Serpent Lake CROW WING COUNTY

Transcription

1 Serpent Lake CROW WING COUNTY Lake Water Quality Summary Serpent Lake is located at Crosby and Deerwood, Minnesota, in Crow Wing County. It covers 1,13 acres, which places it in the upper 1% of lakes in Minnesota in terms of size. Serpent Lake has one intermittent inlet on the east end and one intermittent outlet on the west end. The outlet, Serpent Creek, runs under the city of Crosby to Mahnomen Lake. From there the water eventually flows into the Mississippi River. Because there are no major inlets or outlets to Serpent Lake, it most likely receives most of its inflow from precipitation and groundwater flow; therefore, the land practices occurring around the lakeshore such as septic systems, unnatural shorelines as well as water levels have a larger relative impact on water quality than for a lake that has major inlets. The two cities of Crosby and Deerwood could also be contributing storm water runoff into the lake. Water quality data have been collected on Serpent Lake since 1977 (Tables 2, 3). These data show that the lake is mesotrophic. Mesotrophic lakes are commonly found in north-central Minnesota and have clear water with occasional algal blooms in late summer. The Serpent Lake Association has been involved in numerous activities including water quality monitoring, education, invasive aquatic plant treatment and Healthy Lakes Initiative. Table 1. Serpent Lake location and key physical characteristics. Location Data MN Lake ID: County: Crow Wing Ecoregion: Northern Lakes & Forests Major Drainage Basin: Upper Mississippi Latitude/Longitude: / Invasive Species: Curly-leaf pondweed Physical Characteristics Surface area (acres): 1,13 Littoral area (acres): 338 % Littoral area: 31% Max depth (ft), (m): 65, 19.8 Inlets: 1 intermittent Outlets: 1 Serpent Creek Public Accesses: 2 Table 2: Availability of data and an observation of the quantity of sample points. Data Availability Transparency data Numerous yearly Secchi readings from and through the MPCA CLMP program. Chemical data Inlet/Outlet data Good amount of Phosphorus and Chlorophyll a data. Serpent Lake is currently participating in a Clean Water Partnership Project and conducting inlet and storm water monitoring ( ). Recommendations For recommendations refer to page 19. RMB Environmental Laboratories, Inc. 1 of Serpent Lake

2 Lake Map Figure 1. Map of Serpent Lake illustrating bathymetry, lake sample site locations*, stream inlets and outlets and aerial land use. The green shaded areas in the lake illustrate the littoral zone, where the sunlight can usually reach the lake bottom, allowing aquatic plants to grow. Table 3. Monitoring programs and associated monitoring sites. Monitoring programs include the Citizen Lake Monitoring Program (CLMP), Minnesota Pollution Control Agency (MPCA), Crow Wing County Citizen Lake Monitoring Program (CWCCCLMP), Outdoor Corps Lake Monitoring (OCLM), and Clean Water Partnership (CWP). Lake Site Depth (ft) Monitoring Programs CLMP: , ; MPCA: 1979, 198; CWCCCLMP: 23, 24; OCLM: CWCCCLMP: 23, *The other sites shown on the map don t have any corresponding data in EQuIS. RMB Environmental Laboratories, Inc. 2 of Serpent Lake

3 Average Water Quality Statistics The information below describes available chemical data for Serpent Lake through 211. The data set is limited, and all parameters, with the exception of total phosphorus, chlorophyll a and Secchi depth, are means from at site 21. Minnesota is divided into seven ecoregions based on land use, vegetation, precipitation and geology. The MPCA has developed a way to determine the "average range" of water quality expected for lakes in each ecoregion. For more information on ecoregions and expected water quality ranges, see page 11. Table 4. Water quality means compared to ecoregion ranges and impaired waters standard. Impaired Parameter Mean Ecoregion Range 1 Waters Standard 2 Interpretation Total phosphorus (ug/l) > 3 3 Chlorophyll a (ug/l) > 9 Chlorophyll a max (ug/l) 12 <15 Secchi depth (ft) < 6.5 Dissolved oxygen Dimictic see page 8 Results are within the expected range for the ecoregion. Dissolved oxygen depth profiles show that the deep areas of the lake are anoxic in late summer. Total Kieldahl Nitrogen Indicates insufficient nitrogen to support summer nitrogen-induced (mg/l) algae blooms. Alkalinity (mg/l) Indicates a low sensitivity to acid rain and a good buffering capacity. Color (Pt-Co Units) Indicates very clear water with little to no tannins (brown stain). ph Characteristic of a hard water lake. Lake water with ph less than 6.5 can affect fish spawning and the solubility of metals in the water. Chloride (mg/l) NA Data non-existent. Total Suspended Solids (mg/l) Specific Conductance (umhos/cm) Total Nitrogen :Total Phosphorus NA <1-2 Data non-existent Within the ecoregion average range. 24:1 25:1 35:1 Serpent Lake is most likely phosphorus limited, which means that algae growth is limited by the amount of phosphorus in the lake. 1 The ecoregion range is the 25 th -75 th percentile of summer means from ecoregion reference lakes 2 For further information regarding the Impaired Waters Assessment program, refer to 3 Chlorophyll a measurements have been corrected for pheophytin Units: 1 mg/l (ppm) = 1, ug/l (ppb) RMB Environmental Laboratories, Inc. 3 of Serpent Lake

