Water Use Development of an Oil Sands Boreal Forest Reclamation Site During the First 12 Years Following Inception

Following large-scale surface mining operations, large tracts of land in the boreal region of Western Canada need to be reclaimed.  A greater understanding of how these novel ecosystems function and develop with regard to water use is crucial to developing defensible regulatory practices and protocols.  Ecosystem water use is important to consider during construction and assessment in order to ensure adequate moisture availability for the vegetation while minimizing the potential upward migration of saline groundwater.  A 12-year eddy covariance measurement record (2003-2014) is analyzed in order to understand how a reclaimed boreal forest has developed during its initial growth period.  South Bison Hills is a reclaimed oil sands saline-sodic clay shale overburden depot that was topped with 100 cm of glacial till and 20 cm of peat mineral mix.  The site was seeded with barley (Hordeum sp) in 2001 to reduce erosion of the soil cover while boreal tree species, aspen (Populus tremuloides Michx.) and spruce (Picea glauca), were planted in 2004.  Results from this unique long-term record indicate that the reclaimed site underwent step changes in structure and function corresponding to the transition of dominant vegetation cover from grassland to forest.  Leaf area index (LAI) increased from a growing season peak of 0.9 in 2003 to 4.0 in 2014 with step increases in 2008 and 2013.  These step increases are also evident as a decrease in the Bowen ratio and an increase in canopy conductance and evapotranspiration.  This may be explained by the general increase of vegetation cover and transition in the dominant vegetation to trees.  Priestley-Taylor Alpha and decoupling coefficient did not change greatly.  Water use efficiency increased slightly over time until the last 4 years where it has remained relatively constant around 9.3 g CO₂/ kg H₂O.  These trends in water usage and relationships indicate that the ecosystem is not experiencing stress associated with water availability shortages.  Further study on the development of this site under changing and potentially stressful conditions would be invaluable to understanding the resilience of this ecosystem.