Modelling the response of soil and soil solution chemistry upon roofing a forest in an area with high nitrogen deposition

In the Speuld forest, the Netherlands, the dynamic soil acidification model NuCSAM has been applied to a manipulation experiment in which part of the forest was roofed to control nitrogen (N) and sulphur (S) deposition. The r oofed area was divided into two subplots watered artificially; one received ambient N and S deposition and one with pristine N and S deposition. Conce ntration measurements on each plots showed a high (time-dependent) spatial variability. Statistical analyses of the concentrations on both subplots sh owed small but significant effects of the reduction in deposition on nitrat e (NO3), sulphate (SO4) and aluminium (Al) concentrations. The statistical significance of the effects was minimised by the large spatial variability within the plots. Despite these shortcomings, simulated concentrations were generally within the 95% confidence interval of the measurements although the effect of a reduction in N deposition on soil solution chemistry was un derestimated due to a marked decline in N-uptake by the vegetation.