References of "Limnology & Oceanography"
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See detailProduction of dissolved organic matter by phytoplankton and its uptake by heterotrophic prokaryotes in large tropical lakes
Morana, Cédric; Sarmento, Hugo; Descy, Jean-Pierre et al

in Limnology & Oceanography (2014), 59(4), 1364-1375

In pelagic ecosystems, phytoplankton extracellular release can extensively subsidize the heterotrophic prokaryotic carbon demand. Time-course experiments were carried out to quantify primary production ... [more ▼]

In pelagic ecosystems, phytoplankton extracellular release can extensively subsidize the heterotrophic prokaryotic carbon demand. Time-course experiments were carried out to quantify primary production, phytoplankton excretion, and the microbial uptake of freshly released dissolved organic carbon (DOC) derived from phytoplankton extracellular release (DOCp) in four large tropical lakes distributed along a productivity gradient: Kivu, Edward, Albert, and Victoria. The contributions of the major heterotrophic bacterial groups to the uptake of DOCp was also analyzed in Lake Kivu, using microautoradiography coupled to catalyzed reporter deposition fluorescent in situ hybridization. The percentage of extracellular release (PER) varied across the productivity gradient, with higher values at low productivity. Furthermore, PER was significantly related to high light and low phosphate concentrations in the mixed layer and was comparatively higher in oligotrophic tropical lakes than in their temperate counterparts. Both observations suggest that environmental factors play a key role in the control of phytoplankton excretion. Standing stocks of DOCp were small and generally contributed less than 1% to the total DOC because it was rapidly assimilated by prokaryotes. In other words, there was a tight coupling between the production and the heterotrophic consumption of DOCp. None of the major phylogenetic bacterial groups that were investigated differed in their ability to take up DOCp, in contrast with earlier results reported for standard labeled single-molecule substrates (leucine, glucose, adenosine triphosphate). It supports the idea that the metabolic ability to use DOCp is widespread among heterotrophic prokaryotes. Overall, these results highlight the importance of carbon transfer between phytoplankton and bacterioplankton in large African lakes. [less ▲]

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See detailSeasonal and interannual variations of community metabolism rates of a Posidonia oceanica seagrass meadow
Champenois, Willy ULg; Borges, Alberto ULg

in Limnology & Oceanography (2012), 57(1), 347-361

We report gross primary production (GPP), community respiration (CR), and net community production (NCP) over a Posidonia oceanica meadow at 10 m in Corsica (Bay of Revellata) based on the open water O2 ... [more ▼]

We report gross primary production (GPP), community respiration (CR), and net community production (NCP) over a Posidonia oceanica meadow at 10 m in Corsica (Bay of Revellata) based on the open water O2 mass balance from a data set of hourly measurements with an array of three O2 optodes deployed from August 2006 to October 2009. The method was checked by comparison with discrete measurements of metabolic rates derived from benthic chamber incubations also based on the diel change of O2. This comparison was satisfactory and actually highlights the potential caveats of benthic incubation measurements related to O2 accumulation in small chambers leading to photorespiration and an underestimation of GPP. Our data confirmed previous P. oceanica meadows GPP and CR values, strong seasonal variations, and net autotrophy. High-resolution data revealed strong interannual variability, with a decrease of GPP by 35% and NCP by 87% during 2006-2007 characterized by a mild and less stormy winter compared with 2007-2008 and 2008-2009. P. oceanica meadows are then expected to decrease export of organic carbon to adjacent communities (decrease of NCP), since a decrease in frequency and intensity of marine storms is expected in the future in the Mediterranean Sea as a result of a northward shift of the Atlantic storm track. [less ▲]

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See detailCarbonate chemistry in the coastal zone responds more strongly to eutrophication than to ocean acidification
Borges, Alberto ULg; Gypens, N.

