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87-407: The Fens or Fenlands in eastern England are a naturally marshy region supporting a rich ecology and numerous species. Most of the fens were drained centuries ago, resulting in a flat, dry, low-lying agricultural region supported by a system of drainage channels and man-made rivers ( dykes and drains) and automated pumping stations . There have been unintended consequences to this reclamation, as

174-425: A marsh is a wetland that is dominated by herbaceous plants rather than by woody plants . More in general, the word can be used for any low-lying and seasonally waterlogged terrain. In Europe and in agricultural literature low-lying meadows that require draining and embanked polderlands are also referred to as marshes or marshland. Marshes can often be found at the edges of lakes and streams, where they form

261-581: A different set of organisms. Saltwater marshes are found around the world in mid to high latitudes , wherever there are sections of protected coastline. They are located close enough to the shoreline that the motion of the tides affects them, and, sporadically, they are covered with water. They flourish where the rate of sediment buildup is greater than the rate at which the land level is sinking. Salt marshes are dominated by specially adapted rooted vegetation, primarily salt-tolerant grasses. Salt marshes are most commonly found in lagoons , estuaries , and on

348-522: A freshwater marsh, the ocean tides affect this form of marsh. However, without the stresses of salinity at work in its saltwater counterpart, the diversity of the plants and animals that live in and use freshwater tidal marshes is much higher than in salt marshes. The most severe threats to this form of marsh are the increasing size and pollution of the cities surrounding them. Ranging greatly in size and geographic location, freshwater marshes make up North America's most common form of wetland. They are also

435-576: A habitat for many species of plants, animals, and insects that have adapted to living in flooded conditions or other environments. The plants must be able to survive in wet mud with low oxygen levels. Many of these plants, therefore, have aerenchyma , channels within the stem that allow air to move from the leaves into the rooting zone. Marsh plants also tend to have rhizomes for underground storage and reproduction. Common examples include cattails , sedges , papyrus and sawgrass . Aquatic animals, from fish to salamanders , are generally able to live with

522-512: A habitat free from fish, which eat the eggs and young of amphibians. An example is the endangered gopher frog . Similar temporary ponds occur in other world ecosystems, where they may have local names. However, vernal pool can be applied to all such temporary pool ecosystems. Playa lakes are a form of shallow freshwater marsh in the southern high plains of the United States. Like vernal pools, they are only present at certain times of

609-457: A low amount of oxygen in the water. Some can obtain oxygen from the air instead, while others can live indefinitely in conditions of low oxygen. The pH in marshes tends to be neutral to alkaline , as opposed to bogs , where peat accumulates under more acid conditions. Marshes provide habitats for many kinds of invertebrates, fish , amphibians, waterfowl and aquatic mammals. Marshes have extremely high levels of biological production, some of

696-794: A major generator of silt, which accumulated to form the fertile soils of north India and Bangladesh, and the loess of central Asia and north China. Loess has long been thought to be absent or rare in deserts lacking nearby mountains (Sahara, Australia). However, laboratory experiments show eolian and fluvial processes can be quite efficient at producing silt, as can weathering in tropical climates. Silt seems to be produced in great quantities in dust storms, and silt deposits found in Israel, Tunisia, Nigeria, and Saudi Arabia cannot be attributed to glaciation. Furthermore, desert source areas in Asia may be more important for loess formation than previously thought. Part of

783-578: A number of Christians sought the isolation that could be found in the wilderness of the Fens. Later classified as saints, often with close royal links, they include Guthlac , Etheldreda , Pega , and Wendreda . Hermitages on the islands became centres of communities which later developed as monasteries with massive estates. In the Life of Saint Guthlac , a biography of the East Anglian hermit who lived in

870-440: A number of mechanisms. However, the main process is likely abrasion through transport, including fluvial comminution , aeolian attrition and glacial grinding. Because silt deposits (such as loess , a soil composed mostly of silt ) seem to be associated with glaciated or mountainous regions in Asia and North America, much emphasis has been placed on glacial grinding as a source of silt. High Asia has been identified as

957-482: A platy or bladed shape. This may be characteristic of how larger grains abrade, or reflect the shape of small quartz grains in foliated metamorphic rock , or arise from authigenic growth of quartz grains parallel to bedding in sedimentary rock . Theoretically, particles formed by random fracturing of an isotropic material, such as quartz, naturally tend to be blade-shaped. The size of silt grains produced by abrasion or shattering of larger grains may reflect defects in

