Abstract
The quantitative development of planktonic crustaceans in Lake Balkhash has been studied in relation to water transparency, pH, mineralization, ion concentrations, ion ratios, content of easily oxidizable organic matter, nutrients, and heavy metals. It is shown that the decrease in the abundance of animals in a brackish part of the lake area is caused by a high concentration of K + at a relatively low amount of Ca 2+ and Na + ions. The dependence of quantitative development of planktonic crustaceans on the content of nutrients, mineralization, concentrations of the main ions (except for alkali metals) and their ratio is not manifested for all species. Pollution of the lake by heavy metals has caused either a sharp decrease or an increase in the range of variations of the abundance of crustaceans.