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78-844: Kaipara Harbour is a large enclosed harbour estuary complex on the north western side of the North Island of New Zealand. The northern part of the harbour is administered by the Kaipara District and the southern part is administered by the Auckland Council . The local Māori tribe is Ngāti Whātua . By area, the Kaipara Harbour is one of the largest harbours in the world. It covers 947 square kilometres (366 sq mi) at high tide, with 409 square kilometres (158 sq mi) exposed as mudflats and sandflats at low tide. According to Māori tradition,

156-495: A dendritic , treelike outline although they can be straight and without significant branches. This pattern is inherited from the dendritic drainage pattern of the flooded river valley. The drowning of river valleys along a stretch of coast and formation of rias results in an extremely irregular and indented coastline. Often, there are naturally occurring islands, which are summits of partly submerged, pre-existing hill peaks. (Islands may also be artificial, such as those constructed for

234-573: A harsh environment for organisms. Sediment often settles in intertidal mudflats which are extremely difficult to colonize. No points of attachment exist for algae , so vegetation based habitat is not established. Sediment can also clog feeding and respiratory structures of species, and special adaptations exist within mudflat species to cope with this problem. Lastly, dissolved oxygen variation can cause problems for life forms. Nutrient-rich sediment from human-made sources can promote primary production life cycles, perhaps leading to eventual decay removing

312-529: A number of coastal water bodies such as coastal lagoons and brackish seas. A more comprehensive definition of an estuary is "a semi-enclosed body of water connected to the sea as far as the tidal limit or the salt intrusion limit and receiving freshwater runoff; however the freshwater inflow may not be perennial, the connection to the sea may be closed for part of the year and tidal influence may be negligible". This broad definition also includes fjords , lagoons , river mouths , and tidal creeks . An estuary

390-486: A perception amongst locals that commercial fishers have damaged fisheries in the Kaipara. Locals have been frustrated in their attempts to gain government support. The veteran filmmaker Barry Barclay has examined this in his 2005 documentary, The Kaipara affair . Currently (2007) about 219,000 cubic metres of sand is mined each year from the entrance and tidal deltas of the Kaipara. This sand contributes over half

468-774: A sheltered harbour as elongated sand dune barriers formed at the harbour's mouth. Over the last two million years, the harbour has cycled between periods of being a forested river valley and a flooded harbour, depending on changes in the global sea level . The present harbour formed approximately 8,000 years ago, after the Last Glacial Maximum . The Kaipara Harbour is a productive marine ecosystem , with diverse habitats and ecotones . There are tidal reaches, intertidal mudflats and sandflats, freshwater swamps , maritime rushes , reed beds and coastal scrublands . The area includes 125 square kilometres of mangrove forest . with subtidal fringes of seagrass . The Kaipara

546-444: A timber port on this river, and provided shipping services about the Kaipara. When the timber ran out, Helensville developed sheep and dairy farms, and more recently nut plantations, vineyards and deer farms. Further south, Riverhead was an important trading link with the Kaipara and Helensville, and a centre for gum digging. Also set by a river, it milled timber and flour, and made paper. Later it turned to tobacco. From 1929 to 1933,

624-408: A type of ecosystem in some estuaries that have been negatively impacted by eutrophication. Cordgrass vegetation dominates the salt marsh landscape. Excess nutrients allow the plants to grow at greater rates in above ground biomass, however less energy is allocated to the roots since nutrients is abundant. This leads to a lower biomass in the vegetation below ground which destabilizes the banks of

702-563: A well-mixed water column and the disappearance of the vertical salinity gradient . The freshwater-seawater boundary is eliminated due to the intense turbulent mixing and eddy effects . The lower reaches of Delaware Bay and the Raritan River in New Jersey are examples of vertically homogeneous estuaries. Inverse estuaries occur in dry climates where evaporation greatly exceeds the inflow of freshwater. A salinity maximum zone

