Ryan Lalonde | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Ryan Lalonde. This seminar is open to the general public to attend.

Thesis Topic: Growing Woody Plants in Oil Sands Fine Tailings
MSc with Drs. Brad Pinno and Derek MacKenzie.

Seminar 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 hazards 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, 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 NO 3 – 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, 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. Our results found that there were no differences between the biochar treatment and the non-biochar treatments.