Abstract :
Almost one-quarter of Australia’s population of 17 million and a large proportion of its industry are concentrated in the restricted area of Greater Metropolitan Sydney. Heavy metal loadings of the surficial sediment which mantles the four deeply incised estuaries dissecting this region and the adjacent continental shelf are being investigated to determine potential sources, and to understand the processes of dispersion and accumulation.
The Parramatta River/Port Jackson and Georges River/Botany Bay estuaries have been major repositories for urban/industrial waste and are heavily impacted by anthropogenic metalliferous (Cu, Zn, Ni, Pb) loadings. The majority of estuarine areas are greatly in excess of background values. The most elevated regions are the upper reaches of estuaries and bay ends. Generally, the central sections of these estuaries are less elevated, but still above background values, whereas for some metals, the lower reaches and mouth areas approach background values. In limited parts of the inner shelf, most of these metals are above background values, but for the majority of the continental shelf, values are close to background.
The strong down-estuary decline in metals and lower metal levels in the marine environment is probably source-related, rather than due to a dilution by less enriched coarse sediment. The source of offshore metal enrichment is coastal sewage outfalls and/or dissolved and suspended material escaping the estuaries. Marginally elevated metal concentrations on the inner shelf in excess of that observed in the lower estuary, are probably indicative of some sourcing from sewage outfalls.
In terms of public health, the majority of the Parramatta River/Port Jackson estuary is in excess of guidelines, and tributaries and bay ends of both estuaries are markedly in excess of these levels for all elements. Offshore surficial sediments are mostly within guideline levels.
