CH₄ flux from peatlands: a new measurement method

Abstract

Peatlands are important sources of atmospheric CH 4 , a potent greenhouse gas. Identifying the controls on CH 4 flux from peatlands requires detailed investigation of fluxes at small scales (the microform scale) where flux chambers are best deployed for measurement. Using chambers presents challenges, not least that of how the CH 4 concentration in chamber gas should be measured. Current field approaches usually involve either (i) online measurement with a flow-through laser absorption spectroscopy instrument or (ii) online or offline analysis of CH 4 by gas chromatography-flame ionization detector (GC-FID) analysis. Online measurement restricts the number of chambers that can be monitored to c. 10 and their spatial spread to a distance of 10-20 m from the CH 4 analyser and is not suited to large-scale studies. GC-FID may present logistical difficulties when conducting research at remote sites because of the need for frequent calibration and, hence, calibration gases. Generally, it is not suited to non-laboratory applications. An alternative is to analyse syringe samples of chamber gas near the field site using a modified laser spectroscopy instrument. We show how such a modification may be made. The theory of our modification is presented, as are the results obtained using it. It is shown that the instrument with the modification compares favourably with GC-FID and can be used near remote field sites in the absence of laboratory facilities. We present flux data from a peatland in Wales, where the flux-chamber CH 4 concentrations were obtained using the modified instrument.

The importance of episodic ebullition methane losses from three peatland microhabitats: a controlled‐environment study

“…Unfortunately, field measurements of steady CH 4 fluxes have not to our knowledge been made at Longbridgemuir. They have, however, been made at Cors Fochno using 27‐litre static chambers as described in Baird et al (2010). The field rates recorded from hollows from Cors Fochno in 2008 during summer conditions are similar to those found for the Cors Fochno samples and range from 18 to 100 mg CH 4 m −2 day −1 (mean, n = 5).…”

Greenhouse gas emissions from urban ponds are driven by nutrient status and hydrology

“…Headspace CH 4 and CO 2 concentrations were measured on a Picarro GasScouter equipped with a sampling loop (Baird et al. ) and converted to dissolved concentrations according to Henry's law (Weiss , Wiesenburg and Guinasso ). The following analyses of water samples were performed by the SWEDAC‐accredited Geochemical Laboratory at the Swedish University of Agricultural Sciences (for detailed information, refer to SLU , Fölster et al.…”

Controls on methane emissions from Alnus glutinosa saplings

“…The concentration of CH 4 extracted from pore water was analysed by cavity‐ring down laser spectroscopy using the method of Baird et al . (). Dissolved concentrations of CH 4 were calculated using Henry's law.…”