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The paper presents some methodological approaches to the development of the aquatic ecosystems state classifier according to integral hydrochemical indicators. The classifier has been developed based on the analysis of the Roshydromet long-term routine hydrochemical information for a large number of rivers and their reaches located in various natural and climatic zones of Russia. Criteria for assessing the state of aquatic ecosystems have been established taking into account water salinity: from natural, equilibrium, and stressful to critical or catastrophic. Testing of the methodological approaches and verification of the state assessment results was carried out by the example of individual river ecosystems in the European part of Russia. The majority of ecologically safe river ecosystems functioning in their natural state have been shown to belong to waters with low salinity and to be located in northern regions. In the center and the south of the European part of Russia, river ecosystems in equilibrium, stressful, or critical state dominate.
Reshetnyak et al. (Mon,) studied this question.