Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary) |
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Authors: | Frédéric Gazeau Jean-Pierre Gattuso Jack J Middelburg Natacha Brion Laure-Sophie Schiettecatte Michel Frankignoulle Alberto Vieira Borges |
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Institution: | 1. Laboratoire d’Océanographie de Villefranche, Centre National de la Recherche Scientifique (CNRS)-Université de Paris 6, B. P. 28, F-06234, Villefranche-sur-mer Cedex, France 2. Unité d'Océanographie Chimique (B5), Interfaculty Centre for Marine Research, (MARE), Université de Liège, B-4000, Sart Tilman, Belgium 4. Netherlands Institute of Ecology (NIOO-KNAW) Centre for Estuarine and Marine Ecology, Postbus 140, 4400 AC, Yerseke, The Netherlands 5. Department of Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, B-1050, Brussels, Belgium
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Abstract: | Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the
Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the
1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m−2 d−1) decreasing seaward (22–37 mmol C m−2 d−1). A significant decrease of NIT was observed with regard to previous investigations although this process still represents
up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed
to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time
in the estuary with values ranging from −300 to 165 mmol C m−2 d−1. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published
benthic metabolic rates. A NEP of −39±8 mmol C m−2 d−1 was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from
June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure
applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the
inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much
lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m−2 d−1) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear. |
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