Anthropogenic trace metals in sediment and settling particulate matter on a high-energy continental shelf (Sydney, Australia)

The anthropogenic contribution of trace metals to settling particulate matter (SPM) and surficial sediments was determined on the high-energy continental shelf adjacent to Sydney, Australia. Settling particulate matter and surficial sediment was collected in the vicinity of a major sewage outfall and at five control sites on the middle shelf (80–100 m water depth). Sediment traps were deployed on 10 occasions for up to 2 weeks during the summer and winter of 1995 and SPM was analyzed for Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Cobalt, Fe, Mn and Ni act conservatively in SPM and in sediments regionally and are used as normalizing elements to determine anthropogenic enrichment. Surficial sediments and SPM are enriched in Ag, Cr, Cu, Pb and Zn near a major ocean outfall and at four of the five control sites, although sewage particles contribute <5% of trace metals in the total sample. Silver is the most sensitive trace metal tracer for establishing the presence of sewage particulate matter. Sewage particulate matter flux near the outfall was estimated using a two endmember mixing model and is below 0.5 g m−2 day−1 during all deployment periods. The mean sewage particulate matter flux at sampling locations 30 km and 60 km north of the outfall are <0.13 g m−2 day−1 and <0.01 g m−2 day−1, respectively, indicating an efficient dispersal of anthropogenic material on this high energy continental shelf.