4 Water Quality Characteristics - Historical Means and Ranges Table 5. Water quality means and ranges for primary sites. Parameters Site 21 Primary Site 23 Total Phosphorus Mean (ug/l): Total Phosphorus Min: 11 5 Total Phosphorus Max: Number of Observations: Chlorophyll a Mean (ug/l): 5 5 Chlorophyll-a Min: <1. <1. Chlorophyll-a Max: Number of Observations: 1 28 Secchi Depth Mean (ft): Secchi Depth Min: Secchi Depth Max: Number of Observations: Figure 2. Serpent Lake total phosphorus, chlorophyll a and transparency historical ranges. The arrow represents the range and the black dot represents the historical mean (Chemical data represents site 23, secchi data represents site 21). Figure adapted after Moore and Thornton, [Ed.] Lake and Reservoir Restoration Guidance Manual. (Doc. No. EPA 44/5-88-2) RMB Environmental Laboratories, Inc. 4 of Serpent Lake

5 Transparency (Secchi Depth) Transparency is how easily light can pass through a substance. In lakes it is how deep sunlight penetrates through the water. Plants and algae need sunlight to grow, so they are only able to grow in areas of lakes where the sun penetrates. Water transparency depends on the amount of particles in the water. An increase in particulates results in a decrease in transparency. The transparency varies year to year due to changes in weather, precipitation, lake use, flooding, temperature, lake levels, etc. The annual means for Serpent Lake range from ft (Figure 3). Transparency was highest in , followed by a slight decline from There is a gap in data from For trend analysis, see page 1. Transparency monitoring should continue annually at site 21 to track future water quality conditions. 3 Transparency: Annual Means 25 Secchi Depth (ft) Long term Mean Site 21 Figure 3. Annual mean transparency for site 21 Serpent Lake transparency ranges from 7 to 3 feet throughout the summer. This range is indicative of a dynamic lake. Figure 4 shows the seasonal transparency dynamics. Serpent Lake transparency is highest in early June, and then declines steadily throughout the summer. Many deep lakes in northern Minnesota rebound in clarity in late September early October; however, data does not exist for those dates for Serpent Lake. In the future, Secchi depth data should be collected for Serpent Lake until mid-october. Some lakes vary throughout the summer (dynamic lakes) while some lakes stay constant. The transparency dynamics have to do with algae population dynamics and lake turnover. RMB Environmental Laboratories, Inc. 5 of Serpent Lake

6 Secchi Depth (ft) Transparency: Seasonal Dynamics Figure 4. Seasonal transparency dynamics and year-to-year comparison (site 21). The black line represents the pattern in the data. User Perceptions When volunteers collect secchi depth readings, they record their perceptions of the water based on the physical appearance and the recreational suitability. These perceptions can be compared to water quality parameters to see how the lake "user" would experience the lake at that time. Looking at transparency data, as the secchi depth decreases the perception of the lake's physical appearance rating decreases. Serpent Lake was rated as being "not quite crystal clear" 74% of the time between at site 21 (Figure 5). Physical Appearance Rating 26% % Crystal clear water 74% Not quite crystal clear a little algae visible 26% Definite algae green, yellow, or brown color apparent 74% % High algae levels with limited clarity and/or mild odor apparent % Severely high algae levels Figure 5. Physical appearance rating, as rated by the volunteer monitor (site 21). RMB Environmental Laboratories, Inc. 6 of Serpent Lake

