The Role of Sediment Resuspension on Metal Uptake by Filter-Feeding Estuarine Organisms (Sydney Estuary, Australia)

Abstract

Sediments in Sydney estuary are contaminated by metals including copper, lead and zinc and are resuspended into the water column due to natural and anthropogenic causes. These metals are also highly enriched in the tissues of the native filter-feeding oyster Saccostrea glomerata and is thought to be caused by the ingestion of resuspended sediments. To establish this link, a consolidated approach of field, laboratory and numerical analyses was conducted. Firstly, bottom sediments, suspended particulate matter and oyster samples were analysed for metals over three years in Sydney estuary. Correlations were investigated between oysters to sediments and SPM and a significant mismatch was observed between field and transplanted oysters, with strong regressions in the latter to fine sediments and SPM, but a lack in the former. Resuspension was replicated in the laboratory and a gradient of metal concentrations and resuspended loads were exposed to oysters in a two month mesocosm experiment. No relationship was determined between either variables to oyster metal bioaccumulation. To confirm either dissolved or particulate metal uptake, a radioisotope tracer study exposed oysters to gamma-emitting 65Zn, a first for an Australian bivalve species using 65Zn. The resulting biokinetic uptake and loss rates were used to construct a steady-state model and particulate sources were determined to be the greatest contributor. The mesocosm and radiotracer experiment results were used to formulate a novel, dynamic, coupled biokinetic-equilibrium model to investigate the mechanisms and processes governing oyster metal bioaccumulation. The coupled model concluded that dissolved organic matter commanded a dominant influence on metal bioaccumulation patterns for many metals by sequestering them and reducing their bioavailability. The present work demonstrated that dietary uptake of resuspended, contaminated sediments is unlikely to be a key source of metals to filter-feeding oysters.