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

Sulphur emissions from the Sudbury, Ontario, metal smelting industry have a ffected thousands of lakes in Ontario, Canada. Reductions in these emission s during the 1970's resulted in reduced lakewater SO4 concentrations and ot her water quality changes in the 1970's and 1980's. Further declines in lak ewater SO4 concentrations have accompanied additional recent S emission red uctions achieved by 1994. Recent (1997) SO4 concentrations are still relate d 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 concent rations, was the best correlate with recent SO4 concentrations, indicating that some slowly-flushing, oligotrophic lakes still exhibit a "Sudbury" eff ect. Most lakes beyond 45 km, however, showed SO4 declines and recent SO4 c oncentrations comparable to lakes around Dorset, similar to 200 km from Sud bury, suggesting that these lakes are now most affected by the long-range a tmospheric transport of S.