Assessment of future anthropogenic change and associated benthic risk in coastal environments using sedimentary metal indicators

Indicators of estuarine health are frequently compromised by large, natural temporal and spatial variance, which often mask long-term environmental trends and confound remedial actions. Ecosystem indicators seldom provide information on the pristine condition or the history of anthropogenic change of a water body. The current investigation used sedimentary metals and novel field and analytical techniques to determine the pristine condition and assess the magnitude and history of human-induced temporal and spatial change of an estuarine system. Two vintages of normalised metal concentrations in surficial sediment (1992 and 2007) indicate Cu and Zn concentrations have increased over the period, while Pb concentrations have declined – a change verified by strategically located sedimentary cores. Assuming no change in metals supply and dispersion, Cu and Zn are predicted to increase in concentration and areal extent, whereas Pb concentrations and areal cover will decrease. High concentrations of sedimentary Cu may be having an adverse affect on the health of benthic animals over extensive areas, which are predicted to expand if no remedial strategy is implemented. ► Vintage and current surficial sediment metals data provide 15-year change. ► This change is verified by sediment cores taken in selected locations. ► Dated cores provide chronology of changes in this highly contaminated estuary. ► Past trends allow possible future condition to be modelled. ► Metal signatures suggest probable sources of metals.