Sediment resuspension on the middle continental shelf adjacent to Sydney, Australia - evidence using 210Pb

Full text: A regional survey of surficial sediments on the central NSW continental margin has established anthropogenic contributions of trace metals from the urban centres of Sydney, Newcastle and Wollongong. The anthropogenic contributions are discernible in the sediment fine fraction (<63μm) but not in the bulk sediment. On the middle shelf adjacent to the Malabar deepwater ocean sewage outfall, south of Sydney, sediment fine fractions display an anthropogenic trace metal signature. Sediment trap deployments have shown that large amounts of middle shelf sediments are resuspended frequently, therefore dispersing anthropogenic sediment- and sewage particulate matter-bound trace metals efficiently. Frequent sediment resuspension and dispersion prevent an accumulation of trace metals to highly enriched levels. Middle shelf surficial sediments from four locations at water depths between 80 m to 89 m were analysed for 210Pb and trace metals to determine long-term sedimentation rates and zones of sediment mixing due to resuspension. Muddy middle shelf sediments display a shallow surficial mixing zone, increasing in depth in sandy sediment. Sandy middle shelf sediments have therefore a greater resuspension potential during frequent storm events and are unlikely to act as long-term contaminant sinks