Response of acid lakes in the UK to reductions in atmospheric deposition of sulfur

Abstract

United Kingdom emissions of sulfur dioxide declined by 82% between 1970 and 2000. This decline has been accompanied by reductions in the atmospheric deposition of anthropogenic sulfur. A further expected response, possibly delayed, is a reduction in sulfur concentrations, as sulphate, in upland surface waters. Associated water quality changes, including an increase in alkalinity and reduction in acidity are also anticipated. We examine annual data from 1988 to the present from 10 lakes in the UK acid waters monitoring network for evidence of changes in water chemistry as a response to reductions in the atmospheric deposition of sulfur. We show that there is a close association between reduction in sulfur deposition and reduction in lake water concentrations of sulphate and this provides some supporting evidence for the efficacy of the international agreements to reduce S emissions. However, only 3 of the 10 lakes show an upward trend in alkalinity, and this is not related in a simple fashion to reductions in sulphate concentrations. This suggests that recovery from acidification, measured as an increase in pH and alkalinity, while requiring a reduction in sulphate concentration, may not occur over the same time scale.