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...
Main Authors: | , , , , , , , , , , , |
---|---|
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 |
_version_ | 1819209295710912512 |
---|---|
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>−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. |
first_indexed | 2024-12-23T05:53:01Z |
format | Article |
id | doaj.art-5fd9817d7c564bfa901681f3522cbf0e |
institution | Directory Open Access Journal |
issn | 1726-4170 1726-4189 |
language | English |
last_indexed | 2024-12-23T05:53:01Z |
publishDate | 2014-08-01 |
publisher | Copernicus Publications |
record_format | Article |
series | Biogeosciences |
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 – Université de Toulouse – CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceLaboratoire d'Aérologie – Université de Toulouse – CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceLaboratoire d'Aérologie – Université de Toulouse – CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceNam Theun 2 Power Company Limited (NTPC), Environment & Social Division – Water Quality and Biodiversity Dept. – Gnommalath Office, P.O. Box 5862, Vientiane, Lao PDREnvironnement Illimite, 1453 rue Saint Timothee, Montreal QC, CanadaLaboratoire d'Aérologie – Université de Toulouse – CNRS UMR 5560; 14 Av. Edouard Belin, 31400, Toulouse, FranceLaboratoire d'Aérologie – Université de Toulouse – 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 – Water Quality and Biodiversity Dept. – Gnommalath Office, P.O. Box 5862, Vientiane, Lao PDRNam Theun 2 Power Company Limited (NTPC), Environment & Social Division – Water Quality and Biodiversity Dept. – 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>−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 |
work_keys_str_mv | AT cdeshmukh physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT dserca physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT cdelon physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT rtardif physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT mdemarty physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT cjarnot physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT ymeyerfeld physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT vchanudet physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT pguedant physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT wrode physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT sdescloux physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 AT fguerin physicalcontrolsonchsub4subemissionsfromanewlyfloodedsubtropicalfreshwaterhydroelectricreservoirnamtheun2 |