The use of vintage surficial sediment data and sedimentary cores to determine past and future trends in estuarine metal contamination (Sydney estuary, Australia)

The objectives of the present investigation were to determine past trends in sediment contamination and possibly predict future trends. Multiple vintages of surficial sediment metal data, from a quasi-decadal 'Status and Trends' programme, were used to provide large-scale spatial information on current status and temporal change. This information was augmented by sediment cores, specifically located to verify surface sediment data and to determine trends at major points of stormwater discharge. The data obtained indicate that surficial sediment metal concentrations have declined, since about the early 1990s, in extensive parts of the upper and central estuaries and have increased slightly in the lower estuary, due mainly to a down-estuary shift in industry and urbanisation. Declining surficial sediment metal concentrations is due to a movement of industry out of the catchment, especially from foreshore areas and the introduction of regulation, which prevent pollutants being discharged directly to the estuary. The major present-day source of metals is stormwater, with minor inputs from the main estuary channel into embayments and runoff from previously contaminated mainland sites. Modelled relaxation rates are optimistic as high metal concentrations in stormwater will slow predicted rates. Stormwater remediation should be the main managerial focus for this estuary. Multiple vintages of surficial sediment metal data covering the past 30 years, supplemented by sedimentary core data, have allowed past and future contamination trends to be determined. This type of science-based information provides an important tool for strategic management of this iconic waterway.