Misplaced Pages

#166833

97-666: Ham Wall is an English wetland National Nature Reserve (NNR) 4 kilometres (2.5 mi) west of Glastonbury on the Somerset Levels . It is managed by the Royal Society for the Protection of Birds (RSPB). Since the last Ice Age , decomposing plants in the marshes of the Brue valley in Somerset have accumulated as deep layers of peat that were commercially exploited on a large scale in

194-711: A sink or a source of carbon, depending on the specific wetland. If they function as a carbon sink, they can help with climate change mitigation . However, wetlands can also be a significant source of methane emissions due to anaerobic decomposition of soaked detritus , and some are also emitters of nitrous oxide . Humans are disturbing and damaging wetlands in many ways, including oil and gas extraction , building infrastructure, overgrazing of livestock , overfishing , alteration of wetlands including dredging and draining, nutrient pollution , and water pollution . Wetlands are more threatened by environmental degradation than any other ecosystem on Earth, according to

291-472: A firm plan was formulated. Richard Hammett, a local man from Street , was commissioned to conduct a survey of the route in 1826. Hammett had experience of building a manure canal through peat heathland . He considered two main routes; the first followed the course of the River Brue , but was rejected on the grounds of engineering costs, and the interference with its drainage function. The second route followed

388-482: A floating harbour to accommodate vessels of up to 250 long tons (250 t) were dropped, and the entrance lock was moved further along the original course of the River Brue. This saved money, but meant that ships did not have to pay lockage charges to reach Highbridge. The proprietors failed to raise all of the capital promised, and there were financial difficulties. The Commissioners of Sewers were unhappy with some of

485-402: A frequency and duration to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally included swamps, marshes, bogs, and similar areas.' For each of these definitions and others, regardless of the purpose, hydrology is emphasized (shallow waters, water-logged soils). The soil characteristics and

582-548: A number of years, bitterns were first unequivocally proved to have bred at Ham Wall in 2008, and the reserve now typically holds 18–20 breeding males, probably about its maximum capacity, with another 20 males elsewhere in the Avalon Marshes. The reserve has attracted three other heron species that are attempting to colonise the UK. The formerly rare great white egret , first bred in 2012, has nested in small numbers every year since on

679-1248: A polar climate, wetland temperatures can be as low as −50 °C (−58 °F). Peatlands in arctic and subarctic regions insulate the permafrost , thus delaying or preventing its thawing during summer, as well as inducing its formation. The amount of precipitation a wetland receives varies widely according to its area. Wetlands in Wales , Scotland , and western Ireland typically receive about 1,500 mm (59 in) per year. In some places in Southeast Asia , where heavy rains occur, they can receive up to 10,000 mm (390 in). In some drier regions, wetlands exist where as little as 180 mm (7.1 in) precipitation occurs each year. Temporal variation: Surface flow may occur in some segments, with subsurface flow in other segments. Wetlands vary widely due to local and regional differences in topography , hydrology , vegetation , and other factors, including human involvement. Other important factors include fertility, natural disturbance, competition, herbivory , burial and salinity. When peat accumulates, bogs and fens arise. The most important factor producing wetlands

776-540: A portion of the overall water cycle, which also includes atmospheric water (precipitation) and groundwater . Many wetlands are directly linked to groundwater and they can be a crucial regulator of both the quantity and quality of water found below the ground. Wetlands that have permeable substrates like limestone or occur in areas with highly variable and fluctuating water tables have especially important roles in groundwater replenishment or water recharge. Substrates that are porous allow water to filter down through

873-537: A protective barrier to coastal shoreline. Mangroves stabilize the coastal zone from the interior and will migrate with the shoreline to remain adjacent to the boundary of the water. The main conservation benefit these systems have against storms and storm surges is the ability to reduce the speed and height of waves and floodwaters. Glastonbury Canal The Glastonbury Canal ran for approximately 14 miles (23 km) through two locks from Glastonbury to Highbridge in Somerset , England , where it entered

970-489: A reduced depth for navigation. Traffic had to be transhipped to smaller boats at Highbridge, which added to the costs of delivery. Receipts for 1848 were £300, which would indicate that the canal was probably only carrying about 4,000 long tons (4,100 t) per annum. Railways arrived in the area in 1841, with the opening of part of the Bristol and Exeter Railway on 14 June, which eventually reached Exeter in 1844. In late 1846,

1067-481: A roost of thousands of four-spotted chasers . The lesser silver water beetle occurs in the wet woodland, and the very rare leaf beetle Oulema erichsoni was noted in 2015. Apart from the common reed that dominates the marshes, restricted-range plants found in the Brue valley wetlands include rootless duckweed , marsh cinquefoil , water violet , milk parsley and round-leaved sundew . Greater unpredictability in

