Biogeosciences (Nov 2007)
The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia
Abstract
Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, <i>R</i><sub>eco</sub> and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=−92 g C m<sup>−2</sup> yr<sup>−1</sup>, which is composed of an <i>R</i><sub>eco</sub>=+141 g C m<sup>−2</sup> yr<sup>−1</sup> and GPP=−232 g C m<sup>−2</sup> yr<sup>−1</sup>. This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (−14°C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (<i>R<sub>g</sub></i><200 W m<sup>−2</sup>), whereas <i>R</i><sub>eco</sub> depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO<sub>2</sub>e m<sup>−2</sup> yr<sup>−1</sup>, so that the greenhouse gas balance was −64 g C-CO<sub>2</sub>e m<sup>−2</sup> yr<sup>−1</sup>. Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition.