7 As the Secchi depth decreases, the perception of recreational suitability of the lake decreases. Serpent Lake was rated as having "very minor aesthetic problems" 85% of the time from at site 21 (Figure 6). 13% 2% Recreational Suitability Rating 2% Beautiful, could not be better 85% Very minor aesthetic problems; excellent for swimming, boating 13% Swimming and aesthetic enjoyment of the lake slightly impaired because of algae levels 85% % Desire to swim and level of enjoyment of the lake substantially reduced because of algae levels % Swimming and aesthetic enjoyment of the lake nearly impossible because of algae levels Figure 6. Recreational suitability rating, as rated by the volunteer monitor. Total Phosphorus Serpent Lake is phosphorus limited, which means that algae and aquatic plant growth is dependent upon available phosphorus. Total phosphorus was evaluated in Serpent Lake in , 23, and Figure 7 shows phosphorus data since 23. In June, the data are variable between years (range = 5-29 ug/l) and become more comparable by the end of the summer (range = ug/l). Total Phoshorus (ug/l) 35 Total Phoshorus 23 3 Eutrophic Mesotrophic Oligotrophic Figure 7. Historical total phosphorus concentrations (ug/l) for Serpent Lake. The majority of the data points fall into the mesotrophic range. Phosphorus should continue to be monitored to track any future changes in water quality. RMB Environmental Laboratories, Inc. 7 of Serpent Lake

8 Chlorophyll a Chlorophyll a is the pigment that makes plants and algae green. Chlorophyll a is tested in lakes to determine the algae concentration or how "green" the water is. Chlorophyll a (ug/l) Chlorophyll a Chlorophyll a 29 concentrations 4 21 greater than 1 ug/l Minor Algae are perceived as a 2 mild algae bloom, while concentrations greater than 2 ug/l are perceived as a nuisance. Figure 8. Historical chlorophyll a concentrations (ug/l) for Serpent Lake. Chlorophyll a was evaluated in Serpent Lake in 23, and Figure 8 shows all chlorophyll a data since 23. Chlorophyll a concentrations for Serpent remained below 1 ug/l except for two data points in September of 28 and 21, indicating clear water most of the summer Dissolved Oxygen Depth (m) Dissolved Oxygen (mg/l) /26/24 7/26/24 8/26/24 Dissolved Oxygen (DO) is the amount of oxygen dissolved in lake water. Oxygen is necessary for all living organisms to survive except for some bacteria. Living organisms breathe in oxygen that is dissolved in the water. Dissolved oxygen levels of <5 mg/l are typically avoided by game fisheries. Serpent Lake is a moderately deep lake, with a maximum depth of 65 ft. Dissolved oxygen profiles were taken in 24, and shows that Serpent Lake stratifies in the summer (Figure 9). The thermocline occurs between 6-8 meters (2-26 feet). Figure 9. Dissolved oxygen and temperature profile for Serpent Lake on August 13, RMB Environmental Laboratories, Inc. 8 of Serpent Lake

9 Trophic State Index Phosphorus (nutrients), chlorophyll a (algae concentration) and Secchi depth (transparency) are related. As phosphorus increases, there is more food available for algae, resulting in increased algal concentrations. When algal concentrations increase, the water becomes less transparent and the Secchi depth decreases. In order to standardize these three measurements to make them directly comparable, we convert them to a trophic state index (TSI). Table 6. Trophic State Index. Trophic State Index Serpent Lake TSI Total Phosphorus 43 TSI Chlorophyll-a 44 TSI Secchi 37 TSI Mean 42 Trophic State: Mesotrophic Numbers represent the mean TSI for each parameter. The mean TSI for Serpent Lake falls in the mesotrophic range (Figure 1). There is good agreement between the TSI for phosphorus and chlorophyll a, indicating that these variables are strongly related (Table 6). The TSI for Secchi depth was lower than that of total phosphorus and chlorophyll a. This result could be due to the fact that the transparency data set is much larger and covers a much longer span of time than the phosphorus and chlorophyll a data. Mesotrophic lakes (TSI 4-5) are Serpent Lake characterized by moderately clear water most of the summer (Table 7). "Meso" means middle or mid; therefore, mesotrophic means a medium amount of productivity. Mesotrophic lakes are commonly found in north-central Minnesota and have clear water with some algal blooms in late summer. Hypereutrophic Eutrophic Mesotrophic Oligotrophic Figure 1. Trophic state index chart with corresponding trophic status. Table 7. Trophic state index attributes and their corresponding fisheries and recreation characteristics. TSI Attributes Fisheries & Recreation <3 Oligotrophy: Clear water, oxygen throughout Trout fisheries dominate the year at the bottom of the lake, very deep cold water. 3-4 Bottom of shallower lakes may become anoxic (no oxygen). Trout fisheries in deep lakes only. Walleye, Cisco present. 4-5 Mesotrophy: Water moderately clear most of the summer. May be "greener" in late summer. No oxygen at the bottom of the lake results in loss of trout. Walleye may predominate. 5-6 Eutrophy: Algae and aquatic plant problems possible. "Green" water most of the year. Warm-water fisheries only. Bass may dominate. 6-7 Blue-green algae dominate, algal scums and aquatic plant problems. Dense algae and aquatic plants. Low water clarity may discourage swimming and boating. 7-8 Hypereutrophy: Dense algae and aquatic Water is not suitable for recreation. plants. >8 Algal scums, few aquatic plants Rough fish (carp) dominate; summer fish kills possible Source: Carlson, R.E A trophic state index for lakes. Limnology and Oceanography. 22: RMB Environmental Laboratories, Inc. 9 of Serpent Lake

