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2013 Lakes Monitoring Report

Prepared by: Capitol Region Watershed District 1410 Energy Park Drive, Suite 4 Saint Paul, MN 55108 (651) 644-8888 www.capitolregionwd.org June 2014


TABLE OF CONTENTS Acronyms ........................................................................................................................................ i Definitions ..................................................................................................................................... iii List of Figures ................................................................................................................................ v List of Tables ............................................................................................................................... vii 1. Executive Summary ........................................................................................................... 1 2. Introduction ........................................................................................................................ 5 3. Methods............................................................................................................................. 17 4. Climatological Summary .................................................................................................. 25 5. CRWD Lakes Results Summary ....................................................................................... 33 6. Como Lake Results ........................................................................................................... 39 7. Crosby Lake Results ......................................................................................................... 57 8. Little Crosby Lake Results................................................................................................ 71 9. Loeb Lake Results............................................................................................................. 83 10. Lake McCarrons Results .................................................................................................. 99 11. Conclusions & Recommendations .................................................................................. 117 12. References ....................................................................................................................... 123 Appendix A: Technical Memorandum – Statistical Analysis of Lake Data in CRWD.............. 127


ACRONYMS AND ABBREVIATIONS ac BMP cBOD Cd cf cfs Chl-a Cl Cr CRWD CS Cu DNR DO E. coli EPA ft GP GPS ha Hg IBI in kg L lb m MCES MCWG mg mL MnDOT MPCA MS4 MSP NA NCHF NH3

Acre Best Management Practice 5-day Carbonaceous Biochemical Oxygen Demand Cadmium Cubic feet Cubic feet per second Chlorophyll-a Chloride Chromium Capitol Region Watershed District Chronic Standard Copper Department of Natural Resources Dissolved Oxygen Escherichia coli Environmental Protection Agency Foot/Feet Gottfried’s Pit Global Positioning System Hectare Mercury Index of Biological Integrity Inch Kilogram Liter Pound Meter Metropolitan Council Environmental Services Minnesota Climatological Working Group Milligram Milliliter Minnesota Department of Transportation Minnesota Pollution Control Agency Municipal Separate Storm Sewer System Minneapolis-St. Paul International Airport Not Available North Central Hardwood Forest Ammonia 2013 CRWD Lakes Monitoring Report

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Ni NO2 NO3 NOAA NWS OHWL Ortho-P Pb RCD RCLML RCPW sec SRP TB TBI TDS TKN TN TMDL TP TSS UMN VSS WD WMO Zn

Nickel Nitrite Nitrate National Oceanic and Atmospheric Administration National Weather Service Ordinary High Water Level Ortho-phosphate Lead Ramsey Conservation District Ramsey County Lake Management Laboratory Ramsey County Public Works Second Soluble Reactive Phosphorus Trout Brook Trout Brook Storm Sewer Interceptor Total Dissolved Solids Total Kjeldahl Nitrogen Total Nitrogen Total Maximum Daily Load Total Phosphorus Total Suspended Solids University of Minnesota-St. Paul Campus Volatile Suspended Solids Watershed District Watershed Management Organization Zinc

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DEFINITIONS Anthropogenic – resulting from the influence of human beings on nature. Bathymetric – the measurement of water depth in a body of water. Benthic – the ecological region at the bottom of a body of water. Biomanipulation – the deliberate alteration of an ecosystem by adding or removing species. Class 2 Waters – waters of the State that are designated for aquatic life and recreational use. Chlorophyll-a – a type of chlorophyll pigment found in plants used in oxygenic photosynthesis; used as a measure of phytoplankton production in lakes and streams. Conductivity – the measure of the ability of water to pass an electrical current; affected by the presence of inorganic dissolved solids and temperature. Designated Use – the water quality standards regulation requires that States and authorized Indian Tribes specify appropriate water uses to be achieved and protected. Appropriate uses are identified by taking into consideration the use and value of the water body for public water supply, for protection of fish, shellfish, and wildlife, and for recreational, agricultural, industrial, and navigational purposes. Epilimnion – the top layer of water in a lake, characterized in the summer by warm, circulating water. MPCA lake standards are based on water sampled from this layer. Eutrophic – a water body with high nutrient concentrations and primary biological productivity. These waters are murky and an extensive macrophyte population. Algal blooms are common. Fingerling – fish harvested from rearing ponds after one summer of growth. Fry – newly hatched fish ready to be stocked. Hardness – the concentration of calcium and magnesium salts (e.g. calcium carbonate, magnesium carbonate) in a water sample. Hypereutrophic – a water body with excessive nutrient concentrations and primary biological productivity. These waters are characterized by very murky water, frequent algal blooms and fish kills, foul odor, and rough (or less desirable) fish. Hypolimnion – the part of a lake below the thermocline made up of water that is stagnant and of essentially uniform temperature except during the period of overturn.

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Impaired Waters – waters that are not meeting their designated uses because of excess pollutants violating water quality standards (from the MPCA website). Littoral Area/Zone – area of a lake that is less than 15 feet in depth where the majority of plants are found. Mesotrophic – a water body that has intermediate nutrient concentrations and primary biological productivity. These waters are moderately clear and are characterized by late-summer algal blooms, moderate macrophyte populations, and occasional fish kills. Morphometric – describing parameters relating to external form. Oligotrophic – a water body that has low nutrient concentrations and primary biological productivity, and is characterized by clear water, few macrophytes, and salmonid fish. Phytoplankton – the autotrophic plant members of the plankton (drifting organisms) community. Secchi depth – a measure of the transparency of lake water. Stormwater – water that becomes runoff on a landscape during a precipitation event. Stormwater Best Management Practices – activities, practices, and structures designed to reduce stormwater pollution and runoff volume and increase groundwater recharge. Subwatershed – a delineated area of land within a larger watershed where surface waters and runoff drain to a single point before ultimately discharging from the encompassing watershed. Thermal stratification – refers to the changes in temperature at different depths in a lake as a result of the different densities of water at different temperatures. Thermocline – the region in a thermally stratified body of water which separates warmer surface water from cold deep water and in which temperature decreases rapidly with depth. Total Maximum Daily Load – the maximum amount of a substance that can be received by a water body while still meeting water quality standards. This may also refer to the allocation of acceptable portions of this load to different sources. Turbidity – a measure of the relative clarity of a liquid. Turbidity measurements can provide a simple indicator of potential pollution in a sample. Turbid water will appear cloudy or hazy. Watershed – a delineated area of land where surface waters and runoff drain to a single point at a lower elevation. Zooplankton – the heterotrophic animal members of the plankton (drifting organisms) community. 2013 CRWD Lakes Monitoring Report

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LIST OF FIGURES 2 INTRODUCTION Figure 2-1: Capitol Region Watershed District in Ramsey County, Minnesota. ........................ 8 Figure 2-2: Como Lake. .......................................................................................................... 10 Figure 2-3: Crosby and Little Crosby Lakes. ........................................................................... 12 Figure 2-4: Loeb Lake. ............................................................................................................ 14 Figure 2-5: Lake McCarrons. .................................................................................................. 16 3 METHODS Figure 3-1: CRWD 2014 lake and rain gauge monitoring locations. ....................................... 17 4 CLIMATOLOGICAL SUMMARY Figure 4-1: 30-year normal and 2013 monthly precipitation totals for CRWD. ........................ 27 Figure 4-2: Annual precipitation totals (2005-2013) observed in CRWD by MCWG. .............. 28 Figure 4-3: Daily temperature highs and snowpack depths from January to April 2013 as observed at MSP. ............................................................................................................ 32 5 CRWD LAKES RESULTS SUMMARY Figure 5-1: CRWD 2013 vs. historical average TP concentrations and lake standard comparisons. ................................................................................................................... 36 Figure 5-2: CRWD 2013 vs. historical average Chl-a concentrations and lake standard comparisons. ................................................................................................................... 37 Figure 5-3: CRWD 2013 vs. historical average Secchi depths and lake standard comparisons. ........................................................................................................................................ 38 6 COMO LAKE RESULTS Figure 6-1: View of the northwest shoreline of Como Lake. ................................................... 39 Figure 6-2: Como Lake bathymetric map. ............................................................................... 41 Figure 6-3: Como Lake historical lake elevations. .................................................................. 42 Figure 6-4: Como Lake 2013 lake elevations and precipitation. ............................................. 43 Figure 6-5: Como Lake 2013 Secchi/TP/Chl-a comparison .................................................... 45 Figure 6-6: Como Lake historical Secchi/TP/Chl-a comparison.............................................. 46 Figure 6-7: Como Lake 2013 total phytoplankton concentration and TP concentration. ........ 50 Figure 6-8: Como Lake 2013 total zooplankton density and Chl-a concentration................... 50 Figure 6-9: Como Lake 2013 phytoplankton relative abundance............................................ 51 Figure 6-10: Como Lake 2013 zooplankton relative abundance............................................. 51 Figure 6-11: Como Lake 2013 biovolume heat map. .............................................................. 52 Figure 6-12: Como Lake 2013 percent occurrence of vegetation present. ............................. 53 Figure 6-13: Como Lake 2013 average abundance ranking of vegetation present. ............... 54 7 CROSBY LAKE RESULTS Figure 7-1: View of the southwest shoreline of Crosby Lake. ................................................. 57 Figure 7-2: Crosby Lake bathymetric map. ............................................................................. 59 Figure 7-3: Crosby Lake 2013 Secchi/TP/Chl-a comparison. ................................................. 61 Figure 7-4: Crosby Lake historical Secchi/TP/Chl-a comparison. ........................................... 62 Figure 7-5: Crosby Lake 2013 total phytoplankton concentration and TP concentration........ 65 2013 CRWD Lakes Monitoring Report

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Figure 7-6: Crosby Lake 2013 total zooplankton density and Chl-a concentration. ................ 65 Figure 7-7: Crosby Lake 2013 phytoplankton relative abundance. ......................................... 66 Figure 7-8: Crosby Lake 2013 zooplankton relative abundance. ............................................ 66 Figure 7-9: Crosby Lake 2013 biovolume heat map. .............................................................. 67 Figure 7-10: Crosby Lake 2013 percent occurrence of vegetation present. ........................... 68 Figure 7-11: Crosby Lake 2013 average abundance ranking of vegetation present .............. 69 8 LITTLE CROSBY LAKE RESULTS Figure 8-1: View of the southeast shoreline of Little Crosby Lake. ......................................... 71 Figure 8-2: Little Crosby Lake 2013 Secchi/TP/Chl-a comparison. ........................................ 73 Figure 8-3: Little Crosby Lake historical Secchi/TP/Chl-a comparison. .................................. 74 Figure 8-4: Little Crosby Lake 2013 total phytoplankton concentration and TP concentration. ........................................................................................................................................ 76 Figure 8-5: Little Crosby Lake 2013 total zooplankton density and Chl-a concentration. ....... 76 Figure 8-6: Little Crosby Lake 2013 phytoplankton relative abundance. ................................ 77 Figure 8-7: Little Crosby Lake 2013 zooplankton relative abundance. ................................... 77 Figure 8-8: Little Crosby Lake 2013 biovolume heat map....................................................... 78 Figure 8-9: Little Crosby Lake 2013 percent occurrence of vegetation present...................... 79 Figure 8-10: Little Crosby Lake 2013 average abundance ranking of vegetation present. ..... 80 9 LOEB LAKE RESULTS Figure 9-1: View of the boat launch on the east shoreline of Loeb Lake. ............................... 83 Figure 9-2: Loeb Lake historical lake elevations. .................................................................... 85 Figure 9-3: Loeb Lake 2013 lake elevations and precipitation. ............................................... 86 Figure 9-4: Loeb Lake 2013 Secchi/TP/Chl-a comparison. .................................................... 88 Figure 9-5: Loeb Lake historical Secchi/TP/Chl-a comparison. .............................................. 89 Figure 9-6: Loeb Lake 2013 total phytoplankton concentration and TP concentration. .......... 92 Figure 9-7: Loeb Lake 2013 total zooplankton density and Chl-a concentration. ................... 92 Figure 9-8: Loeb Lake 2013 phytoplankton relative abundance. ............................................ 93 Figure 9-9: Loeb Lake 2013 zooplankton relative abundance. ............................................... 93 Figure 9-10: Loeb Lake 2013 biovolume heat map................................................................. 94 Figure 9-11: Loeb Lake 2013 percent occurrence of vegetation present................................ 95 Figure 9-12: Loeb Lake 2013 average abundance ranking of vegetation present. ................. 96 10 LAKE MCCARRONS RESULTS Figure 10-1: View of the west shoreline of Lake McCarrons................................................... 99 Figure 10-2: Lake McCarrons bathymetric map. ................................................................... 101 Figure 10-3: Lake McCarrons historical lake elevations. ...................................................... 102 Figure 10-4: Lake McCarrons 2013 lake elevations and precipitation. ................................. 103 Figure 10-5: Lake McCarrons 2013 Secchi/TP/Chl-a comparison. ....................................... 105 Figure 10-6: Lake McCarrons historical Secchi/TP/Chl-a comparison.................................. 106 Figure 10-7: Lake McCarrons 2013 total phytoplankton concentration and TP concentration. ...................................................................................................................................... 110 Figure 10-8: Lake McCarrons 2013 total zooplankton density and Chl-a concentration. ...... 110 Figure 10-9: Lake McCarrons 2013 phytoplankton relative abundance................................ 111 Figure 10-10: Lake McCarrons 2013 zooplankton relative abundance................................. 111 Figure 10-11: Lake McCarrons 2013 biovolume heat map. .................................................. 112 Figure 10-12: Lake McCarrons 2013 percent occurrence of vegetation present. ................. 114 Figure 10-13: Lake McCarrons 2013 average abundance ranking of vegetation present. ... 115

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LIST OF TABLES 3 METHODS Table 3-1: Average abundance rating and description for aquatic vegetation (RCPW, 2009). ........................................................................................................................................ 19 Table 3-2: Minnesota DNR fish stocking size definitions (DNR, 2014d). ................................ 20 Table 3-3: Deep and shallow lake state water quality standards. ........................................... 21 Table 3-4: Water quality parameter lake grade ranges, percentile ranges, and descripton of lake grade user quality (MC, 2011; Osgood, 1989). ....................................................... 22 Table 3-5: CRWD overall lake grade ranges. ......................................................................... 22 Table 3-6: Phytoplankton types, taxonomic classification, description, and water quality significance. .................................................................................................................... 23 Table 3-7: Zooplankton types, taxonomic classification, description, and water quality significance. .................................................................................................................... 23 4 CLIMATOLOGICAL SUMMARY Table 4-1: Daily and monthly precipitation totals for 2013 compared to the NWS 30-year normals. .......................................................................................................................... 26 Table 4-2: CRWD annual precipitation totals and departure from the NWS 30-year normal. . 29 Table 4-3: Summary of 2013 climatological events. ............................................................... 30 Table 4-4: MSP 2013 monthly temperatures and departure from historical normal temperatures. .................................................................................................................. 30 5 CRWD LAKES RESULTS SUMMARY Table 5-1: CRWD 2013 average, historical average, and lake standards for TP/Chl-a/Secchi depth. .............................................................................................................................. 33 Table 5-2: CRWD 2013 and historical lake grades and averages for TP/Chl-a/Secchi depth. ........................................................................................................................................ 34 6 COMO LAKE RESULTS Table 6-1: Como Lake morphometric data.............................................................................. 41 Table 6-2: Como Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. ....................................................................................................... 47 Table 6-3: Como Lake historical lake grades. ......................................................................... 48 Table 6-4: Como Lake historical record of fish stocking. ........................................................ 55 Table 6-5: Como Lake 2011 fish populations.......................................................................... 55 7 CROSBY LAKE RESULTS Table 7-1: Crosby Lake morphometric data. ........................................................................... 59 Table 7-2: Crosby Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. .......................................................................................... 63 Table 7-3: Crosby Lake historical lake grades. ....................................................................... 63 Table 7-4: Crosby Lake 2004 fish populations. ....................................................................... 70 8 LITTLE CROSBY LAKE RESULTS Table 8-1: Little Crosby Lake morphometric data. .................................................................. 72 2013 CRWD Lakes Monitoring Report

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Table 8-2: Little Crosby Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. .......................................................................................... 75 Table 8-3: Little Crosby Lake historical lake grades. .............................................................. 75 9 LOEB LAKE RESULTS Table 9-1: Loeb Lake morphometric data. .............................................................................. 84 Table 9-2: Loeb Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. ....................................................................................................... 90 Table 9-3: Loeb Lake historical lake grades. .......................................................................... 90 Table 9-4: Loeb Lake historical record of fish stocking. .......................................................... 97 Table 9-5: Loeb Lake 2006 fish populations. .......................................................................... 97 10 LAKE MCCARRONS RESULTS Table 10-1: Lake McCarrons morphometric data.................................................................. 101 Table 10-2: Lake McCarrons historical yearly TP/Chl-a/Secchi depth averages compared to deep lake state standards. ............................................................................................ 107 Table 10-3: Lake McCarrons historical lake grades. ............................................................. 108 Table 10-4: Lake McCarrons historical record of fish stocking. ............................................ 116 Table 10-5: Lake McCarrons 2008 fish populations.............................................................. 116

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1 EXECUTIVE SUMMARY 1.1

CAPITOL REGION WATERSHED DISTRICT

Capitol Region Watershed District (CRWD) in Ramsey County, Minnesota is a special purpose unit of government that manages, protects, and improves water resources within its watershed boundaries. CRWD is a 41 square mile subwatershed nested in the Upper Mississippi River basin that contains portions of five cities, including: Falcon Heights, Lauderdale, Maplewood, Roseville, and Saint Paul. CRWD is highly urbanized with a population of 245,000 and 42% impervious surface coverage. All runoff from CRWD eventually discharges to the Mississippi River from 42 outfall locations within the District. One goal of CRWD is to understand and address the presence of pollutants and their impacts on water quality within the District in order to better protect, restore, and manage local water resources. To address this goal, CRWD established a monitoring program in 2004 to begin assessing water quality and quantity of various District subwatersheds and stormwater best management practices (BMPs) over time. CRWD collects water quality and continuous flow data from major subwatersheds, lakes, ponds, and stormwater BMPs. 1.2

PURPOSE OF REPORT

This annual report focuses on the water quality of the five District lakes (Como, Crosby, Little Crosby, Loeb, and McCarrons) during the 2013 monitoring season (May to September). In addition, specific water quality data (total phosphorus, chlorophyll-a, and Secchi disk depth) for each lake from 2013 were compared to previous monitoring years. Additional biological and physical parameters not previously reported upon are also included in this year’s report. The purpose of this report is to characterize overall lake health and water quality in 2013 and examine trends over time which in turn will inform lake management decisions for continued protection and improvement of District lakes. Previous annual monitoring reports (2005-2012) are available on the CRWD website at www.capitolregionwd.org. 1.3

LAKE MONITORING METHODS

Within CRWD, the five lakes are located in four of the sixteen major subwatersheds (Como, Crosby, McCarrons, and Trout Brook). CRWD organized the collection of water quality data for all of these lakes including information on chemical parameters (i.e., nutrients, pH, and conductivity), physical parameters (i.e., water clarity, dissolved oxygen, and temperature), and biological parameters (i.e., chlorophyll-a, aquatic vegetation type and abundance, and phytoplankton, zooplankton, and fisheries populations).

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Lake data is collected by Ramsey County Public Works, Ramsey Conservation District, and the Minnesota Department of Natural Resources. Also, rainfall data was collected by CRWD from six precipitation gauges across the watershed. 1.4

2013 MONITORING RESULTS

The total amount of precipitation for the 2013 calendar year was 36.36 inches which was 5.75 inches greater than the NWS 30-year normal of 30.61 inches. May 2013 was the wettest month, comprising 20% of the total annual precipitation amount for 2013. April, May, and June were all above average in precipitation, by a total of 9.57 inches above the normal rainfall amounts for these months. Conversely, July to November (with the exception of October) were unseasonably dry, with only a few isolated events during these months. Also of note was a 1.4 inch rain event on October 2 after a period of little to no rainfall. The majority of the yearly precipitation occurred during April to June, and October. In 2013, the water quality of the five District lakes (Como, Crosby, Little Crosby, Loeb, and McCarrons) varied by water body and by time of year. Based on the MPCA eutrophication numeric water quality standards, Little Crosby Lake, Loeb Lake, and Lake McCarrons met the MPCA eutrophication water quality standards (for shallow/deep lakes) for all parameters during the entire 2013 growing season (May to September) (Table 1-1). Como Lake did not meet the MPCA shallow lake standards for total phosphorus (TP) and chlorophyll-a (Chl-a) concentrations, or Secchi disk depth during the entire 2013 growing season (Table 1-1). Crosby Lake met the MPCA shallow lake standards for Chl-a concentration and Secchi depth, but failed for TP concentrations (Table 1-1). Como Lake was the only District lake designated as impaired in 2013 and has been listed on the MPCA 303(d) list since 2002. Table 1-1: CRWD 2013 average, historical average, and lake standards for TP/Chl-a/Secchi depth 2013 Averages

Historical Averages

State Lake Standards

Lake

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

TP (µg/L)

Chl-a (µg/L)

Como

209

47.4

0.8

174

36.1

1.5 2.0 2.5

<60

Secchi (m)

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

<60

<20

≥1.0

<60

<20

≥1.0

<20

≥1.0

Crosby

96

10.6

1.6

68

13.3

Little Crosby

59.8

5.1

3.0

83

8.3

Loeb

27

7.4

3.0

24

4.5

3.3

<60

<20

≥1.0

McCarrons

20

4.1

3.3

34

10.0

2.9

<40

<14

≥1.4

Value does not meet the state standard Value meets the state standard

Lake grades were calculated for each lake based on the 2013 water chemistry data to provide a more understandable depiction of lake health and to better track lake water quality changes over time. The seasonal means of TP, Chl-a, and Secchi depth were examined for 2013 and previous years and grades were based on scoring ranges for each parameter (Table 1-2). Based on the lake grading system, three out of the five CRWD lakes were given good to excellent lake grades, 2013 CRWD Lakes Monitoring Report

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where Lake McCarrons received the highest grade of ‘A’. Both Loeb and Little Crosby Lakes received good grades of ‘B+’ and ‘B’, respectively. An average water quality grade of ‘C’ was given to Crosby Lake and Como Lake received the lowest grade of ‘D’. Table 1-2: CRWD 2013 lake grades and historical lake grades for TP/Chl-a/Secchi depth Lake Como Crosby Little Crosby Loeb McCarrons

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2013 Lake Grade TP Chl-a Secchi F C D D B C C A B B A B A A A

2013 Average D C B B+ A

Historical Lake Grade TP Chl-a Secchi F C C C B C D A B B A A C A B

Historical Average D+ C+ B A B

2014 RECOMMENDATIONS

Based on the results and findings of the 2013 Lakes Monitoring Report, CRWD has several goals and recommendations for 2014 to continue improving the monitoring program and the water quantity and quality dataset. Specifically, CRWD aims to complete the following in 2014:   

   

Install level monitoring equipment in Como Lake, Crosby Lake, and Lake McCarrons to continuously measure lake level throughout the monitoring season. Improve analysis of chemical and physical data previously collected but not fully analyzed in prior reports. Extend the lakes monitoring season to include early spring and late fall in order to capture seasonal variability in lake water quality and improve statistical confidence for trend assessments, including: o Expand monitoring of chemical parameters to include early spring and late fall. o Increase frequency of aquatic vegetation surveys and biovolume analysis to three times per year to monitor in spring, summer, and fall. o Increase phytoplankton and zooplankton data collection to include early spring and late fall. Initiate fisheries surveys annually on all lakes by an external consultant for years that the Minnesota Department of Natural Resources does not survey CRWD lakes. Install temperature monitoring equipment in Como Lake and Lake McCarrons to determine the effect of higher temperature runoff to lake temperature. Conduct lake bottom sediment analyses on all lakes in the winter of 2014-2015 to establish baseline knowledge of sediment data and understand internal pollutant loading of CRWD lakes. Improve analysis of all chemical, physical, and biological data and the interactions of this data to increase understanding of what these parameters are indicating about overall lake health.

