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| Titel |
Hydrogeochemical characterisation of groundwater in a small watershed in a discontinuous permafrost zone. |
| VerfasserIn |
Marion Cochand, John Molson, Johannes A. C. Barth, Robert van Geldern, Jean-Michel Lemieux, Richard Fortier, René Therrien |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141013
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| Publikation (Nr.) |
 EGU/EGU2017-4474.pdf |
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| Zusammenfassung |
| Impacts of climate change can already be seen in northern regions. However, the influence of
increasing temperature and permafrost degradation on groundwater dynamics is still poorly
understood. This study aims to improve knowledge on hydrogeological interactions in
degrading permafrost environments using hydrogeochemical characterisation of
groundwater.
This study is being conducted in a small 2-km2 watershed, in a discontinuous permafrost
zone located close to the Inuit community of Umiujaq, on the eastern shore of Hudson Bay in
northern Québec, Canada. Two aquifers are being investigated, an unconfined shallow sandy
aquifer located in the upper part of the watershed, and a deeper confined aquifer in
sands and gravels located below the permafrost mounds. Precipitation, stream and
surface water as well as ice-rich permafrost lenses were also sampled during field
investigations.
Various hydrogeochemical tracers including major ions, water stable isotopes (δ18OH2O and
δ2HH2O), carbon phases (DIC, DOC, POC), their stable carbon isotopes (δ13C) and dating
tracers (radiocarbon, tritium-helium and CFC/SF6) were analyzed. This characterisation has
contributed to further understanding groundwater origin, evolution and residence time in the
watershed.
Preliminary results show that groundwater has a mainly Ca-HCO3 geochemical signature,
typical for young and poorly evolved water. Furthermore, sample mineralisation is low, and is
likely linked to limited bedrock weathering caused by short residence times, slow reaction
rates as well as low levels of dissolved CO2 due to suppressed biological activity in the
catchment. Inter-annual variation of major ions in the deeper aquifer is low. All groundwater
samples have significant tritium concentrations, around 8.5 TU, reflecting modern recharge.
Ice-rich permafrost lenses within the top four meters of permafrost have a water stable
isotope signature close to modern precipitation and groundwater. This indicates that either
recharge conditions of permafrost ice were similar to current conditions, or freeze-thaw
cycles have drawn modern water into the permafrost mounds. The stream appears to be fed
by groundwater exfiltrating at the base of permafrost mounds in the lower part of the
watershed.
Linking this hydrogeochemical characterisation to groundwater and thermal modelling at the
watershed and permafrost mound scales will improve our knowledge on hydrogeological
interactions in degrading permafrost environments. |
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