Composition and abundance of phytoplankton in Ob River (Western Siberia, Russia)

Abstract

The paper presents the results of phytoplankton study in the Ob (a large Siberian Lowland River) from its source to mouth. The sampling was carried in the period of open water during the last decades on the key sites of the river - near the mouths of large tributaries, big cities and settlements. Based on the complex classification of surface waters, Lake Teletskoye (like the upper reaches of river basins) is distinguished by the lowest trophic status (oligo- and even ultraoligotrophic). The Upper Ob trophicity is estimated as mezotrophic (0.6-2.0 g/m3), the Middle Ob - oligo- (>0.1-0.5), meso- and eutrophic (2.1-10.0 g/m3), the Lower Ob - both oligo- and mezotrophic, and the Gulf of the Ob - from oligo- to meso- and eutrophic one. The results of the saprobiologic analysis suggest that the greatest number of bioindicators belong to β-mesosaprobionts that is indicative of the β-mesosaprobic environment. The ecological state of the sampling area is assessed as "quite pure" by the phytoplankton biomass and "slightly contaminated" - by the Saprobic Index, thus corresponding to I (very pure), II (pure) and III (slightly contaminated) classes of water quality. According to the description of the crisis zones, the environmental status of the river is still good and corresponds to the stages of "reversible changes" and "threshold state". The water quality and ecosystem state in different years are similar that could be evidence of the river ecosystem stability through time and space. Though the Ob ecosystem is capable of self-purification, it calls for further conservation to avoid the water quality deterioration.