A Critical Assessment of Effects of Acidification on Fisheries in North America

Recently the U.S. Environmental Protection Agency sponsored through North Carolina State University, a critical assessment of acid rain effects in the United States. Our charge was to evaluate critically the peer-reviewed, published literature on effects of aquatic biota. Three types of evidence are available: field comparative studies across pH gradients (space or time); laboratory experiments where pH is manipulated; and field experiments in which the pH of lakes or streams is manipulated. Most inferences have been made from comparative studies, the least in field manipulations. Our judgements were that the strength of a statement on effects was increased when two or more types of information supported the conclusion. A weakness in the North American experience is the absence of field manipulative experiments. Also the observed correspondence among results inferred by all three types of evidence, strengthened results available only from comparative studies or only from laboratory studies. After such an analysis, it is clear that when acidification occurs fisheries have been and will be damaged by loss of fish, reductions in benthic and planktonic invertebrates and possibly by the accumulation of periphyton and detritus. Functional responses of aquatic ecosystems are more poorly known. Expected pH values of sensitive waters in the U.S.A. after long-term acidification are expected to be between pH 4.3 and 4.9.