LONG-TERM SIMULATION OF DECREASED ACID LOADING ON FORESTED WATERSHED

The response of a northeastern U.S. hardwood forest to wet and dry dep osition of hydrogen ion and sulfate deposition was performed using the hydro-biogeochemical, lumped-parameter Terrestrial Aquatic Model for Ecosystems (TAME). Results of model calibration and output stream chem istry show that ion-exchange and mineral dissolution processes in the B and C horizons buffer the acidic, ambient atmospheric deposition [86 4 eq-SO4-2/(ha/yr) and 718 eq-H+/(ha/yr)] in this hydrologically tight and flashy watershed. Watershed response to a 50% decrease in total d eposition of acidity over twenty years indicates that the watershed is linear with respect to sulfate (50% decrease in mass outflow) but les s responsive with respect to acid neutralizing capacity, ANC (11% incr ease in stream volume-weighted average ANC concentrations). Only moder ate improvements in ANC can be expected from emission controls and dec reased sulfate deposition.