## 3 Results and Discussion
### Lead, Cobalt and Nickel Concentrations in Bottom Sediments
Chemical processes between pollutants and sediment components may also start in the sediments, which may lead to the formation of insoluble substances, making them stable in the sediment environment. These processes are not only based on the characteristics of pollutants and bottom sediment components, they are also specific for each water body, depending on bathymetric, hydrological and hydro-chemical parameters [71]. When assessing the ecological state of lakes, it is important to study the spatial distribution and migration of heavy metals in the \"water-bottom sediments\" system, where the water body includes both the surface and bottom layers. In the distribution of lead in the surface layer, there is a high increase in the northern part of the lake of up to 0.0057-0.0068 mg/L under the influence of runoff from the Yelovka and Topolevka rivers. In the bottom water layers and bottom sediments, significant lead concentrations are traced in the central, eastern and southeastern parts of the lake, i.e., it migrates from coastal zones to deep waters. There was also a migration of lead detected within the water column, with increasing concentrations from the surface layer to the bottom layer; if we look at an average of 0.0043 mg/L to 0.014 mg/L across the water column, it settles in the upper layers of the bottom sediments at an amount of 7.35 mg kg\({}^{-1}\) (Figure 5). The eastern shallow part of the lake is also subject to lead contamination of the bottom and sediment layers due to human activities. Apparently, the locations of the tourist zone and Urunhaika settlement in the eastern part affect the general ecological state of the lake. Differences in the spatial distribution of cobalt and its sedimentation in the water column in shallow areas of the lake and in the zones influenced by tributaries in the surface layer are relatively small, up to 0.052 mg/L in the surface layer and up to 0.049 mg/L in the bottom layer (Figure 6). No definite regularity in the vertical migration of cobalt can be traced. The average cobalt content in the bottom sediments was 13.56 mg kg\({}^{-1}\), with maximum values in the central zone of up to 14.2 mg kg\({}^{-1}\), and in the zones influenced by the Yelovka River, up to 12.2 mg kg\({}^{-1}\), the rivers Zhirelka and Topolevka, up to 12.9 mg kg\({}^{-1}\), and the rivers Urunhaika and Tikhushka, up to 16.4 mg kg\({}^{-1}\). Highconcentrations of cobalt were detected both in the water column and in sarpopel sediments throughout the bottom of the lake. The influence of rivers can be traced in shallow areas of the surface and bottom water layers. Figure 5: Lead content in the “water-bottom sediments” system (Water surface layer in \(\upmu\)g/L, water bottom layer in \(\upmu\)g/L, bottom sediments in mg/kg, lake water depth in m) of Lake Markakol. The visualization shown in Figure 5 is a 3D model also presented in the Supplementary Material Figure S1. Figure 6: Cobalt content in the “water-bottom sediments” system (Water surface layer in \(\mu\)g/L, water bottom layer in \(\mu\)g/L, bottom sediments in mg/kg, lake water depth in m) of Lake Markakol. The visualization shown in Figure 6 is a 3D model also presented in the Supplementary Material Figure S2. By nature, nickel is a metal with low abundance, and it is found in a dissolved form in natural waters [72; 73]. Nickel migration activity in the \"water--bottom sediments\" system depends on the content of organic compounds in the water and bottom sediments [67; 69; 71]. As can be seen in Figure 7, the spatial distribution of nickel shows the same character for the surface and bottom water layers. Contaminated water masses of Tikhushka, Zhirelka, and Yelovka rivers from the northern part of the lake and of Urunkhaika River from the southeastern part flow into the central zone, reaching 0.033 mg/L in the surface layer, and 0.034 mg/L in the bottom layer, enriching there up to 14.0 mg kg\({}^{-1}\).