Home – Home – Jornals – Geography and Natural Resources 2020 number 3

Based on our hydrological and hydrochemical studies in winter 2018 and on previous data (2001-2017), we analyze results on changes in the chemical components and water quality of the Selenga river and its tributaries obtained at the final stage of a long-lasting low-water period. It was found that after the historically minimum winter river runoff in 2012 and its slight rise in 2014, the winter river discharges in the subsequent period were again abnormally low and contributed to the deterioration of the Selenga water quality. During winter 2018, the concentrations of dissolved oxygen in the Selenga river and its tributaries changed from 6,0 to 10,5 mg/dm ³ (44-70 % of saturation). In some areas of the streams under study (the Selenga river near Novose lenginsk and downstream of the city of Ulan-Ude; the Uda river in Ulan-Ude), where the values were minimal, the water qual ity decreased to the “heavily polluted” category. At the beginning of the current century, the oxygen content in the river during the wintertime was significantly higher (67-99 % of saturation). This gives evidence to a decrease in self-purification capacity. It is found that sulphate concentrations as the indicators of industrial contamination of the river waters have increased through out the Russian section of the Selenga. In the lower reaches of the river, these values reach 16,5-22,2 mg/dm ³ , whereas in the pre-industrial period they varied within 7,2-10,4 mg/dm ³ . Concentrations of biogenic elements were the highest in the areas of input of wastewaters. On the whole, the hydrochemical studies made in 2018 unequivocally indicate the quality deterioration of the Selenga waters in the wintertime due to an anthropogenic impact and a decrease in the water runoff.