References of "Viroux, Laurent"
     in
Bookmark and Share    
See detailTrophic links in the lowland river Meuse (Belgium): importance of the predation exerted by rotifers on bacterio- and protozooplankton.
Joaquim-Justo, Célia ULg; Pirlot, S; Viroux, Laurent et al

Conference (2003, June 07)

Trophic interactions within the plankton of the lowland river Meuse (Belgium) were measured in Spring and Summer (2001). Consumption of bacteria by protozoa was measured by monitoring the radioactivity ... [more ▼]

Trophic interactions within the plankton of the lowland river Meuse (Belgium) were measured in Spring and Summer (2001). Consumption of bacteria by protozoa was measured by monitoring the radioactivity disappearance of 3H-thymidine labelled bacteria. The proportion of protozoan bacterivory attributable to flagellates and ciliates was determined with fluorescently labelled bacteria (FLB). Metazooplankton bacterivory was assessed with 0.5 µm fluorescent microparticles (FMPs) and predation of metazooplankton on ciliates was measured by using natural ciliate assemblages labelled with FMPs as tracer food. Grazing of metazooplankton on flagellates was determined through in situ incubations with manipulated metazooplankton densities. flagellates were the main bacterial consumers their grazing being 91  10 % of total bacterial grazing. Metazooplankton, essentially rotifers, grazing on bacteria was negligible compared to grazing by protozoa and to bacterial production. Protozoa grazing balanced bacterial production in early samplings but was lower in July. Predation of rotifers on heterotrophic flagellates (HF) was generally low (1.765 3.432 mg C m-3 d-1 ), the higher contribution of HF in the diet of rotifers being observed when Keratella cochlearis was the dominant metazooplankter. Predation of rotifers on ciliates was low in the first samples (0.557  0.004 mg C m-3 d-1) in contrast to measurements performed in July (8.722  1.363 mg C m-3d-1). The proportion of protozoa in the diet of rotifers was generally low compared to phytoplankton (< 30% of total carbon ingestion) except when phytoplankton biomass decreased below the incipient limiting level (ILL) of the main metazooplantonic species. In such conditions, protozoa (mainly ciliates) constituted ca. 50% of total rotifer food. These results give evidence that microbial organisms play an important role within the plankton of the river Meuse, ciliates providing an alternative food for metazooplankton when phytoplankton becomes scarce. [less ▲]

Detailed reference viewed: 15 (0 ULg)
Full Text
Peer Reviewed
See detailModelling the impact of benthic filter-feeders on the composition and biomass of river plankton
Descy, Jean-Pierre; Everbecq, Etienne ULg; Gosselain, Véronique ULg et al

in Freshwater Biology (2003), 48(3), 404-417

1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a ... [more ▼]

1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton (Stephanodiscus, Cyclotella -like, large diatoms, Skeletonema and non-siliceous algae) to model filter-feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus -like and Keratella -like rotifers. 2. According to density estimates from field surveys (Bachmann V. et al. (1995) Hydroecologie Appliquee, 7, 185, Bachmann V. & Usseglio-Polatera P. (1999) Hydrobiologia, 410, 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers. 3. The simulations suggest a significant impact of benthic filter-feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton. 4. A daily carbon balance for a typical summer shows the effect of benthic filter-feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches. [less ▲]

Detailed reference viewed: 40 (8 ULg)
Full Text
See detailModélisation de l’impact de mollusques filtreurs sur le phytoplancton de la Moselle.
Descy, Jean-Pierre; Everbecq, Etienne ULg; Gosselain, Véronique ULg et al

in Tribune de l'Eau (La) (2002), 55-56(n° 619-620), 130-138

Le modèle POTAMON (Everbecq & al., 2001) a été utilisé pour simuler l'effet de mollusques bivalves (principalement Dreissena polymorpha) sur le phytoplancton et le zooplancton d'une rivière de plaine, la ... [more ▼]

Le modèle POTAMON (Everbecq & al., 2001) a été utilisé pour simuler l'effet de mollusques bivalves (principalement Dreissena polymorpha) sur le phytoplancton et le zooplancton d'une rivière de plaine, la Moselle. Les simulations suggèrent un impact significatif des mollusques filtreurs sur le phytoplancton, en particulier en été. Les simulations ont également permis d'établir un bilan carbone de la rivière et d'expliquer les déficits en oxygène observés dans la Moselle. [less ▲]

