Owens, Philip N.

Landscape level disturbances occur in nearly every watershed throughout the globe, and as the climate changes, these disturbances will continue to have a significant impact on terrestrial and aquatic ecosystems. Wildfire, timber harvesting, and agricultural expansion are only a few of these disturbances, but each uniquely impacts the sediment regime. While sediment is a necessary and beneficial input to streams and rivers, it also can have negative impacts on the aquatic ecosystem because it can carry contaminants and also be physically detrimental when it settles, clogging spawning habitat. All of these disturbances have occurred historically and in the present in the Nechako River Basin (NRB), a large, regulated watershed in north-central British Columbia, Canada. In the NRB, chinook and sockeye salmon and the Nechako White Sturgeon are species that have been declining in population, in part due to the clogging of their habitat by sand and fine sediment. One way to determine sources of sediment is by using the sediment fingerprinting technique, whereby sediment samples and samples from potential sources are collected and analyzed for a series of physical or biogeochemical properties, and the proportion of sediment coming from each potential source is identified using an unmixing model. After catastrophic wildfires in 2018, research was undertaken to determine the spatial and temporal contamination of soils and sediment by polycyclic aromatic hydrocarbons (PAHs), to determine if burned areas were contributing more sediment than unburned areas to tributaries and the Nechako River mainstem, and to determine the suitability of PAHs as a novel fingerprint. The results found that concentrations of PAHs in the burned soils were elevated immediately post-wildfire, but decreased significantly in subsequent years, and concentrations in sediments were very low. While PAHs were deemed to be non-conservative properties, unmixing modeling using colour showed that burned sources were an important contributor to the tributaries, but less so in the mainstem Nechako River. Agriculture is an important and growing industry in the NRB and is also an important source of sediment. Results from fingerprinting research undertaken in Murray Creek, an important watershed due to its proximity to spawning habitat, found that agriculture was the primary source of sediment in the basin, though channel banks were also important. While the intention was to use compound specific stable isotopes of long chain fatty acids to more specifically pinpoint agricultural fields that were contributing more sediment to the watershed, this semi-novel tracer was unable to discriminate between C3 plant types on a large scale. Taking the entire disturbance regime of the NRB into account, a broader scale fingerprinting study found that sources of sediment are tributary specific, though banks and agriculture were consistently most important. This study also identified that the predicted shift to a rain dominated watershed and earlier freshet will lead to increased potential for erosion from various sources, and that increased incidence of wildfire followed by heavy precipitation may increase sediment loads. Therefore, a number of management changes are suggested, including improving farming practices, post-wildfire landscape rehabilitation, and altering water release practices.

Hudson Bay, a vast inland sea in northern Canada, receives the highest average annual freshwater from the Nelson River system among all other contributing rivers. A rapidly changing climate and flow regulation from hydroelectric developments alter Nelson River streamflows timing and magnitude, affecting Hudson Bay’s physical, biological, and biogeochemical state. Despite recent developments and advances in climate datasets, hydrological models, and computational power, modelling the Hudson Bay system remains particularly challenging. Therefore, this dissertation addresses crucial research questions from the Hudson Bay System (BaySys) project by informing how climate change impacts variability and trends of freshwater-marine coupling in Hudson Bay. To that end, I present a comprehensive intercomparison of available climate datasets, their performance, and application within the macroscale Variable Infiltration Capacity (VIC) model, over the Lower Nelson River Basin (LNRB). This work aims to identify the VIC parameters sensitivity and uncertainty in water balance estimations and investigates future warming impacts on soil thermal regimes and hydrology in the LNRB. An intercomparison of six climate datasets and their equally weighted mean reveals generally consistent air temperature climatologies and trends (1981–2010) but with a prominent disagreement in annual precipitation trends with exceptional wetting trends in reanalysis products. VIC simulations forced by these datasets are utilized to examine parameter sensitivity and uncertainties due to input data and model parameters. Findings suggest that infiltration and prescribed soil depth parameters show prevailing seasonal and annual impacts, among other VIC parameters across the LNRB. Further, VIC simulations (1981–2070) reveal historical and possible future climate change impacts on cold regions hydrology and soil thermal conditions across the study domain. Results suggest that, in the projected climate, soil temperature warming induces increasing baseflows as future warming may intensify infiltration processes across the LNRB. This dissertation reports essential findings in the application of state-of-the-art climate data and the VIC model to explore potential changes in hydrology across the LNRB’s permafrost gradient with industrial relevance of future water management, hydroelectric generation, infrastructure development, operations, optimization, and implementation of adaptation measures for current and future developments.