9:00 am - 10:00 am
Event details: 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 Xuehui (Chris) Sun. This seminar is open to the general public to attend via Zoom:
Thesis Topic: Effects of non-segregated tailings, nitrogen, phosphorus and elemental sulphur on growth of plants in oil sands reclamation soils
Seminar Abstract: Oil sands mining in northeastern Alberta, Canada, has disturbed large areas of the northern boreal forest. These disturbed areas must be restored to pre-disturbance levels after mining closure. During the process of bitumen extraction, large volumes of mine tailings are produced and need to be reclaimed. The extraction of bitumen is carried out with recycled hot water containing NaOH and, as a result, the oil sands tailings have high pH and elevated levels of Na+, which are harmful to plants. To accelerate tailings consolidation, other chemicals may be added, which further affect tailings chemistry and can potentially contribute to their phytotoxicity. To alleviate this concern, Canadian Natural Resources Limited (CNRL) has developed novel tailings technologies to consolidate fine tailings and produce non-segregated tailings (NST) using thickeners in combination with CO2. However, NST may still have negative effects on plants. During oil sands reclamation, a layer of forest mineral soil mix (FMM), that is salvaged from upland boreal forest sites, or peat mineral mix (PMM), that is stripped from the peatlands, are placed on the top of overburden materials and coarse tailings sands before revegetation. The pH of the topsoil may increase due to the high pH of the underlying layers and affect the revegetation efforts. In the present thesis project, two studies have been conducted to address some of the above concerns. In the first study, I examined the effects of soil pH and elemental sulphur on growth and physiological parameters in Saskatoon serviceberry (Amelanchier alnifolia) and beaked hazelnut (Corylus cornuta) seedlings. I found that elemental sulphur was effective in lowering soil pH. However, the addition of elemental sulphur to the pH 5.7 lowered the soil pH to very low levels and impaired growth and physiological performance of Saskatoon serviceberry and beaked hazelnut plants. Saskatoon serviceberry and beaked hazelnut seedlings growing in the soil of pH 8.5 did not substantially benefit from the addition of 5 and 25 g kg-1 elemental sulphur to the soil. The results demonstrated that 5 g kg-1 was not sufficient to lower soil pH to the desirable neutral to slightly acidic level, and 25 g kg-1 was too high and resulted in excessive soil acidity. In the second study, I examined the effects of nitrogen and phosphorus levels in the NST-affected soil on growth and physiological parameters of trembling aspen (Populus tremuloides) and white spruce (Picea glauca) seedlings. I found that the growth and physiological responses of seedlings were superior in the mixture of NST and FMM compared with NST and PMM. Trembling aspen was more affected by NST than white spruce and benefited more from the higher N and P soil levels. The results of both studies may be helpful in addressing some of the important concerns and improving oil sands reclamation efforts.