Reconstructing Boreal Forest Soils Following Oil Sands Mining.

Surface mining to date has disturbed about 600 km2 of land in the Athabasca oil sands region, located in northeastern Alberta, Canada. Following mining, reclamation necessitates the reconstruction of soil-like profiles using salvaged surface mineral materials, peat amendments, and mining by-products. Establishing biogeochemical cycling between these reconstructed soils and plants is one of the most critical factors required to ensure long-term sustainability in reclaimed landscapes. While vegetation growing on recently reclaimed soils relies on peat for its nutrient supply, over time this should be replaced by in situ inputs through litterfall and the build-up of a forest floor layer. The overall objective of this research program was to assess the long-term sustainability of reconstructed oil sands soils by comparing their range of structural and functional variability with that of natural boreal forest soils. Specifically, nutrient availability, organic matter quality, and microbial communities were characterized in a series of reconstructed soils covering different reclamation treatments, vegetation, and age classes, and were compared to the range of natural forest soils found in the region. Results indicated that the peat materials used for reclamation, at least initially, were structurally and functionally different from the natural soil organic matter found in non-disturbed forests. However, several indicators showed an evolution with time since reclamation towards conditions observed at the undisturbed forest soils. In particular, the surficial organic matter layer reflected a shift in composition from peat to woody plant inputs, which occurred faster under aspen than under coniferous (pine and spruce) vegetation. In addition, while microbial community composition in the reconstructed soils differed among reclamation treatments when canopy cover was lower than 30%, differences among stand types became significant at higher (>30%) cover.   Taken together, these results underlie the importance of  building native organic matter within the reconstructed soils, e.g. through the development of a forest floor layer, to foster their evolution towards natural conditions.