Seasonal cryogenic processes control supra-permafrost pore water chemistry in two contrasting Cryosols

• Published in: Geoderma
• Main Authors: Fouché, Julien, Bouchez, Camille, Keller, Catherine, Allard, Michel, Ambrosi, J. P.
• Other Authors: Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème (UMR LISAH), Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro Montpellier, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Centre d'Etudes Nordiques (CEN), Université Laval Québec (ULaval), Financial support was provided by CNRS INSU Chantier Arctique, the Arctic Net Network of Centers of Excellence, and the Arctic Development and Adaptation on Permafrost in Transition (ADAPT) program funded by the Natural Science and Engineering Research Council of Canada (NSERC).
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Lysimeters; Active layer; Arctic permafrost; Soil solution chemistry; Tundra; Thaw front deepening; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; [SDE]Environmental Sciences; [SDV.SA.SDS]Life Sciences [q-bio]/Agricultural sciences/Soil study; Arctic; Nunavik; Canada; Salluit; Ice; permafrost
• Online Access: https://insu.hal.science/insu-03274382; https://insu.hal.science/insu-03274382/document; https://insu.hal.science/insu-03274382/file/Fouche%20et%20al.,%202021_Geoderma.pdf; https://doi.org/10.1016/j.geoderma.2021.115302

International audience Over the last decades, Arctic landscapes have experienced intense warming leading to permafrost degradation and rapid ecosystem changes. Active layer thickening, widespread melting of ground ice and thermo-erosion have affected the mobilization of organic and mineral elements. While the carbon and nitrogen cycles are intensively studied, the soil weathering has been less documented. In the present study, we monitored the chemistry of soil capillary and gravitational pore waters, rainfall and stream waters daily during the growing season in two experimental sites under tussock tundra vegetation in the low-Arctic region, in Salluit (Nunavik, Canada). We aimed to investigate the seasonal thaw controls on the evolution of concentrations of major organic and inorganic elements in the active layer (i.e., seasonally thawed surface layers) of two permafrost soils (Cryosols) differing in parental materials: an ombrotrophic bog (i.e., Histic Cryosol) and post-glacial marine sediments continuously waterlogged (i.e., Turbic Cryosol). In the Histic Cryosol, the electrical conductivity was <100 µS cm−1 and Cl− and Na+ were the dominant soluble ions originating from atmospheric depositions. In the Turbic Cryosol, decarbonated in the first 40 cm, Ca2+ and Mg2+ were the dominant soluble ions in the capillary water reflecting the dissolution of soil minerals, while Cl− and SO42− dominated in gravitational water, illustrating inputs from uphill. In the two soils, Ca2+ and Mg2+ concentrations as well as Mg/Na and Ca/Na increased with depth. Along summer, the soil pore water chemistry evolved with thaw front and water table depths in the two sites. Particularly in the Histic Cryosol, electrical conductivity, solute concentrations, Mg/Na and Ca/Na ratios increased with the thaw front deepening. Our observations suggest that the active layer thickening and increasing supra-permafrost flow contribution, expected to increase with Arctic warming, could lead to a shift in chemistry of pore waters in organic and ...