Modelling trends in soil solution concentrations under five forest-soil combinations in the Netherlands

The influence of forest and soil properties on soil solution concentration and the response of soil solution concentrations upon a reduction in deposition was examined with the dynamic simulation model RESAM. Runs were performed for five different forest-soil combinations in the Netherlands, i.e. for Douglas fir, Scots pine and oak on a Cambic podzol and for Douglas fir on a Carbic podzol and a Gleyic Arenosol. ted concentrations generally decreased in the direction Douglas fir > Scots pine > oak. This was mainly caused by differences in filtering of dry deposition (decreasing in the direction Douglas fir > Scots pine > oak) and in precipitation excess (decreasing in the direction oak > Scots pine > Douglas fir). However, concentrations of some elements, especially NH4 and Ca, were strongly influenced by biocycling. fluence of the considered non calcareous sandy soil types on the soil solution concentrations was relatively small. The influence was mainly caused by differences in N transformation rates. In the Gleyic Arenosol the predicted mineralization and nitrification fluxes were relatively low, whereas the denitrification fluxes were relatively high compared to the podzol soils. Concentrations which are not strongly influenced by biocycling (SO4, Cl) were somewhat higher in the Gleyic Arenosol due to a lower precipitation excess. Al concentrations decreased in the direction Carbic podzol > Gleyic Arenosol > Cambic podzol due to a decreasing amount and dissolution rate of Al-(hydr)oxides in that same direction and a lower acidification in the Gleyic Arenosol. considered forest-soil combinations, a reduction in deposition level caused an increase in pH and a decrease in SO4, NO3, NH4 and Al concentrations. Differences between the rate of de-acidification under the considered three species occurred due to differences in biocycle which result in differences in the ratio between internal and external acid input. In the Gleyic Arenosol a faster de-acidification took place compared to the well-drained podzol soils due to a rise in denitrification upon a rise in pH.