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| Titel |
Seasonal changes in CH4 emissions from an alpine reservoir, Lake Klöntal, Switzerland |
| VerfasserIn |
S. Sollberger, W. Eugster, C. Schubert, B. Wehrli |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063906
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| Zusammenfassung |
| Abstract
Atmospheric methane (CH4) concentration
doubled since the pre-industrialized era and its potential as a greenhouse gas is
25 higher than CO2 over a 100-year horizon. Recent studies showed an important
contribution of inland waters, including hydropower reservoirs, to the global CH4
cycle. However, the large seasonal and latitudinal variability of emissions reported
in the literature highlights the necessity for a better understanding of CH4 emission
mechanisms. The aim of this study was to investigate physical factors (water level
and temperature) that trigger the seasonal pattern of CH4 emissions in a Swiss
alpine reservoir, Lake Klöntal, using multiple methods. Atmospheric CH4 flux was
measured using a fast methane analyzer (FMA, Los Gatos Research) and an eddy
covariance tower set on a floating platform from April to December 2011 (before
ice sets). Emissions were also measured monthly via chambers and calculated from
surface water concentrations using Henry’s law. Methane ebullition was examined
over the lake surface of 5 km2 using a split-beam echosounder. Typical daily
variations of CH4 were measured with the eddy covariance setup within the range
of 0.23 and 7.4 mg CH4 m-2 d-1 (95% confidence interval) and were mainly
related to temperature and solar radiation variability. The seasonal trend shows that
average fluxes increase from 3.0 (April) to 3.7 mg CH4 m-2 d-1 in November.
Much larger fluctuations can be observed in comparison to the chamber results
where the emissions typically increase throughout the day. Furthermore, highest
chamber fluxes were measured in July and October, which does not correspond
with the FMA results (November). This inconsistency is also observed in the flux
estimates calculated from surface concentrations of which the highest fluxes were
in September. Ebullition was only observed (Jul., Sep. and Nov.) in a very shallow
area where it was not possible to use the echosounder. Hence, our measurements
may slightly underestimate the average fluxes, but they do record the magnitude
of these changes via different methods. We thus conclude that the variability of
CH4 fluxes observed throughout the literature and our study is related to both
physical triggers and the method used for measurements. Eddy measurements
are continuous but limited spatially, whereas chamber measurements directly
spatially cover more of the lake surface but at low and intermittent frequency.
The discrepancy between surface concentrations used for flux measurements and
chamber emissions may also be due to the fact that sampling did not occur
simultaneously at the same spot. This study highlights the necessity for future
assessments of CH4 emissions from water bodies to use a combination of methods
in order to account for the various sources of CH4 emission. |
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