Effects of acidity on the phytoplankton and primary productivity of selected northern Ontario lakes

Abstract

The effects of acidity on primary production, species composition, and abundance of phytoplankton were investigated in six lakes in the Sudbury area of Ontario, where pH values lay between 4.05 and 7.15. Significant relationships showing an increase in water transparency and decrease in chlorophyll a concentration with declining pH were found. Percentage similarity of community (PSc) and community coefficient (CC) values were highest between lakes closest in pH, reflecting progressive changes in species composition. As the pH declined, Chlorophyta diminished in importance and the Cyanophyta became dominant. The phytoplankton diversity index (DI) remained relatively unchanged between pH values of 7.0 to 5.0 but decreased at lower values. Primary production in milligrams C metre⁻³ hour⁻¹ was reduced in lakes below pH 5.5; however, as a result of the increase in depth of euphotic zone accompanying more acidic conditions, primary production in milligrams C metre⁻² hour⁻¹ remained high down to pH 4.4, below which it was drastically reduced.