Carbon emission and export from the Ket River, western Siberia

• Published in: Biogeosciences
• Main Authors: Lim, Artem G., Krickov, Ivan V., Vorobyev, Sergey N., Korets, Mikhail A., Kopysov, Sergey, Shirokova, Liudmila S., Karlsson, Jan, Pokrovsky, Oleg S.
• Format: Text
• Language: English
• Published: 2022
• Subjects: ob river; permafrost; taiga; Siberia
• Online Access: https://doi.org/10.5194/bg-19-5859-2022; https://bg.copernicus.org/articles/19/5859/2022/

Despite recent progress in the understanding of the carbon (C) cycle of Siberian permafrost-affected rivers, spatial and seasonal dynamics of C export and emission from medium-sized rivers (50 000–300 000 km 2 watershed area) remain poorly known. Here we studied one of the largest tributaries of the Ob River, the Ket River (watershed = 94 000 km 2 ), which drains through pristine taiga forest of the boreal zone in the West Siberian Lowland (WSL). We combined continuous and discrete measurements of carbon dioxide (CO 2 ) concentration using submersible CO 2 sensor and floating chamber flux ( F CO 2 ), with methane (CH 4 ), dissolved organic and inorganic C (DOC and DIC, respectively), particulate organic C and total bacterial concentrations over an 800 km transect of the Ket River main stem and its 26 tributaries during spring flood (May 2019) and 12 tributaries during summer baseflow (end of August–beginning of September 2019). The partial pressure of CO 2 ( p CO 2 ) was lower and less variable in the main stem (2000 to 2500 µ atm) compared to that in the tributaries (2000 to 5000 µ atm). In the tributaries, the p CO 2 was 40 % higher during baseflow compared to spring flood, whereas in the main stem, it did not vary significantly across the seasons. The methane concentration in the main stem and tributaries was a factor of 300 to 1900 (flood period) and 100 to 150 times lower than that of CO 2 and ranged from 0.05 to 2.0 µ mol L −1 . The F CO 2 ranged from 0.4 to 2.4 g C m −2 d −1 in the main channel and from 0.5 to 5.0 g C m −2 d −1 in the tributaries, being highest during August in the tributaries and weakly dependent on the season in the main channel. During summer baseflow, the DOC aromaticity, bacterial number, and needleleaf forest coverage of the watershed positively affected CO 2 concentrations and fluxes. We hypothesize that relatively low spatial and seasonal variability in F CO 2 of the Ket River is due to a flat homogeneous landscape (bogs and taiga forest) that results in long water residence times ...