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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Groscheová, H; Novák, M; Alewell, C: Changes in the d34S ratio of pore-water sulfate in incubated sphagnum peat, Wetlands, 20/1, 62-69 (2000)
Sulfur transformations in freshwater peat were studied using contrasting stable isotope signatures of atmospheric input (high delta34S) and Sphagnum peat substrate (low delta34S). Wet subsurface peat samples from the Lehstenbach watershed, Fichtelgebirge, Germany were incubated anaerobically at 5 and 15°C. Pore-water sulfate was augmented with natural precipitation at the onset of the experiments. Sulfate concentrations and delta34S ratios of residual pore water were measured in 1-day intervals (9 days) and 1-week intervals (7 weeks) at 15°C, and in 1-week intervals (7 weeks) at 5°C. Initially, SO42- concentrations decreased (by 50 to 85%) and delta34S ratios increased (by as much as 16 parts per thousand) at both temperatures due to bacterially-mediated dissimilatory sulfate reduction. At the higher temperature (15°C), the S isotope effect (Delta delta34S) was higher than at the lower temperature (5°C). On day 4 (at 15°C) and day 29 (at 5°C), the delta34S ratio of pore-water sulfate started to decrease by as much as 20 parts per thousand. The changing S isotope composition provided evidence for a dynamic turnover of the pore-water sulfate pool in anaerobic pest. The observed delta34S pattern could not be explained solely by isotope selectivity of the sulfate-reducing bacteria. Sulfur isotope data indicated a replenishment of the sulfate pool by hydrolysis of ester-sulfate.
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