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109-543: Blagdon Lake lies in a valley at the northern edge of the Mendip Hills , close to the village of Blagdon and approximately 10 miles (16 km) south of Bristol , England. The lake was created by Bristol Water (Bristol Waterworks Company as it was known then), when it dammed the River Yeo , starting construction in 1898, to designs by Charles Hawksley , and completing this in 1905. The Wrington Vale Light Railway

218-428: A 3.25 ft (0.99 m) stroke, were supplied by steam from horizontal Lancashire-type twin flue boilers with Green's economisers at 100 pounds per square inch (6.9 bar). The low-pressure cylinder was 34 inches (86.4 cm) in diameter and has a 7 ft (2.13 m) stroke. Three engines with a fourth on standby could pump water at a rate of 7.5 million imperial gallons (34,000 m) per day, whilst

327-440: A brief spring overturn in addition to longer fall overturn. The relative thermal resistance is the energy needed to mix these strata of different temperatures. An annual heat budget, also shown as θ a , is the total amount of heat needed to raise the water from its minimum winter temperature to its maximum summer temperature. This can be calculated by integrating the area of the lake at each depth interval (A z ) multiplied by

436-418: A campaign has been started to halt the creation of any new quarries and to restrict the activities and expansion of the existing ones. The Mendips are home to a wide range of outdoor sports and leisure activities, including hunting , caving, climbing, and abseiling . The rich variety of fauna and flora also makes it attractive for hillwalking and those interested in natural history. Mendip Activity Centre

545-435: A certain composition of both organic and inorganic elements and compounds. Biological reactions also affect the chemical properties of water. In addition to natural processes, human activities strongly influence the chemical composition of aquatic systems and their water quality. Allochthonous sources of carbon or nutrients come from outside the aquatic system (such as plant and soil material). Carbon sources from within

654-550: A complex suite of mountain and hill ranges across what is now southern Ireland, south-western England, Brittany , and elsewhere in western Europe. As a result of the Variscan mountain-building, the Mendip area now comprises at least four anticlinal fold structures, with an east–west trend, each with a core of older Devonian sandstone and Silurian volcanic rocks . The latter are quarried for use in road construction and as

763-415: A concrete aggregate. The Mendips were considerably higher and steeper 200 to 300 million years ago, and subsequent erosion has resulted in varying geological features including gorges, dry valleys, screes , swallets and others typical of karst landscapes. Beneath the southern escarpment and plateau are caves . There are also areas of limestone pavement and other karst features. Dissolution of

872-560: A lake, river, stream, wetland, estuary etc.) and the structure of the earth surrounding the body of water. Lakes , for instance, are classified by their formation, and zones of lakes are defined by water depth. River and stream system morphometry is driven by underlying geology of the area as well as the general velocity of the water. Stream morphometry is also influenced by topography (especially slope) as well as precipitation patterns and other factors such as vegetation and land development. Connectivity between streams and lakes relates to

981-466: A landscape perspective, by explicitly examining connections between an aquatic ecosystem and its drainage basin . Recently, the need to understand global inland waters as part of the Earth system created a sub-discipline called global limnology. This approach considers processes in inland waters on a global scale, like the role of inland aquatic ecosystems in global biogeochemical cycles . Limnology

1090-590: A large proportion of the annual precipitation falls from showers and thunderstorms at this time of year. Average rainfall is around 800–900 mm (31–35 in). About 8–15 days of snowfall is typical. November to March have the highest mean wind speeds, with June to August having the lightest; the prevailing wind direction is from the south-west. A combination of the rainfall and geology leads to an estimated average daily runoff from springs and boreholes of some 330,000 m (72 million imperial gallons). Bristol Waterworks Company (now Bristol Water ) recognised

1199-593: A mix of barbed wire and sheep fencing. These dry-stone walls are of botanical importance as they support important populations of the nationally scarce wall whitlowgrass ( Draba muralis ). Amongst the plants which occur in the area are the Cheddar pink ( Dianthus gratianopolitanus ), purple gromwell ( Lithospermum purpurocaeruleum ), white rock-rose ( Helianthemum apenninum ), Somerset hair-grass ( Koeleria vallesiana ), and starved wood-sedge ( Carex depauperata ). Twenty Palaeolithic sites have been identified in

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1308-449: A range of flora and fauna and is a Site of Special Scientific Interest . The original suction tanks, which formed the water supply for the steam boilers powering the pumping engines, are now used for trout rearing. The lake, which was originally called the Yeo reservoir , covers 440 acres (180 ha). The River Yeo rises in the centre of Compton Martin village, from there it flows past

1417-423: A significant impact on the behavior of many aquatic organisms. For example, zooplankton's vertical migration is influenced by solar energy levels. Similar to light zonation, thermal stratification or thermal zonation is a way of grouping parts of the water body within an aquatic system based on the temperature of different lake layers. The less turbid the water, the more light is able to penetrate, and thus heat

1526-448: A trout fishery in 1904. The lake is well known for trout fishing from its banks and the fleet of 18 rowing boats for hire. The suction tanks which originally supplied water to the steam boilers for the pumping engines are now used as rearing pools for the fish before they are transferred into the lake. On average 50,000 trout are reared at Blagdon each year by Bristol Water to stock this and surrounding lakes such as Chew Valley Lake and

