We quantified the wholesale transformation of the boreal landscape by open-pit oil sands mining in Alberta, Canada to evaluate its effect on carbon storage and sequestration. Contrary to claims made in the media, peatland destroyed by open-pit mining will not be restored. Current plans dictate its replacement with upland forest and tailings storage lakes, amounting to the destruction of over 29,500 ha of peatland habitat. Landscape changes caused by currently approved mines will release between 11.4 and 47.3 million metric tons of stored carbon and will reduce carbon sequestration potential by 5,734-7,241 metric tons C/y. These losses have not previously been quantified, and should be included with the already high estimates of carbon emissions from oil sands mining and bitumen upgrading. A fair evaluation of the costs and benefits of oil sands mining requires a rigorous assessment of impacts on natural capital and ecosystem services.wetland reclamation | tar sands A n area larger than the state of Rhode Island will eventually be mined by oil sands companies in northern Alberta. These boreal lands must be reclaimed, but despite claims to the contrary (1), operators are not required to return the land to its original state (2). This study was precipitated by the disparity between statements made by the oil sands industry regarding the extent and anticipated success of mine reclamation and their official closure plans, which serve as agreements between mine operators and the Alberta government regarding actual reclamation expectations.Oil sands deposits accessible by open-pit surface mining cover about 475,000 ha of boreal Alberta, 99% of which is already leased (3). Currently, 10 mines have government approval to operate, covering about 167,044 ha (Fig. 1). This is a conservative estimate that excludes the pipelines, roads, seismic lines, and other infrastructure that support the mines. It also excludes impacts from aerial deposition (4) and aquifer dewatering (5) that extend off-site and the area of land associated with the three additional mines currently undergoing environmental review.Constraints imposed by the postmining landscape and the sensitivity of peatland vegetation prevent the restoration of peatlands that dominated the premining landscape. Mine proponents are required to describe the premining landscape and produce closure plans that detail the postmining landscape. Current reclamation regulations do not require the restoration of previous land covers or the restitution of lost carbon formerly stored in soils and vegetation. In place of destroyed peatlands, operators plan to construct upland forest with well-defined drainage channels and subsaline shallow open water wetlands draining into large tailings ponds capped with freshwater. The net effect of this landscape transformation on biodiversity and ecosystem functions has not been assessed. Here we quantify the land cover changes that will result from approved oil sands mine projects and their impact on carbon storage.

The role of deterministic and stochastic processes in community assembly is a key question in community ecology. We evaluated the effect of an abiotic filter (hydroperiod) on the partitioned diversity of three taxonomic groups (birds, vegetation, macroinvertebrates) from prairie pothole wetlands in Alberta, Canada, which naturally vary in water permanence. We observed that alpha and gamma diversity were higher in permanent than temporary wetlands (16–25% and 34–47% respectively, depending on the taxon). This suggests an influence of deterministic constraints on the number of species a wetland can support. Taxa which cannot persist in shallow, temporary wetlands are excluded by the deterministic constraints that a shortened hydroperiod imposes. In contrast, we observed that beta diversity was significantly higher (2–12%) in temporary wetlands than permanent ones, and temporary wetlands supported more unique combinations of community composition than permanent wetlands, despite having a smaller regional species pool. This observation contradicts prior mesocosm studies that found beta diversity mirrored the pattern in gamma diversity along an environmental filtering gradient. We conclude that deterministic processes are more influential in more stable permanent wetlands, whereas stochastic processes play a more important role in assembly in dynamic temporary wetlands that must disassemble and re‐establish annually. Considering three distinct taxonomic groups differing in their relative mobility, our large‐scale field study demonstrates that both stochastic and deterministic processes act together to influence the assembly of multiple communities and that the relative importance of the two processes varies consistently along a gradient of environmental filtering.

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