Contaminant pathways in Port Curtis: Final report - OzCoasts

Contaminant pathways in Port Curtis: Final report2: Dissolved trace metals3. Surveying of the Fitzroy River to above Rockhampton indicated that this majorriver is a source of dissolved metals to the local coastal region. In particular,the Fitzroy contains elevated nickel concentrations which are consistent withsediment studies conducted by the Coastal Zone CRC. Under some flowconditions, the Fitzroy plume may enter The Narrows region and potentiallysupply dissolved metals to Port Curtis.4. There were no conspicuous sources of trace metal within Port Curtis. Metalsin suspended and benthic sediments are low and are not a likely source oftrace metals to the water column. The trace metal distributions in Port Curtisare likely to reflect a mixture of metal inputs including industrial discharges,mobilisation of metals from mangrove regions in The Narrows and the FitzroyRiver plume. Deconvoluting these multiple sources is difficult. Modelling ofcontaminant inputs using a version of the Port Curtis hydrodynamic modelmodified to include inputs from the Fitzroy and The Narrows is probably themost effective way of understanding this complex issue.5. Salinity and pH gradients were observed in Port Curtis. Salinities tend to behigher in the north of Port Curtis than in the surrounding coastal waters. Thiscould reflect evaporation losses in these more sheltered areas where watercirculation is restricted. Water column pH was lowest in The Narrows regionsand is most likely related to acid inputs from the adjacent mangrove regions.6. Particulate metals data indicated that desorption of metals from suspendedsediments is unlikely to be a major source of dissolved trace metals. Theconcentrations of copper and zinc in suspended sediments were, in mostparts, typical of the benthic sediments and did not indicate enrichment ofthese metals. Trace metal inputs to Port Curtis which contribute to theobserved dissolved metal concentrations are most likely to be delivered insolution form.19