Lake Cornelia Use Attainability Analysis

246 Pages·2016·10.17 MB·English

by  Scott Sobiech

Lake Cornelia
Use Attainability Analysis
REVISED DRAFT
Prepared for
Nine Mile Creek Watershed District
January 2010
Prepared by
Barr Engineering Co.
Lake Cornelia
Use Attainability Analysis
Updated Draft

Prepared for
Nine Mile Creek Watershed District

January 2010

4700 West 77th Street
Minneapolis, MN 55435-4803
Phone: [phone]
Fax: [phone]
Executive Summary
Overview
This report describes the results of the Use Attainability Analysis (UAA) for Lake Cornelia in Edina,
MN. The UAA provides the scientific foundation for a lake-specific best management plan that will
permit maintenance of, or attainment of, the intended beneficial uses of Lake Cornelia. 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
Lake Cornelia and the tributary watershed. The conclusions and recommendations are based on
historical water quality data, the results of an intensive lake water quality monitoring in 2004 &
2008, and computer simulations of land use impacts on water quality in Lake Cornelia using
watershed and lake models calibrated to the water quality data sets. 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 Nine Mile Creek District Water Management Plan (Barr, 2007) lists the NMCWD goals for both
the North and South basins of Lake Cornelia as Level III, with the desired use listed as fishing and
aesthetic viewing.
The NMCWD goal was quantified using the standardized lake rating system termed the Carlson’s
Trophic State Index (TSI). This index considers the lake’s total phosphorus, chlorophyll 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.
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All three of the parameters can be used to determine a TSI. However, water transparency is typically
used to develop the TSI (trophic state index based on Secchi disc transparency) because people’s
SD
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 management strategy typically is to “protect” lakes similar to Lake Cornelia.
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 five specific goals are outlined below.
The Water Quantity Goal for Lake Cornelia 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.
The Water Quality Goal for Lake Cornelia currently is a Level III classification level, which is
generally intended for fishing and aesthetic viewing. The Minnesota Department of Natural
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Resources (MDNR) stocks the lake annually with approximately 300 - 400 bluegill for the Fishing in
the Neighborhood Program. The specific NMCWD goal for Level III classification is to achieve and
maintain a TSI between 60 and 70.
SD
The Aquatic Communities Goal for Lake Cornelia is to achieve a water quality that will result in a
diverse and balanced native ecosystem. The MDNR did not include Lake Cornelia’s fisheries-use
classification in the 1992 report, An Ecological Classification of Minnesota Lakes with Associated
Fish Communities (Schupp, 1992). Since the MDNR did not specify the ecological classification for
Lake Cornelia there is no specific fisheries related TSI goal. However, the MDNR stocks the lake
with bluegills as part of the Fishing in the Neighborhood program, and it is the goal of the NMCWD
to achieve water quality that will result in a diverse and balanced native ecosystem.
The Recreational-Use Goal for Lake Cornelia is to achieve water quality that supports the functions
of the lake and maintain a balanced ecosystem. Lake Cornelia is a wildlife lake generally intended
for wildlife habitat, aesthetic viewing and runoff management. Since the MDNR stocks the lake with
bluegill for the Fishing in the Neighborhood Program, a reasonable recreational use goal would be to
achieve Level III water quality.
The Wildlife Goal for Lake Cornelia is to protect existing beneficial wildlife uses. The wildlife goal
can be achieved with no action, especially if the wetlands and natural land surrounding the lake
remain intact.
In additional to the goals set by the NMCWD, the MPCA has developed assessment methodologies,
conducted extensive sampling of lakes, and ultimately derived ecoregion-based lake eutrophication
standards for deep and shallow lakes for total phosphorus, chlorophyll-a, and Secchi depths (MPCA,
2008). For shallow lakes in the North Central Hardwood Forests (NCHF) ecoregion (where Lake
Cornelia is located), the total phosphorus standard established by the MPCA is 60 μg/L, which serves
as the upper threshold for lake water quality. The chlorophyll-a and Secchi disc standards are listed
as less than 20 µg/L greater than 1.0 meters, respectively. Because the water quality in Lake
Cornelia does not meet these standards, it is currently listed on the 2020 (draft) 303(d) impaired
waters list with an expected total maximum daily load (TMDL) study start date of 2013.
Table EX-1 summarizes the 2004 and 2008 water quality in Lake Cornelia as well as the NMCWD
and MPCA goals for the lake.

