The Impacts of Thermal Perturbation and Permafrost Disturbances on Runoff Pathways and Stream Water Quality, Cape Bounty, Melville Island, Nunavut

English Abstract:

The Intergovernmental Panel on Climate Change (IPCC 2013) has projected that continued warming of the Arctic will substantially impact hydrological processes. However, there is limited research examining how runoff dynamics will respond to deepening active layers and permafrost disturbances, specifically active layer detachments (ALDs). Our research addresses this knowledge gap through research carried out at the Cape Bounty Arctic Watershed Observatory (CBAWO) in the Canadian Arctic, where significant localized ALDs occurred in 2007. We used major ion concentrations and stable isotope values (D, 18O and d-excess) as hydrological tracers to determine the relative contribution of different water sources (snowmelt, rainfall, soil water) to hillslope runoff in an undisturbed catchment (Goose) during summer 2012, a season characterized by high air surface temperatures, deep active layer thaw and above normal rainfall. We also investigated the same tracers at this undisturbed catchment and at a recently disturbed catchment (Ptarmigan) at CBAWO from 2006 to 2014 to identify possible longer terms changes in water sources and/or pathway that may have occurred in response to disturbance or interannual variability in climate.

Results indicate that deep active layer thaw increases the storage capacity of for summer rainfall and displaces stored soil water, which affects stream water chemistry as solute-rich waters are moved to the stream. Soil water with the highest solute concentrations are found progressively deeper in the soil profile and at the maximum active layer depth. Hence, the deeper the active layer thaw proceeds, the more likely this water can be moved to the surface following displacement by rainfall. ALDs create new channels for surface flow where meteoric water interacts with exposed solute-rich ground ice. This routing of water through new exposed permafrost soil directly impacts the variability and composition of ion concentrations in stream water. Hydrochemical variability (i.e. greater variations in ion concentrations) appears to increase over time from the onset of the disturbance. Consistent δD and δ18O in stream waters suggest that differences in water pathways, not water sources, may be the dominant control in stream water ion concentration between undisturbed and disturbed catchments.