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1044-687: A pollutant in water the phenomenon is known as siltation . Silt deposited by the Mississippi River throughout the 20th century has decreased due to a system of levees , contributing to the disappearance of protective wetlands and barrier islands in the delta region surrounding New Orleans . In southeast Bangladesh, in the Noakhali district , cross dams were built in the 1960s whereby silt gradually started forming new land called "chars". The district of Noakhali has gained more than 73 square kilometres (28 sq mi) of land in

1131-477: A region in the East of England , the embanked marshes are also known as Fens . Some areas have already lost 90% of their wetlands, including marshes. They have been drained to create agricultural land or filled to accommodate urban sprawl . Restoration is returning marshes to the landscape to replace those lost in the past. Restoration can be done on a large scale, such as by allowing rivers to flood naturally in

1218-493: A road across the Fens to link what later became East Anglia with what later became central England; it runs between Denver and Peterborough . They also linked Cambridge and Ely . Generally, their road system avoided the Fens, except for minor roads designed for exporting the products of the region, especially salt, beef and leather. Sheep were probably raised on the higher ground of the Townlands and fen islands, then as in

1305-566: A severe shock attended by a rumbling noise in Bourn after midday. This was felt in Lincolnshire, Leicestershire and Northamptonshire. Houses tottered, slates, tiles and some chimneys fell. As it was a Sunday, some people ran out of the churches "in great consternation". In 1792 another shock was also felt in Bourne and neighbouring towns. There is evidence of human settlement near the Fens from

1392-1004: A transition between the aquatic and terrestrial ecosystems . They are often dominated by grasses , rushes or reeds. If woody plants are present they tend to be low-growing shrubs, and the marsh is sometimes called a carr . This form of vegetation is what differentiates marshes from other types of wetland such as swamps , which are dominated by trees , and mires , which are wetlands that have accumulated deposits of acidic peat . Marshes provide habitats for many kinds of invertebrates , fish , amphibians , waterfowl and aquatic mammals . This biological productivity means that marshes contain 0.1% of global sequestered terrestrial carbon . Moreover, they have an outsized influence on climate resilience of coastal areas and waterways, absorbing high tides and other water changes due to extreme weather . Though some marshes are expected to migrate upland, most natural marshlands will be threatened by sea level rise and associated erosion . Marshes provide

1479-527: Is detritus (fragments of weathered and eroded rock) with properties intermediate between sand and clay . A more precise definition of silt used by geologists is that it is detrital particles with sizes between 1/256 and 1/16 mm (about 4 to 63 microns). This corresponds to particles between 8 and 4 phi units on the Krumbein phi scale . Other geologists define silt as detrital particles between 2 and 63 microns or 9 to 4 phi units. A third definition

1566-626: Is a particular challenge for civil engineering . The failure of the Teton Dam has been attributed to the use of loess from the Snake River floodplain in the core of the dam. Loess lacks the necessary plasticity for use in a dam core, but its properties were poorly understood, even by the U.S. Bureau of Reclamation , with its wealth of experience building earthen dams . Silt is susceptible to liquefaction during strong earthquakes due to its lack of plasticity. This has raised concerns about

1653-464: Is a project in place aiming at building an indoor stadium for ice sports. If successful, it will have the largest sheet of ice in the country with both a bandy pitch and a speed skating oval . Many historic cities, towns and villages have grown up in the fens, sited chiefly on the few areas of raised ground. These include: Ancient sites include: Some authors have featured the Fens repeatedly in their work. For example: Marsh In ecology ,

1740-647: Is carried through the vadose zone to be deposited in pore space. ASTM American Standard of Testing Materials: 200 sieve – 0.005 mm. USDA United States Department of Agriculture 0.05–0.002 mm. ISSS International Society of Soil Science 0.02–0.002 mm. Civil engineers in the United States define silt as material made of particles that pass a number 200 sieve (0.074 mm or less) but show little plasticity when wet and little cohesion when air-dried. The International Society of Soil Science (ISSS) defines silt as soil containing 80% or more of particles between 0.002 mm to 0.02 mm in size while

