Evaluation of methane emissions from the Ivankovskoye reservoir

The article summarizes materials from a multi-method research of the Ivankovo Reservoir carried out in 2022−2024 to study seasonal changes of methane concentration in water and its emission from the surface. The survey included both methane flux measurement at the water − atmosphere boundary, with due consideration of its spatial variability, and measurement of methane emissions from the bottom sediments. The measurements were carried out by a chamber method (floating and bottom). The samples were processed using the Chromatek-Crystall 5000.2 chromatograph. Sampling locations were chosen taking in account the morphological structure of the reservoir, the type of bottom sediments, and the depth intervals. The measurements have shown that the values of methane flux on longitudinal and transverse sections could differ by two orders of magnitude. Its lowest values are within the areas with sandy bottom. The highest value of methane flux is in the area with significant anthropogenic load, i. e. from the inflow of the Shoshinsky reach to the Ploski village. According to the classification based on the water exchange coefficient, the Ivankovo Reservoir belongs to the group of flow-through reservoirs with seasonal flow regulation; however under certain weather conditions the oxygen deficiency areas appear in the reservoir. During these periods, the methane flux from such areas becomes comparable with that from the low-flow water bodies. Therefore, the summer decrease in flowage and more frequent heat waves are unfavorable factors increasing the methane emission. Low-water periods when the water level decreases relative to the FSL during the navigation period are also unfavorable because of the increase in methane flux. The obtained values of methane flux were compared with published data, and significant differences were found for the spring period. A methodology for estimating methane emission from a reservoir is proposed, taking into account the factors that determine its flux. Seasonal changes in emission are described, and the increased frequency of measurements and the need to measure methane flux over different types of macrophytes are argued.