SECTION 10

#1732851310167

1164-422: A strong influence on wetland water chemistry, particularly in coastal wetlands and in arid and semiarid regions with large precipitation deficits. Natural salinity is regulated by interactions between ground and surface water, which may be influenced by human activity. Carbon is the major nutrient cycled within wetlands. Most nutrients, such as sulfur , phosphorus , carbon , and nitrogen are found within

1261-410: A unique kind of wetland where lush plant growth and slow decay of dead plants (under anoxic conditions) results in organic peat accumulating; bogs, fens, and mires are different names for peatlands. Variations of names for wetland systems: Some wetlands have localized names unique to a region such as the prairie potholes of North America's northern plain, pocosins , Carolina bays and baygalls of

1358-508: A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota, particularly rooted plants, to adapt to flooding". Sometimes a precise legal definition of a wetland is required. The definition used for regulation by the United States government is: 'The term "wetlands" means those areas that are inundated or saturated by surface or ground water at

1455-422: A wetland system includes its plants ( flora ) and animals ( fauna ) and microbes (bacteria, fungi). The most important factor is the wetland's duration of flooding. Other important factors include fertility and salinity of the water or soils. The chemistry of water flowing into wetlands depends on the source of water, the geological material that it flows through and the nutrients discharged from organic matter in

1552-403: A wetland) affects hydro-periods (temporal fluctuations in water levels) by controlling the water balance and water storage within a wetland. Landscape characteristics control wetland hydrology and water chemistry. The O 2 and CO 2 concentrations of water depend upon temperature , atmospheric pressure and mixing with the air (from winds or water flows). Water chemistry within wetlands

1649-558: A whole. To replace these wetland ecosystem services , enormous amounts of money would need to be spent on water purification plants, dams, levees, and other hard infrastructure, and many of the services are impossible to replace. Floodplains and closed-depression wetlands can provide the functions of storage reservoirs and flood protection. The wetland system of floodplains is formed from major rivers downstream from their headwaters . "The floodplains of major rivers act as natural storage reservoirs, enabling excess water to spread out over

1746-577: A wide area, which reduces its depth and speed. Wetlands close to the headwaters of streams and rivers can slow down rainwater runoff and spring snowmelt so that it does not run straight off the land into water courses. This can help prevent sudden, damaging floods downstream." Notable river systems that produce wide floodplains include the Nile River , the Niger river inland delta, the Zambezi River flood plain,

1843-440: Is determined by the pH , salinity , nutrients, conductivity , soil composition, hardness , and the sources of water. Water chemistry varies across landscapes and climatic regions. Wetlands are generally minerotrophic (waters contain dissolved materials from soils) with the exception of ombrotrophic bogs that are fed only by water from precipitation. Because bogs receive most of their water from precipitation and humidity from

1940-412: Is hydrology, or flooding . The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation . Other important factors include soil fertility, natural disturbance, competition, herbivory , burial, and salinity. When peat from dead plants accumulates, bogs and fens develop. Wetland hydrology is associated with

2037-540: Is near the Ham Wall reserve. The network of reserves and private land managed for conservation in the Avalon marshes means that wetland management can be carried out on a landscape scale. Joint schemes include reed bed management across the area, improved pedestrian and cycle access, and the provision of visitor facilities at Ashcott corner between the Ham Wall and Shapwick Heath reserves. Following sporadic appearances by males over

SECTION 20

#1732851310167

2134-729: Is one of the members of the Avalon Marshes Partnership , which also includes the Somerset Wildlife Trust, Natural England, the Hawk and Owl Trust , South West Heritage Trust , the Environment Agency and Historic England which work together on conservation issues in the area. Between 2012 and 2016 the scheme was supported by a Heritage Lottery Fund grant of £1,772,500 with additional investment of £920,080 from other sources. The Avalon Marshes Centre, run by Natural England,

2231-517: Is open and free to enter at all times, although its car park has a charge for non-members of the RSPB and closes at night. There are toilets and a small visitor centre which sells light snacks and is usually open only at weekends. The main access to the reserve on leaving the car park is the Ham Wall loop; this follows the north bank of the canal, crosses at a bridge and returns via a parallel grass track, 2.7 kilometres (1.7 mi) in total. A short spur runs to

2328-451: Is the only place in the world where both crocodiles and alligators coexist. The saltwater crocodile inhabits estuaries and mangroves. Snapping turtles also inhabit wetlands. Birds , particularly waterfowl and waders use wetlands extensively. Mammals of wetlands include numerous small and medium-sized species such as voles , bats , muskrats and platypus in addition to large herbivorous and apex predator species such as

