 µg/ L 45 < [ T P ] < 7 5 µg/ L [T P ] < 6 0 µg/ L [C h l a ] = 1 8 . 5 µg/ L 11 . 7 < [ C h l a ] < 2 5 . 7 µg/ L 18 . 5 < [ C h l a ] < 2 8 . 6 µg/ L 20 < [ C h l a ] < 4 0 µg/ L [C h l a ] < 2 0 µg/ L SD = 1 . 0 m 0. 9 < S D < 1 . 1 m 0. 9 < S D < 1 . 0 m 1. 0 < S D < 2 . 0 m SD > 1 . 0 m TS I SD = 6 0 58 < T S I SD < 6 0 60 < T S I SD < 6 2 50 < T S I SD < 6 0 In d i a n h e a d Y e a r o f R e c o r d = 2 0 0 4 II Pa r i a l b o d y - c o n t a c t S h a l l o w L a k e s C r i t e r i a N / A N / A N/A Protect re c r e a t i o n a l [T P ] = 4 5 . 8 µg/ L 14 . 5 < [ T P ] < 6 7 . 3 µg/ L 44 . 9 < [ T P ] < 9 8 . 6 µg/ L 45 < [ T P ] < 7 5 µg/ L [ T P ] < 6 0 µg/ L [C h l a ] = 8 . 7 µg/ L 2. 3 < [ C h l a ] < 1 2 . 7 µg/ L 8. 1 < [ C h l a ] < 1 9 . 3 µg/ L 2 0 < [ C h l a ] < 4 0 µg/ L [ C h l a ] < 2 0 µg/ L SD = 1 . 1 m 0 . 9 < S D < 1 . 8 m 0. 7 < S D < 1 . 1 m 1. 0 < S D < 2 . 0 m SD > 1 . 0 m TS I SD = 5 8 52 < T S I SD < 6 2 58 < T S I SD < 6 6 50 < T S I SD < 6 0 2 D i s t r i c t I = F u l l y s u p p o r t s a l l w a t e r - b a s e d r e c r e a t i o n a l a c t i v i t i e s i n c l u d i n g s w i m m i n g , s c u b a d i v i n g a n d s n o r k e l i n g . I I = A p p r o p r i a t e f o r a l l r e c r e a t i o n a l u s e s e x c e p t f u l l b o d y c o n t a c t a c t i v i t i e s : s a i l b o a t i n g , w a t e r s k i i n g , c a n o e i n g , w i n d s u r f i n g , j e t s k i i n g . I I I = S u p p o r t s f i s h i n g , a e s t h e t i c v i e w i n g a c t i v i t i e s a n d w i l d l i f e o b s e r v a t i o n I V = G e n e r a l l y i n t e n d e d f o r r u n o f f m a n a g e m e n t a n d h a v e n o s i g n i f i c a n t r e c r e a t i o n a l u s e v a l u e s V = W e t l a n d s s u i t a b l e f o r a e s t h e t i c v i e w i n g a c t i v i t i e s , w i l d l i f e o b s e r v a t i o n a n d o t h e r p u b l i c u s e s . 3 M u n i c i p a l U s e S W I M = P u b l i c s w i m m i n g b e a c h F I S H = D e s i g n a t e d f i s h i n g r e s o u r c e 4 M D N R E x a m i n a t i o n o f t h e M D N R e c o l o g i c a l c l a s s i f i c a t i o n s y s t e m r e v e a l e d t h e T S I SD v a l u e f o r a g i v e n l a k e c l a s s c o u l d v a r y d r a m a t i c a l l y . T h e a b o v e m e a n T S I SD v a l u e w a s p r e s e n t e d i n t h e 19 9 6 N M C W D W a t e r M a n a g e m e n t P l a n . L a k e C l a s s 4 4 m a y b e s u b j e c t t o o c c a s i o n a l w i n t e r k i l l . N P = N o r t h e r n P i k e C A = C a r p B L B = B l a c k B u l l h e a d ( S e c c h i D i s c T r a n s p a r e n c y B a s i s ) La k e La k e C l a s s i f i c a t i o n , B y R e g u l a t o r y A g e n c y 1 T S I SD Ca r l s o n ' s T r o p h i c S t a t e I n d e x s c o r e . T h i s i n d e x w a s d e v e l o p e d f r o m t h e i n t e r r e l a t i o n s h i p s b e t w e e n s u m m e r a v e r a g e S e c c h i d i s c t r a n s p a r e n c i e s a n d e p i l i m n e t i c c o n c e n t r a t i o n s o f c h l o r o p h y l l a a n d t o t a l p h o s p h o r u s . T h e i n d e x re s u l t s i n s c o r i n g g e n e r a l l y i n t h e r a n g e b e t w e e n z e r o a n d o n e h u n d r e d . [ D i s t r i c t v a l u e s c a l c u l a t e d b y B a r r E n g i n e e r i n g C o m p a n y ( f r o m f i e l d d a t a a n d w a t e r q u a l i t y m o d e l p r e d i c t i o n s ) . M P C A v a l u e s t a k e n f r o m t h e 1994 Clean Water Act Re p o r t t o t h e U . S . C o n g r e s s ; a n d M D N R v a l u e s t a k e n f r o m S c h u p p ( 1 9 9 2 ) M i n n e s o t a D e p a r t m e n t o f N a t u r a l R e s o u r c e s I n v e s t i g a t i o n a l R e p o r t N o . 4 1 7 . An e c o l o g i c a l c l a s s i f i c a t i o n o f M i n n e s o t a l a k e s w i t h a s s o c i a t e d f i s h c o m m u n i t i e s .] Ta b l e 9 - 1 Ar r o w h e a d a n d I n d i a n h e a d L a k e s M a n a g e m e n t T a b l e Wa t e r Q u a l i t y , R e c r e a t i o n a l U s e a n d E c o l o g i c a l C l a s s i f i c a t i o n o f , a n d M a n a g e m e n t Ph i l o s o p h i e s , R e f e r e n c i n g C a r l s o n ’ s T r o p h i c S t a t e I n d e x ( T S I ) V a l u e s P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ D a t a \ W Q D a t a \ A H _ I H _ G o a l s T a b l e . x l s P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 97 Table 9-2 NMCWD Water Quality Management Goals Water Quality Management Category Desired TSI Desired TP (µg/L) Desired Chl a (µg/L) Desired Transparency (m) Level I Level I water bodies will support aquatic life and recreation including full-body contact aquatic activities (swimming, snorkeling, etc.) <50 <45 <20 >2.0 Level II Level II water bodies will support aquatic life and recreation except those activities that require full-body contact with the water. Activities may include sailboating, water skiing, canoeing, jet- skiing, wind-surfing, etc. 50-60 45-75 20-40 2.0-1.0 Level III Level III water bodies will support waterfowl or other wildlife, and may be used for non-contact recreational use (boating, fishing, etc.) 60-70 75-105 40-60 1.0-0.6 Level IV Level IV water bodies are generally suitable for aesthetic enjoyment and may be used for runoff management (i.e., stormwater detention). >70 >105 >60 <0.5 These water quality goals can be achieved for the various climatic conditions analyzed as part of this UAA (dry, average, wet and model calibration precipitation conditions) through the implementation of lake management practices. For Arrowhead Lake, management scenarios 3 b and 3d (Curlyleaf pondweed management) will most significantly improve water quality in the lake. Management scenario 2 (copper sulfate treatments) in Indianhead Lake will help achieve the Level II water quality. Figures 9-1 and 9-2 compares the costs and water quality benefits of the various BMPs analyzed under varying climatic conditions for both Arrowhead and Indianhead Lakes, respectively. 