Morphological Characteristics and Influencing Factors of Mercury Occurrence and in Typical Lakes in Cold and Arid Areas

Lakes are an important part of the earth's ecosystem, and heavy metal pollution has always been a key problem in environmental research. Among heavy metals, mercury has unique physical and chemical properties, and its organic derivative, methylmercury, is a highly toxic and bio-rich pollutant. Therefore, it is particularly important to study the transformation mechanism of lakes in cold and arid regions between different seasons and different forms of Hg due to the existence of ice sheets. The content of Hg in the water of typical lakes in Inner Mongolia ranged from 0.02 to 1.82 μg/L, and belonged to water quality Class IV. The MeHg content in the water ranged from 0.1 to 10 ng/L, and some sites exceeded the baseline value of methylmercury concentration in the water. There were significant differences in the contents of Hg, MeHg, and MeHg% in the water during the glacial and non-glacial periods, and the contents of Hg and MeHg in the non-glacial period were significantly higher than those in the glacial period. The Hg content in the sediments of typical lakes in Inner Mongolia was 0.02-1.74 mg/kg. There was a significant enrichment of Hg in the surface sediments of typical lakes in Inner Mongolia that was higher than the average levels of lakes in some areas in China. The Hg concentration of lake surface sediments showed large spatial variability under different land use types in different basins, which included manifested inagricultural irrigation areas> agro-pastoral ecotones> grassland sandy areas. The contents of mercury and methylmercury were affected by the temperature, pH, and salinity. The mercury methylation rate of water is controlled by the salinity and pH. The content of mercury and methylmercury in sediments is mainly affected by the content of organic matter, redox potential, and acidity and alkalinity of sediments.