2425-545: Is usually saturated with water". More precisely, wetlands are areas where "water covers the soil , or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season". A patch of land that develops pools of water after a rain storm would not necessarily be considered a "wetland", even though the land is wet. Wetlands have unique characteristics: they are generally distinguished from other water bodies or landforms based on their water level and on

2522-590: The Avalon Marshes Partnership to coordinate conservation issues across the Somerset Levels. The reserve is open year-round, and has nature trails, hides and viewing points. It lies within the Somerset Levels NNR and the Somerset Levels and Moors' Ramsar and Special Area of Conservation site. Potential future threats may result from increasing unpredictability in the UK climate, leading to heavy summer rains and extensive flooding. Sea level rise will make

2619-560: The Dorset Central Railway to become the Somerset and Dorset Railway . The main line to Glastonbury closed in 1966, while the branches to the dairy at Bason Bridge and the Highbridge Wharf lasted until 1972. The canal started at a lock constructed on the old course of the River Brue, which had been bypassed by a new cut in 1801 and filled in. It then followed the course of the Brue to Cripps Bridge, after which it followed

2716-492: The Millennium Ecosystem Assessment from 2005. Methods exist for assessing wetland ecological health . These methods have contributed to wetland conservation by raising public awareness of the functions that wetlands can provide. Since 1971, work under an international treaty seeks to identify and protect " wetlands of international importance ." A simplified definition of wetland is "an area of land that

2813-666: The Pantanal in South America, and the Sundarbans in the Ganges - Brahmaputra delta. Wetlands contribute many ecosystem services that benefit people. These include for example water purification , stabilization of shorelines, storm protection and flood control . In addition, wetlands also process and condense carbon (in processes called carbon fixation and sequestration ), and other nutrients and water pollutants . Wetlands can act as

2910-644: The River Parrett and from there the Bristol Channel . The canal was authorised by Parliament in 1827 and opened in 1834. It was operated by the Glastonbury Navigation and Canal Company. Most of it was abandoned as a navigation in 1854, when a railway was built along the towpath. An earlier canal had been built in the Middle Ages to supply Glastonbury Abbey and the town with stone and produce. In

3007-460: The Somerset Levels , through which rivers and drainage ditches (locally called " rhynes ") run. There is evidence that the town was served by a medieval canal connecting it to the river system in the Saxon period, and the waterways were later used by the monks who were located at Glastonbury Abbey , both for draining the land and for transport of produce. In the 1750s, the town became a spa town , when

Ham Wall - Misplaced Pages Continue

3104-575: The South Drain , which had been newly constructed following floods in 1794, to connect with the River Brue near Cripps Bridge, and to re-use the old course of that River at Highbridge to create a basin. Hammett estimated that the main work required on the section from Highbridge to the South Drain would be the provision of a towpath. After this, the South Drain would need to be made wider and deeper, but this would aid its drainage function, and would reduce

3201-512: The United Kingdom Biodiversity Action Plan . Both reserves created extensive new reed beds, thereby adding significant additional breeding habitat. Initial funding for the recovery scheme was £60,000 from English Nature in 1994, augmented by two rounds of EU funding in 1996–2000 and 2002–2006. The reserve is about 4 kilometres (2.5 mi) west of Glastonbury and can be accessed by car from the minor road that runs between

3298-444: The atmosphere , their water usually has low mineral ionic composition. In contrast, wetlands fed by groundwater or tides have a higher concentration of dissolved nutrients and minerals. Fen peatlands receive water both from precipitation and ground water in varying amounts so their water chemistry ranges from acidic with low levels of dissolved minerals to alkaline with high accumulation of calcium and magnesium . Salinity has

3395-576: The beavers , coypu , swamp rabbit , Florida panther , jaguar , and moose . Wetlands attract many mammals due to abundant seeds, berries, and other vegetation as food for herbivores, as well as abundant populations of invertebrates, small reptiles and amphibians as prey for predators. Invertebrates of wetlands include aquatic insects such as dragonflies , aquatic bugs and beetles , midges, mosquitos , crustaceans such as crabs, crayfish, shrimps, microcrustaceans, mollusks like clams, mussels, snails and worms. Invertebrates comprise more than half of

3492-455: The levels were exploited to meet horticultural demand for peat . The owners of the workings, Fisons , reached an annual production of 250,000 tonnes (250,000 long tons) in the early-1990s. When the demand for peat fell towards the end of the century, Fisons transferred ownership of much of their land to English Nature (now Natural England ) in 1994, enabling the creation of 13 square kilometres (5.0 sq mi) of wetland nature reserves from