1635-495: A wide distribution across the Mendips and are often found in flooded disused quarries. Several rare butterflies are indigenous to the area, including the nationally scarce pearl-bordered fritillary ( Boloria euphrosyne ), Duke of Burgundy ( Hamearis lucina ), and white-letter hairstreak ( Satyrium w-album ). The large blue butterfly ( Maculinea arion ) became extinct in the hills in the late 1970s. The white-clawed crayfish

1744-841: Is a 58-kilometre (36 mi) long-distance footpath from the Mendips to the Cotswolds, and the Mendip Way covers 80 km (50 mi) from Weston-super-Mare to Frome. The western section runs from the Bristol Channel at Uphill Cliff , affording views over the Somerset Levels, crosses the central Mendip plateau leading down to Cheddar Gorge, and then continues to Wells and Frome. The much longer Monarch's Way runs for 990 km (620 mi), from Worcester to Shoreham-by-Sea in West Sussex. It closely follows

1853-483: Is about 10 °C (50 °F) with seasonal and diurnal variations, but the modifying effect of the sea restricts the range to less than that in most other parts of the United Kingdom. January is the coldest month, with mean minimum temperatures between 1 °C (34 °F) and 2 °C (36 °F). July and August are the warmest, with mean daily maxima around 21 °C (70 °F). In general, December

1962-586: Is accomplished by the effect of gravity on the runoff. Water from the Mendips is also collected in Cheddar Reservoir , which was constructed in the 1930s and takes water from the springs in Cheddar Gorge. The area hosts three semi-natural habitats of national importance: ash – maple woodland ( Fraxinus spp. and Acer spp.) often with abundant small-leaved lime ( Tilia cordata ), calcareous grassland and mesotrophic grassland . Much of

2071-548: Is also nationally rare and is a declining species with small populations in a tributary of the Mells River and the River Chew . The dry stone walls that divide the pasture into fields are a well-known feature of the Mendips. Constructed from local limestone in an "A frame" design, the walls are strong yet contain no mortar; many have been neglected and allowed to disintegrate, or have been replaced or contained by

2180-665: Is based at the Charterhouse Centre in the heart of the AONB. The AONB Unit consists of four staff: a manager, project officer, support officer and part-time planning officer and fixed term project officers. They are supported by volunteer rangers. In 2005 a proposal was submitted to the Countryside Agency to extend the Area of Outstanding Natural Beauty to Steep Holm and Brean Down in the west and towards Frome in

2289-402: Is calculated as the aquatic metabolism rate . Vertical changes in the concentrations of dissolved oxygen are affected by both wind mixing of surface waters and the balance between photosynthesis and respiration of organic matter . These vertical changes, known as profiles, are based on similar principles as thermal stratification and light penetration. As light availability decreases deeper in

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2398-399: Is closely related to aquatic ecology and hydrobiology , which study aquatic organisms and their interactions with the abiotic (non-living) environment. While limnology has substantial overlap with freshwater-focused disciplines (e.g., freshwater biology ), it also includes the study of inland salt lakes. The term limnology was coined by François-Alphonse Forel (1841–1912) who established

2507-444: Is conveyed deeper in the water. Heating declines exponentially with depth in the water column, so the water will be warmest near the surface but progressively cooler as moving downwards. There are three main sections that define thermal stratification in a lake. The epilimnion is closest to the water surface and absorbs long- and shortwave radiation to warm the water surface. During cooler months, wind shear can contribute to cooling of

2616-492: Is evidence of mining in the Mendips dating back to the late Bronze Age, which increased after the Roman invasion, particularly for lead and silver around Charterhouse . The difficult conditions in the area were noted by William Wilberforce in 1789, which inspired Hannah More to begin her work improving the conditions of the Mendip miners and agricultural workers. In the 18th and early 19th centuries 7,300 ha (18,000 acres) of

2725-477: Is linked to water temperatures, changes in temperature affect dissolved oxygen concentrations as warmer water has a lower capacity to "hold" oxygen as colder water. Biologically, both photosynthesis and aerobic respiration affect dissolved oxygen concentrations. Photosynthesis by autotrophic organisms , such as phytoplankton and aquatic algae , increases dissolved oxygen concentrations while simultaneously reducing carbon dioxide concentrations, since carbon dioxide

2834-464: Is located on Warrens Hill Road, on the rim of Batts Combe quarry between Shipham and Charterhouse. Thomas Hardy described the Mendips as "a range of limestone rocks stretching from the shores of the Bristol Channel into the middle of Somersetshire", and several of his books refer to the Mendips or sites on the hills. According to legend, Augustus Montague Toplady was inspired to write

2943-507: Is quarried at several sites. Ash – maple woodland, calcareous grassland and mesotrophic grassland which can be found across the Mendip Hills provide nationally important semi-natural habitats. With their temperate climate these support a range of flora and fauna including birds, butterflies and small mammals. The dry stone walls that divide the pasture into fields are of botanical importance as they support important populations of

3052-454: Is required to visit the vast majority of the caves, but Cheddar Gorge and Wookey Hole Caves are two show caves which are easily accessible to the public. The active Mendip Caving Group and other local caving organisations organise trips and continue to discover new caverns. The Hills conceal the largest underground river system in Britain; attempts to move from one cave to another through

