Phosphorus mobilization from littoral sediments of an inlet region in Lake Delavan, Wisconsin

Rates of P release from littoral sediments of the inlet region of Lake Delavan, Wisconsin, were examined in the laboratory under different redox and pH regimes using sediment systems and also in situ using sediment peppers. In the laboratory, rates of P release from sediments increased about two-fold (i.e., to 7 mg m-2 d-1) under oxic conditions as a result of adjusting the pH of the overlying water from 8.5 to about 9.0. Laboratory rates increased to a maximum of 23 mg m-2 d-1 under anoxic conditions. Both in situ pH and dissolved oxygen (DO) exhibited marked seasonal fluctuations due, primarily, to metabolism by submersed macrophytes, which occupied over 50% of the inlet region. Using continuous records of in situ pH and DO and ranges in rates of P release measured in the laboratory, we estimated an overall mean rate of P release of 5.7 mg m-2 d-1 from the littoral sediments during the summer (April-September) of 1994. Rates of P release estimated from Fickean diffusional fluxes were similar to rates estimated from pH and DO. Our results suggest that aquatic macrophyte communities of the inlet region enhance the mobilization of P from littoral sediment by regulating pH and DO in the surrounding environment.