High sulfate concentrations maintain low methane emissions at a constructed fen over the first seven years of ecosystem development

Highlights: • CH₄ emissions remained low over the first seven years post-construction. • Significant increase in CH₄ emissions in later years. • High SO₄²⁻ concentrations reduce potential CH₄ emissions. • Location of fen will maintain high SO₄²⁻, therefore future CH₄ emissions likely to remain low. Wetlands comprise a large expanse of the pre-disturbance landscape in the Athabasca Oil Sands Region (AOSR) and have become a focus of reclamation in recent years. An important aspect of wetland reclamation is understanding the biogeochemical functioning and carbon exchange, including methane (CH₄) emissions, in the developing ecosystem. This study investigates the drivers of CH₄ emissions over the first seven years of ecosystem development at a constructed fen in the AOSR and looks towards future CH₄ emissions from this site. Specifically, the objectives were to: 1) investigate the environmental controls on CH₄ emissions measured using manual static chambers between 2013 and 2019 and 2) investigate the relationship between water table depth, sulfate (SO₄²⁻) concentrations and CH₄ emissions during the 2019 growing season. Methane emissions remained low throughout the majority of the measurement period; however, in later years, a small but significant increase became apparent. High levels of SO₄²⁻ are likely the cause of the low CH₄ emissions, despite the high-water tables and dominance of vegetation with aerenchyma such as Carex aquatilis and Typha latifolia in later years. Although low CH₄ emissions may be beneficial from a climate warming perspective, the results also suggest that this constructed peatland is not functioning similarly to regional reference fens. Future climate scenarios across Western Boreal Canada could lead to higher air temperatures and changing precipitation patterns, influencing the direction of future CH₄ emissions from this site. However, given the likelihood of this site maintaining extremely high SO₄²⁻ concentrations over the next decade, it is expected that CH₄ emissions will remain low.