Interannual, seasonal, and retrospective analysis of the methane and carbon dioxide budgets of a temperate peatland

[1] Three years (2009–2011) of near-continuous methane (CH4) and carbon dioxide (CO2) fluxes were measured with the eddy covariance (EC) technique at a temperate peatland located within the Marcell Experimental Forest, in northern Minnesota, USA. The peatland was a net source of CH4 and a net sink of CO2 in each year with annual carbon budgets of 26.8 ( 18.7), 15.5 ( 14.8), and 14.6 ( 21.5) g Cm 2 yr 1 for 2009–2011, respectively. Differences in the seasonal hydrometeorological conditions among the three study years were most pronounced during 2011, which was considerably warmer (+1.3 C) and wetter (+40mm) than the 30 year average. The annual CH4 budget was +11.8 ( 3.1), +12.2 ( 3.0), and +24.9 ( 5.6) g Cm 2 yr 1 for the respective years and accounted for 23%–39% of the annual carbon budget. The larger CH4 emission in 2011 is attributed to significant warming of the peat column coupled with a high water table position throughout the entire growing season. Historical (1991–2011) CH4 emissions were estimated based on long-term hydrometeorological records and functional relationships derived from our 3 year field study. The predicted historical annual CH4 budget ranged from +7.8 to +15.2 ( 2.7) g CH4-Cm 2 yr . Recent (2007–2011) increases in temperature, precipitation, and rising water table at this site suggest that CH4 emissions have been increasing, but were generally greater from 1991 to 1999 when average soil temperature and precipitation were higher than in recent years. The global warming potential (considering CO2 and CH4) for this peatland was calculated based on a 100 year time horizon. In all three study years, the peatland had a net positive radiative forcing on climate and was greatest (+187 g Cm ) in 2011. The interannual variability in CH4 exchange at this site suggests high sensitivity to variations in hydrometeorological conditions.