Quantifying the vertical water exchange of dominant tree species in a reclaimed landscape in the Athabasca oil sands region, Alberta

Large-scale oil sands mining in the Athabasca oil sands region has caused significant disturbance to forest and peatland ecosystems of the Western Boreal Plains in northeastern Alberta, Canada. Reclamation of these ecosystems has faced many challenges, including successful re-vegetation of uplands. The trajectory of reclaimed uplands depends on the community structure of tree species, which in turn influences vertical water exchanges via increases in rainfall interception and transpiration. The trajectory therefore influences vadose zone moisture dynamics and reduces water available for recharge to adjacent reclaimed peatlands. The objectives of this study were to assess trends in transpiration of dominant tree species in a reclaimed upland and quantify canopy-rainfall dynamics and its impact on near-surface soil moisture regime and tree water use. To assess these trends, throughfall, interception and stemflow were measured throughout the growing season. Tree transpiration was measured using sap flow sensors, along with soil tension measurements using soil tensiometers. Results indicate that tree transpiration and water use are controlled by water availability, and at this stage (6 years since reclamation), canopy interception has begun to play an important role in partitioning growing season rainfall. At this time in canopy development, transpiration accounted for 52% of water losses from the system, with broadleaf trees contributing 71%. However, coniferous trees had greater interception capabilities, as Picea mariana intercepted 35% and Pinus banksiana 32%, while broadleaf Populus tremuloides and Populus balsamifera contributed 29% and 26%, respectively. As this reclaimed upland canopy continues to evolve, moisture partitioning, including groundwater recharge to the adjacent fen will continue to change over time, suggesting that the successional pathway of constructed watersheds is strongly influenced by hydrometeorological conditions within the first decade.