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2 INTRODUCTION 2.1

CRWD BACKGROUND

Located in Ramsey County, Minnesota the Capitol Region watershed is a small urban subwatershed nested in the Upper Mississippi River basin with all runoff eventually discharging to the Mississippi River. Capitol Region Watershed District (CRWD) is a special purpose unit of government formed in 1998 to manage and protect all water resources within the Capitol Region watershed boundaries. CRWD contains portions of five cities, including: Falcon Heights, Lauderdale, Maplewood, Roseville, and Saint Paul (Figure 2-1). CRWD is highly urbanized with a population of 245,000 and 42% impervious surface coverage. Land use in the watershed is primarily residential with dense areas of commercial, industrial, and institutional uses. 2.2

CRWD WATER QUALITY ISSUES

Urban development in the watershed over time has significantly impacted the health and sustainability of the Mississippi River as well as CRWD lakes, wetlands, and streams. Impervious surfaces generate polluted stormwater runoff which causes poor water quality, increased peak storm flows, decreased groundwater recharge, increased flooding, and loss of biological habitat. Subsequently, stormwater runoff is one of the most significant sources of pollution to CRWD water resources. It delivers fertilizers, pesticides, pet and wildlife waste, nutrients, sediment, heavy metals, and other anthropogenic pollutants to local water bodies. As stormwater runs off the urban landscape, it is collected and conveyed through an extensive network of underground storm sewer pipes that eventually drain to the Mississippi River. A total of 42 outfall pipes discharge into the 13-mile stretch of the Mississippi River bordering CRWD. Both historical and current water quality data of CRWD lakes, ponds, and the Mississippi River indicate that these water bodies are impaired for various pollutants (including nutrients, bacteria, and turbidity) and are not meeting their designated uses for fishing, aquatic habitat, and recreation. The Mississippi River and Como Lake are listed on the Minnesota Pollution Control Agency (MPCA) 2012 303(d) list of impaired waters (MPCA, 2012). Impaired waters require a total maximum daily load (TMDL) study for pollutants of concern including nutrients, turbidity, metals, bacteria, and chloride. The nutrient of primary concern in CRWD is phosphorus. Phosphorus is a biological nutrient which limits the growth of algae in most lakes and streams and is often found in high concentrations in stormwater. Phosphorus occurs naturally in the environment, but in excess can cause the overgrowth of algae and aquatic plants in lakes and rivers which reduces dissolved oxygen levels and increases turbidity of the water column. Common sources of

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phosphorous include fertilizers from lawns and gardens, leaves and grass clippings, pet and wildlife waste, and automobile emissions. CRWD is within the Northern Central Hardwood Forest (NCHF) ecoregion. It is one of seven ecoregions in Minnesota and is characterized as an area with fertile soils with agriculture as the dominant land use in rural areas. In most lakes in the NCHF ecoregion, phosphorous is the least available nutrient; therefore, the concentration of phosphorous controls the extent of algal growth. Algal growth in turn affects the clarity and recreational potential of lakes. Chlorophyll-a (Chl-a) is a pigment present in algae. Measuring Chl-a concentration is a proxy for measuring algal population. Algal blooms can make recreation unpleasant and prevent it entirely, and certain species of algae are toxic to humans and other animals. In addition, as algae die and decompose, oxygen is consumed from the water column and made unavailable for fish and other aquatic animals. Chronic low dissolved oxygen concentrations (<5 mg/L) may result in fish kills and low diversity of aquatic species (Kalff, 2002). Sediment is another major constituent of stormwater runoff. Excessive amounts of sediment negatively impacts water clarity and impairs benthic aquatic habitat. The reduction or removal of sediment from stormwater is essential because other pollutants, such as phosphorus, adhere to sediment particles and are transported in suspension. Sediment originates from erosion of soil particles from construction sites, lawns, stream banks, and lake shores as well as sand application to roadways and parking lots for traction in the winter. Water transparency, or water clarity, (determined using a Secchi disk) is another concern in area lakes. Lakes with high water clarity are generally considered healthier, and are characterized by more submerged aquatic plant growth, as clear water allows light to permeate to lower depth levels (Kalff, 2002). Increased plant growth also provides better habitat for aquatic organisms, including fish. Poor water clarity is a result of increased turbidity caused by suspended sediments, organic matter, and/or phytoplankton (algae). Heavy metals, such as lead and copper, are also pollutants of concern in CRWD because they can be toxic in high concentrations. Also, heavy metals can bioaccumulate in organisms, which is of concern to wildlife and humans. Potential sources of metals from road surface runoff include auto exhaust, tire wear, brakes, and some winter de-icing agents. Pathogens, which include bacteria and viruses, also contribute to the water quality degradation of CRWD water resources. They impact recreation and pose potential health risks to humans. Sources of pathogens include illicit sanitary connections to storm drains, and animal waste. Chloride in water bodies is a contaminant of concern for CRWD. High concentrations of chloride can harm fish and plant life by creating a saline environment. Also, once in dissolved form, chloride cannot be removed from a water body. Chloride is primarily sourced from road salt application for de-icing in the winter months.

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2.3

CRWD LAKE MONITORING PROGRAM GOALS

CRWD was formed to understand and address these water quality impacts and to better protect and manage local water resources. In 2004, CRWD established a monitoring program to assess water quality and quantity of various District subwatersheds and stormwater best management practices (BMPs). Prior to the CRWD monitoring program, limited data was available on stormwater quantity and quality in the watershed. The objectives of the program are to identify water quality problem areas, quantify subwatershed runoff pollutant loadings, evaluate the effectiveness of BMPs, provide data for the calibration of hydrologic, hydraulic, and water quality models, and promote understanding of District water resources and water quality. The CRWD 2013 Lakes Monitoring Report presents information on annual CRWD lake water quality monitoring, including data collection methods and results for water chemistry, physical parameters, and biological parameters. Previous annual monitoring reports (20052012) are available on the CRWD website at www.capitolregionwd.org. Results and analysis of CRWD stormwater monitoring and stormwater BMPs are discussed in separate reports (CRWD, 2014; CRWD, 2012), which are also available on the CRWD website. 2.4

OVERVIEW OF CRWD LAKES

There are five lakes within the boundaries of CRWD: Como Lake, Crosby Lake, Little Crosby Lake, and Loeb Lake in St. Paul, and Lake McCarrons in Roseville (Figure 2-1). The lakes are monitored by Ramsey County Public Works (RCPW) and CRWD to assess overall health and to determine if each lake supports their designated uses for swimming, fishing, and/or aesthetics. All of the lakes receive stormwater runoff (directly and/or indirectly) and are nested within the Mississippi River Basin. Como Lake, Crosby Lake, Little Crosby Lake, and Loeb Lake are classified as shallow lakes and Lake McCarrons is classified as a deep lake. Shallow lakes have a maximum depth less than 15 ft, or more than 80% of the lake within the littoral zone (MPCA, 2014a). The littoral zone is the near-shore area of the lake in which plants grow (Kalff, 2002). Deep lakes have a maximum depth greater than 15 ft, or less than 80% of the lake within the littoral zone (MPCA, 2014a).

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Figure 2-1: Capitol Region Watershed District in Ramsey County, Minnesota. 2013 CRWD Lakes Monitoring Report

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2.4.1 COMO LAKE

Como Lake (Figure 2-2) is a 70.5 acre lake with a maximum depth of 15.5 ft and is located in the City of Saint Paul. The 1,856 acre Como Lake watershed land uses are primarily residential and parkland. Como Lake is classified as a shallow lake because nearly 100% of the lake is considered the littoral zone. The lake has been monitored since 1984, and although water quality has improved slightly over time, there has been an observed cyclical variation in water quality (Noonan, 1998). In an effort to improve water quality in the lake, the Como Lake Strategic Management Plan (CRWD, 2002) was developed in 2002 and can be found on the District website (www.capitolregionwd.org). Como Lake is listed on the MPCAâ&#x20AC;&#x2122;s 2012 303(d) list of impaired waters (MPCA, 2012).

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Figure 2-2: Como Lake.

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2.4.2 CROSBY LAKE & LITTLE CROSBY LAKE

Crosby Lake (45 acres) and Little Crosby Lake (8 acres) (Figure 2-3) are shallow lakes situated in the Mississippi River floodplain in Saint Paul and part of the Crosby Farm Regional Park and the Mississippi River National River and Recreation Area. The lakes are located within the 1,522 acres of Crosby Lake subwatershed; 197 acres of the subwatershed drain to Crosby Lake while 37 acres drain to Little Crosby Lake. The lakes are divided into two separate water bodies by a marsh/bog area 825 ft long. Crosby Lake is classified as a shallow lake because it has a maximum depth of 17 ft and the littoral zone covers 100% of the lake area. Little Crosby Lake is also considered a shallow lake even though it has a maximum depth of 34 ft, because it has a littoral area of 90% (<15 ft in depth). The watershed land uses for both water bodies are primarily parkland, single family residential, and industrial. A management plan for Crosby Lake (which included information regarding Little Crosby Lake) was created in 2012 (CRWD, 2012a), and can be found on the District website (www.capitolregionwd.org). Crosby Lake has been monitored since 2005; Little Crosby Lake has been monitored since 2011. Neither lake met the MPCA water quality standards in 2012. Crosby did not meet the standards again in 2013. Water quality of both lakes, however, is greatly affected by the Minnesota and Mississippi Rivers, since it is located in the floodplain of their confluence.

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Figure 2-3: Crosby and Little Crosby Lakes.

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2.4.3 LOEB LAKE

Loeb Lake (Figure 2-4) is a 9.7 acre shallow lake with a maximum depth of 28 ft and has a littoral area of 81%. Located in Marydale Park in the City of Saint Paul, the predominant land uses in the surrounding drainage area (44 acres) are mixed residential and parkland. The lake has a small drainage area, with no outlets. Loeb Lake has been monitored since 2003 (with the exception of 2004). A management plan for the lake was created in 2009 (CRWD, 2009), and can be found on the District website (www.capitolregionwd.org). Loeb Lake is an unimpaired water body and is not currently on the MPCA 303(d) list.

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Figure 2-4: Loeb Lake.

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2.4.4 LAKE MCCARRONS

Located in the City of Roseville, Lake McCarrons (Figure 2-5) is a 74.7 acre lake with a maximum depth of 57 ft. It is considered a deep lake with less than a 34% littoral zone. Lake McCarrons has a watershed area of 1,070 acres, with land use of mainly mixed residential and open space. Lake McCarrons has been monitored since 1988, and is the only District lake that allows swimming and has development (residential) directly on its shoreline. Lake McCarrons received an alum treatment in 2004 and water quality of the lake has shown improvement since this occurred. A management plan for the lake was created in 2003 (CRWD, 2003), and can be found on the District website (www.capitolregionwd.org). The lake is considered unimpaired and is not currently listed on the MPCA 303(d) list of impaired waters.

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Figure 2-5: Lake McCarrons.

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3 METHODS 3.1

MONITORING LOCATIONS

Figure 3-1 shows the monitoring locations of CRWD lakes, as well as the subwatershed boundaries and rain gauge locations.

Figure 3-1: CRWD 2014 lake and rain gauge monitoring locations. 2013 CRWD Lakes Monitoring Report

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3.2

MONITORING METHODS

3.2.1 LAKE LEVEL

Lake elevation monitoring is organized by the Minnesota Department of Natural Resources (DNR) Lake Level Minnesota Program (DNR, 2014i). This program coordinates the monitoring by organizations and volunteers to gather weekly data of elevations on lakes throughout the state. Lake levels are measured using staff gages that are placed near the lakeshore in a stable and easy-to-access location. Data on lake levels is collected by the DNR Waters staff, then compiled and stored in the LakeFinder database that can be accessed online to view historical lake levels for a particular lake (DNR, 2014g). Lake elevation monitoring by the DNR within CRWD occurs on Como Lake, Loeb Lake, and Lake McCarrons. As this data continues to be compiled, a lake elevation graph is updated in order to view historical fluctuations in lake levels. The ordinary high water level (OHWL) is one other parameter that is shown on these graphs (where applicable). The OHWL is defined as the “highest water level that has been maintained for a sufficient period of time to leave evidence upon the landscape, commonly the point where the natural vegetation changes from predominantly aquatic to predominantly terrestrial” (Scherek, 1993). The OHWL is used to determine regulatory controls, with the Minnesota DNR regulating activity below the OHWL and local units of government regulating activity above the OHWL. By including this as a part of the lake elevation graph, observations can be made as to how current and past years compare to the “normal” lake level. This does not always mean that the lake level ever reaches or surpasses the OHWL, as this level is based on landscape evidence indicating the historical water level and is not an average of past monitored water levels. 3.2.2 CHEMICAL AND PHYSICAL DATA COLLECTION

The 2013 lake water quality data (and all years preceding) was collected by RCPW throughout the growing season (May through September), resulting in a total of eight samples for the monitoring season (RCPW, 2009). The CRWD lakes sampling schedule was determined prior to the start of the monitoring season. At each lake, RCPW staff anchored a watercraft over the deepest part of the lake, and monitored for various water quality parameters. The physical and chemical parameters of depth, temperature, dissolved oxygen, conductivity, and pH were measured at one-meter sampling intervals for the full depth profile of the lake using a multiprobe. From these recordings, the depths of the epilimnion, thermocline, and hypolimnion were recorded. Additionally, at the lake sampling location, water chemistry samples were collected at multiple depths along the profile of the lake. At all lakes, two samples were obtained within the epilimnion, or mixed water layer. If RCPW staff was able to identify thermal stratification (where depths for the divisions between the epilimnion, thermocline, and hypolimnion can be identified), additional water samples from other depths were collected. One additional water sample was collected from within the thermocline and two were collected from within the hypolimnion. Any water samples collected were then stored and transported back to the RCPW lab and analyzed for the following parameters: Chl-a, TP, soluble reactive phosphorous (SRP), total Kjeldahl nitrogen (TKN), nitrate (NO3), ammonia (NH3), and chloride ion concentrations 2013 CRWD Lakes Monitoring Report

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(Cl). Water transparency, or water clarity, was determined with the use of a Secchi disk. A Secchi disk is a black and white patterned disk that is connected to a line or pole. To take a measurement, the Secchi disk is lowered slowly into the water column until the pattern is no longer visible. The depth at which the disk is no longer visible is then recorded. 3.2.3 PHYTOPLANKTON AND ZOOPLANKTON COLLECTION

Phytoplankton and zooplankton data collection occurred at the same time as water quality data collection by RCPW for 2013 and previous monitoring years. For phytoplankton analysis, a composite sample was collected using a plastic tube that was inserted vertically 2 m into the upper layer of the water column. This sample was emptied into a bucket, thoroughly mixed, and a sub-sample was collected and preserved. This water sample was placed in an enclosed cooler and taken back to the lab for analysis (RCPW, 2012). To collect a zooplankton sample, a net tow was lowered down to the observed thermocline (in order to collect samples from the oxygenated layer of the lake), allowed to settle, and then pulled back up to the water surface at a rate of 1 m/sec. The net and capture bucket were drained by swirling the capture bucket which allowed the water to drain out of the net and screen. Once the volume was reduced to 100 mL, the contents of the capture bucket were poured into another container and preserved in a 5% formaldehyde solution, then taken back to the RCPW lab for analysis (RCPW, 2012). 3.2.4 AQUATIC VEGETATION SURVEYS Point-Intercept Survey Method

In 2013, all lakes were surveyed by the Ramsey Conservation District (RCD) for aquatic vegetation presence and abundance using the point-intercept method. This method consisted of using a GPS to pre-select specific monitoring points throughout the full area of the lake. At each evenly spaced (70 m distance) point, a double-tined metal rake was thrown out 1 m from the boat, dragged a distance of 1 m and brought back into the boat. Plant species were identified and given an abundance ranking based on the amount seen on the rake (Table 3-1). Any plants floating on the water surface were also identified. Table 3-1: Average abundance rating and description for aquatic vegetation (RCPW, 2009).

Percent Cover of Tines 81-100 61-80 41-60 21-40 1-20

Abundance Ranking 5 4 3 2 1

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Biovolume Survey Method

To collect data on submerged aquatic vegetation as well as data about the lake bottom, RCD used a Lowrance HDS-5 GPS enabled depth finder to assess evenly spaced transects at a minimum distance of 40 meters. The sonar log data that was collected was then analyzed by CI BioBase software to determine the depth of the lake and the amount of aquatic vegetation (biomass) along each transect. These surveys also produced information estimating lake area and lake water volume. 3.2.5 FISH STOCKING AND SURVEYS

Fish stocking occurs annually through the Minnesota DNR in an effort to improve fishing conditions on selected MN lakes. Roughly 25% of the state's 5,400 fishing lakes have a set stocking schedule (DNR, 2014d). Fish are stocked at different life stages depending on the desired effect in the lake. Table 3-2 describes the different types. Table 3-2: Minnesota DNR fish stocking size definitions (DNR, 2014d). Fry

Fish stocked in lakes shortly after hatching from eggs.

Fingerling

Fish harvested from rearing ponds after one summer of growth.

Yearling

Fish that are a year old at the time of stocking.

Adult

Fish more than 1 year old, usually transferred from other waters.

Fish surveys are conducted every 5-10 years on the majority of Minnesota lakes (more frequently on lakes of higher fishing importance, for example, Lake Mille Lacs) by the DNR. Through fish surveys, DNR employees gain information on the species of fish in a lake in order to make management decisions and understand changes in lake water quality. Fish are collected using various field techniques based on the type and size of fish to be collected. These survey techniques include: gill netting (to capture larger, predator fish), trap netting (to capture smaller panfish), trawl and shoreline seines (to capture young fish), and electrofishing (to survey for bass, crappies and young walleyes). Once captured, information is recorded on the species, count, and weight, as well as how the counts and weights compare to the normal expected range for the species. Data on fish length was also recorded (DNR, 2014d). 3.3

DATA ANALYSIS METHODS

3.3.1 MORPHOMETRIC DATA

Morphometric data (quantitative measurements on the form of the lake and surrounding area) was compiled for each lake. This included information regarding lake surface area, mean and maximum depth, littoral area percentage, lake water volume, watershed area, and watershed-tolake area ratio. The watershed-to-lake area ratio represents how large the watershed is compared to the size of the lake. A high ratio indicates a large portion of land for potential runoff to the lake, while a low ratio indicates a smaller area conducting runoff. In general, having a lower 2013 CRWD Lakes Monitoring Report

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ratio in urban areas decreases external nutrient loading to lakes, which in turn can result in improved water quality. 3.3.2 WATER QUALITY STANDARDS COMPARISON

A lake is considered eutrophic if it has high nutrient levels, low dissolved oxygen concentrations, and frequent algal blooms. Although some lakes are naturally eutrophic, many have become eutrophic as a result of anthropogenic activities. In order to identify eutrophic water bodies in Minnesota, the MPCA established eutrophication numeric water quality standards in lakes for TP, Chl-a, and Secchi depth (Table 3-3) (MPCA, 2014a). In the NCHF ecoregion, a different standard exists for shallow and deep lakes. Seasonal means were determined for each of these parameters based on the eight different monitoring events that occurred between May and September of 2013. For a lake to be considered unimpaired and not eutrophic under the MPCA standards, it is required to meet the standard for both TP concentration and either the Secchi disk depth or Chl-a concentration. Lakes that do not meet the standards may be placed on the MPCA 303(d) list of impaired waters. To account for differences in natural trophic state, the standards vary by ecoregion and lake type. Table 3-3: Deep and shallow lake state water quality standards. Deep Lake Standarda,b

Shallow Lake Standarda,c

Units

Source

TP*

<40

<60

µg/L

Minn. Stat. § 7050.0222

Chlorophyll-a

<14

<20

µg/L

Minn. Stat. § 7050.0222

Secchi depth

≥1.4

≥1.0

m

Minn. Stat. § 7050.0222

Parameter

Standards apply to Class 2B w aters in the North Central Hardw ood Forest ecoregion. Class 2B w aters are designated for aquatic life and recreational use. All standard concentrations apply to chronic exposure. b A deep lake is defined as a lake w ith a maximum depth > 15 feet or one in w hich < 80% of the lake is in the littoral zone . a

c A shallow lake is defined as a lake w ith a maximum depth < 15 feet or one in w hich > 80% of the lake is in the littoral zone.

*MPCA standard for TP is listed in mg/L, but has been converted to µg/L.

3.3.3 LAKE GRADING SYSTEM

In 2013, CRWD introduced the use of a lake grading system for reporting lake water quality (Table 3-4). This was based on the Metropolitan Council’s lake grading system that is used to compare lakes across the metro region and to offer a non-technical value of lake water quality that is more understandable to a wide variety of audiences (Osgood, 1989). The seasonal means of TP, Chl-a, and Secchi depth were examined for 2013 and previous years and grades were based on ranges for each parameter. The range is weighted such that a certain percentage of Minnesota lakes fall into each grade. Each grade corresponds not only to ranges in the three lake eutrophication parameters (TP, Chl-a, and Secchi depth), but also to a recreational value for the lake that provides a description of user quality (MC, 2011). CRWD assigned each letter grade a numerical value (A = 5, B = 4, C = 3, D = 2, F = 1), and the average of these three values 2013 CRWD Lakes Monitoring Report

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provided an overall lake grade (Table 3-5). The ranges in Table 3-5 are based off methods used by the Minnehaha Creek Watershed District in their monitoring reports (MCWD, 2012).

Table 3-4: Water quality parameter lake grade ranges, percentile ranges, and description of lake grade user quality (MC, 2011; Osgood, 1989). Grade A B C D F

Percentile <10 10-30 30-70 70-90 >90

TP (Îźg/l) <23 23-32 32-68 68-152 >152

Chl-a (Îźg/l) Secchi (m) <10 >3.0 10-20 2.2-3.0 20-48 1.2-2.2 48-77 0.7-1.2 >77 <0.7

Description of User Quality Full recreational use capability Very good water quality but some recreational use impairment Average water quality but are recreationally impaired Severly impaired recreational use Extremely poor water quality; little to no recreational use

Table 3-5: CRWD overall lake grade ranges. Grade A AB+ B+ BC+ C CD+ D DF

Range 4.67 - 5.00 4.34 - 4.66 4.01 - 4.33 3.67 - 4.00 3.34 - 3.66 3.01 - 3.33 2.67 - 3.00 2.34 - 2.66 2.01 - 2.33 1.67 - 2.00 1.34 - 1.66 < 1.33

3.3.4 PHYTOPLANKTON AND ZOOPLANKTON LAB ANALYSIS

All methods for lab analysis of phytoplankton and zooplankton were obtained from Ramsey County Lake Management Laboratory (RCLML), a part of RCPW (RCPW, 2012). In the lab, the preserved phytoplankton sample was analyzed and identity/counts were recorded. The classes/phylums that were identified are listed and described in Table 3-6 (Kalff, 2002; UCMP, 2014).

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Table 3-6: Phytoplankton types, taxonomic classification, description, and water quality significance. Phytoplankton

Classification

Bacillariophyta

Class

Chlorophyta

Phylum

Chrysophyta

Class

Cryptophyta

Phylum

Cyanophyta

Phylum

Euglenophyta

Phylum

Pyrrophyta

Phylum

Description

Water Quality Significance Large populations suggest higher levels of dissolved silica needed to Diatoms build external skeletons Greatly contribute to freshwater lake species richness; contribute most Green algae significantly to biomass of eutrophic systems Golden-brown Not overly abundant in eutrophic lakes; more plentiful in oligotrophic, algae clear-water lakes Most prevelant in oligotrophic and mesotrophic lakes; division does Cryptomonads not contain an abundance of species types Blue-green Indicative of highly nutrient-rich (eutrophic and hypereutrophic) lakes; algae large blooms are aesthetically displeasing and some can be toxic Generally small contribution to overall biomass except in small, highly Euglenoids eutrophic bodies of water Typically contribute small portion of total biomass or species richness Dinoflagellates in temperate lakes

To analyze zooplankton, the preserved sample from the field was measured and a subvolume was analyzed for identity/counts. The zooplankton that were identified in this process are shown and described in Table 3-7 (Kalff, 2002). The Cladocerans identified during analysis consisted of Daphnia, Bosminae, Chydorus, Ceridaphnia, Diaphnosoma, and Leptodora. These genuslevel organisms were combined and grouped under the heading â&#x20AC;&#x2DC;Cladoceraâ&#x20AC;&#x2122; for analysis. Table 3-7: Zooplankton types, taxonomic classification, description, and water quality significance. Zooplankton

Classification

Cyclopoida

Order

Calanoida

Order

Nauplii

Genus

Rotifera

Phylum

Cladocera

Suborder

Description Carniverous copepods Omnivorous copepods Juvenile copepods Soft-bodied, multicellular invertebrates Type of crustacean

Water Quality Significance Primarily carniverous crustaceans; feed on other zooplankton and fish larvae but also eat algae, bacteria, and detritus Crustaceans that feed on ciliates as well as algae; change diet based on multiple variables including season and food availability Classified as nauplii during the first 5 or 6 molts (motling occurs 11 times before adulthood) during the life span of a copepod Name originates from rotating wheel of cilia by mouth; important among invertebrates as many species can produce multi-generations per year Mainly important filter-feeders covered by a hard cover; specific species Daphnia are main food source for planktivorous fish

Techniques for creation of phytoplankton and zooplankton figures in the ensuing individual lake results sections were based off methods used in the Minneapolis Park and Recreation Board 2011 Water Resources Report (MPRB, 2011). There are two figures for both phytoplankton and zooplankton. The first figure for phytoplankton compares total phytoplankton concentration and TP concentration from May to September. The first figure for zooplankton compares total zooplankton density and Chl-a concentration from May to September. The second figures depict the relative abundance of each type of phytoplankton and zooplankton in order to examine changes in their populations throughout the months monitored. 2013 CRWD Lakes Monitoring Report

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3.3.5 AQUATIC VEGETATION ANALYSIS Biovolume Analysis

Sonar data was entered into CI BioBase software that generates aquatic vegetation and bathymetric maps (CIBB, 2014). The biovolume heat maps were coded by different color zones to highlight differences in cover of aquatic vegetation (where red indicates that 100% of the water column is being taken up by biovolume, or vegetation is growing to the water surface, and blue indicates 0%, or bare lake bottom). Statistics calculated along with the maps included plant biovolume (the percentage of the water column that is vegetation at a location where vegetation exists) and percent area covered (the amount of the lake area where vegetation exists) (CIBB, 2014). Point-Intercept Analysis

Aquatic vegetation has been monitored infrequently in past years on CRWD lakes. Establishing a baseline of vegetation data for all lakes will be a key factor in making future monitoring decisions. Aquatic vegetation within a lake is dependent on many different factors, including: water clarity, water chemistry, and physical lake parameters (including depth, sediment substrate type, lake size/shape, and shoreline vegetation). Not only does aquatic vegetation stabilize bottom sediment, plants also provide habitat for aquatic animals and are usually the main primary producers in shallow lakes (Kalff, 2002). Collecting data on aquatic vegetation provides baseline information on what vegetation is in the lake, where it exists on the lake, and how much is present. Measuring annual changes in these factors can help identify trends in aquatic vegetation and water quality. Collecting data on aquatic vegetation using the point-intercept method allowed for two primary analyses to occur: computation of percent occurrence and average abundance. Percent occurrence represents the number of times a plant species was observed divided by the number of total sample sites where vegetation was observed. This information gives a good picture of the most common species of aquatic vegetation found on the lake. Average abundance is calculated as the average of the abundance rankings (measured at each location found) for a species. This shows how much vegetation of each species is occurring at the locations where vegetation is noted. A high average abundance ranking indicates thick cover of a species where it is observed. Conversely, a low average abundance ranking indicates minimal growth of a species.

