Response of the Laflamme Lake watersheds Quebec, to reduced sulphate deposition (1981–1992)

Abstract

To verify the effectiveness of Canadian and U.S. programs to reduce SO2 emissions, Environment Canada operates an aquatic ecosystem monitoring program that includes the Laflamme Lake integrated watershed north of Quebec City. Wet atmospheric sulphate deposition to the Laflamme Lake watershed declined between 1981 and 1991, particularly during the latter half of this period. The nitrate concentration increased in precipitation between 1981 and 1991. For the lake water, this resulted principally in a slow reduction in alkalinity between June 1981 and May 1992. After 1986, reductions in lake sulphate concentration were offset principally by reductions in Ca and Mg concentrations. An increase in lake water nitrate concentration was observed after 1986. The gradual loss of lake alkalinity demonstrates that the acid inputs to the lake are still too high for chemical recovery to occur. The potential improvement in lake alkalinity related to reduced sulphate concentration may be lost because of an increasing nitrogen-based acidification.