Фитопланктон равнинной р. Уса и её притоков (бассейн Куйбышевского водохранилища)

Abstract

Data on the status of summer phytoplankton of the Usariver and its tributaries are given. 184 taxa of algae with a rank lower than the genus from 7 divisions were recorded in algoflora, 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 mln cells/L, that of biomass was 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 a significant dynamics of 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 specific 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 the Usinsky 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 the Usinsky Bay. The influence of hydrological conditions, the content of biogens, and anthropogenic impact on the formation of algocenoses is considered. Taxonomic composition, distribution, structural characteristics of algocenoses in the absence of biogenic limiting depend on hydrological factors, biotopic heterogeneity of natural and anthropogenic origin, whereas their relation with the content of biogens in eutrophy conditions has not been revealed. TheShannon species diversity index varied from 0.5 to 2.7 bits/specimen in 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 theUsinskyBay and the mouths of the Muranka and Tisherek rivers, as well as for the communities of the sections of rivers with anthropogenic impact.