Trophic relationships between planktonic microorganisms in the river Meuse (Belgium): A carbon budget

P. Servais, V. Gosselain, C. Joaquim-Justo, S. Becquevort, J. P. Thome, J. P. Descy

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During the period of plankton development (April to October 1996), the trophic relationships among phytoplankton, metazooplankton, protozooplankton and bacterioplankton were quantitatively studied at one location in the Belgian part of the river Meuse. Biomass fluctuations of phytoplankton, metazooplankton, bacteria and protozoa were monitored fortnightly. On the basis of in situ measurements of the fluxes of primary production, metazooplankton grazing, organic matter consumption by bacteria and grazing of bacteria by protozoa, the carbon fluxes between the different compartments of the first trophic levels were estimated on eleven sampling dates. Net primary production was measured from incubations with 14C bicarbonate and grazing of algae by metazooplankton was determined by in situ incubations with labelled algae in a grazing chamber. The algal biomass ingested was corrected for the edible phytoplankton and the carbon assimilated by metazooplankton was calculated taking into account zooplankton assimilation yield estimated from experimental data and from literature values. Bacterial production was evaluated by 3H-thymidine and 3H-leucine incorporation rates, and bacterial carbon demand was calculated taking into account a growth yield of 30%. Measurements of mortality and grazing of bacteria showed that grazing by protozooplankton was the major loss process indicating the main role of this compartment in the control of bacterial biomass. In the studied stretch of the river Meuse, autochthonous production exceeded, in most situations, the allochthonous inputs to the river. On average over the studied period, carbon consumption by metazooplankton and bacteria balanced organic carbon inputs from primary production and external loading. The large part of primary production used by bacteria and indirectly by protozooplankton points to the potential importance of the microbial food web in this river system.

Original languageEnglish
Pages (from-to)625-653
Number of pages29
JournalArchiv fur Hydrobiologie
Issue number4
Publication statusPublished - 1 Jan 2000


  • Bacteria
  • Carbon budget
  • Metazooplankton
  • Phytoplankton
  • Protozooplankton
  • River Meuse


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