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4 CLIMATOLOGICAL SUMMARY 4.1

PRECIPTATION DATA COLLECTION METHODS

CRWD utilizes climatological data collected by the Minnesota Climatology Working Group (MCWG) at the University of Minnesota-St. Paul, and National Weather Service (NWS) at the Minneapolis-St. Paul International Airport (MSP) to calculate annual precipitation and help understand the effects of rainfall on lake water quality. MCWG records precipitation every fifteen minutes from an automatic rain gauge located approximately two miles west of the CRWD office. The data is reported on a public website (http://climate.umn.edu/). Rainfall totals (15-minute and daily) were recorded by CRWD from the MCWG website (MCWG, 2013). Snow and ice totals were not accurately reported by MCWG, so they were not recorded by CRWD from this source. The MCWG rain gauge was used as CRWDâ&#x20AC;&#x2122;s primary precipitation monitoring station because of the gaugeâ&#x20AC;&#x2122;s close proximity to the District. The NWS weather station at MSP, located approximately ten miles south of the CRWD office, records many climate variables for each day, including: maximum, minimum, and average temperature; precipitation (including water amount in snow); snowfall; and depth of snowpack. Data is reported on a public website (www.crh.noaa.gov/mpx/Climate/MSPClimate.php). NWS daily precipitation totals were used if any snow or ice was logged as precipitation. Precipitation amounts as snow-water or ice-water are more accurately measured at this station because of the type of snow measurement device used. 4.2

2013 PRECIPITATION RESULTS

Table 4-1 lists 2013 daily precipitation totals, 2013 monthly precipitation totals, the 30-year monthly normal (1981-2010) (NWS, 2011), and the 2013 departure from historical monthly normals. Monthly totals are compared to the 30-year monthly normals at MSP (Figure 4-1). In 2013, almost all precipitation data from January to April and from November to December was provided by NWS. The May through October precipitation data was provided by MCWG. April, May, and June 2013 were all above average in precipitation with a total of 19.84 inches during these months, equaling 9.57 inches above the 30-year normal for this period (Table 4-1; Figure 4-1). During this time of year, soils are generally saturated, which causes higher runoff volumes from pervious and impervious surfaces. Precipitation in July, August, and September 2013 was a total of 5.60 inches below the 30-year normal for this period.

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Table 4-1: Daily and monthly precipitation totals for 2013 compared to the NWS 30-year normals.

Day

JAN

FEB

MAR APR MAY JUNE JULY AUG SEPT OCT

1

0

0.06

0

0

2

0.01

0.03

0

0

3

0

0.04

0

4

0

0.06

5

0

6 7 8

NOV

DEC

0.35

0.02

0

0

0

0

0

0

0

0

0

0

0

1.43

0

0.12

0

0.2

0

0

0

0

0.05

0

0.32

0

0.09

0.02

0

0

0

0.35

0.19

0.08 0.52

0.05

0.41

0.07

0

0.1

0.01

0.55

0

0.02

0.18

0

0

0.04

0

0.11

0.01

0

0.3

0

0.09

0.05

0

0

0

0

0.18

0 0

0

0.01

0.01

0

0

0

0

0.66

0.34

0

0

0

0

0

0

0.07

0.59

0.78

0

0

0

0

0

0

9

0

0

0.61

0.48

0.07

0

0

10

0.28

0.62

0.01

0.09

0

0

0

0

0.01

0

0

0.06

11

0.02

0

0

0.75

0

0.02

0

0

0

0.2

0

0

12

0

0

0

0.06

0

0.61

0

0

0

0

0

13

0

0.09

0

0.01

0.01

0

1.69

0

0

0

0

0 0.02

14

0

0.09

0.06

0.46

0

0

0

0

0.4

0.59

0

0.06

15

0

0

0.19

0

0

1.22

0

0

0.15

0.77

0

0

0.02

0

0

0

0.02

0.1

16

0.02

0

0

0

0

17

0

0

0

0.26

0.21

0

0

0

0.02

0.37

0.07 0

18

0.01

0.01

0.23

1.02

0.81

0

0

0

0.13

0.08

0

19

0

0

0

0.12

2.05

0

0

0

0.29

0.08

0

20

0

0

0

0

1.06

0

0

0

0.02

0.12

0

0.03 0.02

21

0

0

0

0.15

0.06

2.82

0.13

0

0

0

0.01

0

22

0

0.24

0

0.82

0.07

0.41

0

0

0.01

0.01

0

0.03

0.02

0

0.42

0

0

0

0.01

0

0.06

0

0

0

0

23 24

0

0

0

0

0.27

0

0 0.23

25

0

0

0

0

0.04

0

0.1

0

0

0

0

0.02

26

0

0

0

0.01

0

0.13

0.07

0

0

0

0

0.01

27

0.49

0

0

0

0.01

0

0.12

0

0

0

0

0

28

0

0

0

0.1

0

0.02

0

0

0.2

0

0

0

29

0.03

0

0

1.07

0.66

0.02

0.67

0

0.03

0

0

30

0

0.38

0

0.27

0

0.04

0

0

0.11

0

0.09

31

0

0

0.01

0.08

2.98

1.61

TOTAL Monthly Normal Departure from Normal

0

0.86

0

0

0 0

1.33

2.21

0.36 5.37

7.34

7.13

4.3

0.01 1.23

4.34

0 TOTAL 0.5

1.46

36.36

0.9 0.77

1.89

2.66

3.36

4.25

4.04

3.08

2.43

1.77

1.16

30.61

-0.04 0.56

0.32

2.71

3.98

2.88

-1.06 -2.69 -1.85

1.91

-1.27

0.30

5.75

Data supplied by MCWG Data Supplied by NWS at MSP No Date

2013 CRWD Lakes Monitoring Report

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8

30-Year Normal Monthly Precipitation Totals

7

CRWD 2013 Monthly Precipitation Totals

Precipitation (inches)

6

5

4

3

2

1

0

JAN

FEB

MAR

APR

MAY

JUNE JULY Month

AUG

SEPT

OCT

NOV

DEC

Figure 4-1: 30-year normal and 2013 monthly precipitation totals for CRWD.

2013 CRWD Lakes Monitoring Report

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40

35 30.61

25

10

36.36 30.26

33.62

23.34

21.67

29.72

31.69

15

36.32

20

35.98

Precipitation (inches)

30

5

0 2005

2006

2007

2008

Precipitation (inches)

2009

2010

2011

2012

2013

NWS 30-Year Normal (1981-2010)

Figure 4-2: Annual precipitation totals (2005-2013) observed in CRWD by MCWG.

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The 2005-2013 CRWD annual precipitation data was compared to the NWS 30-year normal for the Minneapolis-St. Paul region (Figure 4-2; Table 4-2). The NWS 30-year normal is recalculated every 10 years. In 2010, the NWS 30-year normal was recalculated for 1981-2010 to be 30.61 inches (formerly 29.41 inches (1971-2000). The total amount of precipitation in 2013 was 36.36 inches, which was 5.75 inches above the 30-year normal, and the wettest year since monitoring began in CRWD in 2005.

Table 4-2: CRWD annual precipitation totals and departure from the NWS 30-year normal. Year

Precipitation (inches)a

Departure from NWS Normal

2005

35.98

(+) 5.37"

2006

31.69

(+) 1.08"

2007

29.72

(-) 0.89"

2008

21.67

(-) 8.94"

2009

23.34

(-) 7.27"

2010

36.32

(+) 5.71"

2011

33.62

(+) 3.01"

2012

30.26

(-) 0.35"

2013

36.36

(+) 5.75

NWS 30-Year Normal

30.61

--

Annual precipitation reported by the Minnesota Climatology Research Group (MCRG) and National Weather Service (NWS)

a

4.3

2013 NOTABLE CLIMATOLOGICAL EVENTS

Other notable climate variables are summarized in Table 4-3. The 2013 snowfall total of 68.9 inches measured at MSP was 14.5 inches higher than the 30-year normal of 54.5 inches. While the average snowfall amount in May is historically only a trace (MCWG, 2014), MSP recorded 0.5 inches on May 3. The last date with a 1 inch snowpack measured at MSP was April 23 (NWS, 2014a). This was 21 days later than the normal date of April 2 (NWS, 2014b). Ice out on lakes also occurred significantly later in 2013. Historical median ice out dates have not been established for any lakes within CRWD (DNR, 2014j), but the Minnesota DNR has collected historical median ice out dates for many lakes near CRWD, including:     

Nokomis (April 4), Powderhorn (April 4), Josephine (April 7), Owasso (April 6), and Phalen (April 5).

2013 CRWD Lakes Monitoring Report

29


The median of the historical median ice out dates for these nearby lakes is April 5. The only lake in CRWD with an ice out date recorded in 2013 was Como Lake (DNR, 2014h). Como Lake’s ice out date was April 23, which was 18 days later than the normal yearly median value of nearby lakes (April 5). Table 4-3: Summary of 2013 climatological events. 2013 Climate Summary Variable

2013

Average

Notes

Total Precipitation (inches)

36.36

30.61

5.75" higher than 30-yr normal

Total Snow (inches)

68.9

54.4

14.5" higher than 30-yr normal

5/3/2013 - 0.5"

N/A

Variable - No data on averages

4/23

4/2

21 days later than normal

Last Significant Snowfall Last date with greater than 1" snowpack Ice Out

4/23

4/5

17 days later than normal

Leaf Off

11/14

N/A

Later than normal

The average monthly temperature, departure from the normal temperature, and daily highs and lows by date are listed in Table 4-4. The 2013 winter and spring months were colder than normal with an average departure from normal of 3.0 °F colder in January through May, November, and December. The 2013 summer months were warmer than normal with an average departure from normal of 2.0 °F warmer from June through October. Overall, the entire year was 0.9 °F below average. Table 4-4: MSP 2013 monthly temperatures and departure from historical normal temperatures Temperature 2013 Average Departure from (°F) normal (°F)

High (°F)

Low (°F)

January

16.9

1.3

41 on 18,11

-12 on 22

February

19.0

-1.8

39 on 13

-13 on 1

March

27.2

-5.6

56 on 30

5 on 20

April

41.0

-6.5

81 on 28

19 on 2, 1

May

58.3

-0.8

98 on 14

32 on 3

June

68.9

0.1

91 on 20

50 on 2

July

75.0

1.2

94 on 18, 17

53 on 28, 27

August

74.7

3.5

97 on 26

56 on 4

September

67.2

5.2

94 on 9,7

44 on 16

October

49.1

0.2

78 on 10

26 on 22

November

33.2

-0.5

56 on 15

7 on 23

December

12.4

-7.3

47 on 28

-13 on 24

Year 2013

45.2

-0.9

98 on 5/14

-13 on 12/24, 2/1

2013 CRWD Lakes Monitoring Report

30


Snowmelt is a significant driver of hydrology in late winter and early spring. Daily snowpack depths recorded at MSP were plotted against daily high temperature in Figure 4-3 (NWS, 2014a). A complete melt was observed on January 9 to January 12 (3 inches to 0 inches). There was no snowpack recorded again until January 28. Snowpack reached a maximum depth of 13 inches on March 6. Snowpack depth went from 6 inches to 0 inches from March 25 to March 30. Snowpack was not recorded again until April 10. Significant melt events occurred on April 13 to April 17 (4 inches to 0 inches), April 19 to April 22 (7 inches to 0 inches), and April 23 to April 24 (3 inches to 0 inches).

2013 CRWD Lakes Monitoring Report

31


14

90

80

Snowpack Depth

12

High Temp

70

10

60

50 8 40 6 30

20

Snowpack Depth (inches)

Daily High Temperature (Degrees F)

Freezing Point

4

10 2 0

-10

0 1/1

1/8

1/15

1/22

1/29

2/5

2/12

2/19

2/26 3/5 Date

3/12

3/19

3/26

4/2

4/9

4/16

4/23

4/30

Figure 4-3: Daily temperature highs and snowpack depths from January to April 2013 as observed at MSP.

2013 CRWD Lakes Monitoring Report

32


5 CRWD LAKES RESULTS SUMMARY 5.1

OVERALL DISTRICT LAKES RESULTS

Table 5-1 shows the 2013 averages, historical averages, and lake standards for TP and Chl-a concentrations and Secchi depth for each lake. The data is shown graphically in Figures 5-1, 52, and 5-3. Overall, there were no broad trends for all lakes in comparison to historical averages. As stated in the methods, in order to meet the lake eutrophication standards, the lake needs to meet the TP standard and either the Chl-a standard or the Secchi depth standard. In 2013, Como Lake and Crosby Lake did not meet the standards. Little Crosby Lake, Loeb Lake, and Lake McCarrons all met the eutrophication standards. In 2013, CRWD determined lake grades for each of its lakes based on the lake grade system created by the Metropolitan Council (Table 5-2) (Osgood, 1989). Three out of the five CRWD lakes were given good to excellent lake grades, where Lake McCarrons received the highest grade of ‘A’ and both Loeb and Little Crosby received good grades of ‘B+’ and ‘B’, respectively. An average water quality grade of ‘C’ was given to Crosby Lake and Como Lake received the lowest grade of ‘D’. All five of the lakes were relatively close to their average historical grades (Table 5-2). Como, Crosby, and Loeb Lakes all decreased by a half of a grade point in water quality in 2013 compared to their historical average grade. Little Crosby Lake stayed the same and Lake McCarrons improved by a full grade point in 2013 compared to the historical average lake grade. Table 5-1: CRWD 2013 average, historical average, and lake standards for TP/Chl-a/Secchi depth. 2013 Averages

Historical Averages

State Lake Standards

Lake

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

Como

209

47.4

0.8

174

36.1

1.5

<60

<20

≥1.0

Crosby

96

10.6

1.6

68

13.3

2.0

<60

<20

≥1.0

Little Crosby

59.8

5.1

3.0

83

8.3

2.5

<60

<20

≥1.0

Loeb

27

7.4

3.0

24

4.5

3.3

<60

<20

≥1.0

McCarrons

20

4.1

3.3

34

10.0

2.9

<40

<14

≥1.4

Value does not meet the state standard Value meets the state standard

2013 CRWD Lakes Monitoring Report

33


Table 5-2: CRWD 2013 and historical lake grades and averages for TP/Chl-a/Secchi depth. Lake Como Crosby Little Crosby Loeb McCarrons

TP F D C B A

2013 Lake Grade Chl-a Secchi C D B C A B A B A A

2013 Average D C B B+ A

Historical Lake Grade TP Chl-a Secchi F C C C B C D A B B A A C A B

Historical Average D+ C+ B A B

In 2013, Wenck Associates, Inc. completed a comprehensive analysis of the historical chemical and physical data of all District lakes (Appendix 1). One valuable conclusion from this report was the need for additional data in order to understand the relationship between the numerous parameters that determine lake health. This report is formatted to include additional recommended data (i.e., biological parameters) and set up a framework for future years where more data can not only be reported upon, but can also be thoroughly analyzed. 5.2

SUMMARY OF INDIVIDUAL LAKES RESULTS

5.2.1 COMO LAKE

Como Lake has been monitored since 1984, so historical averages represent 29 years of data. Como Lake degraded in water quality for all three of the eutrophication parameters in 2013 in comparison to the historical average (Figures 5-1, 5-2, and 5-3). Como Lake has historically not met shallow lake state standards for TP and Chl-a concentrations. This was the case in 2013 as well. Como Lake has historically met shallow lake state water quality standards for Secchi depth, but did not in 2013. 5.2.2 CROSBY LAKE

Crosby Lake has been monitored since 2005, so historical averages represent eight years of data. Crosby Lake degraded in water quality for TP concentration and Secchi depth, and improved in water quality for Chl-a concentration when compared to the historical average (Figures 5-1, 5-2, and 5-3). The 2013 average TP concentration (96 µg/L) was 41% higher than the historical average (68 µg/L). Crosby Lake has historically been impaired for TP concentration, which was also the case in 2013. Crosby Lake has historically met water quality standards for Chl-a concentration and Secchi depth, which was also true in 2013. Crosby Lake’s high historical TP average is primarily due to high TP measurements from 2009-2012. 5.2.3 LITTLE CROSBY LAKE

Little Crosby Lake has been monitored since 2011, so historical averages represent only two years of data. In 2013, Little Crosby Lake improved in water quality when compared to the historical averages for all three eutrophication parameters (Figures 5-1, 5-2, and 5-3). Little Crosby Lake has historically not met shallow lake standards for TP, but met standards for Chl-a and Secchi depth. However, in 2013, Little Crosby Lake met all three shallow lake standards. 2013 CRWD Lakes Monitoring Report

34


5.2.4 LOEB LAKE

Loeb Lake has been monitored annually since 2003 (with the exception of 2004), so historical averages represent nine years of data (2003, 2005-2012). In 2013, Loeb Lake degraded in water quality when compared to the historical averages of all three water quality parameters (Figures 51, 5-2, and 5-3). The 2013 average Chl-a concentration (7.4 µg/L) was 64% higher than the historical average (4.5 µg/L). Loeb Lake has historically met all of the shallow lakes standards. Although the lake had poorer water quality in 2013 compared to previous years, the lake still met the eutrophication standards. 5.2.5 LAKE MCCARRONS

Lake McCarrons has been monitored annually since 1988, so historical averages represent 25 years of data. The lake improved in water quality in 2013 when compared to the historical average for all parameters (Figures 5-1, 5-2, and 5-3). The 2013 average TP concentration (20 µg/L) was 41% lower than the historical average (34 µg/L). The 2013 average Chl-a concentration (4.1 µg/L) was 59% lower than the historical average (10.0 µg/L). Lake McCarrons met the all of the deep lakes standards in 2013; the historical averages met all but two of the deep lake standards as well.

2013 CRWD Lakes Monitoring Report

35


250 Historical Average

2013

CRWD Historical Averages Como (1984 - 2012) McCarrons (1988 - 2012) Crosby (2005 - 2012) Loeb (2003 - 2012) Little Crosby (2011 - 2012)

200

Total Phosphorus Concentration (Âľg/L)

Shallow Lakes Standard Deep Lakes Standard

150

100

50

0 Como

Crosby

Little Crosby

Loeb

McCarrons

Figure 5-1: CRWD 2013 vs. historical average TP concentrations and lake standard comparisons. 2013 CRWD Lakes Monitoring Report

36


50 Historical Average

45

2013

CRWD Historical Averages Como (1984 - 2012) McCarrons (1988 - 2012) Crosby (2005 - 2012) Loeb (2003 - 2012)

40

Chlorophyll-a Concentration (Âľg/L)

Shallow Lakes Standard Deep Lakes Standard 35

30

25

20

15

10

5

0 Como

Crosby

Little Crosby

Loeb

McCarrons

Figure 5-2: CRWD 2013 vs. historical average Chl-a concentrations and lake standard comparisons. 2013 CRWD Lakes Monitoring Report

37


Como

Crosby

Little Crosby

Loeb

McCarrons

0.0

0.4

0.8

Secchi Depth (meters)

1.2

1.6

2.0

2.4 Historical Average 2.8

2013

CRWD Historical Averages Como (1984 - 2012) McCarrons (1988 - 2012) Crosby (2005 - 2012) Loeb (2003 - 2012)

Shallow Lakes Standard 3.2

Deep Lakes Standard

3.6

Figure 5-3: CRWD 2013 vs. historical average Secchi depths and lake standard comparisons. 2013 CRWD Lakes Monitoring Report

38


Como Lake

6 COMO LAKE RESULTS 6.1

COMO LAKE BACKGROUND

Figure 6-1: View of the northwest shoreline of Como Lake.

Como Lake, a 70.5 acre shallow lake located in St. Paulâ&#x20AC;&#x2122;s 348 acre Como Regional Park, is one of the most popular lakes in the area. In 2012, Como Regional Park was the second most frequently visited park in the Twin Cities Regional Parks System, with almost 4.5 million visits over the course of the year (MC, 2013). The lake is frequented by residents and visitors who come for various forms of outdoor recreation, including running/walking and fishing. The lake does not offer swimming opportunities and only allows non-motorized cartop-carried boats and electric trolling motors on the lake for fishing/recreation purposes.

2013 CRWD Lakes Monitoring Report

39


Como Lake

With a volume of 468.8 acre-ft, a littoral area that covers 100% of the lake, and a maximum depth at 15.5 ft (one of two deep areas of the lake), Como is a typical shallow urban lake (Table 6-1; Figure 6-2). Como Lake receives water from the surrounding watershed (1,856 acres), which consists of runoff from residential areas including houses and streets, as well as from Como Golf Course (also located within Como Park). Runoff from the residential areas is directed to the lake through a system of stormwater pipes located under the streets. Located upstream of Como Lake, Gottfried’s Pit receives drainage from Roseville, Falcon Heights, Ramsey County right-of-ways, and the City of St. Paul before being pumped into Como Lake. Water occasionally outflows from the lake at the southeast corner, discharging into the Trout Brook storm sewer system which is routed to the Mississippi River (CRWD, 2002). The shallow depth of the lake, coupled with the large nutrient inputs from upland runoff sources, has had significant negative impacts to the lake’s health. One of the largest problems Como Lake faces is the excessive amount of sediment entering the lake from construction, roads, and general erosion. This has led to the formation of sediment deltas near stormwater inlets to the lake, which reduces overall lake volume, increases water turbidity, and decreases habitat value for the lake’s fish populations. Sediment also provides a means by which other pollutants, including metals and hydrocarbons, can be transported to the lake. To address this problem, in 2001-2002, the lake was dredged to reduce the sediment deltas seen on the southwest side of the lake. This dredging reduced the amount of sediment that had accumulated in the lake and increased lake volume, giving the lake a higher capacity to absorb nutrient inflows. In addition, low oxygen levels during winter months caused partial fish kills dating back to 1945, leading Ramsey County to install an aerator in 1985 (CRWD, 2002). Renovation and a complete restocking of the fish populations in the lake occurred in 1985 after installation of the aerator in an effort to improve water quality through biomanipulation. Fish kills are now a rare occurrence in the lake, resulting only if there is equipment failure or an especially cold winter. Various shoreline improvement projects have been completed on the lake since 2003 by the City of St. Paul and Ramsey Conservation District, with help from CRWD and other organizations. These projects have stabilized the shoreline, reduced erosion, increased habitat for wildlife, replaced non-native invasive plants with native species and improved the aesthetics of the shoreline for visitors. Harvesting of aquatic plants has occurred at various times since the 1980s in order to enhance recreational opportunities. Numerous BMPs have been installed by CRWD, the City of St. Paul, and others in the Como Lake subwatersheds to reduce pollutant loading to the lake. Starting in 2007, the ArlingtonPascal Stormwater Improvement Project was constructed upland of Como Lake, which consisted of a series of BMPs including raingardens, infiltration trenches, an underground facility, and stormwater ponds. Improvements in water quality have been measured in the lake since the completion of the project. More information about these BMPs may be found in the CRWD Stormwater BMP Performance Assessment and Cost-Benefit Analysis (CRWD, 2012b). Despite this upland watershed restoration, Como Lake is still a hypereutrophic lake and is listed on the MPCA’s 2012 303(d) list of impaired waters (MPCA, 2012). Como Lake was first listed 2013 CRWD Lakes Monitoring Report

40


Como Lake

in 1998 for mercury in fish tissue (TMDL plan approved in 2008) and in 2002 for nutrient/eutrophication biological indicators (TMDL plan approved in 2010) (MPCA, 2012). Odor problems due to end of summer algal blooms also continue to be a problem (and have been recorded since 1945). It is hypothesized that the water quality (referring to the TP, Chl-a, and Secchi disk depth) in Como Lake displays a cyclical trend, fluctuating every five to six years between fair and poor water quality (Figure 6-6) (Noonan, 1998). This suggests that the interactions among the biological, chemical, and physical parameters of the lake need to be better understood in order to make informed management decisions to improve the lakeâ&#x20AC;&#x2122;s health. Table 6-1: Como Lake morphometric data. Surface Area (acres)

Maximum Depth (ft)

Littoral Area

Volume (acre-ft)

Watershed Area (acres)

Watershed: Lake Area (ratio)

70.5

15.5

100%

469

1,856

26.3

Figure 6-2: Como Lake bathymetric map. 2013 CRWD Lakes Monitoring Report

41


Como Lake

6.2

LAKE LEVEL

The level of Como Lake has fluctuated around the OHWL (881.4 ft) since monitoring of the lake level began in 1978, varying between 879.2 ft to 883.5 ft, a range of 4.3 ft. The lowest of the range extremes occurred in June 1987, and the highest occurred in October of 2007 (Figure 6-3). The average level for 2013 was 881.3 ft indicating that, on average, normal fluctuations in water level were seen for the lake in 2013. Water level increased from January until the maximum level in July, then decreased from August to September during an extended dry period. Lake levels peaked again in October following a large precipitation event on October 2 (Figure 6-4).

884 Lake Elevation OHWL 883

Elevation (ft above mean sea level)

OHWL is 881.4 ft

882

881

880

879 1978

1983

1988

1993

1998

2003

2008

2013

Year

Figure 6-3: Como Lake historical lake elevations.

2013 CRWD Lakes Monitoring Report

42


Como Lake 883.0

0

1 882.5 Daily Precipitation Total

2

OHWL 3

882.0 OHWL is 881.4 ft

4

881.5

5

Precipitation (inches)

Elevation (ft above mean sea level)

Lake Elevation

6 881.0 7

880.5

8 Jan

Feb

Mar

Apr

May

Jun

Jul Month

Aug

Sep

Oct

Nov

Dec

Figure 6-4: Como Lake 2013 lake elevations and precipitation.

