Overview
The Avon-Heathcote Estuary (Ihutai) is significant to the Canterbury region both culturally and ecologically. Ihutai is a triangular shaped estuary, fed by the Avon River to the north-west and Heathcote River to the south-west. It is the largest shallow, semi-enclosed, tidal wetland in Canterbury. After draining urban Christchurch, the estuary flows east into Pegasus Bay through a narrow inlet between Shag Rock and Brighton Spit. Ihutai is one of 136 wetlands which make up the East Asian-Australasian Flyway network which supports migratory waders and shorebirds. A notable example is the Bar-tailed godwit which has a declining population. The estuary has been part of Māori history since the mid1500’s. It was an important area for mahinga kai (resource gathering) and helped maintain connections for South Island iwis. Ihutai provides habitat for multiple flora species when urbanisation and the development of Christchurch city reduced wetlands elsewhere in the region.
Geology
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Ecology
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Culture
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Geography
Ihutai is a triangular shaped estuary located to the east of Christchurch City, in the South Island of New Zealand. It is fed by two urban rivers (Avon and Heathcote Rivers), which provide drainage to urban Christchurch. The figure adjacent clearly demonstrates the loss of wetlands due to urbanisation, and infilling of this topographically low area. The close proximity to urban areas, place the flora and fauna at risk of degradation due to anthropogenic impacts. The Bromley Oxidation Ponds are located to the northwest of the Avon-Heathcote estuary. The Brighton Spit protects the estuary from direct wave action, assisting sediment accumulation, and development of salt marsh environments. The tides have a large impact to this environment as opposed to smaller river inputs, and an quasi-equilibrium occurs with input and output of sediment. The 2010-2011 Canterbury Earthquake Sequence caused changes to the estuary floor, where subsidence of approximately 0.34m occurred to the northwest of the estuary, 0.22m of uplift occurred to the southwest of the estuary and 0.16m of subsidence occurred on the eastern margin of the estuary.
Ecology
Historically the western edges of the estuary consisted of extensive swamp and native fauna. Today they are covered in developmental and residential infrastructure. Salt marshes are located along undeveloped areas of the estuary and diverse vegetation is present near the Avon River mouth. It is a crucial area for maintaining the genetic and ecological diversity of wetland flora. Wetland vegetation within the low plains ecological district has been reduced to lower than 20% of their previous extent. For example, Horse’s mane lakeweed is at risk and naturally uncommon.
Ihutai is the only urban wetland to be included in the East- Asian-Australasian Flyway network and is recognised internationally for its significance to migratory birds. The estuary is inhabited by the largest amounts of native and arctic shorebirds. The Avon-Heathcote area is a nationally significant site for godwit. After an 11,000km migration from Alaska they use the estuary to feed. Habitat destruction is responsible for a 2% decline in global godwit population.
The estuary supports 23 avian species which are classified as threatened, nationally endangered, nationally vulnerable, at risk, relict, naturally uncommon or recovering. Between 1840-2013, 9 bird species have become locally extinct.
Some of the marine species include red cod, yellow-eyed mullet, eels, flounder, whitebait and trout. Between 1996-2011, 18 marine species have disappeared within the Ihutai habitat.
The Bromley Oxidation ponds discharged processed industrial and domestic sewage into the estuary since early 1800’s. This caused increased enrichment of phosphorus and nitrogen throughout the estuary causing eutrophication. Changes in 2009 saw the Bromley Oxidation ponds cease discharging in the estuary and are now pumped through a long outfall pipe and discharged 3km off New Brighton beach. This was a positive step towards protecting the rich biodiversity of the estuary. This delicate ecosystem is however still at risk of degradation through urbanisation, which would lead to further extinction of both avian and marine species and native fauna.
Ihutai is the only urban wetland to be included in the East- Asian-Australasian Flyway network and is recognised internationally for its significance to migratory birds. The estuary is inhabited by the largest amounts of native and arctic shorebirds. The Avon-Heathcote area is a nationally significant site for godwit. After an 11,000km migration from Alaska they use the estuary to feed. Habitat destruction is responsible for a 2% decline in global godwit population.
The estuary supports 23 avian species which are classified as threatened, nationally endangered, nationally vulnerable, at risk, relict, naturally uncommon or recovering. Between 1840-2013, 9 bird species have become locally extinct.
Some of the marine species include red cod, yellow-eyed mullet, eels, flounder, whitebait and trout. Between 1996-2011, 18 marine species have disappeared within the Ihutai habitat.
The Bromley Oxidation ponds discharged processed industrial and domestic sewage into the estuary since early 1800’s. This caused increased enrichment of phosphorus and nitrogen throughout the estuary causing eutrophication. Changes in 2009 saw the Bromley Oxidation ponds cease discharging in the estuary and are now pumped through a long outfall pipe and discharged 3km off New Brighton beach. This was a positive step towards protecting the rich biodiversity of the estuary. This delicate ecosystem is however still at risk of degradation through urbanisation, which would lead to further extinction of both avian and marine species and native fauna.
Culture
Wetlands are culturally significant to Māori and are highly regarded for their spiritual, physical and prosperous values. Ihutai has been culturally significant for over 600 years as a place for habitation and food gathering. The first iwi to arrive at Christchurch were the Waitaha who lived in two settlements around the estuary.
Around the mid 1500’s the Ngāti Māmoe iwi settled in Christchurch by Mt Pleasant on the estuary shores. A century later the Kaiapoi Pā was formed by Ngāi Tahu north of the Waimakariri River. During this time the estuary was bountiful with different food sources. The nutrient rich soil promoted growth of edible plants such as potatoes/sweet potatoes and fern root. Throughout this period the estuary was the main food source of Canterbury.
Ihutai is a natural link between Lake Ellesmere, the Kowai River and Pegasus Bay. Water transportation via wakas to the main fishing grounds within Pegasus Bay made accessible through Ihutai. This allowed Maori to use Ihutai as a link to maintain intertribal connections throughout the South Island of New Zealand.
In the 21st century the cultural significance of the estuary has changed toward socio-economic use. The shellfish in the estuary, whilst available for foraging come with the risk of E coli bacteria. Recreational activities such as yachting, water-skiing, windsurfing and rowing have become common, however western parts of the estuary are still classified as unsafe for swimming due to bacterial risk (Enterococci).
Around the mid 1500’s the Ngāti Māmoe iwi settled in Christchurch by Mt Pleasant on the estuary shores. A century later the Kaiapoi Pā was formed by Ngāi Tahu north of the Waimakariri River. During this time the estuary was bountiful with different food sources. The nutrient rich soil promoted growth of edible plants such as potatoes/sweet potatoes and fern root. Throughout this period the estuary was the main food source of Canterbury.
Ihutai is a natural link between Lake Ellesmere, the Kowai River and Pegasus Bay. Water transportation via wakas to the main fishing grounds within Pegasus Bay made accessible through Ihutai. This allowed Maori to use Ihutai as a link to maintain intertribal connections throughout the South Island of New Zealand.
In the 21st century the cultural significance of the estuary has changed toward socio-economic use. The shellfish in the estuary, whilst available for foraging come with the risk of E coli bacteria. Recreational activities such as yachting, water-skiing, windsurfing and rowing have become common, however western parts of the estuary are still classified as unsafe for swimming due to bacterial risk (Enterococci).