3589-476: The 260 hectares (640 acres) reserve contained 220 hectares (540 acres) of reed bed, including 75 hectares (190 acres) of deep water channels and ditches, 10 hectares (25 acres) of wet woodland and 30 hectares (74 acres) of grass, the latter being mainly on the bunds and some higher ground. Ham Wall, along with Lakenheath Fen in Suffolk , have been a key part of a bittern recovery programme initiated in 1994 as part of

3686-524: The Avalon hide from the canal footpath, and two further circular walks 1.7 kilometres (1.1 mi) and 1.3 kilometres (0.81 mi) in length are accessed from the grass track, a section of boardwalk also linking the two trails. There are two bird hides and six viewing platforms or screens on the reserve. Dogs on leads are allowed on the Ham Wall loop (which includes public rights of way ), but only assistance dogs can be taken elsewhere. The reserve attracts 70,000 visitors annually. The main management of

3783-420: The Avalon marshes, and non-native marsh frogs occur at Ham Wall and neighbouring Shapwick Heath. A recent intervention has been the construction of a new EDF Energy-funded eel pass to make it easier for European eels to enter the reserve from the nearby River Huntspill and South Drain. The young eels may remain on the reserve for up to 20 years before returning to the sea to breed. Invertebrates found in

3880-483: The Brue were straightened, and new feeder channels constructed. The Glastonbury Canal , which runs through the reserve, was opened in 1833. It was made obsolete from 1854 by the Somerset Central Railway line that once ran next to it on its way from Glastonbury to Highbridge . The railway line closed in 1966. The railway and the canal both carried peat and people. By the twentieth century, large areas of

3977-570: The Commissioners often failed to obtain the levies they required to finance their operations. One of the key promoters for a canal was Richard Prat, who was a lawyer in Glastonbury, had been the town clerk since 1813, and held several important offices in the town. He saw the canal as a way to halt the economic downturn in the town and its drainage problems, and called a meeting in August 1825, at which

Ham Wall - Misplaced Pages Continue

4074-586: The Cripps River to Gold Corner. The first part of the Cripps River was originally part of a loop on the River Brue, which was bypassed by a new cut made under the 1801 act. Gold Corner is at the point where the Huntspill River , the Cripps River and the South Drain meet. Following the course of the enlarged South Drain, a lock raised the level of the canal at Shapwick , while the Drain turned off to run parallel to

4171-513: The Exchequer Bills Commissioners. Construction began once the necessary land had been purchased, but it soon became apparent that the original surveys were inadequate. The canal engineer John Rennie was asked to advise the proprietors, and proposed three options, for boats of 120 to 140 long tons (120–140 t), for boats of 40 to 60 long tons (41–61 t), and for barges which were 5 feet (1.5 m) wide. The first

4268-511: The Levels in November 2012 and following Cyclone Dirk in winter 2013–2014 , the latter leaving 6,900 hectares (17,000 acres) of agricultural land under water for over a month. Water-based sports and recreation elsewhere in the Levels could possibly enable non-native species to invade the wetlands, and the number of visitors to the area can cause congestion on local roads, particularly those coming for

4365-619: The Okavango River inland delta, the Kafue River flood plain, the Lake Bangweulu flood plain (Africa), Mississippi River (US), Amazon River (South America), Yangtze River (China), Danube River (Central Europe) and Murray-Darling River (Australia). Groundwater replenishment can be achieved for example by marsh , swamp , and subterranean karst and cave hydrological systems. The surface water visibly seen in wetlands only represents

4462-511: The Southeastern US, mallines of Argentina, Mediterranean seasonal ponds of Europe and California, turloughs of Ireland, billabongs of Australia, among many others. Wetlands are found throughout the world in different climates. Temperatures vary greatly depending on the location of the wetland. Many of the world's wetlands are in the temperate zones , midway between the North or South Poles and

4559-517: The UK climate may lead to heavy summer rains which would adversely affect ground-nesting birds, invertebrates and other wildlife. Although this inland site is not directly threatened by saltwater incursion in the same way as east coast reserves like RSPB Minsmere and Titchwell Marsh , sea level rise will make the drainage of the Somerset Levels more difficult and current water-pumping facilities may become inadequate. Despite Environment Agency planning, recent significant river flooding events occurred on

4656-401: The UK in the 1997 breeding season. Much of its reed bed habitat was deteriorating, and key coastal sites in eastern England were at risk of saltwater flooding, so an opportunity to create a new inland site was attractive to the RSPB. The peat excavations already had bund walls that allowed the water levels on the reserve to be easily managed in sections, and the workings had removed peat down to