3161-631: Is set in the Mendip Hills and is one of the largest outdoor activity centres in the South West. It is a key part of the local tourism community bringing significant revenue and visitor numbers each year, welcoming 10,000s of visitors. They have a thriving outdoor education program with schools, delivering school residentials. Families and individuals take part in activities including skiing and snowboarding, climbing and abseiling, kayaking and paddle boarding, caving, archery, air rifle, tobogganing and disc golf. Their pop-up campsite, Mendip Basecamp, opened to

3270-468: Is taken up during photosynthesis. All aerobic organisms in the aquatic environment take up dissolved oxygen during aerobic respiration, while carbon dioxide is released as a byproduct of this reaction. Because photosynthesis is light-limited, both photosynthesis and respiration occur during the daylight hours, while only respiration occurs during dark hours or in dark portions of an ecosystem. The balance between dissolved oxygen production and consumption

3379-519: Is that the name is cognate with Mened ( Welsh mynydd ), a Brythonic term for upland moorland. The suffix may be a contraction of the Old English hop , meaning a valley. Possible further meanings have been identified. The first is 'the stone pit' from the Celtic meyn and dyppa in reference to the collapsed cave systems of Cheddar . The second is "mighty and awesome" from

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3488-625: Is the dullest month and June the sunniest. The south-west of England enjoys a favoured location, particularly in summer, when the Azores High extends its influence north-eastwards towards the UK. Cumulus cloud often forms inland, especially near hills, and reduces exposure to sunshine. The average annual sunshine is about 1,600 hours. Rainfall tends to be associated with Atlantic depressions or with convection. In summer, convection caused by solar surface heating sometimes forms shower clouds, and

3597-407: Is the only Mendip breeding site for downy emerald dragonflies. In 2007 the first confirmed sighting of a red kite ( Milvus milvus ) on the Mendips was made at Charterhouse. A range of important small mammals are found in the area, including the hazel dormouse ( Muscardinus avellanarius ) and bats. The hazel dormouse is restricted largely to coppice woodland and scrub, while the bats, including

3706-674: Is the shallowest where the River Yeo enters. It is a hard water area with high mineral content that is vulnerable to eutrophication in the summer, that can cause algal blooms , with transient water layers . As a result, a research programme has been established to observe and measure the limnology of the lake. When full it contains 8,456,000,000 litres (1.860 × 10 imp gal; 2.234 × 10 US gal) and supplies 9,547,000,000 litres (2.100 × 10 imp gal; 2.522 × 10 US gal) of water each year. Water can also be taken from its larger neighbour Chew Valley Lake to balance

3815-467: Is the summit area atop Black Down . The hills gave their name to the former local government district of Mendip , which administered most of the local area until April 2023. The higher, western part of the hills, covering 198 km (76 sq mi) has been designated an Area of Outstanding Natural Beauty (AONB), which gives it a level of protection comparable to a national park . The hills are largely formed from Carboniferous Limestone , which

3924-460: Is with the trophic state index . An oligotrophic lake is characterized by relatively low levels of primary production and low levels of nutrients . A eutrophic lake has high levels of primary productivity due to very high nutrient levels. Eutrophication of a lake can lead to algal blooms . Dystrophic lakes have high levels of humic matter and typically have yellow-brown, tea-coloured waters. These categories do not have rigid specifications;

4033-728: The A38 . Further east, and running almost north to south, are the A37 , A39 , A36 and the A361 . During the late 19th and early 20th century, the Bristol and North Somerset Railway ran roughly parallel to the A37. Further south and west, the Cheddar Valley Line and Wrington Vale Light Railway , branches of the Bristol and Exeter Railway , served towns and villages from Cheddar to Wells. In

4142-578: The Barrow Tanks . Blagdon Lake is designated a Site of Special Scientific Interest (SSSI) of 212.7 hectares (526 acres), created in 1971, largely because of the variety of species and habitats. The area around the pumping station was laid out as an ornamental woodland which includes Scots pine , cedar , larch , spruce , oak , beech , chestnut , willow , lime , holly and maple . A variety of orchids including green-winged orchid ( Anacamptis morio ) and southern marsh-orchids can be seen on

4251-442: The Bristol Channel . The hills gave their name to the rare mineral mendipite , an oxohalide of lead with chlorine with formula Pb 3 Cl 2 O 2 which was first described in the area. A sample of mendipite was found at the head of Ebbor Gorge . Along with the rest of South West England , the Mendip Hills have a temperate climate that is generally wetter and milder than the rest of England. The annual mean temperature

4360-548: The Dartford warbler ( Sylvia undata ), which can be found at Black Down and Crook Peak . In Britain, this species is usually associated with lowland heath. The woodlands at Stock Hill are a breeding site for nightjars ( Caprimulgus europaeus ) and long-eared owls ( Asio otus ). The Waldegrave Pool, part of Priddy Mineries , is an important site for dragonflies , including downy emerald ( Cordulia aenea ) and four-spotted chaser ( Libellula quadrimaculata ). Waldegrave Pool

4469-436: The Mendip Way and Limestone Link . Several explanations for the name "Mendip" have been suggested. Its earliest known form is Mendepe in 1185. One suggestion is that it is derived from the medieval term Myne-deepes . Others suggest it derives from Celtic monith , meaning mountain or hill, with an uncertain second element, perhaps Old English yppe in the sense of upland or plateau. A third explanation

