Carbon and Hydrogen Isotopic Fingerprints of Methane from Canadian Boreal Forest Wetlands.

Carbon and Hydrogen isotopic signatures were determined in methane emitted by wetlands in northern Ontario, and northern Saskatchewan, Canada. The purpose of the work was to help constrain emission signatures for regional and global modelling of methane budgets. In particular there are very few measurements of δ2HCH4 signatures of wetland emissions from northern forests, essential inputs if global modelling is successfully to balance H isotopes.

Sampling was 1) west of Cochrane, Ontario; 2) around and south of Environment Canada's monitoring tower at Fraserdale, N. Ontario; and 3) around and south of Environment Canada's monitoring tower at East Trout Lake, central Saskatchewan. Samples were collected in flexfoil bags during mid-late June 2022, in cool, sometimes rainy conditions, and priority shipped for high-precision laboratory analysis of methane mixing ratio and C and H isotopes at IMAU Utrecht, NL and Royal Holloway, London, UK

Results of individual Keeling plot regressions for isotopic source signature analysis at different locations were variable. In initial results, δ2HCH4 ranged at different sites from -280‰ to -326‰ in Northern Ontario, and -326‰ to -376‰ in Saskatchewan. δ13CCH4 ranged from -62‰ to -69‰ in Northern Ontario and -58‰ to -63‰ in Saskatchewan. These results should be compared with measurements in 2013 that found δ13CCH4 broadly (plotting all data together) around -64.5±0.6‰ in N. Ontario and -63.5±0.6‰ in N. Saskatchewan, though with much local variation and some values around -66‰ at specific sites. There is clear need for low-altitude regional aircraft campaigns, to determine regionally integrated bulk source signatures, in particular to provide data to improve budget modelling by expanding the global database of δ2HCH4 source signatures.

We thank Royal Holloway, EU ATMO-ACCESS TNA and UK NERC for funding support.