Seasonal Dynamics of CH4 and CO2 Concentrations in Bog Lake Severnoe

Bog and lake ecosystems of the boreal region are recognized as important parts of the global biogeochemical carbon cycle. At the same time, many aspects of the gas regime dynamics of bog lakes remain understudied. The paper presents data on the seasonal dynamics of dissolved CH₄ and CO₂ concentrations in the bog lake located in the ridge-lake complex of the Ilassky bog, a typical raised bog in the northern taiga of northwestern Russia, and results of analysis of the seasonal vertical distribution of greenhouse gases in the water column and the dynamics of surface concentrations with increased time resolution. The reasons for and patterns of their variability are considered, including those in relation to the characteristics of the bottom sediments. Concentrations of CH₄ and CO₂ in the water column vary during the year within wide ranges: from 4 to 652 µg/L and from 0.19 to 19 mg/L, respectively. CH₄ concentrations in the surface layer are at approximately the same level from May through August, with values measured in the water (5.9 to 11 µg/L) more than one hundred times higher than the concentrations in equilibrium with the atmosphere (0.04 to 0.05 µg/L), indicating a methane flux to the atmosphere. The CO₂ concentrations decrease throughout the open water period and become lower than the equilibrium concentrations with the atmosphere by the end of August, indicating a change in the flux direction and uptake of CO₂ from the atmosphere. The results showed that, depending on the season, a bog lake can be not only a source but also a sink for atmospheric carbon, 90–99% of which is CO₂ according to literature data.