PHOSPHORUS MOBILIZATION FROM LITTORAL SEDIMENTS OF AN INLET REGION INLAKE-DELAVAN, WISCONSIN

Rates of P release from littoral sediments of the inlet region of Lake Delavan, Wisconsin, were examined in the laboratory under different r edox and pH regimes using sediment systems and also in situ using sedi ment peepers. In the laboratory, rates of P release from sediments inc reased about two-fold (i.e., to 7 mg m(-2) d(-1)) under oxic condition s as a result of adjusting the pH of the overlying water from 8.5 to a bout 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) ex hibited marked seasonal fluctuations due, primarily, to metabolism by submersed macrophytes, which occupied over 50% of the inlet region. Us ing continuous records of in situ pH and DO and ranges in rates of P r elease measured in the laboratory, we estimated an overall mean rate o f P release of 5.7 mg m(-2) d(-1) from the littoral sediments during t he summer (April-September) of 1994. Rates of P release estimated from Fickean diffusional fluxes were similar to rates estimated from pH an d DO. Our results suggest that aquatic macrophyte communities of the i nlet region enhance the mobilization of P from littoral sediment by re gulating pH and DO in the surrounding environment.