Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2

In the present study, we measured independently CH<sub>4</sub> ebullition and diffusion in the footprint of an eddy covariance system (EC) measuring CH<sub>4</sub> emissions in the Nam Theun 2 Reservoir, a recently impounded (2008) subtropical hydroelectric reservoir located...

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Main Authors: C. Deshmukh, D. Serça, C. Delon, R. Tardif, M. Demarty, C. Jarnot, Y. Meyerfeld, V. Chanudet, P. Guédant, W. Rode, S. Descloux, F. Guérin
Format: Article
Language:English
Published: Copernicus Publications 2014-08-01
Series:Biogeosciences
Online Access:http://www.biogeosciences.net/11/4251/2014/bg-11-4251-2014.pdf
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author C. Deshmukh
D. Serça
C. Delon
R. Tardif
M. Demarty
C. Jarnot
Y. Meyerfeld
V. Chanudet
P. Guédant
W. Rode
S. Descloux
F. Guérin
author_facet C. Deshmukh
D. Serça
C. Delon
R. Tardif
M. Demarty
C. Jarnot
Y. Meyerfeld
V. Chanudet
P. Guédant
W. Rode
S. Descloux
F. Guérin
author_sort C. Deshmukh
collection DOAJ
description In the present study, we measured independently CH<sub>4</sub> ebullition and diffusion in the footprint of an eddy covariance system (EC) measuring CH<sub>4</sub> emissions in the Nam Theun 2 Reservoir, a recently impounded (2008) subtropical hydroelectric reservoir located in the Lao People's Democratic Republic (PDR), Southeast Asia. The EC fluxes were very consistent with the sum of the two terms measured independently (diffusive fluxes + ebullition = EC fluxes), indicating that the EC system picked up both diffusive fluxes and ebullition from the reservoir. We showed a diurnal bimodal pattern of CH<sub>4</sub> emissions anti-correlated with atmospheric pressure. During daytime, a large atmospheric pressure drop triggers CH<sub>4</sub> ebullition (up to 100 mmol m<sup>−2</sup> d<sup>&minus;1</sup>), whereas at night, a more moderate peak of CH<sub>4</sub> emissions was recorded. As a consequence, fluxes during daytime were twice as high as during nighttime. <br><br> Additionally, more than 4800 discrete measurements of CH<sub>4</sub> ebullition were performed at a weekly/fortnightly frequency, covering water depths ranging from 0.4 to 16 m and various types of flooded ecosystems. Methane ebullition varies significantly seasonally and depends mostly on water level change during the warm dry season, whereas no relationship was observed during the cold dry season. On average, ebullition was 8.5 ± 10.5 mmol m<sup>−2</sup> d<sup>−1</sup> and ranged from 0 to 201.7 mmol m<sup>−2</sup> d<sup>−1</sup>. <br><br> An artificial neural network (ANN) model could explain up to 46% of seasonal variability of ebullition by considering total static pressure (the sum of hydrostatic and atmospheric pressure), variations in the total static pressure, and bottom temperature as controlling factors. This model allowed extrapolation of CH<sub>4</sub> ebullition on the reservoir scale and performance of gap filling over four years. Our results clearly showed a very high seasonality: 50% of the yearly CH<sub>4</sub> ebullition occurs within four months of the warm dry season. Overall, ebullition contributed 60–80% of total emissions from the surface of the reservoir (disregarding downstream emissions), suggesting that ebullition is a major pathway in young hydroelectric reservoirs in the tropics.
