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 acidi fication model (NUCSAM) was compared with results obtained by a region al 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 a ccounts for seasonal variation in deposition, precipitation, transpira tion, litterfall, mineralization and root uptake. Uncertainty caused b y the neglect of seasonal variability in long-term predictions was inv estigated by a comparison of long-term simulations with RESAM and NUCS AM. Two deposition scenarios for the period 1990-2090 were evaluated. The models were parameterized and validated by using data from an inte nsively monitored spruce site at Selling, Germany. Although both the s easonal and the interannual variation in soil solution parameters were large, the trends in soil solution parameters of RESAM and NUCSAM cor responded quite well. The leaching fluxes were almost similar. General ly it appeared that the uncertainty due to time resolution in long-ter m predictions was relatively small.