A palaeolimnological assessment of the impact of acid deposition on surface waters in North-West Scotland, a region of high sea-salt inputs

Abstract

Recent critical loads assessments suggest that sensitive surface waters in the north-west of Scotland have acidified, whereas earlier surveys indicate little chemical or biological evidence of acidification. It has been suggested that regionally high sea-salt inputs are affecting either critical loads calculations or the susceptibility of surface waters to acidification. We use palaeolimnological techniques to test the hypothesis that the critical load exceedances in north-west Scotland are real. Pre-industrial and present day loch-water pH are inferred from diatom assemblages in sediment cores from 21 lochs in order to estimate recent pH change. The results indicate consistent post-1800 declines in loch-water pH, although the magnitude of this decline is small (<0.4 pH unit) and in most cases within the error of the technique. It is concluded that although slight acidification might have taken place, this has not been of sufficient magnitude to significantly effect most biological communities (e.g. higher plants, invertebrates and fish).