Long Term Water Quality Trends in Wisconsin Lakes. Katie Hein Wisconsin Department of Natural Resources

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1 Long Term Water Quality Trends in Wisconsin Lakes Katie Hein Wisconsin Department of Natural Resources

2 14,3 lakes > 1 hectare

4 Photos: Buzz Sorge

Phosphorus Reduction Actions in Wisconsin

Wastewater Treatment Runoff program Coon

prohibitions Tighten rules for large animal

5 Phosphorus Reduction Actions in Wisconsin Soil Conservation Clean Water Act Wastewater Treatment Runoff program Coon Valley Great Lakes Water Quality Agreement Regulate Concentrated Animal Feeding Operations Discharge <1 mg/l phosphorus statewide Runoff performance standards and prohibitions Tighten rules for large animal farms Fertilizer phosphorus ban Dish detergent <.5% phosphorus by weight Phosphorus criteria for all surface waters Phosphorus budgets for impaired watersheds CAFO s Phosphorus bans

6 Future Nutrient Loading Threats Projected Change in Frequency of 2 Precipitation Events 198 to 255 days/decade Increase in Housing Density

7 Is lake water quality getting better, worse, or staying the same? Melvin McCartney, Lake Monona

8 Long Term Water Quality Monitoring Spring and 3 X s in summer: Secchi depth Temperature/D.O. profile Total Phosphorus Chlorophyll a Conductivity (optional) ph (optional) 1 X in summer: Color Total Kjeldahl Nitrogen NO2+NO3 Alkalinity 5 year cycle: Ca Mg 61 Lakes

9 Trends in Total Phosphorus Over Time 8 lakes decreasing TP 46 lakes no change in TP 6 lakes increasing TP Latitude Average + stdev decrease steady increase

10 Trends in Total Phosphorus Over Time Decrease Steady Increase Vern Wolf Pelican Lac Courte Oreilles Silver Ripley TP Criteria Crystal Total Phosphorus (mg/l)

11 Expand analysis to all WDNR data WDNR Data Download: 218,3 records 151 lakes Data from Up to 34 years of data on a single lake

12 Exclude hypereutrophic lakes (.1 mg/l) from Total Phosphorus analysis 9 8 Number of Lakes hypereutrophic lakes Maximum Annual Average TP (mg/l)

13 Simple linear regressions June 15 September 15 Annual Average Natural logarithm of concentration Color (SU)

14 Limit trend analysis to lakes with at least 3 5 years of data Slope ((ln(unit+1))/yr) Total Phosphorus Alkalinity Total Kjeldahl Nitrogen Calcium NO2+NO Magnesium Total Years of Record

15 Limit trend analysis to lakes with at least 3 5 years of data Slope ((ln(unit+1))/year) Total Phosphorus Total Kjeldahl Nitrogen Color Alkalinity Calcium NO2+NO Magnesium Total Years of Record 1 1.5

16 Trend Slopes Near on Most Lakes median: Slope ((ln(unit+1))/year) TP TKN NO2+NO3 Alkalinity Ca Mg Color

17 3% 27% of lakes had a significant trend Percent Lakes with Significant Trend Total 2 N: Increasing Decreasing TP TKN NO2+NO3 Alk Ca Mg Color

18 Does time period matter? Phosphorus Year

19 Does time period matter? Phosphorus Year

20 Fewer lakes with increasing phosphorus trend in recent years Percent of Lakes with Significant Trend

21 TP (mg/l) TP (mg/l) Rock Lake, Jefferson County ug/l per year Fox Lake, Dodge County ug/l per year TP (mg/l) Devils Lake, Sauk County

22 No Spatial Pattern in Temporal Trends TKN NO2+NO3

23 No Spatial Pattern in Temporal Trends Alkalinity Color

24 No Spatial Pattern in Temporal Trends Calcium Magnesium

25 No Spatial Pattern in Temporal Trends TP

26 Are lakes getting better or worse? Maximum TP (mg/l) TP Stays Low TP Stays High Decreasing Increasing Recreation Criterion Minimum TP (mg/l) no change

27 Reasons for Phosphorus Decline Urbanization of Agricultural Land Septic to Municipal Sewage Algal to Plant Dominated Lake Best Management Practices Melvin McCartne Bruce Werre

28 Reasons for Increasing Phosphorus Agriculture Lake Shore Development Plant to Algal Dominated Lake Climate and Water Levels Carp Exclosure USGS

29 National Aquatic Resource Surveys: Minimally Disturbed Lakes and Streams are Getting Worse (µg/l) from Stoddard et al. 216 Env Sci & Tech

30 National vs. Wisconsin Trends National Reference Lakes 1 All Wisconsin Lakes Median annual TP increase: 1.6 ug/l/year TP in 212 (ug/l) TP in 27 (ug/l).27 ug/l/year n=332 from Stoddard et al. 216 Env Sci & Tech

31 Trends more extreme with less than 3 5 years of data Slope ((ln(unit+1))/yr) Total Phosphorus Alkalinity Total Kjeldahl Nitrogen Calcium NO2+NO Magnesium Total Years of Record

32 Trends in Total Phosphorus from vs. Full Record Full Record Percent Slope Years of Data: 4 31 Start Year: End Year: Percent Slope Full Record Number of Lakes Number of Lakes Full Record Median Slope.35% Percent Slope Median Slope.263% Percent Slope Paired T Test (p<.2)

33 Analytical Approach Consider length of record when drawing conclusions about trends Slopes from 2 years of data much more extreme than those from longer records Simple linear regression over long period of record may mask recent trends Fewer lakes with increasing phosphorus trends in recent years

Summary of Trends Most lakes have not changed over time spans of 3 43 years, but a small percent of lakes have significantly increasing or decreasing

34 Summary of Trends Most lakes have not changed over time spans of 3 43 years, but a small percent of lakes have significantly increasing or decreasing trends. Lack of spatial pattern suggests local watershed processes are important drivers Median slope Calcium, Magnesium NO2+NO3 + TP, TKN, Alkalinity, Color

35 Future Work Analyze potential drivers of change: land cover, climate, policy & management actions Examine nonlinear trends over time Investigate lakes that are vulnerable to eutrophication Celebrate success stories

36 Thanks to Department of Natural Resources lake biologists, summer staff, and citizen volunteers!

Status and Trends of Water Quality in Wisconsin s Lakes, Streams, and Rivers

Status and Trends of Water Quality in Wisconsin s Lakes, Streams, and Rivers Tim Asplund, Matt Diebel, Katie Hein, and Mike Shupryt Water Resources Program, WDNR AWRA Wisconsin Section Annual Meeting March