A multivariate statistical approach to comparative water quality indices at different sites of the Styr River

A comprehensive assessment of surface water quality is a key tool for identifying sources of anthropogenic impact and developing environmental management measures. The Styr River is subject to various hydrochemical and toxicological pressures, which requires systematic monitoring. The aim of the study was to determine the spatial differences in the water quality of the Styr River in two sites (S1 – Pidhaitsi–Boratyn; S2 – Varash) by means of an integrated assessment based on block indices and generalized pollution indices using multivariate statistical analysis approaches. Measurements of hydrochemical, trophic-saprobiological and indicators of chemical toxicity were performed in accredited laboratories in accordance with current standards. An integrated assessment was carried out using the methodology of ecological classification of surface waters with the calculation of Complex Сhemical Іndex (IE); Block Indices: salinity composition (IC), tropho-saprobiological parameters (ІТС), and specific toxic and radiological substances (ІТ); Nutrient Pollution Index (NPI); Eutrophication Index (EI); Heavy Metal Evaluation Index (HEI); Organic Pollution Index (OPI) indices. Principal component analysis (PCA) was used to identify the leading factors of variation. The water quality according to IE = 4.1 corresponds to class III, characterized by satisfactory condition and polluted waters. In both areas, NPI indicates moderate pollution, EI indicates the absence of eutrophication, HPI indicates a low level of heavy metal pollution, and OPI indicates good water quality. PCA revealed an increase in organic and chemical toxicological loads on S2. The integrated assessment methodology in combination with PCA can be applied to other water bodies with complex influences from pollution sources.