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See detailCarbon cycling in a large, meromictic tropical lake (Lake Kivu, East Africa): insights from seasonal monitoring of biogeochemical depth profiles
Morana, C; Darchambeau, F; Muvundja, F et al

Poster (2014, April 27)

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See detailVariability of carbon dioxide and methane in the epilimnion of Lake Kivu
Borges, Alberto ULg; Bouillon, S.; Abril, G. et al

in Descy, J.-P.; Darchambeau, François; Schmid, M. (Eds.) Lake Kivu: Limnology and biogeochemistry of a tropical great lake (2012)

We report a dataset of the partial pressure of CO2 (pCO2) and me-thane concentrations (CH4) in the surface waters of Lake Kivu ob-tained during four cruises covering the two main seasons (rainy and dry ... [more ▼]

We report a dataset of the partial pressure of CO2 (pCO2) and me-thane concentrations (CH4) in the surface waters of Lake Kivu ob-tained during four cruises covering the two main seasons (rainy and dry). Spatial gradients of surface pCO2 and CH4 concentrations were modest in the main basin. In Kabuno Bay, pCO2 and CH4 concentra-tions in surface waters were higher, owing to the stronger influence of subaquatic springs from depth. Seasonal variations of pCO2 and CH4 in the main basin of Lake Kivu were strongly driven by deepen-ing of the epilimnion and the resulting entrainment of water charac-terized by higher pCO2 and CH4 concentrations. Physical and chem-ical vertical patterns in Kabuno Bay were seasonally stable, owing to a stronger stratification and smaller surface area inducing fetch limi-tation of wind driven turbulence. A global and regional cross-system comparison of pCO2 and CH4 concentrations in surface waters of lakes highlights the peculiarity of Kabuno Bay in terms of pCO2 values in surface waters. In terms of surface CH4 concentrations, both Kabuno Bay and the main basin of Lake Kivu are at the lower end of values in lakes globally, despite the huge amounts of CH4 and CO2 in the deeper layers of the lake. [less ▲]

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See detailIn vitro simulation of oxic/suboxic diagenesis in an estuarine fluid mud subjected to redox oscillations
Abril, Gwenael; Commarieu, Marc-Vincent ULg; Etcheber, Henri et al

in Estuarine Coastal And Shelf Science (2010), 88(2), 279-291

Estuarine turbidity maxima (ETMs) are sites of intense mineralisation of land-derived particulate organic matter (OM), which occurs under oxic/suboxic oscillating conditions owing to repetitive ... [more ▼]

Estuarine turbidity maxima (ETMs) are sites of intense mineralisation of land-derived particulate organic matter (OM), which occurs under oxic/suboxic oscillating conditions owing to repetitive sedimentation and resuspension cycles at tidal and neap-spring time scales. To investigate the biogeochemical processes involved in OM mineralisation in ETMs, an experimental set up was developed to simulate in vitro oxic/anoxic oscillations in turbid waters and to follow the short timescale changes in oxygen, carbon, nitrogen, and manganese concentration and speciation. We present here the results of a 27-day experiment (three oxic periods and two anoxic periods) with an estuarine fluid mud from the Gironde estuary. Time courses of chemical species throughout the experiment evidenced the occurrence of four distinct characteristic periods with very different properties. Steady oxic conditions were characterised by oxygen consumption rates between 10 and 40 mu mol L-1 h(-1), dissolved inorganic carbon (DIC) production of 9-12 mu mol L-1 h(-1), very low NE4+ and Mn2+ concentrations, and constant NO3 production rates (0.4 - 0.7 mu mol L-1 h(-1)) due to coupled ammonification and nitrification. The beginning of anoxic periods (24 h following oxic to anoxic switches) showed DIC production rates of 2.5-8.6 mu mol L-1 h(-1) and very fast NO consumption (5.6-6.3 mu mol L-1 h(-1)) and NH4+ production (1.4-1.5 mu mol L-1 h(-1)). The latter rates were positively correlated to NO concentration and were apparently caused by the predominance of denitrification and dissimilatory nitrate reduction to ammonia. Steady anoxic periods were characterised by constant and low NO3- concentrations and DIG and NH4+ productions of less than 1.3 and 0.1 mu mol L-1 h(-1), respectively. Mn2+ and CH4 were produced at constant rates (respectively 0.3 and 0.015 mu mol L-1 h(-1)) throughout the whole anoxic periods and in the presence of nitrate. Finally, reoxidation periods (24-36 h following anoxic to oxic switches) showed rapid NH4+ and Mn2+ decreases to zero (1.6 and 0.8-2 mu mol L-1 h(-1), respectively) and very fast NO production (3 mu mol L-1 h(-1)). This NO3- production, together with marked transient peaks of dissolved organic carbon a few hours after anoxic to oxic switches, suggested that particulate OM mineralisation was enhanced during these transient reoxidation periods. An analysis based on C and N mass balance suggested that redox oscillation on short time scales (day to week) enhanced OM mineralisation relative to both steady oxic and steady anoxic conditions, making ETMs efficient biogeochemical reactors for the mineralisation of refractory terrestrial OM at the land-sea interface. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

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