Pollutant discharge and water quality within the Don River basin
A.P. DEMIN, A.V. ZAITSEVA
Water Problems Institute, Russian Academy of Sciences, Moscow, Russia
Keywords: wastewater structure, specific combinatorial index of water pollution, tributaries of the Don River, pollution sources, monitoring of water bodies, treatment facilities
Abstract
The aim of this article is to study changes in the volume and composition of discharged wastewater, the pollutants they contain, as well as water quality in the Don River basin over a long period. It is found that discharges of sewage, mine 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 km3 over 25 years. The proportion of polluted wastewater decreased from 30.4 to 21.8 %. It is established that in 2020 only every sixth cubic meter of water requiring treatment was treated up to the standards. It is shown that the amount of major pollutants discharged with wastewater during 1995-2020 decreased dramatically. Within the Don River basin as a whole, the discharge of petroleum products decreased by a factor of 6.6; copper, iron, and sulfates decreased by a factor of 4-4.5; biochemical oxygen demand decreased by a factor of 2.8, and the mass of dry residue by a factor of 3.1. At the same time there was a significant increase in the discharge of two substances: nitrates (by a factor of 2.8), and ammonium nitrogen (by a factor of 1.5). The water quality along the stem stream of the Don River both improved and deteriorated. During 2010-2020 the water quality in almost the entire upper and middle Don improved: the quality classes and ranks did not always change, but the value of the specific combinatorial index of water pollution decreased. In the lower reaches of the Don River, the water quality deteriorated. In the Voronezh River basin, the discharge of iron and copper with wastewater decreased by a factor of 8.8 and 4.7; the discharge of organic substances, oil products, sulfates and chlorides decreased by a factor of 3-3.2, and the discharge of dry residue and ammonia nitrogen by a factor of 2-2.3. However, the water quality in the outlet section of the Voronezh reservoir was deteriorating for most of the ingredients. A similar situation was observed in the Severskii Donets River basin. Despite the reduction of the controlled mass of discharged pollutants, there were no improvement of surface water quality in both the stem stream of the Don River and the basins of its large tributaries. This indicates an increase of pollution coming from diffuse sources and bottom sediments.
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