Methodological approach to ecological condition assessment of river system for hydrochemical and hydrobiological indexes

There is a description of a complex condition assessment of small rivers ecosystems for forest-steppal and steppal zones of Middle Volga on the base of hydrochemical and hydrobiological indexes. The Integral Index of Ecological Condition (IIEC) is offered, which gives an opportunity to assess quality of water stream or a river section in numeric type, that allows to range critical levels of anthropogenic loads on an ecosystem. For calculation of the index we use most informative and wide applied in practice hydrochemical methods of water quality assessment (organic matter, mineral forms of nitrogen, phosphates, flying phenols) and hydrobiological indexes (quantity and biomass of macrozoobenthos, number of species, variety of species by Shennon, Biotic Index and Oligohaetic Index of Parele). For example of zoning Chapaevka river ecosystem application of the developed criterion allowed zones of ecological disaster, ecological crisis and relative ecological well-being.