## 5 Conclusions and Future Perspectives  
Bottom sediment actively accumulates heavy metals. As a result, it can be both a primary and a secondary pollution factor of the entire aquatic ecosystem, which is associated with the process of redistributing pollutants in bottom sediment, as a result of which the conditions for the existence of bentnos in the aquatic ecosystem worsen. In the bottom sediment of the Kapshagay Reservoir, high values were determined for zinc (up to 37.0 mg/kg) and lead (up to 8.80 mg/kg). Copper and cadmium concentrations were found to be at lower values, not even reaching 1.0 mg/kg. The assessment of the degree of contamination of the water area of the reservoir showed a low level of \(Zc=1.26\), which can be characterized as \"within the background limits\", and with respect to the sanitary and toxicological danger, it can be classified as acceptable.  
High concentrations of metals were found in the bottom sediment at the mouths of the Kaskelen and Turgen rivers, indicating the significant impact of anthropogenic load on the ecological conditions of Kapshagay Reservoir. The obtained results also indicate the nature of the water pollution of these watercourses, which allows the reservoir to be contaminated with agricultural and domestic wastewater.  
Anthropogenic load, to which the entire ecosystem of the reservoir is exposed, has a very close relationship in the conditional systems between water-bottom sediment and aquatic organisms. The long-term preservation of toxic substances in both water and, especially, in the bottom sediment can be expected. Metal migration through the trophic chain, and the accumulation of toxicants in fish cannot be excluded in the future, which in turn plays an important role in the provision of the population with environmentally friendly fish products.  
More studies on the migration processes of water-bottom sediment systems in water bodies would make it possible to assess the role of bottom sediment in the self-purification of aquatic ecosystems.  
Climate change, causing both decreased runoff and low water level situations in reservoirs and spring floods in combination with a high level of sediment input, has to be considered in future research. What effects will these factors have regarding both input situations and the sorption and desorption of metals in bottom sediment?  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app122211474/s1](https://www.mdpi.com/article/10.3390/app122211474/s1)]([https://www.mdpi.com/article/10.3390/app122211474/s1](https://www.mdpi.com/article/10.3390/app122211474/s1)).  
Conceptualization, T.C., C.O.; methodology, T.C., C.O., A.M. and L.I.; software, A.M. and L.I.; validation, C.O., A.M. and L.I.; formal analysis, C.O. and L.I.; investigation, A.M.; resources, A.M. and L.I.; data curation, T.C.; writing--original draft preparation, A.M., T.C. and C.O., review and editing, C.O.; visualization, L.I. and A.M.; supervision, T.C., C.O. and A.M.; project administration, A.M. and C.O.; funding acquisition, A.M. All authors have read and agreed to the published version of the manuscript.  
This work was carried out in the framework of grant funding by the Committee of Science of the Ministry of Science and Higher Education of the Republic of Kazakhstan No. AP09260361 \"Geoecological monitoring of the deposit environment of Ile river delta and Ile-Balkash State Natural Reserve\".  
We did not use humans or living animals in the research process. In this regard, our research is not subject to the requirements of the Helsinki Convention.  
Not applicable.  
We acknowledge the Kazakh state support of the scientific and technical program IRN No. AP09260361 \"Geoecological monitoring of the deposit environment of Ile river delta and Ile-Balkash State Natural Reserve\" for project funding and the permanent support by the Institute of Geography and Water Security, Ministry of Science and Higher Education, Almaty, Kazakhstan.  
The authors declare no conflict of interest.