Phytoplankton of an Acidic Lake, and Its Responses to Experimental Alterations of pH

Abstract

Carlyle Lake is typical of north-temperate Canadian Shield lakes both morphometrically and in its thermal and oxygen structure; however, the Lake is chemically unusual. Input of acidic melt-water in the spring of 1974 depressed the pH of the Lake to 4.5. The buffering capacity of the Lake has been reduced to such a degree that summer pH levels are about 5.0. Despite this relatively high acidity, the biomass of the phytoplankton community is not low for an oligotrophic circumneutral lake. Although some evidence exists that phytoplankton community biomass is reduced in lakes of pH about 4.5 or below, no such reduction was observed in Carlyle Lake. However, as the numbers of phytoplankton species are reduced when lake pH levels fall below about 5.6, it would appear that community diversity is a more sensitive indicator of acidification of lakes than is community biomass.