Sensitivity of soil acidification model to deposition and forest growth

We report an investigation concerning the impacts of acid deposition and fo rest growth scenarios on simulated soil effective base saturation for a for ested catchment in eastern Finland. These forests have not been managed dur ing the last 150 yr and the area receives low levels of acidifying depositi on. The fluxes of sulphur, nitrogen and base cations were assessed with mod els simulating historic and future deposition, stand uptake and leaching. W e tested the effects of calibrating the modelled deposition time series to high and low estimates of current levels of deposition. The highest future soil base saturation was predicted when using the year with the lowest obse rved sulphur and nitrogen deposition (1993) as representative of the presen t deposition. The lowest historical and future soil base saturation resulte d for using the year with the highest observed deposition of sulphur and ni trogen (1988). All scenarios concerning nutrient uptake, emission reduction levels and timing of the reductions resulted in simulated future soil base saturation values located between those predicted with the high and low ob served present deposition. The standard deviation in the soil base saturati on introduced by varying the present forest biomass and growth was smaller than that produced by varying the present deposition values. (C) 2000 Elsev ier Science B.V. All rights reserved.