Micro-scale spatial distribution of bacterioplankton in the Priplotinny (Near-dam) Reach of the Kuibyshev Reservoir in the early autumn period 2020

A detailed study of the distribution of bacterioplankton and photosynthetic pigments of the Priplotinny Reach of the Kuibyshev Reservoir was carried out in early autumn 2020. The bacterioplankton cell numbers were 0.8-2.1 10⁶ cells ml⁻¹, and the biomass varied from 7 to 56 μg C L⁻¹. The average chlorophyll a concentration of in the integral samples was 2.91 μg L⁻¹, varying in the range of 1.1-9.6 μg L⁻¹ (CV 30.7%). The pheophytin content was relatively low, 19.2 ± 10.4% of chlorophyll concentration, indicating the continued active phytoplankton development in the seston in the fall of 2020. From September 17 to October 3, a weak trend for an increase in bacterioplankton abundance as well as for a decrease in the chlorophyll a concentration and in the average cell volume was revealed. A significant (p < 0.05) correlation between the Chl a concentration in the total biomass of heterotrophic bacteria (r = 0.48) was observed. Under conditions of intense wind mixing, anthropogenic sources of pollution and the inflow of the inflow did not have a significant effect on the size structure of bacterioplankton. No pronounced local spatial complexes of stations were revealed in terms of quantitative and structural parameters of bacterioplankton and chlorophyll concentrations in the investigated part of the reservoir. In general, the concentration of pigments and the abundance and biomass of bacterioplankton correspond to the mesotrophic status of the Reach. Both the total number of bacterioplankton and the chlorophyll content in Pryplotinny Reach at the beginning of autumn 2020 are within the range of long-term monitoring values. While in the summer there is a clear long-term increasing trend of the bacterioplankton abundance, in the autumn the bacterioplankton numbers remain stable throughout the entire reservoir existence period.

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