Abstract
The regional features of transformation in the chemical composition of water in the Lower Volga tributaries and its main trends under anthropogenic impact and climatic variations are presented. Most trends for the principle ions (sulfates, carbonates, calcium and magnesium ions) are increasing, which may be a consequence of ongoing climate change. Moderate decreasing trends prevail in the concentrations of nutrients and organic substances in water. It was found that the trends in metal concentrations are multidirectional. All revealed statistically significant trends for iron and copper compounds are decreasing, and those for manganese are increasing. Based on the analysis of the identified trends in the chemical composition, the river ecosystems of the Lower Volga tributaries are classified into two categories: stable (“healthy”) and transformed (“transitioning”).
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