Simulation of the Potential Impacts of Acidic Deposition on Forest Soils in the South

Abstract

Various criteria have been used to evaluate the sensitivity of soils and waters to acidic desposition (Chap. 5), but these criteria remain largely unvalidated. Two approaches to test the relevance of these criteria are computer simulation modeling and long-term field studies. Simulation models have the advantage of rapid evaluation, but the key processes depicted in models need to be tested against field data to develop confidence in model predictions. Long-term field studies can provide definitive evaluations of sensitivity criteria; unfortunately, long-term historical data are currently limited and cannot be used for regional assessments. In the absence of regionally representative data from long-term projects, we used the MAGIC model (Modeling Acidification of Groundwater in Catchments, Cosby et al. 1985a) to evaluate the sensitivity of a representative set of southern forest soils. We chose this model over others currently available because it depicts critical chemical processes that are thought to control soil water acidification and because its limited data requirements allowed us to use information available in the South (unlike more complicated, data-intensive models such as the Integrated Lake-Watershed Acidification Study [ILWAS]) (Goldstein et al. 1985). Sensitivity of soils was gauged by (1) depletion of exchangeable basic cations, (2) increases in soil-solution concentrations of aluminum, and (3) the alkalinity of drainage waters.