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4578-745: The Mendips ) is a range of limestone hills to the south of Bristol and Bath in Somerset , England. Running from Weston-super-Mare and the Bristol Channel in the west to the Frome valley in the east, the hills overlook the Somerset Levels to the south and the Chew Valley and other tributaries of the Avon to the north. The highest point, at 325 metres above sea level, is Beacon Batch which

4687-647: The Priddy Nine Barrows and Ashen Hill Barrow Cemeteries . The Historic England Archive holds over 1,200 entries for the area, and there are over 600 listed buildings , in addition to over 200 scheduled ancient monuments . These protected monuments range from prehistoric barrows and hillforts to the Black Down bombing decoy from the Second World War. Settlement on the Mendip Hills appears to fall into two types. The first, apparent in

4796-560: The Severn Estuary in Woodspring Bay, downstream from Clevedon and west of the village of Kingston Seymour . The watershed catchment area of the reservoir is 2,144 hectares (5,300 acres). The construction of the reservoir was approved by acts of parliament in 1888 and 1889 as part of a plan to provide drinking water to Bristol , supplementing Barrow Gurney Reservoirs and the "line of works" pipe which carries water from

4905-534: The University of Wisconsin-Madison , Edward A. Birge , Chancey Juday , Charles R. Goldman , and Arthur D. Hasler contributed to the development of the Center for Limnology . Physical properties of aquatic ecosystems are determined by a combination of heat, currents, waves and other seasonal distributions of environmental conditions. The morphometry of a body of water depends on the type of feature (such as

5014-633: The barrows and forts around Priddy and at Dolebury Warren . The caves of Cheddar Gorge have yielded many archaeological remains, as flood waters have washed artefacts and bones into the caves and preserved them in silt. The Cheddar Man , Britain's oldest complete skeleton, was found in Gough's Cave , part of the Cheddar Complex . Within the Mendip Hills AONB, good evidence exists for 286 definite examples of round barrows, including

5123-472: The biodiversity of tropical freshwater systems is typically higher, human impacts are often more severe, and there are important cultural and socioeconomic factors that influence the use and management of these systems. People who study limnology are called limnologists. These scientists largely study the characteristics of inland fresh-water systems such as lakes, rivers, streams, ponds and wetlands. They may also study non-oceanic bodies of salt water, such as

5232-693: The spring and summer . Phosphorus has a different role in aquatic ecosystems as it is a limiting factor in the growth of phytoplankton because of generally low concentrations in the water. Dissolved phosphorus is also crucial to all living things, is often very limiting to primary productivity in freshwater, and has its own distinctive ecosystem cycling . Lakes "are relatively easy to sample, because they have clear-cut boundaries (compared to terrestrial ecosystems) and because field experiments are relatively easy to perform.", which make then especially useful for ecologists who try to understand ecological dynamics. One way to classify lakes (or other bodies of water)

5341-484: The Iron Age onward the ownership of land took on increasing importance, with large landholdings based on the mines or on stock grazing, denying settlers access to the plateau or forcing them off the hills. There is evidence of mining dating back to the late Bronze Age, when there were technological changes in metal-working indicating the use of lead. The Roman invasion, and possibly the preceding period of involvement in

5450-551: The Mendip Hills has, since 1972, been designated an Area of Outstanding Natural Beauty (AONB) under the National Parks and Access to the Countryside Act 1949 . The Mendip Society, which was formed in 1965, helps to raise awareness of this designation and protect the area. The society runs a programme of guided walks and educational presentations. The society also has a small grants fund to assist communities with

5559-539: The Mendip Hills is Charterhouse Cave with a vertical range of 220 m (722 ft). Many caves in the Mendip area were excavated for archaeological and natural history studies by pioneer explorer Herbert E. Balch and were photographed by the early caver Harry Savory at the start of the 20th century using cameras , glass plates and flash powder . Several sites on the Mendips are designated as open access land , and there are many footpaths and bridleways that are generally clearly marked. The Limestone Link

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5668-508: The Mendip Hills. Construction required the provision of sewers to local villages to avoid contamination of the reservoir. The work was designed by Charles Hawksley . In conjunction with the construction work the Wrington Vale Light Railway was established connecting Blagdon with Congresbury on the Cheddar Valley Line and Yatton on the main Bristol to Exeter line . In addition to carrying construction materials for

5777-452: The Mendips is open calcareous grassland, supporting a wide variety of flowering plants and insects. Some parts are deciduous ancient woodland , and some have been used intensively for arable agriculture, particularly since World War I. As the demand for arable land in Britain declined, some areas were returned to grassland, but the use of fertilisers and herbicides has reduced biodiversity. Grazing by rabbits, sheep and cattle maintains

5886-720: The Mendips the Carboniferous Limestone layers are found in the subsurface and are exposed in Avon Gorge , and are overlain by younger strata in Dundry Hill and the Cotswolds , where oolitic limestone of Jurassic age is found at the surface. West of the main Mendip plateau the Carboniferous Limestone continues in Bleadon Hill and Brean Down , and on the islands of Steep Holm and Flat Holm in

