The enrichment of the protected Borovoe Lake with nutrients has taken place within the last 100 years, from the moment the first resort was formed on its shores. The purpose of this study was to assess the current ecological state of Borovoe based on the structure of zooplankton. According to the chemical data, in the summer of 2019, the content of nutrients in the water was, relatively, not high; the content of heavy metals was very low. Twenty-seven species were found in zooplankton. The average abundance of zooplankton was 988.8 thousand ind./m³ with a biomass of 1.52 g/m³. Rotifera dominated. Cladocera sub-dominated. The Shannon index values were 2.31 bit/ind. and 2.57 bit/mg; the values of Clarke’s W-statistics and Δ-Shannon were negative. The abundance of zooplankton increased more than nine times, but the average individual mass of an organism decreased from 0.0112 to 0.0016 mg over the past decade. Despite the relatively low content of nutrients, the structure of zooplankton demonstrated that the nutritional load on Lake Borovoe is currently close to critical. Statistical mapping of the data and redundancy analysis (RDA) showed that the primary source of lake pollution is the village of Borovoe and sanatoriums located on the southeast and northwest coasts.

The diverse anthropogenic load on the transboundary Irtysh River necessitates an assessment of its ecological state, which was the goal of this work. We conducted this research in July 2023 in the upper and lower reaches of the Kazakh part of the Irtysh basin. We determined transparency; temperature; pH; salinity (TDS); oxygen, N-NO₃, N-NO₂, N-NH₄, PO₄, Mn, Fe, Si, Cd, Cu, Zn, Pb, Cr, Co, and Hg contents; permanganate index; and zooplankton variables at 27 stations. We assessed the ecological state of the river by comparing the contents of pollutants with their maximum permissible concentrations (MPC_fw), Classification Scales, and bioindications. An excess of MPC_fw was detected for N-NO₂, Cu, and Fe and locally for Cr and Zn. According to the Classification Scales, most analysed variables corresponded to slightly polluted waters; N-NO₂, Cr, and Zn corresponded to moderately and heavily polluted waters. Zooplankton was represented by 82 species, with an average abundance of 6728 individuals/m³, biomass of 2.81 mg/m³, Shannon index of 1.99–2.08 bit, ∆-Shannon of 0.09, and average individual mass of 0.0019 mg. The spatial distribution of abiotic and biotic variables indicated increased organic and toxic pollution downstream in the Irtysh. Potential sources of pollution of the Irtysh basin are discussed.

The multicomponent composition of wastewater makes it challenging to assess its quality objectively, but the last one is a prerequisite for the safe re-use of wastewater. The solution to this problem should be aimed at finding criteria that make it possible to increase the objectivity of assessing the water quality of reservoirs with multicomponent pollution. This work analyzes the water quality of the Sorbulak wastewater disposal system in the summer of 2017, based on chemical variables and zooplankton structure and assess the long-term changes in the water quality of Sorbulak. According to the Kruskal–Wallis test, in 2017, the differences between the studied water bodies in the content of nutrients and heavy metals were mostly insignificant. From 2000–2002 to 2017, nitrate, nitrite nitrogen, and heavy metals in Sorbulak significantly decreased. Zooplankton communities consisted of a relatively small number of eurybiontic species resistant to environmental factors. The variability of the quantitative variables of zooplankton was associated with the nutrients. Males dominated the population of the cyclopoid copepods Acanthocyclops trajani. In 2000–2002 individuals with morphological anomalies were found in cyclopoid copepods populations, but were absent in 2017. The appearance of individuals with morphological anomalies was associated with copper or lead. The chemical data and structure of zooplankton communities indicated that the toxic pollution of Sorbulak decreased by 2017 compared to 2000–2002. Our results demonstrate that the structural variables of zooplankton communities could be successfully used to assess the water quality of water bodies with mixed pollution. We recommend using not only the traditional set of biological variables (abundance, biomass, diversity indices, and the average mass of an individual), but also data on the structure of species dominance, the sex structure of copepod populations, and the presence of individuals with morphological anomalies for monitoring of water bodies with mixed pollution.

Assessment of the water quality of the Arys River basin based on the spatial distribution of richness of phytoperiphyton communities and abiotic variables was given for the first time. Altogether, 82 species were revealed in phytoperiphyton, including Bacillariophyta of 51, Cyanobacteria of 20, Chlorophyta of 7, and Charophyta of 4. Cluster analysis revealed the uniqueness of the composition of periphyton communities related to the abiotic conditions. The environmental preferences of the algae indicated fresh organic pollution in the lower reaches of the Arys River and weak or moderate levels of organic pollution in the rest of the basin. The ecological mapping of chemical data generally confirmed this conclusion. According to the maps, the highest water quality was revealed in the upper stream of the basin. The middle part of the river basin had the lowest water quality in terms of transparency, nitrite-nitrogen, and nitrate-nitrogen. The downstream of the Arys was characterized by a secondary deterioration in water quality according to the Aquatic Ecosystem State Index (WESI) index. We revealed the complicated interaction between natural and anthropogenic factors that caused changes in water quality in the Arys River basin.

The largest wastewater treatment systems include Sorbulak and Kurty reservoirs, and the small storage ponds were studied in the summer of 2017 and characterized mainly by organic pollution. Phytoplankton communities were represented by species tolerant of organic and toxic pollution. Cyanobacteria dominated in the reservoirs, and dinophyte algae were only in the Kurty Reservoir. According to the results of CCA analysis, only Cr and certain nutrients had a significant effect on the abundance of algae. A statistically positive significant association between the Shannon index and the average algal cell mass was established. The results obtained are a particular example reflecting the non-linearity of changes in plankton communities in the gradient of nutrient loading and eutrophication of aquatic ecosystems.