Predicting reversibility of acidification: The European sulfur story

Because of the deleterious effects of acid rain and the need to predict rev ersibility of acidification, various scientific tools such as modeling, sta ble isotopes and flux/budget calculations have been used in biogeochemical sulfur (S) research. The aim of this study was to evaluate consistencies an d discrepancies between these different tools. While modeling has been seem ingly successful in predicting S dynamics in soil solution and stream water by considering inorganic sulfate sorption and desorption only, stable S is otopes indicate that biological S turnover plays a crucial role for the sul fate released to soil solution and stream water. A comparison of budget cal culations with soil S pools reveals that inorganic sulfate sorption and des orption are the controlling processes as long as deposition is high (> 15 k g S ha(-1)yr(-1)) and soils have a high sulfate sorption capacity. This exp lains the successful model predictions of the last two decades. However, fo r soils with low sulfate sorption capacity and under low sulfate deposition , organic S seems to be a significant source for stream water sulfate and h as to be considered in future modeling.