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| Titel |
Denitrification, anammox and fixed nitrogen removal in the water column of a tropical great lake |
| VerfasserIn |
François Darchambeau, Fleur Roland, Sean A. Crowe, Loreto de Brabandere, Marc Llirós, Tamara Garcia-Armisen, Ozgul Inceoglu, Céline Michiels, Pierre Servais, Cédric D. T. Morana, Steven Bouillon, Filip Meysman, Bart Veuger, Pascal M. Masilya, Jean-Pierre Descy, Alberto V. Borges |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083656
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| Zusammenfassung |
| If rates of microbial denitrification in aquatic systems are poorly constrained, it is much
more the case for tropical water bodies. Lake Kivu [2.50Ë S 1.59Ë S, 29.37Ë E
28.83Ë E] is one of the great lakes of the East African Rift. It is an oligotrophic
lake characterized by anoxic deep waters rich in dissolved gases (methane and
carbon dioxide) and nutrients, and by well oxygenated and nutrient-depleted surface
waters. During the seasonally stratified rainy season (October to May), a nitrogenous
zone characterized by the accumulation of nitrite (NO2-) and nitrate (NO3-) is
often observed in the lower layer of the mixolimnion. It results from nitrification of
ammonium released by decaying organic matter. With the seasonal uplift of the
oxygen minimum zone, the nitrogenous zone becomes anoxic and might be the most
preferential area for fixed nitrogen (N) removal in Lake Kivu. Our work aimed
at identifying and quantifying the processes of N losses by denitrification and/or
anammox in the nitrogenous zone of the Lake Kivu water column. During 5 sampling
campaigns (March 2010, October 2010, June 2011, February 2012 and September 2012),
isotopic labelling experiments were used to quantify denitrification and anammox
rates along vertical profiles at two pelagic stations of the main lake. Moreover,
N2:Ar ratios were estimated during the September 2012 campaign, and 16S rDNA
pyrosequencing was used to describe bacterial community composition during
the last 2 campaigns. No bacteria related to organisms performing anammox was
observed and labelling experiments failed to detect anammox at any locations and any
depths. In Lake Kivu, denitrifying bacteria were mainly related to Denitratisoma
and Thiobacillus genus. Significant denitrification rates were observed at several
occasions, especially under the oxic-anoxic interface in the bottom of the nitracline. The
annual average denitrification rate was estimated at ~150 μmoles N m-2 d-1.
Denitrification was not the only nitrate-consuming process: dissimilative nitrate reduction to
ammonium led to oxidized N removal with the same magnitude than denitrification alone.
Isotopic labelling accompanied by addition of elemental sulfur evidenced that the
upper vertical expansion of denitrification was limited by the abundance of reducing
agents, while oxidized forms of N limited the lower expansion of denitrification. |
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