HomeMy WebLinkAboutFinal Report_Internal Loading in the Swimming Pool and Point of France Ponds
Project Report No. 587
Assessment of Internal Phosphorus Loading in Swimming Pool Pond and Point of France Pond, City of Edina Final Report
By
Poornima Natarajan John S. Gulliver St. Anthony Falls Laboratory University of Minnesota 2 Third Avenue SE Minneapolis, MN 55455 Prepared for: City of Edina 7450 Metro Blvd. Edina, MN 55439
March 2019 Minneapolis, Minnesota
i
Acknowledgements
This project was a contract between the City of Edina and the University of Minnesota St.
Anthony Falls Laboratory (SAFL). Support from the City of Edina including Ross Bintner and
Jessica Vanderwerff Wilson, and the Nine Mile Creek Watershed District is greatly
appreciated. The assistance from Peter Corkery, Peter Olson, Vinicius Taguchi and Robert
Gabrielson with field sampling and laboratory analysis at SAFL is greatly appreciated.
ii
Table of Contents
LIST OF FIGURES .................................................................................................................... III
LIST OF TABLES ...................................................................................................................... IV
1. Introduction ...............................................................................................................................5
2. Methods ......................................................................................................................................5
2a. Site description .............................................................................................................. 5
2b. Laboratory phosphorus (P) release study ...................................................................... 6
2c. In-situ water quality sampling ....................................................................................... 8
3. Results .........................................................................................................................................9
3a. Oxic and anoxic phosphorus release rates ..................................................................... 9
3b. Sediment phosphorus fractions ................................................................................... 11
3c. In situ water quality ..................................................................................................... 13
4. Summary and Recommendations ..........................................................................................17
References ........................................................................................................................................19
Appendix A ......................................................................................................................................20
iii
List of Figures
Figure 1. Locations of the Swimming Pool Pond and Point of France Pond in the City of
Edina, Hennepin County, MN. (source: <www.maps.google.com>) .......................................... 6
Figure 2. Sediment core collection from the (a) Swimming Pool Pond in February 2018, and
(b) Point of France Pond in July 2018. ........................................................................................ 7
Figure 3. Locations of water sample collection and DO, temperature and conductivity profile
monitoring (red circles) in the (a) Swimming Pool Pond and (b) Point of France Pond. ............ 9
Figure 4. Phosphorus release from the (a) Swimming Pool Pond and (b) Point of France Pond
sediment cores under oxic (air bubbling), air off, and anoxic (N2 bubbling) phases at 20 °C. . 10
Figure 5. Average water column dissolved oxygen (DO) concentrations after air supply was
switched off in the sediment cores from the (a) Swimming Pool Pond and (b) Point of France
Pond. .......................................................................................................................................... 10
Figure 6. Phosphorus fractions in the upper 10 cm of sediments in the (a) Swimming Pool
Pond and (b) Point of France Pond sediment cores. Average concentrations in five sediment
cores are plotted. ........................................................................................................................ 12
Figure 7. Sediment phosphorus fractions in the upper 4 cm of sediment cores collected from
the Swimming Pool Pond and Point of France Pond along with other other stormwater ponds in
the Twin Cities Metro area. ....................................................................................................... 13
Figure 8. In situ phosphorus water quality from May to September 2018 in the (a) Swimming
Pool Pond and (b) Point of France Pond. Average phosphorus concentrations in the epilimnion
water samples collected from five locations in the pond are shown. ......................................... 14
Figure 9. Median epilimnion grab sample values in the Swimming Pool Pond and Point of
France Pond plotted along with stormwater ponds monitored by Taguchi et al. (2018b)
(colored circles) in the exceedance probability distribution of total phosphorus concentrations
in the RPBCWD ponds. ............................................................................................................. 15
Figure 10. Time series contour plots of temperature, specific conductivity (SC), and dissolved
oxygen (DO) concentrations in the (a) Swimming Pool Pond and (b) Point of France Pond
from May to September 2018. ................................................................................................... 16
iv
List of Tables
Table 1. Comparison of internal phosphorus release from sediments of the Swimming Pool
Pond and Point of France Pond with other stormwater ponds in the Twin Cities Metro area
(data fromTaguchi et al. 2018b)................................................................................................. 11
Table A- 1. Phosphorus water quality data for the Swimming Pool Pond from May to
September 2018. ........................................................................................................................ 20
Table A- 2. Phosphorus water quality data for the Point of France Pond from May to
September 2018. ........................................................................................................................ 21
Table A- 3. Dissolved oxygen (DO), temperature (T), and specific conductivity (SC) data for
the Swimming Pool Pond from May to September 2018. ......................................................... 22
Table A- 4. Dissolved oxygen (DO), temperature (T), and specific conductivity (SC) data for
the Point of France Pond from May to September 2018. .......................................................... 25
5
1. Introduction
Stormwater ponds are widely implemented stormwater control measures (SCMs) for runoff
quantity and quality control in urban areas. They are primarily used to remove solids and
associated pollutants such as phosphorus from runoff. There is increasing evidence, however,
that some ponds are no longer retaining phosphorus, and have become potential source of
phosphorus (Song et al. 2015). In the Twin Cities area, a water quality survey conducted in 98
stormwater ponds in the Riley Purgatory Bluff Creek Watershed District (RPBCWD) showed
<0.010 mg/L to 8.1 mg/L total phosphorus in the ponds (Forster et al. 2012; RPBCWD 2014).
Further examination of the data showed that 39% of the 98 ponds contained median TP greater
than 0.38 mg/L, the 95% confidence interval (CI) of expected TP in the Twin Cities Metro Area
(Janke et al. 2017; Taguchi et al. 2018b). The high phosphorus level in the ponds above typical
runoff concentration was hypothesized to be due to internal phosphorus release from the
sediments. Laboratory sediment cores and field-scale monitoring of phosphorus mass inputs and
outputs in five ponds provided evidences of internal loading in those ponds (Olsen 2017;
Taguchi et al. 2018b). Since ponds are part of the watershed network that delivers runoff with
phosphorus to lakes and streams, high phosphorus load and algae in ponds present increased
risks of harmful algal bloom occurrences and water quality degradation in the receiving
waterbodies. Therefore, there is a need to assess stormwater ponds so that management strategies
to control phosphorus pollution from ponds can be developed.
This project was originally proposed as a two-part study to assess and treat internal phosphorus
loading in two stormwater ponds in the City of Edina, the Swimming Pool Pond and the Point of
France Pond. The objective of the first part of the study was to investigate internal phosphorus
release from the pond sediments by measuring phosphorus release from pond sediment cores
incubated in the laboratory and monitoring the in situ water quality. If internal loading was found
to be substantial, the objective of the second part of the study was to chemically-inactivate the
sediment phosphorus by treatment. This report presents results of the first part of the study, i.e.,
internal phosphorus loading assessment in the two ponds, and provides recommendations for
pond phosphorus treatment.
