Sulfur speciation, vertical distribution, and seasonal variation in a northern hardwood forest soil, U.S.A

Sulfur biogeochemistry of a northern hardwood forest soil in Bear Brook Watershed, Maine, was studied utilizing 35S in situ. The objectives of study were to characterize different S pools, their vertical distribution, and seasonal variation. Soil cores were used at the field and treated with 35SO42−. The distribution of total and C-bonded S followed a typical pattern of decreasing concentration with soil depth. More than 86% of total 35S added was retained by the soil. Most of the 35S activity was in the organic S pool (up to 73 and 20% of total 35S in C-bonded S and ester-sulfate forms, respectively) in both the forest floor and the mineral soil horizons. Ester sulfate increased with depth from 5.3 to 25.5% of total S. During the summer the relative importance of mineralization to immobilization decreased. Inorganic sulfate was the smallest S pool. However, higher specific activity and turnover rate of the inorganic 35SO42− pool than organic 35S pool indicated that S concentration and solution flux were more regulated by abiotic (adsorption and desorption) than biotic (mineralization and immobilization) processes.