Pollutant Discharge and Water Quality in the Don River Basin

The purpose of this article is to study changes in the volume and composition of discharged wastewaters and the pollutants they contain, as well as changes in water quality, in the Don River basin over a long-term period. It has been revealed that discharges of waste, mining, and collector and drainage waters into the surface water bodies of the Don River basin have decreased almost twice, i.e., from 4.4 to 2.4 km 3 , over 25 years. The proportion of polluted wastewaters has decreased from 30.4 to 21.8%. It has been established that only every sixth cubic meter of water requiring treatment was treated to the standard level in 2020. It is shown that the quantity of major pollutants discharged with wastewater dramatically decreased in 1995–2020. In total, the discharge of oil products in the Don River basin has decreased 6.6 times; the discharge of copper, iron, and sulfates 4–4.5 times; the biochemical oxygen demand 2.8 times; and dry residue weight 3.1 times. At the same time, a significant increase was observed for the discharge of two substances: nitrates (2.8 times) and ammonium nitrogen (1.5 times). The water quality along the stem stream of the Don River both improved and deteriorated. In 2010–2020, the water quality improved almost throughout the upper and middle Don reaches: the quality classes and ranks did not always change; at the same time, the value of the specific combinatorial index of water pollution decreased. The lower reaches of the Don River were characterized by the deterioration of the water quality. In the Voronezh River basin, the discharge of iron and copper with wastewater decreased 8.8 and 4.7 times; the discharge of organic substances, oil products, sulfates, and chlorides 3–3.2 times, and the discharge of dry residue and ammonia nitrogen 2–2.3 times. However, the water quality at the outlet of the Voronezh Reservoir deteriorated with respect to most of the ingredients. A similar situation was observed in the Seversky Donets River basin. Despite the reduction in the controlled mass of discharged pollutants, there was no improvement of surface water quality in either the stem stream of the Don River or the basins of its large tributaries. This indicates an increase of pollution from diffuse sources and bottom sediments.