9.1.3 Aquatic Communities Goal In 1992, the MDNR categorized many Minnesota lakes according to the type of fishery each lake might reasonably be expected to support (An Ecological Classification of Minnesota Lakes with Associated Fish Communities; Schupp, 1992). The MDNR’s ecological classification system takes into account factors such as the lake area, percentage of the lake surface area that is littoral, maximum depth, degree of shoreline development, Secchi disc transparency, and total alkalinity. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 98 However, neither Arrowhead nor Indianhead Lakes has been assigned a MDNR ecological classification. Therefore, the aquatic communities goal for Arrowhead and Indianhead Lakes is to achieve a water quality that helps achieve a balanced ecosystem, which includes diverse growth of native aquatic macrophytes. 9.1.4 Recreational-Use Goal The recreational-use goal for both Arrowhead and Indianhead Lakes is to achieve and maintain the recreational uses outlined by the NMCWD Level II management class. These uses can include fishing, canoeing, sail-boating, wildlife and aesthetic viewing. Recreational uses of both lakes are predominantly limited to residents living around the lakes as there are no public access points on either lake. 9.1.5 Wildlife Goal The wildlife goal for Arrowhead and Indianhead Lakes is to protect existing, beneficial wildlife uses. The wildlife goal can be achieved with no action, especially if changes in the watershed are minimal. However, the invasion of non-native macrophyte species, such as Eurasian watermilfoil and Curlyleaf pondweed, may pose a threat to the wildlife’s use of the Lakes, especially if these invasive species begin replacing native species. Therefore, macrophyte surveys should continue to monitor the growth of the exotic species in Arrowhead Lake and for the presence of invasive species in Indianhead Lake. P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ I n L a k e S u m m a r y . x l s Fi g u r e 9 - 1 Ar r o w h e a d L a k e : E s t i m a t e d S u m m e r A v e r a g e T o t a l P h o s p h o r u s C o n c e n t r a t i o n Fo l l o w i n g B M P I m p l e m e n t a t i o n 020406080 10 0 12 0 1 2 3a 3b 3c 3d BM P S c e n a r i o T o t a l P h o s p h o r u s C o n c e n t r a t i o n ( µ µ µ µ g / L ) $0$20,000$40,000$60,000$80,000$100,000$120,000 Estimated Cost ($) BM P C o s t 19 8 7 - 8 8 D r y C o n d i t i o n 19 9 4 - 9 5 A v e r a g e C o n d i t i o n 20 0 1 - 0 2 W e t C o n d i t i o n 20 0 3 - 0 4 C a l i b r a t i o n C o n d i t i o n MP C A P r o p o s e d S h a l l o w L a k e C r i t e r i a [T P ] < 6 0 µg/ L NM C W D ' s P r o p o s e d W a t e r Q u a l i t y G o a l U p p e r L i m i t o f L e v e l I I C l a s s i f i c a t i o n [T P ] < 7 5 µg/L 20 0 4 O b s e r v e d S u m m e r A v e r a g e BM P L e g e n d Op t i o n 1 Ex i s t i n g ( 2 0 0 4 ) C o n d i t i o n s - N o B M P s Op t i o n 2 A d d i t i o n o f N U R P P o n d A H _ 1 a Op t i o n 3 a Cu r l y l e a f P o n d w e e d M a n a g e m e n t - He r b i c i d e T r e a t m e n t ( 1 5 % L i t t o r a l A r e a ) Op t i o n 3 b Cu r l y l e a f P o n d w e e d M a n a g e m e n t - He r b i c i d e T r e a t m e n t ( 5 0 % L i t t o r a l A r e a ) Op t i o n 3 c Cu r l y l e a f P o n d w e e d M a n a g e m e n t - Me c h a n i c a l H a r v e s t i n g ( 5 0 % L i t t o r a l A r e a ) Op t i o n 3 d Cu r l y l e a f P o n d w e e d M a n a g e m e n t - W i n t e r Dr a w d o w n P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ I n L a k e M o d e l \ I n L a k e S u m m a r y . x l s Fi g u r e 9 - 2 In d i a n h e a d L a k e : E s t i m a t e d S u m m e r A v e r a g e T o t a l P h o s p h o r u s C o n c e n t r a t i o n Fo l l o w i n g B M P I m p l e m e n t a t i o n 020406080 10 0 12 0 1 2 BM P S c e n a r i o T o t a l P h o s p h o r u s C o n c e n t r a t i o n ( µ µ µ µ g / L ) $0$200$400$600$800$1,000$1,200 Estimated Cost ($) BM P C o s t 19 8 7 - 8 8 D r y C o n d i t i o n 19 9 4 - 9 5 A v e r a g e C o n d i t i o n 20 0 1 - 0 2 W e t C o n d i t i o n 20 0 3 - 0 4 C a l i b r a t i o n C o n d i t i o n MP C A P r o p o s e d S h a l l o w L a k e C r i t e r i a [T P ] < 6 0 µg/ L NM C W D ' s P r o p o s e d W a t e r Q u a l i t y G o a l U p p e r L i m i t o f L e v e l I I C l a s s i f i c a t i o n [T P ] < 7 5 µg/ L 20 0 4 O b s e r v e d S u m m e r A v e r a g e BM P L e g e n d Op t i o n 1 N o B M P s Op t i o n 2 Ex i s t i n g ( 2 0 0 4 ) C o n d i t i o n s - C o p p e r S u l f a t e Tr e a t m e n t s i n M a y a n d A u g u s t P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 101 9.2 Recommendations The evaluation of 2004 water quality data for both Arrowhead and Indianhead Lakes suggests that both lakes are in fairly good condition, meeting the NMCWD Level II management class criteria for nearly all climatic conditions. Therefore, the implementation of the BMPs discussed in Section 8.0 is not necessary. However, if the NMCWD feels that the improvement of water quality within these two lakes is of high priority, there are several management options discussed above that will improve t he water quality in each lake. Additionally, it should be emphasized that the promotion of source control through the implementation of nonstructural BMPs throughout the watershed is crucial to protecting the water quality of a lake and helps maintain the performance of the structural and in-lake practices that are currently in place or will be implemented in the future. The following is a discussion of the general recommendations will maintain or improve the water quality in Arrowhead and Indianhead Lakes. 9.2.1 Invasive Species Monitoring & Management The NMCWD should continue to perform periodic macrophyte surveys in both Arrowhead and Indianhead Lakes to monitor the presence/growth of undesirable non-native species such as Eurasian watermilfoil and Curlyleaf pondweed. Macrophyte surveys typically cost $2000 per lake. If the NMCWD feels that management of the non-native macrophyte species, Eurasian watermilfoil and Curlyleaf pondweed, present in Arrowhead Lake is of high priority, these macrophytes can be successfully managed by treatment with herbicides, mechanical harvesting, a winter drawdown of lake levels, or by a combination of these methods. M odeling suggests that about 20 percent of the phosphorus load in Arrowhead Lake is the result of phosphorus release from the die-back of Curlyleaf pondweed, so a reduction in the coverage and density of Curlyleaf pondweed will help improve the water quality of Arrowhead Lake (see Options 3a -d, Table 8-2; Figure 9-1). 