Annual cycle of methane emission from a subarctic peatland

Abstract

[1] Although much attention in recent years has been devoted to methane (CH 4 ) emissions from northern wetlands, measurement based data sets providing full annual budgets are still limited in number. This study was designed to help fill the gap of year-round measurements of CH 4 emissions from subarctic mires. We report continuous eddy correlation CH 4 flux measurements made during 2006 and 2007 over the Stordalen mire in subarctic Sweden (68°20′N, 19°03′E, altitude 351 m) using a cryocooled tunable diode laser. The landscape-scale CH 4 fluxes originated mainly from the permafrost free wet parts of the mire dominated by tall graminoid vegetation. The midseason average CH 4 emission mean was 6.2 ± 2.6 mg m −2 h −1 . A detailed footprint analysis indicates an additional strong influence on the flux by the nearby shallow Lake Villasjön (0.17 km 2 , maximum depth 1.3 m). A stable bimodal distribution of wind flow from either the east or the west allowed separating the lake and mire vegetation signals. The midseason lake emission rates were as high as 12.3 ± 3.3 mg m −2 h −1 . Documented CH 4 fluxes are similar to results obtained by automatic chamber technique and higher than manual chamber measurements made in the wet minerotrophic section dominated by Eriophorum angustifolium. The high fluxes observed from this vegetation type are significant because the areal distribution of this source in the mire is expanding due to ongoing thawing of the permafrost. A simple peat temperature relationship with CH 4 emissions was used to fill data gaps to construct a complete annual budget of CH 4 fluxes over the studied area. The calculated annual CH 4 emissions in 2006 and 2007 equaled 24.5 and 29.5 g CH 4 m −2 yr −1 , respectively. The summer season CH 4 emissions dominated (65%) the annual flux, with the shoulder seasons of spring and autumn significant (25%) and a minor flux from the winter (10%).

Assessing effects of permafrost thaw on C fluxes based on multiyear modeling across a permafrost thaw gradient at Stordalen, Sweden

“…5d). This conclusion is consistent with the field results (e.g., Bäckstrand et al, 2008;Jackowicz-Korczyński et al, 2010). As illustrated by Fig.…”

“…The simulations of average accumulated CH 4 fluxes over non-growing seasons were 9.8 and 13.8 kg CH 4 -C ha −1 at the sphagnum and eriophorum sites, representing 30 and 13 % of mean annual emissions. In the wet area dominated by tall graminoid vegetation, field measurements demonstrated that CH 4 emissions over winter accounted for approximately 19 % of the annually emitted CH 4 (Jackowicz- Korczyński et al, 2010). These results indicate that further tests are necessary to verify the model's predictions of C fluxes during winter periods.…”

The effect of atmospheric turbulence and chamber deployment period on autochamber CO<sub>2</sub> and CH<sub>4</sub> flux measurements in an ombrotrophic peatland

“…On the other hand, Baldocchi et al (2012) reported higher CH 4 emissions at night in a peatland pasture, owing to collapse of the nocturnal boundary layer and elongation of flux footprint to elevated CH 4 source areas in calm conditions. In a subarctic peatland dominated by tall graminoids, no diel cycle in CH 4 flux was seen throughout the year (Jackowicz-Korczyski et al, 2010). Some studies that used autochambers on wetlands have reported CH 4 or total hydrocarbon fluxes for time periods of a day or more Bäckstrand et al, 2010), making it hard to deduce the variability over shorter time periods from their results.…”

Monitoring the Multi-Year Carbon Balance of a Subarctic Palsa Mire with Micrometeorological Techniques

“…Finally, in analysing fluxes the quality flag classification system proposed by Foken et al (2004) was applied. The CH 4 fluxes were gap filled based on the exponential soil temperature relationship presented by Jackowicz-Korczyński et al (2010) while with the CO 2 flux signal two different approaches were applied. The daytime CO 2 fluxes recorded during the growing season were gap filled by applying the light response equation (1) while the rest of the fluxes were parameterized with the night respiration equation (2) (Falge et al 2001).…”