Article (Scientific journals)
Biogeochemistry of a large and deep tropical lake (Lake Kivu, East Africa: insights from a stable isotope study covering an annual cycle
Morana, Cédric; Darchambeau, François; Roland, Fleur et al.
2015In Biogeosciences, 12 (16), p. 4953-4963
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Abstract :
[en] During this study, we investigated the seasonal variability of the concentration and the stable isotope composition of several inorganic and organic matter (OM) reservoirs in the large, oligotrophic and deep tropical Lake Kivu (East Africa). Data were acquired over 1 year at a fortnightly temporal resolution. The _13C signature of the dissolved inorganic carbon (DIC) increased linearly with time during the rainy season, then suddenly decreased during the dry season due to vertical mixing with 13C-depleted DIC waters. The _13C signature of the particulate organic carbon pool (POC) revealed the presence of a consistently abundant methanotrophic biomass in the oxycline throughout the year. We also noticed a seasonal shift during the dry season toward higher values in the _15N of particulate nitrogen (PN) in the mixed layer and _15N-PN was significantly related to the contribution of cyanobacteria to the phytoplankton assemblage, suggesting that rainy season conditions could be more favourable to atmospheric nitrogen-fixing cyanobacteria. Finally, zooplankton were slightly enriched in 13C compared to the autochthonous POC pool, and the _15N signature of zooplankton followed well the seasonal variability in _15N-PN, consistently 3.0_1.1‰heavier than the PN pool. Together, _13C and _15N analysis suggests that zooplankton directly incorporate algal-derived OM in their biomass, and that they rely almost exclusively on this source of OM throughout the year in general agreement with the very low allochthonous OM inputs from rivers in Lake Kivu.
Research center :
FOCUS - Freshwater and OCeanic science Unit of reSearch - ULiège
Disciplines :
Aquatic sciences & oceanology
Author, co-author :
Morana, Cédric ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Chemical Oceanography Unit (COU)
Darchambeau, François ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Océanographie chimique
Roland, Fleur ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Océanographie chimique
Borges, Alberto  ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Océanographie chimique
Muvundja, F.
Kelemen, Z.
Masilya, P.
Descy, Jean-Pierre 
Bouillon, S.
Language :
English
Title :
Biogeochemistry of a large and deep tropical lake (Lake Kivu, East Africa: insights from a stable isotope study covering an annual cycle
Publication date :
2015
Journal title :
Biogeosciences
ISSN :
1726-4170
eISSN :
1726-4189
Publisher :
European Geosciences Union (EGU), Germany
Volume :
12
Issue :
16
Pages :
4953-4963
Peer reviewed :
Peer Reviewed verified by ORBi
European Projects :
FP7 - 240002 - AFRIVAL - African river basins: catchment-scale carbon fluxes and transformations.
Name of the research project :
AFRIVAL
Funders :
CE - Commission Européenne [BE]
Available on ORBi :
since 24 August 2015

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