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Atmospheric CO2 exchange of a small mountain lake: limitations of eddy covariance and boundary layer modeling methods in complex terrain.
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  • Katharina Scholz,
  • Elisabet Ejarque,
  • Albin Hammerle,
  • Martin Johann Kainz,
  • Jakob Schelker,
  • Georg Wohlfahrt
Katharina Scholz
University of Innsbruck

Corresponding Author:[email protected]

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Elisabet Ejarque
WasserCluster Lunz - Biologische Station
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Albin Hammerle
University of Innsbruck
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Martin Johann Kainz
WasserCluster Lunz
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Jakob Schelker
University of Vienna
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Georg Wohlfahrt
University of Innsbruck
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As lakes receive and transform significant amounts of terrestrial carbon, they often act as source of atmospheric CO2. Yet, long-term measurements of lake-atmosphere CO2 exchange with high temporal resolution are sparse. In this study, we measured the CO2 exchange of a small lake situated in complex mountainous topography in the Austrian Alps continuously for one year. We used the eddy covariance (EC) and the boundary layer model (BLM) approaches to estimate the lake’s CO2 source or sink strength and to analyze differences between these methods.
Overall, CO2 fluxes were small and EC measurements indicated influence of low-frequency contributions. Results from both the EC and the BLM methods indicated the lake to be a small source of atmospheric CO2 with highest emissions in fall.
During night-time, the CO2 concentration gradient at the air-water interface decreased due to an increase in atmospheric CO2 above the lake, likely caused by cold and CO2-rich air draining from the surrounding land. Consequently, BLM fluxes were lower during night-time than during daytime. This diel pattern was lacking in the EC flux measurements because the EC instruments deployed at the shore of the lake did not capture low nocturnal lake CO2 fluxes due to the local wind regime.
Overall, this study exemplifies the relevance of the surrounding landscape for lake-atmosphere flux measurements. We conclude that estimating CO2 evasion from lakes situated in complex topography needs to explicitly account for biases in EC flux measurements caused by low-frequency contributions and local wind systems.
Jul 2021Published in Journal of Geophysical Research: Biogeosciences volume 126 issue 7. 10.1029/2021JG006286