Lowering water table reduces carbon sink strength and carbon stocks in northern peatlands

• Published in: Global Change Biology
• Main Authors: Kwon, Min Jung, Ballantyne, Ashley, Ciais, Philippe, Qiu, Chunjing, Salmon, Elodie, Raoult, Nina, Guenet, Bertrand, Göckede, Mathias, Euskirchen, Eugénie, S., Nykänen, Hannu, Schuur, Edward, A. G., Turetsky, Merritt, R., Dieleman, Catherine, M., Kane, Evan, S., Zona, Donatella
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), University of Hamburg, University of Montana, AgroParisTech, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Max Planck Institute for Biogeochemistry (MPI-BGC), Max-Planck-Gesellschaft, Institute of Arctic Biology, University of Alaska Fairbanks (UAF), University of Eastern Finland, Northern Arizona University Flagstaff, University of Colorado Boulder, University of Guelph, USDA Forest Service Rocky Mountain Forest and Range Experiment Station, United States Department of Agriculture (USDA), Michigan Technological University (MTU), University of Sheffield Sheffield, San Diego State University (SDSU), National Science Foundation, Grant/Award Number: DEB-1026415, DEB-1636476 and LTREB-2011276, the NSF Long-Term Research in Environmental Biology Program (NSF LTREB 2011276)., Hannu Nykänen acknowledges Atmosphere and Climate Competence Center (Academy of Finland; 337550), ANR-10-LABX-0100,VOLTAIRE,Geofluids and Volatil elements – Earth, Atmosphere, Interfaces – Resources and Environment(2010), ANR-16-CONV-0003,CLAND,CLAND : Changement climatique et usage des terres(2016), ANR-18-MPGA-0007,POMELO,Evaluation du modèle orienté processus - lien avec les observations(2018), European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: carbon flux; carbon stock; drainage; high latitude; land surface model; manipulation experiment; permafrost thaw; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Arctic; Climate change; permafrost
• Online Access: https://hal.science/hal-03775356; https://hal.science/hal-03775356/document; https://hal.science/hal-03775356/file/Global%20Change%20Biology%20-%202022%20-%20Kwon%20-%20Lowering%20water%20table%20reduces%20carbon%20sink%20strength%20and%20carbon%20stocks%20in%20northern.pdf; https://doi.org/10.1111/gcb.16394

International audience Peatlands at high latitudes have accumulated >400 Pg carbon (C) because saturated soil and cold temperatures suppress C decomposition. This substantial amount of C in Arctic and Boreal peatlands is potentially subject to increased decomposition if the water table (WT) decreases due to climate change, including permafrost thaw-related drying. Here, we optimize a version of the Organizing Carbon and Hydrology In Dynamic Ecosystems model (ORCHIDEE-PCH4) using site-specific observations to investigate changes in CO2 and CH4 fluxes as well as C stock responses to an experimentally manipulated decrease of WT at six northern peatlands. The unmanipulated control peatlands, with the WT <20 cm on average (seasonal max up to 45 cm) below the surface, currently act as C sinks in most years (58 ± 34 g C m−2 year−1; including 6 ± 7 g C–CH4 m−2 year−1 emission). We found, however, that lowering the WT by 10 cm reduced the CO2 sink by 13 ± 15 g C m−2 year−1 and decreased CH4 emission by 4 ± 4 g CH4 m−2 year−1, thus accumulating less C over 100 years (0.2 ± 0.2 kg C m−2). Yet, the reduced emission of CH4, which has a larger greenhouse warming potential, resulted in a net decrease in greenhouse gas balance by 310 ± 360 g CO2-eq m−2 year−1. Peatlands with the initial WT close to the soil surface were more vulnerable to C loss: Non-permafrost peatlands lost >2 kg C m−2 over 100 years when WT is lowered by 50 cm, while permafrost peatlands temporally switched from C sinks to sources. These results highlight that reductions in C storage capacity in response to drying of northern peatlands are offset in part by reduced CH4 emissions, thus slightly reducing the positive carbon climate feedbacks of peatlands under a warmer and drier