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Understanding Ag-Related Trends in Ground-Water Quality, Western Lake Michigan Drainages

This presentation focuses on describing trends and factors affecting atrazine and nitrate in shallow ground water in the Western Lake Michigan Drainages of Wisconsin. It includes an analysis of input history, source of ground water, age of ground water, and other factors.

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Understanding Ag-Related Trends in Ground-Water Quality, Western Lake Michigan Drainages

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  1. Understanding Agriculture-Related Trends in Ground-Water Quality, Western Lake Michigan Drainages, Wisconsin MI WI Western Lake Michigan Drainages Trends: Atrazine Nitrate Lake Michigan MN IA WI IL David SaadUSGS Wisconsin Water Science Center Middleton, WI

  2. USGS National Water-Quality Assessment Program (NAWQA) NAWQA Objectives: Describe water-quality status and trends and improve our understanding of natural and anthropogenic factors affecting water-quality conditions inmany of theNation’s riversand aquifers

  3. NAWQA Ground-water Land-Use Studies Land-use study objective: Status, trends and understanding of factors that affect shallow ground-water quality in an area of specified land use Presentation focus: Describe trends and factors that affect trends of atrazine and nitrate in shallow ground water in the glacial deposits aquifer in an area of corn/alfalfa rotation

  4. Glacial Deposits Sand and gravel Till Fine grained GW Land-use study area: 30 well network (2” pvc) Glacial Deposits aquifer LU=Corn/alfalfa rotation (dairy) Sampled 1994 and 2002 Water QualityAtrazine or deethyl: 28 of 30 wells Nitrate: 28 of 30 wells Wisconsin Lake Michigan

  5. 5 5 5 10 15 EXPLANATION 10 5 year Time of Travel 15 20 25 To understand ag related trends in gw quality need to know: -Input history (ag chem use) -Source of gw -Age of gw -Other factors (climate, chemistry, soils, hydrogeology, well info)

  6. Input history-Wisconsin Atrazine and Nitrogen Use WI Atrazine Rule 1991

  7. To understand trends in ground-water quality need to know: • Input history • Source of ground-water Nearby, upgradient • Age of ground-water Chlorofluorocarbons (CFCs) • Other factors

  8. CFC-based ground-water recharge dates Well 5 CFC-12 Well 24 Well 2 Well 1 Well 15 CFC-11 CFC-113 (Uncertainty based on +/- 1 deg C)

  9. To understand trends in ground-water quality need to know: • Input history • Source of ground-water • Age of ground-water • Other factorsClimate (annual precip), Chemistry (DO), Soils (STATSGO), Hydrogeology (Kh), Well Info (depth, WL)

  10. Land-use Study Trends Analysis:Near-decadal changes (using samples collected in 1994 and 2002)Trends using ground-water age data Correlations to inputs and other factors

  11. Data adjustments to consider when determining trends in water quality:Detection limits If detection limit changes over time, recensor data to a uniform detection limit.Sample variability Are measured differences greater than known sample variability? If not, difference = 0Analytical recovery Does lab reported conc equal environmental conc? Adjust data for poor recovery.

  12. Near-decadal changes: Atrazine + Deethyl atrazine Signed-Rank Test: p=0.02 0.34 Data adjustments: 0.30 -uniform detect limit -sample variability -analytical recovery n=30 n=26

  13. Near-decadal changes: Atrazine + Deethyl atrazine Signed rank: p=0.02 Signed rank: p=0.78 1994 to 2002 Decrease No change Increase Decrease: 13No change: 10Increase: 3 Decrease: 13No change: 0Increase: 13 Data adjustments: -uniform detect limit -uniform detect limit -sample variability -analytical recovery

  14. Near-decadal changes: Nitrate Signed-Rank Test: p=0.04 11.3 Data adjustments: -uniform detect limit -sample variability 6.8 n=30 n=26

  15. 1994 to 2002 Near-decadal changes: Nitrate Signed rank: p=0.04 Data adjustments: -uniform detect limit -sample variability Decrease: 6No change: 7Increase: 13

  16. Trends using ground-water age data

  17. Loess Smooth Loess Smooth Trends using ground-water age data-Atrazine

  18. Loess Smooth Loess Smooth Trends using ground-water age data-Nitrate

  19. Correlation of ground-water concentrations to inputs and other factors: Expected Causal Relationships • Inputs (atrazine/fertilizer use) • Well info (well depth, water level) • Hydrogeology, soil characteristics • Climate (annual precipitation) • Water chemistry (DONO3)

  20. Spearman’s Rho correlations Atrazine + deethyl atrazine: rhop-valueN Soil perm .47 .0003 56 Atrazine use .34 .01 56 Annual precip .30 .02 56

  21. Spearman’s Rho correlations Nitrate: rhop-valueN Fertilizer N use .49 .0001 56 DO .40 .002 56

  22. Summary and Conclusions • Atrazine+deethyl Significant decrease in ground-water concentrations 1994 to 2002 • Nitrate Significant increase in ground-water concentrations 1994 to 2002 • Temporal trends in ground-water concentrations correlated to historical inputs • Atrazine also correlated to precipitation and soil; Nitrate also correlated to DO

  23. Summary and Conclusions • Ground-water age data provides valuable information • Data adjustments are important to consider when determining trends in water quality • To understand trends in ground-water quality need to know more than just changes in concentration.

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