Reginald Somera
Master student
Department of Geology and Geological Engineering
Laval University

Supervised by:

Jean-Michel Lemieux (Regular member)

Research project description

Evaluating Groundwater Contributions to the Carbon and Water Balance of Thermokarst Ponds

Introduction: Evidence of permafrost degradation in Nunavik (Québec, Canada) has been observed over several decades. This is exhibited by increasing subsidence in a number of permafrost mounds, which often results in the formation of thermokarst ponds. While these ponds have traditionally been treated as hydrologically isolated systems, concerns for quantifying their carbon emissions in recent years, warrants a robust understanding of their role in the hydrological cycle. As temperatures are expected to increase in the coming years in Nunavik, a better understanding of the subsurface connections of thermokarst lakes is required. Objectives: To understand the groundwater dynamics of thermokarst ponds, a hydrogeochemical approach will be taken. The objectives of this research are to: 1) interpret lake types at the study site watershed to distinguish thermokarst ponds from those that are not, 2) characterize a geochemical signature of the various lake and pond types in the Tasiapik Valley, and 3) identify subsurface connections between the various lakes and pondsStudy sites: This research will take place in the Tasiapik Valley, located near the Inuit community of Umiujaq, Nunavik, Québec, in the discontinuous permafrost zone. This watershed has been subject to years of geological and geophysical investigations; it has also been previously instrumented with several wells, piezometers, meteorological equipment, and more. An understanding of the broader hydrogeochemical dynamics in the watershed has been established in literature, which will provide a baseline for this study. Material and methods: Hydrological monitoring infrastructure is in place at several locations in the watershed to monitor the subsurface aquifers. As well, some geochemical and isotopic data have previously been collected from subsurface and surficial sources. To meet the objectives, a geomorphological description of all lakes in the valley will be conducted to characterize thermokarst ponds. Then, water samples will be taken from known thermokarst ponds, known lakes of non-permafrost origin, and from the aquifers and aquitard. Once analyzed for their geochemistry and stable isotopes of carbon and water, the geochemical data will be interpreted. These interpretations will be compared to current conceptual models of water fluxes in the valley to better constrain our understanding of subsurface interactions pertinent to thermokarst ponds.Expected results: From this investigation, a carbon isotopic signature of thermokarst ponds in the valley will be identified. This will be linked with the current hydrogeological understanding of the watershed, which will increase insight into the discharges and recharges occurring in thermokarst ponds. We will also provide a more accurate carbon balance of the lakes in this area in relation to greenhouse gas emissions.

Research Site Coordinates

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