1827-601: Is common throughout the geologic record , but it seems to be particularly common in Quaternary formations. This may be because deposition of silt is favored by the glaciation and arctic conditions characteristic of the Quaternary. Silt is sometimes known as rock flour or glacier meal , especially when produced by glacial action. Silt suspended in water draining from glaciers is sometimes known as rock milk or moonmilk . A simple explanation for silt formation

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1914-463: Is little agreement as to the exact dates of the establishment and demise of the forest, but it seems likely that the deforestation was connected with the Magna Carta or one of its early 13th-century restatements, though it may have been as late as 1240. The forest would have affected the economies of the townships around it and it appears that the present Bourne Eau was constructed at the time of

2001-413: Is often found in mudrock as thin laminae , as clumps, or dispersed throughout the rock. Laminae suggest deposition in a weak current that winnows the silt of clay, while clumps suggest an origin as fecal pellets . Where silt is dispersed throughout the mudrock, it likely was deposited by rapid processes, such as flocculation . Sedimentary rock composed mainly of silt is known as siltstone . Silt

2088-528: Is soil rich in silt which makes up some of the most fertile agricultural land on Earth. However, silt is very vulnerable to erosion, and it has poor mechanical properties, making construction on silty soil problematic. The failure of the Teton Dam in 1976 has been attributed to the use of unsuitable loess in the dam core, and liquefication of silty soil is a significant earthquake hazard. Windblown and waterborne silt are significant forms of environmental pollution, often exacerbated by poor farming practices. Silt

2175-634: Is that it is a straightforward continuation to a smaller scale of the disintegration of rock into gravel and sand. However, the presence of a Tanner gap between sand and silt (a scarcity of particles with sizes between 30 and 120 microns) suggests that different physical processes produce sand and silt. The mechanisms of silt formation have been studied extensively in the laboratory and compared with field observations. These show that silt formation requires high-energy processes acting over long periods of time, but such processes are present in diverse geologic settings. Quartz silt grains are usually found to have

2262-443: Is that silt is fine-grained detrital material composed of quartz rather than clay minerals . Since most clay mineral particles are smaller than 2 microns, while most detrital particles between 2 and 63 microns in size are composed of broken quartz grains, there is good agreement between these definitions in practice. The upper size limit of 1/16 mm or 63 microns corresponds to the smallest particles that can be discerned with

2349-594: The Black Sluice . Also this area includes the market town of Spalding and the ancient village of Sempringham . The above were all redrained at one time or another after the Civil War (1642–1649). These areas cover the northern most part of the Fens from Boston right up as far north west as Washingborough near Lincoln along the course of the River Witham and to the north east it extends up as far as

2436-582: The Mesolithic on. The evidence suggests that Mesolithic settlement in Cambridgeshire was particularly along the fen edges and on the low islands within the fens, to take advantage of the hunting and fishing opportunities of the wetlands. Internationally important sites include Flag Fen and Must Farm quarry Bronze Age settlement and Stonea Camp . The Romans constructed the Fen Causeway ,

2523-591: The Nile and Niger River deltas. Bangladesh is largely underlain by silt deposits of the Ganges delta. Silt is also abundant in northern China, central Asia, and North America. However, silt is relatively uncommon in the tropical regions of the world. Silt is commonly found in suspension in river water, and it makes up over 0.2% of river sand. It is abundant in the matrix between the larger sand grains of graywackes . Modern mud has an average silt content of 45%. Silt

2610-541: The Townlands . It is clear that there was some prosperity there, particularly where rivers permitted access to the upland beyond the fen. Such places were Wisbech , Spalding , Swineshead and Boston. All the Townlands parishes were laid out as elongated strips, to provide access to the products of fen, marsh and sea. On the fen edge, parishes are similarly elongated to provide access to both upland and fen. The townships are therefore often nearer to each other than they are to

2697-588: The deforestation , as the town seems to have joined in the general prosperity by about 1280. Though the forest was about half in Holland (Lincolnshire) and half in Kesteven , it is known as Kesteven Forest. Though some signs of Roman hydraulics survive, and there were also some medieval drainage works, land drainage was begun in earnest during the 1630s by the various investors who had contracts with King Charles I to do so. The leader of one of these syndicates

