Tree Cores for Root Bores: Exploring Tree Rooting Behaviour in Bituminous Soils

Abstract

Surface mining in the Athabasca Oil Sands region has disturbed approximately 895 km2 of boreal forest, all of which will need to be reclaimed to a state that is both representative of, and as productive of the surrounding boreal forest. However, much remains to be understood regarding the effects of different reclamation practices on restoring forests on mined landscapes. Reclamation practices, though varied, can involve the construction of landforms using overburden materials such as lean oil sand (LOS, sand containing concentrations < 8% hydrocarbons) with a layer of appropriate soil medium placed on top. While some early studies suggest that there may be negative effects of LOS on tree growth, forests have been growing on natural shallow bitumen deposits since the last ice age. The goal of this thesis is to explore whether using dendrochemical methods can allow us to better understand the relationship between tree rooting behaviour and shallow bitumen. Soil, soil pore water, and tree cores were taken from sites with natural shallow bitumen deposits and analyzed for trace metals enriched in bitumen (vanadium, nickel, molybdenum, and rhenium). Samples were also collected from sites without bitumen present. Significantly elevated concentrations of Ni were observed in trees growing on shallow bitumen deposits. Vanadium was also elevated in trees on bituminous sites though not significantly so. Molybdenum displayed the opposite trend and decreased in trees on bituminous sites. A baseline survey was also conducted on a reclaimed landform constructed using LOS to establish a proper reference against which future research can compare. My thesis establishes that with strong analytical methods and good reference conditions, dendrochemistry is a feasible methodology for monitoring root growth in bituminous soils with V and Ni acting as potential signal elements. This possibility presents reclamation practitioners and researchers with a useful tool to monitor plant growth across both constructed landforms and natural landscapes along with strong data against which to compare future values.