Accumulation of metallic contaminants in surficial sediments on a high energy continental shelf (Sydney, Australia)

Greater Sydney exploits its adjacent ocean as a convenient and cost-effective environment in which to dispose of urban and industrial waste on the assumption that contaminants are readily dispersed on this high energy continental shelf. Size-normalised (< 63 μm) heavy metals data (Pb, Zn, Cu and Ni) show a seaward declining trend across the shelf with highest concentrations immediately adjacent to the coast. Metal values are elevated off major estuaries draining the Sydney catchment and coastal sewage outfalls compared to the adjoining shelf and to other continental shelves. The relative importance of the estuaries and sewage outfalls as sources of anthropogenic material is uncertain. Seasonally-collected sediment taken over a 12-month period shows variation in textural and heavy metal concentrations on the inner shelf. Textural variation is probably due to higher ambient energy on the sea bed associated with winter storms, but the cause of variance in heavy metals is not well understood.