Influence of long-term donor irrigation on quality of underground water in the south-steppe zone of Ukraine (case of the Baraboy River, Odessa Region)

Abstract

The article presents the results of in-situ studies of the chemical composition and quality of underground (subsoil and artesian) water within the basin of the Baraboy River where irrigation of agricultural areas using the water resources of the Dniester River has been carried out since 1967. These water resources are fed into the network of reservoirs and channels of the Lower Dniester Irrigation System. Filtration losses of water from irrigation areas and water supply and sewage systems of settlements replenish the reserves of underground (subsoil) waters increasing the ingress therein of dissolved substances from the sedimentary rocks which leads to increase in the concentrations of certain ingredients included in chemical composition of surface and underground waters within the basin of the Baraboy River. It is shown that groundwater is enriched with nitro-gen compounds containing high concentrations of chlorides, sulfates, calcium and magnesium. Mineralization, toxicity and degree of contamination of underground water increase along the length of the Baraboy River. The chemical composition of the groundwater coming to the riverbed of the Baraboy River does not meet the fishing requirements and worsen the water quality of fish farming water bodies. The results of assessment of groundwater quality at the stations under study give reason to consider these sources of groundwater as an important factor affecting the hydrochemical regime and the quality of the water of the Baraboy River and its reservoirs which should be taken into account when developing the recommendations for optimization of the current hydroecological state of the Baraboy River as a whole. If high mineralization and significant content of principle ions in groundwater can be explained by natural factors, the high level of contamination by biogenic substances is resulted from entering of industrial, domestic and return waters from irrigated areas into aquifers. Such contamination is not a temporary but a permanent phenomenon. In terms of magnesium content artesian waters used for utility and drinking water supply are recognized as «mediocre, suitable with limitations and having undesirable quality». In addition, after 50 years of operation compounds of nitrogen and phosphorus were found in artesian water, and this was not a case in 1960s of the last century. A conclusion on the negative effect of long-term donor irrigation on the quality of underground water and on the need for additional treatment of water of artesian aquifers of the Sarmatian Stage used for centralized water supply was made.