6.3

WATER QUALITY RESULTS

During 2013, Como Lake was sampled eight times from May 3 to September 16 (Figure 6-5). As in previous years, Como Lake was characterized by high TP and Chl-a concentrations, and low Secchi depths. Sampling shows that TP concentrations were lower in the epilimnion of the lake during the beginning of the season (early May to mid-July) than at the end of the season (mid-July to mid-September). The average TP concentration for the first four samples (127 µg/L) was 129% lower than the average of the last four samples (291 µg/L), indicating a strong decrease in water quality between the beginning and the end of the monitoring season. This could be the result of higher rainfall and lower temperatures in the earlier part of the year, as well as potential increased loading from the end of July to September. Epilimnetic Chl-a concentrations exhibited a similar trend. Concentrations at the beginning of the season (35.1 µg/L) were 70% lower than the concentrations at the end of the season (59.6 µg/L). Water transparency peaked in mid-May (Secchi depth of 1.2 m) and generally decreased throughout the remainder of the season. During 2013, higher TP concentrations were generally correlated with higher Chl-a concentrations and lower Secchi depths. This suggests that phosphorus was a primary driver for water clarity in Como Lake during 2013. 2013 CRWD Lakes Monitoring Report

43


Como Lake

Figure 6-6 shows yearly average historical TP concentrations, Chl-a concentrations, and Secchi disk depths graphically. In general, Como Lake has seen overall improvements in water quality since monitoring began in 1984, though each parameter tends to fluctuate annually. It is hypothesized that the lake is cyclic in water quality and biological response (Noonan, 1998), fluctuating between poor and fair water quality generally every five to six years (Figure 6-6). Total phosphorus concentration increased from 2009-2012 and decreased in 2013. Chlorophyll-a concentration has remained relatively fixed over the last four years. Secchi depth was at its deepest in recent years in 2008-2009, but has become shallower since then. The 2013 Secchi depth, however, was 14% deeper than the 2012 Secchi depth. Similar to 2013, the Secchi depth was inversely proportional to TP concentration during the period of record for Como Lake, indicating that phosphorus has consistently been a primary driver for water clarity. Yearly average historical TP concentrations, Chl-a concentrations, Secchi depths, and their comparisons to lake standards are shown in Table 6-2. Como Lake TP yearly average concentrations have exceeded the MPCA standards for all years of monitoring. Chl-a concentrations have also exceeded the standard for the majority of years monitored. Conversely, almost three-quarters of the historical Secchi depth yearly averages met the standards. In 2013, CRWD issued a ‘D’ grade for Como Lake based on the average eutrophication parameters (Table 6-3). In other years, the lake mainly received grades of ‘C’ and ‘D’, with only two years in 1998 and 1999 receiving a ‘B’ grade.

2013 CRWD Lakes Monitoring Report

44


Como Lake 3-May

17-May

7-Jun

3-Jul

23-Jul

9-Aug

0

26-Aug

16-Sep 400

350

300

Secchi Depth (meters)

2 250

3

200

150 4

100

Total Phosphorus and Chlorophyll-aConcentrations (Âľg/L)

1

5 50

6

0 Secchi

TP

Chl-a

Figure 6-5: Como Lake 2013 Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

45


Secchi Depth (meters)

Secchi TP

1 300

2 250

3 200

150

4 100

5 50

6 0

Chl-a

Figure 6-6: Como Lake historical Secchi/TP/Chl-a comparison.

2013 CRWD Lakes Monitoring Report 46

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

0 2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

1992

1991

1990

1989

1988

1987

1986

1985

1984

Como Lake

400

350


Como Lake Table 6-2: Como Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. Year

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

1982

219

67.7

0.7

1984

190

98.7

0.6

1985

225

101.0

0.5

1986

310

38.7

1.1

1987

186

78.0

2.7

1988

137

24.6

2.0

1989

152

24.7

2.0

1990

198

49.3

0.9

1991

224

43.9

0.8

1992

152

26.8

1.2

1993

108

21.8

2.2

1994

121

29.0

1.7

1995

255

51.2

1.4

1996

276

57.6

1.2

1997

141

37.6

1.2

1998

104

9.2

3.2

1999

112

11.3

3.2

2000

133

19.6

2.1

2001

345

36.7

1.2

2002

147

29.2

1.7

2003

161

20.8

1.1

2004

106

13.3

1.8

2005

155

28.3

1.3

2006

138

31.8

1.0

2007

110

23.3

1.1

2008

81

10.4

2.1

2009

83

8.1

2.0

2010

141

39.7

1.2

2011

224

41.8

2012

338

41.5

1.0 0.7

2013

209

47.4

0.8

Value does not meet state standard* Value meets state standard *MPCA shallow lake standards are not to exceed 60 µg/L for TP and 20.0 µg/L for Chl-a, w ith a Secchi disk depth of at least 1.0 m.

2013 CRWD Lakes Monitoring Report

47


Como Lake Table 6-3: Como Lake historical lake grades. Year

TP Grade

Chl-a Grade

Secchi Grade

Overall Grade

1982

F

D

F

F

1984

F

F

F

F

1985

F

F

F

F

1986

F

C

D

D

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

F D D F F D D D F F D D D D F D F D F D D D D D F F F

F C C D C C C C D D C A B B C C C B C C C B A C C C C

B C C D D D B C C C C A A C D C D C C D D C C C D D D

D C C D D D+ C C D D C B B C D C D C D+ D+ D+ C C+ C D D D

2013 CRWD Lakes Monitoring Report

48


Como Lake

6.4

PHYTOPLANKTON AND ZOOPLANKTON

During 2013, Como Lake was sampled for phytoplankton and zooplankton eight times from May 3 to September 16. In 2013, Cyanophyta (blue-green algae) increased in relative abundance from June through the end of the monitoring season in September when it became the dominant type observed (Figure 6-9). Chlorophyta (green algae) remained a major part of the community throughout most of the monitoring season, with the highest levels at the beginning of July. The species dominance of green and blue-green algae was attributed to the steady increase in TP during the same time period (Kalff, 2002). With higher levels of available nutrients, increases in these types of phytoplankton are common. Overall phytoplankton concentrations decreased from June through the end of August, and then increased again in September. This is characteristic of algal blooms dominated by green and blue-green algae. Total phytoplankton concentration was at its highest at the beginning of July when zooplankton concentrations were lowest (Figures 6-7 and 6-8). Zooplankton communities in Como Lake were dominated by Rotifers from May through early June (Figure 6-10). Cladocerans dominated from May through the end of the monitoring season at the end of September. Cladocerans, including the genus Daphnia, are important filter feeders in lake environments. Overall zooplankton density peaked in mid-May, was at its lowest at the beginning of July, and then increased again during August and September (Figure 6-8). Other orders of zooplankton were only present in low numbers throughout the year.

2013 CRWD Lakes Monitoring Report

49


Como Lake 400

12 Total Phytoplankton Concentration TP

350

300

8 250

6

200

150 4

Total Phosphorus Concentration (Âľg/L)

Total Phytoplankton Concentration (1,000/mL)

10

100

2 50

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 6-7: Como Lake 2013 total phytoplankton concentration and TP concentration. 350

90 Total Zooplankton Density Chl-a 80

300

250 60

200

50

40

150

30

Chlorophyll-a Concentration (Âľg/L)

Total Zooplankton Density (1,000/m^3)

70

100 20 50 10

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 6-8: Como Lake 2013 total zooplankton density and Chl-a concentration. 2013 CRWD Lakes Monitoring Report

50


Como Lake 100%

90%

Phytoplankton Relative Abundance

80%

70%

60% Cyanophyta Cryptophyta

50%

Chrysophyta Chlorophyta

40%

Bacillariophyta

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 6-9: Como Lake 2013 phytoplankton relative abundance. 100%

90%

80%

Zooplankton Relative Abundance

70%

60% Cladocera Rotifera

50%

Nauplii Calanoida

40%

Cyclopoida

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 6-10: Como Lake 2013 zooplankton relative abundance. 2013 CRWD Lakes Monitoring Report

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Como Lake

6.5

AQUATIC VEGETATION

6.5.1 BIOVOLUME ANALYSIS

As shown by the biovolume heat map of vegetation in Como Lake, the majority of the lake vegetation occurs along the shorelines, with particularly heavy vegetation on a few specific parts of the northwest and northeast shorelines (Figure 6-11). Overall, Como Lake does not have extensive aquatic vegetation, which could be contributing to poor water quality in the lake. Aquatic plants stabilize bottom sediment which prevents re-suspension of sediments that decreases water clarity (DNR, 2014f). Aquatic plants also intake nutrients for growth, making those nutrients unavailable for use by algae, which reduces algal overabundance and improves water quality.

Figure 6-11: Como Lake 2013 biovolume heat map.

6.5.2 POINT-INTERCEPT SURVEYS

In June of 2013, plant species observed in Como Lake were Canada waterweed, filamentous algae, coontail, curly-leaf pondweed, and slender naiad (Figure 6-12). The species occurring at the most locations throughout the lake in July were Canada waterweed, filamentous algae, flatstem pondweed, and coontail (with sago pondweed, lesser duckweed, and blue-green algae seen at only 4% of the locations). Sago pondweed, while not observed at many locations, was the most abundant where it was seen (Figure 6-13). Other species exhibited average abundance rankings. The presence of Eurasian watermilfoil has not yet been observed in Como Lake.

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Como Lake

The dominant species in June was curly-leaf pondweed (Figure 6-12). As a result of its normal die-back by mid-summer, however, it was absent by the end of July. Curly-leaf pondweed has been observed in vegetation surveys since 2010. This non-native invasive species causes problems by displacing other native plants and forming thick mats on the surface of a lake that disrupt boating and recreation. In addition, when the plants die back in mid-summer, the resulting increase in phosphorus from the decomposing plant material causes disruptive algal blooms (DNR, 2005).

100 6/6/2013 7/24/2013

Percent Occurrence

80

60

40

20

0

Figure 6-12: Como Lake 2013 percent occurrence of vegetation present.

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Como Lake 5 6/6/2013 7/24/2013

Average Abundance Ranking

4

3

2

1

0

Figure 6-13: Como Lake 2013 average abundance ranking of vegetation present.

6.6

FISH STOCKING AND SURVEYS

Fish stocking in Como Lake has focused on bluegill and channel catfish (primary management species for the lake) (Table 6-4). Como Lake is part of the Minnesota DNR’s “Fishing in the Neighborhood” program, which increases angling opportunities for children and families in urban environments, encourages environmental stewardship, and improves knowledge of natural resources (DNR, 2014e). Therefore, these lakes are generally stocked with fish that are better for general angling activities. As a result, numbers of black crappie and bluegill observed were generally higher in the last survey of Como Lake completed in 2011 by the Minnesota DNR (Table 6-5). A wide variety of panfish were present in the lake, as well as a few kinds of piscivorous fish (i.e., northern pike). The next survey date by the Minnesota DNR for Como Lake is set for 2016.

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Como Lake Table 6-4: Como Lake historical record of fish stocking. Year

Bluegill Adult

Channel catfish

Largemouth bass

Adult

Adult

Yearling

Walleye

Yearling

Yearling

Yellow perch

Fingerling

2013

Adult

Yearling

816

1200

486

2011

124

3900

91

3900

24

2010

3593 4

3457

2009 2008 2007

284

2006

1384

155

4502

150

3864

179

414

2005 2004

959

Table 6-5: Como Lake 2011 fish populations. Species

Number of fish caught in each category (inches) 0-5

6-8

9-11

12-14

15-19

20-24

25-29

30+

Total

Black bullhead

0

50

20

1

0

0

0

0

71

Black crappie

103

160

2

0

0

0

0

0

272

Bluegill

201

31

0

0

0

0

0

0

237

Channel catfish

0

0

7

7

2

1

1

0

19

Golden shiner

2

0

0

0

0

0

0

0

2

Hybrid sunfish

9

0

0

0

0

0

0

0

9

Northern pike

0

0

0

0

3

35

10

1

49

Pumpkinseed sunfish

29

0

0

0

0

0

0

0

29

Walleye

0

0

0

0

3

2

0

0

5

White sucker

0

0

0

0

3

0

0

0

3

Yellow bullhead

0

23

9

1

0

0

0

0

33

10

5

0

0

0

0

0

0

16

Yellow perch

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Como Lake

6.7

OVERALL LAKE EVALUATION

Como Lake experiences a cyclic variation in water quality and biological response (Noonan, 1998), fluctuating between poor and fair water quality generally every five to six years. The period of record indicates that phosphorus has consistently been a primary driver for water clarity. It has historically not received very high lake grades, indicating lower user quality. The lake generally supports a fair variety of fish, but does not contain a significant amount of aquatic vegetation. Previous reporting on Como Lake focused on an analysis of TP, Chl-a, and Secchi depth trends over the monitoring season and compared to past monitoring years. Conversely, this report contains more extensive information on lake history, lake morphometric data, lake level, additional water quality analysis (i.e., lake grading), phytoplankton and zooplankton populations, aquatic vegetation communities, and fish populations. For this yearâ&#x20AC;&#x2122;s report, this information was solely reported upon, but not analyzed for trends or relationships between parameters. A more robust analysis will be done in future monitoring reports that examines the interactions between all parameters monitored in order to present a picture of the overall health of Como Lake.

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Crosby Lake

7 CROSBY LAKE RESULTS 7.1

CROSBY LAKE BACKGROUND

Figure 7-1: View of the southwest shoreline of Crosby Lake.

Crosby Lake is situated within Crosby Farm Regional Park in Saint Paul and is also a part of the Mississippi River National River and Recreation Area (part of the National Park Service) (CRWD, 2012a). The park itself is 736 acres and consists of floodplain and bluff areas. It offers various outdoor activities for fishing, canoeing, walking, hiking and winter cross-country skiing. The park has diverse wetland and forest habitats that support a large variety of plants, trees, and wildlife. Crosby Lake is 45 acres and has a maximum depth of 17 ft with a 100% littoral area (Table 7-1; Figure 7-2). It is located in the floodplain area of the park between a large bluff and the main channel of the Mississippi River.

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Crosby Lake

Water flows into the lake during high water periods from wetlands on the east and north sides via culverts. Seepage from the base of the bluff (consisting of sandstone and limestone) is also an input to Crosby Lake. The major groundwater input to the lake comes from the St. Peter aquifer to the west. CRWD developed a lake management plan for Crosby Lake that assessed the current condition of the Lake and characteristics of its watershed, identified the issues of greatest concern, and established management goals and an implementation plan for addressing identified issues (CRWD, 2012a). A key piece of understanding that came out of the plan was the interaction between Crosby Lake and the Mississippi River. As Crosby Lake sits within the floodplain of the Mississippi River, it is intermittently flooded during periods of high water. The normal water level (or ordinary water level) of the lake is 694 ft. The normal pool elevation of the river is 687 ft (CRWD, 2012a). Therefore, under normal, non-flood conditions, groundwater flows from the lake to the river. The lake does not normally directly output to the river. Under high water conditions, however, the river will overflow to the lake near the northeast corner. CRWD determined that a 49,000 cfs flow (equivalent of a stage of 697 ft) would cause an exchange between the river and the lake to occur, equating to a 3-year storm event (meaning that this has a 33% chance of occurring each year) (CRWD, 2012a). Looking at the historical record since 1982, only 2.5% of recorded river flows have been high enough for an exchange to occur. During these exchanges, the water bodies interchange not only water, but nutrients, other pollutants, and biological organisms contained within. Since the start of development of the Crosby Lake Management Plan, a number of water quality improvement projects have been implemented by CRWD, the City of Saint Paul and others to reduce stormwater runoff to Crosby Lake. In 2010, the City of Saint Paul installed filtration swales as part of the reconstruction of the Samuel Morgan pedestrian and bikeway trails along Shepard Road. CRWD provided the City of Saint Paul a grant in 2012 for the installation of a rain garden and swale during the reconstruction of the east end parking lot in Crosby Farm Regional Park. In addition, CRWD supports the Friends of Mississippi Riverâ&#x20AC;&#x2122;s efforts to restore the native prairie areas in Crosby Farm Regional Park. Lastly, as part of the reconstruction of the Madison-Benson Streets area near Crosby Lake in 2013, the City of Saint Paul constructed boulevard tree trench systems and rain gardens to treat street and sidewalk runoff. Management efforts need to take into account the dynamic relationship between the lake and the river. Although water quality has been good in the past, with TP concentrations below the state standards, recent years have shown increasing TP concentrations that have surpassed the standard (Figure 7-4; Table 7-2). The source of these high nutrient concentrations could be from high flow periods of the Mississippi river where large sediment loads enter the lake. For example, the lake was inundated by the river for 103 days in 2011 (Appendix A â&#x20AC;&#x201C; Table 8). Water quality data observed in the years following the inundation showed average TP concentrations well above the normal historical values (Figure 7-4; Table 7-2). From a management perspective, this relationship could make it hard to control and improve Crosby Lake water quality.

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Crosby Lake Table 7-1: Crosby Lake morphometric data. Surface Area (acres)

Maximum Depth (ft)

Littoral Area

Volume (acre-ft)

Watershed Area (acres)

Watershed: Lake Area (ratio)

45.0

17.0

100%

130

197

4.4

Figure 7-2: Crosby Lake bathymetric map.

7.2

LAKE LEVEL

There is no historical lake level data for Crosby Lake from the Minnesota DNR. CRWD will begin monitoring Crosby Lake level in 2014.

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Crosby Lake

7.3

WATER QUALITY RESULTS

Crosby Lake was sampled eight times during 2013, from May 14 to September 25 (Figure 7-3). As in previous years, Crosby Lake was characterized by high TP concentrations, but moderate Chl-a concentrations and Secchi depths. Samples show TP concentrations in the lake exceeded state standards throughout the monitoring season but were lowest at the beginning (May 14) and end (September 25), with an average concentration of 65 µg/L. The six samples taken June 4 to September 4 averaged 107 µg/L; 65% higher than the beginning/end-of-season average. Epilimnetic Chl-a concentrations varied throughout the year, with a peak in late August; the only time the state standard was exceeded. Water transparency peaked on June 4 (exhibiting a Secchi depth of 3.2 m), decreased until mid-July, and remained relatively constant until the end of the growing season (with a Secchi depth average of 1.3 m). During 2013, fluctuations in Chl-a concentration were not generally associated with fluctuations in TP concentration. The trend in Secchi depth was not associated with TP or Chl-a concentrations. This suggests that factors in addition to phosphorus were contributing to algal growth and changes in water transparency in Crosby Lake during 2013. Figure 7-4 shows yearly average historical TP concentrations, Chl-a concentrations, and Secchi disk depths graphically. Crosby Lake has been characterized by high epilimnetic TP concentrations over the last four years. The average TP concentration from 2005-2009 was 41.2 µg/L, while the average TP concentration from 2009-2013 was 108.7 µg/L, a 164% increase from the previous time period. Chlorophyll-a concentrations were markedly high in 2011 (44.3 µg/L), whereas concentrations in 2012 (6.9 µg/L) and 2013 (10.6 µg/L) were closer to the 20052009 average (7.44 µg/L). In the first year Crosby Lake was monitored (2005) the Secchi depth average was the deepest on record at 3.2 m. Since then, Secchi depths have fluctuated annually but have generally decreased as Chl-a concentrations increased. It is noteworthy that despite a record TP concentration average in 2012, the yearly average Chl-a concentration and Secchi depths were similar to 2006-2009 values (years with lower TP concentrations). These trends suggest Crosby Lake Chl-a concentrations have drivers other than phosphorus alone. However, the data suggests that water clarity is principally affected by Chl-a concentration during the period of record. Yearly average historical TP concentrations, Chl-a concentrations, Secchi depths, and their comparisons to lake standards are shown in Table 7-2. Crosby Lake met the standards for all three parameters from 2005-2009 (Table 7-2). From 2010-2013, however, it exceeded the standards for TP, and also for Chl-a in 2011. Crosby Lake has historically ranged between a lake grade of ‘B+’ and ‘C’ (Table 7-3). The most recent grades (2010-2013) have been a ‘C’ as a result of the high TP concentrations during this time period.

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Crosby Lake 4-Jun

25-Jun

16-Jul

1-Aug

19-Aug

4-Sep

25-Sep 140

120

1

100

Secchi Depth (meters)

2

80 3 60

4 40

5

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

14-May 0

20

0

6 Secchi

TP

Chl-a

Figure 7-3: Crosby Lake 2013 Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

61


0

2013

2012

2011

2010

2009

2008

140

120

1

100

Secchi Depth (meters)

2

80 3 60

4 40

5

20

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

2007

2006

2005

Crosby Lake

0

6 Secchi

TP

Chl-a

Figure 7-4: Crosby Lake historical Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

62


Crosby Lake Table 7-2: Crosby Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. Year

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

2005

50.0

2.5

3.2

2006

49.5

5.2

2.1

2007

39.3

10.4

2.1

2008

39.0

9.2

1.9

2009

28.0

9.9

2.0

2010

91.0

17.6

1.4

2011

122.0

44.3

1.3

2012

125.7

6.9

2.0

96.0

10.6

1.6

2013

Value does not meet state standard* Value meets state standard *MPCA shallow lake standards are not to exceed 60 µg/L for TP and 20.0 µg/L for Chl-a, w ith a Secchi disk depth of at least 1.0 m.

Table 7-3: Crosby Lake historical lake grades. Year 2005 2006 2007 2008 2009 2010 2011 2012 2013

TP Grade C C C C B D D D D

Chl-a Grade A A B A A B C A B

Secchi Grade A C C C C C C C C

Overall Grade B+ B C+ B B C C C+ C

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Crosby Lake

7.4

PHYTOPLANKTON AND ZOOPLANKTON

Crosby Lake was sampled for phytoplankton and zooplankton eight times during 2013 from May 14 to September 25. There was a diverse phytoplankton community during May and June, with a larger population of Euglenophyta observed during June (Figure 7-7). From mid-July through late September the community was dominated by Chlorophyta. Total concentration of phytoplankton had multiple peaks throughout the summer corresponding to low zooplankton concentrations (Figures 7-5 and 7-6). A large bloom in phytoplankton concentration occurred at the end of August (Figure 7-5). Cladoceran (important lake filter-feeders including the order Daphnia) populations were the most prominent zooplankton type from May until August (Figure 7-8). Populations of Cladocerans, Rotifers, Nauplii, and Calanoids were observed in the remaining months of the year. Overall zooplankton concentration had peaks in May, June, and July (Figure 7-6).

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Crosby Lake 12

140 Total Phytoplankton Concentration TP

Total Phytoplankton Concentration (1,000/mL)

100 8

80 6 60

4 40

2

Total Phosphorus Concentration (Âľg/L)

120

10

20

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 7-5: Crosby Lake 2013 total phytoplankton concentration and TP concentration. 30

350 Total Zooplankton Density Chl-a

25

250 20

200 15 150

10 100

Chlorophyll-a Concentration (Âľg/L)

Total Zooplankton Density (1,000/m^3)

300

5

50

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 7-6: Crosby Lake 2013 total zooplankton density and Chl-a concentration. 2013 CRWD Lakes Monitoring Report

65


Crosby Lake 100%

90%

Phytoplankton Relative Abundance

80%

70%

60%

Pyrrhophyta Euglenophyta Cyanophyta

50%

Cryptophyta Chrysophyta

40%

Chlorophyta Bacillariophyta

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 7-7: Crosby Lake 2013 phytoplankton relative abundance. 100%

90%

80%

Zooplankton Relative Abundance

70%

60% Cladocera Rotifera

50%

Nauplii Calanoida

40%

Cyclopoida

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 7-8: Crosby Lake 2013 zooplankton relative abundance. 2013 CRWD Lakes Monitoring Report

66


Crosby Lake

7.5

AQUATIC VEGETATION

7.5.1 BIOVOLUME ANALYSIS

As viewed in the biovolume heat map of vegetation for Crosby Lake, aquatic vegetation makes up a majority of the lakeâ&#x20AC;&#x2122;s water column (higher vegetation areas are denoted with red, where no vegetation is shown as blue) (Figure 7-9). In the deeper middle of the lake there are small pockets of vegetation (indicated as green on the map).

Figure 7-9: Crosby Lake 2013 biovolume heat map.

7.5.2 POINT-INTERCEPT SURVEYS

In June, dominant vegetation species on Crosby Lake included lesser duckweed, white water lily, sago pondweed and filamentous algae (all receiving average abundance rankings) (Figure 7-10; Figure 7-11). By July, the most abundant species had changed to coontail, star duckweed, and filamentous algae. Coontail had the highest average abundance in June and July, making it one of the dominant plant species in the lake. Filamentous algae was another dominant plant, observed during both months monitored with a modestly high average abundance ranking. The presence of Eurasian watermilfoil has not yet been observed in Crosby Lake. However, curly-leaf pondweed appeared for the first time in the 2013 survey. While it was not found at many locations in the lake in 2013 (Figure 7-10) and was not overly abundant at the locations in which it was found (Figure 7-11), this is still an undesirable species to see emerge. Curly-leaf 2013 CRWD Lakes Monitoring Report

67


Crosby Lake

pondweed is a non-native invasive species. It causes problems by displacing other native plants and forming thick mats on the surface of a lake that disrupt boating and recreation (DNR, 2005). In addition, when the plants die back in mid-summer, the resulting increase in phosphorus from the decomposing plant material causes disruptive algal blooms (DNR, 2005).

100 6/13/2013 7/25/2013

Percent Occurrence

80

60

40

20

0

Figure 7-10: Crosby Lake 2013 percent occurrence of vegetation present.

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Crosby Lake 5 6/13/2013 7/25/2013

Average Abundance Ranking

4

3

2

1

0

Figure 7-11: Crosby Lake 2013 average abundance ranking of vegetation present.

7.6

FISH STOCKING AND SURVEYS

Crosby Lake does not have a history of fish stocking by the Minnesota DNR. The last survey of fish populations in Crosby Lake was completed in 2004 by the Minnesota DNR (Table 7-4). As the DNR does not stock this lake, populations observed are naturally present in the lake, and are influenced by overflow from the Mississippi River during high water levels. The largest population of fish observed was bluegills, followed by pumpkinseed sunfish. This indicates that previously in Crosby Lake, a majority of the fish were planktivorous panfish. Northern pike were also seen in moderate abundance. Dogfish, common carp, golden shiner, and white sucker were also found in low abundance in Crosby Lake during the 2004 survey, but were not measured for length to include in Table 7-4 (DNR, 2014g). Crosby Lake is scheduled to be surveyed again in the summer of 2014.

