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Lake Michigan Mass Balance Study - Atrazine

LMMB Study
Overview Contaminants

Lake Michigan Atrazine

Figure 7. Atrazine use - kilograms per square kilometer (U.S. Geological Survey, 1991) range from less than 0.5 to more than 25.0. Relatively heavy application in 1991 is shown in the corn growing regions of Illinois, Indiana, and Ohio. Application and prevailing wind patterns around Lake Michigan may contribute to atrazine loads.

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Figure 8. Historical tributary and wet deposition loadings of atrazine to Lake Michigan. Tributaries show a steady increase from 1964 through 1978, holds fairly steady with some change until about 1984, then declines steadily through 1998. Wet deposition show lower loading rates increasing slightly from 1963 through 1978, holds steady with some change through 1998.

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Figure 9. Atrazine loads (kg/yr) to Lake Michigan from major monitored and unmonitored tributaries, 1994-199
  • Fox River 623 kilograms per year
  • Sheboygan River 62 kilograms per year
  • Milwaukee River 87 kilograms per year
  • Grand Calumet River 23 kilograms per year
  • St. Joseph River 1559 kilograms per year
  • Kalamazoo River 484 kilograms per year
  • Grand River 1264 kilograms per year
  • Muskegon River 144 kilograms per year
  • Pere Marquette River 26 kilograms per year
  • Manistique River 0.43 kilograms per year
  • Menominee River 33 kilograms per year
  • Calculated loads for monitored tributaries 4305 kilograms per year
  • Calculated loads for unmonitored tributaries 959 kilograms per year

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Figure 10. Lake Michigan atrazine mass balance (including Green Bay), 1994.
  • 1994 atrazine inventory - 184,310 kilograms
  • watershed loading - 5264 kg/year
  • export to Lake Huron - 2546 kg/year
  • atmospheric wet deposition - 2493 kg/year
  • loss to decay - 1662 kg/year
  • input from Lake Huron - 482 kg/year
  • absorption 227 kg/year
  • export via Chicago Diversion - 146 kg/year
  • volatilization - 50 kg/year
  • dry deposition, settling, sediment resuspension and net burial are negligible.

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Figure 11. Lake Michigan atrazine forecasts (LM2-Toxic Model)
  • Atrazine concentrations at constant loads (no further action) appear to level off at 66 ng/L about the year 2200
  • modeling a 35% reduction of total load levels off at model year 2005
  • 100% reduction of tributary load and 100% reduction of total load show significant reductions in atrazine concentrations

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Figure 12. Atrazine effects thresholds compared to observations and model predictions.
  • average 1994 measured Lake Michigan concentration - 37 ng/L
  • average 2005 forecasted (modeled) Lake Michigan concentration - 44 ng/L
  • average 2263 forecasted (modeled) Lake Michigan concentration - 66 ng/L
  • maximum 1995 forecasted (modeled) Lake Michigan nearshore concentration - 350 ng/L
  • phytoplankton production - 2,300 ng/L
  • maximum 1995 measured St. Joseph River concentration - 2,700 ng/L
  • human drinking water Maximum Contaminant Level (MCL) - 3,000 ng/L
  • freshwater plant and animal effects thresholds above 10,000 ng/L

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