in Limnology & Oceanography (2010), 55(1), 346-353

The accumulation of anthropogenic CO2 in the ocean has altered carbonate chemistry in surface waters since preindustrial times and is expected to continue to do so in the coming centuries. Changes in ... [more ▼]

The accumulation of anthropogenic CO2 in the ocean has altered carbonate chemistry in surface waters since preindustrial times and is expected to continue to do so in the coming centuries. Changes in carbonate chemistry can modify the rates and fates of marine primary production and calcification. These modifications can in turn lead to feedback on increasing atmospheric CO2. We show, using a numerical model, that in highly productive nearshore coastal marine environments, the effect of eutrophication on carbon cycling can counter the effect of ocean acidification on the carbonate chemistry of surface waters. Also, changes in river nutrient delivery due to management regulation policies can lead to stronger changes in carbonate chemistry than ocean acidification. Whether antagonistic or synergistic, the response of carbonate chemistry to changes of nutrient delivery to the coastal zone (increase or decrease, respectively) is stronger than ocean acidification. [less ▲]

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See detailBiogeochemistry of the Tana estuary and delta (northern Kenya)
Bouillon, Steven; Dehairs, Frank; Schiettecatte, Laure-Sophie et al

in Limnology & Oceanography (2007), 52(1), 45-59

The estuarine mixing zone of the Tana River (northern Kenya) and an extensive deltaic area just south of the estuary were sampled in April 2004 with the aim of identifying the distribution, sources, and ... [more ▼]

The estuarine mixing zone of the Tana River (northern Kenya) and an extensive deltaic area just south of the estuary were sampled in April 2004 with the aim of identifying the distribution, sources, and processing of particulate and dissolved organic carbon (POC, DOC) and inorganic carbon (DIC). C4 inputs from the catchment contributed ,50% to the POC pool in the Tana River and estuary, and in the mangrove creek water column and intertidal sediments. The d13C values of DOC, however, were typically much more negative than that of POC, indicating a substantially higher contribution by C3 and/or mangrove-derived carbon in the DOC pool. The undersaturation of O2, high pCO2, and the nonconservative nature of DIC and d13CDIC suggest a strongly heterotrophic water column, particularly in the freshwater part of the Tana and in the tidal creeks in the delta, where high additional inputs of organic matter were observed. However, some of these sites showed d18ODO signatures lower than the atmospheric equilibrium (i.e., +24.2%) indicative of significant O2 production by photosynthesis. Therefore, the heterotrophic signature in the water column is likely the result of a strong interaction with the large intertidal areas, whereby respiratory activity in sediments and in the overlying water column during tidal inundation leave a marked signature on the water column. This is confirmed by the covariation between salinity-normalized total alkalinity and DIC, whose slope indicates an important role for anaerobic diagenetic processes. If our data are representative for other large river systems in the region, current estimates are likely to underestimate suspended matter and both inorganic and organic C fluxes to the Indian Ocean from tropical east Africa. [less ▲]

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See detailAssessment of the processes controlling the seasonal variations of dissolved inorganic carbon in the North Sea
Bozec, Y.; Thomas, H.; Schiettecatte, L. S. et al

in Limnology & Oceanography (2006), 51(6), 27462762

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), and inorganic nutrients to assess the abiotic and biological processes governing the ... [more ▼]

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), and inorganic nutrients to assess the abiotic and biological processes governing the monthly variations of DIC. During winter, advection and air–sea exchange of CO2 control and increase the DIC content in the surface and deeper layers of the northern and central North Sea, with the atmosphere supplying CO2 on the order of 0.2 mol C m22 month21 to these areas. From February to July, net community production (NCP) controls the seasonal variations of DIC in the surface waters of the entire North Sea, with a net uptake ranging from 0.5 to 1.4 mol C m22 month21. During the August–December period, NCP controls the seasonal variations of DIC in the southern North Sea, with a net release ranging from 0.5 to 0.8 mol C m22 month21. Similarly, during the April–August period in the deeper layer of the northern North Sea, the NCP was the main factor controlling DIC concentrations, with a net release ranging from 0.5 to 5.5 mol C m22 month21. In the surface layer of the North Sea, NCP on the basis of DIC was 4.3 6 0.4 mol C m22 yr21, whereas, NCP on the basis of nitrate was 1.6 6 0.2 mol C m22 yr21. Under nutrient-depleted conditions, preferential recycling (extracellular) of nutrients and intracellular mechanisms occurred and were responsible for the non-Redfield uptake of DIC versus nitrate and phosphate. [less ▲]

