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70-555: The Estuary of the Heathcote and Avon Rivers / Ihutai is the largest semi-enclosed shallow estuary in Canterbury and remains one of New Zealand's most important coastal wetlands . It is well known as an internationally important habitat for migratory birds , and it is an important recreational playground and educational resource. It was once highly valued for mahinga kai ( Māori for food gathering). The Avon River / Ōtākaro enters

140-425: A day. Flax leaves were cut, bundled, taken to the mill and fed through a stripping machine. The slimy fibre was bunched, washed and the muka hung to dry. About ten days later the muka was scutched and baled for export, though some mills had ropewalks for local production. Production peaked between 1901 and 1918, but rust , depression and pasture replacing flax swamps , resulted in almost all mills closing by

210-573: 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

280-487: A medieval gambeson , slowing musket balls to be wounding rather than deadly. In winter 1823 Captain John Rodolphus Kent went to Foveaux Strait , filled 14 large casks with flax, bought 1,100 lb (500 kg) of dressed flax, and took 25 flax plants. That trip was by way of an experiment to confirm the value of flax, but he continued trading until 1836 and several other traders followed his example. Thus, by

350-529: 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

420-537: A screw press £12; building £185. So the inventions were quickly taken up, flax mills increasing from 15 in 1867, to 110 in 1874, though another source says there were 161 mills by 1870, employing 1,766. A & G Price built almost 100 flax machines in 1868 and, by August 1869, had sold 166. The fibre was coarser than hand-stripped flax, but by 1868 machines could produce about 250 kg (550 lb) per day, compared to about 1 kg (2.2 lb) by hand stripping. Improvements by 1910 increased that to 1.27 tonnes

490-787: A total of 175 different invertebrate species were found to inhabit the Charlesworth Reserve in the Avon-Heathcote Estuary / Ihutai. 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

560-408: 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

630-550: 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

700-436: 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

770-470: 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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840-495: A year, could produce 2 tons of fibre, equating to £40 a year, or a net profit of £27 0s 3d, the cost being estimated at £12 19s 9d. For 4 tons the cost was calculated as depreciation 12s, 8 men's wages @ 25s a week, £10; an engineman £1 15; 12 lads @ 12s, £7 4s; 24 tons of green flax @ 15s £18; packing, baling, etc. £4; 2 tons 8cwt. of coal, £2 8s and freight etc., £5. Machinery was estimated at £500 – 8 hp engine with Cornish boiler £200; 4 strippers @ £22, £88; scutching hooks, £15;

910-455: 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

980-451: Is a mild anaesthetic , and Māori traditionally applied the sap to boils and various wounds, to aching teeth, to rheumatic and associated pains, ringworm and various skin irritations, and scalds and burns. Splints were fashioned from korari (flower stalks) and leaves, and fine cords of muka fibre utilise the styptic properties of the gel before being used to stitch wounds. Harakeke is used as bandages and can secure broken bones much as plaster

1050-509: 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

1120-411: 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

1190-1027: Is laboriously washed, pounded and hand wrung to make soft for the skin. It is difficult to dye fibres made from harakeke, however paru (an iron-rich mud) can be used to dye the fabric black. The cords (muka whenu) form the base cloth for intricate cloaks or garments (kākahu) such as the highly prized traditional feather cloak (kahu huruhuru). Different type of cloaks, such as kahu kiwi and kahu kākā, were produced by adorning them with colourful feathers from different native birds, such as kiwi , kākā (parrot), tūī , huia and kererū (woodpigeon). Fibres of various strengths were used to fashion eel traps (hinaki), massive fishing nets (kupenga) and lines, bird snares, cordage for ropes, baskets ( kete ), bags, mats, clothing, sandals (paraerae), buckets, food baskets (rourou), and cooking utensils etc. The handmade flax cording and ropes had such great tensile strength that they were used to successfully bind together sections of hollowed out logs to create huge ocean-going canoes ( waka ). With

1260-560: 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

1330-551: Is shallow with the mean at high water of ordinary spring tides (HWOST) of 1.4 metres (4.6 ft)—and is predominantly intertidal , as only about 15 percent of the area lies below low water of ordinary spring tides (LWOST). The estuary's official name became Estuary of the Heathcote and Avon Rivers / Ihutai as a result of the Ngāi Tahu Claims Settlement Act 1998 . The Estuary formed around 450 years ago and covers around 880 hectares (3.3 square miles). In 1989

1400-634: Is the Colorado River Delta in Mexico, historically covered with marshlands and forests, but now essentially a salt flat. Flax in New Zealand New Zealand flax describes the common New Zealand perennial plants Phormium tenax and Phormium colensoi , known by the Māori names harakeke and wharariki respectively. Although given the common name 'flax' they are quite distinct from

1470-639: 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

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1540-454: Is used today. Chemical analysis shows the antifungal, anti-inflammatory drug, musizin, and laxative anthraquinones are in common and mountain flaxes. During the early Musket Wars and later New Zealand Wars , Māori used large, thickly woven flax mats to cover entrances and lookout holes in their "gunfighter's pā " fortifications. Some warriors wore coats of heavily plaited Phormium tenax , which gave defense characteristics similar to

