Trace metal distributions in two saltmarsh substrates, Illawarra region, New South Wales

Abstract

The vertical and lateral distributions of Pb, Cu, Zn and Fe in the substrates of two saltmarshes, 3 and 14km respectively, from the heavy industrial centre of Port Kembla have been determined. Particulate matter within the sediment reflects the differing contribution to each site from this point source, which is highlighted by the presence of up to 70% of anthropogenic components in the finer sediment in the saltmarsh at Purry Burry Point. The particulate material derived from industrial and pyrometallurgical processes has previously been assumed to be inert in the surrounding environment. However, in the intertidal zone occupied by the saltmarshes, the redox conditions of the substrate exert a major control over the distribution of both trace metals and diagenetic iron mineralogy. The distribution of Fe in the substrates at both sites is strongly controlled by redox conditions, with the secondary Fe oxides akageneite (β-FeOOH) and goethite (α-FeOOH) developing in response to oxidising conditions, whereas pyrite and marcasite are stable under reducing conditions. Redox values also probably influence the distribution of trace mentals, with zinc profiles from Purry Burry Point showing peaks in concentration in response to redox boundaries within the substrate. Lead and copper are less responsive, indicating these trace metals may be contained in relatively inert phases such as slag.