9.2.2 Copper Sulfate Treatments in Indianhead Lake Copper sulfate is typically not a means of controlling algal growth and phosphorus in Indianhead Lake because it is a temporary solution that does not reduce the source of the nutrient loading. However, during the summer of 2004, there were two applications of copper sulfate per the request of the lake homeowner association. Water quality data and modeling suggest that there was an improvement in lake water quality due to these treatments. However, there is only one year of water quality data and the impact directly related to copper sulfate treatments was not able to be quantified. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 102 9.2.3 Aeration Again, we do not recommend the use of aerators as a means of maintaining or improving water quality. However, there are several submerged aerators operating continuously in both Arrowhead and Indianhead Lakes. These were installed more than a decade ago for the lake homeowner association. These were operating during the 2004 water quality sampling period and may have influenced the observed water quality. However, because only one year of data is available for both lakes, we are unable to determine the impact the aerators have on the overall water quality of each lake. 9.2.4 Additional Recommendations The in-lake models developed for Arrowhead and Indianhead Lakes are based on calibration of the of water quality data collected in 2004. However, models were unable to be verified due to having only one year of water quality data. If the NMCWD should decide to continue with a water quality monitoring program, it is recommended that the aerators in both lakes be turned off during the sampling season. Additionally, any sort of chemical treatment should not be used during this monitoring period. The use of aerators and chemical treatments appears to alter the water quality of the lake and does not provide insight to the actual baseline water quality status of the resource. The monitoring should follow the same protocol as the 2004 sampling period, monitoring various water quality parameters as well as phytoplankton and zooplankton communities. A fishery survey would also be recommended for Indianhead Lake as there is currently no information on the fishery. 9.2.5 Public Participation It should also be mentioned that it is a general NMCWD goal to encourage public participation in all NMCWD activities and decisions that may affect the public. In accordance with this goal, the NMCWD seeks to involve the public in the discussion of this UAA. This goal is expected to be achieved through a public meeting to obtain comments on the Arrowhead and Indianhead UAA. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 103 References Bannerman, R., K. Baun, M. Bohn, P. Hughes, and D. Graczyk. 1983. Evaluation of Urban Nonpoint Source Pollution Management in Milwaukee, Wisconsin, Volume I. Urban Stormwater Characteristics, Pollutant Sources and Management by Street Sweeping. Prepared for the U.S. Environmental Protection Agency, Region V, Chicago, IL. PB 84-114164. Barr 1973. The Nine Mile Creek Watershed District Overall Plan. Barr 1992. Minneapolis Chain of Lake Monitoring Study. Prepared for the Minneapolis Park and Recreation Board. Barr 1996. Nine Mile Creek Watershed District Water Management Plan. Prepared for Nine Mile Creek Watershed District Barr 1999a. City of Minnetonka Water Resources Management Plan. Prepared for the City of Minnetonka. Barr 1999b. Round Lake Use Attainability Analysis. Prepared for Nine Mile Creek Watershed District. Barr 2001. Big Lake Protection Grant LPT-67: Big Lake Macrophyte Management Plan Implementation, Volume 1: Report, Barr 2003. Bryant Lake Use Attainability Analysis. Prepared for Nine Mile Creek Watershed District. Barr, 2003. City of Edina Comprehensive Water Resource Management Plan Prepared for the City of Edina Barr 2003. Smetana Lake Use Attainability Analysis. Prepared for Nine Mile Creek Watershed District. Barr 2003. Southeast, Southwest, and Northwest Anderson Lake Use Attainability Analyses. Prepared for Nine Mile Creek Watershed District. Barten, J. and E. Jahnke 1997. Suburban Lawn Runoff Water Quality in the Twin Cities Metropolitan Area, 1996 and 1997. Barten, J. 1995. Quantity and Quality of Runoff from Four Golf Course in the Twin Cities Metropolitan Area. Report to the Legislative Commission on Minnesota Resources. Carlson, R. 1977. “A Trophic Status Index for Lakes.” Limnology Oceanography 22(2): 361-9. Catling, P.M. and I. Dobson. 1985. “The Biology of Canadian Weeds. 69. Potamogeton crispus L.” Can. J. Plant Sci. Rev. Can. Phytotechnie. Ottawa: Agricultural Institute of Canada, 65 (3): 655-668. Chapra, S.C., and S.J. Tarapchak, 1976. “A Chlorophyll a Model and its Relationship to Phosphorus loading plots for Lakes.” Water Res. Res. 12(6): 1260-1264. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 104 Cooke, G.D., E.B. Welch, S.A. Peterson, and P.R. Newroth. 1993. Restoration and Management of Lakes and Reservoirs, Second Edition. Lewis Publishers, Boca Raton, FL. 548 pp. Dillon, P.J. and F.H. Rigler. 1974. “A test of a simple nutrient budget model predicting the phosphorus concentrations in lake water.” J. Fish. Res. Bd. Can. 31: 1771-1778. Garn, H. S. 2004. Effects of Lawn Fertilizer on Nutrient Concentration I Runoff from Lakeshore Lawns, Lauderdale Lake, Wisconsin. USGS Water-Resources Investigations Report 02-4130. Getsinger, et al. 2001. Whole-Lake Applications of Sonar for Selective Control of Eurasian Watermilfoil Heiskary, S. A. and C. B. Wilson. 2005. Minnesota Lake Water Quality Assessment Report: Developing Nutrient Criteria Third Edition. Minnesota Pollution Control Agency. Heiskary, S. A. and C. B. Wilson. 