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

• Main Authors: Vorobyev, Sergey N., Karlsson, Jan, Kolesnichenko, Yuri Y., Koretz, Mikhail, Pokrovsky, Oleg S.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Arctic; Arctic Ocean; Kolyma; Yukon; Ice; lena river; permafrost; Siberia
• Online Access: https://doi.org/10.5194/bg-2021-109; https://bg.copernicus.org/preprints/bg-2021-109/

Greenhouse gas (GHG) emissions from inland waters of permafrost-affected regions is one of the key factor 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 remain 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 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 Lena (range 400–1400 µatm) and tributaries (range 400–1600 µatm) was oversaturated and 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 and the proportion of deciduous needle-leaf forest and riparian vegetation. Based on gas transfer coefficients obtained from rivers of the Siberian permafrost zone, we calculated CO 2 emission for the main stem and tributaries. Typical fluxes ranged from 1 to 2 g C m −2 d −1 (> 99 % CO 2 , < 1 % CH 4 ) which is comparable with CO 2 emission measured in Kolyma, Yukon and Mackenzie and permafrost-affected rivers in western Siberia. The areal C emissions from lotic waters of the Lena watershed were quantified via 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 of open water period and no emission under ice, the annual C emissions from the whole Lena basin range from 5 to 10 Tg C yr −1 , which is comparable to the DOC and DIC lateral export to the Arctic Ocean.