Please use this identifier to cite or link to this item: http://lrc.quangbinhuni.edu.vn:8181/dspace/handle/DHQB_123456789/3960
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dc.contributor.authorK.-M., Erkkilä-
dc.contributor.authorA., Ojala-
dc.date.accessioned2018-09-04T08:25:54Z-
dc.date.available2018-09-04T08:25:54Z-
dc.date.issued2018-
dc.identifier.urihttp://lrc.quangbinhuni.edu.vn:8181/dspace/handle/DHQB_123456789/3960-
dc.description.abstractFreshwaters bring a notable contribution to the global carbon budget by emitting both carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) to the atmosphere. Global estimates of freshwater emissions traditionally use a wind-speed-based gas transfer velocity, <i>k</i><sub>CC</sub> (introduced by Cole and Caraco, 1998), for calculating diffusive flux with the boundary layer method (BLM). We compared CH<sub>4</sub> and CO<sub>2</sub> fluxes from BLM with <i>k</i><sub>CC</sub> and two other gas transfer velocities (<i>k</i><sub>TE</sub> and <i>k</i><sub>HE</sub>), which 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. Results show that BLM fluxes were mainly lower than EC, with the more recent model <i>k</i><sub>TE</sub> giving the best fit with EC fluxes, whereas FC measurements resulted in higher fluxes than simultaneous EC measurements. We highly recommend using up-to-date gas transfer models, instead of <i>k</i><sub>CC</sub>, for better flux estimates. <br><br> BLM CO<sub>2</sub> flux measurements had clear differences between daytime and night-time fluxes with all gas transfer models during both stratified and mixing periods, whereas EC measurements did not show a diurnal behaviour in CO<sub>2</sub> flux. CH<sub>4</sub> flux had higher values in daytime than night-time during lake mixing period according to EC measurements, with highest fluxes detected just before sunset. In addition, we found clear differences in daytime and night-time concentration difference between the air and surface water for both CH<sub>4</sub> and CO<sub>2</sub>. This might lead to biased flux estimates, if only daytime values are used in BLM upscaling and flux measurements in general. <br><br> FC measurements did not detect spatial variation in either CH<sub>4</sub> or CO<sub>2</sub> flux over Lake Kuivajärvi. EC measurements, on the other hand, did not show any spatial variation in CH<sub>4</sub> fluxes but did show a clear difference between CO<sub>2</sub> fluxes from shallower and deeper areas. We highlight that while all flux measurement methods have their pros and cons, it is important to carefully think about the chosen method and measurement interval, as well as their effects on the resulting flux.en_US
dc.language.isoenen_US
dc.publisherCopernicus Publicationsen_US
dc.subjectScienceen_US
dc.subjectBiologyen_US
dc.subjectEcologyen_US
dc.subjectLifeen_US
dc.subjectGeologyen_US
dc.titleMethane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer methoden_US
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