2. Methods
2a. Site description
The Swimming Pool Pond (area = 0.0125 km2; depth = 0.305 – 2.13 m) and the Point of France
Pond (area = 0.0257 km2; depth = 0.305 – 2.44 m) are located south of Hwy 62 in the City of
Edina (Figure 1). The ponds are located in a heavily-urbanized area, consisting of commercial
and high-density residential land use, in the north Lake Cornelia watershed (part of Lower
Minnesota River watershed), in the Nine Mile Creek Watershed District. Outflows from the
Point of France Pond are routed to the Swimming Pool Pond, which in turn discharges into north
6
Lake Cornelia, a 303(d) list impaired lake due to eutrophic conditions. Toxic algae were reported
in the lake in summer 2016 and 2017.
Figure 1. Locations of the Swimming Pool Pond and Point of France Pond in the City of Edina,
Hennepin County, MN. (source: <www.maps.google.com>)
2b. Laboratory phosphorus (P) release study
i.Pond sediment coring
Sediment cores were collected from the Swimming Pool Pond in February 2018. Six intact cores,
containing approximately 0.2 m sediment and 0.8 m overlying pond water, were collected by
driving a piston corer through holes drilled in ice (Figure 2a). Five sediment cores from the Point
of France Pond were collected from a canoe in July 2018 (Figure 2b). The P release study on the
Point of France Pond sediments was conducted based on the Swimming Pool Pond study results,
hence the sediment coring was performed in the later part of summer.
7
Figure 2. Sediment core collection from the (a) Swimming Pool Pond in February 2018, and (b)
Point of France Pond in July 2018.
ii. Sediment-water columns
The cores collected from the ponds were incubated at 20 °C at the St. Anthony Falls Laboratory
(SAFL). The water column above the sediment was drained, filtered to remove particulates and
refilled into the columns. In the first phase of the P release experiments, the water column was
mixed by air bubbling to determine if oxic P release occurred from the sediments. Then, air
bubbling was switched off, and the dissolved oxygen (DO) concentration in the water 8 cm
above the sediment, and the concomitant P release were monitored. In the final phase, P release
was measured under an anoxic water column created by bubbling ultrapure nitrogen gas (DO < 1
mg/L). When the water column was kept mixed with air or nitrogen gas, water samples for P
measurements were drawn from the center of the water columns, on an approximately weekly
basis. In the unmixed phase (air off), one water sample was taken ~8 cm above the sediment and
a second sample at the center of the total water column height. Two sampling points were
necessary because a concentration gradient can develop during unmixed state, and the two
measurements were used to estimate the average P concentration in the entire water column. The
frequency of water sampling was adjusted from 1 day to 7 days during the unmixed phase to
observe the rate of change of P mass in the water column. The increase in ortho-phosphorus
(ortho-P) mass (where, mass = concentration × water volume) during a given incubation period
was used to determine the P release rate (mg/m2/day, i.e., P mass per sediment surface area of the
core per time). P flux during the unmixed phase was determined using data from the first 15
days. The mean P release and 67% confidence interval (CI) of the mean was calculated for each
(a) (b)
8
phase. As a measure of the sediment oxygen demand (SOD), the Michaelis-Menten kinetic
model was fit to the DO levels in the unmixed water column (air off phase) (Olsen 2017): 𝑆𝑆=𝑆𝑆𝑚𝑚𝑚𝑚𝑚𝑚[𝐶𝐶𝑂𝑂2]𝐾𝐾𝑀𝑀+[𝐶𝐶𝑂𝑂2]
where S is the substrate consumption rate, Smax is the maximum dissolved oxygen consumption
rate, CO2 is the substrate (oxygen) concentration, and KM is the half-consumption concentration.
A constant KM of 1.4 mg/L was used for all cores. The assumption is that all DO reduction
comes from the microbial oxygen demand of the sediments, so KM represents the surface of the
sediments.
iii.Sediment phosphorus fractionation
At the end of core incubation, the top 10 cm of the sediments was extruded from the columns
and analyzed for P species using the sequential chemical extraction procedure (Engstrom 2010).
The amounts of loosely-bound P, iron-bound P, aluminum-bound P, mineral-bound P, labile
organic P and residual organic P in the sediments were determined at 1-cm interval for the 0 – 5
cm depth and at 2- or 3-cm interval for the 5 – 10 cm depth. The P forms were used to
understand the potential for P release under changing environmental conditions (loosely-bound P
is dissolved or easily disassociated from a solid; iron-bound P is attached to an iron compound in
the sediments; aluminum-bound P is attached to an aluminum compound in the sediments;
mineral-bound P is attached to other minerals (typically calcium) in the sediments; labile organic
P is the organic P that is available for microbial degradation, and residual organic P is not
available for microbial degradation). Water content and organic matter content (loss on ignition
at 550 °C) were also determined in the sediment samples.
2c. In-situ water quality sampling
Water quality of the ponds was sampled on a bi-weekly basis from May through September
2018. Surface grab water samples were collected from 5 to 6 locations (Figure 3) using a Van
Dorn sampler, and analyzed for total phosphorus, dissolved phosphorus, and soluble reactive
phosphorus concentrations (Standard Methods 4500-P, APHA AWWA, WPCF 1995) using a
spectrophotometer (detection limit = 10 µg/L P). If stratification was detected, an additional
water sample was collected below the stratification depth. The surface to bottom profiles of DO,
temperature and conductivity were also taken at 25-cm intervals using a Hach WQ40D handheld
meter with DO and conductivity sensors.
9
Figure 3. Locations of water sample collection and DO, temperature and conductivity profile
monitoring (red circles) in the (a) Swimming Pool Pond and (b) Point of France Pond.
3.Results
3a. Oxic and anoxic phosphorus release rates
Under aerated (oxic) conditions, the Swimming Pool Pond sediment cores maintained low ortho-
P levels in the water columns (Figure 4a). The average P release rate of -0.14 ± 0.08 (67% CI)
mg/m2/day suggested a small decrease in the water column ortho-P concentration occurred under
oxic conditions. Once the air supply was switched off, the water column DO levels started
decreasing due to the sediment oxygen demand (Figure 5a). The DO concentrations dropped
below 1 mg/L after ~5 days in most cores. Smax, the maximum oxygen consumption by the
biologically active sediments, ranged between 1.76 and 4.2 g/m2/day in the six cores. As DO was
consumed, the pond sediments started releasing P resulting in increased ortho-P concentrations
in the water columns. However, measurable P increase occurred in only three out of the six
cores. The average P release from the six cores was thus relatively small at 1.16 ± 0.45
mg/m2/day during the first 15 days of the 22-day unmixed phase. In the next phase with an
anoxic mixed water column, ortho-P release continued to occur at 1.09 ± 0.36 (67% CI)
mg/m2/day. The sediment cores that appeared to be sandy (collected near the pond inlets) showed
minimal P release under the two anoxic phases.