10 Trend Analysis For detecting trends, a minimum of 8-1 years of data with 4 or more readings per season are recommended. Minimum confidence accepted by the MPCA is 9%. This means that there is a 9% chance that the data are showing a true trend and a 1% chance that the trend is a random result of the data. Only short-term trends can be determined with just a few years of data, because there can be different wet years and dry years, water levels, weather, etc, that affect the water quality naturally. There is not enough historical data to perform trend analysis for total phosphorus or chlorophyll a on Serpent Lake. Site 21 has enough transparency data to perform a short-term and long-term trend analysis; however there is a large gap in data between 1982 and 21 (Table 8). The data was analyzed using the Mann Kendall Trend Analysis. Table 8. Trend analyses for Serpent Lake. Lake Site Parameter Date Range Trend Probability 21 Transparency , Declining 95% 21 Transparency No Trend Transparency Trends 3 25 Short-term trend Long-term trend Secchi Depth (ft) Figure 11. Transparency trend (ft) for site 26 from Site 21 shows a statistically significant declining trend in transparency from , and (Figure 11). There is a large gap in data between 1982 and 21 and then the short-term analysis from shows no trend in transparency. This means that the transparency is currently staying the same. Figure 11 shows that in , Serpent Lake used to have transparency readings as high as 25-3 feet, while in the past decade, the peak transparency hasn t been above 22 feet. Transparency monitoring should continue at site 21 so that this trend can be tracked in future years without data gaps. RMB Environmental Laboratories, Inc. 1 of Serpent Lake

11 Ecoregion Comparisons Minnesota is divided into 7 ecoregions based on land use, vegetation, precipitation and geology (Figure 12). The MPCA has developed a way to determine the "average range" of water quality expected for lakes in each ecoregion. From , the MPCA evaluated the lake water quality for reference lakes. These reference lakes are not considered pristine, but are considered to have little human impact and therefore are representative of the typical lakes within the ecoregion. The "average range" refers to the 25 th - 75 th percentile range for data within each ecoregion. For the purpose of this graphical representation, the means of the reference lake data sets were used. Serpent Lake is in the Northern Lakes and Forests Ecoregion. The total phosphorus and chlorophyll a concentrations for Serpent Lake are within the expected ecoregion ranges (Fig 13a-b). The transparency (Secchi depth) is better than the expected ecoregion range (Fig 13c). Figure 12. Map of Minnesota with the seven ecoregions Total Phosphorus (ug/l, ppb) Chlorophyll-a (ug/l, ppb) Secchi depth (ft) increased algae NLF Serpent Lake Ecoregion NLF Ecoregion Serpent Lake a b c 35 NLF Ecoregion Serpent Lake crystal clear Figures 13a-c. Serpent Lake ranges compared to Northern Lakes and Forest Ecoregion ranges. The Serpent Lake total phosphorus and chlorophyll a ranges are from 19 data points collected in May-September of 23, and The Serpent Lake Secchi depth range is from 133 data points collected in May- September from and RMB Environmental Laboratories, Inc. 11 of Serpent Lake

12 Inlet/Outlet Data Assessment In 26, citizen volunteers monitored the Serpent Creek outlet. They collected water transparency data, precipitation data, and observations on stream appearance and recreational suitability through the MPCA CSMP (Figure 13). These data show that the transparency of Serpent Creek is excellent, even after rainfall (Figure 14). In the T-tube used for transparency, 1 cm is the maximum clarity that can be measured. The appearance of Serpent Creek was observed to be clear or cloudy, and the recreational suitability was rated as good to very good each sample date except for 7/3/6 (Table 9). The Crow Wing SWCD is currently ( ) conducting a Clean Water Partnership project that involves monitoring the lake, inlets and stormwater around Serpent Lake. This study will help determine restoration and implementation projects around the lake. Stream Physical Appearance Stream Recreational Suitability Date 6/2/6 1A. CLEAR 1. VERY GOOD >1 6/11/6 1A. CLEAR 1. VERY GOOD >1 6/18/6 1A. CLEAR 2. GOOD >1 6/27/6 2. CLOUDY 2. GOOD >1 7/2/6 2. CLOUDY 2. GOOD >1 7/3/6 1A. CLEAR 5. VERY POOR >1 T-Tube Transparency (cm) Table 9. Serpent Creek appearance rating by date Figure 14. Location of Serpent Creek monitoring site Transparency vs Precipitation in Serpent Creek.8.7 Precipitation (inches) T-Tube Transparency Precipitation (inches) T-Tube Transparency.1 2 5/15/6 5/25/6 6/4/6 6/14/6 6/24/6 7/4/6 7/14/6 7/24/6 8/3/6 8/13/6 9/22/6 Figure 15. Stream transparency as related to precipitation in Serpent Creek, 26. RMB Environmental Laboratories, Inc. 12 of Serpent Lake

