The Impact of LFH Mineral Mix on the Function of Reclaimed Landscapes in the Athabasca Oil Sands Region, Alberta, Canada

Abstract

The Athabasca Oil Sands Region (AOSR), located within the Western Boreal Plains (WBP) is characterized by a mosaic of boreal uplands and peatlands that dominate the terrain. These landscapes are underlain by oil-bearing formations (bituminous sands) and are disturbed or completely removed during resource exploration and extraction. Oil companies operating in the AOSR are mandated by the Government of Alberta to return their leased lands to an equivalent land capability. In doing so, new landscapes are constructed using materials salvaged from the pre-mined landscape and by-products from the mining process itself. Successful reclamation rests on an understanding of the soil physical properties that characterize these materials and how they impact intended function, both at the time of placement and in later years of reclamation. This research specifically focuses on the use of LFH mineral mix (hereafter referred to as LFH) as a cover soil in reclaimed landscapes and how its properties impact functionality. The temporal evolution of LFH was assessed using six reclamation study sites of six distinct ages (4 years post reclamation – 11 years post reclamation). A series of soil physical properties were analyzed in the top 10 cm of the LFH profile and while certain properties did follow a trend with time, other properties were likely an intrinsic property of the LFH upon placement. The dynamic nature of LFH captured within the time frame of this study contributes to an improvement in hydrological response with time (increasing α and maximum infiltration rates). Properties such as soil organic matter and bulk density, that would less readily change under biotic and abiotic forces impact the initial quality of LFH upon placement. And, while higher initial quality does improve the likelihood of success in early years of reclamation, sites of lower initial quality still performed as intended. Considering the entire soil profile, LFH over subsoil (glacial till or tailings sand) is likely to form a percolation barrier. The presence of these barriers (hydraulic or capillary) can be detected using easily obtained soil physical properties and they should be considered along with the intended function of a reclaimed landscape. Both types of barriers can benefit vegetation as water is held above the interface of the two materials, increasing field capacity and thus available water holding capacity. However, their behaviour in relation to increasing soil moisture conditions differs. While a hydraulic barrier is weakened, allowing more water to steadily move beyond the interface, a capillary barrier is broken through, and the two materials remain hydraulically connected until the barrier is restored. The behaviour of a capillary barrier could benefit landscapes where percolation into the subsurface is crucial to success.