5995-494: The Mendips, many based on the particular geology of the area. The hills are recognised as a national centre for caving and cave diving , as well as being popular with climbers, hillwalkers and natural historians. Wookey Hole Caves and some of the caves in Cheddar Gorge are open as show caves ; however, many of the caves of the Mendip Hills are only accessible to members of caving clubs. Long-distance footpaths include

6104-412: The Mendips, of which eleven represent faunal remains and lithic artefacts recovered from caves. The remaining eight sites refer to surface lithic discoveries, and the artefacts found include points, scrapers, and handaxes. Twenty-seven Mesolithic finds are represented by flint and chert lithics. Large numbers of artefacts have been found near Neolithic , Iron Age , and Bronze Age features, such as

6213-455: The Mendips, reflect the arrival of this new road. Much of the high plateau, however, remained uncultivated and unenclosed until the 18th century, resulting in many roads remaining as narrow winding lanes between high banks and hedges or stone walls. Where the tracks had their origins as drovers roads , they typically become open roads with wide verges. The roads tend to follow the line of gorges and valleys, as at Cheddar Gorge. The more major of

6322-612: The Mendips: the Devonian sandstones visible around Blackdown and Downhead and the Carboniferous Limestones, which dominate the hills and surround the older rock formations. There are nine active quarries and a host of disused sites, several of which have been designated as geological Sites of Special Scientific Interest by English Nature. Because of the effect quarrying has on the environment and local communities,

6431-584: The Neolithic and Bronze Age Britain periods, and repeated on a small scale in the Middle Ages and post-medieval era, comprised occupation by self-sufficient groups in small communities or isolated farms. The second was represented in the Iron Age Britain and Roman periods by large sites with specialist functions, existing by virtue of their ability to exert power over lowland producers. From

6540-583: The Old English moen and deop . The rock strata known as the Carboniferous Limestone were laid down during the early Carboniferous Period , about 320–350 million years ago. Subsequently, much of northwestern Europe underwent continental collision throughout the late Paleozoic Era , culminating in the final phases of the Variscan orogeny near the end of the Carboniferous, 300 million years ago. This tectonic activity produced

6649-412: The River Yeo through a compensation channel and an overflow weir and spillway take flood water downstream. Blagdon Pumping Station and Visitor Centre includes science and environment exhibits and hands-on displays as well as a room dedicated to the charity WaterAid . One of the two steam-driven beam engines is still working occasionally. Outside this is space for picnics and a nature trail. When

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6758-534: The area closed in the 1960s. Although the Roman Fosse Way crossed the hills, the main roads generally avoid the higher areas and run along the bottom of the scarp slope on the north and south of the hills. The western end of the hills is crossed by the M5 motorway and A38 . Further east, and running almost north to south, are the A37 and A39 . A wide range of outdoor sports and leisure activities take place in

6867-432: The boilers consumed 8.5 tons of coal per day. A mechanical efficiency of 90% was claimed, the 30-inch (76.2 cm) diameter pump bucket, 3.5 ft (1.07 m) strike and plunger diameter of 21 inches (53.3 cm) gave a pump output of 107 imperial gallons (490 L) per stroke. They ran until 1949, when two engines from the north engine house were replaced by electric pumps. In 1950 automatic shutdown equipment

6976-415: The borders of the lake. A variety of water birds can be seen around the lake including: great crested grebe ( Podiceps cristatus ) and little grebe ( Tachybaptus ruficollis ), cormorant ( Phalacrocoracidae ), mute swan ( Cygnus olor ), Canada goose ( Branta canadensis ), duck (Anatidae), shoveller ( Anas clypeata ) and gadwall ( Anas strepera ). Common buzzards ( Buteo buteo ) can be seen on

7085-552: The classification system can be seen as more of a spectrum encompassing the various levels of aquatic productivity. Tropical limnology is a unique and important subfield of limnology that focuses on the distinct physical, chemical, biological, and cultural aspects of freshwater systems in tropical regions . The physical and chemical properties of tropical aquatic environments are different from those in temperate regions , with warmer and more stable temperatures, higher nutrient levels, and more complex ecological interactions. Moreover,

7194-452: The common heathland on the hills were enclosed . In World War II a bombing decoy was constructed on top of Black Down at Beacon Batch. More recently, the mast of the Mendip transmitting station , micro-hydroelectric turbines and a wind turbine have been installed. There are several quarries on the Mendip Hills . Some of the stone is still carried by Mendip Rail ; the other railways in

7303-468: The conservation and enhancement of the landscape and to encourage its enjoyment and celebration. As their landscapes have similar scenic qualities, AONBs may be compared to the national parks of England and Wales . In contrast to national parks, which have their own authorities and legal power to prevent unsympathetic development, very few statutory duties are imposed on the local authorities within an AONB. However, further regulation and protection of AONBs

7412-559: The current roads often started as turnpikes in the 16th century. These avoid the highest areas of the hills. To the north of the western part of the Mendips, the A368 separates the hills from the Chew Valley , while on the southern edge the A371 similarly runs along the bottom of the scarp slope between the hills and the Somerset Levels . The western end of the hills is crossed by the M5 motorway with access at junctions 21 and 22, along with

7521-404: The depletion of bottom-water dissolved oxygen; when dissolved oxygen concentrations are below 2 milligrams per liter, waters are considered hypoxic . When dissolved oxygen concentrations are approximately 0 milligrams per liter, conditions are anoxic . Both hypoxic and anoxic waters reduce available habitat for organisms that respire oxygen, and contribute to changes in other chemical reactions in

