Processes controlling Fe,Mn and Zn in sediments of northern Chesapeake Bay |
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| Authors: | George R Helz Scott A Sinex Kenneth L Ferri Maynard Nichols |
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| Institution: | 1. Department of Chemistry, University of Maryland, College Park, Maryland, U.S.A.;2. Virginia Institute of Marine Sciences, College of William and Mary, Gloucester Point, Virginia, U.S.A. |
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| Abstract: | The dominant physical and chemical processes that control Fe, Mn and Zn are explored by comparing the compositions of sediments and their sources. The and ratios in sediment are found to be largely unaffected by local hydraulic sorting (unlike the actual concentrations of Fe, Mn and Zn) and thus are useful indicators of origin. The sediments in northern Chesapeake Bay have markedly lower and ratios than those found in the Susquehanna River (dissolved plus suspended) under ordinary flow, but not under high flow conditions. Since high flow conditions dominate sediment transport, seaward loss of a major fraction of the river-derived Mn and Zn need not be invoked to reconcile sediment and river compositions. Sediments in the seaward end of the northern bay have higher and ratios than their principal external source, the eroding shore deposits. The excess Zn appears to be derived from the atmosphere; the required depositional flux of Zn is consistent with measurements of the total atmospheric flux. The excess Mn can be explained by remobilization of roughly 5% of the river-borne Mn from sediments in the landward part of the northern bay. Because rare floods influence sediment composition markedly, comparing suspended particles in the river at ordinary stages with resuspended sediment in the estuary would lead to the false interpretation that Mn and Zn were being desorbed in the saltwater. |
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| Keywords: | estuaries sediment diagenesis trace elements iron manganese zinc |
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