Effects of sulphur deposition on lake-water chemistry in Ontario, Canada

Abstract

Clear links between regional lake acidification and the deposition of strong acids from the atmosphere have not been reported for North America^1,2. This is unlike the situation in Scandanavia^3–5, where acidification of lakes on a regional basis corresponds closely with the sulphur deposition pattern. Sulphur deposition in Ontario, Canada, decreases from south to north⁶, with localized high deposition rates found in the Sudbury region^7,8. We compared the chemical attributes of 1,168 lakes in different sulphur deposition zones defined by increments of 0.25 g S m⁻² yr⁻¹. As sulphur deposition increased, lake SO²⁻₄ concentration increased, and alkalinity concentration and pH decreased. Increasing importance of organic acids did not result in lower alkalinity or pH. In the zones with sulphur deposition >1.0gm⁻²yr⁻¹, almost one quarter of the lakes had pH values that would be expected to result in adverse biological effects.