4753-403: The UK. The site is divided into several sections with independently controllable water levels, and machinery and cattle are used to maintain the quality of the reed beds. There are important breeding populations of wetland birds including the rare little bittern and great white egret , and the area hosts several other uncommon animals and plants. The RSPB works with other organisations as part of

4850-494: The US, the best known classifications are the Cowardin classification system and the hydrogeomorphic (HGM) classification system. The Cowardin system includes five main types of wetlands: marine (ocean-associated), estuarine (mixed ocean- and river-associated), riverine (within river channels), lacustrine (lake-associated) and palustrine (inland nontidal habitats). Peatlands are

4947-610: The United States' commercial fish and shellfish stocks depend solely on estuaries to survive. Amphibians such as frogs and salamanders need both terrestrial and aquatic habitats in which to reproduce and feed. Because amphibians often inhabit depressional wetlands like prairie potholes and Carolina bays, the connectivity among these isolated wetlands is an important control of regional populations. While tadpoles feed on algae, adult frogs forage on insects. Frogs are sometimes used as an indicator of ecosystem health because their thin skin permits absorption of nutrients and toxins from

SECTION 50

#1732851310167

5044-587: The area were in turn colonised by wet woodland. When the plants died in the oxygen-poor environment they decayed to form peat , and as the layers built up they eventually formed a large raised bog , which may have covered 680 square kilometres (260 sq mi) in Roman times. The formation of the bog was aided by the Somerset Levels' large water catchment area, high rainfall in the Mendips and Blackdown Hills and raised marine clay deposits which restricted drainage to

5141-484: The canal but to its north. The railway ran between the two waterways, crossing to the south side of the canal immediately after the single arched aqueduct and syphon over the South Drain. The remains of the three-arched aqueduct and syphon over the River Brue are still visible, near the old railway bridge, and from there the canal headed towards Glastonbury , passing the Ham Wall and Street Heath nature reserves and making

5238-581: The course of the River Brue by the straightening of major loops at Highbridge and East Huntspill , and to construct the North and South Drains , which collected water from the peat moorlands and channelled it into the lower River Brue. Under the terms of the act, two small canals, called Galton's Canal and Brown's Canal, were built near the North Drain to serve peat extraction workings. The drainage works were not wholly successful in preventing flooding, and

5335-399: The creation of a railway between Highbridge and Glastonbury in 1850, and the Somerset Central Railway was authorised by Parliament on 17 June 1852. The canal was transferred to the new company, and was used to speed the construction of the railway, earning £312 in the year ending September 1853. The line followed the route of the canal closely, with much of it built on the towpath. The canal

5432-518: The diggings. English Nature handed the management of 230 hectares (570 acres) at Ham Wall to the Royal Society for the Protection of Birds (RSPB), managing the rest of the land itself apart from an extension to the Somerset Wildlife Trust 's existing reserve at Westhay Moor . The reserve name derives from the Ham Wall rhyne which flows through the site. "Rhyne" is a local name for drainage channels between plots of land, pronounced reens in

5529-454: The drainage of the Levels more difficult, and current water pumping facilities may become inadequate. At the end of the last glacial period , about 10,000 years ago, the river valley that would eventually form the Somerset Levels gradually became salt marsh as the melting glaciers caused sea levels to rise. By around 6,500 to 6,000 years ago the marshes had become reed beds interspersed with rhynes (ditches) and open water, and parts of

5626-466: The early 19th century a new canal was proposed to improve commerce in Glastonbury and help with drainage of the surrounding area of the Somerset Levels . Several alternative routes were considered and costed before obtaining an Act of Parliament and issuing a prospectus to raise funds for the building of the canal. Construction commenced in the 1820s; however it was more expensive than envisaged and further funds had to be raised. It finally opened in 1833 but

5723-520: The east and rhine in the west of the Levels area. "Ham" is an old term for pasture or meadow , and the Ham Wall may have been a bank to hold water on the flooded fields. Ham Walls lies within the Somerset Levels National Nature Reserve and the Somerset Levels and Moors Ramsar and Special Area of Conservation site. The impetus for creating the Ham Wall reserve was the plight of the bittern , with only 11 males present in

5820-622: The equator. In these zones, summers are warm and winters are cold, but temperatures are not extreme. In subtropical zone wetlands, such as along the Gulf of Mexico , average temperatures might be 11 °C (52 °F). Wetlands in the tropics are subjected to much higher temperatures for a large portion of the year. Temperatures for wetlands on the Arabian Peninsula can exceed 50 °C (122 °F) and these habitats would therefore be subject to rapid evaporation. In northeastern Siberia , which has

