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In this paper, the self-purification potential of water bodies and watercourses in the Arshalinsky district was studied in an administrative unit of the Akmola region: Bolshaya Saryoba, Malaya Saryoba, Zhaltyrkol (Arhaniya), Koigeldy, Zhangula, and a section of the Yesil River. The self-cleaning ability of water bodies was assessed by such oxygen indicators as the amount of dissolved oxygen and BOD5. In water samples from water bodies, the dominant phytoplankton and zooplankton species were identified as possible agents or indicators of the self-purification capacity of water bodies. The task of the work was to identify the relationship of self-cleaning ability with inorganic pollution, saprobity.

The research object is water, bottom sediments in Akmola region lakes located in the intensive agriculture area. The territory of Akmola region is subjected to intensive human impacts, including the inevitable pollution with agricultural pesticides, which are ecotoxicants. The work has carried out hydrochemical studies in technogenic polluted lakes: general hydrochemical indicators, persistent organic pollutant content. The POPs in the samples were determined on the gas chromatograph Clarus 580 (PerkinElmer) with a mass spectrometer detector Clarus-SQ 8. According to the analysis results, the general hydrochemical pollution is classified as an average. The MPC excess indicators in the Akmola region lakes are observed for salt ammonium (up to 0.002 MPC), magnesium (up to 1.15 MPC), nitrites (up to 1.12 MPC), petroleum products (up to 1.98 MPC), iron (up to 2.0 MPC), SSAS (up to 3.8 MPC). High concentration indicators for the sulphate (3.5 MPC), copper (4.3 MPC), magnesium (1.125 MPC). Mainly the lakes are dominated by sulfates, ion chloride. But in general among 21 investigated POPs 8 substances are accumulated in bottom sediments of the investigated Zhalauly, Tastykol lakes, Unnamed Lake to the south of Akkol village, Itemgen lake, Zhalanash lake near Malinovka village (near Astana city), Kokay, Yesey, Bolshoe Chebachie.

The article describes study of the hydrochemistry of Taldykol lake system, consisting of the Big and Small Taldykol lakes, in the city of Nur-Sultan. The aim of the work is to assess the anthropogenic impact on the ecosystem of steppe wetlands located in the center of the developing capital. Sampling was carried out from 8 sites of the lake system in autumn 2020. The results of hydrochemical analysis of water samples made it possible to assess the level of chemical pollution and anthropogenic impact on the ecosystem, which, due to rapid urbanization, the lakes have been exposed to for decades. Now, due to the artificial fragmentation of lakes, the surface communication between the sites is disrupted, as evidenced by the different composition of pollutants in water bodies. Nevertheless, to draw up a complete picture and assess the anthropogenic impact on the Taldykol lake ecosystem, it is necessary to consider the results of a comprehensive study of lakes, which includes a number of additional works.

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