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Stable isotopes were used to study sulfur dynamics in forest soils of the Czech Republic (Central Europe), one of the most polluted regions in the world. δ34S ratios were determined in vertical soil profiles in 18 small forested catchments covering a wide range of pollution levels from 8.8 to 78.8 kg of S ha-1 yr-1. All sites exhibited an increase in δ34S ratios from topsoil to mineral soil, regardless of the distance from major point sources of atmospheric pollution. Of these 18 sites, 15 sites were characterized by a smooth positive isotope signal with the highest δ34S in the deepest level sampled. The remaining three sites had a δ34S maximum in the second deepest horizon. With increasing soil depth, the positive δ34S signals accompanied a negative S concentration gradient. Our findings constrain the relative roles of various mechanisms of sulfur isotope redistribution in the soil depth profile. Even at extremely high atmospheric deposition (>70 kg of S ha-1 yr-1) sulfur appears to be cycled through an organic S pool in the forest soil.

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Oxygen (O) and sulfur (S) isotope systematics in bog water sulfates were determined for six Sphagnum dominated wetlands located in the British Isles and the Czech Republic, Central Europe. Comparison of a polluted and unpolluted site showed that 4 times higher atmospheric S inputs led to 3 times higher bog water sulfate concentrations and substrate S concentrations, 3 times increased ranges of substrate S concentrations, and 3 times increased ranges of d 34 S values. Sites with elevated atmospheric S inputs exhibited greater geochemical variability in wetland S species. Sulfate O-S isotope composition of bog pore water at a depth of 40 cm below surface differed from that of surface bog water, indicating that dissimilatory bacterial sulfate reduction, a process known to discriminate against the heavier isotopes 18 O and 34 S, occurred in surface peat layers. While bacterial sulfate reduction remained to be one of the main isotope-selective processes for sulfate in peat, it could not fully explain the O-S isotope systematics of peat waters. The 'residual' sulfate was not simultaneously enriched in the heavier isotopes 18 O and 34 S. Mixing of residual sulfate following bacterial sulfate reduction with the product of S 2À reoxidation, cleavage of esters, and isotope exchange reactions may have contributed to the decoupling of the d 34 S SO4 and d 18 O SO4 values. Large within-site differences in d 18 O SO4 and d 34 S SO4 (up to 13 and 15&, respectively) indicated little communication between the 0 and 40 cm peat depth at some sites. Extremely high d 18 O SO4 and d 34 S SO4 values found in several peat bog water samples from Connemara (Ireland), Thorne Moors (England) and Ocean (Czech Republic) were not seen in streams draining the wetlands. Direct runoff of atmogenic sulfate constituted a significant portion of the bog outflow. At the wetland scale, zones of dissimilatory bacterial sulfate reduction form pockets whose lateral hydrological fluxes are small.