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Crosby Lake Table 7-4: Crosby Lake 2004 fish populations. Species

Number of fish caught in each category (inches)

Total

0-5

6-8

9-11

12-14

15-19

20-24

25-29

30+

Black bullhead

0

1

4

0

0

0

0

0

5

Black crappie

15

4

0

0

0

0

0

0

19

Bluegill Hybrid sunfish

108

20

0

0

0

0

0

0

128

8

2

0

0

0

0

0

0

10

Northern pike Pumpkinseed sunfish Yellow bullhead Yellow perch

7.7

0

0

0

0

11

12

4

1

28

59

1

0

0

0

0

0

0

60

0

3

0

0

0

0

0

0

3

0

2

0

0

0

0

0

0

2

OVERALL LAKE EVALUATION

In 2013, Crosby Lake showed trends in Secchi disk depth that were not associated with TP or Chl-a concentrations. This suggests that factors in addition to phosphorus were contributing to algal growth and changes in water transparency in Crosby Lake during the year. In addition, the average yearly TP concentration of the lake was markedly higher in recent years (2010-2013). Historically, Crosby Lake has received average lake grades, indicating that it generally has average water quality. The lake contained extensive vegetation during the 2013 surveys and average populations of planktivorous fish. Previous reporting on Crosby Lake focused on an analysis of TP, Chl-a, and Secchi depth trends over the monitoring season and compared to past monitoring years. Conversely, this report contains more extensive information on lake history, lake morphometric data, lake level, additional water quality analysis (i.e., lake grading), phytoplankton and zooplankton populations, aquatic vegetation communities, and fish populations. For this yearâ&#x20AC;&#x2122;s report, this information was solely reported upon, but not analyzed for trends or relationships between parameters. A more robust analysis will be done in future monitoring reports that examines the interactions between all parameters monitored in order to present a picture of the overall health of Crosby Lake.

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Little Crosby Lake

8 LITTLE CROSBY LAKE RESULTS 8.1

LITTLE CROSBY LAKE BACKGROUND

Figure 8-1: View of the southeast shoreline of Little Crosby Lake.

Little Crosby Lake is 8 acres with an average depth of 7 ft and a maximum depth of 34 ft. Little Crosby Lake is a shallow lake with a littoral area of 88% (Table 8-1). Little Crosby Lake is connected to Crosby Lake through a marsh/bog area 825 ft long. For information on Little Crosby Lake Background, see Crosby Lake Background (page 63). Little Crosby Lake has only been monitored since 2011. In the past three years of monitoring for TP, it exceeded the state standard in 2011-2012 and was at the standard limit in 2013 (Table 82). The source of these high nutrient concentrations could be from high flow periods of the river, bringing large sediment loads into the lake, which is hard to manage and control. 2013 CRWD Lakes Monitoring Report

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Little Crosby Lake Table 8-1: Little Crosby Lake morphometric data. Surface Area (acres)

Maximum Depth (ft)

Littoral Area

Volume (acre-ft)

Watershed Area (acres)

Watershed: Lake Area (ratio)

8.0

34.0

88%

59

37

4.6

8.2

LAKE LEVEL

There is no historical lake level data for Little Crosby Lake from the Minnesota DNR. CRWD will begin monitoring Crosby Lake level in 2014. General trends in lake level can be seen by looking at Crosby Lake level, as these two bodies of water are indirectly connected. 8.3

WATER QUALITY RESULTS

Little Crosby Lake was sampled eight times in 2013, from May 14 to September 25 (Figure 8-2). As in the previous two years, Little Crosby Lake was higher in TP concentrations, but these TP concentrations are relatively low when compared to Como and Crosby Lakes. It had low Chl-a concentrations and deep Secchi depths. Samples show epilimnetic TP concentrations peaked in late June to Mid-July and generally decreased through the end of the season. The Chl-a concentration peaked early to mid-August and decreased though the end of the season. Water clarity generally improved as the growing season progressed and always met the state standard. During 2013, the August peak in Chl-a lagged the July peak in TP by approximately one month. Contrary to expectations, deep Secchi depths were recorded during high TP concentrations in June and July. In addition, the August 19 sampling date had one of the lowest TP concentrations of the year but the highest Chl-a concentration. This suggests that Chl-a concentrations may have been driven by factors other than TP concentration, or another factor was causing Chl-a concentrations to lag TP. Higher Chl-a concentrations were generally associated with shallower Secchi depths in 2013. Figure 8-3 shows yearly average historical TP concentrations, Chl-a concentrations, and Secchi disk depths graphically. Little Crosby Lake has improved with respect to TP and Chl-a concentrations between each year of monitoring. Secchi depths improved from 2011-2012 and stayed constant from 2012-2013. Throughout the last three years, high water transparency has been associated with lower TP and Chl-a concentrations. Yearly average historical TP concentrations, Chl-a concentrations, Secchi depths, and their comparisons to lake standards are shown in Table 8-2. Little Crosby Lake TP concentrations exceeded the MPCA standards for 2011 and 2012, while all other parameters met the lake standards. In 2013, however, all parameters met the state standard. The lake received grades of ‘A’ for both Chl-a and Secchi depth in 2012 and 2013, but as a result of an average TP grade, received an overall grade of ‘B+’ for these years (Table 8-3). Overall, Little Crosby Lake exhibited relatively high water quality for the years monitored.

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Little Crosby Lake 4-Jun

25-Jun

16-Jul

1-Aug

19-Aug

4-Sep

25-Sep 140

120

1

100

Secchi Depth (meters)

2

80 3 60

4 40

5

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

14-May 0

20

0

6 Secchi

TP

Chl-a

Figure 8-2: Little Crosby Lake 2013 Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

73


2013

2012

2011

Little Crosby Lake

0

140

100

Secchi Depth (meters)

2

80 3 60

4 40

5

20

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

120

1

0

6 Secchi

TP

Chl-a

Figure 8-3: Little Crosby Lake historical Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

74


Little Crosby Lake Table 8-2: Little Crosby Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. Year

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

2011

101.7

11.4

2.0

2012

65.1

5.1

3.1

2013

60.0

5.1

3.0

Value does not meet state standard* Value meets state standard *MPCA shallow lake standards are not to exceed 60 µg/L for TP and 20.0 µg/L for Chl-a, w ith a Secchi disk depth of at least 1.0 m.

Table 8-3: Little Crosby Lake historical lake grades. Year

TP Grade

Chl-a Grade

Secchi Grade

Overall Grade

2011 2012 2013

D C C

B A A

C A A

C B+ B+

8.4

PHYTOPLANKTON AND ZOOPLANKTON

Little Crosby Lake was sampled for phytoplankton and zooplankton eight times in 2013, from May 14 to September 25. Euglenophyta were the dominant type of phytoplankton during the month of May in Little Crosby Lake (Figure 8-6). From the beginning of June until the end of the season, however, phytoplankton populations were dominated by Chlorophyta (green algae) and Cyanophyta (blue-green algae). Chlorophyta commonly occurs in smaller ponds, giving the water a grass-green color (Kalff, 2002). The small increase in phytoplankton concentration observed at the end of August corresponds to a decrease in zooplankton concentration at the same time (Figures 8-4 and 8-5). Total phytoplankton concentrations were lower from June through September than the beginning of the year, dropping from 12,000/mL in May to below 2,000/mL. This was due to the sharp disappearance of Euglenophyta populations. While the majority of the phytoplankton biomass in the lake was green and blue-green algae after June, there was not a significant amount of overall phytoplankton biomass. Cladoceran (important lake filter-feeders including the order Daphnia) populations were the most prominent zooplankton type throughout the monitoring season at Crosby Lake (Figure 8-7). Populations of Cyclopoids, Calanoids, Nauplii, and Rotifers were also prominent throughout the year. Density peaked at the beginning of June and reached its lowest point at the end of that same month (Figure 8-5).

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Little Crosby Lake 14

90 Total Phytoplankton Concentration TP 80

12

10 60

8

50

40

6

30 4

Total Phosphorus Concentration (Âľg/L)

Total Phytoplankton Concentration (1,000/mL)

70

20 2 10

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 8-4: Little Crosby Lake 2013 total phytoplankton concentration and TP concentration. 10

350 Total Zooplankton Density Chl-a

9

300

250

7

6 200 5 150 4

3

100

Chlorophyll-a Concentration (Âľg/L)

Total Zooplankton Density (1,000/m^3)

8

2 50 1

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 8-5: Little Crosby Lake 2013 total zooplankton density and Chl-a concentration. 2013 CRWD Lakes Monitoring Report

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Little Crosby Lake 100%

90%

Phytoplankton Relative Abundance

80%

70%

60%

Pyrrhophyta Euglenophyta Cyanophyta

50%

Cryptophyta Chrysophyta

40%

Chlorophyta Bacillariophyta

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 8-6: Little Crosby Lake 2013 phytoplankton relative abundance. 100%

90%

80%

Zooplankton Relative Abundance

70%

60% Cladocera Rotifera

50%

Nauplii Calanoida

40%

Cyclopoida

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 8-7: Little Crosby Lake 2013 zooplankton relative abundance. 2013 CRWD Lakes Monitoring Report

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Little Crosby Lake

8.5

AQUATIC VEGETATION

8.5.1 BIOVOLUME ANALYSIS

As viewed in Figure 8-8, the majority of Little Crosby Lake contains aquatic vegetation, with this vegetation consuming the full water column in almost all locations where vegetation is observed.

Figure 8-8: Little Crosby Lake 2013 biovolume heat map.

8.5.2 POINT-INTERCEPT SURVEYS

In 2013, Little Crosby Lake had a robust aquatic vegetation community with nine different species of plants observed by late summer. Six of these species were also present in June (Figure 8-9). Star duckweed and sago pondweed were the two species occurring most frequently throughout the lake, with sago pondweed being the dominant type in June, and star duckweed becoming more prominent in late July. While coontail was found at only a third of the sites in both months surveyed, it was highly abundant by late July (Figure 8-10). Most plants, while found on many points in the lake, were not especially abundant at each location (with the exception of coontail). Curly-leaf pondweed, a non-native invasive species, was present in both June and July at 33% of locations where vegetation was found (Figure 8-9) and at relatively low abundance rankings (Figure 8-10). It was previously observed in the lake in 2011, but was absent in 2012 surveys. 2013 CRWD Lakes Monitoring Report

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Little Crosby Lake

Curly-leaf pondweed causes problems by displacing other native plants and forming thick mats on the surface of a lake that disrupt boating and recreation. In addition, when the plants die back in mid-summer, the resulting increase in phosphorus from the decomposing plant material causes disruptive algal blooms (DNR, 2005).

100 6/14/2013 7/25/2013

Percent Occurrence

80

60

40

20

0

Figure 8-9: Little Crosby Lake 2013 percent occurrence of vegetation present.

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Little Crosby Lake 5 6/14/2013 7/25/2013

Average Abundance Ranking

4

3

2

1

0

Figure 8-10: Little Crosby Lake 2013 average abundance ranking of vegetation present.

8.6

FISH STOCKING AND SURVEYS

There is no history of fish stocking for Little Crosby Lake by the Minnesota DNR, nor have any fish surveys been completed for this lake. CRWD plans to survey fish populations on Little Crosby Lake during the summer of 2014. 8.7

OVERALL LAKE EVALUATION

Little Crosby Lake has a relatively short monitoring record when compared to the other District lakes. Since beginning monitoring in 2011, it exhibited relatively stable Chl-a concentrations and Secchi disk depths, and decreased in TP concentration between the 2011 and 2013 monitoring years. Much of the lake area was covered by extensive vegetation in 2013, and contained a moderate diversity of plant species by mid-summer. Previous reporting on Little Crosby Lake focused on an analysis of TP, Chl-a, and Secchi depth trends over the monitoring season and compared to past monitoring years. Conversely, this 2013 CRWD Lakes Monitoring Report

80


Little Crosby Lake

report contains more extensive information on lake history, lake morphometric data, lake level, additional water quality analysis (i.e., lake grading), phytoplankton and zooplankton populations, aquatic vegetation communities, and fish populations. For this yearâ&#x20AC;&#x2122;s report, this information was solely reported upon, but not analyzed for trends or relationships between parameters. A more robust analysis will be done in future monitoring reports that examines the interactions between all parameters monitored in order to present a picture of the overall health of Little Crosby Lake.

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Little Crosby Lake

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Loeb Lake

9 LOEB LAKE RESULTS 9.1

LOEB LAKE BACKGROUND

Figure 9-1: View of the boat launch on the east shoreline of Loeb Lake.

Loeb Lake, located in Marydale Park in the northwestern portion of the City of St. Paul, is a 9.7 acre lake with a maximum depth of 28 feet and an 81% littoral area (Table 9-1). The area has a walking path, childrenâ&#x20AC;&#x2122;s play area, picnic areas, a fishing pier, and a boat launch. The surrounding area is primarily residential land use. The watershed area contributing inflow to the lake is 44 acres. Water enters the lake from the north half of the watershed through sheet flow traveling through Marydale Park, as well as a storm sewer that collects runoff from Mackubin Street between Maryland and Jessamine Avenues (CRWD, 2009). Runoff from the south half of the watershed enters Loeb Lake through 2013 CRWD Lakes Monitoring Report

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Loeb Lake

two different storm sewers. The storm sewers drain streets on the south and east sides of the lake, discharging to a stormwater pond on the southeast corner. A pipe directly connects this pond to Loeb Lake. There are no direct outlets from Loeb Lake. Loeb Lake has been monitored since 2003 and has had relatively stable TP, Chl-a, and Secchi disk depth values that have consistently met the state standards. Therefore, lake conditions have appeared to remain stable in the past nine years. Previous winter kills of fish have been observed in Loeb Lake, but have not occurred since 2000, when an aerator was installed in the lake (CRWD, 2009). Future management efforts on Loeb Lake should focus on reduced loading in the surrounding watershed and naturalizing the shoreline (CRWD, 2009). Both of these actions would reduce the subsequent influx of nutrients into the lake. While water quality is currently very high, good management efforts around the lake to prevent further increases in nutrient inputs will be key in preventing lake degradation. Table 9-1: Loeb Lake morphometric data. Surface Area (acres)

Maximum Depth (ft)

Littoral Area

Volume (acre-ft)

Watershed Area (acres)

Watershed: Lake Area (ratio)

9.7

28.0

81%

84

44

4.5

9.2

LAKE LEVEL

Loeb Lake level has been monitored since 2003, with the exception of May 2004 through February 2006 when level data was not available (Figure 9-2). Loeb Lake does not have an OHWL to compare the current year to historical â&#x20AC;&#x153;normalâ&#x20AC;? lake levels. The lowest recorded water level of the lake occurred in May 2009 at a level of 848.6 ft. Lake levels were at their highest in August 2011 and July 2013, with levels of 851.63 ft and 851.58 ft, respectively. In 2013, lake level increased from January until it peaked on July 3, then decreased through the rest of the year (Figure 9-3).

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Loeb Lake 852

Elevation (ft above mean sea level)

851

850

849

848 2003

2004

2005

2006

2007

2008 Year

2009

2010

2011

2012

2013

Figure 9-2: Loeb Lake historical lake elevations.

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853.5

0

853.0

1

852.5

2

Daily Precipitation Total

852.0

3

Lake Elevation

851.5

4

851.0

5

850.5

6

850.0

7

849.5

Precipitation (inches)

Elevation (ft anove mean sea level)

Loeb Lake

8 Jan

Feb

Mar

Apr

May

Jun

Jul Month

Aug

Sep

Oct

Nov

Dec

Figure 9-3: Loeb Lake 2013 lake elevations and precipitation.

9.3

WATER QUALITY RESULTS

Loeb Lake was sampled eight times during 2013 from May 3 to September 16 (Figure 9-4). As in previous years, Loeb Lake was characterized by low TP and Chl-a concentrations, and deep Secchi depths. TP levels were highest (57.5 Âľg/L) during the first sampling event on May 3. Samples show decreasing TP concentrations until early July, increasing until August 9, then remaining stable through the end of the season. Chlorophyll-a concentrations varied throughout the growing season without a temporal trend, indicating that it was not phosphorus-driven. The high Chl-a value observed on August 26 could be a result of the sampling event occurring either during or directly after a bloom, making the sample potentially unrepresentative of the general Chl-a value during this time period. Secchi depths were generally shallower during the first three samples (average 2.2 m) and deeper during the last five samples (average 3.5 m). The data suggests that during 2013, higher water clarity was generally associated with lower Chl-a concentrations.

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Loeb Lake

Figure 9-5 shows yearly average historical TP concentrations, Chl-a concentrations, and Secchi disk depths graphically. Based on the historical data since 2005, water quality has been fairly steady in Loeb Lake. Total phosphorus concentrations decreased from 2003-2008, but have increased since 2009. Chl-a concentrations have been low and varied only slightly throughout the period of record. Concentrations were low from 2005-2012, with an average of 4.1 µg/L. Conversely, 2003 and 2013 were characterized by higher Chl-a concentrations, 7.1 µg/L and 7.4 µg/L, respectively. Secchi depths were shallowest in 2003 (2.7 m). Averages were deep in 2005 and 2006 (3.8 m and 3.7 m) and have been generally getting shallower since. As with 2013, higher water transparency was generally associated with lower Chl-a concentrations throughout the period of record. Yearly average historical TP concentrations, Chl-a concentrations, Secchi depths, and their comparisons to lake standards are shown in Table 9-2. Loeb Lake has had a stable and consistently positive water qualtity history. It has not exceeded the average summer TP, Chl-a or Secchi disk depth standards in its monitoring history. The overall lake grade has historically been an ‘A’, with only one ‘B’ grade occurring in 2003 (2004 was not monitored) (Table 9-3). The high water quality lake grades associated with Loeb Lake indicate that it continues to be one of the highest water quality lakes in the District.

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Loeb Lake 17-May

7-Jun

3-Jul

23-Jul

9-Aug

26-Aug

16-Sep 140

120

1

100

Secchi Depth (meters)

2

80 3 60

4 40

5

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

3-May 0

20

0

6 Secchi

TP

Chl-a

Figure 9-4: Loeb Lake 2013 Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

88


0

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

Loeb Lake

50

45

40

35 Secchi Depth (meters)

2 30

3

25

20 4 15

10 5 5

6

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

1

0 Secchi

TP

Chl-a

Figure 9-5: Loeb Lake historical Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

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Loeb Lake Table 9-2: Loeb Lake historical yearly TP/Chl-a/Secchi depth averages compared to shallow lake state standards. Year

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

2003

37.5

7.1

2.7

2004

N/A

N/A

N/A

2005

31.0

3.8

3.8

2006

26.5

4.0

3.7

2007

17.4

4.5

3.3

2008

18.0

4.8

3.2

2009

15.6

3.5

3.4

2010

21.0

4.0

3.5

2011

25.0

4.3

3.0

2012

27.1

4.2

3.1

2013

27.0

7.4

3.0

Value does not meet state standard* Value meets state standard *MPCA shallow lake standards are not to exceed 60 µg/L for TP and 20.0 µg/L for Chl-a, w ith a Secchi disk depth of at least 1.0 m.

Table 9-3: Loeb Lake historical lake grades. Year 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

TP Grade C N/A B B A A A A B B B

Chl-a Grade A N/A A A A A A A A A A

Secchi Grade B N/A A A A A A A A A A

Overall Grade B N/A A A A A A A A A A

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Loeb Lake

9.4

PHYTOPLANKTON AND ZOOPLANKTON

Loeb Lake was sampled eight times during 2013 from May 3 to September 16. From May to July in Loeb Lake, concentrations of Chlorophyta, Cryptophyta, Euglenophyta and Crysophyta were observed in varying amounts (Figure 9-8). Phytoplankton concentrations were dominated by Cyanophyta and Chlorophyta from July through the end of the monitoring season. Total phytoplankton concentration peaked at the beginning of June then fluctuated between low and high concentrations (consisting mainly of Cyanophyta) from July through September (Figures 96 and 9-8). Dominance of the zooplankton community shifted from Cyclopoids from May through June to Cladocerans from July through September (Figure 9-9). Cladocerans, including the genus Daphnia, are important filter feeders in lake environments. Nauplii were present throughout the year, while Calanoids and Rotifers were observed beginning in June and in small densities throughout the rest of the monitoring season. Total zooplankton density generally stayed consistently high throughout the monitoring season, with few intense low periods (Figure 9-7).

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Loeb Lake 70

5 Total Phytoplankton Concentration TP (µg/L)

60

50

3 40

30 2

20

Total Phosphorus Concentration (µg/L)

Total Phytoplankton Concentration (1,000/mL)

4

1 10

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 9-6: Loeb Lake 2013 total phytoplankton concentration and TP concentration. 20

140 Total Zooplankton Density Chl-a

18

120

100

14

12 80 10 60 8

6

40

Chlorophyll-a Concentration (µg/L)

Total Zooplankton Density (1,000/m^3)

16

4 20 2

0

0 May

Jun

Jul

Aug

Sep

Month

Figure 9-7: Loeb Lake 2013 total zooplankton density and Chl-a concentration. 2013 CRWD Lakes Monitoring Report

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Loeb Lake 100%

90%

Phytoplankton Relative Abundance

80%

70%

60%

Pyrrhophyta Euglenophyta Cyanophyta

50%

Cryptophyta Chrysophyta

40%

Chlorophyta Bacillariophyta

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 9-8: Loeb Lake 2013 phytoplankton relative abundance. 100%

90%

80%

Zooplankton Relative Abundance

70%

60% Cladocera Rotifera

50%

Nauplii Calanoida

40%

Cyclopoida

30%

20%

10%

0% May

Jun

Jul

Aug

Sep

Month

Figure 9-9: Loeb Lake 2013 zooplankton relative abundance. 2013 CRWD Lakes Monitoring Report

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Loeb Lake

9.5

AQUATIC VEGETATION

9.5.1 BIOVOLUME ANALYSIS

Figure 9-10 shows that a large majority of Loeb Lake has extensive vegetation, as indicated by the areas in red (where 100% of the water column contains vegetation). The middle area of the lake (the deepest part) does not contain any vegetation.

Figure 9-10: Loeb Lake 2013 biovolume heat map.

9.5.2 POINT-INTERCEPT SURVEYS

There was not a wide variety of plant species present at the beginning of June, with only coontail, curly-leaf pondweed, and Eurasian watermilfoil seen at average abundances (Figure 911). As curly-leaf pondweed and Eurasian watermilfoil both experience die-off around midsummer, they were not spotted when surveyed again at the end of June. Instead, additional vegetation such as filamentous algae, lesser duckweed, sago pondweed, and flatstem pondweed were observed. Coontail was present at all locations where vegetation was seen on both survey dates. The average abundance rating of this plant type, however, almost doubled between survey times at the beginning of June and the end of July (Figure 9-12). Other plant types identified were less abundant. The presence of both curly-leaf pondweed and Eurasion watermilfoil in Loeb Lake presents potential problems for future management decisions. Curly-leaf pondweed and Eurasian 2013 CRWD Lakes Monitoring Report

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Loeb Lake

watermilfoil are both non-native invasive species, causing problems by displacing other native plants, and forming thick mats on the surface of a lake that disrupt boating and recreation (DNR, 2014b; DNR, 2005). In addition, when curly-leaf pondweed plants die back in mid-summer, the resulting increase in phosphorus from the decomposing plant material can cause disruptive algal blooms (DNR, 2005). The spreading of Eurasian watermilfoil makes it an especially difficult plant to manage, as a new plant can grow from just a tiny piece of an original plant. This makes it easy to float and grow quickly in other areas of a lake, as well as be transported between lakes on boat trailers and fishing gear (WSDE, 2014). Both species have been observed in Loeb Lake since 2005.

100 6/3/2013 7/23/2013

Percent Occurrence

80

60

40

20

0

Figure 9-11: Loeb Lake 2013 percent occurrence of vegetation present.

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Loeb Lake 5 6/3/2013 7/23/2013

Average Abundance Ranking

4

3

2

1

0

Figure 9-12: Loeb Lake 2013 average abundance ranking of vegetation present.

9.6

FISH STOCKING AND SURVEYS

Loeb Lake is part of the Minnesota DNR’s “Fishing in the Neighborhood” program which provides angling opportunities for children and families in urban environments, encourages environmental stewardship, and improves knowledge of natural resources (DNR, 2014e). Therefore, these lakes are stocked with fish that are better for general angling activities. As seen in Table 9-4, the main fish type stocked in Loeb Lake in recent years are adult bluegill, with black crappie, catfish and walleye (important management species in the past). Panfish (i.e., black crappie, bluegill, and hybrid/green/pumpkinseed sunfish) were the most abundant observed fish types in the 2006 Loeb Lake survey conducted by the Minnesota DNR (Table 9-5). Of the panfish observed, bluegill and hybrid sunfish populations were the highest. Loeb Lake is scheduled to be surveyed again by the Minnesota DNR in 2014.