7630-421: The depth of the water column which sunlight is able to penetrate and where most plant life is able to grow is known as the photic or euphotic zone. The rest of the water column which is deeper and does not receive sufficient amounts of sunlight for plant growth is known as the aphotic zone . The amount of solar energy present underwater and the spectral quality of the light that are present at various depths have

7739-450: The difference between the summer (θ sz ) and winter (θ wz ) temperatures or ∫ {\displaystyle \displaystyle \int } A z (θ sz -θ wz ) The chemical composition of water in aquatic ecosystems is influenced by natural characteristics and processes including precipitation , underlying soil and bedrock in the drainage basin , erosion , evaporation , and sedimentation . All bodies of water have

7848-542: The east, the Somerset and Dorset Joint Railway ran south from Bath into Dorset , and also served Wells. These have all now closed, but Mendip Rail has freight lines to carry limestone from the quarries of the Mendip Hills . There is also the East Somerset Railway which is an operational heritage railway . The Somerset Coal Canal reached some of the pits of the Somerset Coalfield in

7957-598: The east. Many of the villages on the Mendips have their own parish councils , which have some responsibility for local issues. Local people also elect councillors to district councils or to unitary authorities. The 198 km (76 sq mi) of the AONB are split across four districts: Mendip District Council 87.67 km (33.8 sq mi), Sedgemoor District Council 34.03 km (13.1 sq mi), Bath and North East Somerset Council 36.95 km (14.3 sq mi), and North Somerset Council 39.35 km (15.2 sq mi). The population on

8066-548: The eastern end of the Mendips. In recent centuries the Mendips, like the Cotswolds to the north, have been quarried for stone to build the cities of Bath and Bristol, as well as smaller towns in Somerset. The quarries are now major suppliers of road stone to southern England, among them producing around twelve million tonnes of limestone every year, employing over two thousand people, and turning over approximately £150 million per annum. There are two main rock types on

8175-645: The field with his studies of Lake Geneva . Interest in the discipline rapidly expanded, and in 1922 August Thienemann (a German zoologist) and Einar Naumann (a Swedish botanist) co-founded the International Society of Limnology (SIL, from Societas Internationalis Limnologiae ). Forel's original definition of limnology, "the oceanography of lakes", was expanded to encompass the study of all inland waters, and influenced Benedykt Dybowski 's work on Lake Baikal . Prominent early American limnologists included G. Evelyn Hutchinson and Ed Deevey . At

8284-401: The grassland habitat. Of the many bird species found in the Mendips, the peregrine falcon ( Falco peregrinus ), which has gradually recolonised the area since the 1980s, is particularly significant. It breeds on sea and inland cliffs and on the faces of active and disused quarries. The upland heaths of the west Mendips have recently increased in ornithological importance due to colonisation by

8393-404: The higher plateau is widely dispersed in small farms and hamlets, although rather than working in agriculture or forestry, most people now commute to employment in surrounding cities and towns. The largest village on the plateau on the western Mendips is Priddy , which had a population of 624 at the 2011 census along with the smaller hamlet of Charterhouse . The larger villages and towns are on

8502-454: The hills were enclosed, mainly with dry stone walls that today form a key part of the landscape. In 2006 funding was obtained to maintain and improve the walls, which had steadily deteriorated over the years. In World War II, a bombing decoy was constructed on top of Black Down at Beacon Batch in an attempt to confuse bombers aiming to damage the city of Bristol, and piles of stones (known as cairns ) were created to prevent enemy aircraft using

8611-502: The hilltop as a landing site. In the 1960s, the tallest mast in the region at 293 metres (961 ft) above ground level, the Mendip UHF television transmitter , was installed on Pen Hill near Wells , one of the highest points of the Mendips. The transmitter's antenna rises to almost 589 metres (1,932 ft) above sea level. Since 2003, arguments have raged over plans to erect a wind turbine near Chewton Mendip. The proposal

8720-511: The internal affairs of the south of England, was inspired, in part, by the mineral wealth of the Mendips. William Wilberforce 's visit to Cheddar in 1789, during which he saw the poor circumstances of the locals, inspired Hannah More to begin her work improving the conditions of the Mendip miners and agricultural workers. Under her influence, schools were built and children were formally instructed in reading and Christian doctrine. Between 1770 and 1813 some 7,300 ha (18,000 acres) of land on

8829-568: The lake first opened there were four Woolf compound rotative beam pumping engines, housed in two separate buildings. They were built by Glenfield & Kennedy of Kilmarnock between 1900 and 1905. The engine's beam is 34 ft (10.36 m) long and weighs 17 tons. The flywheel is 20 ft (6.10 m) in diameter and weighs 20 tons, having a crank throw of 3.5 ft (1.07 m). Each beam engine had an output of 170 horsepower (130 kW) at 17  rpm . The high-pressure cylinders, 21 inches (53.3 cm) in diameter and with

8938-441: The landscape drainage density , lake surface area and lake shape . Other types of aquatic systems which fall within the study of limnology are estuaries . Estuaries are bodies of water classified by the interaction of a river and the ocean or sea. Wetlands vary in size, shape, and pattern however the most common types, marshes, bogs and swamps, often fluctuate between containing shallow, freshwater and being dry depending on

