Hydrochemistry of sediment pore water in the Bratsk reservoir (Baikal region, Russia)

V I Poletaeva,E N Tirskikh,M V Pastukhov

doi:10.1038/s41598-021-90603-x

Abstract

This study aimed to identify the factors responsible for the major ion composition of pore water from the bottom sediments of the Bratsk water reservoir, which is part of the largest freshwater Baikal-Angara water system. In the Bratsk reservoir, the overlying water was characterized as HCO3–Ca–Mg type with the mineralization ranging between 101.2 and 127.7 mg L−1 and pore water was characterized as HCO3–SO4–Ca, SO4–Cl–Ca–Mg and mixed water types, which had mineralization varying from 165.9 to 4608.1 mg L−1. The ionic composition of pore waters varied both along the sediment depth profile and across the water area. In pore water, the difference between the highest and lowest values was remarkably large: 5.1 times for K+, 13 times for Mg2+, 16 times for HCO3−, 20 times for Ca2+, 23 times for Na+, 80 times for SO42−, 105 times for Cl−. Such variability at different sites of the reservoir was due to the interrelation between major ion concentrations in the pore water and environmental parameters. The major factor responsible for pore water chemistry was the dissolution of sediment-forming material coming from various geochemical provinces. In the south part of the reservoir, Cl−, Na+ and SO42− concentrations may significantly increase in pore water due to the effect of subaqueous flow of highly mineralized groundwater.

Highlights

In contrast to natural water, reservoir basins are specific water bodies formed under the influence of both natural and technogenic factors, which lead to irreversible changes in their hydrological, hydrochemical, and hydrobiological regimes[1]
Concentrations of major ions in the water of the Bratsk reservoir channel part are presented in Figure S1 (Supporting information) and Table 2
The concentrations of the major ions in the overlying water taken from the Bratsk reservoir were found to be similar to those from Lake Baikal (Table 2)

Summary

Introduction

In contrast to natural water, reservoir basins are specific water bodies formed under the influence of both natural and technogenic factors, which lead to irreversible changes in their hydrological, hydrochemical, and hydrobiological regimes[1]. As sedimentation conditions and factors influencing the geochemical environment in artificial reservoirs are different from those of natural basins, the study of sediment pore water in the Bratsk Reservoir is of particular relevance given the possibility of applying the obtained results and conclusions to other large reservoirs. The Bratsk reservoir, a result of damming the Angara River due to the construction of the Bratsk Hydroelectric Plant, is located in the Baikal region of Russia (Fig. 1) It is one of the largest reservoirs in the world: its full storage capacity approximates 170 km[3], the water surface area is equal to 5470 km[2], the length is over 500 km, the maximum depth exceeds 150 m, and the maximum width is 25 km. According to hydrological conditions in the reservoir, variable (from Usolie-Sibirskoe town to Svirsk town) and permanent (downstream Svirsk town) backwater effect zones can be recognized

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Results

Discussion

Conclusion