Diatoms in algocenoses of bental as indicators of water quality in the mouth of the Oka river (Russia)

Based on the characteristics of the composition and structure of the estuaria of the Oka rive, the second tributary of the Volga river located in the Nizhny Novgorod region. It is shown that the high species saturation of bottom algocenoses with diatoms and their abundance allow, in general, to obtain reliable bioindication characteristics. Satisfactory correspondence of the ecological indicators of diatom flora to the chemistry of the Oka waters was demonstrated. We carried out a comparative assessment of the values of the saprobitary indices calculated using the lists of indicator organisms by different authors, as well as the indices of eutrophication pollution (EPI) and pollution by T. Watanabe with the advantage of using the R. Wegl list (1983). The use of different approaches for assesing water quality reliably reflected the spatial and temporal aspects of self-purification processes in the river and demonstrated similar results. During the period of maximum rates of self-purification, the minimum degree of pollution by organic substances of the waters of the Oka river corresponded to the level of mean values of the β-mesosaprobic zone. At the same time, bioindication by communities of Epilithon gave slightly better results in comparison with communities of Epiphyton and Epipelon.