Monitoring of Hydrochemical Indices of the Desna, Stryzhen and Bilous Rivers

The dynamics of hydrochemical indices of the Desna River and its tributaries, including the Stryzhen and Bilous rivers, during 2021-2023 are analyzed in the paper. Qualitative and quantitative changes in the following parameters in the water of the rivers are described: dissolved oxygen, biochemical oxygen demand (BOD<sub>5</sub>), chemical oxygen demand (ChOD<sub>Mn</sub>), phosphate ions, ammonium, nitrite and nitrate nitrogen, total iron (Fe<sup>3+</sup> and Fe<sup>2+</sup>), and manganese. An increase in the concentration of pollutants in the water of the Desna River downstream of the city of Chernigiv (after the tributaries Stryzhen and Bilous flow into it) compared to the water upstream of the city of Chernigiv was detected. In 2021-2022, a significant increase in the concentration of the following indices was revealed: ChODMn, nitrite nitrogen, total iron (Fe<sup>3+</sup> and Fe<sup>2+</sup>), and manganese. In 2023, the number of parameters exceeding limiting permissible concentrations reliably increased, in particular: BOD<sub>5</sub>, ChOD<sub>Mn</sub>, ammonium and nitrite nitrogen, total iron (Fe<sup>3+</sup> and Fe<sup>2+</sup>), and manganese. It has been found that the water quality in the Desna River downstream of the city of Chernigiv depends on abiotic factors: soil composition, water and air temperature, atmospheric pressure, precipitation, but to a larger extent on anthropogenic factors, including the inflow of pollutants with surface runoff, discharge of untreated and insufficiently treated municipal wastewater and industrial waters, and technogenic pollution due to military operations. It is emphasized that the water quality of the Desna River is most affected by the waters of the Bilous River.