11 Jan 2021

11 Jan 2021

Review status: a revised version of this preprint is currently under review for the journal BG.

Spatial and temporal variability of pCO2 and CO2 emissions from the Dongjiang River in South China

Boyi Liu1, Mingyang Tian2, Kaimin Shih3, Chun Ngai Chan1, Xiankun Yang4, and Lishan Ran1 Boyi Liu et al.
  • 1Department of Geography, the University of Hong Kong, Hong Kong SAR, China
  • 2Institute for Geology, Center for Earth System Research and Sustainability (CEN), Universität Hamburg, Hamburg, Germany
  • 3Department of Civil Engineering, the University of Hong Kong, Hong Kong SAR, China
  • 4School of Geographical Sciences, Guangzhou University, Guangzhou,510006, China

Abstract. CO2 efflux at the water–air interface is an essential component of the riverine carbon cycle. However, the lack of spatially resolved CO2 emission measurement still hinges the accuracy of estimates on global riverine CO2 emissions. By deploying floating chambers, seasonal changes in river water CO2 partial pressure (pCO2) and CO2 evasion from the Dongjiang River in South China were investigated. Lateral soil CO2 input and dilution effect caused by precipitation played critical roles in controlling riverine pCO2 in small rivers, while the decomposition of allochthonous organic carbon is responsible for pCO2 variability in large rivers. Temperature-normalized gas transfer velocity (k600) in small rivers were 8.29 ± 11.29 m d−1 and 4.90 ± 3.82 m d−1 for the wet season and dry season, respectively, which were nearly 70 % higher than that of large rivers (3.90 ± 5.55 m d−1 during the wet season and 2.25 ± 1.61 m d−1 during the dry season). A significant correlation was observed between k600 and flow velocity but not wind speed regardless of river size. Majority of the surveyed rivers were net CO2 source, exhibiting substantial seasonal variations. The mean CO2 flux was 300.1 and 264.2 mmol m−2 d−1 during wet season for large and small rivers, respectively, 2-fold larger than that during dry season. The absence of commonly observed higher CO2 fluxes in small rivers could be associated with the depletion effect caused by abundant and consistent precipitation in this subtropical monsoon catchment.

Boyi Liu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2020-477', Anonymous Referee #1, 08 Feb 2021
    • AC1: 'Reply on RC1', Lishan Ran, 25 Mar 2021
  • RC2: 'Comment on bg-2020-477', Anonymous Referee #2, 12 Feb 2021
    • AC2: 'Reply on RC2', Lishan Ran, 25 Mar 2021

Boyi Liu et al.

Data sets

Riverine CO2 Emission Datasets: Dongjiang River Boyi Liu

Boyi Liu et al.


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Short summary
CO2 concentrations in small rivers are mainly controlled by lateral soil CO2 input, while the decomposition of organic carbon controls the CO2 variation in large rivers. CO2 fluxes in the wet season, compared to that in the dry season, are 2-fold larger due to high CO2 concentration and turbulence caused by high flow velocity. The absence of high CO2 fluxes in small rivers could be associated with the depletion effect caused by abundant precipitation under the subtropical monsoon climate.