Malakhov, Y. (2019, November). Intertidal microphytobenthos of Te Ihutai Avon Heathcote Estuary (areas adjacent to the oxidation ponds). University of Canterbury.

Over the last 100 years wastewater discharge has significantly deteriorated the environmental health and recreational appeal of the Ihutai Estuary, indicated by a severe increase in microphytobenthos (MPB). Wastewater was diverted from the estuary into a new oceanic outfall in March 2010, however, the 2010-2011 Canterbury earthquakes altered the estuary’s hydrological regime, temporarily enriching the area with raw sewage.

Commissioned in November 2019 by the Avon-Heathcote Estuary Ihutai Trust, the aim of this study was to assess the state of MPB communities in the upper reaches of the Ihutai Avon Heathcote Estuary. Overall, it found that 2019 MPB communities of the upper Ihutai were typical for the brackish mudflat habitat in the area, indicating recovery since the 2010-11 earthquakes. MPB populations appeared diverse and did not indicate localised point-source nutrient enrichment. Notably, however, there was moderate eutrophication in the upper Ihutai, and natural features of the area, including muddy sediment and reduced flushing, was found to increase the risk of worsening eutrophication.

Following these findings, the report recommended regular estuarine health monitoring and mitigation measures to track and aid future estuary recovery. It also suggested more detailed studies of nutrient budgets may be needed to identify current eutrophication sources.