Coates, A. (2022). Christchurch City Council ocean outfall: 2022 benthic biological survey. Bioresearchers. 

In March 2010, a new ocean outfall was commissioned by the Christchurch City Council to discharge treated wastewater into the coastal marine environment, replacing discharge into the Ihutai Avon-Heathcote estuary. As part of the 2006 resource consent granted by Environment Canterbury (ECan) for the construction, operation, and maintenance of outfall, effects on the receiving environment must be monitored. This 2022 report is the third survey since 2010 and involved the collection of sediment and seabed biota samples around the outfall and at a control site near the Waimakariri River mouth.

Overall, sediment within 200m of the outfall sites contained significantly higher concentrations of total organic carbon (TOC), nitrogen, arsenic, lead, nickel, and zinc. All parameters related to contaminant and mud ratios were elevated around the outfall compared to control sites, however, they were lower than ANZECC guidelines and consent limits. As a result, it was concluded that sediment quality around the outfall was likely not having any significant adverse effects on sediment infauna.

Regarding benthic communities, there were no patterns in species diversity or significant increases in abundance or richness related to the distance the outfall. Species abundance and richness also varied significantly between survey years. As a result, it was concluded that the discharge was likely not having a significant effect on benthic communities, and that factors other than the discharge may be influencing benthic communities in the area.