Post-extraction restored peatland methane production and emission

Peatland degradation due to human activities is contributing to rising
atmospheric CO2 levels. Restoring the carbon (C) sink function in
degraded peatlands and preventing further stored C losses is a key
climate mitigation strategy, given the global scale of peatland
disturbance. Active restoration at a post-extraction peatland in
Canada has been shown to successfully re-establish net CO2 uptake
rates similar to undisturbed peatlands within a decade or two.
However, lower than expected CH4 emissions suggest recovery of
belowground C cycling processes may lag behind recovery of the surface
net flux. Using closed chamber measurements over a warm season, we
determined that restored Sphagnum, which covers two thirds of the
site, was a net zero source of CH4. Emissions from the restored site
were primarily attributed to vascular plant substrate inputs, measured
as acetate, and plant-mediated transport. The carbon isotopic
fractionation factor for CH4 and CO2 in the restored former peat field
pore water exhibited α < 1.060 even deeper in the cutover peat
profile (0.8 m depth), evidence of a dominance in acetoclastic methane
production. In contrast, isotopic fractionation in the former drainage
ditches showed a balance of acetoclastic and hydrogenotrophic
methanogenesis deeper in the profile, indicative of some bulk peat C
turnover. This study shows that the legacy of substrate quality in the
cutover peat in reducing CH4 production and thus emission, can aid in
reducing the climate warming impact of newly restored peatlands.