Atmospheric CO2 exchange of a small mountain lake: limitations of eddy
covariance and boundary layer modeling methods in complex terrain.
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
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