5917-494: The following areas: According to the Ramsar Convention: The economic worth of the ecosystem services provided to society by intact, naturally functioning wetlands is frequently much greater than the perceived benefits of converting them to 'more valuable' intensive land use – particularly as the profits from unsustainable use often go to relatively few individuals or corporations, rather than being shared by society as

SECTION 60

#1732851310167

6014-464: The interface between truly terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet highly dependent on both." In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. Under the Ramsar international wetland conservation treaty , wetlands are defined as follows: An ecological definition of

6111-462: The known animal species in wetlands, and are considered the primary food web link between plants and higher animals (such as fish and birds). Depending on a wetland's geographic and topographic location, the functions it performs can support multiple ecosystem services , values, or benefits. United Nations Millennium Ecosystem Assessment and Ramsar Convention described wetlands as a whole to be of biosphere significance and societal importance in

6208-570: The landscape was owned by the church in the Middle Ages when substantial areas were drained and the rivers diverted, but the raised bogs remained largely intact. Only the Inclosure Acts of the 18th century, mostly between 1774 and 1797, led to significant draining of the peat bogs, although the River Brue still regularly flooded the reclaimed land in winter. Following the Somerset Drainage Act 1801 ( 41 Geo. 3. (U.K.) c. lxxii), parts of

6305-425: The levy on the local landowners, as the canal company would then be responsible for its maintenance. Two locks would be required on this upper section, with a total rise of just 7 feet (2.1 m). He did not believe that cutting a canal through peat would present serious engineering problems as a result of his previous experience with the manure canal, but he seriously underestimated the cost at £9,000. A prospectus

6402-832: The plants and animals controlled by the wetland hydrology are often additional components of the definitions. Wetlands can be tidal (inundated by tides) or non-tidal. The water in wetlands is either freshwater , brackish , saline , or alkaline . There are four main kinds of wetlands – marsh , swamp , bog , and fen (bogs and fens being types of peatlands or mires ). Some experts also recognize wet meadows and aquatic ecosystems as additional wetland types. Sub-types include mangrove forests , carrs , pocosins , floodplains , peatlands, vernal pools , sinks , and many others. The following three groups are used within Australia to classify wetland by type: Marine and coastal zone wetlands, inland wetlands and human-made wetlands. In

6499-450: The railway company attempted to buy the canal to prevent its use by rival railway companies. The sale was agreed in principle in June 1847, and was authorised by an act of Parliament passed on 30 June 1848. The shareholders received £7,372 in 1850, and the canal company was dissolved in 1851. There was friction between the new owners and the Commissioners of Sewers. The railway company proposed

6596-482: The reed bed. Rare visitors to the reserve in recent years include a collared pratincole and a whiskered tern in 2016, a singing male pied-billed grebe and a squacco heron in 2013, and a blue-winged teal in 2012. Otters breed on the reserve and two artificial holts have been placed in the reed beds for their use. Water voles can also be found in suitable habitat. Grass snakes , three species of newts , common toads and common frogs are found throughout

6693-407: The reed beds instead of the more usual trees, garganeys (typically two to three pairs), marsh harriers (three nesting females in 2017), hobbies , bearded tits and Cetti's , reed and sedge warblers . A winter evening roost of common starlings is one of the largest in the UK, and attracts visitors to see hundreds of thousands, sometimes millions, of these birds assemble before descending into

6790-716: The reserve and the neighbouring wetlands. The little bittern was present from 2009, bred in 2010, and has been present every year since, although breeding by this reclusive bird is difficult to prove in such a large expanse of reed bed. At least six birds, including four males, were present in spring 2017. The third coloniser is the cattle egret which had bred elsewhere in Somerset from 2008 to 2010. An influx in 2017 led to six pairs attempting to breed at Ham Wall, four successfully, and 30 birds were present in January 2018. Other typical wetland species include grey herons , some of which nest in

6887-431: The reserve involves cutting the reeds in rotation to rejuvenate the reed beds and prevent their drying out. Two machines are used, an amphibious Truxor tracked reed cutter to harvest wetter areas, and a faster Softrak for islands and where water levels have been lowered. Native breeds of cattle are also used to graze the reed bed margins. The cut reeds are turned into a peat-free compost and sold for domestic use. The RSPB

6984-481: The revenues generated were inadequate, and there were problems with water levels on the upper section. In 1840, the Prat brothers, whose legal firm had played a major part in the creation of the canal, disappeared, leaving a financial shortfall of over £40,000. It appears that they had put up most of the extra costs of construction, and may have borrowed some money from client's funds. They were declared bankrupt and Richard Prat

