Investigating Aerobic and Anaerobic Methane Oxidation in Oil Sands Tailings Facilities

Abstract

Oil remains a vital economic driver, fueled by a growing global population and rising resource consumption. Canada holds the third-largest proven oil reserves in the world, with much of it in the Alberta Oil Sands Region (AOSR). Surface mining in the AOSR produces tailings, a mixture of water, sand, silt, clay, and residual bitumen, which are stored in large tailings facilities covering ~300 km2. These facilities can be a regional source of methane that is generated through microbial methanogenesis in the anoxic fluid fine tailings (FFTs). While methane oxidation can mitigate emissions in natural systems, its occurrence and extent in tailings systems are poorly constrained. This thesis investigated methane production and consumption at two AOSR tailings facilities (Site A and Site B) by using dissolved methane concentration trends, stable carbon isotope analysis, and phospholipid fatty acid (PLFA) biomarkers for methanotrophic activity. Across both sites, dissolved methane [CH4] in the water column was low but increased sharply with depth across the interface boundary and in the FFT, exhibiting saturated conditions. The methane concentration revealed a consumption profile upwards across the FFT-water interface, suggesting methane loss by either aerobic oxidation and/or transport mechanisms. Isotope data (δ13C-CH4 and δ13C-CO2) revealed a multi-pathway system for methane production, with limited fractionation evidence for methane oxidation. PLFA analysis of pooled biomarkers (C16:1 and C18:1) showed increased abundance upwards at the interface and into water column. Isotopic signatures of these PLFAs suggested some relative methanotrophy at Site A due to the depletion of C16:1 relative to C18:1 and other PLFAs, but strong methane-derived carbon incorporation at Site B. These findings demonstrate site-specific and spatial variability in the geochemical conditions that may be controlling aerobic methane oxidation within these systems and limiting methane release into the atmosphere.