Environmental risks assessment of the Kogylnyk River nutrient pollution based on probit functions

Abstract

The relevance of the study is associated with the need to determine the risks of high and catastrophic levels of water pollution of the Kogylnyk River. The water quality of this river affects the environmental condition of the northern part of Sasyk lake and reservoir. This artificial reservoir that was created as part of the estuary used to be one of components of the Danube-Dniester irrigation system in the past and can be used for irrigation in the post-war period in the future. As the North-Western Black Sea region is an agricultural region of Ukraine, the article focuses on the pollution of the river by specific nutrients (ammonium, nitrite, nitrate, phosphate). The subject of the study covers the environmental risks assessment of the Kogylnyk River present-day pollution. Hydrochemical observations of the State Water Resources Agency of Ukraine were used as input materials of the research. Such observations were carried out across the upper (below the border with the Republic of Moldova) and lower sections of the river. The number of samples taken in the upper section was 80, and 56 – in the lower section. Water quality was assessed using a modified water pollution index (WPI). The risks of nutrient pollution were evaluated based on a statistical approach using a probit function. It was found that the water quality in the upper section is worse than the one in the lower section. The research indicated a close correspondence between water quality indicators and environmental risk values. In the upper section, the risks of catastrophic pollution have a probability of their occurrence that is equal to 46.1%, and the risks of high pollution – 41.1%, with 87.2% constituting a total percentage. In the lower section, the probability of a high level pollution risk is equal to 33.3%, with no critical risk identified during the observation period. The trophic status of the water body along the river length varies from hypertrophic and polytrophic on the upper course to eutrophic and mesotrophic on the lower course. The decrease in pollution levels in the river's lower section is due to the processes of biological, physical and chemical self-purification of the aquatic ecosystem. Since nutrients have a predominantly anthropogenic origin, the water quality improvement of the Kogylnyk River across the territory of Ukraine is associated with the reduced flow of municipal and agricultural wastewater entering the river. Nutrient pollution requires implementation of additional measures such as improving the culture of farming taking place in the catchment area (for example, during conservation of fertilizers and their application).