Assessment of changes in the water quality along the length of the Siverskyi Donets river at the beginning of the 21st century

Abstract

The relevance of the problem consists in the need to achieve a "good status" of water in the rivers of Ukraine according to the objectives of the Water Framework Directive. The aim of the work is to identify the main trends of water quality changes over time and along the length of Siverskyi Donets River based on data of the hydrochemical observations for the period from 1985 to 2015 inclusive. To establish the water quality we used integral assessments based on hydrochemical indicators such as pollution coefficient, water pollution index, generalized index of water state in accordance with the water quality standards for fishery. The article shows that use of mandatory (priority) chemical indicators in the calculations of the pollution coefficient and the water pollution index does not reflect a real degree of water pollution, since it does not take into account a significant amount of pollutants. It was discovered that major pollutants in the main river include suspended substances, chromium, nitrite nitrogen, phenols, sulfates. For the right-bank tributaries of Siversky Donets (illustrated by the example of the Kryvyi Torets River) originating from Donetsk Upland heavy metals (chromium, copper, zinc) pollution is typical. The degree of pollution based on the coefficient of pollution for average multi-year period is deemed as catastrophic, and based on the index of water pollution it is labelled with IV (contaminated) and V (very contaminated) quality classes indicating a violation of the ecosystem stability. Based on the generalized index, the water is also classified as "contaminated". The calculations based on various integral indicators of water quality revealed that pollution of the Siversky Donets River increases downstream. This is due to growing anthropogenic impact (municipal and industrial waters of large cities, discharge of mine and open pit waters into surface waterways, withdrawal of the runoff for its redirection to canals and water conduits, presence of diffuse sources of pollution by biogenic and organic substances). The beginning of the 21st century saw a trend towards improvement established in the chronological course of integral indicators of water quality which was associated with decrease production volumes. According to the generalized index of water state the water quality of the main river gradually changes from “contaminated” and “very contaminated” to “moderately contaminated”, but contamination by heavy metals, biogenic and organic substances remains high.