780-436: A wholly marine embayment to any of the other estuary types. The most important variable characteristics of estuary water are the concentration of dissolved oxygen, salinity and sediment load. There is extreme spatial variability in salinity, with a range of near-zero at the tidal limit of tributary rivers to 3.4% at the estuary mouth. At any one point, the salinity will vary considerably over time and seasons, making it

858-477: A wide effect on the surrounding water bodies.  In turn, this can decrease fishing industry sales in one area and across the country. Production in 2016 from recreational and commercial fishing contributes billions of dollars to the United States' gross domestic product (GDP). A decrease in production within this industry can affect any of the 1.7 million people the fishing industry employs yearly across

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936-801: Is a migratory bird habitat of international significance. Forty–two coastal species are known, and up to 50,000 birds are common. Rare species use the harbour for feeding during summer before returning to the Northern Hemisphere to breed, such as the bar-tailed godwit , lesser knot , and turnstone . Threatened or endangered native species, such as the North Island fernbird , fairy tern , crake , Australasian bittern , banded rail , grey‑faced petrels , banded and NZ dotterels , South Island pied oystercatcher , pied stilt , and wrybill are also present . Significant local populations of black swan , pūkeko , and grey duck also breed in

1014-455: Is a dynamic ecosystem having a connection to the open sea through which the sea water enters with the rhythm of the tides . The effects of tides on estuaries can show nonlinear effects on the movement of water which can have important impacts on the ecosystem and waterflow. The seawater entering the estuary is diluted by the fresh water flowing from rivers and streams. The pattern of dilution varies between different estuaries and depends on

1092-513: Is derived from the Latin word aestuarium meaning tidal inlet of the sea, which in itself is derived from the term aestus , meaning tide. There have been many definitions proposed to describe an estuary. The most widely accepted definition is: "a semi-enclosed coastal body of water, which has a free connection with the open sea, and within which seawater is measurably diluted with freshwater derived from land drainage". However, this definition excludes

1170-478: Is expected to generate 0.75 MW averaged over time. The peak level of generation for the combined turbines is about 200 MW. This exceeds the projected peak electricity needs of Northland . It would have environmental benefits in offsetting annual carbon emissions from a thermal-based, gas turbine generator of 575,000 tonnes of carbon. The project was costed at about $ 600 million and to be economic would have to be scaled up rapidly to near full capacity. However, while

1248-411: Is formed, and both riverine and oceanic water flow close to the surface towards this zone. This water is pushed downward and spreads along the bottom in both the seaward and landward direction. Examples of an inverse estuary are Spencer Gulf , South Australia, Saloum River and Casamance River , Senegal. Estuary type varies dramatically depending on freshwater input, and is capable of changing from

1326-566: Is less restricted, and there is a slow but steady exchange of water between the estuary and the ocean. Fjord-type estuaries can be found along the coasts of Alaska , the Puget Sound region of western Washington state , British Columbia , eastern Canada, Greenland , Iceland , New Zealand, and Norway. These estuaries are formed by subsidence or land cut off from the ocean by land movement associated with faulting , volcanoes , and landslides . Inundation from eustatic sea-level rise during

1404-420: Is needed on biodiversity in the Kaipara Harbour and habitats in associated coastal areas. A recent pilot survey found that habitats in the estuaries are still extensive, but ninety percent of land cover is no longer indigenous wetland or vegetation. Even if the key existing areas were to be protected, further buffers and corridors that give better connection between the natural areas would be needed to encourage

1482-547: Is the Colorado River Delta in Mexico, historically covered with marshlands and forests, but now essentially a salt flat. Drowned river valley A ria ( / ˈ r iː ə / ; Galician : ría , feminine noun derived from río , river) is a coastal inlet formed by the partial submergence of an unglaciated river valley . It is a drowned river valley that remains open to the sea. Typically rias have

