The ongoing reclamation of boreal forest areas that are impacted by oil sands mining involves the construction of wetlands as desirable land uses. Constructed wetlands receiving peat-mining runoff are known to be major sources of greenhouse gas (GHG) emissions to the atmosphere. However, the GHG dynamics of a fen that is constructed with drained peat substrate and receives runoff containing effluents of salt and Naphthenic acids is not known. Using a fen constructed in the post-mining landscape of the Athabasca oil sands region, a study was conducted to quantify the emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) over the first two growing seasons following revegetation. The specific objective of this study is to evaluate the effect of revegetation strategies and other environmental characteristics on the fen GHG emissions over the growing season. Relative to a natural fen, our results show significantly lower fluxes of CH4 (p < 0.001), which correlate with higher bulk density, lower organic matter, and higher pH and SO42- concentration in the constructed fen. Revegetation did not stimulate CH4 production, but increased CO2 uptake and reduced the global warming potential of N2O emissions by 63CO2-e m-2 yr-1 relative to the non-vegetated control. These results suggest that revegetation strategies and water chemistry might be more important controls on GHG dynamics than substrate quality in a constructed fen. Although present conditions in the constructed fen support a net GHG sink function, additional monitoring is required to evaluate if this condition will persist in the long-term. We recommend that future reclamation projects should consider the potential effects of construction materials on water chemistry prior to use in fen reclamation.