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Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method

Freshwaters 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>...

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Tác giả chính: K.-M., Erkkilä, A., Ojala
Ngôn ngữ:English
Năm xuất bản: Copernicus Publications 2018
Chủ đề:
Science
Biology
Ecology
Life
Geology
Truy cập Trực tuyến:http://lrc.quangbinhuni.edu.vn:8181/dspace/handle/DHQB_123456789/3960
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spelling oai:localhost:DHQB_123456789-39602018-10-22T08:43:53Z Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method K.-M., Erkkilä A., Ojala Science Biology Ecology Life Geology Freshwaters 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. 2018-09-04T08:25:54Z 2018-09-04T08:25:54Z 2018 http://lrc.quangbinhuni.edu.vn:8181/dspace/handle/DHQB_123456789/3960 en Copernicus Publications
institution Trung tâm Học liệu Đại học Quảng Bình (Dspace)
collection Trung tâm Học liệu Đại học Quảng Bình (Dspace)
language English
topic Science
Biology
Ecology
Life
Geology
spellingShingle Science
Biology
Ecology
Life
Geology
K.-M., Erkkilä
A., Ojala
Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
description Freshwaters 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.
author K.-M., Erkkilä
A., Ojala
author_facet K.-M., Erkkilä
A., Ojala
author_sort K.-M., Erkkilä
title Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
title_short Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
title_full Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
title_fullStr Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
title_full_unstemmed Methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
title_sort methane and carbon dioxide fluxes over a lake: comparison between eddy covariance, floating chambers and boundary layer method
publisher Copernicus Publications
publishDate 2018
url http://lrc.quangbinhuni.edu.vn:8181/dspace/handle/DHQB_123456789/3960
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score 9,463379

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