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2784-658: The fen violet will be seeded. The Fens Waterways Link is a scheme to restore navigation to some of the drainage works. It is planned to bring the South Forty-Foot Drain and parts of the Car Dyke into use as part of a route between Boston and Cambridge. The Fens is the origin of English bandy and Fen skating . It is the base of Great Britain Bandy Association and in Littleport there

2871-598: The 17th century described the Fenland as entirely above sea level (in contrast to the Netherlands), the area now includes the lowest land in the United Kingdom. Holme Fen in Cambridgeshire, is around 2.75 metres (9 ft 0 in) below sea level. Within the Fens are a few hills, which have historically been called "islands", as they remained dry when the low-lying fens around them were flooded. The largest of

2958-620: The 6th century but was revived in the mid-10th-century monastic revival. In the 11th century, the whole area was incorporated into a united Anglo-Saxon England . The Fens remained a place of refuge and intrigue. It was here that Alfred Aetheling was brought to be murdered and here where Hereward the Wake based his insurgency against Norman England . Fenland monastic houses include the so-called Fen Five ( Ely Cathedral Priory , Thorney Abbey , Croyland Abbey , Ramsey Abbey and Peterborough Abbey ) as well as Spalding Priory . As major landowners,

3045-597: The County Record Office in Cambridge. The major part of the draining of the Fens was effected in the late 18th and early 19th century, again involving fierce local rioting and sabotage of the works. The final success came in the 1820s when windpumps were replaced with powerful coal-powered steam engines , such as Stretham Old Engine , which were themselves replaced with diesel-powered pumps, such as those at Prickwillow Museum and, following World War II ,

3132-861: The Fen Tigers tried to sabotage the drainage efforts. Two cuts were made in the Cambridgeshire Fens to join the River Great Ouse to the sea at King's Lynn – the Old Bedford River and the New Bedford River , the latter being known also as the Hundred Foot Drain . Both cuts were named after the Fourth Earl of Bedford who, along with some gentlemen adventurers ( venture capitalists ), funded

3219-463: The Fens during the early 8th century, Saint Guthlac was described as attacked on several occasions by people he believed were Britons , who were then living in the Fens. However, Bertram Colgrave, in the introduction to one edition, doubts this account, because of the lack of evidence of British survival in the region. British place names in the area are "very few". Monastic life was disrupted by Danish (Anglo-Saxon) raids and centuries of settlement from

3306-434: The Fens include Boston , Downham Market , King’s Lynn , Mildenhall , March , Spalding , and Wisbech . The Fens are very low-lying compared with the chalk and limestone uplands that surround them – in most places no more than 10 metres (33 ft) above sea level. As a result of drainage and the subsequent shrinkage of the peat fens, many parts of the Fens now lie below mean sea level . Although one writer in

3393-469: The Fens is involved in environmental stewardship schemes, under which 270 miles (430 km) of hedgerow and 1,780 miles (2,860 km) of ditches are managed, providing large wildlife corridors and habitat for endangered animals such as the water vole . In 2003, the Great Fen Project was initiated to return parts of the Fens to their original pre-agricultural state. The periodic flooding by

3480-451: The Fens were once permanently flooded, creating lakes or meres , while others were flooded only during periods of high water. In the pre-modern period, arable farming was limited to the higher areas of the surrounding uplands, the fen islands, and the so-called "Townlands", an arch of silt ground around the Wash , where the towns had their arable fields. Though these lands were lower than

3567-782: The Lindsey Level inhabited by farmers by 1638, but the onset of the Civil War permitted the destruction of the works until the act of Parliament that led to the formation of the Black Sluice Commissioners, the Black Sluice Drainage Act 1765 ( 5 Geo. 3 . c. 86 ). Many original records of the Bedford Level Corporation, including maps of the Levels, are now held by Cambridgeshire Archives and Local Studies Service at

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3654-553: The North Sea, which renewed the character of the Fenlands, was characterised conventionally by the 1911 Encyclopædia Britannica as "ravaged by serious inundations of the sea". The modern approach is to allow a little farmland to be flooded again and turned into nature reserves . By introducing fresh water, the organisers of the project hope to encourage species such as the snipe , lapwing and bittern . Endangered species such as

