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Large-scale mining for oil extraction in the boreal forests of Northern Alberta has led to a disturbance footprint of ~900 km2 of land; which must be reclaimed to equivalent land capabilities. Microorganisms are sensitive to anthropogenic disturbances and play an essential role in the cycling of soil nutrients and plant growth, making them potential indicators of ecosystem function. Thus, the objective of this work was to determine the impact of land reclamation on the composition and function of soil microbial communities in the Athabasca Oil Sands Region (AOSR). We evaluated bacterial community composition via high throughput sequencing of 16S rRNA genes and soil functional diversity by community-level physiological profiling (CLPP). The ranges of variability for these factors observed in soils reclaimed with either peat-mineral mix (PMM), forest floor-mineral mix (FFM), or FFM diluted with sand (Sand-FFM), were compared to that of undisturbed reference soils (NS) and a vegetation removed soil (VR). Differences between reclamation soils and natural soils were clearly discernible, with reclamation imposing a more drastic disturbance to the boreal forest than that of removal of vegetation alone. VR changed the structure of the soil microbial community and increased the overall diversity, within-community interactions, and heterogeneity; while reclamation shifted the microbial community structure to an even greater extent, placing it outside the range of natural variability. Among reclamation substrates, FFM showed the highest level of similarity to the range of natural variability and PMM showed the least. Altogether, our findings underscore the profound impact of anthropogenic activities associated with large-scale mining on soil biological activity, microbial communities, and edaphic profiles. These alterations are of such magnitude that they render the affected soils significant divergent from the reference undisturbed boreal forest soil. [ABSTRACT FROM AUTHOR]