Abstract. Boreal peatlands represent a globally important store of
carbon, and disturbances such as wildfire can have a negative feedback to
the climate. Understanding how carbon exchange and greenhouse gas (GHG)
dynamics are impacted after a wildfire is important, especially as boreal
peatlands may be vulnerable to changes in wildfire regime under a rapidly
changing climate. However, given this vulnerability, there is very little in the
literature on the impact such fires have on methane (CH4) emissions.
This study investigated the effect of wildfire on CH4 emissions at a
boreal fen near Fort McMurray, Alberta, Canada, that was partially burned by the
Horse River Wildfire in 2016. We measured CH4 emissions and
environmental variables (2017–2018) and CH4 production potential (2018)
in two different microform types (hummocks and hollows) across a peat burn
severity gradient (unburned (UB), moderately burned (MB), and severely burned
(SB)). Results indicated a switch in the typical understanding of boreal
peatland CH4 emissions. For example, emissions were significantly lower
in the MB and SB hollows in both years compared to UB hollows.
Interestingly, across the burned sites, hummocks had higher fluxes in 2017
than hollows at the MB and SB sites. We found typically higher emissions at
the UB site where the water table was close to the surface. However, at the
burned sites, no relationship was found between CH4 emissions and water
table, even under similar hydrological conditions. There was also
significantly higher CH4 production potential from the UB site than the
burned sites. The reduction in CH4 emissions and production in the
hollows at burned sites highlights the sensitivity of hollows to fire,
removing labile organic material for potential methanogenesis. The
previously demonstrated resistance of hummocks to fire also results in
limited impact on CH4 emissions and likely faster recovery to pre-fire
rates. Given the potential initial net cooling effect resulting from a
reduction in CH4 emissions, it is important that the radiative effect
of all GHGs following wildfire across peatlands is taken into account.
Wildfire overrides hydrological controls on boreal peatland methane emissions
