A snapshot of water quality from sampling freshwater invertebrates in Purau stream, Lyttelton Harbour/Whakaraupō

Abstract

Whaka-Ora Healthy Harbour is a partnership between Te Hapū o Ngāti Wheke, Te Rūnanga o Ngāi Tahu, the Lyttelton Port Company, Environment Canterbury and Christchurch City Council. The partnership is working to restore the ecological and cultural health of Lyttelton Harbour/Whakaraupō in conjunction with resident groups. The restorative focus includes: increasing indigenous biodiversity; protecting and restoring mahinga kai values; providing a safe place for recreation; and protecting the harbour for future generations. Currently, issues relating to the health of the harbour have been identified, such as sedimentation, erosion, high nutrient levels, and bacterial contaminants, which cumulatively impact on indigenous biodiversity and coastal water quality. Purau Bay is one of the large bays located on the southern side of Lyttelton Harbour/Whakaraupō, located also within the wider Banks Peninsula/Te Pātaka o Rākaihautū area. Purau Bay has a permanently flowing stream that winds its way through a variety of land uses, including indigenous vegetation, pastoral farmland, and residential properties before discharging into the harbour. This study takes a snapshot of the environmental quality of Purau Stream by examining the diversity of aquatic invertebrates as an indicator of the stream health at two sites along the stream. The results from the macroinvertebrate community index (MCI) were compared to Te Wharau catchment in nearby Orton Bradley Park, where contemporaneous data were also collected from two locations within the stream. The condition of both streams was assessed as being in overall good health, although the MCI was lower at the Purau bridge site compared to the upstream site and the Te Wharau stream sites. Previous water quality sampling by Environment Canterbury at the bridge indicates that although the current condition is classified as good, the long-term trend is may be declining water quality. These results contribute to informing progress towards the partnership's long-term plan for these streams, which is “to enhance the riparian margins and water quality to a state where sensitive species are present”: The current condition of both streams is contextualised within past changes to the catchment, through the presentation of a brief overview of historical events.