Multi-Year Water Balance Assessment of a Constructed Wetland, Fort McMurray, Alberta

English Abstract:

Surface mining for oil sands strips away the boreal landscape, leaving behind open pits, tailings and overburden piles. While previous reclamation efforts have focused on upland forests, rebuilding wetland systems is less well understood. The success of constructed wetlands is dependent on the supply and storage of water to promote wetland vegetation, peat accumulation and limit elevated salinity. In 2012, Syncrude Canada Ltd. completed construction of the Sandhill Fen Watershed (SFW), a 52-ha upland-wetland system designed to evaluate wetland reclamation strategies. SFW includes upland hummocks, vegetated swales, a water storage pond, fen wetland and an underdrain system. The objective of this study is to develop a water balance for the SFW. A semi-distributed water balance approach was utilized to quantify fluxes and stores within different landscape units. Fresh water was pumped into the system from a nearby lake, and outflow was measured at a weir and sump that collected surface and subsurface drainage. ET was measured using three eddy covariance towers at upland and lowland sites. Precipitation was quantified using tipping buckets, snow surveys, and continuous depth and SWE measurements. 29 near surface wells measured water table fluctuations in along with deep piezometers measuring deeper flow pathways. Results reported range from January 2013 through October 2014 and present the calculation of water balance components in the upland and lowland areas. In 2013, lateral inflow and outflow dominated hydrological fluxes and precipitation was higher than the climatic normal. In 2014, pumps remained mostly off, with vertical fluxes controlling the water balance. Lateral redistribution of water from uplands to wetlands was observed in 2014. Higher ET rates were observed in 2013 than 2014 at upland and lowland locations, with higher ET from the lowland tower in both years. Water table in 2013 fluctuated greatly, while in 2014, water table slowly declined throughout the summer and responded to large rain events in the fall. With 2013 highly managed, and 2014 climatically normal with little artificial controls, comparisons between these years provide insight on how management practices influence the hydrologic dynamics and the overall water balance of the SFW.