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 highest in 2021 in the Shklo River – 3.5 MPC and in the Vishnya River in Chernove village – 2.9 MPC, however, in 2022, it decreased to 1.8 MPC across the study area. The COD value in 2021 in all investigated observation points was above the norm, the highest in the Vishnya River, in Chernove village – 2.3 MPC, in 2022, it significantly decreased across the study area, the highest was in the Shklo River in urban-type settlement Krakivets – 1.6 MPC. A high content of ammonium salts and nitrites was recorded in 2022, respectively: in the Shklo River – 3.8 MPC and 2.7 MPC; in the Vishnya River in Chernove village – 2.5 MPC and 3.2 MPC. The phosphate content was highest in 2022 in the Vishnya River in Chernove village (2.6 MPC), however, in 2021 and 2022, it was below the permissible level across the study water area. In all observation points of the Syan River sub-basin, a significant zinc content was observed in the water, the highest was in 2020 in the Vyаr River in Pidmostychi village (5.2 MPC) and in 2022 in the Shklo River in urban-type settlement Krakivets – 4.7 MPC. A high content of sulfates was observed in the Shklo river, especially in 2020 (4.4 MPC), which may be the cause of the influence of the Yavorivsky “Sirka” quarry. Regarding the assessment of water quality in the Syan River sub-basin by pollution levels, in all observation points during the analyzed period, the water is mainly characterized as “slightly polluted”, only at the observation point of the Vishnya River in Mostyska in 2020 and 2021 – “moderately polluted”, in the Zavadivka River, Grushiv village in 2020 the water was “slightly polluted; bordering on clean”.