13 Lakeshed Data and Interpretations Lakeshed Understanding a lakeshed requires an understanding of basic hydrology. A watershed is defined as all land and water surface area that contribute excess water to a defined point. The MN DNR has delineated three basic scales of watersheds (from large to small): 1) basins, 2) major watersheds, and 3) minor watersheds. The Mississippi River - Brainerd Major Watershed is one of the watersheds that make up the Upper Missisippi River Basin, which eventually drains south to the Gulf of Mexico (Figure 16). This major watershed is made up of 128 minor watersheds. Serpent Lake is located in minor watershed 19 (Figure 17). Figure 16. Pine River Watershed. Figure 17. Minor Watershed 19. The MN DNR also has evaluated catchments for each individual lake with greater than 1 acres surface area. These lakesheds (catchments) are the building blocks for the larger scale watersheds. Serpent Lake falls within the Serpent (195) lakeshed (Figure 18). Though very useful for displaying the land and water that contribute directly to a lake, lakesheds are not true watersheds because they do not show the water flowing into a lake from upstream streams or rivers. While some lakes may have only one or two upstream lakesheds draining into them, others may be connected to a large number of lakesheds, reflecting a larger drainage area via stream or river networks. For further discussion of Serpent Lake s full watershed, containing all the upstream lakesheds, see page 17. The data interpretation of the Serpent Lake Figure 18. The Serpent (195) Lakeshed. This area is the land and water surface that flow directly into Serpent Lake. RMB Environmental Laboratories, Inc. 13 of Serpent Lake

14 lakeshed is only the immediate lakeshed, not including the upstream lakesheds, as this area is the land surface that flows directly into Serpent Lake. The lakeshed vitals table identifies where to focus organizational and management efforts for each lake (Table 9). Criteria were developed using limnological concepts to determine the effect to lake water quality. KEY Possibly detrimental to the lake Warrants attention Beneficial to the lake Table 9. Serpent Lake lakeshed vitals table. Lakeshed Vitals Rating Lake Area 1,13 acres descriptive Littoral Zone Area 338 acres descriptive Lake Max Depth 65 ft. descriptive Lake Mean Depth NA NA Water Residence Time NA NA Miles of Stream 1.2 descriptive Inlets Outlets 1 Unnamed (intermittent) 1 Serpent Creek (intermittent) Major Watershed 12 - Crow Wing River descriptive Minor Watershed 19 descriptive Lakeshed 195 descriptive Ecoregion Northern Lakes and Forest descriptive Total Lakeshed to Lake Area Ratio (total lakeshed includes lake area) 3:1 Standard Watershed to Lake Basin Ratio (standard watershed includes lake areas) 6:1 Wetland Coverage 8.5% Aquatic Invasive Species Public Drainage Ditches Public Lake Accesses 2 Curly-leaf pondweed None Miles of Shoreline 8.92 descriptive Shoreline Development Index 1.9 Public Land to Private Land Ratio :1 Development Classification General Development Miles of Road 22.4 descriptive Municipalities in lakeshed Crosby and Deerwood County Forest Management: Forestry Practices Feedlots None City Sewer & Individual Subsurface Sewage Sewage Management Treatment Systems (Inspection and assessment required for all permits and property transfers within the Shoreland Protection Zone) Healthy Lakes & Rivers Partnership program, Lake Management Plan 1999 Lake Vegetation Survey/Plan MN DNR, 29 RMB Environmental Laboratories, Inc. 14 of Serpent Lake

