Abstract
Abstract. We measured methane ebullition from a patterned boreal bog situated in the Siikaneva wetland complex in southern Finland. Measurements were conducted on water (W) and bare peat surfaces (BP) in three growing seasons (2014–2016) using floating gas traps. The volume of the trapped gas was measured weekly, and methane and carbon dioxide (CO2) concentrations of bubbles were analysed from fresh bubble samples that were collected separately. We applied a mixed-effect model to quantify the effect of the environmental controlling factors on the ebullition. Ebullition was higher from W than from BP, and more bubbles were released from open water (OW) than from the water's edge (EW). On average, ebullition rate was the highest in the wettest year (2016) and ranged between 0 and 253 mg m−2 d−1 with a median of 2 mg m−2 d−1, 0 and 147 mg m−2 d−1 with a median of 3 mg m−2 d−1, and 0 and 186 mg m−2 d−1 with a median of 28 mg m−2 d−1 in 2014, 2015, and 2016, respectively. Ebullition increased together with increasing peat temperature, weekly air temperature sum and atmospheric pressure, and decreasing water table (WT). Methane concentration in the bubbles released from W was 15–20 times higher than the CO2 concentration, and from BP it was 10 times higher. The proportion of ebullition fluxes upscaled to ecosystem level for the peak season was 2 %–8 % and 2 %–5 % of the total flux measured with eddy covariance technique and with chambers and gas traps, respectively. Thus, the contribution of methane ebullition from wet non-vegetated surfaces of the bog to the total ecosystem-scale methane emission appeared to be small.
Highlights
Bogs were commonly feared, as people saw mysterious lights that gave rise to the tales of the “will o’ the wisps” that lure travellers from their paths to sink into bog holes (Meredith, 2002)
More methane ebullition was found from W than from bare peat surfaces (BP), and within the pools more bubbles were released from open water (OW) than from EW
We found variation between the three studied growing seasons, as ebullition rate was generally higher in the wettest year (2016)
Summary
Bogs were commonly feared, as people saw mysterious lights that gave rise to the tales of the “will o’ the wisps” that lure travellers from their paths to sink into bog holes (Meredith, 2002). Nowadays, these lights are thought to be the spontaneous combustion of peatland gases, such as methane, bubbling into the atmosphere, rather than deceptive fairies. Currently peatlands are more known for their climate-cooling impact as small carbon sinks and the storage of a third of the global soil carbon stock (Strack, 2008), they are a major natural source of methane, a potent climate warming greenhouse gas (IPCC, 2014). It has been predicted that carbon dioxide (CO2) uptake typically offsets sustained methane emissions in natural ecosystems in the long term (i.e. several centuries), albeit with large spatiotemporal variability (Petrescu et al, 2015)
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