Transformation of zooplankton communities during pollution and restoration of lakes

Abstract

Studies were carried out on three lakes in Kazan (Russia). The lakes were severely polluted due to sewage discharge of industrial enterprises. In the period of 1984-1995 measures were taken for two lakes to restore their water quality. According to the project, the majority of industrial waste water was assigned to the treatment plant; at the bottom, contaminated sediment was cleaned, sewers were built, temporary flowage was organized, and beach was equipped. Water quality in lakes has improved considerably. We investigated changes in zooplankton communities during the recovery measures immediately after their completion and 20 years later. We have found that the response of zooplankton to pollution reduction is represented by the increase in the number of zooplankton species, a number of dominant species, abundance and biomass. A share of Cladocera increased in the Nizhniy Kaban Lake, while Copepoda and Cladocera shares increased in lake Sredniy Kaban. Enhanced development of these groups of zooplankton caused corresponding changes in taxonomic indicators based on the ratio of the values of abundance and biomass of zooplankton major groups, saprobic index. Follow-up study of the lakes showed that with existing high anthropogenic load, repeated remediation is required in 15-20 years.