## 4 Discussion  
An important natural factor in the spatial distribution of bottom sediment in water bodies is sedimentation processes, which depend on several factors. These processes are traced in the distribution of metals in the bottom sediment of the reservoir, which can form various complexes or salts of metals, as well as their occurrence in the lithosphere of the object under study. In acidic environment, microelements such as lead, cadmium, copper, zinc, manganese, nickel, cobalt, iron, and chromium are the most mobile; in an alkaline environments, the most mobile microelements include arsenic, selenium, uranium, molybdenum; while those mobile in a wide range include lithium, rubidium, cesium, fluorine, bromine, boron [21; 22; 23; 24; 75]. Besides the pH value, the mobility of metals also depends on the granulometric and mineralogical composition of the mineral substrate and the degree of its humus content. Light and slightly humus soils are usually depleted in heavy metals compared to silt and organic matter, since the minerals found in clay and humus have a greater absorption capacity [76; 77]. In this regard, in the water-bottom sediment system, the copper content in the water from the upper reaches (4.7 ug/L) to the dam zone (1.6 ug/L) decreases, but in the bottom sediment, these values have a different character, because from the upper reaches (0.16 mg/kg) to the dam zone, the concentration of copper (0.36 mg/kg) increases, which is associated with a change in the granulometric composition of the bottom sediment from a sandy to a silty and clayey composition. In the process of migration and sedimentation, the mobility of copper in the aquatic environment is explained by the nature of the precipitation of its compounds and the content of this metal in the lithosphere (47.0 mg/kg) of the reservoir [64]. Lead and cadmium concentrations in the aquatic ecosystem of the Kapshagay Reservoir show the same behavior as pollution with copper, with high concentrations from the upper reaches to the dam zone in the aquatic environment and the bottom sediment. A different trend is observed for pollution of the water ecosystem of the reservoir with zinc, whereby the polluted water mass (9.8 ug/L) increases towards the dam zone (13.7-13.8 ug/L) before being deposited in the estuarine zone, with the pronounced clayey  
Figure 8: Seasonal inflow of heavy metals along the Iii River in the border cross-section Dobyn (2013) [54]. and muddy bottom of the tributary rivers Turgen and Kaskelen reaching concentrations of up to 37.0 and 35.0 mg/kg, while at the dam zone they reach up to 33.0 mg/kg. High values of zinc in the bottom sediment may depend on its content in the lithosphere c.f., [64], which may reach up to 83.0 mg/kg. We studied the mobile forms of metals in the aquatic ecosystem of the Kapshagay Reservoir. However, determining the proportion of metals in the aquatic environment itself and in bottom sediment, along with the proportion of secondary pollution is a difficult task, both in theoretical and practical terms, since all processes are subject to various factors, including weather conditions (wind, waves, rain). Nevertheless, other authors ([PERSON]; [PERSON] and [PERSON]) have also successfully determined Zn, Cu, Pb and Cd in the bottom sediment of Lake Czernyakovskoe, located within the borders of Warsaw (Poland), as reported in [78; 79; 80]. The results of this study showed that in the bottom sediment of Chernyakov Lake, fractions associated with both iron and manganese oxides (for lead and zinc) as well as with organic substances (for copper), carbonate fractions (for cadmium) predominate [81; 82; 83; 84]. This confirms the need to monitor sediments not only in Chernyakov Lake, but also their applicability to other water bodies, both in terms of total concentrations and in terms of the determination of the forms of the metal compounds in the bottom sediment.