1560-646: Is the whitefish species from the European Alps . Eutrophication reduced the oxygen levels in their habitats so greatly that whitefish eggs could not survive, causing local extinctions. However, some animals, such as carnivorous fish, tend to do well in nutrient-enriched environments and can benefit from eutrophication. This can be seen in populations of bass or pikes. Eutrophication can affect many marine habitats which can lead to economic consequences. The commercial fishing industry relies upon estuaries for approximately 68 percent of their catch by value because of

1638-604: The Caspian tern . The birds have moved to other parts of Kaipara Harbour, possibly due to human disturbance. An air weapons range used by the New Zealand Defence Force is a short distance south of the spit. Māori settlements and marae have been scattered around the harbour margins for hundreds of years. The waterways of the Kaipara provided, and still provide, Māori with resources and a ready means of moving between marae. Today most marae are associated with

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1716-540: The Chesapeake Bay Bridge-Tunnel .) A ria coast is a coastline having several parallel rias separated by prominent ridges, extending a distance inland. The sea level change that caused the submergence of a river valley may be either eustatic (where global sea levels rise), or isostatic (where the local land sinks). The result is often a very large estuary at the mouth of a relatively insignificant river (or else sediments would quickly fill

1794-748: The Holocene Epoch has also contributed to the formation of these estuaries. There are only a small number of tectonically produced estuaries; one example is the San Francisco Bay , which was formed by the crustal movements of the San Andreas Fault system causing the inundation of the lower reaches of the Sacramento and San Joaquin rivers . In this type of estuary, river output greatly exceeds marine input and tidal effects have minor importance. Freshwater floats on top of

1872-610: The Mandovi estuary in Goa during the monsoon period. As tidal forcing increases, river output becomes less than the marine input. Here, current induced turbulence causes mixing of the whole water column such that salinity varies more longitudinally rather than vertically, leading to a moderately stratified condition. Examples include the Chesapeake Bay and Narragansett Bay . Tidal mixing forces exceed river output, resulting in

1950-509: The Manukau , and is the single most significant wetland for west coast fisheries. In 2009, NIWA scientists discovered that 98 percent of snapper on the west coast of the North Island were originally juveniles from nurseries in the Kaipara. Snapper is New Zealand's largest recreational fishery , and is also a commercial fishery with an annual export value of $ 32 million. The findings show how fragile some fish stocks can be, and highlights

2028-640: The Mid-Atlantic coast, and Galveston Bay and Tampa Bay along the Gulf Coast . Bar-built estuaries are found in a place where the deposition of sediment has kept pace with rising sea levels so that the estuaries are shallow and separated from the sea by sand spits or barrier islands. They are relatively common in tropical and subtropical locations. These estuaries are semi-isolated from ocean waters by barrier beaches ( barrier islands and barrier spits ). Formation of barrier beaches partially encloses

2106-516: The Ngāti Whātua sub-tribes, Te Taoū and Te Uri-o-Hau . These sub-tribes both descend from the chief Haumoewhārangi who settled on the north end of the Kaipara entrance at Poutō . He was killed in an argument about kūmara (sweet potatoes). His widow Waihekeao developed a partnership with a Tainui warrior chief, Kāwharu. Kāwharu led several destructive campaigns around Kaipara. Eventually the descendants of Waihekeao and Haumoewhārangi came to control

2184-734: The Severn Estuary in the United Kingdom and the Ems Dollard along the Dutch-German border. The width-to-depth ratio of these estuaries is typically large, appearing wedge-shaped (in cross-section) in the inner part and broadening and deepening seaward. Water depths rarely exceed 30 m (100 ft). Examples of this type of estuary in the U.S. are the Hudson River , Chesapeake Bay , and Delaware Bay along

