## 3 Results and Discussion  
### Lead, Cobalt and Nickel Concentrations in the Water Column  
Heavy metals, such as lead, cobalt and nickel, can enter into the aquatic environment of Lake Markakol together with mining wastes and runoff via the lake's coastal areas, as well as atmospheric precipitation, forming compounds with water particles and settling on the bottom of the water body. In addition, cobalt may enter the aquatic environment as a result of leaching from rocks [19; 32; 36; 37]. According to the results of the spectrometric analysis, lead concentrations exceed the maximum permissible concentrations (Pb: 5.0 \(\mathrm{\SIUnitSymbolMicro g}\)/L [33]) in all selected samples from 2.6 to 6.8 \(\mathrm{\SIUnitSymbolMicro g}\)/L (Figure 2), with the exception of the concentrations in the surface water layer of the lake. In the zones influenced by inflowing rivers, the average lead contents are as follows: at the mouth of Matabai River, 4.5 \(\mathrm{\SIUnitSymbolMicro g}\)/L; at Yelovka River, 6.5 \(\mathrm{\SIUnitSymbolMicro g}\)/L; and at Topolevka River, 5.7 \(\mathrm{\SIUnitSymbolMicro g}\)/L (Figure 3). These concentrate towards the central zone of the lake. In the bottom layer, high concentrations of lead were localized in the deep-water part, up to 13.0-16.2 \(\mathrm{\SIUnitSymbolMicro g}\)/L, indicating deposition in bottom sediments (Figure 2). As described below, the bottom sediments were identified as sapropel. Therefore, suspended substances were present in the bottom layer since there are suspensions at the boundary of the bottom sediments and bottom water layer. Water masses with lead concentrations exceeding the norms were registered in the rivers Urunhaika, 10.4 \(\mathrm{\SIUnitSymbolMicro g}\)/L, and Yelovka, 14.1 \(\mathrm{\SIUnitSymbolMicro g}\)/L (Figure 3) [19; 35]. As depicted in Figure 2, the correlation between the lead concentration in surface and bottom layers (r = \(-\)0.7) indicates that there is a statistical relationship between the two water layers, and the coefficient of determination (R\({}^{2}\)) value of 0.4956 provides additional information on the relationship between the water layers, indicating active biogeochemical processes occurring in the water column, particularly desorption processes, which can lead to secondary pollution. For example, such desorption processes can be initiated by changing weather, temperature, pH, redox reactions, and turbation conditions. Cobalt was determined in high concentrations in the aquatic environment of the lake: in the surface layer, it was 36.8-67.5 \(\mathrm{\SIUnitSymbolMicro g}\)/L, and in the bottom layer, it was 25.5-69.2 \(\mathrm{\SIUnitSymbolMicro g}\)/L. High concentrations of these metals were analyzed throughout the lake water area, especially in the shallow zones influenced by the Tikhushka (67.5 \(\mathrm{\SIUnitSymbolMicro g}\)/L), Zhirelka (53.0 \(\mathrm{\SIUnitSymbolMicro g}\)/L) and Yelovka (64.3 \(\mathrm{\SIUnitSymbolMicro g}\)/L) rivers, and in the bottom water layers of the Tikhushka (53.0 \(\mathrm{\SIUnitSymbolMicro g}\)/L), Zhirelka (35.2 \(\mathrm{\SIUnitSymbolMicro g}\)/L) and Yelovka (51.4 \(\mathrm{\SIUnitSymbolMicro g}\)/L) rivers (Figure 2). High concentrations of cobalt are characteristic of all the inflowing rivers: 43.3 \(\mathrm{\SIUnitSymbolMicro g}\)/L at Yelovka River; 61.1 \(\mathrm{\SIUnitSymbolMicro g}\)/L at Topolevka River; 44.9 \(\mathrm{\SIUnitSymbolMicro g}\)/L at Matabai River; and 64.3 \(\mathrm{\SIUnitSymbolMicro g}\)/L at Urunhaika River (Figure 3). High nickel values were detected in both surface and bottom layers, ranging from 13.5 to 49.0 \(\mathrm{\SIUnitSymbolMicro g}\)/L and from 17.2 to 49.0 \(\mathrm{\SIUnitSymbolMicro g}\)/L, respectively (Figure 2).