SULFUR ISOTOPE SIGNALS IN FOREST SOILS OF CENTRAL-EUROPE ALONG AN AIR-POLLUTION GRADIENT

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. delta(34)S ratios were determined in vertical soil profi les 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 delta(34)S ratios from topsoil to mineral soil, regardles s of the distance from major point sources of atmospheric pollution. O f these 18 sites, 15 sites were characterized by a smooth positive iso tope signal with the highest delta(34)S in the deepest level sampled. The remaining three sites had a delta(34)S maximum in the second deepe st horizon. With increasing soil depth, the positive delta(34)S signal s accompanied a negative S concentration gradient. Our findings constr ain the relative roles of various mechanisms of sulfur isotope redistr ibution in the soil depth profile. Even at extremely high atmospheric deposition (>70 kg of S ha(-1) yr(-1)) sulfur appears to be cycled thr ough an organic S pool in the forest soil.