2262-463: The Tasman Sea . It narrows to a width of 6 kilometres (3.7 mi), and is over 50 metres (160 ft) deep in parts. On average, Kaipara tides rise and fall 2.10 metres (6.9 ft). Spring tidal flows reach 9 km/h (5 knots) in the entrance channel and move 1,990 million cubic metres per tidal movement or 7,960 million cubic metres daily. The harbour head is a hostile place. Big waves from

2340-689: The Whakapirau Community Website) have become quiet backwaters. Pahi has become a launch point for houseboats and fishing. Matakohe has a museum which commemorates the kauri industry and the early Pākehā settlers. Today, Dargaville is the principal centre in the Kaipara area. Its population levelled in the 1960s. It is the country's main kūmara (sweet potato) producer. Much of the coastal fishing industry in New Zealand depends on mangrove forests . About 80% of fish caught commercially are linked to food chains dependent on

2418-478: The black-tailed godwit , rely on estuaries. Two of the main challenges of estuarine life are the variability in salinity and sedimentation . Many species of fish and invertebrates have various methods to control or conform to the shifts in salt concentrations and are termed osmoconformers and osmoregulators . Many animals also burrow to avoid predation and to live in a more stable sedimental environment. However, large numbers of bacteria are found within

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2496-475: The Auckland region means the road costs of transporting sand from further parts of the country are avoided. Concerns about possible negative consequences of this sand mining have also been raised. In 2008, Crest Energy, a power company, received resource consent to install about 200 underwater tidal turbines in the Kaipara Harbour, which would use the substantial tidal flows moving in and out every day near

2574-529: The Crown settled the historical claims of Te Uri o Hau , a hapū of the northern Kaipara Harbour. As part of the settlement, access to and the rights of the hapū to gather oysters within the existing "Maori Oyster Areas" were recognised. In 2008, resource consent was given to Biomarine to establish New Zealand's largest oyster farm in the Kaipara. The farm is projected to produce about NZ$ 30 million in annual exports and 100 new jobs. In recent years, there has been

2652-592: The Department of Conservation had approved the project, and had made substantial environmental monitoring conditions part of the consent, the project also had objectors on the grounds of claimed influences on the local ecosystems and charter fishing (see the section above on fisheries ). Appeals before the Environment Court are still likely. The project was put on hold by Crest Energy in late 2013; its director Anthony cited several issues that prevented

2730-500: The Kaipara Harbour. Te Uri-o-Hau was founded by Hakiputatōmuri, and controlled the northern part of Kaipara Harbour. Te Taoū was founded by Mawake, and controlled the south. In 1839, European settlers began arriving in the Kaipara to fell and mill kauri trees and build boats for local requirements. Despite the perilous bar at the harbour entrance, the Kaipara became a busy timber port from the 1860s, shipping thousands of tonnes of kauri timber and gum . The first sailing ship wrecked at

2808-601: The Riverhead State Forest was developed from 5,000 ha of exhausted gum land. As the kauri ran out, the Kaipara became a backwater. After 1920 the gum and timber industries dwindled, and farming, mainly dairying, took over. In particular, there is dairying on the rich Ruāwai flats . These flats are below sea level, and are protected by a stopbank and a drainage system. Coastal sawmill settlements at Tinopai , Arapaoa, Batley , Matakohe , Oneriri, Ōruawharo, Pahi , Paparoa , Tanoa and Whakapirau (history photos on

2886-535: The Tasman Sea break over large sandbanks about five metres below the surface, two to five kilometres from the shore. The sand in these sandbanks comes mainly from the Waikato River . Sand discharged from this river is transported northward by the prevailing coastal currents. Some of this sand is carried into the Kaipara harbour entrance, but mostly cycles out again and then continues moving northwards along

2964-400: The United States. Estuaries are incredibly dynamic systems, where temperature, salinity, turbidity, depth and flow all change daily in response to the tides. This dynamism makes estuaries highly productive habitats, but also make it difficult for many species to survive year-round. As a result, estuaries large and small experience strong seasonal variation in their fish communities. In winter,

