Preprints
https://doi.org/10.5194/esd-2021-30
https://doi.org/10.5194/esd-2021-30

  07 May 2021

07 May 2021

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

Accounting for surface waves improves gas flux estimation at high wind speed in a large lake

Pascal Perolo1, Bieito Fernández Castro2,3, Nicolas Escoffier1, Thibault Lambert1, Damien Bouffard4, and Marie-Elodie Perga1 Pascal Perolo et al.
  • 1Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, 1015, Switzerland
  • 2Physics of Aquatic Systems Laboratory, Margareth Kamprad Chair, Swiss Federal Institute of Technology Lausanne, Lausanne, 1015, Switzerland
  • 3Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, SO14 3ZH, United Kingdom
  • 4Eawag, Swiss Federal Institute of Aquatic Science and Technology, Surface Waters – Research Management, Kastanienbaum, 6047, Switzerland

Abstract. The gas transfer velocity (k) is a major source of uncertainty when assessing the magnitude of lake gas exchange with the atmosphere. For the diversity of existing empirical and process-based k models, the transfer velocity increases with the level of turbulence near the air-water interface. However, predictions for k can vary by a factor of 2 among different models. Near-surface turbulence results from the action of wind shear, surface waves and buoyancy-driven convection. Wind shear has long been identified as a key driver, while recent lake studies have shifted the focus towards the role of convection, particularly in small lakes. In large lakes, wind fetch can however be long enough to generate surface waves and contribute to enhance gas transfer, as widely recognised in oceanographic studies. Here, field values for gas transfer velocity were computed in a large hardwater lake, Lake Geneva, from CO2 fluxes measured with an automated (forced diffusion) flux chamber and CO2 partial pressure measured with high frequency sensors. k estimates were compared to a set of reference limnological and oceanic k models. Our analysis reveals that accounting for surface waves generated during windy events significantly improves the accuracy of k estimates in this large lake. The improved k model is then used to compute k over a one-year time-period. Results show that episodic extreme events with surface waves (6 % occurrence, significant wave height > 0.4 m) can generate more than 20 % of annual cumulative k and more than 25 % of annual net CO2 fluxes in Lake Geneva. We conclude that for lakes whose fetch can exceed 15 km, k-models need to integrate the effect of surface waves.

Pascal Perolo 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 esd-2021-30', Anonymous Referee #1, 04 Jun 2021
    • AC1: 'Reply on RC1', Pascal Perolo, 27 Jul 2021
  • RC2: 'Comment on esd-2021-30', Anonymous Referee #2, 07 Jun 2021
    • AC2: 'Reply on RC2', Pascal Perolo, 27 Jul 2021

Pascal Perolo et al.

Pascal Perolo et al.

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Short summary
Wind blowing over the ocean creates waves, which by increasing the level of turbulence, promote gas exchange at the air-water interface. In this study we measured for the first time enhanced gas exchanges by wind-induced waves at the surface of a large lake. We adapted an ocean-based model to account for surface waves on gas exchange in lakes. We finally show that intense wind events with surface waves contribute disproportionately to the annual CO2 gas flux in a large lake.
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