Institute News

Conference 2003
Greening the City:
Bringing Biodiversity Back
into the Urban Environment


A National Biodiversity Hot-spot from the Treatment of Urban Wastewater - The Bromley Oxidation Ponds and Te Huingi Manu Wildlife Reserve, Christchurch

Andrew Crossland (Parks & Waterways Unit, Christchurch City Council)

In pre-European times, the extensive wetlands of Christchurch/Otautahi supported tens of thousands of resident and migratory wetland birds. The annual lifecycle of many species involved a period either breeding, moulting, wintering, or transiting through the Christchurch area. The development of a city and its surrounding agricultural hinterland completely transformed the pre-European landscape to the point where more than 90% of local wetland area was destroyed. However, wetland birds have proven to be highly resilient with many species continuing to breed locally or to occur as seasonal visitors. Currently, peak numbers of wetland birds using Christchurch waterways and wetlands exceed 40,000 individuals of 45+ species. Many of these wetland birds utilise human-created (artificial sites) and up to half of them congregate at one site, the Bromley Oxidation Ponds.

The 240 ha Bromley Oxidation Ponds and c. 100 ha of surrounding pastureland comprise the Te Huingi Manu Wildlife Refuge. The site is located adjacent to the western shoreline of the Avon-Heathcote Estuary and is managed by the Christchurch City Council. The primary function of the oxidation ponds is to treat the wastewater generated by a city of 350,000 people. However, an important secondary function is to provide breeding, feeding and roosting opportunities for wetland birds. Currently some 5000 New Zealand Scaup (Aythya novaeseelandiae), comprising 15-20% of the World population; 7000 Australasian Shoveler (Anas rhynchotis), 4000 Grey Teal (Anas gracilis), 2500 Paradise Shelduck (Tadorna variegata), 2500 Canada Goose (Branta canadensis) and 1000 Black Swan (Cygnus atratus) moult or winter on the Bromley Oxidation Ponds, establishing the site as one of New Zealand's most important sites for waterfowl.

Three of the six ponds have well-vegetated islands, which provide nesting habitat for 8 species of waterfowl and 3 species of cormorant. A predator control programme in place for 7 years and an abundant source of food in the form of aquatic invertebrates combine to produce high rates of breeding success. 150-200 pairs of the endemic New Zealand Scaup breed annually on the ponds, producing 1000+ fledglings. These have spread to recolonise waterways throughout Christchurch and the Canterbury Plains, leading to an unprecedented population recovery in this once near-threatened species over the last 10 years.

Conference sponsored by:

British Council NZ
The Community Trust
Landcare Research

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Last updated: August 25, 2003