HEAVY-METAL HISTORY FROM CORES IN WELLINGTON-HARBOR, NEW-ZEALAND

Analysis of ten heavy metals (Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Zn) in six sediment cores from Wellington Harbour show both anthropogenic enrichments and diagenetic modifications. Absolute concentrations dete rmined by two methods, x-ray fluorescence and acid leaching for bioava ilability, are not comparable. However, vertical trends in concentrati ons of the cored sediment are comparable. To assess levels of anthropo genic pollution, enrichment factors (enriched concentrations in upper core divided by background levels in lower core) are preferred over in dex of accumulation (I-geo) values because preindustrial or background levels of heavy metals are well constrained. The ten metals are place d into three groups: (1) Cu, Pb, and Zn, which show the most anthropog enic enrichment; (2) As, Cd, Cr, Ni, and Sb, which are often associate d with anthropogenic pollution but show only minor enrichment; and (3) Fe and Mn, which are diagenetically enriched. Assuming harbor waters are well mixed, anthropogenic enrichments of Cu, Pb, and Zn, are time correlative, but the degree of enrichment depends on the method of ana lysis and core location. Levels of As, Cd, Pb, and Zn show small varia tions in preindustrial sediments that are not related to changes in gr ain size and probably result from changes in the oxidation-reduction p otential of the sediments and salinity of the pore waters.