3042-513: The above definition of an estuary and could be fully saline. Many estuaries suffer degeneration from a variety of factors including soil erosion , deforestation , overgrazing , overfishing and the filling of wetlands. Eutrophication may lead to excessive nutrients from sewage and animal wastes; pollutants including heavy metals , polychlorinated biphenyls , radionuclides and hydrocarbons from sewage inputs; and diking or damming for flood control or water diversion. The word "estuary"

3120-424: The area. Land habitats adjacent to the harbour support some rare botanical species, including native orchids, the king fern , and the endangered kaka beak . In particular, Papakanui Spit on the south head of the harbour entrance, a mobile sandspit , is important as a breeding and roosting area for the New Zealand dotterel and the fairy tern . It also has areas of pingao . The spit was an important habitat for

3198-452: The bottom where they are harmless. Historically the oysters filtered the estuary's entire water volume of excess nutrients every three or four days. Today that process takes almost a year, and sediment, nutrients, and algae can cause problems in local waters. Some major rivers that run through deserts historically had vast, expansive estuaries that have been reduced to a fraction of their former size, because of dams and diversions. One example

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3276-409: The causes of which have not been identified. Concerns in recent years about the size and availability of scallops have resulted in temporary closures of the scallop fisheries. Early versions of oyster farming occurred between the early 1900s and 1950s. Thousands of tons of rocks were placed along the shorelines to act as an additional substrate on which the natural rock oyster could grow. In 2002,

3354-409: The dissolved oxygen from the water; thus hypoxic or anoxic zones can develop. Nitrogen is often the lead cause of eutrophication in estuaries in temperate zones. During a eutrophication event, biogeochemical feedback decreases the amount of available silica . These feedbacks also increase the supply of nitrogen and phosphorus, creating conditions where harmful algal blooms can persist. Given

3432-401: The effects of modifying the estuarine circulation. Fjord -type estuaries are formed in deeply eroded valleys formed by glaciers . These U-shaped estuaries typically have steep sides, rock bottoms, and underwater sills contoured by glacial movement. The estuary is shallowest at its mouth, where terminal glacial moraines or rock bars form sills that restrict water flow. In the upper reaches of

3510-593: The entrance to the harbour was the Aurora in April 1840. The brigantine Sophia Pate was wrecked at South Head in August 1841 with the loss of all 21 on board. The Wairoa is the main river feeding the Kaipara from the north. Thirty kilometres upstream, the town of Dargaville was established. The stretch of water to Dargaville is broad and straight and provides an easy to navigate route into what were then kauri forests in

3588-601: The estuary impacted by human activities, and over time may shift the basic composition of the ecosystem, and the reversible or irreversible changes in the abiotic and biotic parts of the systems from the bottom up. For example, Chinese and Russian industrial pollution, such as phenols and heavy metals, has devastated fish stocks in the Amur River and damaged its estuary soil. Estuaries tend to be naturally eutrophic because land runoff discharges nutrients into estuaries. With human activities, land run-off also now includes

3666-424: The estuary, the depth can exceed 300 m (1,000 ft). The width-to-depth ratio is generally small. In estuaries with very shallow sills, tidal oscillations only affect the water down to the depth of the sill, and the waters deeper than that may remain stagnant for a very long time, so there is only an occasional exchange of the deep water of the estuary with the ocean. If the sill depth is deep, water circulation

3744-776: The estuary, with only narrow inlets allowing contact with the ocean waters. Bar-built estuaries typically develop on gently sloping plains located along tectonically stable edges of continents and marginal sea coasts. They are extensive along the Atlantic and Gulf coasts of the U.S. in areas with active coastal deposition of sediments and where tidal ranges are less than 4 m (13 ft). The barrier beaches that enclose bar-built estuaries have been developed in several ways: Fjords were formed where Pleistocene glaciers deepened and widened existing river valleys so that they become U-shaped in cross-sections. At their mouths there are typically rocks, bars or sills of glacial deposits , which have