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spelling doaj.art-5fd9817d7c564bfa901681f3522cbf0e2022-12-21T17:57:53ZengCopernicus PublicationsBiogeosciences1726-41701726-41892014-08-0111154251426910.5194/bg-11-4251-2014Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2C. Deshmukh0D. Serça1C. Delon2R. Tardif3M. Demarty4C. Jarnot5Y. Meyerfeld6V. Chanudet7P. Guédant8W. Rode9S. Descloux10F. Guérin11Laboratoire d'Aérologie &ndash; Université de Toulouse &ndash; CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceLaboratoire d'Aérologie &ndash; Université de Toulouse &ndash; CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceLaboratoire d'Aérologie &ndash; Université de Toulouse &ndash; CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceNam Theun 2 Power Company Limited (NTPC), Environment & Social Division &ndash; Water Quality and Biodiversity Dept. &ndash; Gnommalath Office, P.O. Box 5862, Vientiane, Lao PDREnvironnement Illimite, 1453 rue Saint Timothee, Montreal QC, CanadaLaboratoire d'Aérologie &ndash; Université de Toulouse &ndash; CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceLaboratoire d'Aérologie &ndash; Université de Toulouse &ndash; CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceElectriciteì de France, Hydro Engineering Centre, Sustainable Development Dpt, Savoie Technolac, 73373, Le Bourget du Lac, FranceNam Theun 2 Power Company Limited (NTPC), Environment & Social Division &ndash; Water Quality and Biodiversity Dept. &ndash; Gnommalath Office, P.O. Box 5862, Vientiane, Lao PDRNam Theun 2 Power Company Limited (NTPC), Environment & Social Division &ndash; Water Quality and Biodiversity Dept. &ndash; Gnommalath Office, P.O. Box 5862, Vientiane, Lao PDRElectriciteì de France, Hydro Engineering Centre, Sustainable Development Dpt, Savoie Technolac, 73373, Le Bourget du Lac, FranceUniversité de Toulouse; UPS GET, 14 Avenue E. Belin, 31400, Toulouse, FranceIn the present study, we measured independently CH<sub>4</sub> ebullition and diffusion in the footprint of an eddy covariance system (EC) measuring CH<sub>4</sub> emissions in the Nam Theun 2 Reservoir, a recently impounded (2008) subtropical hydroelectric reservoir located in the Lao People's Democratic Republic (PDR), Southeast Asia. The EC fluxes were very consistent with the sum of the two terms measured independently (diffusive fluxes + ebullition = EC fluxes), indicating that the EC system picked up both diffusive fluxes and ebullition from the reservoir. We showed a diurnal bimodal pattern of CH<sub>4</sub> emissions anti-correlated with atmospheric pressure. During daytime, a large atmospheric pressure drop triggers CH<sub>4</sub> ebullition (up to 100 mmol m<sup>−2</sup> d<sup>&minus;1</sup>), whereas at night, a more moderate peak of CH<sub>4</sub> emissions was recorded. As a consequence, fluxes during daytime were twice as high as during nighttime. <br><br> Additionally, more than 4800 discrete measurements of CH<sub>4</sub> ebullition were performed at a weekly/fortnightly frequency, covering water depths ranging from 0.4 to 16 m and various types of flooded ecosystems. Methane ebullition varies significantly seasonally and depends mostly on water level change during the warm dry season, whereas no relationship was observed during the cold dry season. On average, ebullition was 8.5 ± 10.5 mmol m<sup>−2</sup> d<sup>−1</sup> and ranged from 0 to 201.7 mmol m<sup>−2</sup> d<sup>−1</sup>. <br><br> An artificial neural network (ANN) model could explain up to 46% of seasonal variability of ebullition by considering total static pressure (the sum of hydrostatic and atmospheric pressure), variations in the total static pressure, and bottom temperature as controlling factors. This model allowed extrapolation of CH<sub>4</sub> ebullition on the reservoir scale and performance of gap filling over four years. Our results clearly showed a very high seasonality: 50% of the yearly CH<sub>4</sub> ebullition occurs within four months of the warm dry season. Overall, ebullition contributed 60–80% of total emissions from the surface of the reservoir (disregarding downstream emissions), suggesting that ebullition is a major pathway in young hydroelectric reservoirs in the tropics.http://www.biogeosciences.net/11/4251/2014/bg-11-4251-2014.pdf
spellingShingle C. Deshmukh
D. Serça
C. Delon
R. Tardif
M. Demarty
C. Jarnot
Y. Meyerfeld
V. Chanudet
P. Guédant
W. Rode
S. Descloux
F. Guérin
Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2
Biogeosciences
title Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2
title_full Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2
title_fullStr Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2
title_full_unstemmed Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2
title_short Physical controls on CH<sub>4</sub> emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2
title_sort physical controls on ch sub 4 sub emissions from a newly flooded subtropical freshwater hydroelectric reservoir nam theun 2
url http://www.biogeosciences.net/11/4251/2014/bg-11-4251-2014.pdf
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