HomeMy WebLinkAboutVegetation and Water Quality Issues Presentation, Nov. 2016Nine Mile Creek Watershed District and City of Edina
November 3, 2016
Lake Cornelia Vegetation and Water Quality
Issues
Presentation Overview
•Urbanization and land use changes
•Historical data compared with WQ
Standards
•Changes in curly-leaf pondweed
coverage and density
•2016 blue-green algae bloom and
public health advisory
•What is the shared vision for Lake
Cornelia?
Lake Cornelia watershed
Watershed area ~1,000 acres
Urbanization has significantly changed
Lake Cornelia watershed
1940 195319571964
District WQ monitoring program
Water Quality
Lake Cornelia water quality has
consistently failed to meet State
shallow lake water quality
standards
Water Quality –Secchi Disc Transparency
0.6
0.4 0.4 0.4
0.3
0.4
0.5
0.4 0.4
0.8
0.2
0.3
0.4
0.5
0.6
0
0.2
0.4
0.6
0.8
1
1.2
2003 2004 2005 2006 2007 2008 2009 2013 2015 2016
Se
c
c
h
i
D
e
p
t
h
(
m
)
Secchi Disc Transparency (m)
North Cornelia
South Cornelia
MPCA Shallow Lake Standard
SD >1.0 m
Water Quality –Chlorophyll a
149
70
58
69
90
42 45 50
97
36
95
61
35
68 72
0
50
100
150
200
2003 2004 2005 2006 2007 2008 2009 2013 2015 2016
Ch
l
-a
(µ
g
/
L
)
Chloropyll-a Concentration (µg/L)
North Cornelia
South Cornelia
MPCA Shallow Lake
Standard
Chl-a <20 µg/L
Water Quality –Total Phosphorus
283
164 165 169
228
153
111
165 162
114
162 150
114 122
149
0
50
100
150
200
250
300
2003 2004 2005 2006 2007 2008 2009 2013 2015 2016
TP
(µ
g
/
L
)
Total Phosphorus Concentration (µg/L)
North Cornelia
South Cornelia
MPCA Shallow Lake Standard
TP <60 µg/L
*
Phosphorus Sources to Cornelia-
2010 Study by NMCWD
Watershed
Runoff
76%
Atmospheric
Deposition
1%
Internal
Phosphorus
Loading
14%
Other
9%
Source: Lake Cornelia Use Attainability Analysis, NMCWD 2010
Annual phosphorus
budget under average
climatic conditions
Vegetation/Curly-leaf Pondweed
Overview
2004
•Curly-leaf pondweed (CLP) not observed; no vegetation > 3 feet north
basin or 2 feet south basin
2008
•Light growth of CLP at 1 north basin and 2 south basin locations; no
vegetation > 3 feet north basin or 2 feet south basin
2013
•CLP not observed in north basin in June; light growth of CLP observed
at south basin in June and both basins in August
2015
•CLP throughout both basins in June and August; very dense in June, less
dense in August; dying off in August
2016
•Very dense CLP throughout both basins in June; CLP not observed in
August; no vegetation > 3 ft in August
Lake Cornelia –South Basin –June 2013
Lake Cornelia –South Basin –June 2015
Lake Cornelia –South Basin –August 2015
Lake Cornelia –South Basin –June 2016
Lake Cornelia –South Basin –August 2016
Aquatic Communities -Phytoplankton
Blue-green algae blooms –many
different possible forms & colors
•Blue-green algae can produce toxins
•World Health Organization (WHO) –guidelines to determine risk of health impacts from blue-green algae
•No risk when < 20,000 blue-greens per mL
•Low risk when blue-greens are between 20,000 and 100,00 per mL
•Moderate risk when blue-greens >100,000 per mL
•High risk –whenever blue-green scum is present
Blue-green Algal Blooms
Blue-Green Algal Blooms
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
180,000
200,000
220,000
240,000
260,000
280,000
300,000
320,000
340,000
4/
2
2
/
2
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1
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8
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1
1
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Bl
u
e
-Gr
e
e
n
s
(
U
n
i
t
s
p
e
r
m
L
)
Cornelia Lake -South Basin
Moderate Risk of Adverse Health Effects
Low Risk of Adverse Health Effects
No Risk of Adverse Health Effects
Algal
scum was
present
near
shore
Algal Toxin Testing
Saxitoxin Anatoxin-a Microcystins/
nodularins
Cylindrospermopsin
Neurotoxin
(nervous
system)
Neurotoxin
(nervous
system)
Hepatoxin
(Liver/gut)
Hepatoxin
(Liver/gut)
Not Detected in
Lake Cornelia
Not Detected in
Lake Cornelia
High levels in
Lake Cornelia
9/7/16 in
north/south
basins; 9/21/16 in
south basin
Not Detected in Lake
Cornelia
Toxin
Name
Toxin Type
(impact)
What is the Shared Vision for the Future of
Lake Cornelia?