Paleoecological investigation of recent lake acidification in the northern Great Lakes states

Abstract

Paleoecological analyses of sediments from nine northern Great Lakes states (NGLS) lakes reveal small pH changes in seven of these lakes since 1860, four of these being declines. The largest diatom-inferred (DI) pH declines of 0.5 pH units were found in Brown L. and Denton L., Wisconsin. Two other lakes with suspected total alkalinity declines (based on an acidification model and on historical water chemistry, respectively), McNearney L., Michigan, and Camp 12 L., Wisconsin, have not acidified recently according to diatom-inference techniques. Many of the observed trends of increasing pH are coincident with logging; floristic composition of diatom assemblages also changed coincident with fisheries manipulations in some lakes, but these floristic trends did not affect DI pH. Sediment core profiles of Pb, S, and polycyclic aromatic hydrocarbons provide a record of atmospheric deposition of fossil fuel combustion products beginning around the turn of the century; onset is later and accumulation rates are smaller than for other northeastern study regions of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) Project. The response of diatom species to lakewater pH in the NGLS region is very strong and similar to response in other regions. Overall, there is little paleoecological evidence that acidic deposition has caused significant acidification of lakes in the NGLS region.