Preprints
https://doi.org/10.5194/egusphere-2024-1644
https://doi.org/10.5194/egusphere-2024-1644
26 Jun 2024
 | 26 Jun 2024
Status: this preprint is open for discussion.

Temporal dynamics and environmental controls of carbon dioxide and methane fluxes measured by the eddy covariance method over a boreal river

Aki Vähä, Timo Vesala, Sofya Guseva, Anders Lindroth, Andreas Lorke, Sally MacIntyre, and Ivan Mammarella

Abstract. Boreal rivers and streams are significant sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere.  Yet the controls and the magnitude of these emissions remain highly uncertain, as current estimates are mostly based on indirect and discrete flux measurements. In this study, we present and analyse the longest CO2 and the first ever CH4 flux dataset measured by the eddy covariance (EC) technique over a river. The field campaign (KITEX) was carried out during June–October 2018 over the River Kitinen, a large regulated river with a mean annual discharge of 103 m3 s−1 located in northern Finland. The EC system was installed on a floating platform, where the river was 180 m wide and with a maximum depth of 7 m.  The river was on average a source of CO2 and CH4 to the atmosphere. The mean CO2 flux was 0.36 ± 0.31 μmol m−2 s−1 and the highest monthly flux occurred in July. The mean CH4 flux was 3.8 ± 4.1 nmol m−2 s−1 and it was also highest in July. During midday hours in June, the river acted occasionally as a net CO2 sink. In June–August, the nocturnal CO2 flux was higher than the daytime flux. The CH4 flux did not show any statistically significant diurnal variation. Results from a multiple regression analysis show that pattern of daily and weekly mean fluxes of CO2 are largely explained by partial pressure of CO2 in water (pCO2w), photosynthetically active radiation (PAR), water flow velocity and wind speed. Water surface temperature and wind speed were found to be the main drivers of CH4 fluxes.

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Aki Vähä, Timo Vesala, Sofya Guseva, Anders Lindroth, Andreas Lorke, Sally MacIntyre, and Ivan Mammarella

Status: open (until 07 Aug 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1644', Mingxi Yang, 03 Jul 2024 reply
    • RC3: 'Reply on RC1', Alex Zavarsky, 09 Jul 2024 reply
  • RC2: 'Comment on egusphere-2024-1644', Alex Zavarsky, 09 Jul 2024 reply
Aki Vähä, Timo Vesala, Sofya Guseva, Anders Lindroth, Andreas Lorke, Sally MacIntyre, and Ivan Mammarella
Aki Vähä, Timo Vesala, Sofya Guseva, Anders Lindroth, Andreas Lorke, Sally MacIntyre, and Ivan Mammarella

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Short summary

Boreal rivers are significant sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere but the controls of these emissions are uncertain. We measured four months of CO2 and CH4 exchange between a regulated boreal river and the atmosphere with eddy covariance. We found statistical relationships between the gas exchange and several environmental variables, the most important of which were dissolved CO2 partial pressure in water, wind speed, and water temperature.