1990. Minnesota Lake Water Quality Assessment Report Second Edition A Practical Guide for Lake Managers. Minnesota Pollution Control Agency. Heiskary, S. A. and W. W. Walker. 1988. Developing Phosphorus Criteria for Minnesota Lakes. Lake and Reservoir Management. 4:1-9. Heiskary, S.A. and J.L. Lindbloom. 1993. Lake Water Quality Trends in Minnesota. Minnesota Pollution Control Agency. Water Quality Division. Helsel, D. and T. Zagar. 2003a. Big Muskego Story: Rehabilitating A Large Shallow Lake. Lakeline, Spring 2003. Helsel, D., Madsen, J., and B. James. 2003b. Changes in Sediment, Water Quality, and Aquatic Plants. Lakeline, Spring 2003. Holdren, C., W. Jones and J. Taggart. 2001. Managing Lakes and Reservoirs. N. Am. Lake Manage. Soc. and Terrene Inst. in coop. with Off. Water Assess. Watershed Prot. Div. U.S. Environ. Prot. Agency, Madison, WI. I.E.P., Inc. 1990. P8 Urban Catchment Model. Version 2.4. Prepared for the Narragansett Bay Project. Providence, Rhode Island. James, W.F, J.W. Barko, and H.L. Eakin. 2001. Direct and Indirect Impacts of Submerged Aquatic Vegetation on the Nutrient Budget of an Urban Oxboe Lake. APCRP Technical Notes Collection (ERDC TN-APCRP-EA-02), U.S. Army Research and Development Center, Vicksburg, MS. LaMarra, V.J., Jr. 1975. “Digestive activities of carp as a major contributor to the nutrient loading of lakes.” Verh. Int. Verein. Limnol. 19: 2461-2468. McComas, S., and J. Stuckert. 2000. “Pre-emptive Cutting as a Control Technique for Nuisance Growth of Curly-leaf Pondweed, Potamogeton crispus.” Verh. Internat. Verein Limnol. 27:2024-2051. Minnesota Pollution Control Agency (MPCA). 1988. Minnesota Lake Water Quality Assessment Report. Minnesota Pollution Control Agency (MPCA). 1989. Protecting Water Quality in Urban Areas. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 105 Minnesota Pollution Control Agency. 1998. Minnesota Lake Water Quality Assessment Data: 1997—An Update to Data Presented in the Minnesota Lake Water Quality Assessment Report: 1990. Water Quality Division. Prepared for the Environmental Protection Agency Moore, L., and K. Thornton, (Eds.). 1988. Lake and Reservoir Restoration Guidance Manual. EPA 440/5-88-002 Moyle, J.B. and N. Hotchkiss. 1945. The Aquatic and Marsh Vegetation of Minnesota and its Value to Waterfowl. Minnesota Department of Conservation Technical Bulletin No. 3, 122 p. Nurnberg, G.K. 1984. “The Prediction of Internal Phosphorus Loads in Lakes with Anoxic Hypolimnia.” Limnology and Oceanography 29(1): 111-124. Nürnberg, G.K. 1984. “The prediction of internal phosphorus loads in lakes with anoxic hypolimnia.” Limnol. Oceanogr 29(1): 111-124. Osgood, R.A. 1989. Assessment of Lake Use-Impairment in the Twin Cities Metropolitan Area. Prepared for the Minnesota Pollution Control Agency. Metropolitan Council Publication 590- 89-130. 12 pp. Pullmann. 1992. (The Lake Association Leader’s Aquatic Vegetation Management Guidance Manual. Prepas, E.E., J. Babin, T.P. Murphy, P.A. Chambers, G.J. Sandland, A. Ghadouanis, and M. Serediak. 2001. “Long-term Effects of Successive Ca(OH)2 and CaCO3 Treatments on the Water Quality of Two Eutrophic Hardwater Lakes.” Freshwater Biology. 46:1089-1103. Reed, C.F. 1977. “History and Distribution of Eurasian Watermilfoil in United States and Canada.” Phytologia 36: 417-436. Reedyk, S., E.E. Prepas, and P.A. Chambers. 2001. “Effects of Single Ca(OH)2 Doses on Phosphorus Concentration and Macrophyte Biomass of two Boreal Eutrophic Lakes over 2 Years.” Freshwater Biology. 46:1075-1087. Rhode Island Department of Environmental Management. 1990. The Land Management Project. Scherer, N.M., H.L. Gibbons, K.B. Stoops, and M. Muller. 1995. “Phosphorus Loading of an Urban Lake by Bird Droppings.” Lake and Reserv. Manage. 11(4): 317-327. Schueler, T.R. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban BMPs. Prepared for Washington Metropolitan Water Resources Planning Board. Metropolitan Washington Council of Governments, Washington, D.C. 275 pp. Schupp, D.H. 1992. An Ecological Classification of Minnesota Lakes with Associated Fish Communities. Minnesota Department of Natural Resources. Investigational Report 417. 27 pp. Stauffer, T.R. 1987. “Vertical Nutrient Transport and its Effects on Epilimnetic Phosphorus in Four Calcareous Lakes.” Hydrobiologia. 154: 87-102. Swain, Edward B., Monson, Bruce A., Pillsbury, Robert W. 1986. Use of Enclosures to Assess the Impact of Copper Sulfate Treatments on Phytoplankton. Proceedings of the Fifth International Symposium on Lake Management (1985), North American Lake Management Society, 1986. p. 303-308. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Report_UAA_71706_JAK2_Final.DOC 106 Sweetwater Technology Corp. 1997. Aluminum Dose Calculation for Applying Alum (or Alum and Sodium Aluminate) to Inactive Phosphorus Release from Lake Bottom Sediments. Valley, R.D. and R.M. Newman. 1998. “Competitive Interactions Between Eurasian Watermilfoil and Northern Milfoil in Experimental Tanks”. Journal of Aquatic Plant Management. 36(2): 121-126. Vighi, M. and Chiaudani, G. 1985. “A Simple Method to Estimate Lake Phosphorus Concentrations Resulting from Natural, Background, Loadings”. Water Res. 19(8): 987-991. Vollenweider, R. A. 1976. Advances in Defining Critical Loading Levels for Phosphorus in Lake Eutrophication. Mem. 1st. Ital. Idrobiol. 33:53-83. Walker, W.W. 1987. Phosphorus Removal by Urban Runoff Detention Basins. Lake and Reservoir Management: Volume III. North American Lake Management Society. Welch, E.B. and G.D. Cooke. 1999. “Effectiveness and Longevity of Phosphorus Inactivation with Alum.” Journal of Lake and Reservoir Management. 15(1):5-27 Wilson, C.B. and W.W. Walker, The Minnesota Lake Eutrophication Analysis Procedure (MINLEAP), MPCA, 1988. Wisconsin Department of Natural Resources. Wisconsin Lake Modeling Suite (WILMS).2004. World Health Organization. 