Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2017-56
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
02 Mar 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
Kukka-Maaria Erkkilä1, Ivan Mammarella1, David Bastviken2, Tobias Biermann3, Jouni J. Heiskanen1, Anders Lindroth4, Olli Peltola1, Miitta Rantakari1,5, Timo Vesala1,6, and Anne Ojala6,7 1Department of Physics, University of Helsinki, P.O. Box 68, 00014 Helsinki, Finland
2Department of Thematic Studies – Water and Environmental Studies, Linköping University, Linköping, Sweden
3Centre for Environmental and Climate Research, Lund University, Sölvegatan 37, 223 62 Lund, Sweden
4Department of Physical Geography and Ecosystem Sciences, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
5Department of Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 Helsinki, Finland
6Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 Helsinki, Finland
7Department of Environmental Sciences, University of Helsinki, Niemenkatu 73, 15140 Lahti, Finland
Abstract. Freshwaters bring a notable contribution to the global carbon budget by emitting both carbon dioxide (CO2) and methane (CH4) to the atmosphere. Global estimates of freshwater emissions traditionally use a wind speed based gas transfer coefficient, kCC, for calculating diffusive flux with the boundary layer method (BLM). We compared CH4 and CO2 fluxes from BLM with kCC and two other gas transfer coefficients (kTE and kHE), that include the effects of water-side cooling to the gas transfer besides shear-induced turbulence, with simultaneous eddy covariance (EC) and floating chamber (FC) fluxes during a 16-day measurement campaign in September 2014 at Lake Kuivajärvi in Finland. The measurements included both lake stratification and water column mixing periods. A clear increase in both CH4 and CO2 fluxes was detected right after turnover started. Results show that kCC model underestimates both CH4 and CO2 fluxes compared to EC measurements and the more recent model kTE gives the best fit with EC fluxes. In the stratified period, kHE and kCC used in BLM calculation have similar diurnal variation for CO2 flux, while kTE gives an opposite diurnal cycle. This is probably due to water friction velocity derived from EC measurements in kTE model instead of direct waterside turbulence measurements in this study. In the mixing period all models agree well with each other on diurnal variation for both CH4 and CO2. We highly recommend using up to date gas transfer models, instead of kCC, for better flux estimates.

FC measurements did not detect spatial variation in either CH4 or CO2 flux over Lake Kuivajärvi. EC measurements, on the other hand, did not show any spatial variation in CH4 fluxes, but a clear difference between CO2 fluxes from shallower and deeper areas. Fluxes measured with FC were systematically higher than EC fluxes, partly due to deficiencies in the EC method.


Citation: Erkkilä, K.-M., Mammarella, I., Bastviken, D., Biermann, T., Heiskanen, J. J., Lindroth, A., Peltola, O., Rantakari, M., Vesala, T., and Ojala, A.: Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method, Biogeosciences Discuss., doi:10.5194/bg-2017-56, in review, 2017.
Kukka-Maaria Erkkilä et al.
Kukka-Maaria Erkkilä et al.
Kukka-Maaria Erkkilä et al.

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Short summary
Global estimates of freshwater greenhouse gas emissions are usually based on simple gas transfer models that underestimate the emissions. Thus, comparison of different gas transfer models is required for evaluating the uncertainties. This study compares three mostly used methods for estimating greenhouse gas emissions over lakes. We conclude that simple gas transfer models underestimate the emissions and more recent models should be used for global freshwater greenhouse gas emission estimates.
Global estimates of freshwater greenhouse gas emissions are usually based on simple gas transfer...
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