Oxygen Depletion in Lake Erie: Modeling the Physical,Chemical, and Biological Interactions, 1972 and 1979

Models of the thermal structure, transport, and oxygen uptake within the water column and sediment are combined to examine the interaction of physical and biochemical processes resulting in oxygen depletion in the central basin hypolimnion of Lake Erie. While the oxygen demand in water and sediment may vary slightly from year to year, the oxygen supply to the hypolimnion due to physical processes is quite variable. Detailed calculations show that in years with relatively calm weather (e.g., 1979), physical processes supply only about 10% of the amount needed to offset demand due to uptake in the water and sediment during stratified periods. As the hypolimnion also tends to be relatively shallow in such years, the available oxygen is often quickly depleted. In contrast, during windy years (e.g., 1972) physical sources can supply about 40% of the oxygen consumed and, since the hypolimnion tends to be thicker, the oxygen concentration seldom reaches the anoxic level. It is concluded that analysis with oxygen depletion as an indicator of Lake Erie's recovery due to phosphorus control must consider variability in oxygen sources as a result of physical processes.