Ecological assessment of surface water conditions of the Danube river

Purpose. To provide a comprehensive environmental assessment and forecasting of the condition of surface waters of the Danube River within the Ukrainian section (Reni – Izmail – Vylkove), with a focus on the dynamics of key hydrochemical indicators over the period 2010–2024. Special attention is given to the influence of anthropogenic factors, including intensive navigation, industrial pressure, and the environmental consequences of military actions, which have altered the hydrological regime and deteriorated water quality. Methods. System analysis, statistical data processing, distribution analysis, and regression modeling were employed to assess retrospective dynamics and predict future trends in water quality. The information was sourced from long-term monitoring data collected at observation stations in the cities of Kiliya, Vylkove, and the river’s mouth. Results. The analysis focused on six key water quality indicators: phosphates, ammonium, sulfates, chlorides, biochemical oxygen demand over five days (BOD₅), and dissolved oxygen concentration. Phosphate and ammonium compounds exhibited seasonal fluctuations, attributed to discharges of organic and agricultural origin. Sulfate concentrations were found to be highly variable, combining both natural and anthropogenic sources, while chloride levels remained stable with signs of chronic influence. The analysis of BOD₅ and dissolved oxygen indicators suggests a potential for self-purification, although certain periods revealed deterioration in oxygen balance, particularly due to localized organic overload and disrupted hydrodynamics. Developed regression models allowed the identification of relationships between hydrological changes, port activity intensity, and pollution levels. Conclusions. The main environmental issues of the lower Danube were identified as organic and mineral pollution, eutrophication, decreased oxygen levels, hydromorphological changes, and threats posed by armed conflict. Despite these challenges, the river retains a capacity for partial self-recovery, especially under reduced anthropogenic pressure. Restoring ecological balance will require the implementation of systematic monitoring, modernization of wastewater treatment facilities, effective pollution source management, and Ukraine’s active participation in international environmental regulatory mechanisms, such as the Danube Commission. The modeling results can be used to forecast water environment conditions in both peacetime development and post-war recovery scenarios.