7081-584: The sea; the same impermeable material underlies the peat, which in places is up to 7.3 metres (24 ft) thick. The Somerset Levels have been occupied since the Neolithic period, around 6,000 years ago, when people exploited the reed swamps for resources and started to construct wooden trackways such as the Sweet and Post Tracks , and they were the site of salt extraction during the Romano-British period. Much of

7178-429: The soil and underlying rock into aquifers which are the source of much of the world's drinking water . Wetlands can also act as recharge areas when the surrounding water table is low and as a discharge zone when it is high. Mangroves , coral reefs , salt marsh can help with shoreline stabilization and storm protection. Tidal and inter-tidal wetland systems protect and stabilize coastal zones. Coral reefs provide

7275-537: The soil of wetlands. Anaerobic and aerobic respiration in the soil influences the nutrient cycling of carbon, hydrogen, oxygen, and nitrogen, and the solubility of phosphorus thus contributing to the chemical variations in its water. Wetlands with low pH and saline conductivity may reflect the presence of acid sulfates and wetlands with average salinity levels can be heavily influenced by calcium or magnesium. Biogeochemical processes in wetlands are determined by soils with low redox potential. The life forms of

7372-412: The soils and plants at higher elevations. Plants and animals may vary within a wetland seasonally or in response to flood regimes. There are four main groups of hydrophytes that are found in wetland systems throughout the world. Submerged wetland vegetation can grow in saline and fresh-water conditions. Some species have underwater flowers, while others have long stems to allow the flowers to reach

7469-515: The sources of water include tidal wetlands , where the water source is ocean tides ); estuaries , water source is mixed tidal and river waters; floodplains , water source is excess water from overflowed rivers or lakes; and bogs and vernal ponds , water source is rainfall or meltwater . The world's largest wetlands include the Amazon River basin , the West Siberian Plain ,

7566-406: The spatial and temporal dispersion, flow, and physio-chemical attributes of surface and ground waters. Sources of hydrological flows into wetlands are predominantly precipitation , surface water (saltwater or freshwater), and groundwater. Water flows out of wetlands by evapotranspiration , surface flows and tides , and subsurface water outflow. Hydrodynamics (the movement of water through and from

7663-709: The surface of the water. When trees and shrubs comprise much of the plant cover in saturated soils, those areas in most cases are called swamps . The upland boundary of swamps is determined partly by water levels. This can be affected by dams Some swamps can be dominated by a single species, such as silver maple swamps around the Great Lakes . Others, like those of the Amazon basin , have large numbers of different tree species. Other examples include cypress ( Taxodium ) and mangrove swamps. Many species of fish are highly dependent on wetland ecosystems. Seventy-five percent of

7760-490: The surface. Submerged species provide a food source for native fauna, habitat for invertebrates, and also possess filtration capabilities. Examples include seagrasses and eelgrass . Floating water plants or floating vegetation are usually small, like those in the Lemnoideae subfamily (duckweeds). Emergent vegetation like the cattails ( Typha spp.), sedges ( Carex spp.) and arrow arum ( Peltandra virginica ) rise above

7857-457: The surrounding environment resulting in increased extinction rates in unfavorable and polluted environmental conditions. Reptiles such as snakes , lizards , turtles , alligators and crocodiles are common in wetlands of some regions. In freshwater wetlands of the Southeastern US, alligators are common and a freshwater species of crocodile occurs in South Florida. The Florida Everglades

7954-457: The twentieth century. Consumer demand eventually declined, and in 1994 the landowners, Fisons , gave their old workings to what is now Natural England , who passed the management of the 260 hectares (640 acres) Ham Wall section to the RSPB. The Ham Wall reserve was constructed originally to provide reed bed habitat for the Eurasian bittern , which at the time was at a very low population level in

8051-440: The types of plants that live within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants . A more concise definition is a community composed of hydric soil and hydrophytes . Wetlands have also been described as ecotones , providing a transition between dry land and water bodies. Wetlands exist "...at

8148-407: The underlying marine clay, a depth of 2 metres (6.6 ft) in this area. Water levels were managed using sluices , pipes and wind-pumps to create reed beds with about 20% open water, and the ditches were deepened and widened to restrict reed encroachment and provide a habitat for fish, particularly common rudd , introduced to provide food for the bitterns. By the completion of major works in 2013,

8245-731: The villages of Meare on the B3151 and Ashcott on the A39 . Route 3 of the Sustrans National Cycle Network runs near the reserve. The nearest bus access is in Ashcott, 4 kilometres (2.5 mi) away, and the railway station in Bridgwater is 15 kilometres (9.3 mi) distant. Natural England's Shapwick Heath NNR is to the west on the opposite side of the Meare-Ashcott road. The reserve

