REGIONAL PRECIPITATION AND SURFACE-WATER CHEMISTRY TRENDS IN SOUTHEASTERN CANADA (1983-1991)

We analyzed for trends of acidification related variables from 1983 to 1992 in precipitation concentrations and deposition at six sites and surface water concentrations at 111 sites located from central Ontario to eastern Newfoundland. Precipitation showed significantly decreasing H+ and SO42- concentrations and deposition in central and eastern Ontario and at one of two sites in Quebec (deposition only). For Ontario surface water sites, only increasing or stable SO42- trends were observed, and these had both concomitant increasing and decreasing trends for pH and (or) acid-neutralizing capacity (ANC). Despite a considerable number of lakes showing decreasing SO42- trends in Quebec, pH and ANC also decreased. Quebec was also the only region showing extensive evidence of increasing NO3-. The opposite situation was observed in Atlantic Canada lakes where despite increasing SO42-, the dominant trend observed for pH and ANC was increasing. Trends observed for pH and ANC were used to classify the acidification status of our surface water sites: 60 of the 111 sites were found to be stable (i.e., showing no trends), 17 were continuing to acidify, and 34 were improving.