Multi-year Assessment of Water and Energy Exchange From an Oil Sands Reclamation Cover, Fort McMurray, Canada

The oil sands mining industry in Canada has made a commitment to return disturbed areas to an equivalent capability to that which existed prior to mining. In the landscape reconstruction process, ecosystems are created that bare little similarity to the pre-existing boreal forest at the onset of reclamation. However, certification requires successful reclamation, which can in part be evaluated through long-term ecosystem studies. A reclamation site, informally named South Bison Hill (SBH) has had growing season water and energy balances observed since 2003 utilising the eddy covariance technique. SBH was capped with a 0.2 m peat-glacial till mixture overlying 0.8 m of reworked glacial till soil. The site was seeded to barley cultivar (Hordeum spp.) in the summer of 2002 and later planted to white spruce (Picea glauca) and aspen (Populus spp.) in the summer/fall of 2004. Since 2003, the major species atop SBH has changed dramatically and by 2009, an aspen stand predominated with heights in excess of 2 m. Climatically, mean growing season (June–August) temperatures did not vary more than 2°C for a given month, yet precipitation varied considerably as 2004 had 91 mm of rain during June–August while 2008 had 271 mm during the same period. With the exception of a dry 2004, SBH increasingly partitioned energy into latent heat, on average, year after year. At the onset of the measurement, SBH approximately ~55% of net radiation (June–August average) partitioned into latent heat. 2004 had ~47%, yet the evaporative ratio increased consistently thereafter to values ~70% in 2009. Larger latent heat fluxes cannot be attributed solely to climate as increased leaf area index, interception and a longer leaf-out period have increased total evaporation. In most years, evaporation exceeds summer rainfall, utilising snowmelt recharge to sustain evaporation rates. Using natural aspen stands as a comparison, it is expected that water use from the soil cover will continue to increase as the ecosystem ages.