3741-538: The Roman period, water levels fell once again. Settlements developed on the new silt soils deposited near the coast. Though water levels rose once again in the early medieval period, by this time artificial banks protected the coastal settlements and the interior from further deposits of marine silts. Peats continued to develop in the freshwater wetlands of the interior fens. The wetlands of the fens have historically included: Major areas for settlement were: In general, of

3828-430: The U.S. Department of Agriculture puts the cutoff at 0.05mm. The term silt is also used informally for material containing much sand and clay as well as silt-sized particles, or for mud suspended in water. Silt is a very common material, and it has been estimated that there are a billion trillion trillion (10 ) silt grains worldwide. Silt is abundant in eolian and alluvial deposits, including river deltas , such as

3915-613: The Wash , and are an area of nearly 1,500 sq mi (3,900 km) in the south east of Lincolnshire , most of Cambridgeshire (which also includes parts of the old historic county of Huntingdonshire ), and western most parts of Norfolk and Suffolk . Most of the Fens lie within a few metres of sea level . As with similar areas in the Netherlands , much of the Fenland originally consisted of fresh- or salt-water wetlands. These have been artificially drained and continue to be protected from floods by drainage banks and pumps. With

4002-545: The combined capacity to pump 16,500 Olympic-size swimming pools in a 24-hour period or to empty Rutland Water in 3 days. As of 2008, there are estimated to be 4,000 farms in the Fens involved in agriculture and horticulture, including arable, livestock, poultry, dairy, orchards, vegetables and ornamental plants and flowers. They employ about 27,000 people in full-time and seasonal jobs. In turn, they support around 250 businesses involved in food and drink manufacturing and distribution, employing around 17,500 people. Over 70% of

4089-561: The construction and were rewarded with large grants of the resulting farmland. The work was directed by engineers from the Low Countries . Following this initial drainage, the Fens were still extremely susceptible to flooding, so windpumps were used to pump water away from affected areas. The Company of Adventurers were more formally incorporated in 1663 as the Bedford Level Corporation . However, their success

4176-513: The crystal structure of the quartz, known as Moss defects. Such defects are produced by tectonic deformation of the parent rock, and also arise from the high-low transition of quartz: Quartz experiences a sharp decrease in volume when it cools below a temperature of about 573 °C (1,063 °F), which creates strain and crystal defects in the quartz grains in a cooling body of granite. Mechanisms for silt production include: Laboratory experiments have produced contradictory results regarding

4263-548: The distant farms in their own parishes. After the end of Roman Britain, there is a break in written records. It is thought that some Iceni may have moved west into the Fens to avoid the Angles , who were migrating across the North Sea from Angeln (modern Schleswig ) and settling what would become East Anglia . Surrounded by water and marshes, the Fens provided a safe area that was easily defended and not particularly desirable to invading Anglo-Saxons . It has been proposed that

4350-471: The early 19th century. There may have been some drainage efforts during the Roman period, including the Car Dyke along the western edge of the Fenland between Peterborough and Lincolnshire, but most canals were constructed for transportation. How far seaward the Roman settlement extended is unclear owing to the deposits laid down above them during later floods. The early post-Roman settlements were made on

4437-558: The earthquake damage potential in the silty soil of the central United States in the event of a major earthquake in the New Madrid Seismic Zone . Silt is easily transported in water and is fine enough to be carried long distances by air in the form of dust . While the coarsest silt particles (60 micron) settle out of a meter of still water in just five minutes, the finest silt grains (2 microns) can take several days to settle out of still water. When silt appears as

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4524-637: The edge of the Lincolnshire Wolds to the seaside town of Skegness . These were drained in the 18th and 19th centuries. At the end of the most recent glacial period , known in Britain as the Devensian , ten thousand years ago, Britain and continental Europe were joined by the ridge between Friesland and Norfolk . The topography of the bed of the North Sea indicates that the rivers of

4611-470: The effectiveness of various silt production mechanisms. This may be due to the use of vein or pegmatite quartz in some of the experiments. Both materials form under conditions promoting ideal crystal growth, and may lack the Moss defects of quartz grains in granites. Thus production of silt from vein quartz is very difficult by any mechanism, whereas production of silt from granite quartz proceeds readily by any of

4698-415: The fen-islands was the 23-square-mile (60 km) Kimmeridge Clay island, on which the cathedral city of Ely was built: its highest point is 39 metres (128 ft) above mean sea level. Without artificial drainage and flood protection, the Fens would be liable to periodic flooding, particularly in winter due to the heavy load of water flowing down from the uplands and overflowing the rivers. Some areas of

4785-443: The fine silt produced in dust storms and the coarse silt fraction possibly representing the fine particle tail of sand production. Loess underlies some of the most productive agricultural land worldwide. However, it is very susceptible to erosion. The quartz particles in silt do not themselves provide nutrients, but they promote excellent soil structure , and silt-sized particles of other minerals, present in smaller amounts, provide

4872-641: The fringes of large rivers. The different types are produced by factors such as water level, nutrients, ice scour , and waves. Large tracts of tidal marsh have been embanked and artificially drained. They are usually known by the Dutch name of polders . In Northern Germany and Scandinavia they are called Marschland , Marsch or marsk ; in France marais maritime . In the Netherlands and Belgium, they are designated as marine clay districts. In East Anglia ,

4959-447: The highest in the world, and therefore are important in supporting fisheries. Marshes also improve water quality by acting as a sink to filter pollutants and sediment from the water that flows through them. Marshes partake in water purification by providing nutrient and pollution consumption. Marshes (and other wetlands) are able to absorb water during periods of heavy rainfall and slowly release it into waterways and therefore reduce

5046-536: The highest parts of the drained fen are now only a few metres above mean sea level, only sizeable embankments of the rivers, and general flood defences, stop the land from being inundated. Nonetheless, these works are now much more effective than they were. The Fens today are protected by 60 miles (97 km) of embankments defending against the sea and 96 miles (154 km) of river embankments. Eleven internal drainage board (IDB) groups maintain 286 pumping stations and 3,800 miles (6,100 km) of watercourses, with

5133-401: The laboratory using the pipette method, which is based on settling rate via Stokes' law and gives the particle size distribution accordingly. The mineral composition of silt particles can be determined with a petrographic microscope for grain sizes as low as 10 microns. Vadose silt is silt-sized calcite crystals found in pore spaces and vugs in limestone . This is emplaced as sediment

5220-611: The land between the rivers. The internal drainage was organised by levels or districts, each of which includes the fen parts of one or several parishes . The details of the organisation vary with the history of their development, but the areas generally include: Bourne Fen and Deeping Fen lie in the southern most parts of Lincolnshire, between the Rivers Welland and the Bourne Eau with the River Glen running between

5307-520: The land level has continued to sink and the dykes have been built higher to protect it from flooding. Fen is the local term for an individual area of marshland or former marshland. It also designates the type of marsh typical of the area, which has neutral or alkaline water and relatively large quantities of dissolved minerals , but few other plant nutrients . The Fens are a National Character Area , based on their landscape, biodiversity, geodiversity and economic activity. The Fens lie inland of

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5394-478: The less stable peat. Since the 19th century, all of the acid peat in the Fens has disappeared. Drying and wastage of peats has greatly reduced the depth of the alkaline peat soils and reduced the overall elevation of large areas of the peat fens. It is also recorded that peat was dug out of the East and West Lincolnshire fens in the 14th century and used to fire the salterns of Wrangle and Friskney. In later centuries it

5481-469: The magnitude of flooding. Marshes also provide the services of tourism, recreation, education, and research. Marshes differ depending mainly on their location and salinity . These factors greatly influence the range and scope of animal and plant life that can survive and reproduce in these environments. The three main types of marsh are salt marshes , freshwater tidal marshes , and freshwater marshes . These three can be found worldwide, and each contains

5568-529: The monasteries played a significant part in the early efforts at drainage of the Fens. During most of the 12th century and the early 13th century, the south Lincolnshire fens were afforested . The area was enclosed by a line from Spalding, along the River Welland to Market Deeping , then along the Car Dyke to Dowsby and across the fens to the Welland. It was deforested in the early 13th century. There

5655-486: The most diverse of the three types of marsh. Some examples of freshwater marsh types in North America are: Wet meadows occur in shallow lake basins, low-lying depressions, and the land between shallow marshes and upland areas. They also happen on the edges of large lakes and rivers. Wet meadows often have very high plant diversity and high densities of buried seeds. They are regularly flooded but are often dry in

