EGU21-9553
https://doi.org/10.5194/egusphere-egu21-9553
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

The CO2 exchange of a small mountain lake as affected by the local thermo-topographically driven flow regime

Katharina Scholz1, Tom Battin2, Elisabet Ejarque3, Albin Hammerle1, Martin Kainz3, Jakob Schelker3,4, and Georg Wohlfahrt1
Katharina Scholz et al.
  • 1Department of Ecology, University of Innsbruck, Innsbruck, Austria (katharina.scholz@student.uibk.ac.at)
  • 2Environmental Engineering Institute - IIE, School of Architecture, Civil and Environmental Engineering-ENAC, École polytechnique fédérale de Lausanne, Lausanne, Switzerland
  • 3WasserCluster Lunz, Lunz am See, Austria
  • 4Department of Limnology and Biological Oceanography, University of Vienna, Vienna, Austria

Lakes receive large amounts of carbon (C) from the surrounding catchment and, together with the connecting streams, play an important and active role in the global C cycle. The received C can either be lost through the outflow and eventually transported to the ocean, or transformed and stored in sediments or outgassed to the atmosphere. Globally, lakes are estimated to emit 0.3 – 0.64 Pg C m-2 in form of CO2 annually.  Although subalpine and alpine lakes were observed to be supersaturated with CO2, long-term measurements of lake-atmosphere CO2 exchange are sparse. Several methods to quantify water-atmosphere gas exchange exist, like chambers, eddy covariance (EC), mass-balance or gradient based methods including boundary layer models (BLM), each having its own advantages and disadvantages. However, quantifying CO2 exchange in aquatic ecosystems has often proved to be challenging. Here, both the BLM and the EC methods were used to estimate the air-water CO2 exchange of Lake Lunz, a small lake situated in complex mountainous topography of the Austrian Alps. The results indicated that the lake was a small source of CO2. Fluxes were affected by the thermo-topographic flow regime of the field site and its surroundings which drove the local wind pattern but also determined the local atmospheric CO2 concentration.  During most nights, a significant increase in atmospheric CO2 was observed which decreased the differential CO2 concentration at the air-water interface and therefore led to decreased nocturnal CO2 efflux. This diurnal pattern, however, was obscured in the EC measurements, because the method itself highly depends on the local wind regime. Because lakes are an integral part of mountain ranges which are characterized by catchments with complex topography, our findings are most likely of broader impact.

How to cite: Scholz, K., Battin, T., Ejarque, E., Hammerle, A., Kainz, M., Schelker, J., and Wohlfahrt, G.: The CO2 exchange of a small mountain lake as affected by the local thermo-topographically driven flow regime, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9553, https://doi.org/10.5194/egusphere-egu21-9553, 2021.

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