1999. Toxic Cyanobacteria in Water: A guide to their public health consequences, monitoring and management. Appendices Appendix A Data Collection Methods P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Appendix\APPENDIXA_AH_IH_DataCollection Methods.doc A-1 Methods The Arrowhead and Indianhead Lakes UAA included the collection and analysis of data from the lake and its watershed. The methods discussion includes: • Lake water quality data collection • Ecosystem data collection A.1 Lake Water Quality Data Collection In 2004, representative sampling stations were selected (i.e., located at the deepest location in the lake basin) for both Arrowhead and Indianhead Lakes. Samples were collected monthly between the end of April and beginning of September. During August samples were collected biweekly. Table A-1 lists the water quality parameters that were sampled and specifies at what depths samples or measurements were collected. Dissolved oxygen, temperature, specific conductance, turbidity and Secchi disc were measured in the field, whereas water samples were analyzed in the laboratory for total phosphorus, soluble reactive phosphorus, total Kjeldahl nitrogen, nitrate + nitrite nitrogen, chlorophyll a, and pH. The procedures for chemical analyses of the water samples are shown in Table A-2. Generally, the methods can be found in Standard Methods for Water and Wastewater Analysis. A.2 Ecosystem Data Collection Ecosystem describes the community of living things within Arrowhead and Indianhead Lakes and their interaction with the environment in which they live and with each other. During June through September 2004, ecosystem data collection included: • Phytoplankton – A composite 0-2 meter sample was collected during each water quality sampling event described in the previous section. • Zooplankton – A zooplankton sample was collected (i.e., bottom to surface) during each water quality sampling event described in the previous section. • Macrophytes – Macrophyte surveys were collected during June and August 2004. P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Appendix\APPENDIXA_AH_IH_DataCollection Methods.doc A-2 Table A-1. Arrowhead and Indianhead Lakes Water Quality Parameters Parameters Depth (Meters) Sampled or Measured During Each Sample Event Dissolved Oxygen Surface to bottom profile X Temperature Surface to bottom profile X Specific Conductance Surface to bottom profile X Secchi Disc — X Total Phosphorus 0-2 Meter Composite Sample X Total Phosphorus Profile at 1.0 meter intervals from 3 meters to 0.5 meters above lake bottom X Soluble Reactive Phosphorus 0-2 Meter Composite Sample X Total Kjeldahl Nitrogen (TKN) 0-2 Meter Composite Sample X Nitrate + Nitrite Nitrogen 0-2 Meter Composite Sample X pH 0-2 Meter Composite Sample X pH Profile at 1.0 meter intervals from 3 meters to 0.5 meters above lake bottom X Turbidity 0-2 Meter Composite Sample X Chlorophyll a 0-2 Meter Composite Sample X P:\Mpls\23 MN\27\2327634\_MovedFromMpls_P\Indianhead_Arrowhead_UAA\Report\Appendix\APPENDIXA_AH_IH_DataCollection Methods.doc A-3 Table A-2. Procedures for Chemical Analyses Performed on Water Samples Analysis Procedure Reference Total Phosphorus Persulfate digestion, manual ascorbic acid Standard Methods, 18th Edition (1992) modified per Eisenreich, et al., Environmental Letters 9(1), 43-53 (1975) Soluble Reactive Phosphorus Manual ascorbic acid Standard Methods, 18th Edition modified per Eisenreich, et al., Environmental Letters 9(1), 43-53 (1975) Total Nitrogen Persulfate digestion, scanning spectrophotometric Bachman, Roger W. and Daniel E. Canfield, Jr., 1991. A Comparability Study of a New Method for Measuring Total Nitrogen in Florida Waters. Report submitted to the Florida Department of Environmental Regulation. Total Kjeldahl Nitrogen Nitrate + Nitrite Nitrogen Chlorophyll a Spectrophotometric Standard Methods, 18th Edition, 1992, 10200 H pH Potentiometric measurement, glass electrode Standard Methods, 16th Edition, 1985, 423 Specific Conductance Wheatstone bridge Standard Methods, 16th Edition, 1985, 205 Temperature Thermometric Standard Methods, 16th Edition, 1985, 212 Dissolved Oxygen Electrode Standard Methods, 16th Edition, 1985, 421F Turbidity Phytoplankton Identification and Enumeration Inverted Microscope Standard Methods, 16th Edition, 1985, 1002F (2-d), 1002H (2) Zooplankton Identification and Enumeration Sedgewick Rafter Standard Methods, 16th Edition, 1985, 1002F (2-d), 1002H Transparency Secchi disc Phytoplankton and zooplankton samples were identified and enumerated to provide information on species diversity and abundance. The macrophyte community was surveyed to determine species location, composition, and abundance. Appendix B Arrowhead and Indianhead Lakes 2004 Macrophyte Surveys NottoScale ARROWHEADLAKE MACROPHYTESURVEY AUGUST 23,2004P: 2 3 \ 2 7 \ 0 0 3 \ L a k e M a c r o p h y t e M a p s \ A R R O W H E A D \ 2 0 0 4 \ A U G U S T 2 0 0 4 . C D R R L G 0 1 - 2 0 - 0 5 Submerged AquaticPlants: FloatingLeaf: Emergent: No AquaticVegetationFound: CommonName ScientificName Myriophyllumspicatum Ceratophyllumdemersum Nitellasp. Najassp. Zosterelladubia Charasp. Potamogetonsp. Typhasp. Scirpussp. Irisvericolor Eurasionwatermilfoil Coontail Stonewort Bushypondweedandnaiad Waterstargrass Muskgrass Narrowleafpondweed Cattail Bullrush Blueflagiris Nomacrophytesfoundinwater>5.0to6.0'. Macrophytedensitiesestimatedasfollows:1=light;2=moderate;3=heavy. Ceratophyllumdemersumobserved-sporadic,lightdensity. Laketreatedwith"Navigate"on08-09-04. Algalmatspresent. Entirelakeperimeterhasalight(sporadic)densityofNymphaeatuberosa Water Quality Monitoring Location Typhasp. Scirpussp. Scirpussp. Nymphaeatuberosa Nupharmicrophyllum Typhasp. Nitellasp.3 Typhasp. Irisvericolor Irisvericolor Typhasp. Scirpussp. Nymphaeatuberosa Nymphaeatuberosa Nupharmicrophyllum Typhasp. Typhasp. Nymphaeatuberosa Nupharmicrophyllum Scirpussp. Irisvericolor Irisvericolor (Sporadic) Typhasp. Nymphaeatuberosa Nupharmicrophyllum Nymphaeatuberosa Nupharmicrophyllum Whitewaterlily Littleyellowwaterlily Aerators Cascade AeratoronShore Nymphaeatuberosa Myriophyllumspicatum1 Nitellasp.3 Myriophyllumspicatum1 Nymphaeatuberosa Najassp. Zosterelladubia Myriophyllumspicatum(1plant) Algalmats Charasp.1 Myriophyllumspicatum1 Potamogetonsp.