Constraints imposed by the post-mining landscape and the sensitivity of peatland vegetation prevent the restoration of peatlands that dominated the pre-mining landscape, Rooney et al. point out in their paper. In place of the peatlands, operators will construct upland forest with well-defined drainage channels and subsaline shallow open water wetlands draining into large tailings ponds capped with freshwater.

Here we quantify the land cover changes that will result from approved oil sands mine projects and their impact on carbon storage.

...The most striking change to result from reclamation will be the conversion of wetland habitat to upland forest. According to company closure plans, uplands will increase by 15,030 ha on the leaseholds of the four mines [the ones of the 10 for which a direct comparison of pre- and post-mining landscapes is possible], mainly at the expense of peatlands, which will decrease by 12,414 ha (67% of their pre-mining coverage). Wetlands in general will decrease by 11,761 ha, with the loss of peatlands slightly offset by the creation of marsh and riparian shrublands...Scaling up, assuming similar land conversion ratios for the additional six mines, about 29,555 ha of peatlands will be lost as a result of currently approved mining (net wetland loss = 28,002 ha).

—Rooney et al.

Their analysis found that landscape changes caused by currently approved mines will release between 11.4 and 47.3 million metric tons of stored carbon. The breadth of the range reflects uncertainties associated with variability in peat depth, composition, and bulk density.

Converting from units of carbon to CO₂ equivalents, this is between 41.8 and 173.4 t of CO₂ lost, as much as 7-y worth of mining and upgrading emissions at 2010 production levels.

—Rooney et al.

The loss of peatland will also reduce carbon sequestration potential by 5,734–7,241 metric tons C/y.

Additionally, Turcotte’s study of soil organic matter in reclaimed land on oil sands mine leases has demonstrated unexpectedly rapid decomposition of the peat in soil amendments, even the relatively recalcitrant lignin phenols. This suggests that conversion of peatlands to uplands with peat soil amendments transforms a relatively permanent carbon storage pool (historical peatlands) to a temporary one that leaks carbon rather than sequesters it. This is supported by Welham’s model, which predicts that reclaimed forests will require 15 y of growth before carbon sequestration by vegetation begins to exceed the carbon emissions from decomposing peat amendments, suggesting that for years following mining and reclamation, reclaimed land will be a net carbon source.

The post-mining landscape will support >65% less peatland. One consequence of this transformation is a dramatic loss of carbon storage and sequestration potential, the cost of which has not been factored into land-use decisions. To fairly evaluate the costs and benefits of oil sands mining in Alberta, impacts on natural capital and ecosystem services must be rigorously assessed.

—Rooney et al.

Resources

• Rebecca C. Rooney, Suzanne E. Bayley, and David W. Schindler (2012) Oil sands mining and reclamation cause massive loss of peatland and stored carbon. PNAS doi: 10.1073/pnas.1117693108