West, S., Yungnickel, M., & Feickert, J. (2018). Christchurch City Council ocean outfall: 2018 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 2018 report is the second 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, sediments collected greater than 200m away from the outfall had significantly higher concentrations of total dissolved oxygen (TOC), cadmium, chromium, copper, lead, nickel and zinc than sediments collected within 200m of the diffuser. All parameters related to contaminant and mud ratios peaked slightly around the diffuser, however, they were lower than ANZECC guidelines and consent limits, and therefore likely not having significant adverse effects on sediment infauna.

Regarding benthic communities, control sites were significantly different from outfall sites. Species abundance increased with distance from the outfall, while abundance and richness were typically higher in the mixing zone compared to control sites. Species abundance and richness also varied significantly between survey years. It was therefore concluded that changes in sediment quality, species composition, and species abundance were likely affected by the outfall discharges.