Environmental characteristics of the lothic system on the example of small rivers of the Volga river basin: methodological approaches

In this work, the authors review the results of long-time studies of the watercourses of the Volga River Basin with an emphasis on analysis of approaches to ecological classification of rivers. We discuss methods for assessing the ecological state of lotic systems as an information basis for justifying regional criteria for assessing the quality of surface waters by the hydrological, hydrochemical and biological characteristics of plankton and benthic communities.