RECOVERY OF CRUSTACEAN ZOOPLANKTON SPECIES RICHNESS IN SUDBURY AREA LAKES FOLLOWING WATER-QUALITY IMPROVEMENTS

Temporal patterns in the species richness of crustacean zooplankton communities were assessed in eight Sudbury area lakes based on data collected between 1973 and 1986. Excluding a consistently nonacidic reference lake, the study lakes showed general reductions in acidity and trace metal concentrations during this period, related to reduced contaminant emissions from the Sudbury smelters. Despite water quality improvements, several of the study lakes continue to have low pH and elevated trace metal concentrations which have inhibited recovery of zooplankton species richness. However, in lakes with more favourable current pH and lower trace metal concentrations, substantial increases in the average species richness of crustacean plankton communities have occurred, apparently due to both invasion of new species and more frequent occurrence of existing species. These results clearly demonstrate that reductions in acid-forming emissions lead to both chemical and biological improvements in some aquatic systems.