Carbon emission and export from Ket River, western Siberia 2

32 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-size rivers remain poorly unknown. Here we studied one of the largest tributaries of the Ob River, the Ket River (watershed = 94,000 35 km²) which drains through virtually pristine dense taiga forest of the boreal zone in western Siberian Lowland 36 (WSL). We combined continuous in-situ measurements of carbon dioxide (CO 2 ) concentration and flux 37 (FCO 2 ), with methane (CH 4 ), organic and inorganic C (DOC and DIC, respectively), particulate organic C 38 and total bacterial concentrations over a 834-km transect of the Ket River main stem and its 26 tributaries 39 during spring flood and 12 tributaries during summer baseflow. The CO 2 concentration was lower and less 40 variable in the main stem (2000 to 2500 µatm) compared to that in tributaries (2000 to 5000 µatm). The 41 methane concentrations in the main stem and tributaries was a factor of 300 to 1900 (flood period) and 100 42 to 150 (baseflow period) lower than that of CO 2 . The FCO 2 ranged from 0.4 to 2.4 g C m -2 d -1 in the main 43 channel and from 0.5 to 5.0 g C m -2 d -1 in the tributaries, being the highest during August in tributaries and 44 weakly dependent on season in the main channel. Only during summer baseflow, the DOM aromaticity, 45 bacterial number, and needleleaf forest coverage of the watershed positively affected CO 2 concentrations and 46 fluxes. We hypothesize that the relatively low variability in FCO 2 is due to flat homogeneous (bog and taiga 47 forest) landscape that results in long water residence times and stable input of allochthonous DOM, which 48 dominate the FCO 2 . In summer baseflow, the DIC input from deeper flow paths might also contribute to CO 2 49 emission. The open water period (May to October) C emission from the Ket River basin was estimated to 50 Gg C y -1 which is lower than the lateral C export during the same period. Although this estimated C 51 emissions contain uncertainties, stressing the need of better constrained model for medium size bog-forest rivers of the western Siberia Lowland and results obtained from this watershed can be extrapolated to much larger territory, comprising about 1 million km 2 of permafrost-free taiga forest and bog regions of the southern part of WSL. spring

[1]  Dai Yamazaki,et al.  The importance of hydrology in routing terrestrial carbon to the atmosphere via global streams and rivers , 2022, Proceedings of the National Academy of Sciences of the United States of America.

[2]  O. Pokrovsky,et al.  Sizable carbon emission from the floodplain of Ob River , 2021 .

[3]  H. Laudon,et al.  Integrating Discharge‐Concentration Dynamics Across Carbon Forms in a Boreal Landscape , 2021, Water Resources Research.

[4]  W. McDowell,et al.  Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions , 2021, Nature Geoscience.

[5]  O. Pokrovsky,et al.  Carbon emission from Western Siberian inland waters , 2021, Nature Communications.

[6]  C. Peng,et al.  Headwater stream ecosystem: an important source of greenhouse gases to the atmosphere. , 2020, Water research.

[7]  R. Sponseller,et al.  Integrating carbon emission, accumulation and transport in inland waters to understand their role in the global carbon cycle , 2020, Global change biology.

[8]  O. Pokrovsky,et al.  Impact of Permafrost Thaw and Climate Warming on Riverine Export Fluxes of Carbon, Nutrients and Metals in Western Siberia , 2020, Water.

[9]  B. Wild,et al.  Rivers across the Siberian Arctic unearth the patterns of carbon release from thawing permafrost , 2019, Proceedings of the National Academy of Sciences.

[10]  C. Mörth,et al.  Landscape process domains drive patterns of CO2 evasion from river networks , 2019, Limnology and Oceanography Letters.

[11]  H. Laudon,et al.  High carbon emissions from thermokarst lakes of Western Siberia , 2019, Nature Communications.

[12]  O. Pokrovsky,et al.  Biogeochemistry of dissolved carbon, major, and trace elements during spring flood periods on the Ob River , 2019, Hydrological Processes.

[13]  H. Laudon,et al.  High riverine CO2 emissions at the permafrost boundary of Western Siberia , 2018, Nature Geoscience.

[14]  O. Pokrovsky,et al.  Riverine particulate C and N generated at the permafrost thaw front: case study of western Siberian rivers across a 1700 km latitudinal transect , 2018, Biogeosciences.

[15]  H. Laudon,et al.  Carbon dioxide and methane emissions of Swedish low‐order streams—a national estimate and lessons learnt from more than a decade of observations , 2018 .

[16]  V. Engel,et al.  On Factors Influencing Air‐Water Gas Exchange in Emergent Wetlands , 2018 .

[17]  K. Verdin,et al.  Inland waters and their role in the carbon cycle of Alaska. , 2017, Ecological applications : a publication of the Ecological Society of America.

[18]  L. Ran,et al.  Dynamics of riverine CO 2 in the Yangtze River fluvial network and their implications for carbon evasion , 2016 .

[19]  H. Laudon,et al.  Decoupling of carbon dioxide and dissolved organic carbon in boreal headwater streams , 2016 .

[20]  E. Variano,et al.  Air‐water gas exchange by waving vegetation stems , 2016 .

[21]  P. Ciais,et al.  Spatial patterns in CO2 evasion from the global river network , 2015 .

[22]  M. Wallin,et al.  Carbon dioxide evasion from headwater systems strongly contributes to the total export of carbon from a small boreal lake catchment , 2015 .

[23]  H. Laudon,et al.  Carbon dioxide transport across the hillslope-riparian-stream continuum in a boreal headwater catchment , 2014 .

[24]  P. Jones,et al.  Updated high‐resolution grids of monthly climatic observations – the CRU TS3.10 Dataset , 2014 .

[25]  P. Ciais,et al.  Global carbon dioxide emissions from inland waters , 2013, Nature.

[26]  Zhiheng Wang,et al.  Differential mobilization of terrestrial carbon pools in Eurasian Arctic river basins , 2013, Proceedings of the National Academy of Sciences.

[27]  K. Dinsmore,et al.  Temperature and precipitation drive temporal variability in aquatic carbon and GHG concentrations and fluxes in a peatland catchment , 2013, Global change biology.

[28]  J. Rover,et al.  Carbon dioxide and methane emissions from the Yukon River system , 2012 .

[29]  M. Billett,et al.  Spatiotemporal variability of the gas transfer coefficient (KCO2) in boreal streams: Implications for large scale estimates of CO2 evasion , 2011 .

[30]  L. Molot,et al.  Importance of CO2 evasion from small boreal streams , 2010 .

[31]  Ian McCallum,et al.  THE BIOMASAR ALGORITHM: AN APPROACH FOR RETRIEVAL OF FOREST GROWING STOCK VOLUME USING STACKS OF MULTI-TEMPORAL SAR DATA , 2010 .

[32]  George R. Aiken,et al.  Flux and age of dissolved organic carbon exported to the Arctic Ocean: A carbon isotopic study of the five largest arctic rivers , 2007 .

[33]  D. Serça,et al.  Gas transfer velocities of CO2 and CH4 in a tropical reservoir and its river downstream , 2007 .

[34]  L. Tranvik,et al.  Integrating aquatic carbon fluxes in a boreal catchment carbon budget , 2007 .

[35]  R. Wanninkhof.  Relationship between wind speed and gas exchange over the ocean , 1992 .

[36]  C. Gri,et al.  Quantifying CDOM and DOC in major Arctic rivers during ice-free conditions using Landsat TM and ETM + data , 2018 .

[37]  Karen E. Frey,et al.  Impacts of permafrost degradation on arctic river biogeochemistry , 2009 .