Long-term impacts of various emission deposition scenarios on Dutch forest soils

Abstract

The long-term impact of three deposition scenarios on Dutch forest soils was evaluated using the model RESAM (Regional Soil Acidification Model), which is part of the overall DAS (Dutch Acidification Simulation) model. RESAM was applied to seven tree species and fourteen non-calcareous sandy soils covering about 65% of the Dutch forest area. Deposition secenarios for SO x , NO x and NH x were generated for twenty deposition areas by the air transport model of DAS for the period 1965 to 2050. Data related to tree species and soil types were derived from literature surveys, field research, laboratory experiments and model calibration. 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 year showed that the agreement was good for the N content, base saturation, pH and SO4 concentration, reasonable for the NO3 concentration, Al/Ca ratio and Al concentration in the topsoil and unfavourable for the NH4/K ratio and Al concentration in the subsoil. Future trends in soil solution parameters in response to the three scenarios, showed that deposition reductions generally lead to a fast increase in pH and a decrease 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 deposition 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 substantial exceedance of critical values for Al and NO3 concentration and Al/Ca ratio.