HISTORICAL LOADING RECORD OF A POST-DEPOSITIONALLY REACTIVE SUBSTANCE- A MODEL FOR SULFUR IN AN ADIRONDACK LAKE

A model for the distribution of sulfur in the sediments of a lake in t he Adirondack Mountains, New York State, is developed to gain insight into the timing and magnitude of anthropogenic increases in sulfur loa ding. Surficial sulfur concentrations an about 3500 mug/g, increase to 6000-7000 mug/g at a depth of about 6 cm, and then decrease downcore to background levels of about 2500 mug/g. Sulfate concentrations are a bout 60-80 muM in the overlying water and decrease rapidly below the s ediment water interface. This reflects assimilation and/or dissimilato ry reduction of sulfate into the solid phase fractions of the sediment . A mathematical model is constructed assuming sulfur is incorporated into sediments by burial of detrital organic matter and by diffusion w ith subsequent fixation of sulfate from the overlying water. Several h istorical scenarios of atmospheric sulfate loading rates were used as model boundary conditions. Model results are compared with observed se dimentary sulfur profiles. The observed sediment sulfur profiles are b est described using model boundary conditions showing increases in lak e water sulfate concentrations, and thus presumably in atmospheric dep osition, within last 50-60 years.