Paleolimnological evidence of recent acidification in two sudbury (Canada) lakes

Abstract

As a result of an increase in SO 2 emissions from the metal mining and smelting activities in the vicinity of Sudbury, severe detrimental effects have been reported on aquatic ecosystems. However, documentation of the time and rates of lake acidification are not available. The purpose of the present study is to provide this information by utilizing the stratigraphic analysis of sedimentary diatoms from Hannah and Clearwater lakes. The study indicates that, in Hannah Lake, acidification occurred soon after the roasting of ore started at Copper Cliff in the 1880s. Between about 1880 and 1975, the inferred lake water pH declined from a high of 6.0 to a low of 4.6. After the lake was neutralized in 1975 its measured pH increased from 4.3 to ∼ 7.0. This increase was also indicated by an increase in diatom-inferred pH. In Clearwater Lake, acidification commenced after 1930. Between about 1930 and 1970 the pH declined from ∼ 6.0 to ∼ 4.2. Due to reduction in SO 2 emissions, no further pH decline has occurred since about 1970. The study indicates that, in addition to the existing buffering capacity of the lakes, the lake's distance from the point source and past changes in smelting practices may have greatly influenced the onset of acidification in Sudbury lakes.