Analysis of the dynamics of the ecological state of watercourses in the sub-basin of the Syan River

Based on the generalization of the results of regime observations by environmental monitoring services, an analysis of the dynamics of the ecological state of watercourses in the sub-basin of the Syan River (at six observation points) has been carried out. The dynamics of water use in the Syan River sub-basin for 2021–2022 were analyzed, according to which the total discharge in the Syan sub-basin in 2022 decreased by a quarter. The discharge of polluted wastewater in 2022 was a third higher, accordingly, the discharged volume of treated sewage was also lower than in 2021. An analysis of potentially possible sources of pollution of water bodies in the Syan River sub-basin has been carried out. The most significant impact on the water quality change here is caused by the wastewater discharges of municipal enterprises: the municipal enterprises “Novoyavorivskvodokanal” and “Yavorivvodokanal”. A significant cause of surface water pollution is the discharge of wastewater by the private sector. The Yavoriv quarry “Sіrka” causes the ingress of sulfates into the Shklo River, a significant trend towards their reduction has been observed from 2020 to 2022 by 71.9 %. In Lviv region, agriculture accounts for about 11%, which also negatively affects the state of water bodies. According to the results of monitoring of surface waters within the Ukrainian part of the Vistula River basin, presented by the Basin Water Resources Management of the Western Bug and Syan Rivers for 2021–2022, a high total content of pesticides was observed in 2022, in particular, at the observation point of the Vishnya River in Mostyska – about 5.5 µg/dm3. Also, a high content of manganese, zinc and iron was recorded here. The analysis of monitoring observations of the state of water bodies in the Syan River sub-basin and the calculated water pollution coefficients based on them show that the cleanest water in this area is the water of the Vyar River (the highest Pollution Index in 2021 – 1.463) and the water of the Zavadivka River (the highest Pollution Index in 2021 – 1.218). The most polluted water was the water of the Vishnya River at the observation point in Mostyska, especially due to the high content of iron (7.6 MPC) and manganese (30 MPC), where the pollution coefficient in 2020 was 4.761, and in 2022, it decreased by half. Also, the water of the Shklo River in urban-type settlement Krakivets was quite polluted, where the pollution coefficient in 2022 was 2.057. The BOD5 value was high