Similar results were obtained for the Point of France Pond sediment cores (Figure 4b). A very
small release of sediment P occurred under oxic conditions (0.83 ± 0.23 mg/m2/day), which can
be attributed to the mineralization of labile organic phosphorus in the sediments (Jensen and
Andersen 1992). After the air supply was turned off, it took almost 7 days for the DO levels to
reach below 1 mg/L, and the Smax ranged between 2.0 and 4.9 g/m2/day in the five cores (Figure
5b). Once again, responses to low DO conditions were highly variable among the five cores,
yielding an average P release rate of 4.09 ± 3.21 mg/m2/day during the air off phase (note the
67% CI). This average P release under anoxic conditions is relatively high. In contrast, the
Swimming Pool Pond Point of France Pond (a) (b)
10
following phase with an anoxic mixed water column had an anoxic P release from these
sediments that was relatively low at 0.39 ± 0.17 mg/m2/day.
Figure 4. Phosphorus (ortho-P) release from the (a) Swimming Pool Pond and (b) Point of
France Pond sediment cores under oxic (air bubbling), air off, and anoxic (N2 bubbling) phases
at 20 °C. Solid lines separate the three phases of the P release study.
Figure 5. Average water column dissolved oxygen (DO) concentrations after air supply was
switched off in the sediment cores from the (a) Swimming Pool Pond and (b) Point of France
Pond. Measurements were taken at 8 cm above the sediment surface. Error bars are 67%
confidence interval (CI) of the mean measurements.
(a) (b)
(a) (b)
11
The P release rates for the two Edina pond sediments were compared to other ponds in the Twin
Cities Metro area (Table 1; Taguchi et al. 2018b). The anoxic P release rates and the DO
depletion rates for the Swimming Pool Pond and Point of France Pond are relatively low when
compared to some of the high P release-ponds. Low sediment microbial activity, which is
supported by the lower sediment oxygen demand and organic matter content, is related to the P
release rate from the sediments. This is because oxygen demand is indicative of opportunistic
aerobic respiration by microbes and organic matter present a source of microbial food (Taguchi
et al. 2018b).
Table 1. Comparison of internal phosphorus release from sediments of the Swimming Pool Pond
and Point of France Pond with other stormwater ponds in the Twin Cities Metro area (data from
Taguchi et al. 2018b).
Pond Oxic Flux Rate (mg/m2/day)
Anoxic Flux Rate (mg/m2/day)
Smax (g/m2/day) Organic matter content (%)*
A -1.27 ± 0.71 7.51 ± 2.93 4.21 ± 0.47 30%
B -0.14 ± 0.76 5.62 ± 1.80 4.23 ± 0.95 86%
C -4.38 ± 2.89 1.09 ± 0.26 1.94 ± 0.19 15%
D -5.80 ± 1.94 2.27 ± 0.49 1.85 ± 0.63 16%
E -19.78 ± 3.37 3.18 ± 2.76 5.19 ± 0.59 27%
Swimming Pool Pond -0.14 ± 0.08 1.16 ± 0.45 3.07 ± 0.48 19%
Point of France Pond 0.83 ± 0.23 4.09 ± 3.21 2.51 ± 0.53 24%
*upper 11 or 10 cm sediments
3b. Sediment phosphorus fractions
The water content in the Swimming Pool Pond sediments ranged from 71 – 91% in the four
cores analyzed, and these cores contained an average of 23% dry weight organic matter content
in the upper 10 cm depth. One core, which was collected near the pond inlet, was predominantly
sandy in appearance and contained 15% moisture content and 2% organic matter content. The
sediment core collected near the inlet in the Point of France contained 40% moisture content and
7% organic matter content. The other sediment core samples contained 66 – 91% water content
and an average of 27% organic matter content.
The sediment P pool in the Swimming Pool Pond and Point of France Pond cores provided an
indication of the relationship between the observed P release in the laboratory cores and the
releasable phosphorus fractions. The average concentrations of the various phosphorus species in
the upper 10 cm sediment depth of the cores from the two ponds is plotted in Figure 6. In the
Swimming Pool Pond, the average total P pool in the top 4 cm of sediments was composed of
<0.05% loosely-bound P, 11% iron-bound P, 14% aluminum-bound P, 28% mineral-bound P,
12
32% labile organic P and 15% residual P. The Point of France Pond sediment’s total P
fractionation consisted of 0.18% loosely-bound P, 9.3% iron-bound P, 22% aluminum-bound P,
29% mineral-bound P, 21% labile organic P and 19% residual P, on average. The cores with
sandier appearance varied from other cores in the P composition; they generally contained a
large fraction of mineral-bound P and were low in organic P (data not shown). Overall, more P
was tied up in the relatively unavailable forms in the sediments (i.e., Al- and mineral-bound)
than the P present in the easily-releasable forms (i.e., loosely-bound and iron-bound). Labile
organic P, that has the potential to become bioavailable after being broken down by
microbacteria, was the more substantial mobile P form in the pond sediments.
Figure 6. Phosphorus fractions in the upper 10 cm of sediments in the (a) Swimming Pool Pond
and (b) Point of France Pond sediment cores. Average concentrations in five sediment cores are plotted. For each depth interval, concentration is plotted at the mid-point of the depth interval
(for example, concentration for 0 – 1 cm depth is plotted at 0.5 cm).
Comparison to other stormwater ponds sampled by Taguchi et al. (2018) provides a perspective
on the mobilization of phosphorus from the pond sediments (Figure 7). The upper 4 cm of
sediments from the Edina ponds contained relatively low amounts of the redox-sensitive forms
of phosphorus, i.e., the loosely-bound and iron-bound fractions. The potentially-releasable labile
organic P in the Edina pond sediments was lower than ponds A and B that exhibited high anoxic
P release rates (Table 1). Phosphorus was mostly associated with aluminum and calcium in the
Edina pond sediments, and this phosphorus is not influenced by changes in oxygen conditions.
(a) (b)
13
The low anoxic P releases measured from the Edina ponds are thus explained by the relatively
low concentrations of redox-P and organic P species.
Figure 7. Sediment phosphorus fractions in the upper 4 cm of sediment cores collected from the
Swimming Pool Pond and Point of France Pond along with other stormwater ponds in the Twin
Cities Metro area (data from Taguchi et al. 2018b) (Error bars are standard deviations). Loosely-bound P is primarily dissolved P in the pore water, labile organic bound P can be converted into
ortho-P over time, mineral-bound is primarily associated with calcium, and residual organic
bound P is considered refractory.
3c. In situ water quality
The water quality data collected in 2018 are provided in Appendix A (Table A- 1 and Table A-
2). The phosphorus concentrations in the pond water were generally in the low to moderate range
during the growing season (Figure 8). In the Swimming Pool Pond, the average concentrations in
the epilimnion grab water samples contained 59 – 167 µg/L total phosphorus, 10 – 44 µg/L
dissolved phosphorus and 1 – 22 µg/L soluble reactive phosphorus. Concentrations in the Point
of France Pond were in a similar range; 69 – 135 µg/L total phosphorus, 10 – 85 µg/L dissolved
phosphorus and 1 – 34 µg/L soluble reactive phosphorus. The May to September average was 94
± 35 (Std. Dev.) µg/L total phosphorus, 32 ± 11 µg/L dissolved phosphorus and 13 ± 6 µg /L
soluble reactive phosphorus in the Swimming Pool Pond. Point of France Pond contained 97 ±
23 µg/L total phosphorus, 36 ± 21 µg/L dissolved phosphorus and 15 ± 10 µg /L soluble reactive
phosphorus during summer.
