Water quality assessment of Katlabukh Lake and inflowing rivers

Abstract

The estuary zone of the Danube forms a large bog delta with a total area of about 5640 km2 of Danube lakes (Kahul, Katlabukh, Yalpuh, Kytay, Sasyk), which in recent years are subject to intensive anthropogenic pollution. After their damming and transformation into water reservoirs, water exchange is carried out with the help of a system of locks and channels, without forced water supply, which has significantly affected deterioration, both the regime of lakes and their hydrochemical condition. This is especially true for the Katlabukh and Kytay lakes, which have much worse conditions of water exchange because of their geographical location and the anthropogenic impact on the catchement area of the rivers falling into the lakes, there is a need for thorough analysis of their hydrologic and hydrochemical regimes in order to provide appropriate recommendations. The object of the study is the surface waters of the lake Katlabukh and the rivers that fall into it. The aim of the work is to assess the water quality of the lake Katlabukh and the studied rivers according to modern methods and the possibility of using their water resources. For the characteristics of hydrochemical regime of the rivers Yenika, Tashbunar, Velykyy Katlabukh, Katlabukh lake, the data of the monitoring laboratory of waters of Danube regional office of water resources for the period of 2000-2018 years were used. The water pollution index (WPI) and the water pollution coefficient (WPC) were used to assess the water quality of the investigated objects. For carrying out the relevant calculations the maximum permissible concentrations for the fishing purpose were applied as the strictest. Summing up the results of the water quality assessment of the investigated objects it is possible to note that the worst WPI can be attributed to the river Tashbunar, where 95% of surface waters are estimated as moderately polluted, influencing significant anthropogenic impact, the level of which is close to the limit of ecosystem stability. River Velykyy Katlabukh has 79% of surface waters of this class, river Yenika has 63%, and Lake Katlabukh has 28%. But according to the estimation of the water pollution coefficient (WPC), the surface waters of the rivers Yenika and Velykyy Katlabukh are the most polluted. Such high pollution rates are provided by heavy metals, chlorides, nitreous nitrogen, which are not included in the methodology of WPI. According to the provided calculations, the highest indicators of water pollution coefficient were obtained for the Yenika River in 2002 -2.88, in 2014 - 2.45, in 2015 -2.54. These waters are classified as moderately polluted. Conclusion. The conducted studies show that currently the sources of water supply in Lake Katlabukh are in an unsatisfactory condition, and according to a lot of indicators of microbiological, biogenic, chemical pollution, as well as the level of mineralization, they exceed regulatory requirements, which makes them unsuitable (without deep cleaning) for water supply to almost all groups of water users. The main reason for the unsatisfactory quality of water in the lake can be considered the low water levels during the last two years and the inability to fill the lake before the lower limited level and the anthropogenic impact of the rivers that flow into the lake and, having very high levels of pollution, worsen the situation even more. In order to improve the state of surface waters in Lake Katlabukh, it is necessary to increase water exchange, preferably with the use of additional forced water supply, taking into account its geographical position, to develop a program of specific measures, to ensure compliance with environmental legislation by all water users.