The Integrated Catchment Study of Auckland City (New Zealand): Fate of Contaminants in Coastal Receiving Environments

The Coastal Receiving Environment Assessment (CREA) forms part of the Integrated Catchment Study (ICS) of Auckland City, New Zealand. The scope of CREA included modelling the fate of contaminants discharged from Auckland City and adjacent councils to coastal receiving environments in the Waitemata and Manukau Harbours to assist in assessment and mitigation of public and ecological health risks. Hydrodynamic, particle tracking and contaminant accumulation models were used as the basis for numerical model predictions of long-term sediment and particulate zinc accumulation in the coastal benthos. The modelling approach included the effects of settling, re-suspension, wind wave-induced bottom shear stresses and bioturbation. The contaminant accumulation model was used to project long term zinc accumulation and investigate relative impacts of different stormwater quality improvement scenarios. Upper and mid-Whau and Tamaki Estuaries contain high levels of zinc that are expected to continue to rise under most feasible contaminant reduction scenarios. Reduction scenarios can result in improvement in zinc accumulation in some outer settling zones and decreased zinc discharge to middle harbour areas. Results from CREA provide information about the potential benefits of contaminant reduction scenarios, facilitating investigation of options and management practices in targeted locations in upstream catchments where infrastructure investment can be most effectively directed.