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