A MODEL FOR SULFUR ACCUMULATION IN SOFT-WATER LAKE-SEDIMENTS

A geochemical model for sulfur in soft water lake sediments of the Adi rondack Mountains, New York, is developed to gain insight into the tim ing and magnitude of historical changes in sulfur loading. Surficial s ulfur concentrations range from 3500 to 10,000 mu g g(-1), increase to 6000 to >20,000 mu g g(-1) at a depth of 2-6 cm, and then decrease do wncore to background revels of 2500-7500 mu g g(-1). Sulfate concentra tions are about 50-80 mu M in the overlying water and decrease rapidly below the sediment-water interface. A mathematical model is construct ed assuming sulfur is incorporated into sediments by burial of detrita l organic matter and by diffusion of dissolved sulfate from the overly ing water with subsequent fixation into the sediment solids. Several s cenarios of historical sulfate deposition were examined as model bound ary conditions. The observed sediment sulfur profiles are best modeled using boundary conditions showing loading increases of about a factor of 8 since about 1940. Assuming as much as a decade of retention of s ulfate within the terrestrial portion of the ecosystem, this suggests that significant increases in sulfate deposition rates began sometime about 1930 in this area.