Sulphate in Sudbury, Ontario, Canada, lakes: Recent trends and status

Sulphur emissions from the Sudbury, Ontario, metal smelting industry have affected thousands of lakes in Ontario, Canada. Reductions in these emissions during the 1970's resulted in reduced lakewater SO4 concentrations and other water quality changes in the 1970's and 1980's. Further declines in lakewater SO4 concentrations have accompanied additional recent S emission reductions achieved by 1994. Recent (1997) SO4 concentrations are still related to distance from the Sudbury smelters. A strong inverse relationship with distance is evident to about 45 km, and is most pronounced in lakes within about 20 km. In lakes beyond 45 km, dissolved organic carbon (DOC), which was correlated with hydrological response time and total phosphorus concentrations, was the best correlate with recent SO4 concentrations, indicating that some slowly-flushing, oligotrophic lakes still exhibit a "Sudbury" effect. Most lakes beyond 45 km, however, showed SO4 declines and recent SO4 concentrations comparable to lakes around Dorset, similar to 200 km from Sudbury, suggesting that these lakes are now most affected by the long-range atmospheric transport of S.