9047-409: The limestone produced many of the gorges including Cheddar Gorge and Burrington Combe . Springs are a common feature of the eastern part of the hills, a number of which have associated tufa deposits. Black Down is a moorland area, with its steeper slopes covered in bracken ( Pteridium ) and its flatter summit in heather ( Calluna ) and grasses rather than the pasture which covers much of

9156-515: The lower slopes of the western hills, often in river valleys. Axbridge , with a population of 2,057, and Cheddar (5,755), both within the Sedgemoor district, together with the Mendip town of Shepton Mallet (10,369) and the city of Wells (10,636) are along the southern border of the hills. The North Somerset parishes of Blagdon (1,116), and the parishes of Compton Martin (508), East Harptree (644) and West Harptree (439), lie along

9265-562: The nationally rare lesser ( Rhinolophus hipposideros ) and greater horseshoe bats ( Rhinolophus ferrumequinum ), have a number of colonies in buildings, caves, and mines. A rare and endangered species, the greater horseshoe bat is protected under the Wildlife and Countryside Act 1981 and is listed in Annex ;II of the 1992 European Community Habitats Directive . Amphibians such as the great crested newt ( Triturus cristatus ) have

9374-401: The nationally scarce wall whitlowgrass ( Draba muralis ). The origin of the name "Mendip" is unclear, but it is known that there has been human habitation since Palaeolithic and Mesolithic times with a range of artefacts being recovered from caves. Neolithic , Iron Age , and Bronze Age features such as barrows are numerous with over 200 scheduled ancient monuments recorded. There

9483-512: The northern edge. Further east are the towns of Midsomer Norton and Radstock and the village of Paulton (population 5,302) within the unitary authority of Bath and North East Somerset. In the middle of the 1st century, ancient tracks across the hills were superseded by the Roman Fosse Way , from Bath to Ilchester , a branch of which served the Charterhouse lead mines. Stratton-on-the-Fosse and Lydford-on-Fosse , two villages of

9592-421: The past and this is reflected in areas of contaminated rough ground known locally as "gruffy". The word "gruffy" is thought to derive from the grooves that were formed where the lead ore was extracted from veins near the surface. Other commodities obtained included calamine ( zinc ore), manganese , iron, copper and baryte . The eastern area reaches into parts of the Somerset Coalfield . North and east of

9701-419: The plateau. The main body of the range is an extended plateau, 6–8 km (4–5 miles) wide and generally about 240 metres (800 ft) above sea level. In some places lead and zinc ores have mineralised the limestone and the dolomitic conglomerate . From the time of Roman Britain until 1908, the hills were an important source of lead. These areas were the centre of a major mining industry in

9810-505: The public in 2020 and in 2023 was named Gold Campsite at the Bristol, Bath and Somerset Tourism Awards. Large areas of limestone on the Mendips have been worn away by water, making the hills a national centre for caving . Some of the caves have been known about since the establishment of the Mendip lead mining industry in Roman times. However, many have been discovered or explored only in the 20th century. Specialist equipment and knowledge

9919-404: The reservoir and pumping station it also provided passenger services. Later the railway was used to bring coal for the pumps. Passenger traffic ceased in 1931 and the line to Blagdon closed completely in 1950. The lake is relatively shallow, with an average depth of 14 ft (4.3 m) and only 42 ft (13 m) at its deepest point near the dam at the west end of the lake. The eastern end

10028-601: The route taken by Charles II after his defeat at the Battle of Worcester in 1651. The route enters Somerset near Chewton Mendip and crosses the Mendip Hills heading for Wells. A shorter local path, the 72-kilometre (45 mi) long Mendip Pub Trail, connects six pubs owned by Butcombe Brewery. The trail runs from Hinton Blewett through Priddy, Axbridge, Bleadon , Rowberrow , and Compton Martin. Various forms of oval short-track racing, including F1 and F2 stock cars , have taken place at Mendips Raceway since 1969. The track

10137-400: The supply. The dam extends 175 ft (53 m) below ground to the solid rock underlying the valley. It was built of puddled clay with a central concrete core and faced with granite on the lake side. A 24-inch-diameter (610 mm) pipe through the dam leads to the pumping station while a larger one is used to remove silt collecting against the dam. A flow of water is maintained in

10246-551: The surrounding hills and both Eurasian sparrowhawk ( Accipiter nisus ) and kestrel breed. Occasional visitors include: osprey ( Pandion haeliatis ), goshawk ( Accipiter gentilis ), Eurasian hobby ( Falco subbuteo ), nuthatch and great spotted woodpecker ( Dendrocopos major ). The ruddy darter dragonfly ( Sympetrum sanguineum ) can also be seen. In the wood at the western end of the lake there are populations of badgers , roe deer ( Capreolus capreolus ) and foxes . Mendip Hills The Mendip Hills (commonly called

10355-797: The system, such as algae and the microbial breakdown of aquatic particulate organic carbon , are autochthonous . In aquatic food webs, the portion of biomass derived from allochthonous material is then named "allochthony". In streams and small lakes, allochthonous sources of carbon are dominant while in large lakes and the ocean, autochthonous sources dominate. Dissolved oxygen and dissolved carbon dioxide are often discussed together due their coupled role in respiration and photosynthesis . Dissolved oxygen concentrations can be altered by physical, chemical, and biological processes and reaction. Physical processes including wind mixing can increase dissolved oxygen concentrations, particularly in surface waters of aquatic ecosystems. Because dissolved oxygen solubility

