Methane emissions from wetlands in the zone of discontinuous permafrost: Fort Simpson, Northwest Territories, Canada

Abstract

We examined the influence of water table position, temperature, vegetation, and CH₄ storage on CH₄ flux at 22 wetland sites located in the zone of discontinuous permafrost, near Fort Simpson, Northwest Territories. Sites ranged from frozen peat plateaux and palsas with collapse scars to fens and bogs and ponds. Mean summer CH₄ emissions ranged from −1.3 to 255 mg m⁻² d⁻¹, and the variation among sites was best explained by mean water table position (r² = 0.62, n = 19). Large CH₄ fluxes (>30 mg m⁻² d⁻¹) and high water tables occurred in ponds and graminoid sites, whereas small fluxes (−2 d⁻¹) and low water tables occur in shrub and woody sites. These relationships were upheld across several northern boreal regions, based on water table depth and broad ecological criteria. CH₄ turnover times were generated by comparing surficial fluxes and storage within the saturated portion of the peat profile. Graminoid sites had CH₄ turnover times from 1 to 4 days, whereas shrub or woody sites had longer turnover times, ranging from weeks to years. We estimated an overall flux of ∼18 mg m⁻² d⁻¹ for the landscape around Fort Simpson. This CH₄ flux may increase with the onset of global warming, owing to the fragility of permafrost, resulting in the formation of collapse scars with high CH₄ emission rates.