Studies of interannual and seasonal variability of balance of carbon and permafrost rock mass in typical tundra ecosystem in Northeast of Russia

In past decades, tundra ecosystems in the Arctic rapidly changed. Greenhouse gases emission from frozen organic carbon after permafrost thaw have the higher potential to increase effect of climate change in this region. Thawing and degradation of permafrost have been observed in many circumpolar research sites. The analysis of the multiyear complex observations of vegetation and permafrost dynamics in the tundra station «Chokurdakh» of SakhaFluxNet were carried out in this study. Carbon dioxide and methane fluxes in the typical tundra ecosystem in the Indigirka river lowlands in the Northeast of Russia were measured. The net carbon dioxide fluxes were higher compared to other sites, with a net ecosystem gas exchange (NEE) = –92 gCm⁻²yr⁻¹, which is composed of soil respiration of the ecosystem (Reco) = 141 gCm⁻²yr⁻¹ and gross primary production of tundra vegetation (GPP) = –232 gCm⁻²yr⁻¹. This large carbon sink could be explained by the continental climate of the site with low winter soil temperatures (–14°C) that decrease the respiration rates, and short, but relatively warm summers (10.4°C), stimulating high photosynthesis rates. The methane flux was 28 gC-CO2m⁻²yr⁻¹, so that the greenhouse gas balance was −64 gCCO2m⁻²yr⁻¹. The methane fluxes were highly sensitive to hydrological conditions and vegetation composition of the site. The importance of the vegetation composition and surface topography for protection of the active layer of permafrost and direction of the carbon flux were investigated. The strong vulnerability of the Arctic tundra even to small-scale changes of vegetation cover was shown. The development of a thaw pond after removing the shrub shifted the plots in our experimental site from a sink of methane into a source. The representative data for the tundra ecosystems, interannual and seasonal variability of the carbon balance are analyzed for the purpose of identification of trends. Nowadays, the tundra ecosystems are weak stock of carbon in comparison with the permafrost forest ecosystems of the Northeast of Russia. According to our long-term eddy-covariance data, the annual carbon sink in the tundra – 0.7 ± 0.2 tCha^-1yr^-1, in the larch forest is 2.0 ±0.5 tCha^-1yr^-1. An approximation of the long-term data of eddy-covariance indicates the positive trend of an increase in the accumulation of carbon in the future in the tundra ecosystems owing to the climate change and expansion of an area of growth of tree and shrub species to the North.

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