Growing Woody Plants in Oil Sands Fine Tailings
Lalonde, R. 2019.
Abstract
Fine fluid tailings (FFT) are a by-product created during the extraction of bitumen from
oil sands mining operations. Over 975 million m3 of FFT are currently being stored in tailings
ponds in the Athabasca oil sands region (AOSR) of Alberta, Canada. These tailings cause
industrial and environmental concerns due to storage and management issues, and potential
hazard to the surrounding environment. A potential solution for managing these tailings ponds is
to dewater them through technologies such as centrifugation and use the dewatered FFT cake as
a subsoil material in reclamation. The FFT would need to be capped with suitable soil and depth
in order to support plant growth and meet reclamation requirements. The optimal minimal
capping material and depth are not well studied.
In the first study (Chapter 2), a 16-week greenhouse study was conducted to assess
whether FFT cake and caps of various mixes and depths (0, 5, 10 and 20 cm depth) of forest
floor mineral mix (FFMM) and peat mineral mix (PMM) would support plant growth of
trembling aspen (Populus tremuloides - native broadleaf tree) and beaked willow (Salix bebbiana - native broadleaf shrub). S. bebbiana had a greater survival rate (100%) when grown
directly in FFT cake compared to P. tremuloides (16.7%). The same S. bebbiana seedlings had
10 times higher foliar concentrations of Al, Cr and Ti compared to any other treatments. Plants
grown directly in FFT cake were negatively impacted by high water content and low nitrate
supply rates. S. bebbiana can tolerate and survive in these high metal, saturated soil, and low
NO3- conditions while P. tremuloides could not. However, adding any soil cap significantly
increased aboveground biomass for both species. The capping material that best supported plant
growth was a mixture of FFMM and PMM, although differences among soil types were not
large. The 5 cm capping depths for PMM and FFMM in P. tremuloides had significantly reduced aboveground biomass, likely caused by the FFT cake's poor draining which resulted in saturated
soils. Results from this study show that capping FFT cake at a minimum depth of 10 cm
substantially improves woody plant growth, and S. bebbiana and P. tremuloides are potentially
suitable species for tailings reclamation.
In the second study (Chapter 3), biochar was added to one of the capping treatments (1:1
ratio of PMM and FFMM at 10 cm depth over FFT cake) to determine if it had any positive
effect on plant growth. The results found that there were no differences between the biochar
treatment and the non-biochar treatments.