Detailed reference viewed: 23 (4 ULg)
Full Text
Peer Reviewed
See detailPotamon: A Dynamic Model for Predicting Phytoplankton Composition and Biomass in Lowland Rivers
Everbecq, Etienne ULg; Gosselain, Véronique ULg; Viroux, Laurent et al

in Water Research (2001), 35(4), 901-12

POTAMON is a unidimensional, non-stationary model, designed for simulating potamoplankton from source to mouth. The forcing variables are discharge, river morphology, water temperature, available light ... [more ▼]

POTAMON is a unidimensional, non-stationary model, designed for simulating potamoplankton from source to mouth. The forcing variables are discharge, river morphology, water temperature, available light and nutrient inputs. Given the description of several algal categories, POTAMON allows to simulate algal "successions" at a particular site, as well as longitudinal changes of potamoplankton composition and biomass. The algal categories differ by their physiology, their loss rates, and their sensitivity to grazing by zooplankton. Two zooplankton categories were considered, Brachionus-like and Keratella-like, which differ by their clearance rate, their incipient limiting level, their selectivity towards phytoplankton, and their growth yield. The model simulates satisfactorily the onset and the magnitude of the phytoplankton spring bloom in the Belgian part of R. Meuse, the biomass decrease in early summer, and the autumn bloom. It also renders the major variations of algal assemblages along the river. The model allows to confirm that the main driving variables of potamoplankton dynamics in a eutrophic river are physical factors: discharge and related variables (e.g. retention time), light and temperature. In addition, the simulations confirm that the zooplankton-phytoplankton interaction may result in phytoplankton biomass fluctuations and compositional changes. POTAMON can be useful to explore plankton dynamics in a large river, and it may become a tool to test various management measures. [less ▲]

Detailed reference viewed: 39 (7 ULg)
Full Text
Peer Reviewed
See detailGrazing by large river zooplankton: a key to summer potamoplankton decline? The case of the Meuse and Moselle rivers in 1994 and 1995
Gosselain, Véronique; Descy, Jean-Pierre; Viroux, Laurent et al

in Hydrobiologia (1998)

To explain summer declines in phytoplankton biomass in large rivers, we compared the effect of zooplankton grazing on the planktonic algae of two large European rivers, the Meuse and the Moselle. In situ ... [more ▼]

To explain summer declines in phytoplankton biomass in large rivers, we compared the effect of zooplankton grazing on the planktonic algae of two large European rivers, the Meuse and the Moselle. In situ grazing was measured during two years (1994 and 1995), using the Haney method. Total zooplankton community filtration rates recorded in the river Meuse ranged between 1 and 32% of the water volume filtered per day. A drastic algal decline was observed early July both years and may be explained by high densities of a rotiferdominated zooplankton community (500–700 ind. l􀀀1) with more than 75%of Brachionus calyciflorus. During the summer period in 1994, when grazingwas over 20%, edible algal biomasswas controlled by a diversified rotifer community (up to 2500 ind.l􀀀1), while a nonedible algal assemblage developed. In contrast, phytoplankton biomass remained comparatively lowin the Moselle throughout the lowflowperiod, as did zooplankton numbers duringmost of this time (fewer than 200 ind. l􀀀1 during the summer period). The proportion of crustaceans in this zooplanktonwas rather higher than in the Meuse, and they dominated at times, in biomass as well as in numbers. Nevertheless, measured in situ grazing rates (1–15%) could not explain the low summer algal biomass, even if low filtration rates may at times represent a significant carbon loss for phytoplankton, when and where net algal production was low. As a conclusion, the role of phytoplankton – zooplankton interactions in controlling algal biomass in large rivers is discussed. [less ▲]

Detailed reference viewed: 26 (0 ULg)
Full Text
See detailModélisation du bilan en oxygène dans la Moselle
Descy, Jean-Pierre; Everbecq, Etienne ULg; Gosselain, Véronique et al

Report (1993)

L'objet de ce travail était d'expliquer les diminutions de concentration en oxygène dissous rencontrées dans le secteur de la Moselle situé entre Metz et Trèves. A cette fin, un modèle déterministe de la ... [more ▼]

L'objet de ce travail était d'expliquer les diminutions de concentration en oxygène dissous rencontrées dans le secteur de la Moselle situé entre Metz et Trèves. A cette fin, un modèle déterministe de la qualité des eaux de surface initialement développé pour la Meuse a été utilisé. [less ▲]

Detailed reference viewed: 12 (0 ULg)