LBNL Researchers Evaluate Methane Production, Oxidation, and Emissions Across Polygon Tundra Gradients

Using field measurements of methane flux and stable isotopes, NGEE Arctic researchers identify spatial patterns in methane emissions and underlying metabolic processes across polygon types and features

In a manuscript recently published in Global Change Biology, LBNL researchers Lydia Smith Vaughn, Mark Conrad, Markus Bill, and Margaret Torn present results of a two-year field methane study in the Barrow Environmental Observatory. Using measurements of surface methane and CO2 fluxes, concentrations and stable isotope compositions of methane and DIC at 3 depths in the soil, and soil moisture and temperature, this study identifies important predictors of methane emissions and microbial methane production pathway across a range of polygon types and features representing varying degrees of permafrost degradation. Averaged across all polygon features (centers, rims, and troughs), methane emissions from low-centered polygons were ~9 times as high as from flat- and high-centered polygons. While this pattern in methane emissions followed an overall soil moisture gradient, statistical results indicate that methane emissions depend on microtopographic position and polygon type to a greater degree than soil moisture could explain. Specifically, low-centered polygons with intact ice wedges had higher methane emissions, a greater contribution of acetate cleavage to methane production, and lower methane oxidation than did flat- and high-centered polygons.  This relationship persisted even in the relatively dry rims of low-centered polygons and the saturated troughs of flat- and high-centered polygons. In contrast with many previous studies, these findings document a mechanism whereby loss of subsurface ice can lead to local decreases in tundra methane emissions.

Reference:

Vaughn LJS, ME Conrad, M Bill, and MS Torn. 2016. Isotopic insights into methane production, oxidation, and emissions in Arctic polygon tundra. Global Change Biology 22: 3487-3502. http://dx.doi.org/10.1111/gcb.13281

Figure 6. Greenhouse gas emissions, classified by polygon type, position, and measurement month.  (a) Net CH4 flux in nmol CH4 m-2 s-1 and (b) ecosystem respiration in mol CO2 m-2 s-1 were measured from each feature of 4 flat/high-centered (FHC) and 3 low-centered (LC) polygons. Standard errors were calculated from field replicates.

 

Contact Person: 
Lydia Smith Vaughn (lydiajsmith@lbl.gov), Lawrence Berkeley National Laboratory