The net exchange of methane with high Arctic landscapes during the summer growing season

Abstract. High Arctic landscapes are essentially vast cold deserts interspersed with streams, ponds and wetlands. These landscapes may be important consumers and sources of the greenhouse gas methane (CH₄), though few measurements exist from this region. To quantify the flux of CH₄ (F_CH4) between the atmosphere and high Arctic landscapes on northern Ellesmere Island, Canada, we made static chamber measurements over five and three growing seasons at a desert and wetland, respectively, and eddy covariance (EC) measurements at a wetland in 2012. Chamber measurements revealed that, during the growing season, desert soils consumed CH₄ (−1.37 ± 0.06 mg-CH₄ m⁻² d⁻¹), whereas the wetland margin emitted CH₄ (+0.22 ± 0.14 mg-CH₄ m⁻² d⁻¹). Desert CH₄ consumption rates were positively associated with soil temperature among years, and were similar to temperate locations, likely because of suitable landscape conditions for soil gas diffusion. Wetland F_CH4 varied closely with stream discharge entering the wetland and hence extent of soil saturation. Landscape-scale F_CH4 measured by EC was +1.27 ± 0.18 mg-CH₄ m⁻² d⁻¹ and varied with soil temperature and carbon dioxide flux. F_CH4 measured using EC was higher than using chambers because EC measurements incorporated a larger, more saturated footprint of the wetland. Using EC F_CH4 and quantifying the mass of CH₄ entering and exiting the wetland in stream water, we determined that methanogenesis within wetland soils was the dominant source of F_CH4. Low F_CH4 at the wetland was likely due to a shallow organic soil layer, and thus limited carbon resources for methanogens. Considering the prevalence of dry soils in the high Arctic, our results suggest that these landscapes cannot be overlooked as important consumers of atmospheric CH₄.