Developing and assessing efficient hydrocarbon bioremediation strategies for cold-temperature soils and sediments: Two case studies in northern Canada.

Petroleum hydrocarbon contamination is extensive in northern Canada and very damaging to its fragile environment. Bioremediation is a cost-efficient and sustainable approach for onsite treatment at many contaminated sites in the North. The thesis examines the efficacy of bioremediation of petroleum hydrocarbon-contaminated soils by nutrient biostimulation, under different environmental conditions. The first chapter of this thesis investigated the role of temperature (7 oC, -5 oC, and freeze-thaw cycles) and biostimulation regimes on the bioremediation of Arctic diesel in a northern soil from the village Kangirsuk in Nunavik (Northern Quebec). Several metrics were used to study these trends in a microcosm study: hydrocarbon levels, alkane monooxygenase (alkB) and 16S rRNA gene and transcript abundance (qPCR), the community structure (16S rRNA gene and transcript sequencing), and several metrics derived from the 16S sequencing data such as α-diversity (Faith’s phylogenic diversity) and representative metabolic pathways (PiCrust2). The key conclusions derived from all these analyses were as follows: Whilst degradation extents in that timescale were small at constantly frozen conditions, some indicators (qPCR, PiCrust2) showed bacteria capable of degrading diesel were appearing. Both the freeze-thaw and the 7 oC systems had high degradation, but whilst nutrients had a large role in degradation in the summer (7 oC), the main determinant for bioremediation in the freeze-thaw was concluded to be access to hydrocarbons. Pseudomonodales order were overwhelmingly correlated with hydrocarbon degradation. The study also indicates nutrient addition could cause osmotic toxicity and bioremediation treatability studies should follow a plan that maximizes treatability extents whilst minimizing additions to the site. The second chapter of this thesis studied the role of temperature (5 oC, 0-1 oC), oxygen, and nutrient addition on bioremediation of F3 hydrocarbons in three northern sediments in a water management pond for the water treatment plant of a diamond mine in the Northwest Territories. This was studied in a microcosm study where hydrocarbon levels were tracked and related to site microbiology (16S rRNA gene qPCR/sequencing) and physio-chemical properties. The key findings were that degradation slowed at around 700-1000 ppm, that degradation could occur at winter temperatures but much slower than in the summer, and that the nickel and chromium levels across the three sites were correlated with inhibiting hydrocarbon bioremediation and microbial growth. Thus, the thesis analyzed and illustrated some key trends in hydrocarbon bioremediation in two separate and contrasting case studies in northern Canada

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