Chemical Responses of Acidic Lakes in the Sudbury, Ontario, Area to Reduced Smelter Emissions, 1981–89

Monitoring of acidic lakes in the Sudbury, Ontario, area showed that general changes in water quality (increases in pH and acid-neutralizing capacity; decreases in concentrations of SO 4 2− , Ca 2+ , Mg 2+ , Al, and Mn) have continued through the mid-1980's, following substantial reductions in sulphur emissions from area smelters in the late 1970's. By the late 1980's, these trends had levelled off, or even reversed in some lakes. No general, temporal trends were evident during the 1980's for concentrations of Cu, Ni, or Zn, metals directly associated with the smelter emissions. The widespread water quality improvements seen in lakes of the Sudbury area provide very strong support for the use of source controls to combat aquatic acidification. However, the fact that many Sudbury area lakes are still highly acidic and metal contaminated demonstrates that additional emission controls, which are being implemented, are essential in this region.