Thesis Defence: Quantification of sediment and organic-carbon fluxes in a boreal sub-arctic river (Dezadeash River, Southern Yukon, Canada)

Angelina Nikolaeva, supervised by Dr. Alessandro Ielpi, will defend their thesis titled “Quantification of sediment and organic-carbon fluxes in a boreal sub-arctic river (Dezadeash River, Southern Yukon, Canada)” in partial fulfillment of the requirements for the degree of Master of Science in Earth and Environmental Sciences.

An abstract for Angelina Nikolaeva’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

Abstract

Rivers act as global agents in transporting sediment, including organic carbon (OC) in various forms, and connect upland environments to oceans. As climate change transforms northern environments, Arctic rivers therein have been subject to substantial change in their geomorphic and biogeochemical processes. However, owing to the remote nature of (sub-)Arctic watersheds, limited studies have attempted to directly quantify river mass fluxes in relation to their morphodynamics. It is therefore necessary to develop novel methodologies to estimate sediment and carbon budgets using site-specific measurements that can be upscaled to predict watershed-wide dynamics. This study aims to estimate sediment and total OC fluxes in the meandering Dezadeash River, which is found in the sub-Arctic region of southern Yukon, Canada. Two methodological approaches are presented herein: one based on timelapse photogrammetry and soil total-OC geochemistry, and one on hydrology and aqueous geochemistry. The photogrammetric analysis revealed that over the observed timespan (1948–2023), the migration rate of the Dezadeash River increased, possibly in response to changes in permafrost and vegetation coverage along its floodplain. This analysis also revealed that the Dezadeash River floodplain exported 0.44(-0.35)(+1.76) kT of total OC per year over the investigated period. In contrast, the hydrologic methodology determined a yearly total OC export of 4.68(-1.42)(+4.45) kT yr 1, as well as yearly fluxes for total suspended sediment and total dissolved sediment of, respectively, 28.13(-20.66)(+80.66) kT and 112.38(-42.65)(+66.85) kT per year. The difference in OC export between the two approaches reveals different contributions from floodplain and upland catchments, as well as possible sensitivity to the timescales over which these metrics are integrated. Overall, this research establishes a novel methodological approach to estimate biogeochemical fluxes along remote watersheds, which may serve to inform broader-scale carbon budgets under contexts of ongoing and future climatic change.