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Loeb Lake Table 9-4: Loeb Lake historical record of fish stocking. Year

Bluegill

Black crappie Adult

Adult

2013

Channel catfish

Largemouth bass

Adult

Adult

Yearling

Yearling

Walleye Yearling

185

2012 2011

Yearling

Fingerling

Fry

610

152 26

144 74

50

2009

207

106

47

622

2008

244

380

55

1290

2007

69

1018

38

1040

2010

2006 2005

689

709

1211

138

630

13,000

524 9

242

2004

34

10,000

19

10,000

3

149

10,000

627

444

Table 9-5: Loeb Lake 2006 fish populations. Species

Number of fish caught in each category (inches)

Total

0-5

6-8

9-11

12-14

15-19

20-24

25-29

30+

Black bullhead

0

1

8

0

0

0

0

0

Black crappie

1

6

0

0

0

0

0

0

7

32

16

0

0

0

0

0

0

50

Bluegill

9

Green sunfish

1

0

0

0

0

0

0

0

1

Hybrid sunfish

23

3

0

0

0

0

0

0

26

Largemouth bass

0

1

0

0

0

0

0

0

1

Pumpkinseed sunfish

4

2

0

0

0

0

0

0

6

White sucker

0

0

0

0

1

0

0

0

1

9.7

OVERALL LAKE EVALUATION

Loeb Lake exhibits the best water quality of any District lake, and has historically received an ‘A’ lake grade, indicating high water quality and user quality. This could be the result, however, of a very small watershed: lake area ratio, with very little runoff (carrying external pollutants) entering the lake. Loeb Lake held an abundant amount of aquatic vegetation in 2013, but most species monitored (aside from coontail) only showed moderate abundance throughout the lake area. Previous reporting on Loeb Lake focused on an analysis of TP, Chl-a, and Secchi depth trends over the monitoring season and compared to past monitoring years. Conversely, this report contains more extensive information on lake history, lake morphometric data, lake level, additional water quality analysis (i.e., lake grading), phytoplankton and zooplankton populations, aquatic vegetation communities, and fish populations. For this year’s report, this information was solely reported upon, but not analyzed for trends or relationships between parameters. A more robust analysis will be done in future monitoring reports that examines the interactions between all parameters monitored in order to present a picture of the overall health of Loeb Lake. 2013 CRWD Lakes Monitoring Report

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Loeb Lake

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Lake McCarrons

10 LAKE MCCARRONS RESULTS 10.1 LAKE MCCARRONS BACKGROUND

Figure 10-1: View of the west shoreline of Lake McCarrons.

Lake McCarrons is a 74.7 acre, deep lake located in the city of Roseville. With a maximum depth of 57 ft and a 36% lake littoral area, it supports a variety of activities including swimming, boating, and fishing (Table 10-1; Figure 10-2). The beach and boat ramp are maintained during the summer months by RCPW. Lake McCarrons County Park, located on the east shore of the lake, also supports visitors to the lake with a beach building, picnic shelter, and boat access with car/trailer parking. The 1,070 acre watershed of Lake McCarrons consists of residential properties, commercial and public areas, highway, wetland/grassland/woodland areas, and a park bordering it on the east 2013 CRWD Lakes Monitoring Report

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Lake McCarrons

side. The outlet of the Villa Park Wetland Treatment System located on the western edge of the lake is the primary inlet to Lake McCarrons. A secondary inlet enters on the north side of the lake via William Street Pond. It has one main outlet at the east end of the lake. This outlet is the headwaters of the Trout Brook-West Branch Subwatershed, where water enters the Trout Brook Storm Sewer Interceptor (CRWD, 2003). Multiple projects to improve water quality have been completed in recent years in the watershed draining to Lake McCarrons. In 1987, the Villa Park Wetland Treatment System became operational, which consisted of a 2.4 acre pond that empties into a series of five wetland cells. These cells then drain to a final terminal wetland which overflows at high levels to Lake McCarrons. The purpose of this system is to channel stormwater through a series of wetlands that decreases flow velocity. This allows sediments and bound nutrients to settle before entering the lake. This system reduced the amount of total phosphorus and dissolved phosphorus entering the lake (CRWD, 2003). In 2004, improvements to the system were made which removed the pipes connecting the wetland treatment cells, improved the berms, and constructed timber weirs at each of the wetland outflows to provide a fixed and stabile overflow. In 2013, CRWD dredged several of the wetland cells in the Villa Park System. A total of more than 17,000 cubic yards of sediment was removed from the system to improve stormwater treatment and residence time before water flows into Lake McCarrons. In October of 2004, CRWD completed an alum treatment on Lake McCarrons, in which 492 tons of aluminum sulfate was applied below the surface of the lake. In this type of treatment, alum binds to free phosphorus particles causing them to drop out of the water column and settle on the bottom of the lake (Kennedy and Cook, 1982). This removes phosphorus from the water column, as well as prevents additional phosphorus release from the bottom sediments (CRWD, 2003). Water quality after this alum treatment showed improvements when compared to prealum treatment water quality (CRWD, 2003). One of the primary water quality concerns continues to be the flow of phosphorus into the lake, as stormwater is still the largest portion of inflow to the lake. Currently, Lake McCarrons is considered unimpaired and is not listed on the MPCA 303(d) list of impaired waters. While Lake McCarrons currently exhibits good water quality and is considered unimpaired, it still has concerns that need to be addressed in the future to improve the quality of the lake. For example, intermittent fish kills have occurred in Lake McCarrons in the past. These are caused by incomplete fall lake mixing, and early winter freeze and snow (CRWD, 2003). When this occurs, there is not enough oxygen in the lake to support fish populations, resulting in a full or partial fish kill. Another on-going management issue is the presence of invasive species on the lake including carp, Eurasian watermilfoil, and curly-leaf pondweed, all of which have been observed in recent years. Excessive aquatic vegetation growth on the west end of the lake has become a management concern, and CRWD anticipates plant removal on this part of the lake during 2014.

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Lake McCarrons Table 10-1: Lake McCarrons morphometric data. Surface Area (acres)

Maximum Depth (ft)

Littoral Area

Volume (acre-ft)

Watershed Area (acres)

Watershed: Lake Area (ratio)

74.7

57.0

34%

1,892

1,070

14.3

Figure 10-2: Lake McCarrons bathymetric map.

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Lake McCarrons

10.2 LAKE LEVEL Lake McCarrons level has been consistently below the OHWL of 842.2 ft throughout the historical lake level record (Figure 10-3). The water level came close to the OHWL in 1984 and 1997. A significantly low water level period occurred from 1932-1939. The water level has consistently stayed within 840-842 ft for the past 35 years. The 2013 lake level rose slightly from the beginning of the year until mid-May, and then steadily decreased throughout the summer (Figure 10-4). In October 2013, it peaked again following a large rain event on October 2.

843 OHWL is 842.2 ft

Elevation (ft above mean sea level)

842

841

840 Lake Elevation OHWL 839

838

837 1924

1929

1934

1939

1944

1949

1954

1959

1964

1969 Year

1974

1979

1984

1989

1994

1999

2004

2009

Figure 10-3: Lake McCarrons historical lake elevations.

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102

2014


Lake McCarrons 844.0

0

843.5

1

Daily Precipitation Total Lake Elevation

2

OHWL

OHWL is 842.21 ft 842.5

3

842.0

4

841.5

5

841.0

6

840.5

7

840.0

8 Jan

Feb

Mar

Apr

May

Jun

Jul Month

Aug

Sep

Oct

Nov

Dec

Figure 10-4: Lake McCarrons 2013 lake elevations and precipitation.

2013 CRWD Lakes Monitoring Report

103

Precipitation (inches)

Elevation (ft above mean sea level)

843.0


Lake McCarrons

10.3 WATER QUALITY RESULTS Lake McCarrons was sampled eight times in 2013 from May 6 to September 9 (Figure 10-5). Sampling shows the highest epilimnetic TP concentration (29 µg/L) during the first sampling event on May 6, which then dropped significantly by the end of May. After May, TP concentration increased through mid-July and then decreased until the end of the season. Chl-a concentrations were variable throughout the season, and did not follow the same trend as TP. Concentrations peaked in mid-June (7.6 µg/L), then dropped to a season low in late July (0.99 µg/L). Water transparency was highest in late May (with a Secchi depth of 5.9 m). Water transparency then decreased until late July, followed by an increase through the end of the season. After June 2013, high water transparency was generally associated with low TP concentrations, which indicated TP was a major driver of water transparency during 2013. Figure 10-6 shows yearly average historical TP concentrations, Chl-a concentrations, and Secchi disk depths graphically. Since the 2004 alum treatment, the lake has experienced a significant improvement in water quality. The average TP concentration from 2005-2013 (16.1 µg/L) is 62% lower than the 1988-2004 average TP concentration (42.2 µg/L). The average Chl-a concentration from 2005-2013 (3.9 µg/L) is 70% lower than the 1988-2004 average TP concentration (12.8 µg/L). The average Secchi depth from 2005-2013 (3.8 m) is 58% deeper than the 1988-2004 average depth (2.4 m). Overall, the alum treatment is still shown to be helpful in improving water quality in the lake, and will likely remain helpful for many more years. The efficacy of the treatment will continue to be monitored in upcoming years. Recent years (2011-2013) have shown slightly higher TP and Chl-a concentrations, resulting in shallower Secchi disk depths (2005-2010 had an average of 4.1 m, while 2011-2013 had an average of only 3.1 m). Throughout the period of record (before and after alum treatment), high Chl-a concentrations have generally been associated with high TP concentrations. Low Secchi depths have generally been associated with high Chl-a and TP concentrations, indicating that they are primary drivers for water clarity in Lake McCarrons. Yearly average historical TP concentrations, Chl-a concentrations, Secchi depths, and their comparisons to lake standards are shown in Table 10-2. Lake McCarrons has only exceeded the state standards two times in its history of monitoring: for TP in 1988 and Chl-a in 1995. Since 2004, the lake has received an ‘A’ grade, indicating that it has had consistently high water quality since the alum treatment (Table 10-3).

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Lake McCarrons 28-May

13-Jun

2-Jul

22-Jul

7-Aug

22-Aug

9-Sep 140

120

1

100

Secchi Depth (meters)

2

80 3 60

4 40

5

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

6-May 0

20

0

6 Secchi

TP

Chl-a

Figure 10-5: Lake McCarrons 2013 Secchi/TP/Chl-a comparison. 2013 CRWD Lakes Monitoring Report

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Secchi Depth (meters)

Secchi TP

1

100

2

80

3 60

4 40

5 20

6

2013 CRWD Lakes Monitoring Report

Total Phosphorus and Chlorophyll-a concentrations (Âľg/L)

0 2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

1992

1991

1990

1989

1988

Lake McCarrons

140

120

0

Chl-a

Figure 10-6: Lake McCarrons historical Secchi/TP/Chl-a comparison.

106


Lake McCarrons Table 10-2: Lake McCarrons historical yearly TP/Chl-a/Secchi depth averages compared to deep lake state standards. Year

TP (µg/L)

Chl-a (µg/L)

Secchi (m)

1988

81.0

16.4

1.1

1989

32.0

11.7

1.8

1990

49.0

14.8

2.7

1991

47.0

14.5

1.9

1992

25.0

7.2

2.7

1993

44.0

8.7

2.8

1994

37.0

9.7

3.1

1995

50.0

22.6

2.3

1996

37.0

10.6

2.7

1997

49.0

12.8

2.3

1998

29.0

16.3

2.1

1999

37.0

9.4

2.5

2000

38.0

17.3

2.2

2001

31.0

6.6

3.3

2002

46.0

16.3

2.1

2003

39.0

12.7

2.1

2004

47.0

10.4

2.9

2005

18.0

4.2

4.0

2006

14.7

3.5

4.0

2007

14.8

3.8

3.9

2008

12.0

2.3

4.7

2009

12.0

2.8

4.1

2010

16.0

3.3

4.0

2011

20.0

7.7

2.9

2012

17.5

3.7

3.2

2013

20.0

4.1

3.3

Value does not meet state standard* Value meets state standard *MPCA deep lake standards are not to exceed 40 µg/L for TP and 14.0 µg/L for Chl-a, w ith a Secchi disk depth of at least 1.4 m.

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Lake McCarrons Table 10-3: Lake McCarrons historical lake grades. Year 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

TP Grade D C C C B C C C C C B C C B C C C A A A A A A A A A

Chl-a Grade B B B B A A A C B B B A B A B B B A A A A A A A A A

Secchi Grade D C B C B B A B B B C B B A C C B A A A A A A B A A

Overall Grade C C+ B C+ B+ B B+ C+ B B B B B A C+ C+ B A A A A A A A A A

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Lake McCarrons

10.4 PHYTOPLANKTON AND ZOOPLANKTON Lake McCarrons was sampled eight times in 2013 from May 6 to September 9. The phytoplankton population in Lake McCarrons was dominated by Euglenophyta in the month of May (Figure 10-9). This early spring bloom of phytoplankton was likely a result of high nutrient availability (as seen by a peak in TP concentration) and increased light availability (Heiskary and Markus, 2010; UWE, 2004). Cyanophyta peaked in June and was dominant for the remainder of the monitoring season. A significant drop in total phytoplankton concentration was observed between these two population blooms (Figure 10-7). This event corresponded to an increase in zooplankton during the same time period (Figure 10-8). Small populations of Chlorophyta were observed throughout the year and Cryptophyta appeared in small amounts at the end of May and the beginning of August. Aside from the peak concentrations occurring at the beginning of May (Euglenophyta) and middle of June (Cyanophyta), overall phytoplankton concentration generally stayed low (<1,000/mL) (Figure 10-7). The zooplankton population of Lake McCarrons was divided among populations of Cyclopoids, Calanoids, Nauplii, and Cladocerans for the entire monitoring season (Figure 10-10). Overall, the population peaked in mid-June and decreased throughout the remainder of the summer with the exception of a small peak at the end of August (Figure 10-8).

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Lake McCarrons 7

35 Total Phytoplankton Concentration

6

30

5

25

4

20

3

15

2

10

1

5

0

Total Phosphorus Concentration (Âľg/L)

Total Phytoplankton Concentration (1,000/mL)

TP

0 May

Jun

Jul Month

Aug

Sep

Figure 10-7: Lake McCarrons 2013 total phytoplankton concentration and TP concentration. 60

8 Total Zooplankton Density Chl-a 7

50

40 5

4

30

3 20

Chlorophyll-a Concentration (Âľg/L)

Total Zooplankton Density (1,000/m^3)

6

2

10 1

0

0 May

Jun

Jul Month

Aug

Sep

Figure 10-8: Lake McCarrons 2013 total zooplankton density and Chl-a concentration. 2013 CRWD Lakes Monitoring Report

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Lake McCarrons 100%

90%

Phytoplankton Relative Abundance

80%

70%

60%

Pyrrhophyta Euglenophyta Cyanophyta

50%

Cryptophyta Chrysophyta

40%

Chlorophyta Bacillariophyta

30%

20%

10%

0% May

Jun

Jul Month

Aug

Sep

Figure 10-9: Lake McCarrons 2013 phytoplankton relative abundance. 100%

90%

80%

Zooplankton Relative Abundance

70%

60% Cladocera Rotifera

50%

Nauplii Calanoida

40%

Cyclopoida

30%

20%

10%

0% May

Jun

Jul Month

Aug

Sep

Figure 10-10: Lake McCarrons 2013 zooplankton relative abundance. 2013 CRWD Lakes Monitoring Report

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Lake McCarrons

10.5 AQUATIC VEGETATION 10.5.1 BIOVOLUME ANALYSIS

The biovolume heat map of Lake McCarrons shows that the majority of the aquatic vegetation in the lake occurs along the shallow areas near the shoreline (Figure 10-11). Aquatic plants are most abundant along the western end of the lake, where the red color indicates that 100% of the water column contains aquatic vegetation.

Figure 10-11: Lake McCarrons 2013 biovolume heat map.

10.5.2 POINT-INTERCEPT SURVEYS

Eurasian watermilfoil was the most frequently occurring plant in Lake McCarrons in 2013 in both surveys, recorded at 84% of the locations where vegetation was observed in June and 72% in July (Table 10-12). Coontail and filamentous algae were both observed at roughly 50% of the locations in both months. While there was a large diversity of plant species observed in Lake McCarrons by the middle of the summer, the majority of these occurred infrequently throughout the lake. Where vegetation was observed, the plants with the highest abundance rankings were Eurasian watermilfoil, coontail, filamentous algae, and Canada waterweed in June, and coontail, filamentous algae, and white water lily in July (Table 10-13). None of the species observed,

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Lake McCarrons

however, were found in high abundance (with rankings ranging from 1.3 to 2.67) in the June and July surveys. Filamentous algae received below average abundance rankings in both June and July. Filamentous algae can become a nuisance species when in high abundance as it forms thick, green mats on the water surface that can impede lake activities. It is also indicative of excessive nutrients (especially phosphorus) entering a lake, which is common in urban lakes like Lake McCarrons (DNR, 2014c). As shown in Figures 10-12 and 10-13 below, the presence of Eurasian watermilfoil and curlyleaf pondweed were observed in Lake McCarrons in 2013, and have been observed surveys since 2005. Curly-leaf pondweed and Eurasian watermilfoil are both non-native, invasive species, causing problems by displacing other native plants and forming thick mats on the surface of a lake that disrupt boating and recreation (DNR, 2014b; DNR, 2005). In addition, when curly-leaf pondweed plants die back in mid-summer, the resulting increase in phosphorus from the decomposing plant material causes disruptive algal blooms (DNR, 2005). Eurasian watermilfoil spreads easily, as a new plant can grow from just a tiny piece of an original plant. It can easily float and grow quickly in other areas of a lake, as well as be transported between lakes on boat trailers and fishing gear (WSDE, 2014). While neither is especially abundant and the lake still has a robust composition of plants, the presence of these two species is still a management concern; especially since Eurasian watermilfoil is observed at the majority of locations where vegetation is found.

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Lake McCarrons 100 6/3/2013 7/23/2013

Percent Occurrence

80

60

40

20

0

Figure 10-12: Lake McCarrons 2013 percent occurrence of vegetation present.

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Lake McCarrons 5 6/3/2013 7/23/2013

Average Abundance Ranking

4

3

2

1

0

Figure 10-13: Lake McCarrons 2013 average abundance ranking of vegetation present.

10.6 FISH STOCKING AND SURVEYS Previous stocking in Lake McCarrons has included black crappie, northern pike, and walleye, which has occurred intermittently (Table 10-4). The last survey of fish populations completed by the Minnesota DNR was in 2008, which showed a large variety of panfish (Table 10-5). Bluegill were present in very large numbers and were also the most abundant fish type in the lake. While only two common carp were caught in the survey, DNR staff observed hundreds spawning in the shallow areas of the lake during the June visit (DNR, 2014g). Staff also noted that largemouth bass were noted in larger abundance in the shallow areas than the survey (which found only two) indicates. The next fish population survey in Lake McCarrons is scheduled to be conducted by the Minnesota DNR during the summer of 2014.

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Lake McCarrons Table 10-4: Lake McCarrons historical record of fish stocking. Year

Black crappie Adult

Adult

2009 2007

Northern pike

Walleye

Yearling

Fry

80 630

2005

124

2004

75,000

Table 10-5: Lake McCarrons 2008 fish populations. Species Black crappie

Number of fish caught in each category (inches) 0-5

6-8

9-11

12-14

15-19

20-24

25-29

30+

Total

0

3

2

0

0

0

0

0

5

41

340

0

0

0

0

0

0

390

Common carp

0

0

0

0

0

0

2

0

2

Green sunfish

1

1

0

0

0

0

0

0

2

Hybrid sunfish

7

6

0

0

0

0

0

0

13

Largemouth bass

0

1

1

0

0

0

0

0

2

Bluegill

Northern pike

0

0

0

0

0

0

0

1

1

Pumpkinseed sunfish

4

0

0

0

0

0

0

0

4

White sucker

0

0

0

1

0

0

0

0

1

Yellow bullhead

0

1

7

3

0

0

0

0

11

10.7 OVERALL LAKE EVALUATION Lake McCarrons has displayed significant improvements in water quality since the 2004 alum treatment to reduce TP levels in the lake. While the lake only exceeded the eutrophication parameter state standards twice in its monitored history, it only received average lake grades before the treatment. Since 2004, it has received an ‘A’ lake grade, indicating that it has had very good water quality in recent years. One general management concern is the extensive vegetation on the west end of the lake, which the District has been focused on addressing. Previous reporting on Lake McCarrons focused on an analysis of TP, Chl-a, and Secchi depth trends over the monitoring season and compared to past monitoring years. Conversely, this report contains more extensive information on lake history, lake morphometric data, lake level, additional water quality analysis (i.e., lake grading), phytoplankton and zooplankton populations, aquatic vegetation communities, and fish populations. For this year’s report, this information was solely reported upon, but not analyzed for trends or relationships between parameters. A more robust analysis will be done in future monitoring reports that examines the interactions between all parameters monitored in order to present a picture of the overall health of Lake McCarrons.

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11 CONCLUSIONS & RECOMMENDATIONS 11.1 CONCLUSIONS In 2013, the water quality of the five District lakes (Como, Crosby, Little Crosby, Loeb, and McCarrons) varied by water body and by time of year. Some of the lakes improved in water quality, while other lakes degraded compared to historical averages. Based on the MPCA eutrophication numeric water quality standards, Little Crosby Lake, Loeb Lake, and Lake McCarrons met the MPCA standards for all parameters during the 2013 growing season. Crosby Lake met the MPCA shallow lake standards for Chl-a concentration and Secchi disk depth, but failed for TP concentration. Como Lake did not meet any of the MPCA shallow lake standards for TP concentration, Chl-a concentration, or Secchi disk depth during the 2013 growing season. Total phosphorus was an important driver for water quality in most of the District lakes. High phosphorus in lakes can cause overgrowth of algae (measured by Chl-a concentrations) and aquatic plants, which reduces water clarity. Phosphorus will continue to be a contaminant of concern in CRWD as inputs of fertilizers, leaves, grass clippings, pet/wildlife waste, and automobile emissions in this urban watershed are very prevalent and difficult to control. Water quality improvement projects upstream of lakes that reduce the amount of phosphorus runoff will continue to be a priority in the District. Chlorophyll-a was also a principle driver for water quality in some District lakes in 2013. Invasive species (both plant and animal) will continue to be a concern for future management, though they are not currently observed in alarming amounts in any CRWD lake. Curly-leaf pondweed was observed in all lakes, Eurasian watermilfoil was observed in Loeb Lake and Lake McCarrons, and common carp were observed in Lake McCarrons. Invasive species can cause harm to lakes through displacement of native species and disruption of the food chain, both of which can affect overall lake health. CRWD lakes are an important district resource, providing both economic (e.g. recreational resources) and environmental (e.g. flood attenuation) benefits. Understanding overall health of CRWD lakes in order to improve them for both kinds of benefits will be beneficial for the District and the region. Como Lake, Loeb Lake and Lake McCarrons are important community resources within the District as they are easily viewed and accessed by many people on a daily basis. Therefore, these lakes will continue to be a focal point for management. Como Lake has also exhibited a cyclical pattern in water quality for the monitored eutrophication parameters in past years, which will continue to be studied and analyzed in order to understand the lakeâ&#x20AC;&#x2122;s water quality. Loeb Lake and Lake McCarrons have had historically good water quality, but will continue to be monitored in the future to identify annual changes and trends.

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This report also contained additional information on biological data not previously reported upon in CRWD monitoring reports, including phytoplankton and zooplankton populations, aquatic vegetation communities, and fish populations. All of these parameters affect lake water quality and are important components in analyzing overall lake health. This report solely focused on reporting this new information, but not analyzing it. Future reports will contain more analysis of biological data, in conjunction with the chemical and physical data monitored. 11.2 RECOMMENDATIONS 11.2.1 ACCOMPLISHMENTS IN 2013

It is the goal of CRWD to continually improve the monitoring program with new ideas in order to advance the program in quality, efficiency, and usefulness. The monitoring program aims to collect and analyze high quality data from District lakes to better understand the water quality in individual lakes as well as how the watershed as a whole could be affecting lake water quality. Data collection and analysis through the monitoring program helps to further CRWD’s mission “to protect, manage and improve the water resources of the Capitol Region Watershed District.” In 2013, CRWD made progress towards the goals stated in the 2012 Monitoring Report for lake monitoring and reporting. These goals were: 1. Incorporate additional statistical analysis of lakes water quality data and long-term lake trends into 2013 lakes data analysis (completed in 2013 by Wenck Associates, Inc. (Appendix A)). 2. Complete additional biological data assessment and analysis of CRWD lakes to determine causes of water quality changes and trends. With respect to Goal 1, an analysis by CRWD was underway but was not completed in time to incorporate any statistical analysis into this 2013 report. However, the Wenck report demonstrated the District’s need for a more thorough understanding of missing pieces of data to make better assessments of lake health. It served as a catalyst to develop a work plan for the 2014 monitoring season (and future monitoring seasons) that expands and initiates additional lake monitoring. This additional monitoring is related to Goal 2: increasing monitoring and assessment of biological parameters of District lakes. Additional biological data supplements the chemical and physical parameters which have been included in previous CRWD monitoring reports. Biological data has been gathered in previous years, but due to incompleteness or inconsistencies, this data has not been analyzed or included in previous reporting. As a result of Goal 2, the 2013 report contains additional data that was not previously reported on, including lake elevation data, a lake grading system, phytoplankton and zooplankton community composition, aquatic vegetation type/occurrence/abundance, and fisheries surveys. The 2014 monitoring season will include and expand on these biological parameters.

