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 use for the first time the recently built infrared high-resolution spectrometer, SPectrometre Infra-Rouge In situ Tropospherique to (1) measure in situ CH4 fluxes in natural and artificial peatland plot and (2) observe online bubbling events with quantification of CH4 emission fluxes corresponding to this very sudden degassing event. The closed dynamic chamber method was used and the gas concentration was measured every 1.5 s. 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 Sphagnum and Betula plots and in a wet artificially bared peat area with Eriophorum vaginatum. The results show that the CH4 emissions estimated with the SPectrometre Infra-Rouge In situ Tropospherique (SPIRIT) are consistent with those already published. The high emissions, both through diffusion and bubbling in the Eriophorum plot, were on the same order as the emissions estimated in natural shallow pools. During daytime, CH4 bubbling was higher in May (54.7% 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 (65.5%) than in daytime (54.7%). This has an important implication for carbon budget assessment in peatlands. The recently built infrared spectrometer, SPIRIT, was able to reliably measure CH4 fluxes and quantify CH4 flux during the degassing of bubbles. 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 and (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.