Growing season energy and water exchange from an oil sands overburden reclamation soil cover, Fort McMurray, Alberta, Canada

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The oil sands mining industry in Canada is required to return mining areas to a land capability equivalent to that which existed prior to mining. During the reclamation process, ecosystems are created that bear little similarity to boreal forests that existed prior to mining. Quantifying the water balance of reclaimed ecosystems is critical in establishing whether there is sufficient moisture for vegetation growth and in the fate of salts, which can be toxic when drawn to the surface or leached out of the covers. At Syncrude Canada Ltd's Mildred Lake mine north of Fort McMurray, Alberta, the surface energy balance was measured atop a reclaimed saline-sodic overburden pile during three growing seasons using eddy covariance. At the onset of the study, the dominant vegetation was foxtail barley, which changed to sweet clover in 2004, and a low-density species mix in 2005, including some aspen and white spruce seedlings. The 2005 growing season was cooler and wetter than 2003 and 2004, and there were seasonal differences in the delivery of precipitation among years. There were distinct differences in the surface energy balance among the study years related to weather, soil moisture, vegetation and stage of growth. Latent heat was the largest consumer of energy in 2003, and mid-day fluxes of sensible and latent heat were approximately equal. In 2004, sensible heat became the dominant flux, primarily due to prolonged dry periods, whereas the wet 2005 season had the greatest latent heat flux density of any year. Ground heat flux declined throughout the growing season and ranged between 3 and 17% of net radiation. Total evapotranspiration was 246, 224 and 283 mm for 2003, 2004 and 2005, respectively. A total derivative analysis of the Penman-Monteith equation reveals the influence of available energy, vapour pressure deficit and surface conductance in controlling evapotranspiration.

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