Big Chetac Lake Getting Rid of the Green Phase 3. Nutrient Budget and Management Data Analysis Report

Transcription

1 Big Chetac Lake Getting Rid of the Green Phase 3 Nutrient Budget and Management Data Analysis Report

2 Prepared for: Big Chetac Chain Lake Association and Wisconsin Department of Natural Resources Prepared by: Short Elliot Hendrickson Inc.

3 Special Thanks to: Bernie Lenz (formerly of SEH) Craig Roesler, WDNR *for assistance in writing this report Big Chetac Chain Lake Association *for patience and understanding

4 General Lake Information Surface Area = 2,406 acres this is about 25% larger than what is stated in the DNR Lake Book Maximum Depth 28 ft Average Depth 14 ft Drainage Lake Watershed = approx. 34,541 acres A little more than 14 to 1 watershed to lake ratio

5 0 Big Chetac Lake Watershed Heron Creek Benson Creek Red Cedar Springs Direct Drainage Watershed = 34,541 acres Turtle Pond Knuteson Creek Not in the immediate watershed for Big Chetac Lake Hwy 48 Tributary

6 General Impressions Lake is highly eutrophic (nutrient rich) Lake has lots of Curly-leaf leaf pondweed, an invasive species Lake is well developed around the shoreline Lake use and enjoyment are impaired due to poor water quality and excessive weeds (at least with CLP)

7 Six Phase Lake Study to be completed: Phase One (2007) Water quality, lake stage, and tributary sampling data collection for Phase Three analysis Phase Two (2007) Groundwater, internal loading, and CLP data collection for Phase Three Phase Three ( ) 09) Nutrient and Water Budget Analysis today s s discussion Phase Four ( Historical Sediment Core Sampling and Analysis Phase Five (2008) Full point-intercept intercept plant survey Phase Six (2009) Lake User Survey and Comprehensive Lake/Aquatic Plant Management Plan

8 Water Budget Lake Volume 41,141,263 m 3 (33,354 acre-feet) Tributary and Watershed In-flow 37,188 m 3 /day Outflow to Birch Lake and over the dam 26,671 m 3 /day Precipitation, Evaporation, and Lake Storage also taken into account Rainfall = 13.6 Evaporation from Lake = 21.2 Lake Storage = 1.1 Total Hydraulic Residence Time approx. 3 years Based on 2007 data from May through September Dry year, except in late August and September

9 In-Lake Water Quality Three lake sites: North, Central, and South Basins 15 dates between May and September 2007 Essentially every meter from surface to bottom Total Phosphorous, Total Nitrogen, Chlorophyll a,, and water clarity (Secchi disk) Temperature, Dissolved Oxygen, and ph Profiles also collected

10 Goals of Lake Sampling Determine seasonal changes in phosphorus mass, algal abundance and ph Determine the total in-lake phosphorous mass for the year Determine if Big Chetac Lake was nitrogen or phosphorous limited. Determine the time period for which each basin became anoxic or oxygen depleted in the bottom waters

11 Big Chetac Lake trends Total P & Chlorophyll Concentrations (0-2m) and Secchi Disk Averages for Big Chetac Lake 5/9/2007 5/20/2007 6/10/2007 6/24/2007 7/2/2007 7/8/2007 7/16/2007 7/23/2007 8/6/2007 8/20/2007 9/3/2007 9/17/ /1/2007 Sampling Dates /25/2007 TP & Chl (ug/l) Secchi (ft) Total Phosphorous Chlorophyll Secchi Depth Linear (Total Phosphorous) Linear (Chlorophyll) Linear (Secchi Depth)

12 Total In-Lake Phosphorous Mass Phosphorous sampling at three basins, top to bottom, multiple times Calculate amount of phosphorous at each depth in each basin, each time Record the increases The difference between the minimum phosphorous mass and the maximum phosphorous mass during the year shows the lake s response to inputs of phosphorus It doesn t t matter how much phosphorous is coming into a lake, if if the lake can handle it!

13 Big Chetac Can t t Handle It!! 2007 In-Lake Phosphorous Mass North Basin Central Basin South Basin Whole Lake /25/2007 5/2/2007 5/9/2007 5/16/2007 5/23/2007 5/30/2007 6/6/2007 6/13/2007 6/20/2007 6/27/2007 7/4/2007 7/11/2007 7/18/2007 7/25/2007 8/1/2007 8/8/2007 8/15/2007 8/22/2007 8/29/2007 9/5/2007 9/12/2007 9/19/2007 9/26/ /3/2007 Sampling Dates Phosphorous (lbs)

14 In-lake Mass per Basin Percent In-lake Phosphorous Mass by Basin South Basin 24% North Basin 44% Central Basin 32%

15 Nitrogen or Phosphorous Nitrogen or Phosphorous Limited? 2007 Seasonal TN:TP Ratios (Whole Lake) /3/2007 5/2/2007 5/9/2007 5/16/2007 5/23/2007 5/30/2007 6/6/2007 6/13/2007 6/20/2007 6/27/2007 7/4/2007 7/11/2007 7/18/2007 7/25/2007 8/1/2007 8/8/2007 8/15/2007 8/22/2007 8/29/2007 9/5/2007 9/12/2007 9/19/2007 4/25/2007 9/26/2007 Sampling Dates Ratio (TN:TP)

16 Total Mass of Phosphorous in Big Chetac Lake in ,624 lbs increase of phosphorous from May to September 2007 Now, where did it come from? Other?

