Trace metals in the Westerschelde Estuary: a case-study of a polluted, partially anoxic estuary
Baeyens, W.F.J. (Ed.) (1998). Trace metals in the Westerschelde Estuary: a case-study of a polluted, partially anoxic estuary. Developments in Hydrobiology, 128. Springer Netherlands: Dordrecht. ISBN 978-0-7923-5158-0; e-ISBN 978-94-017-3573-5. XVI, 167 pp. https://dx.doi.org/10.1007/978-94-017-3573-5
Part of: Dumont, H.J. (Ed.) Developments in Hydrobiology. Kluwer Academic/Springer: The Hague; London; Boston; Dordrecht. ISSN 0167-8418, more
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- Baeyens, W.F.J., editor, more
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| Abstract |
excerpt from the introduction to this volumeOceans and lakes are characterised by great residence times and can thus be considered to be in a state of equilibrium or quasi-equilibrium. Estuaries, by contrast, which constitute the interface between freshwater and marine ecosystems, are biogeochemically and physically very dynamic. Strong gradients in physical and chemical variables such as temperature, pH, salinity, dissolved oxygen, nutrients and the amount and composition of particulates result from the mixing of freshwater and saline constituents. These gradients provoke increased biogeochemical processes, generally resulting in a geochemical filter (the area of high turbidity, showing enhanced adsorption-desorption processes) and a biological filter (the area of high plankton activity showing a high accumulation of trace metals as well as a high uptake of nutrients). Both filters disturb the conservative mixing pattern of the trace metals in an estuary. Four additional aspects make the Scheldt estuary very particular and different from other estuaries: (1) the Scheldt is a tide-governed estuary, which means greater residence times; (2) the upper estuary receives large inputs of biodegradable organic matter which leads to oxygen depletion in winter and to anoxic conditions in summer; (3) inputs of toxic pollutants from the industrial zone of Antwerp occur in the upper estuary; (4) the anoxic zone, the zone of pollutant input and the zone of the turbidity maximum coincide geographically. The Scheldt estuary is therefore an ideal field laboratory for the study of biogeochemical processes which do not occur elsewhere, or occur only partially, to a very slight extent or in a specific compartment such as the sediments. More specifically, redox processes involving trace metals, the formation of non-labile metal complexes or the methylation of mercury occur as a result of anoxic conditions and the high load of organic matter. Several models describing in detail the transport, sedimentation and speciation of the trace metals in this well-mixed estuary (all major estuaries in EC countries adjacent to the North Sea or the Atlantic Ocean are well-mixed) are presented in this volume. A comparison of the metal concentrations over a 15-year period shows a net reduction in the pollution level. |
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