Abstract
The Balkhash Lake is a unique natural water body with a gradient of the total content of dissolved salts along its longitudinal axis and the increased level of toxic pollutions.To assess the spatial distribution of environmental factors along the Balkhash Lake surface, methods of bioindication and statistical mapping were used.An assessment of the overall level of toxic pollution was carried out using the Water Ecosystem State Index (WESI).Phytoplankton has been used to assess the ecological state of the Balkhash Lake in the summer of 2004.A total of 92 species were found in the algal communities, with prevalence of Chlorophyta in the western, fresher water part, and Bacillariophyta in the eastern, brackish part.Mapping showed a positive relationship between the species richness in algal Divisions and macrophytes.Changes in the proportion of indicator species within the composition of phytoplankton reflected the spatial gradient of depth, TDS, pH-values, organic pollution.According to bioindication data, the waters of the Balkhash Lake are moderately polluted, water quality class III.The WESI index calculation revealed the effect of the total toxic pollution on the phytoplankton of the Western Balkhash.The spatial distribution of the WESI index showed that in the zone the influence of river flow has stimulating effect of biogenic elements on phytoplankton but was partially leveled by the increased level of toxic pollution.