17 Sources and Sinks Sources Sedimentation Fertilizer Agriculture Urban or residential runoff Decaying plant material Fecal matter (birds, animals, people) Waste treatment Sinks Encumbered by the sediment in a lake Plant uptake from the sediment Algae uptake from the water Outflow from a lake Animals that are herbivores Waste Treatment

18 Phosphorous Sources Looked at in this Study Atmospheric Deposition Groundwater Flow Septic System Curly-leaf leaf pondweed Internal Loading (recycling) Tributary Loading (larger watershed) Near Shore/Shoreline Contributions We didn t t look at goose poop! Sorry.

19 1. Atmospheric Deposition phosphorous found in the dust and other particulate matter that is blown over and settles into the lake cleansed from the air when it rains 506 lbs (4% of total P) Natural Source Field cover crops, dampened roads, etc

20 2. Groundwater Contributions Determined by measuring groundwater flow and TP concentrations in the water 12 peizometers installed around the lake. Hydraulic head measured in each to determine amount and direction of flow Water sampling from the peizometers to determine TP concentrations Natural Source Can be made worse when flowing through failing septic systems

21 Groundwater Results flows into the lake primarily from the north and west flows out primarily to the south and east approximately 4,990,670 gallons of ground water flows into the lake per day 499 lbs of phosphorous or 4% of the total seasonal load

22 This is what it looks like.

23 3. Septic Systems Survey of almost all systems completed by Sawyer County, Summer 2008 Based on 62% agreement of the Lake Association Goals of the survey To identify compliant, non-compliant, and failing systems To issue orders for correction to the worst offenders Attempted to survey 378 systems Tied in with groundwater study

24 Results Big Chetac Lake OWS Survey Results did not allow, 30 (8%) order for correction, 5 (1%) inconclusive, 17 (4%) fail, 46 (12%) pass, 280 (75%) pass fail inconclusive did not allow order for correction

25 Factors to consider when calculating Septic System Input Groundwater Flow Failing and Passing Systems Per capita years the system is in use (people years) Export coefficient based on average discharge of phosphorous from household septic and gray water Soil retention coefficient based on soil type and slope of shoreline

26 Septic Contribution Calculations Groundwater from east to west 292 passing systems 81 failing 46 failing + (17 x 0.5) inconclusive + (30 x 0.9) did not allows = 81 failing House discharge coefficient of 0.5 kg/capita/year Based on a phosphorous ban on laundry detergent Could range from 0.3 to 0.8 Soil retention coefficient of 0.9 Based on a scale from 0 (all phosphorous in the soil gets to the lake) to 1 (no phosphorous gets to the lake) Sandy loam soil, good permeability, and good drainage around most of Big Chetac Lake

27 Calculations continued: Capita Years - determined by multiplying the number of people in a household by the total time they use the septic system Sawyer County Surveyed Septic Owners when they could, not a great response 30% permanent, 1.92 people/house, 365 days of use (51% of total permanents surveyed) 70% seasonal, 2.67 people/house, days of use (19% seasonals surveyed)

28 Total Septic Contributions All septic systems regardless of groundwater flow 373 Septic Systems included lbs of phosphorous 1.2 % of total load All septic systems with groundwater flow considered 108 Septic systems included 32 lbs of phosphorous < 1% of total load

29 4. Curly-leaf leaf Pondweed You got lots of it!!

30 25-35% of the lake s surface area (depends on what surface area you use) 66% of littoral (plant growing) zone 621 acres in June of 2008 Approx. 9,696 tons of CLP Rice Lake has approximately 3000 tons, and harvests annually about 1000 tons.

31 How much phosphorous from CLP? Approximately 3,500 lbs (1.75 tons) could be added seasonally if all phosphorous in the CLP went back into the lake Not all phosphorous taken up by CLP is released back into the lake (see next slide) A better, more conservative value might be 1,761 lbs or 15% of the total load

32 How does a plant use up and return phosphorous in a lake?

33 5. Sediment Phosphorous Release (internal recycling or release of phosphorous) Need to know total time the lake becomes depleted of oxygen near the bottom Need to know seasonal ph levels in the lake Need to know release rates for phosphorous from the bottom sediments under different situations For Big Chetac we needed this information for each basin

34 Dissolved Oxygen Concentrations North Basin N-0-2 N-2.5 N-3.5 N-4.5 Central Basin /28/07 6/17/07 8/6/07 9/25/ N-5.5 N-6.5 N-7.5 C-0-2 C-2.5 C-3.5 C-4.5 C-5.5 South Basin 0 16 S-0-2 4/28/07 5/18/07 6/7/07 6/27/07 7/17/07 8/6/07 8/26/07 9/15/07 10/5/07S /25/ /28/2007 6/17/2007 8/6/2007 9/25/2007 Dissolved Oxygen (mg/l) S-3.5 S-4.5 S-5.0

