ABSTRACT
Deposition of atmospheric pollutants is occurring over much of eastern North America. While evidence exists of long-term reductions in pH and alkalinity of sensitive surface waters and adverse impacts on aquatic life, much of it is circumstantial. Cause and effect relationships have not been substantiated and many scientific uncertainties must be resolved before decisions concerning emissions controls can be made. This paper addresses the issues of information gaps, scientific uncertainties, and risks in making policy decisions to protect sensitive lake resources from acid precipitation. Circumstantial evidence may be all that decisionmakers can realistically expect from science in the short term, and information gaps inevitably will remain. On such an issue of public significance as acid precipitation, a cogent understanding of existing scientific facts and the use of prudence and equity are needed on the part of decisionmakers to ensure that necessary steps are taken in the face of uncertainty to protect sensitive lake resources from acidification.