Application of sediment-bound heavy metals in studies of estuarine health: a case study of Brisbane Water estuary, New South Wales

A case study is presented to assess the use of sedimentary chemical indicators for estuarine health. Reliable and efficient estuarine indicators are essential for management and monitoring purposes. Estuarine and fluvial sediments from Brisbane Water estuary were analysed for heavy metals to assess the quality of sediments and to determine the source and dispersion of contaminants in the estuary. Brisbane Water, 50 km north of Sydney, is a shallow (5 m in main water body), wave-dominated barrier estuary with a generally sparsely developed catchment, except in the north where it is urbanised and industrialised. Heavy-metal loadings calculated for sub-catchments and the distribution of metals in surficial sediment identified Narara Creek, which drains the urbanised northern part of the catchment, as the main source of contaminants. Vertical profiles of sedimentary contaminants show that contamination continues to increase rapidly in all parts of the waterway to the present day. Concentrations of Cu, Pb and Zn in sediment adjacent to Narara Creek exceeded lower guideline levels, although moderate bioavailability (40% for Cu, Pb and Zn) suggests the risk posed by sediments to benthic populations is low. Sediments in all parts of Brisbane Water show evidence of minor anthropogenic influence with maximum human-induced change (up to 5 enrichment) in the north of the estuary. Results demonstrate the use of sediment-bound heavy metal as an appropriate indicator of estuarine health.