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Reservoir and Lake Nutrient Criteria

Reservoir and Lake Nutrient Criteria. A Different Approach. D.V. Obrecht, J.R. Jones & M.K. Knowlton – MU Limnology. UMBRELLA APPROACH. 1) Reference reservoirs and lakes – 75 th percentile 2) All reservoirs and lakes – 25 th percentile 3) EPA’s 304(a) criteria. Oxbow lakes (n=12)

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Reservoir and Lake Nutrient Criteria

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  1. Reservoir and Lake Nutrient Criteria A Different Approach D.V. Obrecht, J.R. Jones & M.K. Knowlton – MU Limnology

  2. UMBRELLA APPROACH • 1) Reference reservoirs and lakes – 75th percentile • 2) All reservoirs and lakes – 25th percentile • 3) EPA’s 304(a) criteria

  3. Oxbow lakes (n=12) TP = 212 ug/L TN = 1.56 mg/L Reservoirs (n=135) TP = 45 ug/L TN = 0.73 mg/L

  4. ReservoirTP (µg/L)range of geomeans Maysville (n=10) 182 116 – 300 Grindstone (n=5) 147 90 - 218 Unionville (n=10) 98 68 - 155 Long Branch (n=20) 48 30 - 115 Viking (n=16) 26 19 - 40 Forest (n=19) 23 14 - 44

  5. STEP APPROACH Designated Use Impairment of use Algal biomass Nutrient levels Criteria level

  6. Drinking Water Supply Impairments -taste and odor -clogging of filters -algal toxins

  7. There may be too many factors that influence water quality and too much variability within and among systems to allow for the setting of a single set of criteria to be used by the state for regulation.

  8. EPA allows some flexibility: …(states can) develop their own criteria which reflect more locally representative conditions. …prioritize their waters…..Such an approach should include a mechanism for evaluating the sensitivity of all waters…considering current and expected land use… EPA memorandum, Nov. 14, 2001

  9. A Different Approach!

  10. A lake is a reflection of its watershed.

  11. Total Phosphorus (µg/L) Cropland (%)

  12. A reservoir is also a reflection of its watershed, and the intensity of that reflection is dictated by hydrology.

  13. Regression model results Equation r2 TP = 4.27 + 0.36 %crop 0.62 TP = 5.53 + 0.33 %crop – 0.50DH 0.73 TP = 5.20 + 0.35crop% - 0.37 DH + 0.12 FI 0.77 DH is dam height, a surrogate from reservoir morphology FI is flushing index

  14. Can we use agriculture to classify reservoirs? USGS photo

  15. Reservoirs were built into landscapes that had already been altered. No Restoration Water quality in a reservoir is a function of morphology/hydrology and location within the landscape.

  16. Harvested acres of corn, 1920 58,000 – 87,000 ac 30 counties 7,600 – 34,000 ac 36 counties 34,000 – 58,000 ac 26 counties 87,000 – 169,000 ac Between 11% and 21% of total Missouri land surface dedicated to just corn production in 1920! 22 counties

  17. Missouri’s reservoirs >10 acres in size Year completed # % 1800-1920 122 8 1920-1940 267 18 1940-1960 68 5 1960-1980 909 61 1980-1995 121 8

  18. This approach allows the state to: -Identify and protect the reservoirs that have low watershed impacts. -Identify and focus efforts on the reservoirs that have higher nutrient concentration than expected, given watershed land use and hydrology. -Gauge the potential for successful nutrient reduction by looking at the factors that control in-reservoir nutrient concentrations. And focus limited resources ($$) on those reservoirs where improvements can be made.

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