Annual cycles of methane emission from a subarctic peatland

Although much attention in recent years has been devoted to methane (CH4) emissions from northern wetlands, measurement based datasets providing full annual budgets are still limited in number. This study was designed to help fill the gap of year-round measurements of CH4 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, alt. 351 m) using a cryocooled tunable diode laser (TDL). The landscape scale CH4 fluxes originated mainly from the permafrost free wet parts of the mire dominated by tall graminoid vegetation. The midseason average CH4 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 the shallow Lake Villasjön (0.17 km2, max depth 1.3 m). A stable bimodal distribution of wind flow from either the easier 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. Fluxes from a homogeneous area dominated by Eriophorum augustifolium agree well with automatic chamber measurements located in similar vegetation in the wet minerotrophic parts of the peatland. 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 CH4 emissions was used to fill data gaps to construct a complete annual budget of CH4 fluxes over the studied area. The calculated annual CH4 emissions in 2006 and 2007 equaled 24.5 and 29.5 g CH4 m-2 y-1 respectively. These are considerably higher annual sums than what has earlier been estimated for this mire based on manual cha