(narrowleaf)2-3 Najassp.1 Nymphaeatuberosa Not to Scale ARROWHEAD LAKE MACROPHYTE SURVEY JUNE 14, 2004P: 2 3 \ 2 7 \ 0 0 3 \ L a k e M a c r o p h y t e M a p s\ A R R O W H E A D \ 2 0 0 4 \ J U N E 2 0 0 4 . C D R R L G 0 8 - 0 4 - 0 4 Submerged Aquatic Plants: Floating Leaf: Emergent: No Aquatic Vegetation Found: Common Name Scientific Name Myriophyllum spicatum Ceratophyllum demersum Nitella sp. Typha sp. Scirpus sp. Iris vericolor Eurasion watermilfoil Coontail Stonewort Cattail Bullrush Blue flag iris No macrophytes found in water > 5.0 to 6.0'. Macrophyte densities estimated as follows: 1 = light; 2 = moderate; 3 = heavy. Potamogeton crispus turions are present. Evidence of lake treated to kill Potamogeton crispus Ceratophyllum demersum observed - sporadic, light density Eurasion watermilfoil observed (1-2 plants), light density (floating pieces). Water Quality Monitoring Location Typha sp. Scirpus sp. Nymphaea tuberosa Nuphar microphyllum Typha sp. Nitella sp. 3 Typha sp. Iris vericolor Nymphaea tuberosa Iris vericolor Nymphaea tuberosa Typha sp. Scirpus sp. Nymphaea tuberosa Nymphaea tuberosa Nuphar microphyllum Typha sp. Typha sp. Nymphaea tuberosa Nuphar microphyllum Scirpus sp. Iris vericolor Iris vericolor (Sporadic) Typha sp. Nymphaea tuberosa Nuphar microphyllum Nymphaea tuberosa Nuphar microphyllum White waterlily Little yellow waterlily Aerators Cascade Aerator on Shore Not to Scale INDIANHEAD LAKE MACROPHYTE SURVEY AUGUST 23, 2004P: 2 3 \ 2 7 \ 0 0 3 \ L a k e M a c r o p h y t e M a p s\ I N D I A N H E A D \ 2 0 0 4 \ A U G U S T 2 0 0 4 . C D R R L G 0 1 - 2 0 - 0 5 Submerged Aquatic Plants: Floating Leaf: Emergent: No Aquatic Vegetation Found: Common Name Scientific Name Riccia fluitans Nitella sp. Potamogeton spp. (narrowleaf) Iris sp. (yellow flower) Typha sp. Scirpus sp. Acorus calamus Sagittaria sp. Slender riccia Stonewort Narrowleaf pondweed Yellow Iris Cattail Bullrush Sweetflag Arrowhead Macrophytes found in entire lake, less dense near center of water body. Macrophyte densities estimated as follows: 1 = light; 2 = moderate; 3 = heavy. Water treated with copper sulfate in May, 2004 Water color indicates that "Aqua Shade" may have been used. Nitella sp. 1-2 Potamogeton sp. Aerators Water Quality Monitoring LocationTypha sp. Scirpus sp. Iris sp. (yellow flower) Typha sp. Acorus calamus Acorus calamus Iris sp. (yellow flower) Iris sp. (yellow flower) Typha sp. Nitella sp. 1 Sagittaria sp. Iris sp. (yellow flower) Scirpus sp. Iris sp. (yellow flower) Nitella sp. 3 Iris sp. (yellow flower) Nitella sp. 1 Typha sp. Scirpus sp. Iris sp. (yellow flower) Riccia fluitans Sagittaria sp. Sagittaria sp. Typha sp. Nitella sp. 3 Sagittaria sp. Not to Scale INDIANHEAD LAKE MACROPHYTE SURVEY JUNE 14, 2004P: 2 3 \ 2 7 \ 0 0 3 \ L a k e M a c r o p h y t e M a p s\ I N D I A N H E A D \ 2 0 0 4 \ J U N E 2 0 0 4 . C D R R L G 0 8 - 0 9 - 0 4 Submerged Aquatic Plants: Floating Leaf: Emergent: No Aquatic Vegetation Found: Common Name Scientific Name Riccia fluitans Nitella sp. Potamogeton spp. (narrowleaf) Iris sp. (yellow flower) Typha sp. Scirpus sp. Acorus calamus Sagittaria sp. Slender riccia Stonewort Narrowleaf pondweed Yellow Iris Cattail Bullrush Sweetflag Arrowhead Macrophytes found in entire lake, less dense near center of water body. Macrophyte densities estimated as follows: 1 = light; 2 = moderate; 3 = heavy. Water treated with copper sulfate in May, 2004 Water color indicates that "Aqua Shade" may have been used. Nitella sp. 1-2 Potamogeton sp. Aerators Water Quality Monitoring LocationTypha sp. Scirpus sp. Iris sp. (yellow flower) Typha sp. Acorus calamus Acorus calamus Iris sp. (yellow flower) Iris sp. (yellow flower) Typha sp. Nitella sp. 1 Sagittaria sp. Iris sp. (yellow flower) Iris sp. (yellow flower) Scirpus sp. Iris sp. (yellow flower) Nitella sp. 3 Iris sp. (yellow flower) Nitella sp. 1 Typha sp. Scirpus sp. Iris sp. (yellow flower) Riccia fluitans Appendix C Pond Data Drainage Area Subwatershed Name Normal Pool Area (acres) Existing Dead Storage* (ac-ft) Existing Flood Pool Area (acres) Existing Flood Pool Storage (ac-ft) Existing Outlet (inches) Arrowhead Lake Ponds AH_1 27 278 27 27 10' Weir AH_32 0.1 0.17 0.7 2.56 24" AH_4 0.18 0.72 0.33 0.83 12" AH_6 1.05 4.2 3.5 24 21" Indian Head Ponds IH_1 14.1 61.3 26.4 457 10' Weir IH_14 0.59 2.36 1 4 12" Arrowhead and Indianhead Lakes Existing Pond Information Appendix C *Existing Dead Storage was estimated from field surveys, city water management plans, as-built plans, or wetland inventories Appendix D Arrowhead and Indianhead Lakes 2004 Water Quality Data Date Max Depth (m) Sample Depth (m) Secchi Depth (m) Chl. a (ug/L) Turbidity (NTU's) D. O. (mg/L) Temp (°C) Sp. Cond. (µmho/cm @ 25°C) Total P (mg/L) Ortho P (mg/L) Total Kjeldahl Nitrogen (mg/L) Nitrate + Nitrite Nitrogen (mg/L) pH (S.U.) 4/21/04 1.6 0-1.5 1.1 8.7 3.2 ----725 0.041 <0.006 0.83 <0.020 9.2 0.0 11.2 13.5 725 ---- 1.0 11.1 13.5 725 ---- 6/10/04 2.7 0-2 0.8 6.7 4.1 ----626 0.110 0.023 1.1 <0.020 7.4 0.0 3.6 21.2 624 ---- 1.0 3.4 21.2 624 ---- 2.0 3.4 21.2 624 ---- 2.5 2.9 20.6 632 0.110 7.4 7/7/04 2.7 0-2 0.9 11.0 3.7 ----649.25 0.084 0.019 0.91 <0.020 7.7 0.0 5.1 22.4 651 ---- 1.0 5.0 22.2 650 ---- 2.0 4.5 21.9 648 ---- 2.5 2.4 21.7 648 ---- 8/11/04 2.4 0-2 1.2 17.0 3.1 ----653.666667 0.056 0.007 0.69 0.034 7.7 0.0 6.1 19.1 654 ---- 1.0 6.0 19.2 654 ---- 2.0 6.0 19.3 653 ---- 8/24/04 2.4 0-2 1.0 27.0 3.1 ----671.666667 0.056 <0.006 0.77 <0.020 7.9 0.0 7.8 21.5 672 ---- 1.0 7.3 21.2 672 ---- 2.0 6.2 21.0 671 ---- 9/10/04 2.4 0-2 1.0 31.0 3.4 ----665.666667 0.055 <0.006 0.60 <0.020 8.0 0.0 7.7 21.4 666 ---- 1.0 7.4 21.1 665 ---- 2.0 6.7 21.0 666 ---- Aerators were operating during all sampling events. Arrowhead Lake Date Max Depth (m) Sample Depth (m) Secchi Depth (m) Chl. a (ug/L) Turbidity (NTU's) D. O. (mg/L) Temp (°C) Sp. Cond. (µmho/cm @ 25°C) Total P (mg/L) Ortho P (mg/L) Total Kjeldahl Nitrogen (mg/L) Nitrate + Nitrite Nitrogen (mg/L) pH (S.U.) 4/21/04 1.4 0-1 1.4 3.6 1.7 ----245 0.024 <0.006 0.54 <0.020 8.4 0.0 9.0 14.0 245 ---- 1.0 9.0 13.9 245 ---- 6/10/04 2.1 0-1.5 1.1 6.7 2.3 ----281.333333 0.044 <0.006 <0.50 <0.020 7.5 0.0 5.3 21.6 282 ---- 1.0 5.3 21.7 281 ---- 