14
Figure 8. In situ phosphorus water quality from May to September 2018 in the (a) Swimming
Pool Pond and (b) Point of France Pond. Average phosphorus concentrations in the epilimnion
water samples collected from five locations in the pond are shown. Error bars are 67% CI of the
mean measurements. Water samples were collected on a biweekly basis.
The median TP concentrations in the Swimming Pool Pond and Point of France Pond are
compared to five other stormwater ponds intensively monitored by Taguchi et al. (2018b), who
also developed the probability exceedance distribution of TP concentrations in the RPBCWD
ponds (Figure 9). The TP concentrations in the Swimming Pool Pond and Point of France Pond
were much lower than 0.38 mg/L, the upper 95% CI of expected runoff TP in the Twin Cities
(a)
(b)
15
Metro Area (Janke et al. 2017). The TP levels were also much lower than the median
concentrations monitored in other stormwater ponds in the area.
Figure 9. Median epilimnion grab sample values in the Swimming Pool Pond and Point of
France Pond plotted along with stormwater ponds monitored by Taguchi et al. (2018b) (colored
circles) in the exceedance probability distribution of total phosphorus concentrations in the
RPBCWD ponds (figure adapted from Taguchi et al. 2018b). Red line is the upper 95%
confidence interval (CI) of the expected TP in runoff in the Twin Cities Metro area.
The DO, temperature, and conductivity measured in the ponds over the entire summer period are
summarized in Appendix A (Table A- 3 and Table A- 4). The in situ DO concentrations and
water temperature presented evidence of mixed water column conditions in the ponds, which
could be a reason for the low to moderate phosphorus levels in the pond water. The Swimming
Pool Pond was mixed and oxic during most of the summer (Figure 10a). Bottom DO lower than
1 mg/L was detected only during two instances in August 2018 (see 8/8/18 and 8/22/18 data in
Table A- 3), although it is possible that the DO probe was in the sediments at those low depths
and recorded very low DO concentration. In the Point of France Pond, thermal stratification and
low bottom DO were observed intermittently (Figure 10b), although DO less than 1 mg/L was
not recorded anytime (Table A- 4). Nonetheless, strong thermal stratification that could cause the
pond bottom to turn anoxic was not observed in both pond during summer 2018.
16
Figure 10. Time series contour plots of temperature, specific conductivity (SC), and dissolved
oxygen (DO) concentrations in the (a) Swimming Pool Pond and (b) Point of France Pond from
May to September 2018. Vertical lines show times when profiles were taken at the ponds; linear
interpolation is used to fill the time series between pond visits. A 1 mg/L DO threshold is
indicated by black line, which is visible only in the DO plot for the Swimming Pool Pond during
August 2018.
(a)
(b)
17
High conductivity was measured from the beginning of monitoring in May 2018, and was likely
high prior to May sampling. Such high specific conductivity values are attributed to chlorides
contributed by road salt input (Taguchi et al. 2018b). Conductivity gradually decreased from
May through August as chloride was flushed out of the pond, although it took longer for the
chloride levels to drop in the Swimming Pool Pond, which is downstream of the Point of France
Pond. Chemostratification is a phenomenon that has been observed in some ponds that exhibited
strong summertime stratification and low bottom DO (Taguchi et al. 2018b). However, such
stratification due to high chloride concentrations did not appear to be strong and impact DO
levels in the Edina ponds.
The maintenance of primarily oxic and well-mixed water column in situ suggests that conditions
are less favorable for internal P release to occur from the sediments during the warmer months.
Under oxic conditions, the sediments exhibited very low or no release of P (Table 1), which
means P contribution from internal loading can be expected to be negligible in both ponds. In
addition to mixing due to stormwater inflows, it is hypothesized that low sheltering from trees
around the ponds was a factor in aiding wind mixing of the pond water column and thus
preventing a sustained stratification that could have led to anoxia.
4. Summary and Recommendations
a)The Swimming Pool Pond sediments did not release P under oxic conditions. Low P release
occurred under anoxic conditions, at a rate of 1.16 ± 0.45 mg/m2/day.
b) In the Point of France Pond, very low oxic P release was measured (0.83 ± 0.23 mg/m2/day).
Anoxic P release rate was relatively low and highly variable among the sediment cores, at
4.09 ± 3.21 mg/m2/day.
c)The impact of water column dissolved oxygen concentrations on the P release behavior was
variable among the sediment cores, indicating the influence of sediment microbial activity
and sediment characteristics on the potential for sediment P release.
d)Characterization of the sediment P fractions showed majority of P in the redox insensitive
aluminum- and mineral-bound pool, i.e., not releasable under low oxygen conditions. The
readily-mobile form of redox-P and potentially-mobile organic P were present in low (redox-
P)to moderate (labile organic P) concentrations when compared to other stormwater ponds
in the Twin Cities. The sediment P composition supports the low anoxic P release rates
measured in the laboratory cores.
e)In situ monitoring showed low to moderate total phosphorus concentrations in the ponds
during the growing season.
f)Surface to bottom profiles of DO and temperature were indicative of a mixed water column
in the ponds during most of summer 2018, with intermittent stratification that lasted only for
a brief amount of time.
g) High conductivity was measured in the ponds in May 2018, likely due to chlorides from road
salt input. Gradual decrease in conductivity was noticed due to the mixing of pond water and
flushing out of chloride in the pond discharge.
18
h)Together, these data suggest that conditions in the ponds are such that the water columns are
mixed and primarily oxic during warmer months, indicating little to no internal P release and
a minor impact on the pond water column phosphorus concentration.
i) Present conditions in the Swimming Pool Pond and Point of France Pond suggest that the
ponds are providing treatment of phosphorus. Thus, chemical treatment of sediment to reduce
internal phosphorus loading is currently not recommended.
j)Should conditions change to favor the development of anoxia in the pond, the potential for
internal P release from the pond sediments could increase. One scenario would be increase in
sheltering around the ponds that would result in poor mixing and stronger stratification
causing low DO in the bottom of the pond. It is recommended that the sheltering around the
pond be kept minimal to allow wind mixing of the pond.
19
References
APHA, AWWA, WPCF (1995), Standard methods for the examination of water and wastewater, 19th Ed., American Public Health Association (APHA), the American Water Works Association (AWWA),
and the Water Environment Federation (WEF, former Water Pollution Control Federation or WPCF),
Washington, D.C. Engstrom, D. (2010). Sediment phosphorus extraction procedure high sample throughput. Modified by
Robert Dietz and Michelle Natarajan (2015).
Forster, P., Austin, D., Scharf, R., Carroll, J., and Enochs, M. (2012). Rethinking stormwater pond nutrient removal. Oral presentation at the 2012 Minnesota Water Resources Conference. St. Paul,
MN.
