## 3 Results and Discussion
### Lead, Cobalt and Nickel Concentrations in Bottom Sediments
Thus, the assessment of bottom sediment pollution of Lake Markakol had its own peculiarity. That is why it was important to take into account the peculiarities of sapropelic sediments and their influence on the chemical processes associated with heavy metals. The evaluation of the bottom sediments has to consider that the upper layer of sapropel is subject to rapid agitation and mixing in the lake due to hydrodynamic processes, as sarppel is a product of destructive processes, which may well be a source of secondary pollution in the lake. According to the results of the bottom sediment analyses of heavy metals, it is also possible to study historical pollution since bottom sediments are also archives of former pollution present in the water body [51; 52; 53; 54]. Increased concentrations of organic and biogenic compounds in the lake water can contribute to the accumulation of heavy metals in the bottom sediments [55; 56; 57; 58]. The mobility of high gross concentrations of cobalt (30 ug g\({}^{-1}\) and more), copper (10 ug g\({}^{-1}\) and more) and nickel (200 ug g\({}^{-1}\) and more) or a part of them in the bottom sediments of Lake Yantamoye could be one reason for the increased percentage of sick fish or fish with pathologies [59; 60]. Thus, the maximum ability to concentrate heavy metals is possessed by suspended solids and bottom sediments, then plankton, bentnos and fish. Exposure to heavy metals can lead to pathological changes in the liver, kidneys, gonads and gills, as well as impaired fish growth and maturation [61]. According to the results of scientific research, \"Pasvik Water Quality until 2013\", nickel accumulates in the kidneys and gills' mercury, accumulates in the liver and kidneys, and its content is highest in predatory species (in the muscle tissues of perch and pike) [62; 63]. Consequently,  
Figure 4: Lead, cobalt and nickel concentrations in Lake Markakol bottom sediments at 20 measuring points. studying the food chain, including the migration of heavy metals from sources of pollution to humans, permissible limits of metal concentrations in biological environments and characterization of the level of anthropogenic load and risk to public health, is of both theoretical and practical importance [64; 65]. Spatial Distribution and Migration Activity of Lead, Cobalt and Nickel in the \"Water-Bottom Sediments\" System  
Of particular interest to us was the fact that Lake Markakol, which is an endemic natural region of both East Kazakhtan and Kazakhtan as a whole, could be subject to pollution of anthropogenic origin [5; 7; 8; 9]. When studying the lake's heavy metal pollution, it was necessary to present a general picture of the anthropogenic load on the whole aquatic ecosystem. This study and the pollution assessment of the lake could be insufficient without examining more spatial dimensions. Therefore, water samples from the bottom layer and bottom sediments were also taken to visualize the spatial distribution of lead, cobalt and nickel in the system \"water-bottom sediments\". According to some authors [66; 67; 68; 69; 70], the mechanisms of pollutant transfer from water mass to bottom sediments, including minerals and organic mud, and back, involve two-way processes of sorption and desorption, affecting the preservation and accumulation of pollutants within aquatic ecosystems. Sorption can occur through electrostatic forces, ion exchange and other chemical interactions. Clays and other minerals are able to retain contaminated substances, making them less mobile in aquatic environments. Sedimentation and accumulation is where particles to which pollutants were sorbed undergo sorption and can settle to the bottom of a water body through the process of sedimentation. This is where the formation of a layer of bottom sediments takes place. The accumulation of contaminants in bottom sediments may occur as a consequence of their gradual sedimentation from the aqueous phase.