Sulfur pool sizes and stable isotope ratios in HUMEX peat before and immediately after the onset of acidification

Total nonsulfate sulfur (TS), reduced inorganic sulfur (RIS), ester sulfate (ES) and carbon bonded sulfur (CBS) pool sizes, and TS and RIS stable sulfur isotopes were examined in peat cores from control and experimental sites within the Skjervatjern catchment before and 8.5 months after the onset of acidification. The total amount of excess sulfate added to the catchment up to this point was less than expected due to mechanical problems. There have been no observable effects on sulfur cycling within the peat soils. The results from this study, however, provide insight into the natural factors controlling sulfur cycling in this system and suggest that dissimilatory sulfate reduction plays a key role. For instance, the control site, which apparently receives the highest input of sulfate because of its position within the catchment drainage system, has the highest TS, RIS, and CBS pool sizes, the lowest C:S ratios, and the most negative δ 34S TS ratios. All of these characteristics are consistent with a dissimilatory origin for a substantial portion of the peat sulfur. Thus, a mechanism that can potentially store and neutralize at least some of the acidic sulfate to be added to this system is already in operation. The ultimate ability of dissimilatory reduction to store sulfur will be tested as the acidification of the Skjervatjern catchment proceeds and will provide important information on how other wetland ecosystems respond to excessive acidic sulfate inputs.