Assessment of critical levels of pollution of water bodies based on the statistical distribution of the occurrence of macrozoobenthos species

A methodology for substantiating the environmental risk of technogenic pollution of water bodies is described based on the results of bioindication using macrozoobenthos communities. At the first stage, on the basis of statistical methods, the estimation of extreme values of hydrochemical factors, at which the occurrence of each species is unlikely, was carried out. Based on these data, the statistical distribution of the species sensitivity (SSD) was simulated. To illustrate the methodology, the results of a long-term hydrobiological survey of macrozoobenthos on 102 small and medium-sized rivers in the Middle and Lower Volga basin were used. The threshold values of eight indicators of river water pollution providing a preset permissible probability of environmental risk are given.