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Table EX-1
Lake Cornelia Management Table
Water Quality, Recreational Use and Ecological Classification of, and Management
Philosophies for Lake Cornelia, Referencing Carlson’s Trophic State Index (TSI) Values
(Secchi Disc Transparency Basis)
MPCA
Shallow Lake Water Current Summer Average Water Quality District Management
Lake Quality Standards Conditions (TSISD)1 District Water Quality Goal 2 Strategy
North Cornelia Year of Record III
2004 2008 Fishing and aesthetic Unspecified
viewing
[TP] < 60 µg/L 164 µg/L 153 µg/L 105 µg/L ≥ [TP] > 75 µg/L
[Chl-a] < 20 µg/L 70 µg/L 51 µg/L 60 µg/L ≥ [Chl-a] > 50 µg/L
SD > 1.0 m 0.4 m 0.4 m 0.6 m ≤ [SD] < 1.0 m
TSI = 73 TSI = 73 70 ≥ TSI > 60
SD SD SD
South Cornelia Year of Record III
2004 2008 Fishing and aesthetic Unspecified
viewing
[TP] < 60 µg/L 190 µg/L 150 µg/L 105 µg/L ≥ [TP] > 75 µg/L
[Chl-a] < 20 µg/L 95 µg/L 61 µg/L 60 µg/L ≥ [Chl-a] > 50 µg/L
SD > 1.0 m 0.2 m 0.3 m 0.6 m ≤ [SD] < 1.0 m
TSI = 83 TSI = 77 70 ≥ TSI > 60
SD SD SD
1 TSISD Carlson's Trophic State Index score. This index was developed from the interrelationships between summer average Secchi disc transparencies and
epilimnetic concentrations of chlorophyll a and total phosphorus. The index results in scoring generally in the range between zero and one hundred. [ District
values calculated by Barr Engineering Company (from field data and water quality model predictions). MPCA values taken from the 1994 Clean Water Act Report
to the U.S. Congress; and MDNR values taken from Schupp (1992) Minnesota Department of Natural Resources Investigational Report No. 417. An ecological
classification of Minnesota lakes with associated fish communities.]
2 District
I = Fully supports all water-based recreational activities including swimming, scuba diving and snorkeling.
II = Appropriate for all recreational uses except full body contact activities: sailboating, water skiing, canoeing, wind surfing, jet skiing.
III = Supports fishing, aesthetic viewing activities and wildlife observation
IV = Generally intended for runoff management and have no significant recreational use values
V = Wetlands suitable for aesthetic viewing activities, wildlife observation and other public uses.
* MPCA and MDNR TSI scores were provided by the agency without evaluation by the District.
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Lake Characteristics
Lake Cornelia is located in the north central portion of Edina. The lake is part of a natural marsh
area. Lake Cornelia is comprised of a north (North Cornelia) and south (South Cornelia) basin,
connected by a 12-inch culvert under 66th Street (with an invert elevation of 859 feet MSL) on the
south side of the North Cornelia, and a secondary 12-inch pipe located on the southeast side of the
North Cornelia (with an invert elevation of 860.22 feet MSL). The elevation in North Cornelia is
ultimately controlled by the outlet structure on South Cornelia. The outflow from South Cornelia
discharges over a weir structure at 859.1 feet MSL and flows through an extensive storm sewer
system to Lake Edina.
North Cornelia
North Cornelia has a water surface of approximately 19 acres, a maximum depth of 5 feet, and a
mean depth of approximately 3 feet at a normal water surface elevation of 859.1. At this elevation
the lake volume is approximately 61 acre-feet. The water level in the lake is controlled mainly by
weather conditions (snowmelt, rainfall, and evaporation), by the outlet capacity of the pipe on North
Cornelia, and by the elevation of the outlet structure located on South Cornelia.
South Cornelia
South Cornelia has a water surface of approximately 31 acres, a maximum depth of 7 feet, and a
mean depth of 4.2 feet at a normal surface elevation of 859.1. At this elevation the lake volume is
approximately 130 acre-feet. The water level in the lake is controlled by the elevation of the weir
structure at the south side of the lake.
Water Quality Problem Assessment
Baseline Lake Water Quality Status
The Minnesota Lake Eutrophication Analysis Procedure (MnLEAP) is intended to be used as a
screening tool for estimating lake conditions and for identifying “problem” lakes. MnLEAP is
particularly useful for identifying lakes requiring “protection” versus those requiring “restoration”
(Heiskary and Wilson, 1990). In addition, MnLEAP 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). Results of
MnLEAP modeling done for Lake Cornelia suggest that the lake could achieve “better” water quality
than is currently observed (Heiskary and Lindbloom, 1993). For the MnLEAP analysis, Lake
Cornelia was treated as a single basin, rather than two separate basins. The results of the various
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models used to estimate the baseline total phosphorus (TP) concentration are summarized in Table
EX-2.
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. Alkalinity data from 2008 was used as well as epilimnetic specific conductivity data
collected throughout the summer of 2004 and 2008 to predict the total phosphorus concentration
range from natural, background loadings.
Finally, the Wisconsin Lake Modeling Suite (WiLMS) model (WI-DNR, 2004) was also used to
estimate Lake Cornelia’s water quality under natural (predevelopment) watershed conditions. The
WiLMS model (Lake Total Phosphorus Prediction Module) uses an annual time step and predicts
spring overturn, growing season mean, and annual average TP concentrations in lakes. The model
uses information about the lake and watershed characteristics in conjunction with 13 different
published phosphorus prediction regressions to predicted the expected in-lake TP. The historic
watershed information for Lake Cornelia was used to estimate the model input parameters and the
expected water quality in Lake Cornelia.
Table EX-2 Summary of Lake Cornelia Baseline Water Quality Modeling Results
Model Lake Expected Water Quality
(Total Phosphorus)
MnLEAP Lake Cornelia 55 – 97 ug/L
(North & South)
Vighi and Chiaudani North Cornelia 34 – 40 ug/L
(1985) – Alkalinity
South Cornelia 34 – 40 ug/L
Vighi and Chiaudani North Cornelia 27 – 61 ug/L
(1985) – Specific South Cornelia 27 – 66 ug/L
Conductivity
WiLMS (Canfield and Lake Cornelia 53 – 133 ug/L
Bachman (1981)) (North & South)