3822-609: The fish community is dominated by hardy marine residents, and in summer a variety of marine and anadromous fishes move into and out of estuaries, capitalizing on their high productivity. Estuaries provide a critical habitat to a variety of species that rely on estuaries for life-cycle completion. Pacific Herring ( Clupea pallasii ) are known to lay their eggs in estuaries and bays, surfperch give birth in estuaries, juvenile flatfish and rockfish migrate to estuaries to rear, and anadromous salmonids and lampreys use estuaries as migration corridors. Also, migratory bird populations, such as

3900-400: The great biodiversity of this ecosystem. During an algal bloom , fishermen have noticed a significant increase in the quantity of fish. A sudden increase in primary productivity causes spikes in fish populations which leads to more oxygen being utilized. It is the continued deoxygenation of the water that then causes a decline in fish populations. These effects can begin in estuaries and have

3978-425: The harbour mouth to produce electricity for approximately 250,000 homes. Crest planned to place the turbines at least 30 metres deep along a ten kilometre stretch of the main channel. Historical charts show this stretch of the channel has changed little over 150 years. The output of the turbines will cycle twice daily with the predictable rise and fall of the tide. Each turbine will have a maximum output of 1.2 MW, and

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4056-420: The impacts do not end there. Plant death alters the entire food web structure which can result in the death of animals within the afflicted biome . Estuaries are hotspots for biodiversity , containing a majority of commercial fish catch, making the impacts of eutrophication that much greater within estuaries. Some specific estuarine animals feel the effects of eutrophication more strongly than others. One example

4134-456: The importance of protecting natural habitats, like the Kaipara. Native rock oysters are plentiful on the rocky shores, and the introduced Pacific oysters flourish lower in the intertidal zone. There are cockles and tuatua on the lower tidal flats, mussels from low tide on the rocks to subtidal beds closer to the mouth of the harbour, and scallops in the tidal channels. The scallop population has periodic incidences of high mortality,

4212-515: The interior of the peninsula at the northeast of the harbour, one of them ending near the town of Maungaturoto , only ten kilometres (6 mi) from the Pacific Ocean coast. The harbour has extensive catchments feeding five rivers and over a hundred streams, and includes large estuaries formed by the Wairoa , Otamatea, Oruawharo , Tauhoa (Channel) and Kaipara . A number of small islands off

4290-544: The interior. Dargaville flourished and immigrants from Britain and Croatia were attracted to the area. Ships up to 3,000 tons carried timber and logs out along the Wairoa to defy the bar at the harbour entrance before continuing on, usually to another New Zealand port or across the Tasman to Australia. The Kaipara River is the principal river feeding Kaipara Harbour from the south. From 1863 Helensville established itself as

4368-448: The land and sedimentation in the harbour. Shellfish abundance has declined, especially toheroa, scallops, tuatua, cockles and pipi. Finfish like mullet, snapper, kanae and school shark have diminished. Habitat fragmentation has also occurred. Natural vegetation in the Kaipara catchments have been reduced to islands of wetlands and forest in human-made landscapes—separated by urban areas, roads, exotic forests and pastures. More information

4446-444: The main issues, with "ninety-nine per cent of the rivers in the catchment [are] polluted". As part of the worldwide trend, there is a decline in biodiversity within the Kaipara. The timber industry removed most of the native forest. Much of the kauri and kahikatea forest, and scrub and riparian vegetation, has been replaced with farm and urban areas. Mangrove forests and wetlands have been "reclaimed". Soil erosion has increased on

4524-520: The mangroves, and at least 30 species of fish use mangrove wetlands at some stage of their life cycle. The marine and estuarine areas in the Kaipara Harbour breed snapper , mullet , flounder , sole , kahawai , white trevally , gurnard , yellow‑eyed mullet and skates , rays and sharks . The Kaipara is the largest estuarine harbour on the west coast of New Zealand and provides significant areas of suitable breeding grounds and habitats for juvenile fish. It has fewer problems with water quality than

