Quantifying water use and rainfall partitioning of dominant tree species in a post-mined landscape in the Athabasca Oil Sands Region, Alberta

Large-scale oil sands mining has caused significant disturbances to forest and wetland ecosystems in the Western Boreal Plains of Northeastern Alberta. Provincial and federal laws mandate restoration of these systems in an attempt to return the landscape to pre-disturbed conditions. Reclaiming these important ecosystems has faced many challenges including re-vegetation of uplands to a state of self-sustainability and productivity. The Nikanotee Fen Watershed in Fort McMurray, Alberta, is a post-mined landscape consisting of a constructed upland-fen peatland connected through runoff and groundwater. The design of these systems’ impacts many components of the ecosystem, including vegetation growth and productivity. Changes in soil moisture dynamics at the site have been attributed to the development in soil and vegetation cover in the upland, leading to significant changes in the ecosystem. The trajectory of reclaimed sites depends on the population of tree species, such as conifers or broadleaf. Development of the tree canopy will lead to increases in precipitation interception and transpiration, ultimately reducing water available for recharge to the adjacent wetland. Characterizing vegetation distribution and composition and their impacts on the water balance may help improve reclamation techniques for future projects. Understanding the functioning of constructed ecosystems and the controls of tree communities on water use will feedback to influence soil moisture dynamics. Soil moisture dynamics dictate water availability for tree growth, recharge and system function, ultimately influencing the uplands ability to support low-lying systems. The objectives of the study are to assess the trends in transpiration of dominant tree species throughout the growing season; quantify throughfall, stemflow and interception of dominant tree species and understand the role they play in intercepting precipitation and its impact on near-surface soil moisture regime and tree water use. The study used a variety of meteorological, hydrological and biometric methods to assess the suitability of dominant tree species used in reclamation projects. To examine the variability in tree water use across the upland, vegetation surveys were completed, and several dominant tree species were instrumented with Stem Heat Balance sap flow sensors to determine individual species’ transpiration rates. Rainfall was partitioned into interception, throughfall and stemflow alongside monitoring soil moisture dynamics and soil water potential to determine the plant available water. Results indicate that tree transpiration is a dominant control on water use at the site averaging 51% of total evapotranspiration and is controlled by water availability. Canopy interception is beginning to play an important role in partitioning growing season rainfall with broadleaf tree species, Populus balsamifera and Populus tremuloides, averaging 25.7% and 28.5%, respectively. Coniferous tree species, Picea mariana and Pinus banksiana, averaged 34.5% and 31.5%, respectively. While vegetation is currently in the early stages of development, rainfall redistribution may become an important consideration when selecting tree communities in reclamation projects