Janke, B. D., Finlay, J. C., and Hobbie, S. E. (2017). “Trees and streets as drivers of urban stormwater nutrient pollution.” Environmental Science & Technology, 51(17), 9569-9579.
Jensen, H.S., and Andersen, F.O. (1992). Importance of Temperature, Nitrate, and pH for Phosphate
Release from Aerobic Sediments of Four Shallow Eutrophic Lakes. Limnology and Oceanography, 37(3), 577-589.
Olsen, T. (2017). Phosphorus dynamics in stormwater ponds. Master’s Thesis, University of Minnesota,
Minneapolis, MN. Riley Purgatory Bluff Creek Watershed District (2014). Stormwater pond project: 2013 Report, 1-54.
<http://rpbcwd.org/news/2013-stormwater-pond-report/> (accessed January 2016). Song, K., Xenopoulos, M. A., Marsalek, J., and Frost, P. C. (2015). “The fingerprints of urban nutrients: dynamics of phosphorus speciation in water flowing through developed landscapes.”
Biogeochemistry, 125, 1-10. Taguchi, V., Olsen, T., Natarajan, P., Janke, B., Finlay, J., Stefan, H. G., Gulliver, J.S., and Bleser, C.S.
(2018a.) Urban stormwater ponds can be a source of phosphorus. UPDATES Newsletter, 13(2), St.
Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN. Taguchi, V., Olsen, T., Janke, B., Stefan, H. G., Finlay, J., and Gulliver, J.S. ( 2018b). Phosphorus release
from stormwater ponds, Chapter in Stormwater Research Priorities and Pond Maintenance, Final
Report, Minnesota Pollution Control Agency, St. Paul, MN.
20
Appendix A
Table A- 1. Phosphorus water quality data for the Swimming Pool Pond from May to September 2018.
5/16/18 5/16/18 5/16/18 5/30/18 5/30/18 5/30/18 6/13/18 6/13/18 6/13/18 6/27/18 6/27/18 6/27/18 7/11/18 7/11/18 7/11/18
TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L)
Site 1 Epi 57 42 13 74 45 19 58 29 8 131 58 16 115 37 20
Site 1 Hypo 71 34 19
Site 2 Epi 61 39 17 83 42 21 68 36 14 126 53 16 110 34 18
Site 2 Hypo 90 32 21 134 51 6 120 45 18
Site 3 Epi 84 53 13 89 45 19 66 53 23 99 25 6 100 42 22
Site 3 Hypo 76 6 13 67 22 15
Site 4 Epi 117 17 27 94 40 19 53 38 16 132 38 12 127 52 20
Site 4 Hypo 85 44 23 117 35 10
Site 5 Epi 57 20 13 74 32 21 71 48 10 107 40 8 130 50 22
Site 5 Hypo 126 49 17
Site 6 Epi 47 49 17 91 29 15 71 33 12 109 40 6 96 47 30
Site 6 Hypo 76 29 21
7/26/18 7/26/18 7/26/18 8/8/18 8/8/18 8/8/18 8/22/18 8/22/18 8/22/18 9/11/18 9/11/18 9/11/18 9/26/18 9/26/18 9/26/18
TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L) TP (µg/L) TDP (µg/L) SRP (µg/L)
Site 1 Epi 108 40 14 86 27 13
Site 1 Hypo 102 24 14
Site 2 Epi 110 45 10 76 27 14 169 32 6 64 38 1 70 10 10
Site 2 Hypo
Site 3 Epi 158 53 18 76 39 11 181 32 3 84 12 1 54 10 9
Site 3 Hypo
Site 4 Epi 128 43 14 71 21 13 158 22 5 83 9 1 54 10 10
Site 4 Hypo 89 27 13
Site 5 Epi 136 33 18 72 29 13 150 27 6 42 61 1 63 10 9
Site 5 Hypo 101 31 14 152 20 1
Site 6 Epi 116 30 12 71 24 13 180 17 10 55 6 1 56 10 9
21
Table A- 2. Phosphorus water quality data for the Point of France Pond from May to September 2018.
5/16/18 5/16/18 5/16/18 5/30/18 5/30/18 5/30/18 6/13/18 6/13/18 6/13/18 6/27/18 6/27/18 6/27/18 7/11/18 7/11/18 7/11/18
TP TDP SRP TP TDP SRP TP TDP SRP TP TDP SRP TP TDP SRP
Site 1 Epi 83 33 25 106 27 27 120 83 35 91 10 10 118 50 10
Site 1 Hypo 207 22 27 118 27 23
Site 2 Epi 109 32 23 115 118 35 73 40 10 125 37 10
Site 2 Hypo 86 56 12 133 34 14
Site 3 Epi 100 63 21 136 34 25 128 76 37 78 38 12 116 40 12
Site 3 Hypo 67 14 19 95 25 25 133 73 37 137 32 12
Site 4 Epi 91 25 25 115 78 37 81 35 14 114 45 14
Site 4 Hypo 138 78 35 167 37 18
Site 5 Epi 86 53 21 142 44 30 120 71 35 94 35 16 117 26 10
Site 5 Hypo 96 33 17 84 59 28 135 73 31 101 33 18
Site 6 Epi 133 44 28 116 83 29 115 30 14 105 19 10
Site 6 Hypo 91 47 27 133 83 38 84 45 21 127 29 12
7/26/18 7/26/18 7/26/18 8/8/18 8/8/18 8/8/18 8/22/18 8/22/18 8/22/18 9/11/18 9/11/18 9/11/18 9/26/18 9/26/18 9/26/18
TP TDP SRP TP TDP SRP TP TDP SRP TP TDP SRP TP TDP SRP
Site 1 Epi 133 43 8 73 29 13 99 17 1 68 6 3 78 38 12
Site 1 Hypo 72 24 18 87 25 1
Site 2 Epi 143 33 14 76 29 14 82 25 3 61 1 1 80 16 12
Site 2 Hypo 64 26 16
Site 3 Epi 132 48 16 61 36 14 70 34 1 120 22 1 109 12 14
Site 3 Hypo
Site 4 Epi 145 55 8 64 24 14 66 18 1 58 9 1 92 10 10
Site 4 Hypo 81 24 14
Site 5 Epi 132 38 18 71 27 13
Site 5 Hypo
Site 6 Epi 128 28 6 67 26 13 80 27 1 48 12 1 75 9 12
Site 6 Hypo
22
Table A- 3. Dissolved oxygen (DO), temperature (T), and specific conductivity (SC) data for the
Swimming Pool Pond from May to September 2018. H is the depth of sampling in the water
column.
