Integrating Multi-Index and Hydrochemical Assessment of the Polissya Lakes (Western Ukraine): The Role of Natural Factors and Local Anthropogenic Impacts

The lakes of Polissya represent the most extensive natural complex of freshwater lakes in Ukraine. They are ecologically sensitive systems where a complex interaction between the natural landscape, geochemical conditions, and localized anthropogenic pressure controls water quality. This study aimed to provide an integrated assessment of surface water quality, trophic status, metal contamination, irrigation suitability, and water aggressiveness for nine lakes using hydrochemical parameters and composite indices. Therefore, water quality was evaluated based on in situ measurements and laboratory analyses of major ions, nutrients, organic matter indicators, and trace metals, followed by the calculation of five widely applied water quality indices, the organic pollution index, the heavy metal pollution index, the trophic state indices, the irrigation indices, and the aggressiveness index. The autumn monitoring period was selected to capture relatively stable hydrochemical conditions in the absence of pronounced thermal stratification, allowing for consistent inter-lake comparison. However, the results should be interpreted as representative of autumn conditions and not as reflecting full annual variability. The results indicate that most lakes exhibit good to excellent water quality, low mineralization, and a stable hydrocarbonate-calcium water type. Elevated organic pollution and reduced integral water quality were identified for Domashnie Lake, linked to higher nutrients, organic matter indicators under urban-agricultural land use. Increased values of the heavy metal pollution index in selected lakes were primarily associated with natural Fe enrichment and localized inputs of Ni, Zn, and Cu. Trophic conditions ranged from oligotrophic to mesotrophic, while irrigation suitability remained generally high. Overall, natural factors dominate water chemistry, whereas anthropogenic impacts are spatially limited and locally significant.