5742-539: The names of West Walton , Walsoken and Walpole suggest the native British population, with the Wal- coming from the Old English walh , meaning "foreigner". However, the villages are in close proximity to the old Roman sea wall, so the wal- element is more probably from wal or weal , meaning "wall". Walton is generally believed to mean "wall-town", Walsoken to mean "the district under particular jurisdiction by

5829-787: The necessary nutrients. Silt, deposited by annual floods along the Nile River , created the rich, fertile soil that sustained the Ancient Egyptian civilization. The closure of the Aswan High Dam has cut off this source of silt, and the fertility of the Nile delta is deteriorating. Loess tends to lose strength when wetted, and this can lead to failure of building foundations. The silty material has an open structure that collapses when wet. Quick clay (a combination of very fine silt and clay-sized particles from glacial grinding)

5916-537: The next few thousand years both saltwater and freshwater wetlands developed as a result. Silt and clay soils were deposited by marine floods in the saltwater areas and along the beds of tidal rivers, while organic soils, or peats, developed in the freshwater marshes. Fenland water levels peaked in the Iron Age; earlier Bronze and Neolithic settlements were covered by peat deposits, and have only recently been found after periods of extensive droughts revealed them. During

6003-513: The past 50 years. With Dutch funding, the Bangladeshi government began to help develop older chars in the late 1970s, and the effort has since become a multi-agency operation building roads, culverts , embankments, cyclone shelters, toilets and ponds, as well as distributing land to settlers. By fall 2010, the program will have allotted some 100 square kilometres (20,000 acres) to 21,000 families. A main source of silt in urban rivers

6090-419: The peat fens before the peat shrinkage began, the more stable silt soils were reclaimed by medieval farmers and embanked against any floods coming down from the peat areas or from the sea. The rest of the Fenland was dedicated to pastoral farming , fishing, fowling , and the harvesting of reeds or sedge for thatch. In this way, the medieval and early modern Fens stood in contrast to the rest of England, which

6177-440: The problem may be the conflation of high rates of production with environments conducive to deposition and preservation, which favors glacial climates more than deserts. Loess associated with glaciation and cold weathering may be distinguishable from loess associated with hot regions by the size distribution. Glacial loess has a typical particle size of about 25 microns. Desert loess contains either larger or smaller particles, with

6264-463: The sheltered side of a shingle or sandspit . The currents there carry the fine particles around to the quiet side of the spit, and sediment begins to build up. These locations allow the marshes to absorb the excess nutrients from the water running through them before they reach the oceans and estuaries. These marshes are slowly declining. Coastal development and urban sprawl have caused significant loss of these essential habitats. Although considered

6351-426: The small electric stations that are still used today. The dead vegetation of the peat remained undecayed because it was deprived of air (the peat being anaerobic). When it was drained, the oxygen of the air reached it, since then the peat has been slowly oxidizing. This, together with the shrinkage on its initial drying and the removal of soil by the wind, has meant that much of the Fens lies below high tide level . As

6438-521: The southern part of eastern England flowed into the Rhine , thence through the English Channel . From the Fens northward along the modern coast, the drainage flowed into the northern North Sea basin . As the ice melted, the rising sea level drowned the lower lands, leading ultimately to the present coastline. These rising sea levels flooded the previously inland woodland of the Fenland basin; over

6525-497: The spring, or on a small scale by returning wetlands to urban landscapes. Silt Silt is a common material, making up 45% of average modern mud . It is found in many river deltas and as wind-deposited accumulations, particularly in central Asia, north China, and North America. It is produced in both very hot climates (through such processes as collisions of quartz grains in dust storms ) and very cold climates (through such processes as glacial grinding of quartz grains.) Loess

6612-492: The summer. Vernal pools are a type of marsh found only seasonally in shallow depressions in the land. They can be covered in shallow water, but in the summer and fall, they can be completely dry. In western North America, vernal pools tend to form in open grasslands, whereas in the east, they often occur in forested landscapes. Further south, vernal pools form in pine savannas and flatwoods . Many amphibian species depend upon vernal pools for spring breeding; these ponds provide

6699-566: The support of this drainage system, the Fenland has become a major arable agricultural region for grains and vegetables. The Fens are particularly fertile, containing around half of the grade 1 agricultural land in England. The Fens have been referred to as the "Holy Land of the English" because of the former monasteries, now churches and cathedrals , of Crowland , Ely , Peterborough , Ramsey and Thorney . Other significant settlements in