15 Land Cover / Land Use The activities that occur on the land within the lakeshed can greatly impact a lake. Land use planning helps ensure the use of land resources in an organized fashion so that the needs of the present and future generations can be best addressed. The basic purpose of land use planning is to ensure that each area of land will be used in a manner that provides maximum social benefits without degradation of the land resource. Figure 19. The Serpent Lake (195) lakeshed land cover ( Changes in land use, and ultimately land cover, impact the hydrology of a lakeshed. Land cover is also directly related to the lands ability to absorb and store water rather than cause it to flow overland (gathering nutrients and sediment as it moves) towards the lowest point, typically the lake. Impervious intensity describes the lands inability to absorb water, the higher the % impervious intensity the more area that water cannot penetrate in to the soils. Monitoring the changes in land use can assist in future planning procedures to address the needs of future generations. Phosphorus export, which is the main cause of lake eutrophication, depends on the type of land cover occurring in the lakeshed. Figure 19 depicts Serpent Lake s lakeshed land cover. The University of Minnesota has online records of land cover statistics from years 199 and 2 ( Table 11 describes Serpent Lake's lakeshed land cover statistics and percent change from 199 to 2. Due to the many factors that influence demographics, one cannot determine with certainty the projected statistics over the next 1, 2, 3+ years, but one can see the transition within the lakeshed from agriculture and water acreages to forest, grass/shrub/wetland, and urban acreages. The largest change in percentage and acreage is the decrease in agriculture cover, with declines of 68.5% and 246 acres, respectively. In addition, the impervious intensity has increased, which has implications for storm water runoff into the lake. The increase in impervious intensity is consistent with the increase in urban acreage. RMB Environmental Laboratories, Inc. 15 of Serpent Lake

16 Table 11. Serpent Lake lakeshed land cover statistics and % change from 199 to 2 ( % Change Land Cover Acres Percent Acres Percent 199 to 2 Agriculture % Decrease Forest % Increase Grass/Shrub/Wetland % Increase Water 1, , % Decrease Urban % Increase Impervious Intensity % 3, , % Decrease % Increase % Decrease % Increase % Increase % Increase % Increase Total Area 3,316 3,316 Total Impervious Area (Percent Impervious Area Excludes Water Area) % Increase Demographics Serpent Lake is classified as a general development lake. General development lakes usually have more than 225 acres of water per mile of shoreline and 25 dwellings per mile of shoreline, and are more than 15 feet deep. The Minnesota Department of Administration Geographic and Demographic Analysis Division extrapolated future population in 5-year increments out to 235. Compared to Crow Wing County as a whole, Irondale and Deerwood Townships have higher extrapolated growth projections, while the cities of Crosby and Deerwood have lower extrapolated growth projections (Figure 2). Figure 2. Population growth projection for Crow Wing County and the townships and cities around Serpent Lake. (source: te.mn.us/resource.html?id= 19332). Percentage of 26 Population 5% 4% 3% 2% 1% Population Growth Projection Irondale Township; 26 population: 1,21 Deerwood Township; 26 population: 1,35 City of Crosby; 26 population: 2,313 City Deerwood; 26 population: 576 Crow Wing County; 26 population: 61,38 % Extrapolation RMB Environmental Laboratories, Inc. 16 of Serpent Lake

17 Serpent Lake Lakeshed Water Quality Protection Strategy Each lakeshed has a different makeup of public and private lands. Looking in more detail at the makeup of these lands can give insight on where to focus protection efforts. The protected lands (easements, wetlands, public land) are the future water quality infrastructure for the lake. Developed land and agriculture have the highest phosphorus runoff coefficients, so this land should be minimized for water quality protection. The majority of the land within Serpent Lake s lakeshed is made up of private forested uplands and pasture or shrubland (Table 12). This land can be the focus of development and protection efforts in the lakeshed. Table 12. Land ownership, land use/land cover, estimated phosphorus loading, and ideas for protection and restoration in the lakeshed (Sources: Crow Wing County parcel data, National Wetlands Inventory, and the 26 National Land Cover Dataset). Private (66%) 34% Public (%) Developed Agriculture Forested Uplands Other Wetlands Open Water County State Federal Land Use (%) 11% 3.4% 19.5% 23.6% 8.5% 34% % % % Runoff Coefficient Lbs of phosphorus/acre/ year Description Focused on Shoreland Cropland Focus of development and protection efforts Open, pasture, grassland, shrubland Protected Potential Phase 3 Discussion Items Shoreline restoration Restore wetlands; CRP Forest stewardship planning, 3 rd party certification, SFIA, local woodland cooperatives Protected by Wetland Conservation Act County Tax Forfeit Lands State Forest National Forest DNR Fisheries approach for lake protection and restoration Credit: Peter Jacobson and Michael Duval, Minnesota DNR Fisheries In an effort to prioritize protection and restoration efforts of fishery lakes, the MN DNR has developed a ranking system by separating lakes into two categories, those needing protection and those needing restoration. Modeling by the DNR Fisheries Research Unit suggests that total phosphorus concentrations increase significantly over natural concentrations in lakes that have watershed with disturbance greater than 25%. Therefore, lakes with watersheds that have less than 25% disturbance need protection and lakes with more than 25% disturbance need restoration (Table 13). Watershed disturbance was defined as having urban, agricultural and mining land uses. Watershed protection is defined as publicly owned land or conservation easement. RMB Environmental Laboratories, Inc. 17 of Serpent Lake

