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| Titel |
Anaerobic methane oxidation in two tropical freshwater systems |
| VerfasserIn |
Fleur Roland, François Darchambeau, Sean A. Crowe, Alberto V. Borges |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090989
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| Publikation (Nr.) |
 EGU/EGU2014-5252.pdf |
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| Zusammenfassung |
| Lake Kivu is one of the East African Great Lakes. It is located at the border between Rwanda
and the Democratic Republic of the Congo. It is a deep meromictic lake characterized by
huge amounts of methane (CH4) (60 km3 at 0°C and 1 atm) dissolved in its deep waters.
Two thirds of the CH4 originates from anoxic bacterial reduction of dissolved carbon
dioxide and one third from anaerobic degradation of settling organic material. CH4
then diffuses slowly from the monimolimnion to surface waters where many is
oxidised by methanotrophic microorganisms. In Lake Kivu, this biological oxidation of
CH4 could occur with different final electron acceptors: oxygen (aerobic oxidation)
but also nitrate (NO3-), nitrite, sulfate (SO42-), iron (Fe) or manganese (Mn) in
anaerobic conditions. If the anaerobic oxidation of CH4 (AOM) is generally coupled to
SO42- reduction in marine waters, electron acceptors of the AOM were rarely
investigated in freshwater systems. Five field campaigns were conducted from 2011 to
2013 during periods with contrasted ventilations of the upper water column. The
dry season is characterized by a deeper mixing of surface waters ended by a steep
gradient of physico-chemical conditions at the redox interface, while during the
rainy season the mixed layer is shallower and ended at its deeper part by a NO3-
accumulation zone. Sampling was conducted in the main basin of Lake Kivu but also in a
particular sub-basin located northeast of the lake, the Kabuno Bay. Both systems are
meromictic but differ in terms of morphometry and geochemistry with a shallower
permanent chemocline and higher concentrations of CH4, Fe and Mn in the anoxic
waters in Kabuno Bay compared to the main lake. Samples were collected for the
measurements of CH4 concentrations and the various potential electron acceptors
of the AOM. CH4 oxidation rates were measured along vertical profiles at 5 m
and 0.5 m depth intervals respectively in the main basin and Kabuno bay water
columns. Results indicate high rates of AOM in both main basin (up to 7 μmol L-1
d-1) and Kabuno bay (up to 16 μmol L-1 d-1). In the main basin, we observed a
co-occurrence of the AOM and the SO42- reduction in the dry season. During the rainy
season, higher oxidation rates occurred in the NO3- accumulation zone, which is in
favour of a coupling between AOM and NO3- reduction. In Kabuno Bay, the higher
AOM rates were observed at depths with highest particulate Fe concentrations.
Our results suggest that AOM coupled with SO42-reduction may occur during the
dry season in the main basin, whereas this oxidation could be coupled with NO3-
reduction during the rainy season. In Kabuno Bay, the co-occurrence of the Fe [III]
peak with high AOM suggests a coupling between the AOM and Fe reduction. |
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