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Historical input, mobility and retention of major elements and trace metals in salt marshes of the Scheldt estuary
Zwolsman, J.J.G.; Berger, G.W.; van Eck, G.Th.M. (1999). Historical input, mobility and retention of major elements and trace metals in salt marshes of the Scheldt estuary, in: Zwolsman, J.J.G. Geochemisch gedrag van zware metalen in het Schelde-estuarium = Geochemistry of trace metals in the Scheldt estuary. Geologica Ultraiectina, 171: pp. 91-112
In: Zwolsman, J.J.G. (1999). Geochemisch gedrag van zware metalen in het Schelde-estuarium = Geochemistry of trace metals in the Scheldt estuary. Geologica Ultraiectina, 171. PhD Thesis. Universiteit Utrecht: Utrecht. ISBN 90-5744-030-X. 183 pp., more
In: Geologica Ultraiectina. Universiteit Utrecht: Utrecht, more

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Keywords
    Accumulation; Mobility; Salt marshes; Trace elements; Trace metals; ANE, Netherlands, Westerschelde [Marine Regions]; Marine; Brackish water

Authors  Top 
  • Zwolsman, J.J.G., more
  • Berger, G.W.
  • van Eck, G.Th.M., more

Abstract
    The distribution of major elements and trace metals has been studied in two radiodated salt marsh sediment cores (core K and core E) of the Scheldt estuary, in order to determine the recent pollution history and to assess the impact of diagenetic processes. The sedimentation rates, based on 210Pb and 137Cs inventories, were 0.84–0.90 cm/yr in core E and 1.3–1.7 cm/yr in core K. The sediments show a vertical redox zonation with an oxic upper layer, where trace metals are mobilized, overlying a reduced layer where the metals are precipitated. Though these diagenetic processes have greatly modified the original trace metal distribution, anthropogenic maxima could be identified for Cd, Cr, Cu, Pb, and Zn during the mid-sixties. A second pollution maximum was found at the end of the seventies for Cd, Cu, Pb, and Zn. The down-core distributions of Mn, Fe, total S, CaCO3, Sr, Co, and Ni are controlled by diagenetic processes, whereas the P profiles reflect both anthropogenic and diagenetic impacts.

    Rapid remobilization of trace metals occurs after their deposition on the marshes due to the occurrence of oxic conditions in the upper sediment layer, preventing precipitation of metal sulfides from the pore waters. Though the metals are partly reprecipitated in the reduced sediment layer (e.g. as sulfides), the inventory of the cores suggests that Cr is the only metal which is completely retained by the sediments. Slight losses are observed for Fe, Co, and Pb (11–14%), moderate losses for Zn, Cu, and Ni (19–25%), and high losses for P, Mn, and Cd (40–50%). Similar mobilization of trace metals is to be expected in other salt marshes if a distinct oxic sediment layer is present.


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