Open Collections

Brown, Emily

University of British Columbia

The movement of water from land to the ocean serves as a biogeochemical link between terrestrial and marine systems, through which terrestrial disturbances can impact aquatic systems. Wildfire is a major terrestrial disturbance, however its influence on the ocean is understudied. As anthropogenic pressures change fire regimes globally, this connection must be better understood. Occupying 233,000 km² in British Columbia, Canada, 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. First, 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. Next, I quantified the export of black carbon (BC), a product of biomass burning, in the Fraser River. Seasonal hydrology and landscape topography were important drivers of the timing and quality of BC in the Fraser River. Global estimates of riverine BC export do not consider seasonal hydrology, but this study suggests that inclusion of these factors may close some of the gaps that currently exist in global BC budgets. Finally, 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. Overall, this research found that wildfire has significant influence on water quality and carbon cycling in the Fraser River, and that seasonal hydrology plays an important role in the land-to-ocean mobilization of pyrogenic materials.

Text

2024-12-20

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89961

Oceanography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/