, Volume 47, Issue 2, pp 167–186 | Cite as

Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition

  • L. Hellings
  • F. Dehairs
  • M. Tackx
  • E. Keppens
  • W. Baeyens


We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (δ13CPOC) and suspended matter (δ13CPOC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest δ13CDIC values are observed due to enhanced input of CO2 from decomposition of 13C-depleted terrestrial plant detritus (average δ13CDIC = −/14.3‰). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative δ13CDIC values (average δ13CDIC = −9.9‰). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 μgl−1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 μgl−1. Furthermore, in winter the very narrow range of δ13CPOC (from −26.5 to −27.6‰) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer δ13CPOC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in 13C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of 13C/12C fractionation by phytoplankton is attempted.

Zeeschelde stable carbon isotopes dissolved inorganic carbon particulate organic carbon 


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Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • L. Hellings
    • 1
  • F. Dehairs
    • 1
  • M. Tackx
    • 2
  • E. Keppens
    • 3
  • W. Baeyens
    • 1
  1. 1.Department of Analytical ChemistryVrije Universiteit BrusselBrusselsBelgium
  2. 2.Department of Ecology and SystematicsVrije Universiteit BrusselBrusselsBelgium
  3. 3.Department of GeologyVrije Universiteit BrusselBrusselsBelgium

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