SITE 1 SITE 2 SITE 3
Sampling
date
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
5/16/18
0.00 9.6 18.8 2972 0.00 10.4 18.7 2969 0.00 10.1 19.1 2955
0.25 12.7 18.1 2992 0.25 10.4 18.9 2964 0.25 10.2 19.0 2953
0.50 15.7 17.0 3263 0.50 10.3 19.0 2959 0.50 10.4 19.0 2963
0.75 0.75 10.5 19.0 2961 0.75 15.1 18.5 2952
1.00 1.00 18.3 18.2 3379
1.25
5/30/18
0.00 4.4 23.9 2430 0.00 4.2 24.2 2350 0.00 5.3 24.2 2210
0.25 3.9 24.3 2430 0.25 4.0 24.1 2153 0.25 5.1 24.3 2199
0.50 2.8 23.8 2040 0.50 4.1 24.3 2160 0.50 5.1 24.3 2200
0.60 1.4 23.8 2067 0.75 3.5 24.2 2290 0.75 5.0 24.3 2200
1.00 4.3 24.2 2037 1.00 2.9 24.3 2220
1.05 2.57 24.4 2220
6/13/18
0.00 6.4 21.5 2200 0.00 6.8 21.8 2230 0.00 8.1 21.7 2230
0.25 6.7 21.4 2163 0.25 6.8 21.8 2230 0.25 7.3 21.7 2220
0.40 6.6 21.3 2154 0.50 7.4 21.7 2210 0.50 6.9 21.6 2220
0.75 5.6 21.7 2230 0.75 6.6 21.6 2220
1.00 5.5 21.5 2220
6/27/18
0.00 3.7 22.8 949 0.00 3.3 23.2 1044 0.00 4.3 23.2 1001
0.25 3.4 22.9 939 0.25 3.4 23.2 1058 0.25 4.3 23.2 980
0.50 2.8 22.9 929 0.50 3.5 23.2 1061 0.50 4.4 23.1 977
0.60 1.7 22.7 914 0.75 1.7 22.9 975 0.75 4.4 23.2 972
1.00 1.1 22.9 987 1.00 3.2 23.0 975
1.10 2.8 23.0 833
7/11/18
0.00 5.3 25.8 726 0.00 5.4 26.1 723 0.00 5.7 26.2 730
0.25 5.0 26.1 724 0.25 5.3 26.3 722 0.25 5.7 26.3 729
0.50 3.6 25.8 719 0.50 5.0 26.2 722 0.50 5.6 26.3 727
0.60 3.1 25.9 725 0.75 4.7 26.1 719 0.75 5.5 26.3 721
1.00 1.8 25.9 657 1.00 4.8 26.2 724
7/26/18
0.00 5.5 22.5 554 0.00 5.5 23.0 547 0.00 6.1 23.3 557
0.25 5.3 22.9 550 0.25 5.5 23.2 546 0.25 6.0 23.6 556
0.50 5.2 22.9 549 0.50 5.6 23.1 545 0.50 5.9 23.5 555
0.75 5.4 23.2 545 0.75 5.9 23.5 555
1.00 5.8 23.5 553
8/8/18
0.00 8.5 25.1 368 0.00 11.7 25.6 384 0.00 12.2 25.8 385
0.25 6.1 24.1 359 0.25 11.6 25.5 384 0.25 12.3 25.4 382
0.47 6.1 23.9 358 0.50 8.9 24.5 382 0.50 9.6 24.6 382
0.75 10.6 24.9 382 0.75 7.2 24.4 386
1.00 7.9 24.2 384 1.00 5.2 24.3 393
8/22/18 0.00 9.5 22.8 683 0.00 9.4 23.1 687
0.25 9.5 23.0 683 0.25 7.8 22.7 598
23
SITE 1 SITE 2 SITE 3
Sampling
date
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
0.50 8.9 22.7 607 0.50 5.3 22.4 542
0.75 6.0 22.1 520 0.75 5.0 22.3 531
1.00 5.7 22.1 516
9/11/18
0.00 10.6 21.1 331 0.00 10.7 21.1 331
0.25 10.5 21.1 331 0.25 10.7 21.0 331
0.50 10.5 21.1 331 0.50 10.4 21.0 331
0.75 10.5 21.1 330 0.75 10.3 20.9 331
0.95 10.6 20.9 333
9/26/18
0.00 8.8 15.7 147 0.00 8.9 15.2 149
0.25 8.8 15.6 147 0.25 8.8 15.4 148
0.50 8.8 15.5 147 0.50 8.7 15.4 148
0.75 8.5 15.3 148
1.00 8.5 15.3 148
Table A- 4. Continued: Data for sampling sites 4, 5 and 6 in the Swimming Pool Pond.
SITE 4 SITE 5 SITE 6
Sampling
date
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
5/16/18
0.00 10.3 19.1 2960 0.00 10.8 19.0 2973 0.00 9.7 19.6 2984
0.25 10.5 19.0 2957 0.25 10.8 19.0 3017 0.25 10.2 19.4 2964
0.50 9.5 19.0 2971 0.50 11.8 18.8 3053 0.50 11.8 19.1 3070
0.75 12.8 18.6 3116 0.75 15.3 18.9 3148 0.75 14.2 18.9 3161
1.00 14.8 17.8 3250 1.00 16.9 18.0 3267
1.25 18.3 17.1 4075 1.25 17.6 17.3 3507
5/30/18
0.00 4.4 24.4 2340 0.00 5.1 24.6 2420 0.00 4.3 25.0 2670
0.25 4.5 24.5 2310 0.25 5.0 24.8 2400 0.25 2.9 25.2 2680
0.50 4.7 24.5 2300 0.50 5.0 24.7 2410 0.50 3.0 25.1 2840
0.75 4.5 24.5 2300 0.75 4.3 24.7 2700 0.75 1.5 25.1 2830
1.00 3.2 24.4 2350 1.00 3.9 25.1 2770 0.85 0.53 25.1 2840
1.10 2.9 24.2 2350 1.25 1.3 24.9 2860
6/13/18
0.00 7.6 22.0 2230 0.00 6.9 22.3 2230 0.00 9.5 22.4 2220
0.25 7.4 22.1 2230 0.25 8.2 21.8 2220 0.25 8.9 22.0 2220
0.50 7.4 22.1 2230 0.50 7.9 21.8 2230 0.50 6.5 21.7 2220
0.75 8.0 22.0 2230 0.75 7.1 21.7 2240 0.73 4.3 21.5 2230
1.00 5.7 21.6 2230 1.00 7.0 21.6 2240
1.25 6.0 21.7 2240
6/27/18
0.00 4.3 23.3 953 0.00 5.9 23.2 960 0.00 5.5 23.6 1115
0.25 4.2 23.2 948 0.25 5.0 23.2 960 0.25 4.3 23.5 1154
0.50 4.0 23.1 950 0.50 4.3 23.1 956 0.50 2.2 23.4 1251
0.75 4.1 23.1 958 0.75 4.0 23.1 968 0.75 1.9 23.2 1250
1.00 3.8 23.0 967 1.00 2.8 23.2 954
1.25 1.0 23.0 932 1.25 1.1 23.3 1230
24
