Year-round simulated methane emissions from a permafrost ecosystem in Northeast Siberia

Wetlands of northern high latitudes are ecosystems highly vulnerable to climate change. Some degradation effects include soil hydrologic changes due to permafrost thaw, formation of deeper active layers, and rising topsoil temperatures that accelerate the degradation of permafrost carbon and increase in CO₂ and CH₄ emissions. In this work we present two years of modeled year-round CH₄ emissions to the atmosphere from a northeastern Siberian region in the Russian Far East. We use a revisited version of the process-based JSBACH-methane model that includes four CH₄ transport pathways: plant-mediated transport, ebullition and molecular diffusion in the presence or absence of snow. The gas is emitted through wetlands represented by grid cell inundated areas simulated with a TOPMODEL approach. The magnitude of the summertime modeled CH₄ emissions is comparable to ground-based CH₄ fluxes measured with the eddy covariance technique and flux chambers in the same area of study, whereas wintertime modeled values are underestimated by one order of magnitude. In an annual balance, the most important mechanism for transport of methane into the atmosphere is through plants (61 %). This is followed by ebullition (~35 %), while summertime molecular diffusion is negligible (0.02 %) compared to the diffusion through the snow during winter (~4 %). We investigate the relationship between temporal changes in the CH₄ fluxes, soil temperature, and soil moisture content. Our results highlight the heterogeneity in CH₄ emissions at landscape scale and suggest that further improvements to the representation of large-scale hydrological conditions in the model, will facilitate a more process-oriented land surface scheme and better simulate CH₄ emissions under climate change. This is especially necessary at regional scales in Arctic ecosystems influenced by permafrost thaw.