Long-term dynamics of mercury pollution of the Bratsk reservoir bottom sediments, Baikal region, Russia

Abstract

This paper discusses the results of the monitoring of anthropogenic mercury contamination of the upper part of Bratsk reservoir. The paper shows that in the long-term, (1998-2018) there is an ongoing decrease of Hg concentration in the surface layer of bottom sediments. At the same time the study demonstrates that 20 years after the cessation of mercury electrolysis at the Usoliehimprom chemical plant, Hg concentration in the bottom sediments exceeds background levels by 5 to 54 times. Significant part of the Hg in the bottom sediments is stored in organic form, which is potentially dangerous since it may cause secondary contamination of aquatic environment and hydrobionts. The high amplitude of water-level fluctuations in the reservoir is one of the main factors influencing the distribution of mercury in the surface layer of bottom sediments and preventing the sealing of contaminated bottom sediments by terrigenous material.