Environmental controls on CH₄ emission from polygonal tundra on the microsite scale in the Lena river delta, Siberia

Abstract

The carbon budgets of the atmosphere and terrestrial ecosystems are closely coupled by vertical gas exchange fluxes. Uncertainties remain with respect to high latitude ecosystems and the processes driving their temporally and spatially highly variable methane (CH4) exchange. Problems associated with scaling plot measurements to larger areas in heterogeneous environments are addressed based on intensive field studies on two nested spatial scales in Northern Siberia. CH4 fluxes on the microsite scale (0.1–100 m2) were measured in the Lena River Delta from July through September 2006 by closed chambers and were compared with simultaneous ecosystem scale (104–106 m2) flux measurements by the eddy covariance (EC) method. Closed chamber measurements were conducted almost daily on 15 plots in four differently developed polygon centers and on a polygon rim. Controls on CH4 emission were identified by stepwise multiple regression. In contrast to relatively low ecosystem-scale fluxes controlled mainly by near-surface turbulence, fluxes on the microsite scale were almost an order of magnitude higher at the wet polygon centers and near zero at the drier polygon rim and high-center polygon. Microsite scale CH4 fluxes varied strongly even within the same microsites. The only statistically significant control on chamber-based fluxes was surface temperature calculated using the Stefan–Boltzmann equation in the wet polygon centers, whereas no significant control was found for the low emissions from the dry sites. The comparison with the EC measurements reveals differences in controls and the seasonal dynamics between the two measurement scales, which may have consequences for scaling and process-based models. Despite those differences, closed chamber measurements from within the EC footprint could be scaled by an area-weighting approach of landcover classes based on high-resolution imagery to match the total ecosystem-scale emission. Our nested sampling design allowed for checking scaling results against measurements and to identify potentially missed sources or sinks

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

“…Decreased atmospheric pressure results in bubble expansion, which enhances buoyancy force and entails bubble rise (Chen and Slater, 2015). The negative correlation of water and mat temperature with CH 4 and CO 2 fluxes from the pond and CH 4 flux and ER of the floating mat (Tables 1 and 2) was unexpected, as it is consensus that temperature is an important positive control on these fluxes (Pelletier et al, 2014;Roulet et al, 1997;Sachs et al, 2010;Wik et al, 2014). Also the potential effect of wind speed on CH 4 and CO 2 fluxes from the pond was ambiguous.…”

“…Individual bubble events releasing more than 10 µmol CH 4 contributed substantially to summer CH 4 emissions from the floating mat, despite their rare occurrence. When CH 4 emissions of peatlands that contain ponds are quantified, ebullitive and diffusive CH 4 fluxes at the land-water interface hence need to be accounted for and the areal cover of the different microforms and/or plant communities should be thoroughly mapped, as suggested by Sachs et al (2010) for tundra landscape. We also observed 4-to 16-fold increases in CH 4 and CO 2 emissions in late summer that were unrelated to meteorological drivers, such as temperature, wind speed and radiation.…”

Cold season emissions dominate the Arctic tundra methane budget

“…Warmer air temperatures and increased snowfall can potentially increase soil temperatures and deepen the seasonal thawed layer, stimulating CH 4 and CO 2 emissions from the vast stores of labile organic matter in the Arctic (11). The overwhelming majority of prior studies of CH 4 fluxes in the Arctic have been carried out during the summer months (12)(13)(14)(15). However, the fall, winter, and spring months represent 70-80% of the year in the Arctic and have been shown to have significant emissions of CO 2 (16)(17)(18).…”

A stochastic model for the polygonal tundra based on Poisson–Voronoi diagrams

“…where threshold = 10 cm has been inferred from observations of small-scale methane emissions (Sachs et al, 2010). They are controlled by the site's water table height, and different surface types correspond to different emitting characteristics.…”

“…1). Previous works involved closed-chamber and eddy covariance measurements of methane fluxes (see e.g., Sachs et al, 2008Sachs et al, , 2010Wille et al, 2008;Kutzbach et al, 2004), as well as measurements and modeling of hydrological properties , and of surface energy balance (Langer et al, 2011a,b) in this typical periglacial landscape. Recent studies with the help of remote sensing data were able to capture and analyze surface heterogeneity (land cover and surface temperature) and its importance for the landatmosphere water fluxes (Muster et al, 2012;Langer et al, 2010).…”