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11.2.2 RECOMMENDATIONS FOR 2014

For 2014, CRWD has several goals and recommendations that are aimed at improving the lake monitoring program. Goals for 2014 include: 1. Improve lake elevation monitoring: CRWD will establish continuous level monitoring with level loggers in Como Lake, Crosby Lake, and Lake McCarrons in 2014 from the ice-out to ice-in period. Como Lake, Loeb Lake, and Lake McCarrons are currently monitored by the Minnesota DNR Lake Level Minnesota Monitoring Program, which collects level data bi-monthly (DNR, 2014i). Additional monitoring by CRWD will yield continuous level data during the monitoring season. Crosby Lake has not been historically monitored for lake level. By monitoring lake level on Crosby Lake, Mississippi River interactions with the lake can be better understood. Since Little Crosby Lake is so closely connected to Crosby Lake, it will not be monitored for lake level. 2. Analyze additional chemical and physical parameters: CRWD intends to expand the analysis of chemical and physical data previously collected but not fully analyzed in prior reports. Previous CRWD analyses have focused on certain water quality parameters (specifically TP, Chl-a, and Secchi disk depth). Analysis of other water chemistry and physical attributes will allow a better understanding of overall lake health and could potentially allow better prediction of the severity and timing of algal blooms, such as: o Nitrogen: including Ammonia-Nitrogen (NH3-N), nitrate as nitrogen (NO3-N), and Total Kjehldahl Nitrogen (TKN). While the limiting factor for algal growth in CRWD lakes is most often phosphorus, other nutrients such as nitrogen could also be playing a role in temporal blooms. o Chloride: It is a contaminant of concern in metro area lakes. Como Lake was listed on the draft 2014 303(d) Impaired Waters List for chloride (MPCA, 2014b), so this contaminant is becoming more of a management concern in CRWD lakes. o Temperature profile: Temperatures at different depths within the water column are currently measured by RCPW during their summer lake visits. Graphically creating temperature profiles of the lake throughout the monitoring season may also be helpful in explaining water quality trends. o Hypolimnetic water quality: Reports have historically focused on the nutrient concentration of the epilimnion (mixed surface layer) of lakes, since MPCA standards are based on this lake layer. Future reporting will examine hypolimnetic water quality data to determine possible internal phosphorus loading 2013 CRWD Lakes Monitoring Report

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from in-lake sediments. This could help better determine, for example, impacts of flooding from the Mississippi River on Crosby and Little Crosby Lake water quality (CRWD, 2012a). 3. Extend monitoring season of all District Lakes: CRWD will extend the lakes monitoring season to gather more data over a greater time period in order to capture seasonal variability in lake water quality and improve statistical confidence for trend assessments. The season will be expanded for chemical/physical monitoring, aquatic vegetation monitoring, and phytoplankton and zooplankton monitoring, including: o Physical and chemical monitoring: Extend sampling dates to early spring (April) and late fall (October) on all CRWD lakes, depending on climatological factors (e.g. ice-out and ice-in dates). o Vegetation monitoring: A third vegetation monitoring day will be considered for the 2014 monitoring schedule. Biovolume and point intercept vegetation surveys were conducted twice in 2012 and 2013 (late spring and late summer) and conducted inconsistently on select lakes before 2012. By collecting data on aquatic vegetation, information on fluctuations in vegetation type, location, and density can be established. If changes in these factors are observed in future surveys of plant communities, it can be determined if there have been significant changes in water quality and how that could be affecting plant populations, and vice-versa. o Phytoplankton and zooplankton monitoring: Extend early spring (April) and late fall (October) monitoring of phytoplankton and zooplankton on all CRWD lakes, depending on climatological factors (e.g. ice-out and ice-in dates). 4. Initiate fisheries surveys of all District Lakes: CRWD will initiate fisheries surveying of all lakes at least once per year and examine potential effects of non-native, invasive fish populations to lake health. o Fisheries surveys are conducted by Minnesota DNR staff, who surveys most lakes in the state on a 5-10 year cycle. In future monitoring seasons, CRWD will survey fish populations annually during years the DNR will not be surveying the CRWD lakes. o Common carp are an invasive fish that uproot vegetation and stir up bottom sediments, which releases phosphorus into the water column and decreases water clarity (DNR, 2014a). In the most recent fish surveys conducted on CRWD lakes, Lake McCarrons (2008) and Crosby Lake (2004) showed evidence of common carp populations. Although Little Crosby Lake was not independently surveyed 2013 CRWD Lakes Monitoring Report

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for fish, chances are high that it does contain common carp, since it is connected hydrologically to Crosby Lake. No common carp were sampled in Como Lake during the 2011 survey, but common carp have been sampled historically. Due to habitat degradation caused by common carp in the lake, a deliberate rough fish kill using rotenone occurred in 1985 (Noonan, 1998), which eliminated common carp before restocking the lake with native fish. While populations of common carp havenâ&#x20AC;&#x2122;t reestablished themselves in this lake, they could in the future. To become more aware of the impact carp can have, CRWD would like to begin working with other area watershed districts/management organizations to better understand management of carp populations and how the presence of carp has affected the water quality of lakes. 5. Install temperature monitoring equipment in Como Lake and Lake McCarrons: CRWD will install temperature monitoring equipment in Como Lake and Lake McCarrons in 2014 to determine effect of higher temperature runoff to lake temperature. o Como Lake has a large number of stormwater sewers that discharge runoff from the surrounding residential neighborhoods into the lake. This runoff is at a higher temperature than the lake water. Increasing the temperature of a lake reduces the solubility of dissolved oxygen (Kalff, 2002), resulting in less oxygen available for use by aquatic organisms. Continuous monitoring can give CRWD a better idea of the diurnal and seasonal variations in temperature in the lake. o The Villa Park Wetland Treatment System was installed in 1987 and improved in 2004 in the wetland areas northwest of Lake McCarrons. This system reduces the velocity of stormwater runoff to the lake and allows nutrients to settle out of the water and onto the bottom of the wetlands. This decreases the amount of nutrients flowing into Lake McCarrons. However, it also warms the water as it travels through this system, so that the Villa Park outflow to the lake is typically a higher temperature than the internal lake temperature. 6. Conduct sediment analyses of all District lakes: CRWD will conduct sediment analyses on all lakes during the winter of 2014-2015 to establish current understanding of internal sediment loading. o Previous sediment analyses on CRWD lakes were only completed for two lakes for specific projects (i.e.: the 2004 Lake McCarrons alum project and the 2008 Crosby Lake sediment analysis). o CRWD will consider additional sediment surveys in future years.

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7. Complete a comparative analysis of all parameters measured: CRWD will complete a comparative analysis of chemical, physical, and biological parameters to increase understanding of what these parameters are indicating about overall lake health. o CRWD will work with limnologists or other lake experts to conduct thorough analyses of all data and their complex interactions to evaluate water quality and overall lake health. o CRWD will expand comparisons of lakes to other similar metro-area lakes to see how the Districtâ&#x20AC;&#x2122;s lakes relate to those outside of CRWD.

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12 REFERENCES Capitol Region Watershed District (CRWD), 2014. 2013 Stormwater Monitoring Report. Saint Paul, MN. Capitol Region Watershed District (CRWD), 2012a. Crosby Lake Management Plan. Saint Paul, MN. Capitol Region Watershed District (CRWD), 2012b. Stormwater BMP Performance Assessment and Cost-Benefit Analysis. Saint Paul, MN. Capitol Region Watershed District (CRWD), 2009. Loeb Lake and Willow Reserve Management Plan. Saint Paul, MN. Capitol Region Watershed District (CRWD), 2003. Lake McCarrons Management Plan. Saint Paul, MN. Capitol Region Watershed District (CRWD), 2002. Como Lake Strategic Management Plan. Saint Paul, MN. CI BioBase, (CIBB), 2014. Frequently Asked Questions. Contour Innovations. Accessed online from http://cibiobase.com/Home/FAQ Heiskary, S. and H. Markus. Whatâ&#x20AC;&#x2122;s that green stuff? Minnesota Conservation Volunteer. July/August, 2010. Saint Paul, MN. Accessed online from http://www.dnr.state.mn.us/volunteer/julaug10/algae.html Kalff, Jacob. 2002. Limnology. Upper Saddle River, NJ: Prentice Hall. Kennedy, R. H. and Cook, G.D., 1982. Control of Lake Phosphorus with Aluminum Sulfate: Dose Determiniation adn Application Techniques. Journal of the American Water Resouces Assocation, 18: 389-395. doi: 10.1111/j.1752-1688.1982.tb00005.x Metropolitan Council (MC), 2013. Annual Use Estimate of the Metropolitan Region Parks System for 2012. Saint Paul, MN. Accessed online from http://www.metrocouncil.org/getattachment/581b1b25-e04e-4566-b99b-ec3396a100fc/.aspx Metropolitan Council (MC), 2011. 2010 Study of the Water Quality of 185 Metropolitan Area Lakes. Saint Paul, MN. Accessed online from http://es.metc.state.mn.us/eims/related_documents/repository/13201231344.pdf Minneapolis Parks and Recreation Board (MPRB), 2011. Water Resources Report. Minneapolis, MN. Accessed online from http://www.minneapolisparks.org/documents/caring/2011ReportFinalLow.pdf 2013 CRWD Lakes Monitoring Report

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Minnehaha Creek Watershed District (MCWD), 2012. Hydrologic, Hydraulic and Water Quality Technical Report. Deephaven, MN. Accessed online from http://www.minnehahacreek.org/sites/minnehahacreek.org/files/pdfs/Data_Center/2012/2012_Te chnicalReport.pdf Minnesota Climatology Working Group (MCWG), 2013. St. Paul Campus Climatological Observatory: 15-minute precipitation data. Saint Paul, MN. Accessed online from http://climate.umn.edu/doc/observatory.htm Minnesota Climatology Working Group (MCWG), 2014. Minneapolis/St. Paul Metro Snow Resources. Accessed online from http://climate.umn.edu/doc/twin_cities/twin_cities_snow.htm Minnesota Department of Natural Resources (DNR), 2014a. Common carp. Saint Paul, MN. Accessed online from http://www.dnr.state.mn.us/invasives/aquaticanimals/commoncarp/index.html Minnesota Department of Natural Resources (DNR), 2014b. Eurasian watermilfoil. Saint Paul, MN. Accessed online from http://www.dnr.state.mn.us/invasives/aquaticplants/milfoil/index.html Minnesota Department of Natural Resources (DNR), 2014c. Filamentous algae. Saint Paul, MN. Accessed online from http://dnr.state.mn.us/aquatic_plants/algae/filamentous_algae.html Minnesota Department of Natural Resources (DNR), 2014d. Fisheries Lake Surveys. Saint Paul, MN. Accessed online from http://www.dnr.state.mn.us/lakefind/surveys.html Minnesota Department of Natural Resources (DNR), 2014e. Fishing in the Neighborhood. Saint Paul, MN. Accessed online from http://www.dnr.state.mn.us/fishing/fin/moreinfo.html Minnesota Department of Natural Resources (DNR), 2014f. A Guide to Aquatic Plants. Saint Paul, MN. Accessed online from http://dnr.state.mn.us/shorelandmgmt/apg/index.html Minnesota Department of Natural Resources (DNR), 2014g. Lake Finder. Saint Paul, MN. Accessed online from http://www.dnr.state.mn.us/lakefind/index.html Minnesota Department of Natural Resources (DNR), 2014h. 2013 Lake Ice Out Dates. Accessed on-line from http://www.dnr.state.mn.us/ice_out/index.html?year=2013. Minnesota Department of Natural Resources (DNR), 2014i. Lake Level Minnesota. Saint Paul, MN. Accessed online from http://www.dnr.state.mn.us/climate/waterlevels/lakes/index.html Minnesota Department of Natural Resources (DNR), 2014j. Median Lake Ice Out Dates. Accessed on-line from http://www.dnr.state.mn.us/ice_out/index.html?year=median

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Minnesota Department of Natural Resources (DNR), 2005. Invasive, non-native species â&#x20AC;&#x201C; Curlyleaf pondweed. Saint Paul, MN. Accessed online from http://files.dnr.state.mn.us/natural_resources/invasives/aquaticplants/curlyleafpondweed/curlylea f_factsheet.pdf Minnesota Pollution Control Agency (MPCA), 2014a. Guidance Manual for Assessing the Quality of Minnesota Surface Waters for Determination of Impairment: 305(b) Report and 303(d) List. Saint Paul, MN. Accessed online from http://www.pca.state.mn.us/index.php/viewdocument.html?gid=16988. Minnesota Pollution Control Agency (MPCA), 2014b. Impaired Waters List â&#x20AC;&#x201C; The Draft 2014 Impaired Waters List. Saint Paul, MN. Accessed online from http://www.pca.state.mn.us/index.php/water/water-types-and-programs/minnesotas-impairedwaters-and-tmdls/impaired-waters-list.html Minnesota Pollution Control Agency (MPCA), 2012. Final TMDL list of impaired waters. Saint Paul, MN. Accessed online from http://www.pca.state.mn.us/index.php/viewdocument.html?gid=8281. National Weather Service (NWS), 2014a. Local Climate Records. Chanhassen, MN. Accessed online from http://www.crh.noaa.gov/mpx/Climate/MSPClimate.php National Weather Service (NWS), 2014b. Twin Cities Snowfall Records. Chanhassen, MN. Accessed online from http://www.crh.noaa.gov/mpx/?n=mspsnowfall National Weather Service (NWS), 2011. New 1981-2010 Climate Normals. Accessed on-line from http://www.crh.noaa.gov/mpx/?n=mpxclimatenormals Noonan, T.A., 1998. Como Lake, Minnesota: The Long-Term Response of a Shallow Urban Lake to Biomanipulation. Journal of Lake and Reservoir Management. 14(1):92-109. Osgood, R.A., 1989. An Evaluation of Lake and Stream Monitoring Programs in the Twin Cities Metropolitan Area. Metropolitan Council Publ. 590-89-128. Ramsey County Public Works (RCPW), 2012. Quality Assurance and Procedures Manual for the Ramsey County Lake Management Laboratory. Arden Hills, MN. Ramsey County Public Works (RCPW), 2009. Ramsey County Lake Management Program 2009 Lake Sampling Protocal. Arden Hills, MN. Scherek, J. and G. Yakal. (1993). Guidelines for Ordinary High Water Level (OHWL) Determinations. Saint Paul, MN. (Technical Paper 11, Minnesota Department of Natural Resources, Waters). University of California Museum of Paleontology (UCMP), 2014. Taxon Lift. Berkeley, CA. Accessed online from: http://www.ucmp.berkeley.edu/help/taxaform.html 2013 CRWD Lakes Monitoring Report

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University of Wisconsin Extension (UWE), 2004. Understanding Lake Data. Madison, WI. University of Wisconsin Extension Publication G3582. Accessed online from http://www3.uwsp.edu/cnr-ap/weal/Documents/G3582.pdf Washington State Department of Ecology (WSDE), 2014. Non-native Invasive Freshwater Plants: Eurasian Watermilfoil. Olympia, WA. Accessed online from http://www.ecy.wa.gov/programs/wq/plants/weeds/milfoil.html

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APPENDIX A: TECHNICAL MEMORANDUM — STATISTICAL ANALYSIS OF LAKE DATA IN CRWD

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Wenck Associates, Inc.  1800 Pioneer Creek Center  P.O. Box 249  Maple Plain, MN 55359‐0249    800‐472‐2232  (763) 479‐4200  Fax (763) 479‐4242   wenckmp@wenck.com  www.wenck.com 

 

TECHNICAL MEMORANDUM    TO:  Anna Eleria, Capitol Region Watershed District    FROM:  Joe Bischoff, Wenck Associates, Inc.     DATE:  September 18, 2013    SUBJECT:  Statistical Analysis of Lake Data in the Capitol Region Watershed District      Purpose    The purpose of this technical memorandum is to present results from a statistical analysis of lake data in  the Capitol Region Watershed District. The intent of the statistical analysis is to answer the following  questions:     Can the water quality of CRWD lakes be described as generally getting better or worse than was  recorded in the past?     What trends in water quality exist?  Can these trends be verified through statistical methods?   What factors are driving the trends in water quality among the different lakes?     What qualitative statements can be made regarding the causes and effects in the observed  water quality trends? 

To answer these questions, Wenck employed a number of statistical analyses including trend analysis, hypothesis testing, and general descriptive statistics. Results of the analyses for each lake are presented below. Approach CRWD provided Wenck with water quality and biological data for the four lakes to be assessed (Table 1). After review, the project team decided to focus on the water quality parameters (TP, chlorphyll-a, and Secchi) first, and use the biological data where possible to provide context for the water quality data. Fairly long records of phytoplankton and zooplankton data are available for Como, Crosby, and McCarron Lake.

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Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013     

Table 1. Available data for the lake statistical analyses. Data Description

Como

Aquatic vegetation and species survey 2012 Como Lake Turtle Study

Crosby

Loeb 

McCarrons

2012

2012

2012

1999‐2007

2003‐2007

1988‐2007

2005

2010

2011

Crosby Lake Sediment Data Daphnia Size

Little Crosby

2010 1984‐2007

DNR Fisheries‐Lake Management Plan Lake Elevations

1978‐2012

2003‐2004, 2006‐2012 1924‐2012

Lake Sampling Data

1982, 1984‐2012

1999‐2012

2003‐2012

1988‐2012

Macrophyte Surveys

2005, 2010

2009

2005

2005

Phytoplankton Data Zooplankton Data

1984‐2011 1984‐2011

1999‐2011 1999‐2011

2003‐2011 2003‐2011

1988‐1998, 2000‐2011 1988‐1998, 2000‐2011

2011‐2012

To evaluate trends in lake water quality, Wenck employed a series of statistical tests for the period of record. Wenck conducted the following steps in the statistical analysis of the lake data: 1. Evaluate the normality of the data including the residuals and log‐transformed data and  residuals. Levene’s test was used to assess equal variance among the years and the Shapiro‐ Wilks test was used to test for normality of the entire data set as well as each year. These tests  are critical to ensure statistical test assumptions are not violated. Analyses can be conducted on  the data, residuals, log‐transformed data, or log‐transformed residuals.   2. Run pairwise comparisons among the years using either ANOVA (parametric test if assumptions  are met) or Kruskall‐Wallace (non‐parametric test if assumptions are not met) tests to assess  difference among the years. Post‐hoc testing was completed using the Bonferonni test at a 0.1  significance level.   3. Visually plot data sets using time series and box plots to identify potential trends, seasonality, or  other exogenous factors that may be influencing the data set.  4.  Evaluate potential exogenous variables for their influence on the data set. An exogenous  variable is an outside variable that may demonstrate trends that will influence the analysis  variable.  For example, lake water quality data may be influenced by precipitation patterns  causing the analyst to interpret precipitation trends as water quality trends.   5. Monthly plots to evaluate the potential for seasonality in the data set.  6. Autocorrelograms to determine the level of autocorrelation in the data set. Autocorrelograms  lag the data sets to evaluate correlation between sequentially collected samples. So, at lag 1,  two sequentially collected samples are compared for correlation. At lag 2, the first and third  samples in a series are compared for correlation and so on.   2  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      7. Trend analysis for the data set corrected for autocorrelation and seasonality of necessary. The  Mann Kendall‐Tau test was used in most cases which performs the trend assessment on the  ranks of the data sets.   8. A multivariate analysis of lake Trophic Status Index to evaluate drivers of lake water quality.  

Data Description The first step is to describe the data set focusing on the assumptions for each potential statistical test. For example, most parametric statistical hypothesis tests such as ANOVA require the data have a normal distribution and equal variances among groups. In the case where this is not true, alternative nonparametric hypothesis tests such as the Kruskall-Wallace test can to be used. Because parametric testing is more powerful in determining differences among groups or trends, it is worthwhile to check the data and residuals as well as the log transformed data and residuals for the assumptions of equal variance and normality. Data Visualization The second step is to visualize the data set to develop a general understanding of potential trends in the data set or other factors that may be causing trends in the data set. Many potential trends can be recognized using data visualization techniques such as notched box plots, histograms, scatter plots and other plots of the data or residuals of the data. Once any trends are identified at this level, they can be further evaluated using the appropriately selected statistical test. Wenck developed notched box plots by year and month to evaluate trends and statistical differences among the years. The notches in the box plots represent the 95% confidence internal around the mean, so when the notches overlap, there is no statistical difference in the means of the individual data sets. If they do not overlap, the means are likely statistically different. Trend Assessment To evaluate trends, Wenck first evaluated the necessary statistical assumptions for using trend analysis including normality of the data set and equal variance over time. In almost all cases, the data sets were determined to be non-normal. The Mann-Kendall Tau test for trends is nonparametric and is therefore appropriate where the data are non-normal although it still requires equal variance over time. The Mann-Kendall Tau test can also be adjusted for serial autocorrelation, the condition where a previous sample in time is correlated to the current sample, and seasonality.

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Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013     

Differences Among Years The data set was also evaluated for differences among the years to identify groups of years that may be similar. The groupings can then be evaluated for similar conditions such as rainfall or fish abundance to evaluate potential causes. For this analysis, the grouping was completed; however a detailed review of other factors was outside the scope of this assessment. Multivariate Assessment using the Lake Trophic Status Index The interrelationship between simultaneously collected variables can be used to identify conditions in a lake that affect those measured variables. One way this can be done is by evaluating the differences among TSI values for each of the three collected variables (Carlson 1992). Theoretically, the empirical relationships between TP, chlorophyll-a, and Secchi should result in the same TSI value. Because these empirical relationships are derived from regressions that have error terms, some variability can be expected. However, in some situations the differences are not random and can be used to identify factors interfering with the relationship. The figure below represents a plot of the TSI differences with 4 primary zones for interpretation. Table 2 provides some interpretation of the data in each zone. If points fall below the x axis, chlorophyll-a is under predicted suggesting that P is not limiting algal growth, rather algal growth is limited by light availability, nitrogen limitation or zooplankton grazing. Points lying to the right of the y axis indicate better clarity than expected which may be a result of larger algae such as aphanizomenon, a colony forming blue-green algae. Points to the left of the y-axis suggest smaller particles dominate suggesting water color or turbidity is a critical factor. Points lying along the diagonal and to the left of the axis suggest that P and clarity are correlated, but the expected chlorophyll response is not demonstrated. This suggest non-algal turbidity such as clay is controlling water clarity and keeping the P unavailable for algal production.

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Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013     

Carlson and Simpson 1996.

Following is a discussion of the results of the statistical analysis for each lake.

LAKE MCCARRON   Descriptive Statistics    Total phosphorus, chlorophyll‐a and Secchi depth were assessed for basic statistical assumptions such as  normality, equal variance, and central tendencies (Table 2). None of the data sets as a whole are normal  or lognormal, although Secchi depth demonstrates a lognormal distribution in all but one year.                   5  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013        Table 2. General statistical description of Lake McCarrons water quality data.  Statistic No. of observations Minimum Maximum 1st Quartile Median 3rd Quartile Mean Variance (n-1) Standard deviation (n-1) Skewness (Pearson) Kurtosis (Pearson) Standard error of the mean Geometric mean Geometric standard deviation

TP (mg/L) 177 0.009 0.175 0.016 0.026 0.039 0.031 0.001 0.025 3.258 14.539 0.002 0.026

Chl-a (µg/L) 177 0.317 74.800 2.780 6.500 13.370 9.760 107.056 10.347 2.856 12.298 0.787 6.197

Secchi (m) 177 0.700 8.400 1.700 2.750 4.000 2.952 2.199 1.483 0.697 0.206 0.114 2.580

1.862

2.686

1.715

  Summer average phosphorus, chlorophyll‐a and Secchi depth were plotted for Lake McCarrons (Figure  1). Both TP and chlorophyll‐a demonstrate a decreasing trend in concentration with Secchi depth  demonstrating an increasing trend in water clarity. It is important to note that an alum treatment was  performed on the lake in 2004 which essentially breaks the data set into two distinct periods: pre‐ and  post‐alum application. Long term notched box plots demonstrate an improving trend in water quality  (Figure 2).  Pre‐alum variability was quite high with extreme values in TP and chlorophyll‐a. After the  alum treatment the spread of the data decreased significantly for chlorophyll‐a and TP.  It is also  interesting to note that the lake appears to have taken a few years after the alum treatment to reach  the maximum effectiveness (2007‐2010).  The most recent two years demonstrate a broader spread in  the data suggesting that the effectiveness of the alum treatment may be weakening.     Annual Pairwise Comparisons    Data and residuals, including log transformations, for Lake McCarrons was evaluated to test for  normality and equal variance among the sample years (Table 3). To use parametric testing such as an  ANOVA to test for differences among years, the test groups must be normally distributed and have  equal variance. Although some of the Secchi depth data was normally distributed or had equal variances  among years, none occurred in the same grouping.  Therefore, the nonparametric Kruskall‐Wallace test  was selected with a Bonferonni post‐hoc pairwise comparison.             6  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013        Table 3. Evaluation results for tests of normality and equal variance among groups.   Parameter Total Phosphorus Chlorophylla Secchi Depth

Data

Residuals1

Logs of Data Equal Variance?

Normally Distributed?

Equal Variance?

Residuals of Logs1

Equal Variance?1

Normally Distributed?2

Normally Distributed?

Equal Variance?

Normally Distributed?

