Estimates of existing and potential impact of acidification on the freshwater fishery resources and their use in eastern Canada

Abstract

There are over 700,000 lakes in Canada, east of the Ontario-Manitoba border and south of latitude 52. This region supports much of Canada's freshwater fishery resources, mostly in acid-sensitive habitat. Of these lakes, half have alkalinities less than 50 μeq.L⁻¹ and 150,000 have a pH less than 6. There are 14,000 acidic lakes i.e., with a pH less than 4.7.

Models of lake-watershed systems have been developed to predict the future response of fishery resources in eastern Canada. Despite considerable uncertainties in key parameters, the predicted range of losses is not great. The models predict that with current acid deposition, up to 9 % of all lakes will ultimately have a pH less than 5. Reduction of deposition rates, either by 40 % everywhere or to a maximum of 12 kg.ha⁻¹SO₄, greatly reduces the predicted losses. The models give conservative predictions of impact as inclusion of loss of watershed acid neutralizing capacity and fish mortality due to episodic pH depression would indicate greater losses. The freshwater fishery resources of eastern Canada are important economically accounting for 42 × 10⁶ angler-days and $1.4 × 10⁹ yr⁻¹ per year. Up to 10 % of this sector of the Canadian economy could be at risk.