35 Dissolved Oxygen Depletion & North Basin high ph days in 2007 DO depletion 90 days, beginning June 18 th High ph Entire season, beginning June 4th Central Basin DO depletion 23 days, beginning June 18th High ph Entire season, beginning June 10th South Basin DO depletion 5 days, beginning July 5 th High ph Entire season, beginning June 10th

36 What does the previous slide mean? Lots of phosphorous coming from the bottom sediments, internal release, recycling back into the lake for use by algae! Daily Internal Phosphorous Load for each basin and the lake as a w hole /1/2007 5/8/2007 5/15/2007 5/22/2007 5/29/2007 6/5/2007 6/12/2007 6/19/2007 6/26/2007 7/3/2007 7/10/2007 7/17/2007 7/24/2007 7/31/2007 8/7/2007 8/14/2007 8/21/2007 8/28/2007 9/4/2007 9/11/2007 9/18/2007 9/25/2007 Phosphorous (lbs) North Basin Central South Total Sampling Dates

37 How Much? 7,971 lbs of phosphorous being re-released released into the lake from the sediments seasonally 69% of the total phosphorous loading Cumulative Phosphorous Released by the Sediments into Big Chetac Lake Phosphorous Mass (lbs) /8/2007 4/28/2007 5/18/2007 6/7/2007 6/27/2007 7/17/2007 8/6/2007 8/26/2007 9/15/ /5/ /25/2007 Sampling Dates

38 6. Tributary Loading 6 sources of tributary flow into the lake and the rest of the unmonitored watershed were evaluated Nutrient sampling Flow measurement Total Flow into Big Chetac = 15.2 cfs Total Phosphorous Loading = lbs or 7% of total loading

39 0 Big Chetac Lake Watershed Heron Creek Benson Creek Red Cedar Springs Direct Drainage Watershed = 34,541 acres Turtle Pond Knuteson Creek Not in the immediate watershed for Big Chetac Lake Hwy 48 Tributary

40 Tributary Loading lbs of phosphorous from each sub- watershed Phosphorous Loading in lbs from the Big Chetac Lake Watershed Hwy 48 Tributary 1.6 0% Unmonitored % Nearshore Area 38 4% Knuteson Creek % Turtle Pond 4.7 1% Total Phosphorous = lbs or 7% of total loading Benson Creek % Red Cedar Springs % Heron (Squaw) Creek %

41 Sub-Watershed Areas Portion of the Total Watershed (Acres) Unmonitored % Nearshore Area % Hwy 48 Tributary % Turtle Pond % Knuteson Creek 17, % Benson Creek % Red Cedar Springs % Heron (Squaw) Creek %

42 How about the larger Big Chetac Lake Watershed? Total Ground Cover in Acres for the Big Chetac Lake Watershed Open Water % Wetland % Agriculture % Barren % Grassland % Forested Wetland % Forest %

43 7. Near Shore Contributions An area within 200 ft of the shoreline Contains most of the residential development Roads & other impervious surfaces Land use determined by looking at high quality color aerial photos Runoff coefficients (3 levels) for each type of land cover/use used to calculate phosphorous loading from this area

44 Type of Land Use within 200ft of shoreline Lawn Wetlands Open water Forest Buffer strips Impervious surfaces Higher density development Shrub/grassland

45 Total Land Use Nearshore Land Use in Acres within 200 ft of the Shoreline lawn 69 18% Wetlands % Open Water 2.9 1% Forest % Impervious Surface (roadways, driveways, and roof tops) % buffers % densely developed area NW corner of lake % natural shrub/grassland %

46 Phosphorous Loading Low, Medium, and High Values for Phosphorous Loading to Big Chetac Lake from the Near Shore Area (200 ft) in Lbs lb s /y ear Forest Idle Land Residential Wetlands Open Water Land Use TP Mass (Low export coefficient) TP Mass (Med export coefficient) TP Mass (High export coefficient)

47 Nearshore Total Contribution 90 to 468 lbs of phosphorous annually depending on the whether the low, medium, or high coefficient is used Some of the nearshore contribution is already accounted for in groundwater and tributary calculations so the low value is used 90 lbs adjusted for the seasonal value form May through Sept = 54 lbs or <1%

48 Overall Picture May through September 2007 Phosphorous Loading in lbs. to Big Chetac Lake Septic 85 1% Atmosperic 506 4% Nearshore Area (200 ft) 54 0% Unmonitored Watershed % Tributaries/Watershed % Curly Leaf Pond Weed % Groundwater 499 4% Internal Load- Sediments %

49 Summary Internal Loading is the biggest source of phosphorous to the lake at 69% Nearly overwhelms all other contributions Curly-leaf leaf pondweed is also a problem at 15% (conservative) Watershed, nearshore,, and septic system improvements would benefit, but unless the two primary sources are brought under control their impact will be minimal.

50 Management recommendations will be forth coming with the completion of Phase Six of the Project in Fall of 2009 Any Questions?