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See detailInfluence of zooplankton stoichiometry on nutrient sedimentation in a lake system
Darchambeau, François ULg; Thys, I.; Leporcq, B. et al

in Limnology & Oceanography (2005), 50(3), 905-913

We explored rates and stoichiometry (C: N: P ratios) of sinking particles in a temperate reservoir during a 2-yr period. Plankton was sampled weekly, and a sediment trap placed below the metalimnion ... [more ▼]

We explored rates and stoichiometry (C: N: P ratios) of sinking particles in a temperate reservoir during a 2-yr period. Plankton was sampled weekly, and a sediment trap placed below the metalimnion collected sinking particles. There were no significant relationships between the stoichiometry of entrapped material and seston or zooplankton stoichiometry. However the differences in the entrapped C: P and N: P ratios between consecutive trap samplings were negatively correlated with the time variations of the zooplankton C: P and N: P ratios. Zooplankton C: P and N: P ratios were positively correlated with the percentage of copepod biomass in total zooplankton biomass > 250 mu m and negatively correlated with the percentage of cladocerans. Zooplankton biomass > 250 mu m reduced the fraction of N and P primary production lost to sinking (export ratio). The residuals of the N export ratio versus zooplankton biomass relationship were negatively correlated with the zooplankton N: P ratio, whereas there was a positive relationship with the residuals of the P export ratio relationship. These observations support the hypothesis that the regulation of elemental homeostasis in the herbivorous zooplankton consumers occurs at least partly at the assimilation/egestion level. Elements ingested in excess-P for the herbivorous copepods and N for many cladocerans-are concentrated into sinking feces, whereas the deficient elements are captured into biomass. [less ▲]

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See detailGas transfer velocities of CO2 in three European estuaries (Randers Fjord, Scheldt and Thames)
Borges, Alberto ULg; Delille, Bruno ULg; Schiettecatte, Laure-Sophie et al

in Limnology & Oceanography (2004), 49(5), 1630-1641

We measured the flux of CO2 across the air–water interface using the floating chamber method in three European estuaries with contrasting physical characteristics (Randers Fjord, Scheldt, and Thames). We ... [more ▼]

We measured the flux of CO2 across the air–water interface using the floating chamber method in three European estuaries with contrasting physical characteristics (Randers Fjord, Scheldt, and Thames). We computed the gas transfer velocity of CO2 (k) from the CO2 flux and concomitant measurements of the air–water gradient of the partial pressure of CO2 (pCO2). There was a significant linear relationship between k and wind speed for each of the three estuaries. The differences of the y-intercept and the slope between the three sites are related to differences in the contribution of tidal currents to water turbulence at the interface and fetch limitation. The contribution to k from turbulence generated by tidal currents is negligible in microtidal estuaries such as Randers Fjord but is substantial, at low to moderate wind speeds, in macrotidal estuaries such as the Scheldt and the Thames. Our results clearly show that in estuaries a simple parameterization of k as a function of wind speed is site specific and strongly suggest that the y-intercept of the linear relationship is mostly influenced by the contribution of tidal currents, whereas the slope is influenced by fetch limitation. This implies that substantial errors in flux computations are incurred if generic relationships of the gas transfer velocity as a function of wind speed are employed in estuarine environments for the purpose of biogas air–water flux budgets and ecosystem metabolic studies. [less ▲]

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