1.5 5.3 21.7 281 ---- 7/7/04 2.1 0-1.5 1.2 8.9 2.5 ----289.666667 0.047 <0.006 0.73 <0.020 7.6 0.0 5.2 22.3 290 ---- 1.0 5.4 22.1 290 ---- 1.5 5.2 21.8 289 ---- 8/11/04 1.8 0-1.5 0.8 9.4 3.5 ----276.5 0.060 <0.006 0.63 <0.020 7.7 0.0 5.8 19.3 277 ---- 1.0 5.8 19.3 276 ---- 8/24/04 1.8 0-1.5 1.4 13.0 2.8 ----286.333333 0.040 <0.006 0.73 <0.020 8.0 0.0 7.5 22.4 287 ---- 1.0 7.6 21.7 286 ---- 1.5 6.3 21.5 286 ---- 9/10/04 1.8 0-1.5 1.2 5.3 1.8 ----282.333333 0.038 <0.006 <0.50 0.022 7.9 0.0 7.6 21.5 282 ---- 1.0 7.1 21.5 283 ---- 1.5 6.8 21.3 282 ---- Secchi disc on bottom. Aerators on during all sampling events. Indianhead Lake Appendix E Arrowhead and Indianhead Lakes Biological and Fisheries Data ARROWHEAD LAKE SAMPLE: 0-2 METERS STANDARD INVERTED MICROSCOPE ANALYSIS METHOD 4/21/2004 6/10/2004 7/7/2004 8/11/2004 8/24/2004 9/10/2004 DIVISION TAXON units/mL units/mL units/mL units/mL units/mL units/mL CHLOROPHYTA (GREEN ALGAE)Actinastrum Hantzschii 0 0 0 0 0 0 Ankistrodesmus falcatus 0 627 1,093 63 78 273 Ankistrodesmus Brauni 0 0 0 0 0 0 Chlamydomonas globosa 8,655 2,060 15,265 927 3,592 5,231 Closterium sp.0 30 0 0 0 0 Coelastrum microporum 0 0 39 0 0 0 Cosmarium sp.0 30 0 0 0 39 Dictyosphaerium Ehrenbergianum 0 0 0 0 0 0 Elakotothrix gelatinosa 0 0 0 0 0 0 Elakotothrix sp.0 0 0 0 0 0 Oocystis parva 0 30 78 379 468 0 Micractinium quadrisetum 0 0 117 0 0 0 Pandorina morum 0 0 0 0 0 0 Pediastrum Boryanum 0 0 78 0 39 0 Pediastrum simplex 0 0 0 21 0 0 Quadrigula closteriodes 0 0 0 0 0 117 Quadrigula sp.0 0 39 0 0 0 Rhizoclonium hieroglyphyicum 0 119 0 0 0 39 Schroederia Judayi 0 2,418 1,405 63 0 273 Scenedesmus dimorphus 0 0 39 0 0 0 Scenedesmus quadricauda 118 60 195 42 195 156 Scenedesmus sp.59 0 39 0 0 0 Selenastrum minutum 0 358 234 21 39 234 Selenastrum sp.0 0 0 0 0 0 Sphaerocystis Schroeteri (Colony)0 0 39 0 117 195 Staurastrum sp.0 0 39 21 0 0 Tetraedron minimum 0 0 0 0 0 0 Tetraedron muticum 59 0 0 21 0 0 Tetraedron sp.0 0 39 0 0 0 Treubaria setigerum 0 0 234 0 0 39 CHLOROPHYTA TOTAL 8,891 5,731 18,973 1,559 4,529 6,598 CHRYSOPHYTA (YELLOW-BROWN ALGAE)Dinobryon sociale 0 0 0 0 2,538 0 CHRYSOPHYTA TOTAL 0 0 0 0 2,538 0 CYANOPHYTA (BLUE-GREEN ALGAE)Anabaena affinis 0 0 0 21 0 39 Anabaena flos-aquae 0 0 0 0 0 0 Anabaena spiroides v. crassa 0 0 0 0 0 0 Anabaenopsis raciborski 0 0 0 0 0 0 Aphanizomenon flos-aquae 59 30 0 0 273 195 Coelosphaerium Naegelianum 0 0 0 0 0 0 Lyngbya limnetica 0 0 0 0 0 0 Lyngbya sp.0 0 0 0 0 0 Merismopedia tenuissima 0 0 0 21 0 0 Merismopedia sp.0 0 0 0 0 0 Microcystis aeruginosa 0 0 156 42 0 0 Microcystis incerta 0 0 0 0 0 0 Oscillatoria limnetica 59 388 0 0 0 0 Oscillatoria Agardhii 0 0 0 0 0 39 Oscillatoria redekii 0 0 0 21 0 0 Phormidium mucicola 0 0 0 0 0 0 CYANOPHYTA TOTAL 118 418 156 84 273 273 BACILLARIOPHYTA (DIATOMS)Asterionella formosa 0 0 0 0 0 195 Cocconeis placentula 0 0 0 0 0 0 Cymbella sp.59 0 0 0 0 0 Eunotia pectinalis 0 0 0 0 0 0 Fragilaria capucina 236 30 39 105 39 39 Fragilaria crotonensis 0 0 0 0 0 0 Melosira granulata 59 0 429 63 0 39 Navicula sp.0 0 39 0 0 0 Nitzschia sp.0 0 0 0 0 0 Rhizosolenia sp.0 0 0 0 0 0 Rhoicosphenia curvata 0 0 0 0 0 0 Stephanodiscus Hantzschii 59 119 820 21 195 0 Stephanodiscus sp.0 0 0 0 0 0 Synedra acus 59 0 0 0 0 0 Synedra ulna 236 1,104 0 0 0 0 BACILLARIOPHYTA TOTAL 707 1,254 1,327 190 234 273 CRYPTOPHYTA (CRYPTOMONADS)Cryptomonas erosa 20,431 7,582 4,021 1,180 1,874 1,015 CRYPTOPHYTA TOTAL 20,431 7,582 4,021 1,180 1,874 1,015 EUGLENOPHYTA (EUGLENOIDS)Euglena sp.0 0 195 0 0 156 Phacus sp.0 30 156 0 625 6,012 EUGLENOPHYTA TOTAL 0 0 195 0 0 6,168 PYRRHOPHYTA (DINOFLAGELLATES)Ceratium hirundinella 0 0 0 0 0 0 Peridinium cinctum 0 30 234 0 0 39 PYRRHOPHYTA TOTAL 0 30 234 0 0 39 TOTALS 30,147 15,014 24,907 3,013 9,448 14,367 ARROWHEAD LAKE ZOOPLANKTON ANALYSIS 4/21/2004 6/10/2004 7/7/2004 8/11/2004 8/24/2004 9/10/2004 Vertical Tow (m) DIVISION TAXON #/m2 #/m2 #/m2 #/m2 #/m2 #/m2 CLADOCERA Bosmina longirostris 37,844 349,080 107,960 87,535 125,025 70,559 Ceriodaphnia sp.0 0 0 77,809 26,791 10,080 Chydorus sphaericus 0 41,557 9,815 9,726 17,861 10,080 Daphnia ambigua 0 0 0 0 0 0 Daphnia galeata mendotae 0 33,246 9,815 38,905 35,721 30,239 Daphnia pulex 0 8,311 0 0 0 0 Daphnia retrocurva 0 0 0 0 0 0 Diaphanosoma leuchtenbergianum 0 0 19,629 0 0 10,080 Immature Cladocera 0 0 0 0 0 0 CLADOCERA TOTAL 37,844 432,194 147,218 213,975 205,398 131,038 COPEPODA Cyclops sp.94,609 440,506 107,960 29,178 35,721 90,718 Diaptomus sp.0 0 0 0 0 0 Nauplii 245,983 673,225 186,477 29,178 116,095 211,676 Copepodid 0 0 0 0 0 0 COPEPODA TOTAL 340,592 1,113,731 294,437 58,357 151,816 302,394 Asplanchna priodonta 0 0 0 38,905 35,721 30,239 Brachionus sp.0 0 0 0 8,930 0 Filinia longiseta 0 0 0 0 8,930 0 Lecane sp.0 8,311 39,258 106,987 571,543 80,639 Keratella cochlearis 9,461 49,869 117,775 243,153 205,398 50,399 Keratella quadrata 0 0 0 0 0 0 Kellicottia sp.0 0 0 0 0 0 Polyarthra vulgaris 47,304 0 0 0 8,930 151,197 ROTIFERA Trichocerca cylindrica 0 0 0 9,726 8,930 0 Trichocerca multicrinis 0 0 0 0 0 0 ROTIFERA TOTAL 56,765 58,180 157,033 398,772 848,384 312,474 TOTALS 435,200 1,604,105 598,688 671,103 1,205,599 745,906 INDIANHEAD LAKE SAMPLE: 0-2 METERS STANDARD INVERTED MICROSCOPE ANALYSIS METHOD 4/21/2004 6/10/2004 7/7/2004 8/11/2004 8/24/2004 9/10/2004 DIVISION TAXON units/mL units/mL units/mL units/mL units/mL units/mL units/mL CHLOROPHYTA (GREEN ALGAE)Actinastrum Hantzschii 0 0 0 0 0 0 0 Ankistrodesmus falcatus 21 43 302 859 0 384 859 Ankistrodesmus Brauni 0 0 0 0 0 0 0 Chlamydomonas globosa 506 8,081 5,581 2,420 1,728 13,873 2,420 Closterium sp.0 0 0 0 0 0 0 Coelastrum microporum 0 0 0 0 0 0 0 Cosmarium sp.0 0 0 39 0 0 39 Dictyosphaerium Ehrenbergianum 0 0 0 0 0 0 0 Elakotothrix gelatinosa 0 43 0 39 0 35 39 Elakotothrix sp.0 0 0 0 0 0 0 Oocystis parva 0 43 38 0 0 0 0 Micractinium sp.0 0 0 0 21 0 0 Pandorina morum 0 0 0 0 0 0 0 Pediastrum Boryanum 0 0 0 0 0 0 0 Pediastrum simplex 0 0 0 0 21 0 0 Quadrigula sp.0 0 0 0 0 0 0 Rhizoclonium hieroglyphyicum 0 0 0 0 0 0 0 Schroederia Judayi 0 860 38 195 0 35 195 Scenedesmus dimorphus 0 0 0 0 0 0 0 Scenedesmus quadricauda 21 0 0 78 0 105 78 Scenedesmus