The use of vintage surficial sediment data and sedimentary cores to determine past and future trends in estuarine metal contamination (Sydney estuary, Australia) G.F. Birch ⁎, C.-H. Chang, J.-H. Lee, L.J. Churchill Environmental Geology Group, School of Geosciences, The University of Sydney, Sydney, New South Wales, 2006, Australia HIGHLIGHTS • Multiple vintages of surficial sediment metal data provide past and future contamination trends. • Sedimentary metal concentrations are declining in the upper and central in Sydney estuaries. • Declining sediment metal levels due to reduction of industry and introduction of regulation • Major present-day source of sedimentary metals in Sydney estuary is stormwater. • Modelled relaxation rates are optimistic due to high metal stormwater concentrations. abstract article info Article history: Received 27 July 2012 Received in revised form 25 February 2013 Accepted 25 February 2013 Available online 9 April 2013 Keywords: Metals Surficial sediment Estuary Relaxation rate Sydney estuary 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 surfi- cial 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 indus- try 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. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Sydney estuary (Australia) has considerable environmental, eco- nomic, recreational and aesthetic value. However, the system has had to endure considerable stress due to extensive urbanisation and industrialization for more than a century. To maintain the health of such an ecosystem requires a balance between protection and use of the estuary and catchment through coordinated management (Birch, 2007). In recent years, science-based environmental indica- tors, which describe complex interactions between natural and human systems, in simplified terms, have become a central element of resource management (Rice, 2003). The challenge is to choose a set of indicators that may be used in a ‘weight-of-evidence’ approach and which will provide management with information in a less complex fashion for decision-making and planning (Rice, 2003). Sedimentary metals provide an indicator of contaminant-related biological stress and are an easy and inexpensive approach to measure the quality of an aquatic system (Chatterjee et al., 2007). Sediments integrate con- taminants over time and faithfully record the history of chemical condi- tion. Sediments are also the only indicator to provide quantitative information on the pristine condition and specifically, the human com- ponent of environmental change (Birch and Olmos, 2008). Sydney estuary, in central New South Wales, Australia, is one of the most beautiful in the world, and is home to about 4.5 million peo- ple (Birch, 2007). The catchment (500 km 2 ) is highly industrialised Science of the Total Environment 454–455 (2013) 542–561 ⁎ Corresponding author. Tel.: +61 2 93512921. E-mail address: gavin.birch@sydney.edu.au (G.F. Birch). 0048-9697/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scitotenv.2013.02.072 Contents lists available at SciVerse ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv