A process-oriented, deterministic, one-dimensional, numerical dissolved
oxygen simulation model is developed to make projections for lakes with a wide
range of morphometries, trophic levels and climate scenarios. The model is
needed to estimate the potential impact of projected global climate change on
lake water quality and fish populations. The model, combined with a water
temperature stratification model, simulates vertical dissolved oxygen profiles in
stratified lakes in daily time steps throughout the open water season including
met alimneti c oxygen maxima in oligotrophic lakes. The dissolved oxygen
transport equation includes photosynthesis as a source term; biochemical oxygen
demand and plant respiration are sink terms. Oxygen exchange through the
air-water interface and sedimentary oxygen demand through the water-sediment
interface are physical boundary conditions for the dissolved oxygen transport
equation, but treated as source/sink terms in the numerical model. The model
relates biological variables to specified trophic levels. Best values of biological
parameters and rate coefficients are determined by sequential literature search,
model calibration, validation and sensitivity analysis for an array of lakes.
Average standard errors are 1.4 and 1.9 mg l for calibration and validation of
model predictions compared to measurements, respectively. Model predictions of
epilimnetic dissolved oxygen concentrations are found strongly sensitive to net
photosynthetic production rate and surface gas transfer coefficient. Interaction
between surface gas transfer, epilimnetic diffusion and photosynthetic
productivity in the model is examined by an unsteady-state analysis. The
model is applied to 27 lake classes based on lake surface area, maximum depth,
and trophic levels under historical climate conditions in Minnesota. Daily
dissolved oxygen profiles are simulated for each open water season from 1955 to
1979. A future climate scenario, as predicted by the GISS model for a
doubling of atmospheric C02, is also applied. Simulated dissolved oxygen
characteristics of lakes under the historical and the projected future climate
scenario are interpreted and compared. Decreases of dissolved oxygen
concentrations are predicted for most lakes under the projected future climate
Environmental Research Laboratory, US Environmental Protection Agency
Fang, Xing; Stefan, Heinz G..
Modeling of Dissolved Oxygen Stratification Dynamics in Minnesota Lakes under Different Climate Scenarios.
St. Anthony Falls Hydraulic Laboratory.
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