6786-474: The three principal soil types found in the Fenland today, the mineral-based silt resulted from the energetic marine environment of the creeks, the clay was deposited in tidal mud-flats and salt-marsh, while the peat grew in the fen and bog. The peat produces black soils, which are directly comparable to the American muck soils . A roddon , the dried raised bed of a watercourse, is more suitable for building than

6873-592: The two Fens and the area covers both the town of Bourne as well as The Deepings including the villages of Langtoft and Baston . The Lindsey Level, also known as the Black Sluice District, was first drained in 1639 and extends from the Glen and Bourne Eau to Swineshead and then across to Kirton . Its waters is carried mostly though the South Forty-Foot Drain through to the Haven at Boston though

6960-699: The unaided eye. It also corresponds to a Tanner gap in the distribution of particle sizes in sediments : Particles between 120 and 30 microns in size are scarce in most sediments, suggesting that the distinction between sand and silt has physical significance. As noted above, the lower limit of 2 to 4 microns corresponds to the transition from particles that are predominantly broken quartz grains to particles that are predominantly clay mineral particles. Assallay and coinvestigators further divide silt into three size ranges: C (2–5 microns), which represents post-glacial clays and desert dust; D1 (20–30 microns) representing "traditional" loess ; and D2 (60 microns) representing

7047-413: The very coarse North African loess. Silt can be distinguished from clay in the field by its lack of plasticity or cohesiveness and by its grain size. Silt grains are large enough to give silt a gritty feel, particularly if a sample is placed between the teeth. Clay-size particles feel smooth between the teeth. The proportions of coarse and fine silt in a sediment sample are determined more precisely in

7134-626: The wall", and Walpole to mean simply "wall-pole" (Old English wal and pal ). When written records resume in Anglo-Saxon England, the names of a number of peoples of the Fens are recorded in the Tribal Hidage and Christian histories. They include North Gyrwe (Peterborough and Crowland), South Gyrwe (Ely), the Spalda (Spalding), and Bilmingas (part of south Lincolnshire). In the early Christian period of Anglo-Saxon England,

7221-664: The year and generally have a circular shape. As the playa dries during the summer, conspicuous plant zonation develops along the shoreline. Prairie potholes are found in northern North America, such as the Prairie Pothole Region . Glaciers once covered these landscapes, and as a result, shallow depressions were formed in great numbers. These depressions fill with water in the spring. They provide important breeding habitats for many species of waterfowl. Some pools only occur seasonally, while others retain enough water to be present all year. Many kinds of marsh occur along

7308-453: Was primarily an arable agricultural region. Since the advent of modern drainage in the 19th and 20th centuries, the Fens have been radically transformed. Today arable farming has almost entirely replaced pastoral. The economy of the Fens is heavily invested in the production of crops such as grains, vegetables, and some cash crops such as rapeseed and canola . Drainage in the Fenland consists of both river drainage and internal drainage of

7395-445: Was short-lived. Once drained of water, the peat shrank, and the fields lowered further. The more effectively they were drained, the worse the problem became, and soon the fields were lower than the surrounding rivers. By the end of the 17th century, the land was under water once again. Though the three Bedford Levels together formed the biggest scheme, they were not the only ones. Lord Lindsey and his partner Sir William Killigrew had

7482-534: Was the Earl of Bedford, who employed Cornelius Vermuyden as engineer. Contrary to popular belief, Vermuyden was not involved with the draining of the Great Fen in Cambridgeshire and Norfolk in the 1630s, but only became involved with the second phase of construction in the 1650s. The scheme was imposed despite huge opposition from locals who were losing their livelihoods based on fishing and wildfowling. Fenmen known as

7569-563: Was used locally for winter fuel and its digging controlled by the Duchy of Lancaster . Written records of earthquakes in the Fen area appear as early as 1048. According to Historia Ingulfi, p. 64, (1684) this took place in Lincolnshire. In 1117 one affected Holland, Lincs, "endangering and injuring Crowland Abbey ". In 1185 Lincoln was damaged. In 1448 a shock was recorded in south Lincolnshire ( Ingulfi, p. 526). In 1750 John Moore records

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