sp.0 0 0 468 0 0 468 Selenastrum minutum 0 301 0 898 21 140 898 Selenastrum sp.0 0 38 0 0 0 0 Sphaerocystis Schroeteri (Colony)0 0 38 78 21 0 78 Staurastrum sp.0 0 0 0 0 0 0 Tetraedron minimum 0 0 0 0 0 0 0 Tetraedron muticum 0 0 0 39 0 0 39 Tetraedron sp.0 0 75 0 0 0 0 Treubaria setigerum 0 0 0 0 0 0 0 CHLOROPHYTA TOTAL 548 9,370 6,109 5,114 1,812 14,572 5,114 CHRYSOPHYTA (YELLOW-BROWN ALGAE)Dinobryon sociale 0 172 38 820 801 0 820 CHRYSOPHYTA TOTAL 0 172 38 820 801 0 820 CYANOPHYTA (BLUE-GREEN ALGAE)Anabaena affinis 0 0 0 0 0 0 0 Anabaena flos-aquae 0 0 113 0 63 0 0 Anabaena spiroides v. crassa 0 0 0 0 0 0 0 Anabaenopsis raciborski 0 0 0 0 42 35 0 Aphanizomenon flos-aquae 0 0 0 156 0 0 156 Coelosphaerium Naegelianum 0 0 0 0 0 0 0 Lyngbya limnetica 0 0 0 0 0 0 0 Lyngbya sp.0 0 0 0 0 0 0 Merismopedia tenuissima 0 0 0 0 0 0 0 Merismopedia sp.0 129 0 0 0 0 0 Microcystis aeruginosa 0 215 0 78 0 0 78 Microcystis incerta 0 43 0 0 0 0 0 Oscillatoria limnetica 42 0 0 39 42 0 39 Oscillatoria Agardhii 0 0 0 0 0 0 0 Oscillatoria redekii 0 129 0 0 0 0 0 Phormidium mucicola 21 0 0 39 0 0 39 CYANOPHYTA TOTAL 42 387 113 273 147 35 273 BACILLARIOPHYTA (DIATOMS)Asterionella formosa 0 0 0 0 0 0 0 Cocconeis placentula 0 0 0 0 42 0 0 Cymbella sp.0 0 0 0 0 0 0 Eunotia pectinalis 0 0 0 0 0 0 0 Fragilaria capucina 0 0 0 0 21 0 0 Fragilaria crotonensis 0 0 0 0 0 0 0 Melosira granulata 0 0 1,094 0 211 0 0 Navicula sp.0 0 75 39 21 35 39 Nitzschia sp.0 0 0 0 0 0 0 Rhizosolenia sp.0 0 0 0 0 0 0 Rhoicosphenia curvata 0 0 0 0 0 0 0 Stephanodiscus Hantzschii 0 0 830 234 0 0 234 Stephanodiscus sp.0 0 38 0 0 0 0 Synedra acus 0 0 0 0 0 35 0 Synedra ulna 0 8,554 415 351 0 105 351 BACILLARIOPHYTA TOTAL 0 8,554 2,451 625 295 175 625 CRYPTOPHYTA (CRYPTOMONADS)Cryptomonas erosa 3,771 3,868 10,068 312 9,439 6,220 312 CRYPTOPHYTA TOTAL 3,771 3,868 10,068 312 9,439 6,220 312 EUGLENOPHYTA (EUGLENOIDS)Euglena sp.0 0 75 39 0 35 39 Phacus sp.0 688 0 0 0 0 0 EUGLENOPHYTA TOTAL 0 0 75 39 0 35 39 PYRRHOPHYTA (DINOFLAGELLATES)Ceratium hirundinella 21 0 0 39 63 0 39 Peridinium cinctum 0 0 490 78 126 35 78 PYRRHOPHYTA TOTAL 21 0 490 117 190 35 117 TOTALS 4,383 22,351 19,344 7,300 12,684 21,072 7,300 INDIANHEAD LAKE ZOOPLANKTON ANALYSIS 4/21/2004 6/10/2004 7/7/2004 8/11/2004 8/24/2004 9/10/2004 Vertical Tow (m) DIVISION TAXON #/m2 #/m2 #/m2 #/m2 #/m2 #/m2 CLADOCERA Bosmina longirostris 0 0 0 10,257 0 10,610 Ceriodaphnia sp.0 0 0 0 0 0 Chydorus sphaericus 0 10,080 0 0 0 10,610 Daphnia ambigua 20,513 0 0 0 0 0 Daphnia galeata mendotae 0 0 0 0 0 0 Daphnia pulex 0 0 0 0 0 0 Daphnia retrocurva 0 0 0 0 0 0 Diaphanosoma leuchtenbergianum 0 0 0 0 0 0 Immature Cladocera 0 0 0 0 0 0 CLADOCERA TOTAL 20,513 10,080 0 10,257 0 21,221 COPEPODA Cyclops sp.61,540 211,676 0 10,257 0 42,441 Diaptomus sp.0 0 0 0 0 0 Nauplii 112,823 322,554 9,107 51,283 85,944 180,376 Copepodid 0 0 0 0 0 0 COPEPODA TOTAL 174,363 534,230 9,107 61,540 85,944 222,817 Asplanchna priodonta 0 0 0 0 0 127,324 Brachionus sp.0 0 0 0 0 0 Filinia longiseta 0 20,160 0 0 0 0 Lecane sp.0 20,160 0 30,770 9,549 21,221 Keratella cochlearis 71,797 50,399 1,020,006 1,384,648 6,035,155 1,379,343 Keratella quadrata 0 0 0 0 0 0 Kellicottia sp.0 0 0 0 0 0 Polyarthra vulgaris 10,257 10,080 0 0 0 0 ROTIFERA Trichocerca cylindrica 0 10,080 0 0 38,197 0 Trichocerca multicrinis 0 0 0 0 19,099 0 ROTIFERA TOTAL 82,053 110,878 1,020,006 1,415,418 6,102,001 1,527,887 TOTALS 276,930 655,188 1,029,114 1,487,215 6,187,944 1,771,925 Appendix F BMP Cost Estimates P: \ 2 3 \ 2 7 \ 6 3 4 \ I n d i a n h e a d _ A r r o w h e a d _ U A A \ D a t a \ C o s t _ E s t im a t e s \ A H _ I H _ C o s t _ E s t i m a t e . x l s : A p p e n d i x F 7/17/2006 9:30 AM Po n d C o s t * E s t i m a t i o n C h a r t y = 1 0 6 9 3 0 x 0. 5 5 7 7 R 2 = 0 . 9 9 8 $- $1 0 0 , 0 0 0 $2 0 0 , 0 0 0 $3 0 0 , 0 0 0 $4 0 0 , 0 0 0 $5 0 0 , 0 0 0 $6 0 0 , 0 0 0 0. 0 2 . 0 4 . 0 6 . 0 8 . 0 1 0 . 0 1 2 . 0 1 4 . 0 1 6 . 0 Po n d E x c a v a t i o n V o l u m e ( a c - f t ) P o n d C o s t ( $ ) *P o n d C o s t a r e b a s e d o n A c t u a l 2 0 0 5 P r o j e c t B i d T a b s p l u s a n a d d i t i o n a l 3 0 % f o r E n g i n e e r i n g , D e s i g n , C on s t r u c t i o n Ob s e r v a t i o n & A d m i n a n d 1 5 % C o n t i n g e n c i e s . T h i s c h ar t d o e s E X C L U D E w e t l a n d r e s t o r a t i o n / m i t i g a t i o n c o s ts NU R P P o n d A H _ 1 a = 1 . 0 a c - f t Co s t = $ 1 0 6 , 9 3 0 Item Unit Estimated Quantity Unit Price Extention Mobilization (5%)L.S. 1 $275 $275 Mechanical Harvesting (50% of littoral area)Ac.11 $500 $5,500 $5,775 $866.25 $6,641 Item Unit Estimated Quantity Unit Price Extention Mobilization (5%)L.S. 1 $41 $41 Pumping (13 cfs pump)day 3.7 815$ $3,034 $3,075 $923 $461 $4,459 Item Unit Estimated Quantity Unit Price Extention Herbicide Application (15% of littoral area)Ac.3.3 330.00$ $1,089 $1,089 $163 $1,252 Item Unit Estimated Quantity Unit Price Extention Herbicide Application (50% of littoral area)Ac.11 330.00$ $3,630 $3,630 $545 $4,175 Item Unit Estimated Quantity Unit Price Extention Copper Sulfate Application (100% of lake)Ac.22 20.00$ $440 $440 $66 $506 Item Unit Estimated Quantity Unit Price Extention Copper Sulfate Application (100% of lake)Ac.44 20.00$ $880 $880 $132 $1,012 Subtotal Contingencies (15%) Total Preliminary Cost Estimate -- Drawdown of Arrowhead Lake Contingencies (15%) Total Preliminary Cost Estimate -- In-Lake Cooper Sulfate Application to Indianhead Lake (Two Applications) Preliminary Cost Estimate -- Mechanical Harvesting of Curlyleaf Pondweed in Arrowhead Lake Subtotal Contingencies (15%) Total Total Contingencies (15%) Subtotal Engineering, Design, Administration, & Contruction Observation (30%) Total Contingencies (15%) Subtotal Preliminary Cost Estimate -- In-Lake Herbicide Application to Arrowhead Lake Subtotal Contingencies (15%) Total Preliminary Cost Estimate -- In-Lake Cooper Sulfate Application to Indianhead Lake (Single Application) Preliminary Cost Estimate -- In-Lake Herbicide Application to Arrowhead Lake Subtotal P:\23\27\634\Indianhead_Arrowhead_UAA\Data\Cost_Estimates\AH_IH_Cost_Estimate.xls