SINOPSIS

Regularities in distribution of algocenoses in various zones of the river valley and factors determining them were revealed. In the terraqueous ecotones of the Basu river 148 species of algae, belonging to 5 divisions, were found. By their abundance the algae from the divisions Cyanophyta and Bacillariophyta predominated in all areas of the longitudinal profile of the river valley and by their relative occurrence − Bacillariophyta (44%), Cyanophyta (32%), and Chlorophyta (21%). Ecotonic algocenoses differed not only in species composition, but also in abundance, occurrence, range of life forms and in the environmental factor value. The littoral area of the river and the area of the second high level of the central flood plain were the most abundant in the quantity of species; the diversity of the total systemic structure increased and characterized the soil algocenoses by a full range of life forms.