Restoration approach influences carbon exchange at in-situ oil sands exploration sites in east-central Alberta

Abstract

Oil sands exploration activities across the Alberta boreal peatlands requires tree clearing and results in sites being left compressed and with altered understory vegetation. Restoration techniques, including planting trees, mechanical mounding with tree planting, and spreading coarse woody debris have been tested across abandoned oil sands exploration sites. In this study two oil sands exploration sites were monitored 6- and 9-years post-treatment, along with two control areas disturbed 20 years ago with no active restoration treatment. Results were compared to a natural reference site to understand how various restoration techniques influenced carbon flux and growing season carbon balance. Tree ingress was observed across all parts of the restored oil sands exploration sites except a wet control area disturbed 20 years ago. The creation of dry microsites through the mechanical mounding technique substantially increased tree productivity, and we found that 9 years post-restoration the mounded area of an oil sands exploration site had a tree net primary productivity similar to the natural site. This carbon uptake, however, was partially offset by large emissions of methane from pools adjacent to mounds. We found that planting trees only could result in a growing season carbon balance that is within the range of a natural peatland 9 years following restoration. However, our estimates indicate that the mounding treatment 9 years following restoration released less carbon to the atmosphere overall compared to all other restoration treatments and control areas. This restoration technique may be useful if the restoration goal is focused on returning the carbon storage function at disturbed sites. As well as understanding attainability of restoration goals, evaluating ecohydrologic conditions of oil sands exploration sites pre-restoration is critical for informing the most appropriate restoration technique.