Fate of anthropogenic sulfur in a cedar-dominated wetland

Abstract

Surface waters in the New Jersey Pinelands are subjected to large amounts of anthropogenic sulfur deposition. Mass balance data showed that much of the deposited sulfur and associated acidity was retained by watersheds before it reached surface waters. The site of retention appeared to be wetlands, which constitute about 25% of the entire region. Dissimilatory sulfate reduction measurements in peat from a cedar-dominated wetland showed that the peat was capable of reducing substantial amounts of sulfate and could account for all the sulfur deposition retained by the watershed. However, dissimilatory sulfate reduction techniques only measure gross rates of reduction. Thus, confirmation that this process actually accounted for sulfur retention required demonstration that the reduced end products were either permanently stored within the wetland or emitted from the surface. Examination of surface water and peat porewa- ter concentrations of H₂S, DMS, CS₂, COS and DMDS from August to December 1989 showed that H₂S was the dominant volatile reduced sulfur compound. DMS was the only other compound detected. Based on potential emission rates or export in streamwater, transport of reduced sulfur compounds out of the watershed accounted for only 3% of the total sulfur retained. Total sulfur, particularly the carbon-bonded fraction, increased substantially with depth. Furthermore, the lighter ³²S became more important as the amount of total sulfur increased. These pool sizes and stable isotope data are consistent with the hypothesis that anthropogenic sulfur is accumulated in the peat by dissimilatory sulfate reduction and suggest that dissimilatory storage of S may be a common occurrence in wetlands subjected to heavy sulfate deposition.