MODELING SEASONAL AND LONG-TERM DYNAMICS OF ANIONS IN AN ACID FOREST SOIL, SOLLING, GERMANY

A deterministic model was applied to simulate soil water chemistry data, collected during an 18-year period in an acid forest soil in Selling, Germany. In this paper, the hydrochemistry of Cl, NO3 and SO4 is discussed. Seasonal and long-term variations of Cl concentrations in soil solution were successfully simulated as a result of atmospheric deposition and hydrological processes. The marked increase of SO4 concentrations at 90 cm depth during the 1970s could be simulated satisfactorily using adsorption equilibrium. Here we assumed that high SO4 deposition loads in the 1970s entered a soil which had reached a state of near saturation with respect to adsorbed SO4 in the preceding decades. In the 1980s, measured and simulated SO4 concentrations at 90 cm depth decreased, due to reduced SO4 deposition. Modelled resupply of SO4 to solution 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 percolates were lower than observed values. Elevated N concentrations at 90 cm depth occurred when the N-input into the mineral soil exceeded approximately 4 kmol ha(-1) yr(-1).