Multidimensional exploratory techniques, such as the Principal Component Analysis (PCA), have been used to analyze long-term changes in the ﬂow regime and quality of water of the lowland dam reservoir Turawa (south-west Poland) in the catchment of the Mała Panew river (a tributary of the Odra). The paper proves that during the period of 1998–2016 the Turawa reservoir was equalizing the river’s water ﬂow. Moreover, various physicochemical water quality indicators were analyzed at three measurement points (at the tributary’s mouth into the reservoir, in the reservoir itself and at the outﬂow from the reservoir). The water quality assessment was performed by analyzing physicochemical indicators such as water temperature, TSS, pH, dissolved oxygen, BOD5, NH4+, NO3-, NO2-, N, PO43-, P, electrolytic conductivity, DS, SO42- and Cl- . Furthermore, the correlations between all these water quality indicators were analyzed statistically at each measurement point, at the statistical signiﬁ cance level of p ≤ 0.05. PCA was used to determine the structures between these water quality variables at each measurement point. As a result, a theoretical model was obtained that describes the regularities in the relationships between the indicators. PCA has shown that biogenic indicators have the strongest inﬂuence on the water quality in the Mała Panew. Lastly, the differences between the averages of the water quality indicators of the inﬂowing and of the outﬂowing water were considered and their signiﬁcance was analyzed. PCA unveiled structure and complexity of interconnections between river ﬂow and water quality. The paper shows that such statistical methods can be valuable tools for developing suitable water management strategies for the catchment and the reservoir itself.
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