Canadian permafrost stores large pools of ammonium and optically distinct dissolved organic matter

• Published in: Nature Communications
• Main Authors: Fouché, Julien, Christiansen, C., T, Lafrenière, M., J, Grogan, P., Lamoureux, S., F
• Other Authors: Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème (UMR LISAH), Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, 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), Queen's University Kingston, Canada, Center for Permafrost (CENPERM), Department of Geosciences and Natural Resource Management Copenhagen (IGN), Faculty of Science Copenhagen, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH)-Faculty of Science Copenhagen, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH), This research was funded by the Natural Sciences and Engineering Research Council (NSERC) Discovery Frontiers ADAPT program, the ArcticNet Network of Centres of Excellence, and NSERC Discovery grants to
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: ammonium; chemical composition; dissolved organic carbon; dissolved organic matter; permafrost; watershed; [SDV]Life Sciences [q-bio]; [SDV.SA.SDS]Life Sciences [q-bio]/Agricultural sciences/Soil study; Arctic; Canada
• Online Access: https://hal.inrae.fr/hal-02944592; https://hal.inrae.fr/hal-02944592/document; https://hal.inrae.fr/hal-02944592/file/2020_nature_fouche.pdf; https://doi.org/10.1038/s41467-020-18331-w

International audience Permafrost degradation may lead to mobilization of carbon and nutrients and enhance microbial processing rates of previously frozen organic matter. Although the pool size and chemical composition of dissolved organic matter (DOM) are fundamental determinants of the carbon cycle in Arctic watersheds, its source within the seasonally thawing active layer and the underlying permafrost remains largely uncharacterized. Here, we used 25 soil cores that extended down into the permafrost from nine sites across Arctic Canada to quantify dissolved organic carbon (DOC) and nitrogen stocks, and to characterize DOM optical properties. Organic permafrost stores 5–7 times more DOC and ammonium than the active layer and mineral permafrost. Furthermore, the permafrost layers contain substantial low molecular weight DOM with low aromaticity suggesting high biodegradability. We conclude that soil organic matter stoichiometry and cryogenic processes determine permafrost DOM chemistry, and that thawing will mobilize large amounts of labile DOC and ammonium into Arctic watersheds.