A preliminary model of long-term changes in stream acidity in southwestern Scotland

Abstract

A modelling study has been undertaken to investigate long-term changes in stream acidity in Dargall Lane, a sub-catchment of Loch Dee, in Galloway, southwestern Scotland. The model, which includes sea salt effects, is based on the assumption that surface water chemistry is determined by reactions taking place in the soils and rocks within a catchment. Stream chemistry data are used to calibrate the model and the model reproduces the declining pH levels of recent years as indicated by paleoecological analysis. Stream acidity trends are investigated assuming two scenarios for future deposition. Assuming deposition rates are maintained in the future at 1984 levels, the model indicates that stream pH is likely to continue to decline below presently measured values. A 50% reduction in deposition rates would likely result in an increase in the pH of the stream, although the pH will not return to estimated preacidification levels.