1610-719: 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

1680-595: 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

1750-628: 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

1820-702: 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

1890-478: 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

1960-419: The 1930s. Mills were driven by water wheels , small stationary steam engines , or portable engines . With extensive burning of bush, few fire brigades, and little piped water, fire was a hazard for most buildings and flax was no exception. In 1890 a report on a fire in a large quantity of growing flax said, " These fires in most cases arise from gross carelessness, which might easily be avoided. Already in

2030-655: The Canterbury Regional Council and the Christchurch City Council drilled an exploratory bore near the mouth of the Avon River / Ōtakaro discovering layers of fossils and sediment types that showed the area had experienced shifts between being marine, estuary, swamp and floodplain over the last 2 million years. The land underneath the Estuary consists of gravel embedded between fine silts and sands deposited by

2100-476: The Estuary provided an important trading route. In 1837, a whaler named James Robinson Clough also known as Jimmy Robinson married Puawai a local Māori and is said to be the first European to access the Estuary. The Avon–Heathcote Estuary Ihutai Trust was formed in 2002. This resulted from requests from the wider community to act in the estuary's long-term interests. The members of the Trust include representatives from

2170-542: The Northern Hemisphere plant known as flax ( Linum usitatissimum ) . P. tenax occurs naturally in New Zealand and Norfolk Island , while P. colensoi is endemic to New Zealand. They have played an important part in the cultural and economic history of New Zealand for both the Māori people and the later European settlers. Both species and their cultivars have now been widely distributed to temperate regions of

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2240-400: 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,

2310-513: 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"

2380-437: The abundance of food supplied by Ihutai. Traditional food sources around Ihutai included pūtangitangi ( Paradise Shelduck ), pārera ( grey duck ), tuna ( eels ), kanakana ( lamprey ), īnanga (adult whitebait ), pātiki ( flounder ) and pipi (shellfish). In former times a soft-shelled perwinkle snail called whetiko flourished. In March 1848 Governor George Grey negotiated sale of 20 million acres between Kaiapoi and Otago via

2450-452: 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

2520-506: The community, existing groups (Friends of the Estuary and the Christchurch Estuary Association), representatives from Christchurch City Council , Environment Canterbury , tāngata whenua and other agencies. As of 2024, the board also includes scientists such as emeritus professor Islay Marsden , and biologist Lesley Bolton-Ritchie. In the summer of 2021 to 2022, an invertebrate survey was undertaken by Julia Palmer and

2590-412: The desperate need for muskets and ammunition, many Māori moved to unhealthy swamplands where flax could be grown, and there devoted insufficient labour to the production of food, until any survivors were fully equipped, first with musket and ammunition, and then with iron tools. "The taking of slaves increased – slaves who could be put to work dressing flax..." . A burgeoning flax industry developed with

2660-500: The discovery of the South Island by Waitaha ancestor, Rākaihautū . Traditional food gathering or mahinga kai sites of Waitaha , Rapuwai, Kāti Mamoe and subsequently Ngāi Tahu iwi included Ihutai (The Estuary). The nearest kāika (settlements) included Orua Paeroa at Travis Wetland and Te Kai a Te Karoro pā , which was located near to South New Brighton Park, the latter supporting iwi to reside there throughout each year due to

2730-409: 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

2800-452: The early 19th century, the quality of rope materials made from New Zealand flax was known internationally, as was the quality of New Zealand trees which were used for spars and masts. The Royal Navy was one of the largest customers. The flax trade burgeoned, especially after male Māori recognised the advantages of trade and adapted to helping in the harvesting and dressing of flax which had previously been done exclusively by females. Driven by

2870-401: 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

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2940-468: The estuary from the northwest, and the Ōpāwaho / Heathcote River from the south-west. The estuary has a triangular shape, a short inlet connection with Pegasus Bay , and is primarily enclosed by the 4-kilometre (2.5 mi) long Brighton Spit, on which the suburbs New Brighton , South New Brighton and Southshore are located. The most prominent features of the inlet are the single deep channel between Rapanui Rock ("Shag Rock") and Brighton Spit. It

3010-595: 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

3080-424: 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

3150-771: 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

3220-448: The fibre from Phormium tenax has been investigated, but currently it is used only by artists and craftsmen producing handmade papers. From about the 1860s there was an active industry harvesting and processing flax for export, peaking at 32,000 tons in 1916, but the general depression of the 1930s brought the virtual collapse of this trade. In 1963 there were still 14 flax mills producing a total of almost 5,000 tons of fibre per year, but

3290-413: The fibres being used for rope, twine, matting, carpet under felt, and wool packs. Initially wild stands of flax were harvested but plantations were established with three in existence by 1851. A Parliamentary Commission in 1870 reported on all aspects of the flax industry. It listed up to 24 varieties, with many regional variations in names. Several times the possibility of commercial papermaking from

