Revegetation of Tailings Sand Without a Soil Cover in the Alberta Oil Sands

Jay Woosaree
Bruce Anderson
Resource Date:
Page Length

Reclamation in the oil sands in Alberta is a high priority and can be challenging. Suncor Energy is in the process of reclaiming one of its consolidated tailings (CT) ponds (Pond 5). The CT is being capped with a layer of petroleum coke to accelerate the creation of a trafficable surface, and then with tailings sand. As these CT dewater, a temporary reclamation vegetative cover over the tailings sand was needed to stabilise the sand against water and wind erosion prior to final reclamation. Criteria for native plant species selection for the cover crop were based on their ability to grow rapidly, be drought and possibly salt tolerant and provide a vegetation cover for at least three years. This study aims to assess the potential of some native grasses to directly grow and stabilise tailings sand and to determine nutritional requirements for optimal growth. The study was initiated in 2010 (Woosaree et al., 2010). Year 2011 provided an opportunity to study how well these native species continued to adapt and grow on direct tailings sands and if the underlying coke layer from the tailings ponds, presented any limitation to plant growth and survival. Results indicated higher aboveground biomass and percent cover for the native grass seed mix than June grass or fringed brome grass alone. The higher biomass is most likely due to the nature of the species, with June grass being a low stature species compared to the native mix. Fringed brome plants were sparse within the plots, most likely as a result of low emergence in 2010. The greatest benefit of an organic amendment such as alfalfa pellet application appeared to be moisture retention, giving the seeded species a head start to germinate. Root depths measured ranged from 11 to 26 cm allowing the plants to tap deeper into below ground moisture. Plants in the control plots had less vigour, yet were still surviving despite no fertilisers or pellets being applied. A fertiliser rate above 50 kg N/ha did not have a positive effect on the plants. Soil available nitrogen measured in the fall of 2011 was below detectable level. However, plant tissue analysis showed total nitrogen of 1–2.3%. Atmospheric deposition of N and microbial association with the plant roots could contribute to N availability. Microbial analysis revealed six nitrogen fixing bacteria and one plant growth-promoting bacteria to be associated with the native species roots. This study will help to select suitable species for inclusion in seed mixtures for final reclamation.