SITE 4 SITE 5 SITE 6
Sampling
date
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
H
(m)
DO
(mg/L)
T
°C
SC
(µs/cm)
1.35 1.5 22.9 931 1.35 0.9 23.3 1100
7/11/18
0.00 6.51 26.4 726 0.00 5.3 26.5 726 0.00 5.84 26.4 725
0.25 6.15 26.4 724 0.25 5.6 26.5 727 0.25 5.21 26.6 723
0.50 4.94 26.4 730 0.50 5.6 26.6 725 0.50 3.67 26.5 723
0.75 3.87 26.4 734 0.75 4.7 26.5 725 0.75 4.76 26.6 724
1.00 2.86 26.3 733 1.00 3.1 26.5 727
1.25 1.95 26.1 733 1.13 2.6 26.5 729
7/26/18
0.00 6.4 23.3 552 0.00 5.8 23.4 560 0.00 5.6 23.5 553
0.25 6.3 23.4 552 0.25 5.7 23.5 560 0.25 5.4 23.5 554
0.50 6.3 23.4 552 0.50 5.7 23.6 569 0.50 5.5 23.5 552
0.75 6.3 23.4 552 0.75 5.6 23.6 569 0.75 5.4 23.5 553
1.00 6.3 23.4 552 1.00 5.7 23.6 559
1.25 5.7 23.4 552 1.15 5.5 23.6 559
8/8/18
0.00 11.8 27.2 385 0.00 13.2 26.2 384 0.00 12.7 26.7 393
0.25 12.4 25.3 375 0.25 13.4 25.3 384 0.25 11.7 25.4 392
0.50 11.2 24.9 375 0.50 11.3 24.8 388 0.50 10.5 25.0 391
0.75 5.9 24.4 369 0.75 9.3 24.5 396 0.75 7.8 24.6 395
1.00 4.1 24.2 371 1.00 4.7 24.3 402
1.25 0.2 23.8 462 1.25 0.5 24.0 426
8/22/18
0.00 9.7 22.8 628 0.00 8.3 23.1 677 0.00 9.8 23.2 701
0.25 9.1 22.9 621 0.25 7.6 22.8 665 0.25 6.7 22.8 625
0.50 8.9 22.7 550 0.50 6.2 22.6 637 0.50 4.2 22.7 628
0.75 5.8 22.4 554 0.75 5.6 22.4 621
1.00 5.0 22.0 497 1.00 4.9 22.3 608
1.20 0.2 22.3 639
9/11/18
0.00 10.8 21.1 331 0.00 9.9 21.1 332 0.00 9.8 21.4 332
0.25 10.8 21.0 331 0.25 10.2 21.1 331 0.25 9.6 21.2 333
0.50 10.8 21.0 331 0.50 10.3 21.0 331 0.50 9.4 21.2 332
0.75 10.5 20.9 331 0.75 8.7 21.0 332
1.00 9.3 20.6 333 1.00 7.9 20.8 334
1.20 6.6 20.4 336 1.20 6.9 20.6 337
9/26/18
0.00 8.8 15.4 147 0.00 8.8 15.3 148 0.00 9.0 15.2 149
0.25 8.7 15.5 147 0.25 8.8 15.4 148 0.25 9.0 15.4 148
0.50 8.7 15.5 147 0.50 8.8 15.4 148 0.50 8.9 15.4 148
0.75 8.5 15.5 147 0.75 8.3 15.4 148 0.75 8.9 15.4 149
1.00 8.3 15.4 147 1.00 8.2 15.4 148
1.25 8.1 15.4 148 1.25 8.2 15.5 148
25
Table A- 5. Dissolved oxygen (DO), temperature (T), and specific conductivity (SC) data for the
Point of France Pond from May to September 2018. H is the depth of sampling in the water
column.
SITE 1 SITE 2 SITE 3
Sampling date H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm)
5/16/18
0.00 16.2 19.9 2826 0.00 16.1 19.7 2827
0.25 15.7 16.7 3250 0.25 17.1 17.8 3350
0.50 14.9 15.1 3501 0.50 14.8 14.5 3661
0.75 13.8 13.7 4037 0.75 12.1 13.5 3921
1.00 13.2 13.1 4875 1.00 15.8 13.5 5137
1.25 0.85 13.1 >10,000 1.25 0.93 13.1 10,000
1.50 0.19 11.4 >10,000
1.75 0.11 9.7 >10,000
1.95 0.08 8.4 >10,000
5/30/18
0.00 5.0 22.8 1535 0.00 5.01 22.8 1640 0.00 5.17 23.0 1591
0.25 4.9 22.9 1587 0.25 4.78 23.0 1659 0.25 5.1 23.0 1599
0.50 4.1 22.8 1554 0.50 4.36 23.0 1655 0.50 4.9 23.0 1625
0.75 3.0 22.8 1587 0.75 4.46 23.2 1800 0.75 4.2 23.3 1930
1.00 1.6 22.5 2000 1.00 3.16 23.0 1860 1.00 3.65 23.4 2057
1.25 0.97 22.3 2000
1.50 0.51 21.9 2520
1.75 0.06 21.4 3330
2.00 0.02 20.3 4300
6/13/18
0.00 2.5 22.8 1329 0.00 2.39 22.3 1334 0.00 2.0 22.2 1327
0.25 2.3 22.3 1326 0.25 2.29 22.2 1329 0.25 1.9 21.5 1317
0.50 2.0 21.6 1310 0.50 1.7 21.3 1320 0.50 1.8 21.2 1313
0.75 1.4 21.0 1300 0.75 1.56 20.9 1323 0.75 1.6 20.9 1311
1.00 1.2 20.7 1250 1.00 1.5 20.6 1306 1.00 1.9 20.7 1321
1.25 0.34 19.9 1145 1.12 1.43 20.6 1270
1.50 0.12 19.3 1110
6/27/18
0.00 5.1 23.1 365 0.00 4.86 23.1 361 0.00 4.9 23.4 362
0.25 5.1 22.7 365 0.25 5.23 22.7 365 0.25 4.9 22.8 367
0.50 3.8 22.4 368 0.50 4.36 22.4 365 0.50 4.0 22.4 366
0.75 3.4 22.2 369 0.75 3.91 22.3 360 0.75 3.5 22.3 364
1.00 2.8 21.6 326 1.00 1.83 22.0 358 1.00 2.4 21.9 332
1.25 2.5 21.4 317
1.50 2.2 20.9 299
7/11/18
0.00 7.6 25.4 265 0.00 8.7 25.8 263 0.00 8.8 25.9 265
0.25 7.6 25.5 265 0.25 8.2 25.7 264 0.25 8.4 25.7 264
0.50 6.7 25.6 265 0.50 8.1 25.7 265 0.50 8.4 25.7 264
0.75 5.4 25.4 272 0.75 3.9 25.4 273 0.75 5.9 25.6 264
1.00 3.6 25.1 291 1.00 2.3 25.2 1.00 2.8 25.4 366
7/26/18
0.00 7.6 22.3 251 0.00 7.2 22.8 249 0.00 6.8 23.0 257
0.25 7.5 22.6 249 0.25 7.1 22.9 249 0.25 6.8 23.0 250
