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Peat sulfur biogeochemistry changed in several important ways as the result of a catchment-scale acidification manipulation experiment (HUMEX) from June 1990 (immediately before onset of acidification) to June 1994. Porewater sulfate increased markedly at the experimental sites compared to the control, based on measurements immediately after acidification events. Nitrate, which was added in artificial precipitation along with sulfate, was not observed in porewater, even on the acidified side of the catchment. Total S (TS) and reduced inorganic S (RIS) were unchanged at the control site. TS increased significantly at one experimental site and was unchanged at the other. RIS increased significantly at both experimental sites. All of these changes were consistent with increased net dissimilatory sulfate reduction at the experimental sites in response to elevated sulfate deposition. The increase in TS pools at one site was sufficient to account for most of the S deposition at the site over the 3.5 y of the experiment. Analysis of stable S isotopes confirmed trends observed in S pool sizes. Further, the S stable isotope data suggested that, despite stimulation of overall dissimilatory activity by increased S deposition, sulfate reducers at the experimental site were limited by sulfate. |
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