Alewell, C; Giesemann, A: Sulfate reduction in a forested catchment as indicated by d34S values of sulfate in soil solutions and runoff, Isotopes Environm. Health Studies, 32, 203-210 (1996)
Abstract: In a forested catchment in the Fichtelgebirge mountains (NE-Bavaria, Germany) the long term SO42- budget (average 1988 - 1994) indicated that about 40% of the input with throughfall (16.8 kg SO4-S.ha-1.yr-1) was retained in the catchment. In order to identify processes acting as potential SO42- sinks, d34S values of SO42- in soil solutions and runoff were measured between May and November 1994. d34S values of the runoff and the fen were higher (5.8) than the d34S values of the soil solution of the oxic soils in the terrestrial area (3.9). Because there is no lithogenic S source within the catchment, it can be assumed that SO42- deposition is the only S source in the catchment. Thus the results were interpreted as a result of SO42- reduction within the catchment, because the uptake of 32S is favored during the dissimilatory SO42- reduction and 34S is consequently enriched in the soil solution. To estimate the amount of SO42- reduced, isotopic fractionation factors between -9 and -46 were considered, resulting in SO42- reduction rates of 1.8 - 9.3 kg SO42-S.ha-1.yr-1. It was concluded that besides dissimilatory SO42- reduction another sink exists in the catchment (e.g. SO42- sorption in deep soil layers).