As conventional oil reserves deplete and more efficient refining technologies emerge, the use and transportation of heavy fuel oils such as dilbit is rising. Despite the risk of accidental dilbit spills, the fate and behaviour in aquatic systems is largely unknown. The objective of this thesis was to develop new approaches and insights to directly address knowledge gaps surrounding the fate and behaviour of diluted bitumen (dilbit) in freshwater systems.
During the summers of 2017 and 2018, a large-scale collaborative field study was conducted at the International Institute for sustainable Development’s – Experimental Lakes Area (IISD-ELA), a world-renowned freshwater research station located in Northwestern Ontario, Canada. First, two tank-based dilbit spill simulations were carried out at oil:water ratios of 1:8000 and 1:800 v/v (Chapter 2). Here I examined the physical fate and behaviour of dilbit spilled onto the water’s surface for 11 days. In this chapter I provide, for the first time, experimental evidence of dilbit physically sinking after 8 days of environmental weathering in land-based tanks containing natural lake water. Building on the findings of chapter 2, the remaining four chapters focus on a series of 70-d long experimental dilbit spills carried out in limnocorrals (10 m diameter x 1.5 m depth) installed directly in a freshwater lake. Chapter 3 provides, to our knowledge, the most detailed temporal account to date of dilbit submergence in freshwater at multiple oil:water ratios. In Chapter 4 I provide the rates at which over 100 individual hydrocarbons are depleted over time from the dilbit slicks and apply diagnostic ratios to postulate which weathering processes are responsible for the observed depletions. As predicted, evaporation, dissolution, and photooxidation are prominent weathering processes whereas biodegradation is not. I then describe both the short- and long-term behaviour of these compounds as they partition from the dilbit slick to the air, water, and sediments of the limnocorrals in Chapter 5. While the concentrations of polycyclic aromatic hydrocarbons (PAHs) were elevated in the water columns of each treatment, they were orders of magnitude lower than concentrations that pose a toxicological risk. The same was true for all sediment samples except those that were in direct contact with sunken dilbit. This suggests that the major threat of dilbit spills from an ecotoxicological point of view is the dilbit-laden sediments produced by submergence. Finally, I demonstrated the successful application of a mass transfer model to predict the dissolution trends of the highly toxic benzene, toluene, ethylbenzene, and o,m,p-xylene (BTEX) compounds following the dilbit spills. In Chapter 7 I detail the implications and conclusions for each chapter and the thesis as a whole. I also describe areas where future research is needed. In the end, the conclusions of this thesis were: 1) dilbit has the propensity to sink following spills in freshwater, 2) prominent weathering processes include evaporation, dissolution, and photooxidation, 3) our regression design allowed for important relationships between contamination and spill size to be realized, 4) sunken dilbit poses a toxicological threat to aquatic biota, and 5) mass transfer models can accurately predict BTEX dynamics in the water column following a dilbit spill.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/42576 |
| Date | 26 August 2021 |
| Creators | Stoyanovich, Sawyer |
| Contributors | Blais, Jules |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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