MODELING ACIDIFICATION AND RECOVERY IN THE ROOFED CATCHMENT AT LAKE-GARDSJON

The dynamic, biogeochemical model SAFE was applied to a roofed subcatc hment G1 at Gardsjon, Sweden. The roof was installed in 1991, and depo sition of anthropogenic S and N reduced by ca. 90%. Initiated from pre -industrial steady-state conditions. SAFE predicts present levels of b iologically relevant chemical properties (pH, inorganic Al and base ca tions). SAFE overestimates the short-term effects of the manipulation on runoff pH: while the modeled decline in inorganic Al and and base c ations are comparable to observations. Temporal variability and too fe w years of measured data make model to data comparison difficult. Sulf ate desorption, which is not included in SAFE, may introduce a time la g between modeled and measured data. Reductions of S and N inputs by 9 0% will lead to a recovery in pH, low Al but extremely low base cation s concentrations due to replenishment of exchange sites.