8342-504: The water supply. Work resumed in July 1828. At the Glastonbury end, the canal was required to cross the South Drain and the River Brue. Rennie suggested inverted syphons , rather than locking down into the river and up again, and a cast iron aqueduct for the River Brue crossing was obtained for nearly £3,000 from a Glastonbury blacksmith called John Wright. At the Highbridge end, the plans for

8439-477: The waters of the Chalice Well spring were thought to have medicinal properties, but this did not last for long, while the predominant wool and cloth industries declined as the mills of the north of England took the trade. The area was hit by severe floods in 1794, as a result of which the Commissioners of Sewers obtained the Somerset Drainage Act 1801 ( 41 Geo. 3. (U.K.) c. lxxii), which allowed them to improve

8536-501: The wetland include several nationally uncommon aquatic molluscs including the shining ram's-horn snail and the depressed river mussel . Insects include the purple hairstreak , silver-washed fritillary and scarlet tiger moth , although the marsh fritillary , narrow-bordered bee hawk-moth and large marsh grasshopper have been lost to the area since the mid 1990s, suggesting some conservation issues. 19 species of dragonflies and damselflies have been recorded at Ham Wall, including

8633-765: The winter evening starling roost. Wetland Wetlands exist on every continent , except Antarctica . The water in wetlands is either freshwater , brackish or saltwater . The main types of wetland are defined based on the dominant plants and the source of the water. For example, marshes are wetlands dominated by emergent herbaceous vegetation such as reeds , cattails and sedges . Swamps are dominated by woody vegetation such as trees and shrubs (although reed swamps in Europe are dominated by reeds, not trees). Mangrove forest are wetlands with mangroves , halophytic woody plants that have evolved to tolerate salty water . Examples of wetlands classified by

8730-407: The work at Highbridge in 1830, and reported that the contractor "had run away", and work had stopped in 1831. The company had also failed to lodge £1,000 with the Commissioners which was required to cover any costs they might have as a result of the construction of the canal, and they sued for the money in 1831. Even Rennie threatened to sue, as much of his fee remained unpaid. The cost of construction

8827-564: Was about £30,000, but it appears that some debts were never paid. On 16 December 1831 the proprietors borrowed £5,000 from the Exchequer at a 5% rate of interest. The canal finally opened on 15 August 1833, amid celebrations at both ends of the canal and a cavalcade to and from Highbridge to Glastonbury. A second celebration for the "respectable trading classes" was held nine days later. The first cargo of wood from Canada arrived in July 1835. The canal appears to have been successful initially, but

8924-450: Was closed on 1 July 1854, and the lock and aqueducts on the upper section were dismantled. The railway opened on 17 August 1854. The lower sections of the canal were given to the Commissioners for Sewers, for use as a drainage ditch. The final section was retained to provide a wharf for the railway company, which was used until 1936, when it passed to the Commissioners of Sewers and was filled in. The Central Somerset Railway merged with

9021-402: Was issued which contained a detailed breakdown of the likely costs, revenue and profits of such a scheme, and the promoters prepared to obtain an act of Parliament . During this time, someone challenged the original survey and another local surveyor was asked to review it. John Beauchamp suggested that no locks would be required on the upper section, but that costs were likely to be £15,234. This

9118-461: Was later raised to £18,000, and the Glastonbury Navigation and Canal Act 1827 ( 7 & 8 Geo. 4 . c. xli), which authorised the construction of a canal that followed Hammett's plans, was obtained on 28 May 1827. The proprietors were empowered to raise £18,000 by the issue of 360 shares of £50 each, with powers to raise another £5,000 by mortgage, or to borrow any part of the £18,000 from

9215-418: Was only prosperous for a short period. The shortfall in income and engineering problems with water supply and waterlogged peat causing the clay puddling to fracture meant that it was sold to the Bristol and Exeter Railway . They used the canal to transport materials for the construction of the new Somerset Central Railway which opened in 1854. Glastonbury is situated in an area of low-lying land, known as

9312-403: Was removed from office as town clerk and a Commissioner of Sewers, but the firm's collapse had a serious effect on the prosperity of Glastonbury. On the upper section, the final pond prevented the proper drainage of the surrounding land, which being composed of peat, started to swell. This caused the canal itself to rise and the clay puddling to fracture, resulting in further loss of water, and

9409-404: Was ruled out on cost, the third because of the need to transship all goods at Highbridge, and the second was adopted because it allowed the coasters that worked the Bristol Channel to use the canal. This option required locks of 64 feet (20 m) by 18 feet (5.5 m), and was costed at £28,720. The route would be as authorised, but a single lock was required on the upper section to simplify

#166833