10464-407: The time of year. The volume and quality of water in underground aquifers rely on the vegetation cover, which fosters recharge and aids in maintaining water quality. Light zonation is the concept of how the amount of sunlight penetration into water influences the structure of a body of water. These zones define various levels of productivity within an aquatic ecosystems such as a lake. For instance,

10573-540: The two remaining engines and incorporate them as the central feature in the Visitor Centre, including a museum in the old boiler house, which opened in 1988 and attracts over 30,000 visitors a year. The flywheel is now driven by an electric motor. The pumping station is now a Grade II* listed building , while the Gothic -style meter house is Grade II listed and used as a bat sanctuary. Blagdon Lake first opened as

10682-461: The underground rivers led to the development of cave diving in Britain. The first cave dive was attempted at Swildon's Hole in 1934, and the first successful dive was achieved the following year at Wookey Hole Caves, which has the deepest sump in Britain at 76 m (250 ft). The cave complexes at St. Dunstan's Well Catchment , Lamb Leer , and Priddy Caves have been identified as Sites of Special Scientific Interest. The deepest cave in

10791-489: The value of this resource and between 1846 and 1853 created a series of tunnels, pipes, and aqueducts called the "Line of Works", which still carry approximately 18,200 m (4 million imperial gallons) of water a day to Barrow Gurney Reservoirs for filtration and then on to Bristol and the surrounding areas. This collection and conveyance of water from the Chewton Mendip and East and West Harptree areas

10900-531: The village of Ubley and enters Blagdon Lake. From the lake the river flows south of Wrington and Iwood , where there were once a series of watermills along its banks. Its route then takes it around the northern outskirts of Congresbury, and across the North Somerset Levels roughly parallel to the A370 road , past the site of a Roman villa before crossing under the M5 motorway and emptying into

11009-408: The visitor centre which also includes educational facilities for children. The pumping station is now a Grade II* listed building . The 8,456,000,000-litre (1.860 × 10 imp gal; 2.234 × 10 US gal) lake still provides 9,547,000,000 L (2.100 × 10 imp gal; 2.522 × 10 US gal) of drinking water each year, but also acts as a fishing lake. It provides a habitat for

11118-492: The water column, photosynthesis rates also decrease, and less dissolved oxygen is produced. This means that dissolved oxygen concentrations generally decrease as you move deeper into the body of water because of photosynthesis is not replenishing dissolved oxygen that is being taken up through respiration. During periods of thermal stratification, water density gradients prevent oxygen-rich surface waters from mixing with deeper waters. Prolonged periods of stratification can result in

11227-631: The water surface. The thermocline is an area within the water column where water temperatures rapidly decrease. The bottom layer is the hypolimnion , which tends to have the coldest water because its depth restricts sunlight from reaching it. In temperate lakes, fall-season cooling of surface water results in turnover of the water column, where the thermocline is disrupted, and the lake temperature profile becomes more uniform. In cold climates, when water cools below 4 C (the temperature of maximum density) many lakes can experience an inverse thermal stratification in winter. These lakes are often dimictic , with

11336-402: The water. Nitrogen and phosphorus are ecologically significant nutrients in aquatic systems. Nitrogen is generally present as a gas in aquatic ecosystems however most water quality studies tend to focus on nitrate , nitrite and ammonia levels. Most of these dissolved nitrogen compounds follow a seasonal pattern with greater concentrations in the fall and winter months compared to

11445-527: The words of the hymn " Rock of Ages " while sheltering under a rock in Burrington Combe during a thunderstorm in 1763; there is a metal plaque marking the site. Limnology Limnology includes the study of the drainage basin, movement of water through the basin and biogeochemical changes that occur en route. A more recent sub-discipline of limnology, termed landscape limnology , studies, manages, and seeks to conserve these ecosystems using

11554-471: Was added by the Countryside and Rights of Way Act 2000 . The Mendip Hills Partnership, which performs an administrative role, includes the five local authorities that cover the AONB, statutory bodies such as Natural England , together with parish councils and other organisations and groups that have an interest in the conservation and care of the area. The Mendip Hills AONB staff unit of the partnership

11663-432: Was constructed primarily to bring building materials for the lake. The reservoir was formed by the construction of a dam and provided water to the pumping station which originally contained four Woolf compound rotative beam pumping engines , built by Glenfield & Kennedy of Kilmarnock , which have now been replaced by electric pumps. Two of the steam engines have been preserved, with one in working order as part of

11772-411: Was initially rejected by Mendip District Council, with the support of a range of local groups and organisations, on the grounds that the environmental impact on the edge of the AONB outweighed the amount of electricity which would be generated. In April 2006, however, a planning enquiry gave Ecotricity permission to build a 102 m (335 ft) turbine during the following year. The western end of

11881-408: Was installed to prevent damage in the event of a burst main or overloading of the new electric pumps. This meant that it was no longer essential to have staff on site 24 hours a day. The decorative chimney was shortened in the 1960s. In 2014 new split-case vertical pumps and various other new equipment was installed to replace those installed in the 1940s and 1950s. In 1984 it was decided to preserve

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