HEAVY-METAL DISTRIBUTION IN PORE WATERS OF THE CONA MARSH - A PRELIMINARY INVESTIGATION ON SURFACE SEDIMENTS

The results of an investigation about the heavy-metal distribution in pore waters of an estuarine shallow-water system (Cona Marsh, Venice L agoon) are described. The area was sampled for surface and subsurface sediments; pore waters were extracted by centrifugation and heavy-meta l concentration measured by means of PIXE technique. A high variabilit y of heavy-metal concentration was observed in pore waters of sampled sites, as a result of physico-chemical conditions in the water sedimen t column, with a different spatial distribution between two groups of metals (Fe, Mn and Cr vs. Cu, Ni and Zn). Concentration gradients betw een pore and bottom waters were evaluated in order to investigate the metal enrichment as a function of their mobility in the sediment and d iagenesis phenomena.