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MODEL SIMULATIONS OF DISSOLVED OXYGEN CHARACTERISTICS OF MINNESOTA LAKES: PAST AND FUTURE
Citation:
Stefan, H. AND X. Fang. MODEL SIMULATIONS OF DISSOLVED OXYGEN CHARACTERISTICS OF MINNESOTA LAKES: PAST AND FUTURE. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-95/200.
Description:
A deterministic, one-dimensional, unsteady numerical model has been developed, tested, and applied to simulate mean daily dissolved oxygen (DO) characteristics in 27 lake classes in the state of Minnesota. eaeration and photosynthesis are the oxygen sources, while respiration, sedimentary, and biochemical water column oxygen demand are the sinks of oxygen in the model. he lake classes are differentiated by surface area (As), maximum depth (Hmax), and trophic status expressed as Secchi depth (Zs). ecause lake stratification is most important to lake oxygen dynamics, simulated DO characteristics are plotted in terms of a stratification parameter AsIHmax 0.25 and Secchi depth Zs. imulations provide DO profiles on a daily time scale. pecific DO characteristics of ecological and environmental interest are epilimnetic DO, hypolimnetic DO, DO gradient from surface to bottom, and DO minima and maxima. pecific results are as follows: imulated mean daily and weekly DO values in the epilimnion of all lakes for both past and future climate scenarios are near saturation over the summer season. ypolimnetic DO values depend strongly on lake morphometry, trophic status, and time throughout the summer season. uture climate conditions are specified as the historical records from 1955 to 1979, adjusted (monthly) by the 2 x CO2 GISS model output to account for doubling of atmospheric CO2. ith this climate change, weekly averaged epilimnetic DO is projected to drop by less than 2 mg/liter, and will remain above 7 mg/liter throughout the open water season. he hypolimnetic DO reductions after climate change are on the order of 2-8 mg/liter. eriods of anoxia are longer by as much as 80 days. hose changes would alter water quality dynamics in lakes and have a profound effect on lake ecosystems including indigenous fishes. he results presented are useful for evaluating environmental management options.