Sediment-bound metals as indicators of anthropogenic change in estuarine environments

•Sedimentary metals provide the pristine condition and magnitude of anthropogenic change.•This indicator is not confounded by natural spatial and temporal stress as is common.•Thirty-eight estuaries on the Australian central eastern coast have been assessed for impact.•Five categories comprising the Metal Enrichment Index (MEI) quantify human impact on these estuaries.•The MEI compares well other some environmental indicators and provides additional information.

Sedimentary metal indicators were used to assess the environmental ‘health’ of 38 estuaries on the central Australian east coast. Unlike many environmental indicators, the mean enrichment quotient (MEQ) provides the pristine condition and magnitude of anthropogenic change in estuarine condition, not confounded by natural spatial and temporal variation. MEQ is the mean normalised surficial concentration of Cu, Pb and Zn divided by their normalised background concentration. MEQs, identified from an extensive sedimentary database (n = 2269), were used to derive a Metal Enrichment Index (MEI) comprising five impact categories. Population density and proportion of urbanised catchment were consistent with increased sedimentary metal concentrations, whereas estuarine sensitivity and metal enrichment were poorly correlated. No correlation was established between metal enrichment and estuary type or sedimentary facies. MEI can be used as a tool to meet the needs of policy-makers and estuarine managers by providing a tool by which human-induced change may be measured.