Fluvial carbon dioxide emission from the Lena River basin during the spring flood

• Published in: Biogeosciences
• Main Authors: Vorobyev, Sergey N., Karlsson, Jan, Kolesnichenko, Yuri Y., Korets, Mikhail A., Pokrovsky, Oleg S.
• Other Authors: Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: [SDU]Sciences of the Universe [physics]; Arctic; Arctic Ocean; Kolyma; Yukon; Ice; lena river; permafrost; Siberia
• Online Access: https://insu.hal.science/insu-03661462; https://insu.hal.science/insu-03661462/document; https://insu.hal.science/insu-03661462/file/bg-18-4919-2021.pdf; https://doi.org/10.5194/bg-18-4919-2021

International audience Greenhouse gas (GHG) emission from inland waters of permafrost-affected regions is one of the key factors of circumpolar aquatic ecosystem response to climate warming and permafrost thaw. Riverine systems of central and eastern Siberia contribute a significant part of the water and carbon (C) export to the Arctic Ocean, yet their C exchange with the atmosphere remains poorly known due to lack of in situ GHG concentration and emission estimates. Here we present the results of continuous in situ pCO 2 measurements over a 2600 km transect of the Lena River main stem and lower reaches of 20 major tributaries (together representing a watershed area of 1 661 000 km 2 , 66 % of the Lena's basin), conducted at the peak of the spring flood. The pCO 2 in the Lena (range 400-1400 µatm) and tributaries (range 400-1600 µatm) remained generally stable (within ca. 20 %) over the night-day period and across the river channels. The pCO 2 in tributaries increased northward with mean annual temperature decrease and permafrost increase; this change was positively correlated with C stock in soil, the proportion of deciduous needleleaf forest, and the riparian vegetation. Based on gas transfer coefficients obtained from rivers of the Siberian permafrost zone (k=4.46 m d −1 ), we calculated CO 2 emission for the main stem and tributaries. Typical fluxes ranged from 1 to 2 gC m-2 d-1 (>99 % CO 2 , <1 % CH 4 ), which is comparable with CO 2 emission measured in the Kolyma, Yukon, and Mackenzie rivers and permafrost-affected rivers in western Siberia. The areal C emissions from lotic waters of the Lena watershed were quantified by taking into account the total area of permanent and seasonal water of the Lena basin (28 000 km 2 ). Assuming 6 months of the year to be an open water period with no emission under ice, the annual C emission from the whole Lena basin is estimated as 8.3±2.5 Tg C yr −1 , which is comparable to the DOC and dissolved inorganic carbon (DIC) lateral export to the Arctic Ocean.