A deterministic model was applied to simulate soil water chemistry dat
a, collected during an 18-year period in an acid forest soil in Sellin
g, Germany. In this paper, the hydrochemistry of Cl, NO3 and SO4 is di
scussed. Seasonal and long-term variations of Cl concentrations in soi
l solution were successfully simulated as a result of atmospheric depo
sition and hydrological processes. The marked increase of SO4 concentr
ations at 90 cm depth during the 1970s could be simulated satisfactori
ly using adsorption equilibrium. Here we assumed that high SO4 deposit
ion loads in the 1970s entered a soil which had reached a state of nea
r saturation with respect to adsorbed SO4 in the preceding decades. In
the 1980s, measured and simulated SO4 concentrations at 90 cm depth d
ecreased, due to reduced SO4 deposition. Modelled resupply of SO4 to s
olution by desorption was less than observed, particularly in periods
with high water fluxes. In wet periods, when observed N releases from
the litter layer were high, simulated N concentrations in litter perco
lates were lower than observed values. Elevated N concentrations at 90
cm depth occurred when the N-input into the mineral soil exceeded app
roximately 4 kmol ha(-1) yr(-1).