MSc EOAS Defense by
Emily Brown
Influence of fire on aquatic biogeochemistry from the Fraser River to the Salish Sea
The movement of water from land to the ocean serves as a major biogeochemical link between terrestrial and marine systems, through which terrestrial disturbances can impact freshwater systems and coastal oceans. Wildfire is a major terrestrial disturbance, however its influence on the ocean is understudied. As anthropogenic pressures change fire regimes globally, it is important that this connection is better understood. The Fraser River’s basin has significant wildfire history, and the Fraser River has major influence on its receiving waters of the Salish Sea, making this an ideal system in which to investigate the influence of fire on aquatic biogeochemistry from freshwater to the ocean. In Chapter 2, I assessed cumulative impacts of wildfire on Fraser River water quality using historical water quality and fire data. Wildfire in the Fraser River basin explained up to 16.3 % of variance in water quality, and fires burning closer to major waterways had immediate influence on water quality, while farther away wildfires had a delayed influence on water quality. Delayed post-fire increases in the concentrations of water quality variables of importance in the Salish Sea were measured, with implications for coastal ocean productivity and contamination. In Chapter 3, I quantified the export of black carbon (BC), a product of biomass burning, in the Fraser River, and investigated environmental controls on the timing and quality of BC export from the Fraser River basin. Seasonal hydrology and landscape topography were important drivers of variation in the quantity and composition of BC in the Fraser River. Global estimates of riverine BC export do not consider seasonality or hydrology, but this study suggests that inclusion of these factors may close some of the gaps that currently exist in global BC budgets. In Chapter 4, I assessed potential fates of BC as it transits from the Fraser River basin to the Salish Sea. The fate of BC in the ocean is not well understood and is a key knowledge gap in BC cycling and carbon cycling. I found that processes including dilution, photodegradation, biodegradation, and sedimentation act on BC in the marine environment.
Location: ESB 5104
Examining committee:
Brian Hunt (supervisor)
Mark Johnson (committee member)
Tara Martin (external examiner)