Accumulation of Phosphorus and Heavy Metals in the Swan-Canning Estuary, Western Australia

Accumulation rates of P and of Zn, Cd, Pb and Cu were measured in sediment cores from the Swan-Canning Estuary in Western Australia. The main sources of P in sediments are catchments of the major tributaries Ellen Brook and Avon River. Since 1940, anthropogenic P has increased about five times in sediments of Ellen Brook and has almost trebled in sediments of the estuary. Records show that since 1940 dissolved inorganic P in the estuary has increased between two and three times. Though dissolved inorganic P appears to be conservatively mixed in the estuary, sediment inventories suggest that a significant part of the input of P is retained in the estuary. A combination of high concentrations of dissolved P in Ellen Brook and large fluxes of particulate matter from the Avon River could explain this. Concentrations of Zn, Cd, Pb and Cu in sediments have risen significantly since colonial settlement and, unlike P concentrations, have been dominated by inputs from sources near the estuary. Vertical distributions of metals in sediment cores from the estuary suggest that, historically, concentrations of Zn and Cd started increasing first, followed by Cu and then P and Pb.Acid extractable Pb, unlike Zn, Cd and Cu, in surface sediments is greater than expected from equilibration with the water column. This is attributed to the presence of particulate Pb-oxides from road runoff.