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: Academy of Finland, Agence Nationale de la Recherche, H2020 Societal Challenges, National Science Foundation of Sri Lanka
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2022
• Subjects: Arctic; Climate change; permafrost
• Online Access: http://dx.doi.org/10.1111/gcb.16394; https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.16394; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/gcb.16394

Abstract 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 CO 2 and CH 4 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–CH 4 m −2 year −1 emission). We found, however, that lowering the WT by 10 cm reduced the CO 2 sink by 13 ± 15 g C m −2 year −1 and decreased CH 4 emission by 4 ± 4 g CH 4 m −2 year −1 , thus accumulating less C over 100 years (0.2 ± 0.2 kg C m −2 ). Yet, the reduced emission of CH 4 , which has a larger greenhouse warming potential, resulted in a net decrease in greenhouse gas balance by 310 ± 360 g CO 2‐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 CH 4 emissions, thus slightly reducing the positive carbon climate feedbacks of peatlands under a warmer and drier future climate scenario.