Methane Dynamics in a Boreal Peatland: Combining Flux Measurements, Concentration Profiles in the Peat and Microbial Ecology at Different Spatial and Temporal Scales

Peatlands are one of the largest natural sources of methane to the atmosphere and methane is a significant component of the peatland carbon balance. We aimed to study the methane dynamics in a boreal, sedge- dominated fen, Siikaneva, by combining flux measurement using the eddy covariance (EC) technique and chambers, methane concentration measurements in the peat profile from 10 to 270 cm depth, and methane production potentials and microbial community composition at different depths. The temporal pattern in the fluxes was accurately detected with the EC method. The annual methane emission was 12.6 g CH4 m-2. The seasonal variation in the emissions was large, following the seasonality of the soil temperature. A small emission pulse was detected during the snow melt period. Despite the rather homogenous vegetation composition in the site, spatial variation in the fluxes was considerable and mostly controlled by water level and leaf area of sedges. The concentration profiles showed that most of the methane production took place at the depths of 20 and 50 cm, where most living roots are located. Concentrations at 10 cm were lower, indicating methane oxidation. Methane production potentials were highest at the depths of 20 and 10 cm. Production potentials and methanogenic communities varied across the site, especially at the depth of 20 cm. Vegetation was the major controller of the fluxes; plots in which the vegetation was removed showed very low fluxes. Occasionally, however episodic ebullition events were seen, when fluxes from the non-vegetated plots peaked, coinciding with the abrupt decrease in the concentrations in the peat. In conclusion, by combining different methods we can improve our understanding of the peatland methane dynamics.