Uncertainties in long-term predictions of forest soil acidification due to neglecting seasonal variability

Soil and soil solution response simulated with a site-scale soil acidification model (NUCSAM) was compared with results obtained by a regional soil acidification model (RESAM). RESAM is a multi-layer model with a temporal resolution of one year. In addition to RESAM, NUCSAM takes seasonal variability into account since it simulates solute transport and biogeochemical processes on a daily basis. Consequently, NUCSAM accounts for seasonal variation in deposition, precipitation, transpiration, litterfall, mineralization and root uptake. Uncertainty caused by the neglect of seasonal variability in long-term predictions was investigated by a comparison of long-term simulations with RESAM and NUCSAM. Two deposition scenarios for the period 1990-2090 were evaluated. The models were parameterized and validated by using data from an intensively monitored spruce site at Solling, Germany. Although both the seasonal and the interannual variation in soil solution parameters were large, the trends in soil solution parameters of RESAM and NUCSAM corresponded quite well. The leaching fluxes were almost similar. Generally it appeared that the uncertainty due to time resolution in long-term predictions was relatively small.