Methane Emissions and Hydrological Structure of the Zeya Reservoir (Russia) in the Warm Period

Based on the results of field measurements of methane concentrations in water and its specific fluxes from the water surface, the emission of methane in the warm season from the Zeya Reservoir, one of the largest artificial hydropower facilities in Russia, has been assessed for the first time. Data were obtained during field surveys carried out in September 2021 and July 2022. Hydrological and hydrochemical surveys have made it possible to obtain information about the thermal, oxygen, and chemical structure of the reservoir water column, as well as carry out a comprehensive zoning of its water area. A digital model of the relief of the Zeya reservoir bed is developed, which, together with zoning, has made it possible to perform detailed calculations of the total methane emission from the Zeya Reservoir. It has been found that, for the reservoir, the main sources of organic matter and methane are swampy tributaries and runoff of organic matter from the shores, which enters the water area coastal areas. These areas accumulate allochthonous organic matter and are characterized by high methane fluxes. The total CH₄ flux from the Zeya Reservoir surface is significantly higher in summer (when maximum heating of shallow waters is observed) than in the autumn. The CH₄ emission coefficients obtained by the authors from the Zeya Reservoir (8.6–17.2 kgCH₄/ha) correspond to the coefficients presented in the Supplements to the 2019 IPCC Guidelines for Boreal Reservoirs.