Water, Energy and Carbon Balance Research: Recovery Trajectories for OIL SANDS Reclamation and Disturbed Watersheds in the Western Boreal Forest.

The Oil Sand Region (OSR) of North-Central Alberta exists within the sub-humid climate of the Boreal Plains ecozone, which operates within a slight long-term moisture deficit regime. Certain operators have created watersheds that now contain wetlands, whose long-term success ultimately depend upon water being sustained from uplands. However, much recent work in the Plains Region of the Western Boreal Forest suggests that on average it is the wetlands that supply moisture for the productivity of upland forests. Thus, water use of reclaimed forests is going to be a critical factor determining not only the sustainability of these system but also adjacent wetlands. Water Use Efficiency (WUE), which links photosynthesis (Gross Ecosystem Production (GEP)) with water use (Evapotranspiration (ET)), provides a useful metric to compare ecosystems and evaluate their utilization of resources. 41 site years of total growing season water and carbon flux data over 8 sites (four reclamation, four regeneration) were evaluated using eddy covariance micrometeorological towers. WUE shows clear discrimination among ecosystem types as aspen stands assimilate more carbon per unit weight of water than conifers. WUEs also change with time as ecosystems become more effective at transpiring water through plant pathways compared with bare-soil evaporation, which allows an assessment of ability to limit water loss without carbon uptake. In addition, clonal rooting systems allow aspen forests to recover quicker after disturbance than reclamation sites in terms of their WUE. For reclamation sites, there is considerable variability in GEP and ET associated with vegetation establishment, with enhanced ET losses over-riding any significant changes in C uptake, suggesting that long-term mine water management must consider ecosystem pathways if down-gradient wetlands and end of pit lakes are to be sustained.