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| Titel |
High-Temporal-Resolution Measurement of Methane Ebullition From a Stratified, Eutrophic Lake |
| VerfasserIn |
C. Varadharajan, E. Borja, A. P. Tcaciuc, H. F. Hemond |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022383
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| Zusammenfassung |
| Significant amounts of methane can be released to the atmosphere from freshwater
lakes, particularly through bubbling. However, spatial and temporal heterogeneity in
ebullition has complicated efforts to accurately measure such methane emissions. In
2007, bubbling from the Upper Mystic Lake in Massachusetts, US was strongly
episodic, with peak fluxes at the water surface approaching 200 ml/m2/d in late
summer and fall, while average bubble fluxes were approximately 30-45 ml/m2/d.
However the temporal resolution of these measurements was only of the order of a
week. In 2008, under-water bubble traps were equipped with pressure sensors that
measured the gas collected every 5 minutes. Episodes of bubbling were almost
synchronous throughout the lake and tended to last for several days, though the
amount and composition of gas released from the sediment varied considerably
between sites. The onset of bubbling episodes is correlated with drops in hydrostatic
pressure that occurred during periods of low lake water levels. Ebullition fluxes
in 2008 were a factor of 2 less than 2007 fluxes, although the spatial pattern of
bubbling was similar in both years, with deeper locations generally bubbling more
than shallow sites. However, in some cases fluxes varied by as much as a factor of
20 between stations that were only 15-30 m apart, which indicates that sediment
methane sources could be highly localized. The mixing ratio of methane present in the
collected gas ranged from 30% to 90%, and was generally higher at locations that
bubbled more. The partial pressure of total methane present in the lake sediments
was found to be 2 |
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