Comparison of the predicted baseline TP concentrations to observed annual average phosphorus
concentrations indicates that the water quality in Lake Cornelia is worse than it likely was
historically, based on its location, watershed area and lake basin morphometry. The predicted ranges
of TP concentrations indicates that the NMCWD Level III classification goal should be attainable,
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given the appropriate phosphorus loadings to the lake. When compared to the MPCA shallow lakes
standard (60 μg/L), the upper end of the Vighi and Chiaudani predicted natural background TP
concentration range falls right around the standard, indicating that it may be possible to attain the
MPCA shallow lake standard for phosphorus. However, when considering the TP ranges predicted
by the MnLEAP and WiLMS models, the MPCA shallow lake standard may be attainable only on the
very low end of the expected range of TP concentrations, and is likely not attainable for most
conditions.
Lake Cornelia Current Water Quality
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 lake.
The NMCWD conducted intensive water quality monitoring in North and South Cornelia in 2004 and
again in 2008. The Metropolitan Council Citizen Assisted Monitoring Program (CAMP) also
collected water quality data in North Cornelia in 2003, 2005, 2006, 2007, and 2008. Figure EX-1
shows the historic summer average TP and Chl-a concentrations, and transparency data from 2003
through 2008 for Lake Cornelia.
When comparing the three key water quality parameters, North Cornelia has slightly better water
quality than in South Cornelia. However, the 2008 summer average TP, Chl a, and transparency
place both North and South Cornelia in the hypereutrophic category throughout the summer, meaning
that Lake Cornelia is rich in algal nutrients, susceptible to dense algal blooms, and exhibits poor
water clarity. Figure EX-2a and Figure EX-2b show the most recent (2008) water quality throughout
the monitoring season in North and South Cornelia, respectively. The summer averages of the
various water quality parameters for 2004 and 2008 are also summarized in Table EX-1.
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Figure EX-1
Lake Cornelia HistoricSummer Average
Water Quality
(a) Total Phosphorus (b) Chloropyll-a and
(c ) Secchi Disc Transparency
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