4602-525: The many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. Excess oxygen-depleting chemicals in the water can lead to hypoxia and the creation of dead zones . This can result in reductions in water quality, fish, and other animal populations. Overfishing also occurs. Chesapeake Bay once had a flourishing oyster population that has been almost wiped out by overfishing. Oysters filter these pollutants, and either eat them or shape them into small packets that are deposited on

4680-422: The marine environment, such as plastics , pesticides , furans , dioxins , phenols and heavy metals . Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation . They also accumulate in benthic environments, such as estuaries and bay muds : a geological record of human activities of the last century. The elemental composition of biofilm reflect areas of

4758-575: The marsh causing increased rates of erosion . A similar phenomenon occurs in mangrove swamps , which are another potential ecosystem in estuaries. An increase in nitrogen causes an increase in shoot growth and a decrease in root growth. Weaker root systems cause a mangrove tree to be less resilient in seasons of drought, which can lead to the death of the mangrove. This shift in above ground and below ground biomass caused by eutrophication could hindered plant success in these ecosystems. Across all biomes, eutrophication often results in plant death but

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4836-578: The name Kaipara had its origins back in the 15th century when the Arawa chief, Kahumatamomoe , travelled to the Kaipara to visit his nephew at Pouto . At a feast, he was so impressed with the cooked root of the para fern , that he gave the name Kai-para to the district. Kaipara comes from the Māori kai meaning "food", and para meaning "king fern". The harbour extends for some 60 kilometres (37 mi) from north to south. Several large arms extend into

4914-581: The north west region of New Zealand as a whole, but does not tailor quota specifically for the Kaipara. Local iwi feel they are not sufficiently involved in management issues, and to further compound matters, the local iwi is split between Te Uri-o-Hau in the northern part and Te Taoū in the southern part. As of 2011, the environmental state of the harbour has been called as "nearing crisis" and "in significant decline", with shrinking fish and shellfish stocks, more sedimentation, declining water quality and competition for resource use and development being noted as

4992-511: The northern arm of the entrance ( Pouto Peninsula ). It was automated in 1947 and closed in the mid 1950s. The structure still exists and was renovated in 1982–84. In Māori mythology , the ocean-going canoe Māhuhu voyaged from Hawaiki to New Zealand and overturned on the northern side of the entrance. It was commanded by the chief Rongomai , who drowned. His body was eaten by araara (white trevally), and his descendants to this day will not eat that type of fish. The first European shipwreck

5070-440: The now off-balance nitrogen cycle , estuaries can be driven to phosphorus limitation instead of nitrogen limitation. Estuaries can be severely impacted by an unbalanced phosphorus cycle, as phosphorus interacts with nitrogen and silica availability. With an abundance of nutrients in the ecosystem, plants and algae overgrow and eventually decompose, which produce a significant amount of carbon dioxide. While releasing CO 2 into

5148-575: The project from proceeding. He also sold the majority of his shareholdings to Todd Energy Ltd the same year. Management of the Kaipara Harbour does not have a central administration. Management is distributed among the Kaipara District Council, Auckland Council , Northland Regional Council , the Department of Conservation's Northland and Auckland section, and the Ministry of Fisheries. The Ministry of Fishing allocates quota for

5226-561: The recovery of biodiversity. Estuary Most existing estuaries formed during the Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000–12,000 years ago. Estuaries are typically classified according to their geomorphological features or to water-circulation patterns. They can have many different names, such as bays , harbors , lagoons , inlets , or sounds , although some of these water bodies do not strictly meet

5304-609: The ria). The Kingsbridge Estuary in Devon , England, is an extreme example of a ria forming an estuary disproportionate to the size of its river; no significant river flows into it at all, only a number of small streams. The word ria comes from Galician ría which comes from río (river). Rias are present all along the Galician coast in Spain . As originally defined, the term was restricted to drowned river valleys cut parallel to

