Long Term Water Quality Trends in Wisconsin Lakes Katie Hein Wisconsin Department of Natural Resources
14,3 lakes > 1 hectare
Photos: Buzz Sorge
Phosphorus Reduction Actions in Wisconsin 1933 1972 Soil Conservation Clean Water Act Wastewater Treatment Runoff program Coon Valley 1977 1984 1992 22 27 21 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
Future Nutrient Loading Threats Projected Change in Frequency of 2 Precipitation Events 198 to 255 days/decade Increase in Housing Density 194 21
Is lake water quality getting better, worse, or staying the same? Melvin McCartney, Lake Monona
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
Trends in Total Phosphorus Over Time 8 lakes decreasing TP 46 lakes no change in TP 6 lakes increasing TP Latitude 47 46 45 44 43 42 Average + stdev decrease steady increase
Trends in Total Phosphorus Over Time.6.5.4.3.2.1 Decrease Steady Increase Vern Wolf.5.4.3.2.1 Pelican.2.15.1.5 Lac Courte Oreilles.14.12.1.8.6.4.2 1985 199 1995 2 25 21 215 22 2 22 24 26 28 21 212 214 216 1973 1984 1992 1998 24 21.15.12.9.6.3 1973 1984 1992 1998 24 21 1973 1982 199 1995 2 25 21 Silver.6.5.4.3.2.1 Ripley TP Criteria Crystal Total Phosphorus (mg/l) 1973 1982 199 1995 2 25 21
Expand analysis to all WDNR data WDNR Data Download: 218,3 records 151 lakes Data from 1968 215 Up to 34 years of data on a single lake
Exclude hypereutrophic lakes (.1 mg/l) from Total Phosphorus analysis 9 8 Number of Lakes 7 6 5 4 3 2 1 153 hypereutrophic lakes.1.9.1.2.4.6.8 1 1.2 1.4 1.6 Maximum Annual Average TP (mg/l)
Simple linear regressions June 15 September 15 Annual Average Natural logarithm of concentration Color (SU) 35 3 25 2 15 1 5 22 24 26 28 21 212 214 216
Limit trend analysis to lakes with at least 3 5 years of data Slope ((ln(unit+1))/yr).4.3.2.1.1.2.3.4.5 1.5 1.5.5 Total Phosphorus 5 1 15 2 25 3 Alkalinity 1 2.8.6.4.2.2.4 2 1 1 2 Total Kjeldahl Nitrogen 5 1 15 2 25 Calcium 2 4 6 8.3.2.1.1.2.3.4 1.5 1.5.5 NO2+NO3 5 1 15 2 25 Magnesium 5 1 1 3 1 1.5 4 1.5 Total Years of Record
Limit trend analysis to lakes with at least 3 5 years of data Slope ((ln(unit+1))/year).4.3.2.1.1.2.3.4.5 1.5 1.5.5 Total Phosphorus.8.6.4 1.5.2 5 1 15 2 25 3 1.5.2 Total Kjeldahl Nitrogen Color 5 1 15 2 25.4 Alkalinity 2 5 1 15.5 Calcium 1 1 1 2 4 6 8 1 2 2.3.2.1.1.2.3.4 1.5 1.5.5 NO2+NO3 5 1 15 2 25 Magnesium 5 1 1 1.5 3 4 Total Years of Record 1 1.5
Trend Slopes Near on Most Lakes median:.3.25..13.68.94.72 Slope ((ln(unit+1))/year).2.1..1 TP TKN NO2+NO3 Alkalinity Ca Mg Color
3% 27% of lakes had a significant trend Percent Lakes with Significant Trend Total 2 N: 15 1 5 5 1 15 52 92 82 14 29 19 59 Increasing Decreasing TP TKN NO2+NO3 Alk Ca Mg Color
Does time period matter? Phosphorus Year
Does time period matter? Phosphorus Year
Fewer lakes with increasing phosphorus trend in recent years Percent of Lakes with Significant Trend 14 12 1 8 6 4 2 2 4 6 8 198 199 2 27
TP (mg/l) TP (mg/l) Rock Lake, Jefferson County.4.3 +.3 ug/l per year.2.1 198 199 2 21 22 Fox Lake, Dodge County.4.3 4.4 ug/l per year.2.1 198 199 2 21 22 TP (mg/l) Devils Lake, Sauk County.4.3.2.1 197 198 199 2 21 22
No Spatial Pattern in Temporal Trends TKN NO2+NO3
No Spatial Pattern in Temporal Trends Alkalinity Color
No Spatial Pattern in Temporal Trends Calcium Magnesium
No Spatial Pattern in Temporal Trends TP
Are lakes getting better or worse? Maximum TP (mg/l).1.9.8.7.6.5.4.3.2.1 TP Stays Low TP Stays High Decreasing Increasing Recreation Criterion.1.2.3.4.5.1.9.8.7.6.5.4.3.2.1 Minimum TP (mg/l) no change.1.2.3.4.5.6
Reasons for Phosphorus Decline Urbanization of Agricultural Land Septic to Municipal Sewage Algal to Plant Dominated Lake Best Management Practices Melvin McCartne Bruce Werre
Reasons for Increasing Phosphorus Agriculture Lake Shore Development Plant to Algal Dominated Lake Climate and Water Levels Carp Exclosure USGS
National Aquatic Resource Surveys: Minimally Disturbed Lakes and Streams are Getting Worse (µg/l) from Stoddard et al. 216 Env Sci & Tech
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) 1 1 1 1 1 TP in 27 (ug/l).27 ug/l/year n=332 from Stoddard et al. 216 Env Sci & Tech
Trends more extreme with less than 3 5 years of data Slope ((ln(unit+1))/yr).4.3.2.1.1.2.3.4.5 1.5 1.5.5 Total Phosphorus 5 1 15 2 25 3 Alkalinity 1 2.8.6.4.2.2.4 2 1 1 2 Total Kjeldahl Nitrogen 5 1 15 2 25 Calcium 2 4 6 8.3.2.1.1.2.3.4 1.5 1.5.5 NO2+NO3 5 1 15 2 25 Magnesium 5 1 1 3 1 1.5 4 1.5 Total Years of Record
Trends in Total Phosphorus from 27 212 vs. Full Record Full Record Percent Slope 27 212 1.1.8.5.2.1.4 Years of Data: 4 31 Start Year: 1973 27 End Year: 212 215.7.7.4.1.2.5.8 1.1 Percent Slope Full Record Number of Lakes Number of Lakes 2 15 1 5 15 1 5 Full Record Median Slope.35%.7.5.3.1.1.3.5.7.9 1.1 1.3 Percent Slope 27 212 Median Slope.263%.7.5.3.1.1.3.5.7.9 1.1 1.3 Percent Slope Paired T Test (p<.2)
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 trends. Lack of spatial pattern suggests local watershed processes are important drivers Median slope Calcium, Magnesium NO2+NO3 + TP, TKN, Alkalinity, Color
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
Thanks to Department of Natural Resources lake biologists, summer staff, and citizen volunteers!