LONG-TERM IMPACTS OF VARIOUS EMISSION DEPOSITION SCENARIOS ON DUTCH FOREST SOILS

The long-term impact of three deposition scenarios on Dutch forest soi ls was evaluated using the model RESAM (Regional Soil Acidification Mo del), which is pan of the overall DAS (Dutch Acidification Simulation) model. RESAM was applied to seven tree species and fourteen non-calca reous sandy soils covering about 65% of the Dutch forest area. Deposit ion secenarios for SO(x), NO(x) and NH(x) were generated for twenty de position areas by the air transport model of DAS for the period 1965 t o 2050. Data related to tree species and soil types were derived from literature surveys, field research, laboratory experiments and model c alibration. Results discussed here are resticted to important outputs indicating N accumulation or soil acidification. A comparison of model results for 1990 with measurements in 150 forest stands during this y ear showed that the agreement was good for the N content, base saturat ion, pH and SO4 concentration, reasonable for the NO3 concentration, A l/Ca ratio and Al concentration in the topsoil and unfavourable for th e NH4/K ratio and Al concentration in the subsoil. Future trends in so il solution parameters in response to the three scenarios, showed that deposition reductions generally lead to a fast increase in pH and a d ecrease in Al and SO4 concentration and Al/Ca ratio. However, for the NO3 concentration and NH4/K ratio there was a clear time lag between d eposition reduction and concentration reduction which is mainly due to N mobilization from the humus layer. A decrease in average deposition level to 1400 mol(c) ha-1 yr-1 appeared to be sufficient to avoid sub stantial exceedance of critical values for Al and NO3 concentration an d Al/Ca ratio.