Zoobenthos in the tributaries of the Northern Dvina river upper part

The investigation results of zoobenthos in nine tributaries of the Northern Dvina River upper part are discussed. Benthic fauna includes 20 invertebrate taxons. The number of taxons for the studied water streams ranges from 4 to 19. The number of invertebrates in the rivers ranges from 125 to 14 375 inds./m2 being 4934±1651 inds./m2 on the average. The biomass of invertebrates in the rivers varies from 0.09 g/m2 in the Kodima River to 28.77 g/m2 in the Avnyuga River averaging 5.9±3.1 g/m2. By the index of E.V. Balushkina, six of the studied rivers have been determined as moderately polluted streams (the index value 2.9-6.5) and three of them (Yumizh, Kodima and Evda) - as polluted streams.