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.