Phytoplankton of Flowing and Flow-Regulated Stretches of the Ural River in Different Seasons

Abstract—Features of the seasonal changes in the number of species, biomass, and the ratio of taxonomic groups of phytoplankton in flowing and regulated sections of the Ural River are described. In the unregulated section of the river, the maximum number of species was recorded in July and in the upper and lower reaches, in October. The maximum biomass of phytoplankton in the unregulated section of the river and in the lower part of the reservoir was recorded in summer, and in the upper part, in spring. The effect of a combination of a number of parameters of water bodies and environmental factors such as the typology, morphometry, flow velocity, input of substances from the catchment area and from the upper areas, and the temperature on the quantitative characteristics of communities is discussed. The leading role of the water temperature for phytoplankton development is shown in the unregulated sections of the river and in the lower part of the reservoir, which are characterized by environmental conditions that impede the abundant development of phytoplankton: high flow rates, the late onset of biological spring, and low nutrient availability. The biomass values correspond to β-mesotrophic–β-eutrophic waters in the unregulated sections of the river, to β-mesotrophic in the upper part of the reservoir, and to α-β-mesotrophic in the near-dam part. According to the saprobity index, the entire area surveyed is characterized by β-mesosaprobic conditions.