18 Table 13. Suggested approaches for watershed protection and restoration of DNR-managed fish lakes in Minnesota. Watershed Watershed Management Disturbance Protected Comments Type (%) (%) < 25% > 75% Vigilance < 75% Protection 25-6% n/a Full Restoration > 6% n/a Partial Restoration Sufficiently protected -- Water quality supports healthy and diverse native fish communities. Keep public lands protected. Excellent candidates for protection -- Water quality can be maintained in a range that supports healthy and diverse native fish communities. Disturbed lands should be limited to less than 25%. Realistic chance for full restoration of water quality and improve quality of fish communities. Disturbed land percentage should be reduced and BMPs implemented. Restoration will be very expensive and probably will not achieve water quality conditions necessary to sustain healthy fish communities. Restoration opportunities must be critically evaluated to assure feasible positive outcomes. The next step was to prioritize lakes within each of these management categories. DNR Fisheries identified high value fishery lakes, such as cisco refuge lakes. Ciscos (Coregonus artedi) can be an early indicator of eutrophication in a lake because they require cold hypolimnetic temperatures and high dissolved oxygen levels. These watersheds with low disturbance and high value fishery lakes are excellent candidates for priority protection measures, especially those that are related to forestry and minimizing the effects of landscape disturbance. Forest stewardship planning, harvest coordination to reduce hydrology impacts and forest conservation easements are some potential tools that can protect these high value resources for the long term. Serpent Lake is classified with having 36.7% of the watershed protected and 28.6% of the watershed disturbed (Figure 21). Therefore, Serpent Lake should have a protection focus. Goals for the lake should be to limit any increase in disturbed land use and implement best management practices. Figure 22 displays the upstream lakesheds that contribute water to the lakeshed of interest. All of the land and water area in this figure has the potential to contribute water to Serpent Lake, whether through direct overland flow or through a creek or river. Two of the 3 upstream lakesheds have the same management focus (protection). Percent of the Watershed Protected % 75% 1% Serpent Lake (36.7%) Percent of the Watershed with Disturbed Land Cover % 25% 1% Serpent Lake (28.6%) Figure 21. Serpent Lake lakeshed s percentage of watershed protected and disturbed. Figure 22. Upstream lakesheds that contribute water to the Serpent lakeshed. Color-coded based on management focus (Table 13). RMB Environmental Laboratories, Inc. 18 of Serpent Lake

19 Serpent Lake, Status of the Fishery (as of 8/18/28) Serpent Lake is a 1,57 acre lake located between the towns of Crosby and Deerwood. There are two public accesses, one on the east shore and one on the northwest. The lake is heavily developed with over 25 homes/cabins along 9 miles of shoreline. The maximum depth is 65 ft. and about 32% of the lake is 15 ft. deep or less. Shallow water substrates are primarily sand and gravel. The aquatic plant community is relatively diverse with 3 species present. Emergent plants such as bulrush and water lilies are important for shoreline protection, maintaining water quality, and provide essential spawning habitat for bass and panfish species. Submerged plants provide food and cover needed by fish and other aquatic species. Walleyes are currently stocked as fingerlings at a rate of two pounds/littoral acre in alternate (odd numbered) years. The 28 walleye catch of 4.67/GN was average for the lake class and similar to catches going back to The most abundant year class was from 27 (48% of the catch). As a result, average size dropped to 13.5 inches and 1.2 pounds compared to the 22 average of 19.4" and 2.4 pounds. Northern pike were caught in "average" numbers in 28 (6.42/GN) which was similar to the 22 catch of 6.92/GN. The 26 and 25 year classes were most abundant. Average size increased from 2.1" and 1.7 lbs in 22 to 21.5" and 2.3 lbs in 28. Pike growth remained "average." The largemouth bass catch in trap nets showed a statistically valid increase from.5/tn to 1.17/TN in 28. The spring electrofishing catch increased from 43.4 to 72./hr. Average size decreased slightly compared to 22. Smallmouth bass abundance (.75/GN) increased into the "average" category in 28. The spring electrofishing catch rate (5.4/hr) was the same as in 22. Bass growth rates were "average." The bluegill catch of 18.33/TN was similar to that of 22 (17.58/TN) and was near the lake class median value of 19.83/TN. Few bluegills of seven inches of longer were sampled in 28. Black crappie abundance was "low" in trap nets and "average" in gill nets. Most crappies were at least eight inches long in 28. Tulibees and yellow perch are important forage species for the lake's gamefish. Catches of both were in the "low" category in 28. Perch, however, showed a statistically valid increase in abundance, compared to 22. See the link below for specific information on gillnet surveys, stocking information, and fish consumption guidelines. Key Findings / Recommendations Monitoring Recommendations Transparency monitoring at sites 21 and 23 should be continued annually. It is important to continue transparency monitoring weekly or at least bimonthly every year to enable year-to-year comparisons and trend analyses. Ideally, secchi readings and chemistry data are located at the same site on a lake. Historically, secchi data has been collected at site 21 and the chemical data collected at site 23. These two sites are located over the same deep location in the lake, so the data across sites are comparable. Phosphorus and chlorophyll a monitoring should continue at site 23, as the budget allows, to track future water quality trends. RMB Environmental Laboratories, Inc. 19 of Serpent Lake

