Stable sulfur isotopes in forest spring waters from the Fichtelgebirge (Germany)

The potential role of processes discriminating S isotopes, for example dissimilatory SO42- reduction and mineralization, in determining SO42- concentrations was studied in forest spring water. S-isotope composition of sulfate from atmospheric input and forest springs representing a wide range of SO42- concentrations was investigated in the Fichtelgebirge (NE Bavaria, Germany). delta(34)S values in atmospheric input ranged from +3.7 to + 5.7 parts per thousand. In spring waters with SO42- > 150 mu mol l(-1) delta(34)S values were between +4 and +5 parts per thousand, whereas delta(34)S values increased up to +7.2 parts per thousand below 150 mu mol l(-1) SO42-. SO42- mineralization seemed to have no effect on isotopic composition since all delta(34)S values of spring water were higher than input values. Dissimilatory SO42- reduction occurred in springs with SO42- < 150 mu mol l(-1). Spatial heterogeneity in forest soils or flow paths has to be invoked to explain increased delta(34)S values since NO3- concentrations would not allow for SO42- reduction to occur.