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

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Abstract

Since 1985, monitoring activities have been conducted in a network of 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.

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