3360-609: 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

3430-545: The flowers for medicinal purposes and as a general sweetener. Boiled and crushed harakeke roots were applied externally as a poultice for boils, tumours and abscesses, as well as to varicose ulcers. Juice from pounded roots was used as a disinfectant, and taken internally to relieve constipation or expel worms. The pulp of pounded leaves was applied as dressings to bullet, bayonet or other wounds. The gum-like sap produced by harakeke contains enzymes that give it blood clotting and antiseptic qualities to help healing processes. It

3500-400: 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

3570-578: The help of wakas, pre-European Māori deployed seine nets which could be over one thousand metres long. The nets were woven from green flax, with stone weights and light wood or gourd floats, and could require hundreds of men to haul. It was also used to make rigging, sails and lengthy anchor warps, and roofs for housing. Frayed ends of flax leaves were fashioned into torches and lights for use at night. The dried flower stalks, which are extremely light, were bound together with flax twine to make river rafts called mokihi. For centuries, Māori have used nectar from

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3640-420: 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

3710-530: The land purchaser Henry Kemp who obtained Māori signatures to a deed of purchase now referred to as Kemp's Purchase or Kemp's Deed . Governor Grey did not uphold all the terms of Kemp's Deed which included a promise to allow access to traditional mahinga kai and kaika nohoanga (seasonal camps) and by the 1850s Māori were barred from access to their mahinga kai sites around the estuary. Sealers and whalers were often valued by Māori who traded flax and potatoes for steel adzes , axes, muskets and other supplies and

3780-425: The land. Leaves were cut near the base of the plant using a sharp mussel shell or specially shaped rocks, more often than not greenstone ( jade , or pounamu). The green fleshy substance of the leaf was stripped off (the waterproof para), again using a mussel shell, right through to the fibre which went through several processes of washing, bleaching, fixing, softening, dyeing and drying. The flax fibre, called muka ,

3850-416: The last of them closed in 1985. In 1860 Purchas and Ninnis got the country's first patent for a flax machine. It took a ton of leaves a day and produced about 0.2 long tons (200 kg) of fibre. A large mill at Halswell had six of their patent strippers by 1868. Johnstone Dougall (1822–1892), a carpenter, also invented a flax-stripper about 1868, which he put in his first mill at Waiuku . Dougall

3920-604: The leaves of these plants, with very little preparation, they (the Māori) make all their common apparel; and of these they make also their strings, lines and cordage …”. They also made baskets, mats and fishing nets from undressed flax. Māori practised advanced weft twining in phormium fibre cloaks. Plaiting and weaving (raranga) the flax fibres into baskets were but only two of the great variety of uses made of flax by Māori who recognised nearly 60 varieties, and who carefully propagated their own flax nurseries and plantations throughout

3990-525: 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

4060-422: 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

4130-575: 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

4200-440: 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

4270-422: The past the quantity of green flax destroyed by this agency is very great. " Mills were burnt too. By 1890 3,198 people were employed, but average pay was only £73 a year, among the lowest of average wage rates at the time. There were also frequent cases of workers caught in machines. Initially unions were resisted, as in the report of an 1891 strike, which said, "Mr Hall intends to proceed to Auckland for

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4340-459: The purpose of procuring fresh men to work the mill." The Industrial Conciliation and Arbitration Act 1894 and growth of unions improved the low pay and conditions. By 1913 a commentator wrote, " A few years ago flax milling was largely done by boys who received a few shillings per day, now in these more enlightened (?) days a boy gets a man’s wage. For instance the minimum wage paid this season at Mr Rutherford's Te Aoterei mill has been 11s 3d for

4410-676: The rivers and sea. The Brighton Spit which encloses the Estuary was formed by sand carried by the Ashley / Rakahuri and Waimakariri Rivers and as the Spit grew, the mouth of the Avon River / Ōtākaro was forced southward towards that of the Ōpāwaho / Heathcote River, forming the estuary of today. Māori people were the first settlers in Canterbury and arrived around the 13th century according to western archaeological evidence, though Māori whakapapa (genealogies) date settlement before this period of time with

4480-427: 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

4550-411: 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

4620-456: 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

4690-453: 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

4760-835: 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

4830-521: The world as ornamental garden plants – and to lesser extent for fibre production. Although the Māori made textiles from a number of other plants, including tī kōuka , tōī , pingao , kiekie , toetoe and the paper mulberry , the use of harakeke and wharariki was predominant, due to its wide availability, long strands and the ability to create a range of strip widths from the plants. Captain Cook wrote: “Of

4900-428: Was an exception in declining to patent his stripper. Many others patented variations, but the basic design was that leaves were fed between rollers, then hit by iron beaters, revolving faster than the feeder, thus stripping the epidermis from the fibre. Patents included Ritchie in 1862, Gibbons and Nelson in 1870, and Williams in 1893. In boom times flax was profitable. An 1870 news item said an acre, with 2 crops

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