Accounting for surface waves improves gas flux estimation at high wind speed in a large lake
<p>The gas transfer velocity (<span class="inline-formula"><i>k</i></span>) 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 <span class="i...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-11-01
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| Series: | Earth System Dynamics |
| Online Access: | https://esd.copernicus.org/articles/12/1169/2021/esd-12-1169-2021.pdf |
| Summary: | <p>The gas transfer velocity (<span class="inline-formula"><i>k</i></span>) 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 <span class="inline-formula"><i>k</i></span> models, the transfer velocity increases with the level of turbulence near the air–water
interface. However, predictions for <span class="inline-formula"><i>k</i></span> 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, but 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 hard-water lake, Lake Geneva, from <span class="inline-formula">CO<sub>2</sub></span> fluxes measured with an automated (forced diffusion) flux chamber and <span class="inline-formula">CO<sub>2</sub></span> partial
pressure measured with high-frequency sensors. <span class="inline-formula"><i>k</i></span> estimates were compared to a set of reference limnological and oceanic <span class="inline-formula"><i>k</i></span> models. Our analysis
reveals that accounting for surface waves generated during windy events significantly improves the accuracy of <span class="inline-formula"><i>k</i></span> estimates in this large lake. The
improved <span class="inline-formula"><i>k</i></span> model is then used to compute <span class="inline-formula"><i>k</i></span> over a 1-year time period. Results show that episodic extreme events with surface waves (6 %
occurrence, significant wave height <span class="inline-formula">></span> 0.4 <span class="inline-formula">m</span>) can generate more than 20 % of annual cumulative <span class="inline-formula"><i>k</i></span> and more than 25 % of annual
net <span class="inline-formula">CO<sub>2</sub></span> fluxes in Lake Geneva. We conclude that for lakes whose fetch can exceed 15 <span class="inline-formula">km</span>, <span class="inline-formula"><i>k</i></span> models need to integrate the effect of
surface waves.</p> |
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| ISSN: | 2190-4979 2190-4987 |