Abstract
We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (δ13 cdic) and suspended matter(δ 13 CPOC) 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 δ13 cdic values are observed due to enhanced input of CO2 from decomposition of13C-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 δ13 Cpoc (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 δ13 cpoc 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 in13C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of13C/12C fractionation by phytoplankton is attempted.
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References
Baeyens W, Van Eck B, Lambert C, Wollast R & Goeyens L (1998) General description of the Scheldt Estuary. Hydrobiologia 366: 1–14
Billen G, Lancelot C, De Becker E & Servais P (1988) Modelling microbial processes (phyto- and bacterioplankton) in the Schelde Estuary. Hydrobiological Bulletin 22: 43–55
Billiones R (1998) Spatio-temporal distribution of suspended particulate matter in the Scheldt estuary (Belgium) and interactions with mesozooplankton. Doctoral Thesis, Vrije Universiteit Brussel, Belgium
Boutton TW (1991) Stable carbon isotope ratios of natural materials: II. Atmospheric, terrestrial, marine, and freshwater environments. In: Carbon Isotope Techniques (pp 173–184). Academic Press
Cai DL, Tan FC & Edmond JM (1988) Sources and transport of particulate organic carbon in the Amazon River and estuary. Estuarine, Coastal and Shelf Science 26: 1–14
Cifuentes LA, Sharp JH & Fogel ML (1988) Stable carbon and nitrogen isotope biogeochemistry in the Delaware estuary. Limnology and Oceanography 33(5): 1102–1115
Coffin RB, Cifuentes LA & Elderidge PM (1994) The use of stable carbon isotopes to study microbial processes in estuaries. In: Lajtha & Michener (Eds) Methods in Ecology: Stable Isotopes in Ecology and Environmental Science (pp 222–240)
Coplen TB (1996) New guidelines for reporting stable hydrogen, carbon and oxygen isotoperatio data. Geochimica et Cosmochimica Acta 60: 3359–3360
Farquhar GD, Ehlinger JR & Hubick KT (1989) Carbon istope discrimination and photosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology 40: 503–537
Frankignoulle M, Bourge I & Wollast R (1996) Atmospheric CO2 fluxes in a highly polluted estuary (the Scheldt). Limnology and Oceanography 41(2): 365–369
Fry B & Sherr EB (1984) δ13C measurements as indicators of carbon flow in marine and freshwater ecosystems. Contributions in Marine Science 27: 13–47
Geider RJ (1987) Light and temperature dependence of the carbon to chlorophyll a ratio in microalgae and cyanobacteria: Implications for physiology and growth of phytoplankton. New Phytol. 106: 1–34
Goosen NK, Rijswijk P Van & Brockmann U (1995) Comparison of heterotrophic bacterial production rates in early spring in the turbid estuaries of the Scheldt and the Elbe. Hydrobiologia 311: 31–42
Heip C (1988) Biota and abiotic environment in the Westerschelde estuary. Hydrobiological Bulletin 22: 31–34
Keeley JE & Sandquist DR (1992) Carbon: Freshwater plants. Plant, Cell and Environment 15: 1021–1035
Kroopnick P. (1974) Correlations between13C and ∑CO2 in surface waters and atmospheric CO2. Earth Planetary Science Letters 22: 397–403
Marguillier S, Van der Velde G, Dehairs F, Hemminga MA & Rajagopal S (1997) Tropic relationships in an interlinked mangrove-seagrass ecosystem as traced by δ13C and δ15N. Marine Ecology Progress Series 151: 115–121
Meire P, Ysebaert T, Hoffmann M, Van Den Balk E, Debos K, Samanya R, Deregge N, Van Waeyenberge J, Anselin A, Rossaert G & Kuijken E (1994) Ecologisch onderzoek in de Zeeschelde door het instituut voor natuurbehoud: onderbouwing van natuurherstel en natuurontwikkeling. Biologisch Jaarboek, Dodonaea 62: 27–47
Meire P, Hoffman M & Ysebaert T (1995) De Scheide: een stroom natuurtalent. Instituut voor Natuurbehoud, Hasselt: Rapport 95.10.
Middelburg JJ, Klaver G, Nieuwenhuize J & Vlug T (1995) Carbon and nitrogen cycling in intertidal sediments near Doel, Scheldt Estuary. Hydrobiologia 311: 57–69
Middelburg J & Nieuwenhuize J (1998) Carbon and nitrogen stable istopes in suspended matter and sediments from the Schelde Esstuary. Marine Chemistry 60: 217–225
Mook WG (1970) Stable carbon and oxygen isotopes of natural waters in the Netherlands. In: Proceedings IAEA Conference on Isotopes in Hydrology, Vienna (pp 163–190)
Mook WG, Bommerson JC & Staverman WH (1974) Carbon isotope fractionation between dissolved bicarbonate and gaseous carbon dioxide. Earth and Planetary Science Letters 22: 169–176
Mook WG & Tan TC (1991) Stable carbon isotopes in rivers and estuaries. In: Degens ET, Kempe S & Richey JE (Eds) Biogeochemistry of Major World Rivers (pp 245–264). SCOPE, John Wiley and Sons Ltd
Muylaert K, Van Kerckvoorde A, Vyverman W & Sabbe K (1997) Structural characteristics of phytoplankton assemblages in tidal and non-tidal freshwater systems: A case study from the Schelde basin, Belgium. Freshwater Biology 38: 263–276
Ostrom NE, Macko SA, Deibel D & Thompson RJ (1997) Seasonal variation in the stable carbon and nitrogen isotope biogeochemistry of a coastal cold ocean environment. Geochimica et Cosmochimica Acta 61(14): 2929–2942
Quay PD, Emerson SR, Quay BM & Devol AH (1986) The carbon cycle for Lake Washington — A stable isotope study. Limnology and Oceanography 31(3): 596–611
Quay PD, Wilbur DO & Richey JE (1992) Carbon cycling in the Amazon River: Implications from the C compositions of particles and solutes. Limnology and Oceanography 37(4): 857–871
Redfield AC, Ketchum BH & Richards FA (1963) The influence of organisms on the composition of seawater. In: Hill MN (Ed) The Sea, Vol. 2 (pp 26–77). Wiley, New York
Ronday F (1976) Modèles hydrodynamiques. In: Nihoul JCJ (Ed) Projet Mer, Rapport Final, Le Ministère de la Programmation de la Politique Scientifique, Brussels, Vol. 3
Soetaert K & Herman PMJ (1994a) Estimating estuarine residence times in thé Westerschelde (The Netherlands) using a box model with fixed dispersion coefficients. Hydrobiologia 311(1/3): 215–224
Tan FC & Strain PM (1983) Sources, sinks and distribution of organic carbon in the St. Lawrence Estuary, Canada. Geochimica et Cosmochimica Acta 47: 125–132
Wollast R & Duinker JC (1982) General methodology and sampling strategy for studies on the behaviour of chemicals in estuaries. Thalassia Jugoslavica 18: 471–491
Wollast R. (1983) Interactions in estuaries and coastal waters. In: Bolin B & Cook RB (Eds) The Major Biogeochemical Cycles and Their Interactions, SCOPE 21 (pp 385–407). Wiley-Interscience
Wollast R (1988) The Scheldt Estuary. In: Saloms et al. (Eds) Pollution of the North Sea: An Assessment (pp 185–193). Springer
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Hellings, L., Dehairs, F., Tackx, M. et al. Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition. Biogeochemistry 47, 167–186 (1999). https://doi.org/10.1007/BF00994921
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DOI: https://doi.org/10.1007/BF00994921