Humic acids and their migration forms in the waters of the lakes of Eastern Transbaikalia
Results of the quantitative chemical analysis of waters in the lakes of the Onon-Borzya, Ingoda, Torey and Ivano-Arakhley limnic systems in Eastern Transbaikalia are systematized and analyzed. The content of humic acids in the waters under investigation was determined to vary within a broad range. Statistical interrelations between the determined concentrations of humic acids and the major physicochemical parameters of the medium were established. An increase in the concentrations of humic acids and fulvic acids is observed with an increase in pH, total dissolved solids (TDS), chemical oxygen demand, the content of carbonate, sulphate, nitrate ions, sodium and total phosphorus, while a decrease is observed with an increase in the redox potential (Eh). Taking into account the chemical composition of waters, thermodynamic calculations were carried out using MINTEQ software, and the major migration forms of humic acids were determined. It was revealed that humic and fulvic acids are present in lake water mainly in the anion and molecular forms, and in compounds with calcium and magnesium ions. The application of the Stockholm Humic Model (SHM) in thermodynamic calculations allowed us to establish the formation of the complexes of humic acids of different denticity with other metals, however, their content is insignificant for each element separately in comparison with the other forms of migration of the organic matter. Definite dependencies were demonstrated between migration forms and the characteristics of the environment. Molecular and anion forms of humic acids exhibit multidirectional correlations with TDS and pH. An increase in Eh of the system leads to inverse correlations with the molecular and anion forms in comparison with рН and TDS. It is stressed that all the established dependencies are interrelated with the properties of humic acids and their compounds with metals, mineralization and humification of organic substances, the formation of secondary minerals, and the types of studied waters.