Effects of plant species composition and nutrient addition ratio on the efficacy of bioremediation of simulated freshwater oil spills by engineered floating wetlands

The transportation of crude oil across Canada leads to a risk of accidental spills into freshwater environments. Conventional cleanup methods can exacerbate the negative effects of oil spills and delay ecosystem recovery. A less-invasive alternative is the use of engineered floating wetlands (EFWs) – vegetated platforms which promote microbial colonization and biofilm formation in their underwater root-zones – to enhance the biodegradation of spilled oil. This thesis assessed the efficacy of EFWs for removing oil-derived polycyclic aromatic compounds (PACs) from fresh water and the effects of plant species composition and nutrient addition carbon to phosphorus (C:P) ratio on EFW function. Twenty-six (26) ~1550 L mesocosms containing EFWs were exposed to equal-volume spills of water-accommodated fraction (WAF) produced by weathering conventional heavy crude oil (CHV). The EFWs were either planted with a different composition of Typha sp., Carex atherodes, and C. lasiocarpa or had an even species composition and were amended with slow-release fertilizer to achieve a target C:P ratio, based on the carbon content of the WAF. Concentrations of PACs decreased rapidly, with 96.8% of compound classes across the mesocosms declining to baseline concentrations within the first 10 days of the 96-day exposure. There was no evidence to indicate that EFWs had an appreciable effect on PAC removal or that changes in plant species composition or C:P ratio affected EFW function. There were no consistent significant effects of WAF, plant presence, plant species, or C:P ratio on the activity of microbial biofilm or the composition and diversity of the prokaryotic and eukaryotic microbial communities in the root-zone. Results were confounded by low initial PAC concentrations, possibility of PAC sorption to mesocosm plastic, flaws in sample event timing, and tadpole grazing on root biofilm; future research which addresses these experimental limitations is required to support the incorporation of EFWs into freshwater oil spill ...