520, ch. de la Côte-Sainte-Catherine Building
520, ch. de la Côte-Sainte-Catherine
Université de Montréal
Permafrost of arctic environments is well-known for its important role in the long-term storage of organic carbon. Perturbation of this vulnerable reservoir may have major consequences on the global carbon cycle. Thermal-erosion gullying is one of the most rapid permafrost degradation processes. This is initiated by concentrated infiltration of runoff water into sinkholes, which evolve into tunnels expanding into the permafrost, especially into ice-wedge networks. The gullies are created by the collapse of the roof of these tunnels and induce major changes in landscape morphology. A substantial quantity of material is exported as a gully forms and expands, leading to a significant reorganization of the hydrological network. Nutrients accumulated and stored in permafrost for centuries are suddenly released and their mobilization has a direct influence on the water chemistry of the gully stream.
The objective of this study is to quantify the spatial and temporal variation in organic carbon, nutrients and suspended sediment fluxes along a thermal erosion gully of an arctic ice wedges polygon field of Bylot Island, NU.
To investigate those variations, daily water sampling, associated with water temperature, electrical conductivity (EC) and velocity measurements, were conducted from June 15th 2017 to July 30th 2017 and will be conducted in summer 2018 at 13 sites along an active thermal-erosion gully. Water samples were also collected three times a day at the gully outlet during this same period to explore the temporal dynamics of daily matter exports. Subsequent laboratory analyses include dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) concentrations, ion concentrations (including inorganic N), isotopes, and DOM fluorescence. These analyses will provide a specific and precise characterization of the stream chemistry throughout the flow season.
As is the case for typical permafrost hydrologic environments, it is hypothesised that a first pulse of carbon (especially DOC) associated with the snowmelt flow will be observed. However, subsequent lower DOC fluxes are expected as the gully head retreats and as the active layer of unstabilized gully margins thaws and collapses into the channel. A delay between the flow peak and the suspended sediment peak was observed as a result of the limited availability of sediments, induced by the presence of persistent ice and snow in several sections of the channel bed.
By a rigorous daily analysis of carbon, nutrients and sediment fluxes, this study will expand our knowledge of the concrete impacts of permafrost degradation by thermal-erosion gullying and will quantify carbon exports through this degradation process.