Spatial distribution of bacteriobenthos in the priplotinny reach of the Kuibyshev reservoir in the autumn period

Extended studies of the spatial distribution of bacteriobenthos and its saprophytic group in the Priplotinny Reach of the Kuibyshev reservoir in the autumn period of 2020 have been carried out for the first time. The analysis of long-term data of the abundance of bacteria from 1966 till nowadays has been made. During the 54-year period of existence of the Priplotinny Reach, the abundance of bacteriobenthos has increased threefold. In 2020, the abundance of bacteria varied in the range of 2.47-25.59×109 cells mL-1, the biomass - 0.10-2.43 μg mL-1, the abundance of saprophytic bacteria was 1.4-6.8×105 CFU/ mL-1. The spatial distribution of autumn bacteriobenthos and its saprophytic group is significantly influenced by the granulometric composition of bottom sediments, the content of organic matter, and the hydrodynamic regime. The minimum abundance and biomass of bacteria were found in sands and silted sands, the maximum - in gray aleuritic and fine-aleuritic silts. The influence of the Usinsky Bay on the formation of the quantitative structure of bacteriobenthos is shown - the total abundance of bacteria increases and the abundance of saprophytes decreases from the confluence of the river Usa to the dam. Regularities of the spatial distribution of saprophytic bacteria were revealed: 1 - an increase in the abundance in sandy sediments compared to finely dispersed gray silts, 2 - a decrease in the abundance along the trans-verse profile from the coast of the left bank to the central zone and to the deep-water zone of the right bank. In the morphological structure, an increase in the proportion of cocci in the total abundance of bacteriobenthos increases in sandy sediments in coastal shallow waters, and the proportion of sticks, on the contrary, increases in fine-grained silts in deep-water zones.