Assessment of the water pollution level and the environmental status of rivers in the Siverskyi Donets basin by BOD5
Authors: Loboda N. S. , Katynska І. V. , Smalii О. V. 
Published: December 2020

The paper topicality consists in the necessity for determination of the environmental status of the rivers in the Siverskyi Donets Basin and assessment of the possibilities for them to achieve ‘good environmental status’ under the modern climatic conditions and the anthropogenic load. Siverskyi Donets is the main river in the Eastern Ukraine. There are large industrial zones at the water catchment area. Among them, there are the Donetsk Coal Basin and the industrial complexes within the City of Kharkiv, which have exerted influence on surface water quality for decades. A method for assessment of the pollution level and the environmental status of waters by the hydrochemical index of BOD5 (biochemical oxygen demand for 5 days) is used in the paper.
The paper is aimed at identification of the main trends in water quality changes by hydrochemical index of BOD5. The object of research is a pollution of the rivers at the Siverskyi Donets Basin by industrial, municipal and mine wastewaters. The subject of research is an assessment of water qualitative status by BOD5.
The hydrochemical observation data for 7 gauges at the main river and 7 tributaries for the period of 1990-2015 were used in the paper. The major attention is focused on the most polluted rivers in the Eastern Ukraine: the Udy and the Kryvyi Torets. The quality of the Udy River water is largely determined by the municipal wastewater from Kharkiv. The Kryvyi Torets River belongs to the Donbas rivers, where pollution by mine water and wastewater from industrial enterprises is significant.
Pollution levels, environmental status and saprobity were determined by the average annual indices of BOD5. Empirical probabilities for occurrence of a certain pollution parameter at various gauges were calculated for comparative analysis.
It is found that a BOD5 downward trend has been prevalent on the rivers at the Siverskyi Donets catchment area in the early 21st century. The highest BOD5 values were observed on the Donbas tributaries and the Udy River (downstream from the City of Kharkiv), as well as upstream and downstream from Lysychansk, and the lowest ones were observed on the Oskil River.
It is also revealed that in the early 21st century, the main river water has a ‘threshold’ environmental status (β-mesosaprobic zone), except for the Lysychansk gauge, where the status is ‘irreversibly altered’ owing to the inflow of polluted water from Donbas rivers into the Siverskyi Donets.
Research into the Udy River water quality upstream and downstream from the industrial city of Kharkiv has shown that the water in the upper reaches of this river is classified as ‘clean’ and ‘moderately polluted’, and the environmental status may become ‘good’ in the future. Downstream from the city, the water is mostly ‘dirty’, and the environmental status is ‘irreversibly altered’, which corresponds to the α-mesosaprobic zone. For the Kryvyi Torets River (the Donbas Region), owing to the impact of organic pollution, the environmental status is defined as ‘threshold’, ‘irreversibly altered’ and it has begun to deteriorate in recent years.
To improve the environmental status of the Donbas rivers, the reduction in discharges of untreated municipal and industrial wastewater into surface watercourses, as well as the construction of state-of-the-art sewage treatment plants are necessary.