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For the first time, an assessment of the taxonomic and quantitative structure of the phytobenthos of seven saline rivers in the basin of the hypersaline Lake Elton (Volgograd region) is presented. The main types of algal communities developing on substrates were revealed: diatom phytobenthos, communities of diatoms with cyanoprokaryotes, cyanobacterial films and mats, and epiphyton. The phytobenthos consists of local, mosaic-distributed communities with a small similarity in their species composition. The structure of algal communities is determined by Bacillariophyta (with the predominance of species of g. Navicula) and Cyanoprokaryota (of the gg. Phormidium, Leptolyngbya, and Geitlerinema). The abundance and biomass values vary widely, reaching their highest values (109 834–417 472 million cells/m2 and 523.6–567.6 g/m2) in cyanobacterial communities of mesohaline rivers at a water salinity reaching 16–19 g/L. Mineralization as a factor influencing the structure of communities most rigidly acts in the mouth sections of rivers, by controlling the composition of the dominant species. For critical salinity values (>70 g/L), characteristic structural transformations of communities by the type of replacement of planktonic and benthic Bacillariophyta and Cyanoprokaryota by planktonic Chlorophyta (of the g. Dunaliella) and picoplankton were revealed. [ABSTRACT FROM AUTHOR]

For the first time, an assessment of the taxonomic and quantitative structure of the phytobenthos of seven saline rivers in the basin of the hypersaline Lake Elton (Volgograd region) is presented. The main types of algal communities developing on substrates were revealed: diatom phytobenthos, communities of diatoms with cyanoprokaryotes, cyanobacterial films and mats, and epiphyton. The phytobenthos consists of local, mosaic-distributed communities with a small similarity in their species composition. The structure of algal communities is determined by Bacillariophyta (with the predominance of species of g. Navicula) and Cyanoprokaryota (of the gg. Phormidium, Leptolyngbya, and Geitlerinema). The abundance and biomass values vary widely, reaching their highest values (109 834–417 472 million cells/m2 and 523.6–567.6 g/m2) in cyanobacterial communities of mesohaline rivers at a water salinity reaching 16–19 g/L. Mineralization as a factor influencing the structure of communities most rigidly acts in the mouth sections of rivers, by controlling the composition of the dominant species. For critical salinity values (>70 g/L), characteristic structural transformations of communities by the type of replacement of planktonic and benthic Bacillariophyta and Cyanoprokaryota by planktonic Chlorophyta (of the g. Dunaliella) and picoplankton were revealed. [ABSTRACT FROM AUTHOR]

Abstract—Data on the status of summer phytoplankton of the Usa River and its tributaries are given. In total 184 taxa of algae with a rank lower than the genus from eight divisions were recorded in algal flora, with Bacillariophyta (43–57% of the composition) and Chlorophyta (23–47%) predominating in the rivers. The abundance range in algocenoses was 0.02–5.2 million cells/L; of biomass, 0.01–1.8 mg/L; the content of chlorophyll-a, was 0.01–3.1 μg/L. The ecological heterogeneity along the watercourse causes significant dynamics in the taxonomic composition, which is characterized by mosaic distribution in different areas, and changes in the quantitative structure of plankton communities. An increase in the species diversity, abundance, biomass, and chlorophyll-a concentration from the source to the mouth of rivers is noted. The ecotone effect in the zone of mixing and transformation of the waters of the lower reaches of the watercourses and Usinskii Bay of the Kuibyshev Reservoir is expressed in an increase in the diversity and amount of algae, an increase in the coenotic role of Cyanoprokaryota and planktonic green algae of the Chlorococcales order, which are dominant in Usinskii Bay. The influence of hydrological conditions, the content of nutrients, and the anthropogenic impact on the formation of algocenoses is discussed. The taxonomic composition, distribution, structural characteristics of algocenoses in the absence of nutrient limiting depend on hydrological factors, and biotopic heterogeneity of natural and anthropogenic origin have been studied, whereas their relation to the content of nutrients in eutrophic conditions has not been revealed. The Shannon species diversity index varied from 0.5 to 2.7 bits/specimen in the river algocenoses. The minimum values were noted on the upstream sections of the rivers; the complexity of the structure is typical for the algocenoses of the mixing zones of the waters of the upper part of Usinskii Bay and the mouths of the Muranka and Tisherek rivers, as well as for the communities of the sections of rivers with anthropogenic impact. [ABSTRACT FROM AUTHOR]