Lake Acidification Recovery can be Monitored using Chrysophycean Microfossils

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Abstract
Chrysophyte scales in a sediment core from Swan Lake, Sudbury, Ontario were studied to examine their sensitivity for inference of recent lakewater pH change. The study indicates that, corresponding to an increase in metal mining and smelting activity in the Sudbury basin, lake acidification commenced in 1940. However, as a result of reductions in SO2 emissions in the early 1970's, the lake's pH has recovered from its chronic low pH of 4.0 in 1977 to its high of 5.6 in 1987. The chrysophyte-inferred pH recovery mirrors the increase in measured lakewater pH. The study identifies the potential of chrysophytes to document recent pH recovery in soft-water lakes containing undisturbed sediments. The approach offers promise for understanding the response in lakes of poorly buffered regions to decreased atmospheric loadings of SO2 and in establishing and implementing SO2 mitigation standards.