5382-416: The sand requirements for Auckland . The sand is used in the production of concrete and asphalt, and also in drainage systems and beach nourishment . A suction pump is usually used to extract the sand from the seabed. It is pumped into a barge as a sand and water slurry. As the barge loads, shells and other objects are screened out and the sea water drained back to the sea. The availability of sea sand within

5460-427: The seawater in a layer that gradually thins as it moves seaward. The denser seawater moves landward along the bottom of the estuary, forming a wedge-shaped layer that is thinner as it approaches land. As a velocity difference develops between the two layers, shear forces generate internal waves at the interface, mixing the seawater upward with the freshwater. An examples of a salt wedge estuary is Mississippi River and

5538-411: The sediment which has a very high oxygen demand. This reduces the levels of oxygen within the sediment often resulting in partially anoxic conditions, which can be further exacerbated by limited water flow. Phytoplankton are key primary producers in estuaries. They move with the water bodies and can be flushed in and out with the tides . Their productivity is largely dependent upon the turbidity of

5616-400: The shoreline are connected to the mainland by mudflats at low tide. The Kaipara Harbour is broad and mostly shallow, as it is formed from a system of drowned river valleys . The harbour shoreline is convoluted by the entry of many rivers and streams, and is about 800 kilometres (500 mi) long, being the drainage catchment for about 640,000 ha of land. The harbour entrance is a channel to

5694-440: The structure of the country rock that was at right angles to the coastline. However the definition of ria was later expanded to other flooded river valleys regardless of the structure of the country rock. For a time European geomorphologists considered rias to include any broad estuarine river mouth, including fjords . These are long narrow inlets with steep sides or cliffs, created in a valley carved by glacial activity . In

5772-456: The volume of freshwater, the tidal range, and the extent of evaporation of the water in the estuary. Drowned river valleys are also known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley. This is the most common type of estuary in temperate climates. Well-studied estuaries include

5850-453: The water and atmosphere, these organisms are also intaking all or nearly all of the available oxygen creating a hypoxic environment and unbalanced oxygen cycle . The excess carbon in the form of CO 2 can lead to low pH levels and ocean acidification , which is more harmful for vulnerable coastal regions like estuaries. Eutrophication has been seen to negatively impact many plant communities in estuarine ecosystems . Salt marshes are

5928-835: The water. The main phytoplankton present are diatoms and dinoflagellates which are abundant in the sediment. A primary source of food for many organisms on estuaries, including bacteria , is detritus from the settlement of the sedimentation. Of the thirty-two largest cities in the world in the early 1990s, twenty-two were located on estuaries. As ecosystems, estuaries are under threat from human activities such as pollution and overfishing . They are also threatened by sewage, coastal settlement, land clearance and much more. Estuaries are affected by events far upstream, and concentrate materials such as pollutants and sediments. Land run-off and industrial, agricultural, and domestic waste enter rivers and are discharged into estuaries. Contaminants can be introduced which do not disintegrate rapidly in

6006-404: The west coast. The southern sandbanks at the entrance are constantly accumulating and releasing this sand. These treacherous sandbanks shift and change position, and are known locally as the graveyard . The graveyard is responsible for more shipwrecks than any other place in New Zealand, and has claimed at least 43 vessels—some say as many as 110. For this reason, a lighthouse was built in 1884 on

6084-516: Was the Aurora , a 550-ton barque, in 1840, and the most recent was the yacht Aosky in 1994. Today, the remains of wrecks still become visible under certain tidal and sand conditions. The Kaipara is rarely used today for shipping, and no large settlements lie close to its shores, although many small communities lie along its coastline. The Kaipara Harbour is a drowned river valley system, which first formed 2-3 million years ago as an open bay, becoming

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