0.50 7.4 22.7 249 0.50 7.0 22.9 249 0.50 6.9 23.0 250
26
SITE 1 SITE 2 SITE 3
Sampling date H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm)
0.75 7.3 22.8 249 0.75 7.0 22.9 249 0.75 6.7 23.0 250
1.00 7.2 22.9 249 1.00 7.0 22.9 249 1.00 6.7 23.0 249
1.25 6.4 22.9 250 1.25 6.87 23.0 249
1.50 4.73 22.9 251
8/9/18
0.00 11.2 25.2 215 0.00 11.7 25.3 214 0.00 12.2 25.6 214
0.25 11.7 25.3 217 0.25 11.4 25.2 214 0.25 12.2 25.2 214
0.50 10.6 25.2 221 0.50 10.2 25.2 214 0.50 10.3 24.9 216
0.75 4.86 24.3 260 0.75 5.7 24.1 239 0.70 9.1 24.9 217
1.00 2.8 23.6 246
8/22/18
0.00 7.5 23.3 298 0.00 8.6 23.4 292 0.00 8.3 24.1 295
0.25 7.0 22.6 296 0.25 7.2 22.7 292 0.25 7.1 22.7 291
0.50 5.5 22.2 295 0.50 5.7 22.3 293 0.50 7.1 22.6 291
0.75 4.6 22.1 295 0.75 5.3 22.2 293
1.00 4.1 22.1 299 0.95 4.9 22.1 294
1.25 3.8 22.1 302
1.50 3.6 22.0 299
1.75 3.5 22.0 297
2.00 0.14 22.0 330
9/11/18
0.00 9.8 21.0 188 0.00 9.7 20.4 187 0.00 10.4 21.1 183
0.25 9.6 20.6 187 0.25 9.7 20.4 187 0.25 10.5 20.8 183
0.50 9.4 20.1 187 0.50 9.5 20.4 187 0.50 10.1 20.5 182
0.75 8.8 20.1 192 0.75 9.0 20.3 186
1.00 7.4 19.8 200 1.00 7.1 20.1 187
1.25 6.5 19.7 208
9/26/18
0.00 5.0 15.2 101 0.00 5.0 15.1 101 0.00 5.2 15.1 100
0.25 4.9 15.2 101 0.25 5.0 15.1 101 0.25 5.1 15.2 100
0.50 4.9 15.2 101 0.50 5.0 15.1 101 0.50 5.1 15.2 100
0.75 4.8 15.2 101 0.75 4.9 15.1 101 0.75 5.0 15.2 100
1.00 4.5 15.2 101 0.90 4.8 15.1 102
1.25 4.4 15.2 101
1.50 4.3 15.2 102
1.75 4.3 15.2 102
Table A- 6. Continued: Data for sampling sites 4, 5 and 6 in the Point of France pond.
SITE 4 SITE 5 SITE 6
Sampling date H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm)
5/16/18
0.00 17.7 19.3 2806
0.25 18.6 18.1 3275
0.50 20.6 15.3 3910
0.75 15.6 14.0 4278
5/30/18 0.00 5.22 22.9 1609 0.00 6.6 23.1 1813 0.00 5.25 23.2 1724
27
SITE 4 SITE 5 SITE 6
Sampling date H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm) H (m) DO (mg/L) T °C SC (µs/cm)
0.25 5.12 22.9 1594 0.25 5.6 23.3 1808 0.25 5.09 23.3 1729
0.50 4.87 22.9 1588 0.50 5.4 23.3 1798 0.50 5.14 23.3 1732
0.75 4.64 22.9 1594 0.75 4.7 23.3 1796 0.75 4.56 23.3 1786
1.00 3.86 23.3 1830
6/13/18
0.00 2.19 22.6 1330 0.00 1.8 22.4 1350 0.00 1.88 23.0 1330
0.25 2.08 22.7 1327 0.25 1.6 21.7 1331 0.25 1.1 21.7 1316
0.50 2.11 22.5 1325 0.50 1.4 21.3 1331 0.50 1.45 21.3 1325
0.75 1.96 21.3 1310 0.75 1.94 21.0 1320
6/27/18
0.00 5.18 22.9 362 0.00 4.5 23.5 366 0.00 4.77 23.5 366
0.25 4.48 22.6 363 0.25 3.5 22.8 366 0.25 2.53 22.7 367
0.50 4.02 22.4 360 0.50 2.4 22.5 367 0.50 2.53 22.4 357
0.75 2.89 22.2 357 0.75 0.1 22.3 354 0.75 1.62 22.1 332
0.90 2.24 22.1 357
7/11/18
0.00 8.0 26.3 266 0.00 10.4 26.5 262 0.00 10.0 26.8 262
0.25 8.0 25.9 266 0.25 9.9 26.4 261 0.25 10.1 26.7 262
0.50 7.1 25.7 265 0.50 9.8 26.3 261 0.50 9.5 26.5 262
0.75 3.9 25.4 273 0.65 8.8 26.2 261 0.75 6.7 25.8 262
1.00 3.7 25.3 300 1.00 5.52 25.6 495
7/26/18
0.00 7.4 22.9 250 0.00 7.6 23.0 248 0.00 8.1 23.2 247
0.25 7.5 23.0 250 0.25 7.5 23.1 248 0.25 6.8 23.1 248
0.50 7.5 23.0 249 0.50 7.5 23.1 248 0.50 6.7 23.1 248
0.75 7.4 22.9 249 0.65 7.4 23.1 247 0.75 6.3 23.0 248
8/9/18
0.00 11.9 25.5 214 0.00 10.6 25.9 212 0.00 11.1 26.7 213
0.25 10.8 25.4 213 0.25 14.2 25.5 214 0.25 13.4 25.7 215
0.50 11.1 25.2 216 0.50 13.8 25.2 214 0.50 14.3 25.4 215
0.75 9.1 24.3 220 0.75 10.7 24.6 218 0.70 10.5 25.0 367
1.00 1.5 23.7 228
8/22/18
0.00 9.6 23.5 292 0.00 9.7 23.4 291
0.25 9.3 22.9 290 0.25 9.6 22.7 289
0.50 8.1 22.3 290 0.50 8.8 22.4 289
0.75 5.9 22.1 291 0.75 6.0 22.0 291
0.76 5.3 22.0 292 1.00 5.4 22.0 292
9/11/18
0.00 10.3 21.0 186 0.00 10.3 21.5 184
0.25 10.3 20.9 185 0.25 10.2 21.2 183
0.50 10.3 20.7 184 0.50 10.3 21.1 183
0.75 10.3 20.5 183.9 0.75 10.2 20.7 183
1.00 9.7 20.3 182.9 1.00 8.3 20.2 184
9/26/18
0.00 5.2 15.1 101 0.00 5.2 15.2 101
0.25 5.1 15.1 101 0.25 4.9 15.1 100
0.50 5.0 15.1 101 0.50 4.9 15.1 101
0.75 5.0 15.1 101 0.75 4.8 15.1 101
1.00 4.3 15.1 101 1.00 4.4 15.1 101