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lakes with a high mineral content. Lakes with a mineral content that exceeds that of the oceans of the world (35 g/kg) are sometimes included in this category, as are lakes with a solute content greater than 25 g/kg. Lakes with a salt content between1 ‰ and 35‰ (or 25‰) are referred to as slightly saline, or brackish. Lakes with high salt concentrations consist of nearly or fully saturated solutions, which provide the necessary conditions for the crystallization of salts and their subsequent settling to the bottom as deposits. The water in such natural salt lakes is called brine.
Salt lakes are most prevalent in arid regions. They occupy undrained basins or form along seashores in isolated bays and lagoons. The accumulation of salts in such lakes is due to the inflow of dissolved mineral salts into undrained basins from rivers, underground waters, and atmospheric precipitation; this inflow is followed by intensive evaporation. Salt lakes, which represent a final stage in the movement of mineral substances into undrained regions, are a characteristic feature of arid terrains. There also are azonal salt lakes in areas where dissolved salt deposits or highly mineralized underground waters come up through the ground.
The high salt concentration in salt lakes determines their distinctive thermal and dynamic regime. The diffusion of heat from the lake’s surface to its bottom is impeded by the increased viscosity of the highly mineralized water; thus, the thin surface layer of brine may reach a temperature of 40°-50°C in the summer. During the winter, the brine in certain lakes does not freeze above a temperature of — 20°C; as a result, the benthic waters in deep salt lakes maintain temperatures below 0°C throughout the summer. In shallow salt lakes with clear water, the effect of solar radiation on the lake bottom may raise the water temperature to 65°C.
According to the chemical composition of their waters, salt lakes are classified into three basic groups: carbonate (soda), sulfate (bitter), and chloride (salt). The chemical composition of salt lakes is primarily determined by the composition of the waters feeding them. Changes in the ratio between the volume of water flowing into a salt lake and the surface evaporation observed during different seasons and during years marked by variable water content, as well as the temperature regime of the brine, bring about periodic changes in mineralization and chemical composition.
Salt lakes are invaluable to the national economy. They provide vital raw material for the chemical, food, and other industries. Salt, soda, Glauber’s salt, magnesium chloride and bromine, iodine, and boron compounds are among the products extracted from salt lakes. Hydrogen sulfide mud, formed in sulfate salt lakes, is widely used therapeutically.
REFERENCESDzens-Litovskii, A. I. Solenye ozera SSSR i ikh mineral’nye bogatstva. Leningrad, 1968.
Dzens-Litovskii, A. I. “Istoriia issledovaniia solenykh ozer.” In the collection Ozera semiaridnoi zony SSSR. Leningrad, 1970.
Alekin, O. A. Osnovy gidrokhimii. Leningrad, 1970.
K. K. EDELSTEIN