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| Titel |
Methanotrophy within the water column of a large meromictic tropical lake (Lake Kivu, East Africa) |
| VerfasserIn |
C. Morana, A. V. Borges, F. A. E. Roland, F. Darchambeau, J.-P. Descy, S. Bouillon |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 7 ; Nr. 12, no. 7 (2015-04-07), S.2077-2088 |
| Datensatznummer |
250117888
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| Publikation (Nr.) |
 copernicus.org/bg-12-2077-2015.pdf |
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| Zusammenfassung |
| The permanently stratified Lake Kivu is one of the largest freshwater
reservoirs of dissolved methane (CH4) on Earth. Yet CH4 emissions
from its surface to the atmosphere have been estimated to be 2 orders of
magnitude lower than the CH4 upward flux to the mixed layer, suggesting
that microbial CH4 oxidation is an important process within the water
column. A combination of natural abundance stable carbon isotope analysis
(δ13C) of several carbon pools and 13CH4-labelling
experiments was carried out during the rainy and dry season to quantify (i)
the contribution of CH4-derived carbon to the biomass, (ii)
methanotrophic bacterial production (MBP), and (iii) methanotrophic
bacterial growth efficiency (MBGE), defined as the ratio between MBP and
gross CH4 oxidation. We also investigated the distribution and the
δ13C of specific phospholipid fatty acids (PLFAs), used as
biomarkers for aerobic methanotrophs. Maximal MBP rates were measured in the
oxycline, suggesting that CH4 oxidation was mainly driven by oxic
processes. Moreover, our data revealed that methanotrophic organisms in the
water column oxidized most of the upward flux of CH4, and that a
significant amount of CH4-derived carbon was incorporated into the
microbial biomass in the oxycline. The MBGE was variable (2–50%) and
negatively related to CH4 : O2 molar ratios. Thus, a comparatively
smaller fraction of CH4-derived carbon was incorporated into the
cellular biomass in deeper waters, at the bottom of the oxycline where
oxygen was scarce. The aerobic methanotrophic community was clearly
dominated by type I methanotrophs and no evidence was found for an active
involvement of type II methanotrophs in CH4 oxidation in Lake Kivu,
based on fatty acids analyses. Vertically integrated over the water column,
the MBP was equivalent to 16–60% of the average phytoplankton particulate
primary production. This relatively high magnitude of MBP, and the
substantial contribution of CH4-derived carbon to the overall biomass
in the oxycline, suggest that methanotrophic bacteria could potentially
sustain a significant fraction of the pelagic food web in the deep,
meromictic Lake Kivu. |
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