No

No

Yes

No

No

No

Yes

No

No

No

Yes

No

No

No

Yes

No

Yes

No

No

Yes

Yes

No

No

Yes

1

Levene’s test  Shapiro‐Wilks test 

2

  The Kruskall‐Wallace and Bonferonni tests demonstrated significant differences among the years for all  three parameters (Attachment 1).   A total of 81 pairs were significantly different than one another for  TP. Most of the years prior to the alum treatment were significantly higher in TP than those years after  the treatment except for 1989, 1992, 1994, and 1998 with 2008 and 2009 significantly lower than all the  other years.      Only 27 pairs of years were significantly different than one another for chlorophyll‐a.  The most recent  two years are statistically similar than almost all the other years, although based on visual inspection  (Figure 2) the spread of the data is tighter in more recent years. The fact that the most recent years of  chlorophyll‐a data are similar to most years suggests that other factors may be affecting mean algal  abundance or that the effectiveness of the alum treatment is diminishing. Overall, the post‐alum  treatment chlorophyll‐a abundance is significantly lower.  However, the reduced phosphorus  concentrations appear to have reduced significant algal blooms (decreased spread in the data).      Only 2008, when Secchi depth was at its highest, demonstrated a significant difference than most of the  pre‐alum treatment period.  This is slightly surprising given the significant reductions in chlorophyll‐a  and total phosphorus. Other factors are likely controlling Secchi depth at these lower chlorophyll‐a  concentrations and 2008 likely presents the best achievable Secchi depth when addressing only  phosphorus and chlorophyll‐a.     Trend Assessment    Based on the visual assessment of water quality data in Lake McCarrons it is clear that there are two  distinct periods to evaluate trends including the pre‐ and post‐alum treatment periods. An assessment  of trends needs to focus on these two periods.     Exogenous Variables    7  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      Before evaluating trends in a lake data set, exogenous variables that may be causing a pattern in the  data must be evaluated and removed if present. An exogenous variable is a variable other than time  that may have considerable influence on the response variable. These variables are usually natural such  as rainfall, temperature or stream flow.  For lakes, especially those with long residence times such as  Lake McCarron, the most common potential exogenous variable is rainfall.    To test for rainfall as a factor, monthly total precipitation was regressed against monthly average TP  concentrations for the period of record (Figure 3). No relationship between TP and monthly  precipitation totals was found for the data or the logs of the data. Consequently, it was concluded that  rainfall totals does not need to be accounted for in the trend analysis.     Seasonality and Autocorrelation    Two other factors that need to be accounted for in any trend analysis including serial autocorrelation  and seasonality.  Seasonality is important in lakes since they demonstrate a clear growing season along  with a dormant season. However, most of the monitoring data were collected during the growing  season meaning that years to year comparisons are not likely to include much seasonality in the data.  Monthly notched box plots confirm this assumption (Figure 4). Only Secchi depth for one month  (August) demonstrated a significant difference among the months. Based on this assessment, using the  seasonally adjusted Kendall Tau trend test is not necessary.     Lake data tend to be serially autocorrelated due to long residence times. To evaluate serial  autocorrelation, correlograms were developed for each of the three parameters (Figure 5).  Autocorrelograms evaluate autocorrelation using time lags in the data. For our analysis, we chose a lag  period of 12 to account for annual data.  Typical sampling in Lake McCarrons was 7 samples over the  summer growing season. However, a lag period of 12 allows for evaluation of autocorrelation within a  sampling year and between years. All three parameters demonstrated autocorrelation within any given  year but not between years. Consequently, autocorrelation must be accounted for in the trend analysis.     Trend Assessment    Because a major event (alum treatment) occurred in Lake McCarron, the trend assessment must  account for both the pre‐ and post‐alum conditions. Total phosphorus conditions before and after the  alum treatment were statistically different (Figure 6).     No trends were detected in either the pre‐ or post‐alum treatment data sets using the Mann‐Kendall  trend test with a significance value of 0.05.  Trends tests on the overall data set do demonstrate an  improving trend in water quality although this is solely a result of the alum treatment conducted in  2004.     Multi‐Variate Assessment     8  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      The multivariate TSI comparison for Lake McCarrons did not present a great deal of information about  the lake (Figure 7). Essentially, Lake McCarrons appears to be a typically P limited lake.  Much of the  data do fall right of the y‐axis suggesting that larger particles such as Aphanizomenon dominate water  clarity. This is further corroborated by the lack of significant improvements in water clarity after the  alum treatment where algae were reduced but the water clarity was already relatively good.     Potential Divers of Water Quality    Lake McCarrons Conclusions    1. Water quality in Lake McCarrons after the alum treatment was statistically better than the pre‐ alum water quality for all three parameters. Water quality appears to have peaked in 2008  through 2010 and may be trending poorer in the past two years.  However, it is impossible to  tell if this is just annual variability and visual observations of the data suggest that the alum  treatment is still effective.   2. Prior to the alum treatment, peak total phosphorus concentrations were typically observed in  the spring (April‐May) samples suggesting high runoff loads during these periods.  3. No statistical trends were detected in water quality data for either pre‐ or post‐alum conditions  in Lake McCarrons. However, recent spread in total phosphorus and Secchi depth data suggest  that water quality may be changing and the alum treatment effectiveness may be weakening.  However, other data such as sediment cores are needed to evaluate current sediment release.  4. Other than 2008 and 2009, mean chlorophyll‐a data after the alum treatment was statistically  similar to many of the pre‐treatment years suggesting there was not a great overall reduction in  algal abundance in the lake.  However, mean algal abundance has been reduced and it does  appear to have eliminated significant algae blooms in the lake.   5. Water clarity overall did increase significantly after the alum treatment. However, year to year  comparisons suggest that the clarity is not significantly different than many of the previous  years. It is important to note that the year to year tests have less statistical power due to the  lower sample size in each given year. So, water clarity was improved for much of the year, but  some years still may demonstrate water clarity similar to past years even though overall algal  abundance is lower. 2008 is likely the best achievable Secchi depth by controlling phosphorus  alone.   6. Based on the multi‐variate assessment of the Trophic Status Index, Lake McCarrons appears to  be a typical P‐limited lake where larger particles dominate and zooplankton grazing likely plays a  factor is algal abundance. 

    9  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013     

    Como Lake Descriptive Statistics    Total phosphorus, chlorophyll‐a and Secchi depth were assessed for basic statistical assumptions such as  normality, equal variance, and central tendencies (Table 4). Chlorophyll‐a had a wide range of values  resulting a large standard deviation.     Table 4. General statistical description of Lake McCarrons water quality data.  Statistic No. of observations Minimum Maximum 1st Quartile Median 3rd Quartile Mean Variance (n-1) Standard deviation (n-1) Skewness (Pearson) Kurtosis (Pearson) Standard error of the mean Geometric mean Geometric standard deviation

TP (mg/L) 307 0.031 0.970 0.089 0.129 0.228 0.182 0.023 0.150 2.358 6.879 0.009 0.142

Chl-a (ug/L) 307 0.1 223.3 6.8 20.1 49.4 32.8 1261.7 35.5 1.9 4.8 2.1 16.5

Secchi (m) 307 0.20 4.20 0.70 1.20 2.20 1.58 1.09 1.05 0.86 -0.31 0.06 1.26

1.974

3.9

2.00

  A visual review of the summer average total phosphorus concentrations  for Como Lake suggest a  somewhat cyclical patter of several years of high phosphorus concentrations followed by a few years of  lower concentrations (Figure 8 and Figure 9).  Both response variables follow similar patterns.  The  patterns may reflect cyclical life cycles of fish, particularly panfish, which can follow boom‐bust patterns.   The fishery may ultimately affect zooplankton grazing and chlorophyll‐a abundance. Although there  appears to be a cyclical pattern, there is no apparent trend in the data or major shift at any point in  time.     Annual Pairwise Comparisons    Data and residuals, including log transformations, for Como Lake were evaluated to test for normality  and equal variance among the sample years (Table 5). To use parametric testing such as an ANOVA to  test for differences among years, the test groups must be normally distributed and have equal variance.   10  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      No of the groups followed these assumptions. Therefore, the nonparametric Kruskall‐Wallace test was  selected with a Bonferonni post‐hoc pairwise comparison.       Table 5. Evaluation results for tests of normality and equal variance among groups.  Parameter Total Phosphorus Chlorophylla Secchi Depth

Data

Residuals1

Logs of Data Equal Variance?

Normally Distributed?

Equal Variance?

Residuals of Logs1

Equal Variance?1

Normally Distributed?2

Normally Distributed?

Equal Variance?

Normally Distributed?

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

1

Levene’s test  Shapiro‐Wilks test 

2

  Pairwise comparisons for Como Lake TP suggest that there are not many significant differences from  year to year since only 22 pairs demonstrated statistically significant differences and where most  differences were between extreme years. These results suggest that although there appears to be  differences in the spread of the data among years, average conditions are not significantly different.     Both chlorophyll‐a and Secchi follow a similar cyclical pattern, however they demonstrate more  difference among pairs, especially Secchi depth (Figure 9).  The fact that more differences were not  picked up in chlorophyll‐a is likely a result of the high variances in many of the years. For Secchi, there  were 70 statistically different pairs. The greater number differences among years for water clarity  suggest that water clarity is controlled by multiple factors and not just TP and chlorophyll‐a abundance.     Further exploration of the cyclical patterns in the lake data may reveal other factors affecting water  clarity such as changes in the fish community, patterns of vegetation change, and potential climatic  patterns.     Trend Assessment    Exogenous Variables    Precipitation was evaluated as a potential factor affecting water quality trends in Como Lake (Figure 10).  No relationship was found between monthly TP concentrations and monthly precipitation totals.     Seasonality and Autocorrelation    Box plots of monthly data suggest some seasonality in the data collected for Como Lake (Figure 11).  It is  important to note that the majority of the data were collected in the summer months.  Because so few  11  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      of the data are collected outside of the summer months, seasonality in the trend assessment can be  ignored.     The data do present autocorrelation, especially in those data collected in that same year (Figure 12).   Data collected between years do not appear to be autocorrelated which is expected since the residence  time of Como Lake is likely relatively short. Serial autocorrelation was accounted for in the trend  assessment.     Trend Assessment    Total phosphorus in Como Lake did demonstrate a significant decreasing trend, although it was not  significant if seasonality is included.  Based on the relatively small data set outside of the summer  season, the non‐seasonally adjusted test is acceptable.  A trend test on the summer average TP did not  result in a significant trend in the data. Neither chlorophyll‐a or Secchi depth resulted in a significant  trend.     Multi‐Variate Assessment     The multivariate assessment resulted in a number insights about Como Lake including:    1. phosphorus is not limiting algal growth, and that a phosphorus surplus may exist in the lake  2. Zooplankton grazing plays a large role in controlling water clarity in Como Lake. This is similar to  conclusions by Noonan (1998) who determined cyclical patters in lake water quality are a result  of complex interactions between submerged aquatic vegetation, zooplankton grazing, nutrient  cycling and fish abundance.   3. Vegetation in Como Lake is currently sparse (CRWD 2012) correlating to lower daphnia  abundance (Figure 14) and poorer water quality.  Potential Drivers of Water Quality    Como Lake Conclusions    1. Cyclical patterns in water quality suggest that outside factors that follow cyclical patterns may  be affecting water quality in Como Lake. Noonan (1998) concluded that although “bottom‐up”  nutrient controls play a factor in Como Lake, other factors such as plant abundance, fisheries,  and zooplankton abundance are also critical in controlling water quality.   2. Secchi depth demonstrated many more statistically different years than either chlorophyll‐a or  TP, suggesting that other factors may be affecting water clarity.  Some potential factors include  wind resuspension of sediment, changes in zooplankton abundance, TSS inflow, or rough fish  activity.   12  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      3. A statistically significant decreasing trend in TP was detected in Como Lake, although a trend  test on the summer average data was not significant. However, statistical differences among the  years in TP did not pick up significant patterns, confounding the results.  It appears that TP is  possibly decreasing in Como Lake, but more data will improve the prediction.   4. Based on the data, management of water quality in Como Lake should focus on the submerged  aquatic vegetation community as well as nutrient reductions. Fish abundance is also an  important factor.     Crosby Lake    Total phosphorus, chlorophyll‐a and Secchi depth were assessed for basic statistical assumptions such as  normality, equal variance, and central tendencies (Table 6).  None of the parameters were normally or  log‐normally distributed.     Table 6. General statistical description of Lake McCarrons water quality data.  Statistic No. of observations Minimum Maximum Range 1st Quartile Median 3rd Quartile Mean Variance (n-1) Standard deviation (n-1) Skewness (Pearson) Kurtosis (Pearson) Standard error of the mean Geometric mean Geometric standard deviation

TP (mg/L) 87 0.010 0.330 0.320 0.032 0.051 0.091 0.066 0.002 0.050 2.415 8.414 0.005 0.053 1.895

Chl-a (µg/L) 87 0.2 47.0 46.8 2.8 4.7 8.8 8.0 75.6 8.7 2.2 5.0 0.9 5.1

Secchi (m) 87 0.50 4.90 4.40 1.63 2.00 2.88 2.26 0.85 0.92 0.55 -0.23 0.10 2.07

2.6

1.55

  Plots of the summer mean water quality for Crosby Lake show a decrease in water quality over the past  five years with increasing TP and chlorophyll‐a concentrations and decreasing water clarity (Figure 15). It  is important to note that although chlorophyll‐a demonstrates an increase over the past 8 years, the  concentrations still remain below the state standard of 20 µg/L as a summer average. Secchi disk  transparency has decreased over the years but still remains greater than the state standard of greater  than 1 meter.     13  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      Notched box plots for water quality suggest that water quality may be degrading with the most recent  period showing greater extremes and spread in the data especially for TP and chlorophyll‐a (Figure 16).  TP demonstrated statistically significant increases in the past three years.     Annual Pairwise Comparisons    Data and residuals, including log transformations, for Crosby Lake were evaluated to test for normality  and equal variance among the sample years (Table 7). To use parametric testing such as an ANOVA to  test for differences among years, the test groups must be normally distributed and have equal variance.  None of the parameters had normal distributions or equal variance among the groups. Therefore, the  nonparametric Kruskall‐Wallace test was selected with a Bonferonni post‐hoc pairwise comparison.       Table 7. Evaluation results for tests of normality and equal variance among groups.  Parameter Total Phosphorus Chlorophylla Secchi Depth

Data

Residuals1

Logs of Data Equal Variance?

Normally Distributed?

Equal Variance?

Residuals of Logs1

Equal Variance?1

Normally Distributed?2

Normally Distributed?

Equal Variance?

Normally Distributed?

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

1

Levene’s test  Shapiro‐Wilks test 

2

  Pairwise comparisons for TP show the last three years being statistically higher than most other years  2001, 2002, 2005 and 2006.  So, although the last three years are higher, these TP levels in the lake are  not unprecedented. Chlorophyll‐a doesn’t follow the same patter as TP with 2012 statistically similar to  all other years and only 2010 and 2011 being statistically higher than the lowest of the previous years.  Secchi depth follows chlorophyll‐a patterns suggesting that algal abundance is likely the primary driver  for water clarity in Crosby Lake.     Trend Assessment    Exogenous Variables    Precipitation was evaluated as a potential factor affecting water quality trends in Crosby Lake (Figure  17). No relationship was found between monthly TP concentrations and monthly precipitation totals.     Seasonality and Autocorrelation    The majority of data collected for Crosby Lake were collected in the summer months which did not  demonstrate statistical differences for TP or chlorophyll‐a but did have some differences for Secchi  14  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      (Figure 18).  Because the three parameters are related, a non‐seasonally adjusted Kendall Tau is  appropriate, but both should be evaluated for Secchi.     Crosby Lake demonstrated serial autocorrelation in any given year’s data set, but not between years  (Figure 19).  Consequently, serial autocorrelation needs to be accounted for in the trend assessment.     Trend Assessment    A Mann‐Kendall Tau test was positive for all three parameters with increasing trends in both TP and  chlorophyll‐a and a seasonally adjusted decreasing trend in Secchi depth. The trend was also significant  for the annual average data for all three parameters. Crosby Lake is trending toward poorer water  quality.     One factor that may be affecting water quality for Crosby Lake is interaction with the Mississippi River.  Table 8 shows the number of days by year that the Mississippi River was at an elevation that would  discharge to Crosby Lake (Elev. 697 feet). Although the Mississippi River interacts with Crosby Lake  periodically over the past 15 years, the lake has received inputs from the River for the past 4 years with  the Lake being flooded for 103 days in 2011. Similarly, in 2001 and the following year, water quality was  poor following 63 days of inundation by the River.  It appears likely that inundation from the Mississippi  River is a significant factor affecting water quality in Crosby Lake.     Table 8.  Annual days the Mississippi River is at an elevation that interacts with Crosby Lake (Wenck  2012).   Year  Number of Days Mississippi River  Interacts with Crosby Lake  1999  14  2000  0  2001  63  2002  0  2003  0  2004  0  2005  0  2006  19  2007  0  2008  0  2009  15  2010  36  2011  103  2012  10  15  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013              Multi���Variate Assessment     The multivariate TSI approach suggests that Crosby Lake is not typically limited by P, but may be limited  by other factors such as light or P‐availability (Figure 20).  The graph suggests that not all of the TP in the  water column is available for algal production and may be adhered to small particles such as clay or  other TSS components. TP may be increasing in the lake, but it does not appear to all be readily available  for algal production.  Because there is a P surplus, other factors need to be considered in managing  Crosby Lake including fisheries and submerged aquatic vegetation abundance.     Potential Divers of Water Quality    Crosby Lake Conclusions    1. Water quality in Crosby Lake’s three most recent years demonstrates an increase in total  phosphorus and a decrease in water clarity. Algal abundance is high in 2010 and 2011, although  water quality in 2012 was typical of previous years even though TP was higher. This suggests  that water quality in Crosby Lake is degrading but that algal abundance is not necessarily  controlled directly by TP (some fraction of phosphorus may be unavailable or zooplankton  grazing may play a role).   2. Water clarity appears to be primarily driven by algal abundance.   3. Statistical trend testing verifies that water quality in Crosby Lake is trending poorer with  increases in total phosphorus and chlorophyll‐a and decreases in water clarity. However, this  may be a function of inundation by the Mississippi River which occurred for 164 days over the  past 4 years.     Loeb Lake    Total phosphorus, chlorophyll‐a and Secchi depth were assessed for basic statistical assumptions such as  normality, equal variance, and central tendencies (Table 9).  Secchi depth is normally distributed for  Loeb Lake. TP and chlorophyll‐a were not normally or log‐normally distributed. Variance for all three  parameters was low.           16  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013                Table 9. General statistical description of Lake McCarrons water quality data.  Statistic No. of observations Minimum Maximum Range 1st Quartile Median 3rd Quartile Mean Variance (n-1) Standard deviation (n-1) Skewness (Pearson) Kurtosis (Pearson) Standard error of the mean Geometric mean Geometric standard deviation

TP (mg/L) 70 0.012 0.093 0.081 0.017 0.022 0.027 0.024 0.000 0.012 3.166 14.803 0.001 0.022 1.459

Chl-a (ug/L) 70 1.1 21.8 20.7 2.4 3.4 6.3 4.5 10.5 3.2 2.5 10.1 0.4 3.7 1.9

Secchi (m) 70 1.90 4.60 2.70 2.80 3.35 3.80 3.29 0.45 0.67 -0.25 -0.75 0.08 3.22 1.24

  Loeb Lake does not demonstrate much variability in water quality between years (Figure 21 and 22).   2003 appears to have the worst water in the data record although the lake still met state water quality  standards.     Annual Pairwise Comparisons    Data and residuals, including log transformations, for Loeb Lake was evaluated to test for normality and  equal variance among the sample years (Table 8). To use parametric testing such as an ANOVA to test  for differences among years, the test groups must be normally distributed and have equal variance.  Secchi depth was normally distributed in all years and demonstrated equal variance. Chlorophyll‐a was  log‐normally distributed and logs had equal variance among the years. TP residuals were normally  distributed and had equal variance among the groups. Therefore, the parametric GLM (ANOVA) test was  selected with a Bonferonni post‐hoc pairwise comparison.       Table 8. Evaluation results for tests of normality and equal variance among groups.  Parameter Total Phosphorus

Data

Residuals1

Logs of Data

Equal Variance?1

Normally Distributed?2

Yes

No

Equal Variance?

Yes

Normally Distributed?

No

Equal Variance?

Yes

Residuals of Logs1 Normally Distributed?

Yes

Equal Variance?

Normally Distributed?

Yes

No

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Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      Chlorophylla Secchi Depth

Yes

No

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

1

Levene’s test  Shapiro‐Wilks test 

2

  Pairwise comparisons for Loeb Lake suggest that there is some variability from year to year especially in  TP, but water quality generally has remained consistent over the past 9 years. 2003, 2006, and 2012  were higher in TP than most other years but no differences were identified in chlorophyll‐a  concentrations.      Trend Assessment    Exogenous Variables    Precipitation was evaluated as a potential factor affecting water quality trends in Loeb Lake (Figure 23).  No relationship was found between monthly TP concentrations and monthly precipitation totals.     Seasonality and Autocorrelation    The majority of data collected for Loeb Lake were collected in the summer months but there is some  variability (Figure 24).  Consequently, a seasonally adjusted Mann‐Kendall Tau should be applied.      Crosby Lake demonstrated serial autocorrelation in TP, but not in Secchi or chlorophyll‐a data (Figure  25).  Autocorrelation is accounted for in TP, but not the other parameters.     Trend Assessment    No water quality trends were detected in Loeb Lake.         Multivariate Assessment    The multivariate TSI assessment for Loeb Lake suggests that the lake is typically P‐limited although  zooplankton grazing may play a role in expected algal abundance (Figure 26).     Potential Drivers of Water Quality    Loeb Lake Conclusions    18  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      1. Water quality is fairly consistent in Loeb Lake with no trends detected in TP, chlorophyll‐a or  Secchi depth.  2. Comparisons among years yield few differences with only TP showing some differences among  years.   3. The multivariate TSI assessment suggests that Loeb Lake is a fairly typical P‐limited lake.     SUMMARY    Following is a summary of the results of the analysis.     Can the water quality of CRWD lakes be described as generally getting better or worse than was  recorded in the past?      In general, water quality in CRWD lakes is fairly stable with a few demonstrating signs of eutrophication.  Lake McCarron demonstrates improved water quality as a direct result of the alum treatment conducted  in 2004. Although the alum treatment visually demonstrates some signs of weakening, no statistical  trends were identified suggesting that water quality is degrading. Como Lake demonstrates a cyclical  pattern in water quality that is likely directly tied to changes in submerged aquatic vegetation and  zooplankton abundance. Total phosphorus concentrations in Como Lake appear to be improving. Water  quality in Crosby Lake appears to be degrading with higher TP and chlorophyll‐a concentrations resulting  in decreased water clarity. Water quality in Loeb Lake appears to be stable with relatively good water  quality.       What trends in water quality exist?  Can these trends be verified through statistical methods?    Statistical methods applied to CRWD lake water quality demonstrated relatively stable water quality in  the lakes except for Crosby Lake. Lake McCarrons had no significant trends prior to or after the alum  treatment suggesting that water quality is stable in the lake. Detecting statistical trends in water quality  in Como Lake is very difficult due to the complex interactions of vegetation and zooplankton on water  quality. Although statistical results were weak, total phosphorus concentrations appear to be improving  suggesting that other factors are controlling water clarity. Crosby Lake demonstrates a statistically  significant trend toward poorer water quality with increased phosphorus and chlorophyll‐a  concentrations and decreased water clarity.  Loeb Lake remains stable.     What factors are driving the trends in water quality among the different lakes?      The lakes demonstrated a variety of factors controlling water quality. Both Lake McCarrons and Loeb  Lake appear to be phosphorus limited lakes where nutrient controls remain the best approach for  controlling eutrophication. Both Crosby Lake and Como Lake are more typical shallow lakes that  19  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      demonstrate other factors affecting water quality including vegetation, zooplankton and fish  abundance. Crosby Lake is further complicated by its connection to the Minnesota River which has the  potential to bring in large quantities of sediment and nutrients during flood periods. The degrading  water quality trend in Crosby Lake is most likely attributed to flooding frequency since there are no  apparent changes in the watershed that lead to additional nutrient loading.     What qualitative statements can be made regarding the causes and effects in the observed water  quality trends?    Lakes in the CRWD watershed have relatively stable water quality; however both Como Lake and Crosby  Lake are sensitive to factors other than nutrient loading including submerged vegetation, zooplankton  and fish abundance. Crosby Lake has the additional pressures of nutrient and sediment loading from the  Minnesota River. Monitoring and managing biological conditions in these two lakes is critical to  successfully improving and maintain water quality. For Crosby Lake, managing the input of sediment and  nutrients from the Minnesota River could stabilize water quality, although managing flood water inputs  is very difficult. It may take direct management such as alum addition or other phosphorus inactivation  to be effective. Long term nutrient load management is effective for both Loeb and McCarrons Lake. The  long term effectiveness of the McCarrons Lake alum treatment poses the greatest risk for water quality  degradation in the lake.     What monitoring recommendations can be made to improve assessing lake conditions in the CRWD?  How should lake health be assessed moving forward?     For the two deep lakes, continuing the current monitoring (TP, chlorophyll‐a, and Secchi plus field  parameters) is sufficient for assessing the health of the lake. Monitoring of the phytoplankton and  zooplankton communities provide some insight into the health of the lake too, but are not critical. For  the shallow lakes, the standard water quality parameters are important, but so is the submerged aquatic  vegetation community. The best measure of healthy shallow lake is the clarity of the water and the  diversity and robustness of the submerged aquatic vegetation community. So, annual (or every few  years) vegetation surveys are critical in assessing lake health.  Zooplankton, phytoplankton, and fish  surveys can be useful in assessing mechanisms controlling water quality.     Following is a description of the analytical results for each of the lakes.     Lake McCarrons    Lake McCarrons is a deep lake that received an alum treatment in 2004.  Watershed BMPs have also  been introduced over the periods of record, specifically the Villa Parks wetland complex.  Water quality  improved significantly after the alum treatment with reduced TP and chlorophyll‐a and increased Secchi  depth. Prior to the alum treatment, no trends were identified in water quality suggesting that conditions  were fairly stable.  After the alum treatment, water quality improved greatly over a 3 to 4 year period;  20  W:\07 Programs\Monitoring & Data Acquisition\Lakes\2013 Lakes Analysis ‐ Wenck\Technical Memo\Technical Memo FINAL\Lake Trend Assessment Technical Memo FINAL.docx 

 


Technical Memo  Statistical Analysis of Lake Data in the Capitol Region Watershed District   Capitol Region Watershed District  September 18, 2013      however recent data is demonstrating that the effectiveness of the alum treatment may be diminishing  although no water quality trend was detected.     Como Lake    Como Lake, a shallow lake, demonstrates a cyclical pattern in water quality that may be related to other  factors such as a boom‐bust fishery.  The pattern should be explored further in relation to fish and  zooplankton data. Como Lake did have a significant decreasing trend in TP, although statistical testing  among years could not pick up the differences. There may be a long term, slow decrease in TP  concentrations, albeit a very small one. Water clarity appears to be affected by factors beyond algal  abundance, but the lake is phosphorus limited.     Crosby Lake    Although water quality in Crosby Lake is fairly good, water quality is decreasing in the lake over the past  13 years. Total phosphorus and chlorophyll‐a had significant increasing trends while Secchi depth had a  significant decreasing trend.  Water clarity followed a similar trend as algal abundance suggesting algal  abundance is the primary factor controlling water clarity.      Loeb Lake    Overall, Loeb Lake demonstrated consistent water quality over the period of record with little to no  variation in chlorophyll‐a or Secchi depth. Loeb Lake appears to be a P‐limited lake that has not  experienced any major changes in water quality in the past 9 years.     REFERENCES    Wenck Associates Inc. 2012. Crosby Lake Management Plan.  Report to the Capitol Region Watershed  District.  

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2013 Lakes Monitoring Report