 |
| Titel |
Physical controls on CH4 emissions from a newly flooded subtropical freshwater hydroelectric reservoir: Nam Theun 2 |
| VerfasserIn |
C. Deshmukh, D. Serça, C. Delon, R. Tardif, M. Demarty, C. Jarnot, Y. Meyerfeld, V. Chanudet, P. Guédant, W. Rode, S. Descloux, F. Guérin |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 15 ; Nr. 11, no. 15 (2014-08-13), S.4251-4269 |
| Datensatznummer |
250117546
|
| Publikation (Nr.) |
 copernicus.org/bg-11-4251-2014.pdf |
|
|
|
|
|
| Zusammenfassung |
In the present study, we measured independently CH4 ebullition and
diffusion in the footprint of an eddy covariance system (EC) measuring
CH4 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 CH4 emissions anti-correlated with atmospheric
pressure. During daytime, a large atmospheric pressure drop triggers CH4
ebullition (up to 100 mmol m−2 d−1), whereas at night, a more
moderate peak of CH4 emissions was recorded. As a consequence, fluxes
during daytime were twice as high as during nighttime.
Additionally, more than 4800 discrete measurements of CH4 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−2 d−1 and ranged from 0 to
201.7 mmol m−2 d−1.
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 CH4 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 CH4 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. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|