Suzanne Couture

RECENT RECOVERY OF LAKE WATER QUALITY IN SOUTHERN QUEBEC FOLLOWING REDUCTIONS IN SULFUR EMISSIONS

Since 1985, monitoring activities have been conducted in a networkof 43 lakes comprising the Québec portion of the Long-Range Transport of Airborne Pollutants (LRTAP) program. The results to date indicate that Québec lakes generally are responding positively to the generalized decline in precipitation sulfate (SO42-), with 40 of the 43 lakes now showing steep declines in SO42- concentrations. The drop in SO42- was associated with a significant decrease in Ca2+ concentrations in 77% of the lakes (67% for Mg2+ concentrations). Overall, the acid-neutralizing capacity was increasing in 19 lakes and decreasing only in three, while 21 lakes showed no temporal trends. Compared with previous trend studies of the LRTAP-Québec network for the period of 1985–1993, the longer period (1985–1999) shows a clear improvement, with the proportion of lakes that were acidifying changing from 24 to 7% and with the proportion of lakes that were recovering changing from 16 to 35%. These observations suggest that the recent drop in SO42- deposition in the northeastern U.S. and eastern Canada was significant enough to allow chemical recovery for a significant proportion of Québec lakes.

Recent recovery and acid-neutralizing capacity of lake waters in southern Quebec following reductions in sulfur emissions

Since the American and Canadian clean air legislations were imp1emented, su1phur deposition declined from 30% to 45% between 1990 and 2000. These major reductions have resulted in general decrease in su1phate (SOi-) concentrations in surface waters in eastern North America (SKJELKVALE et al. 2005). We assessed recent changes in surface water chemistry in the province of Quebec in response to changes in atmospheric deposition.