20 Overall Conclusions Overall, Serpent Lake has good water quality, and is in fair shape for lakeshed protection. It is a mesotrophic lake (TSI=42) with no trend in transparency data over the past decade. When looking at the long-term data, however, there is a declining trend in transparency. None of the lakeshed is in public ownership, and 37% of the watershed is protected, while 29% of the watershed is disturbed (Figure 21). Priority Impacts to the lake The priority impact to Serpent Lake is the surrounding development and any future development. The entire City of Deerwood and part of the City of Crosby are located in this lake s watershed. Storm water runoff from storm sewers and impervious surfaces, such as parking lots, can contribute pollutants to the lake with little to no filtration. Present and future individual housing development will also impact water quality. The land area (2 nd tier) to the south of Serpent Lake currently has some development, but based on the subdivided parcels it has the potential to increase housing density dramatically (Figure 18). There are currently 25 homes the 9 miles of shoreline around Serpent Lake. The concern with increased development is the conversion of forested land to a land use with increased impervious surfaces, such as roofs, driveways, and well groomed lawns. Phosphorus loading will increase when land use changes from forested to developed. Septic system maintenance is also extremely important for near shore properties. A way to mitigate pollutant inputs is through the installation of Best Management Practices (BMPs). In additional to housing development, roads are also an impervious surface that can increase pollutant loading. There are numerous roads near the shoreline, including State Highway 6. BMPs could also be installed to mitigate the impacts of roads in the lakeshed. Serpent Lake lakeshed is fortunate to have wetlands scattered throughout the watershed. These areas will slow the water flowing toward the lake and provide some filtration of pollutants prior to it entering the lake. Best Management Practices Recommendations The management focus for Serpent Lake should be to protect the water quality and to restore the lakeshed. Protection/restoration efforts should be focused on managing and/or decreasing the impact caused by additional development, and impervious surface area. Project ideas include protecting land with conservation easements, enforcing county shoreline ordinances, smart development, shoreline restoration, rain gardens, and septic system maintenance. Although it may not be possible to decrease the impervious area in the lakeshed, it is possible to reduce the impact of the impervious surface by retaining stormwater instead of allowing it to runoff into the streams. Projects that would have the best chance of improving the water quality of Serpent Lake include stormwater runoff and sedimentation reduction in the cities of Crosby and Deerwood, and buffer strips along the inlets to the lake. Future Studies A future study that would better pinpoint the impacts on the lake is a watershed flow analysis. A watershed flow analysis could also be done using GIS software to see the areas of heaviest runoff into the lake. This analysis would also help pinpoint locations to install BMPs to mitigate increases in impervious surfaces. A simpler option to this study would be on the ground reconnaissance to locate impervious surfaces that connect directly to the lake. RMB Environmental Laboratories, Inc. 2 of Serpent Lake

21 County-wide Recommendation In order to better manage the impact of septic systems on lake water quality, it is recommended that the county implement a lake-wide septic inspection program. In a program such as this, the county would focus on one to three lakes a year, pull septic system records on those lakes, and require old systems to be inspected. This program can rotate through the county doing a few lakes each year. Organizational contacts and reference sites Serpent Lake Association DNR Fisheries Office Regional Minnesota Pollution Control Agency Office Crow Wing Soil and Water Conservation District Crow Wing County Environmental Services Department Minnesota Drive, Brainerd, MN brainerd.fisheries@state.mn.us 7678 College Road, Suite 15, Baxter, MN , Crow Wing County Land Services Building 322 Laurel St. Suite 13, Brainerd, MN Crow Wing County Land Services Building 322 Laurel St. Suite 14, Brainerd, MN Funding This project was funded in part by the Board of Water & Soil Resources and the Initiative Foundation, a regional foundation. RMB Environmental Laboratories, Inc. 21 of Serpent Lake