Soil methane data from a wildfire chronosequence in northern Sweden

In situ gas fluxes were measured over one week using a static chamber method during August 2006. Samples were stored in exetainer vials (Labco, UK) for up to one month prior to analyses. Concentrations of CH4 were analysed by gas chromatography, on a PerkinElmer Autosystem XL Gas Chromatograph (GC) with Flame Ionization Detector, and results were calibrated using certified gas standards. CH4 was separated isothermally on a 2 m Poropak Q 50x80 mesh packed column at 40 deg C, with N2 as the carrier gas. CH4 fluxes from ex situ cores were measured from the top 25 cm of soil (or to the bedrock where soil depth was less than 25 cm) in 2006 and then through the entire humus profile to the bedrock (20-85 cm depth) in 2007. In 2006, intact cores (11 cm diameter, 25 cm depth) were removed from each island (40 per island size classification) and were weighed on the day of collection. Cores were stored at 12 deg C in the dark until measurement and were maintained at their field collected moisture content using an artificial rain solution. In 2007, one full profile core (0.15 m diameter) was collected from each island humus profile to the bedrock in July 2007. A similar static chamber approach (volume = 0.0021 m3, diameter = 0.15 m) for measuring soil CH4 fluxes, applied under the same measurement conditions as previously described. In situ gas samples were collected from within the soil atmosphere in the humus profiles of each island over 4 days in July 2007. Four stainless steel sampling probes (19 gauge, 0.69 mm inner diameter) were inserted into the soil profiles 30 minutes before soil atmosphere samples were collected at 15, 35, 55 and 75 cm depth (dead-space volume = 0.06, 0.13, 0.21, 0.28 ml, respectively). From each probe a 100 ml sample was collected with 90 ml being transferred to a 50 ml Wheaton bottle with butyl rubber stopper and crimp top seals and 9 ml to a 3.6 ml exetainer vial. After collection each butyl rubber stopper and crimp top was sealed with wax. Analyses of the 13C values of CH4 were completed within one month at the Centre for Ecology & Hydrology, Lancaster. Full details are in supporting information associated with this record.