Transformations of Organic and Inorganic Sulfur: Importance to Sulfate Flux in an Adirondack Forest Soil

Abstract

Sulfate flux from forest soils as a result of inputs from acidic deposition is thought to be a critical process in regulating acidification of surface waters. The purpose of this study was to evaluate biotic transformations of sulfur in an Adirondack Mountain forest soil by adding ³⁵S-sulfate to the forest floor. In September 1983 to each of two 0.5 m² plots, 2.22 × 10¹⁰ dpm of ³⁵S-sulfate was added in 4 liters of solution. Analysis of soil horizons from the plot at the end of the six week incubation indicated that 70 and 99 percent of the added ³⁵S was retained in the soil at plots 1 and 2, respectively. More than 70 percent of the ³⁵S was found in Oa, Bh, and Bs1 horizons. In O horizons greater than 80 percent of the ^3sS was found as organic sulfur, whereas in mineral horizons most was found as adsorbed sulfate. These findings indicated that a portion of the sulfate moving through the soil is both rapidly immobilized in the forest floor and adsorbed in the mineral horizons. On a net basis, however, the soil is not accumulating sulfur so that mineralization and desorption must equal immobilization and adsorption.