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In situ quantification of CH4 bubbling events from a peat soil using a new infrared laser spectrometer

Abstract : CH4 emissions from peatlands are space- and time-dependent. The variety of efflux routes contributes to these variabilities. CH4 bubbling remains difficult to investigate since it occurs on a timescale of seconds. The aims of this study were to test the capacity of a recently built infrared high resolution spectrometer, SPIRIT (SPectrometre Infra-Rouge In situ Troposphérique), to (1) measure in situ CH4 fluxes, (2) observe online bubbling events with quantification of CH4 emission fluxes corresponding to this very sudden degassing event. Material and methods: The closed dynamic chamber method was used and the gas concentration was measured every 1.5 seconds. Emission fluxes were calculated by the accumulation rate of CH4 against time. Measurements were undertaken during daytime in March 2009 and during day- and nighttime in May 2009, in a bare peat area, temporarily forming a shallow pool. Results and discussion: The results show that the CH4 emissions estimated with the SPIRIT ranged from 2.79 to 86.0 mg CH4-C m-2 h-1. These values are consistent with those already published. The high emissions, both through diffusion and bubbling, were on the same order as the emissions estimated in natural shallow pools. During daytime, CH4 bubbling was higher in May (56.2% of the total emission) than in March (40.7%) probably because of increased CH4 production and accumulation in peat. In May, bubbling was higher at nighttime (68.6%) than in daytime (56.2%). This has an important implication for carbon budget assessment in peatlands, particularly in boreal areas. Conclusions: The recently built infrared spectrometer, SPIRIT, was able to reliably measure CH4 fluxes and quantify CH4 flux during the degassing of a bubble. The emissions obtained are in agreement with previously published data using other measurement techniques. The results of this preliminary work highlight (1) the importance of shallow pools in peatland CH4 emissions, (2) the sensitivity of such fluxes to atmospheric pressure, a relation that has not been fully investigated or taken into account in assessing peatland carbon balance.
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Sébastien Gogo, Christophe Guimbaud, Fatima Laggoun-Défarge, Valéry Catoire, Claude Robert. In situ quantification of CH4 bubbling events from a peat soil using a new infrared laser spectrometer. Journal of Soils and Sediments, Springer Verlag, 2011, 11 (4), pp.545-551. ⟨10.1007/s11368-011-0338-3⟩. ⟨insu-00521762⟩