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Patterns of stable S isotopes in a forested catchment as indicators for biological S turnover

Research paper by Christine Alewell, Matthias Gehre

Indexed on: 01 Dec '99Published on: 01 Dec '99Published in: Biogeochemistry



Abstract

Despite intensive biogeochemical research during the last thirty years, the relative importance of biological S turnover for the overall SO42− budget of forested catchments remains uncertain. The objective of the present study was (i) to gain new insight into the S cycle of theLehstenbach catchment (Northeastern Bavaria, Germany) through the analysis of stable isotopes of S and (ii) to differentiate between sites which are ‘hot spots’ for SO42− reduction and sites where mineralization and adsorption/desorption processes are more important. The δ34S values and SO42− concentrations of soil solutions, throughfall and groundwater at four different sites as well as runoff of the catchment were measured. The relatively low variability of δ34S in throughfall and bulk precipitation was in contrast to the high temporal and spatial variability of δ34S in the soil solution. Sulfate in the soil solution of upland sites was slightly depleted in34S compared to input values. This was most likely due to S mineralization. Sulfate in the soil solution from wetland soils was clearly enriched in34S, indicating dissimilatory SO42− reduction. The observed spatial and temporal patterns of34S turnover and SO42− concentrations might explain the overall balanced S budget of the catchment. At a time of decreasing anthropogenic deposition SO42− is currently released from upland soils. Furthermore, mineralization of organic S may contribute to SO42− release. Wetland soils in the catchment represent a sink for SO42− due to dissimilatory SO42− reduction.