Exposed riverine sediments, or ERS, are composed of silt, sand and gravel deposited by streams but exposed as water level falls.
Other terms for ERS include river shingle, point bars, berms and shoals and they are most common in actively meandering and braided rivers.
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An exposed shoal. | An intermittent braided water course showing fluvial deposits. | A sand bar and the opposite bank. |
Unspecified river, Bangladesh | Medano Creek, Great Sand Dunes National Park and Preserve, Colorado, United States | Namoi River, New South Wales, Australia |
Adrian Fowles of the Countryside Council for Wales and members of the UK Environment Agency in 1993 coined ‘exposed riverine sediments’ as a term to describe the full scope of these related microhabitats. Their aim in-so-doing was to reduce confusion and pull together the conservation and scientific investigation of these habitats. Bates and Sadler (2005) [1] have since further defined exposed riverine sediments as:
Exposed, within channel, fluvially deposited sediments (gravels, sands and silts) that lack continuous vegetation cover, whose vertical distribution lies between the levels of bankfull and the typical baseflow of the river.
Therefore, eroding river banks are ERS because they are usually composed of fluvially deposited sediment. Whereas areas of the stream bed and over-bank deposits are not ERS because they are only exposed when water levels are unusually low and are more elevated than the bankfull level respectively.
The term ERS is slowly becoming more common and has now been used in a large number of published papers, for example:
A casual glance at ERS would suggest a harsh, relatively un-inhabited habitat with little value. However, ERS habitats are of considerable conservation importance because of their high species diversity, high degree of species specialisation, and large number of rare and endangered species. ERS are of substantial importance for a small number of vertebrate species, such as the rare little ringed plover, but for the most part their value lies in their invertebrate fauna.
The United Kingdom Biodiversity Action Plan, for example, lists eight species of beetle:
and two species of stilleto fly:
that are associated with ERS.
ERS rely on a continued supply of sediment from upstream, and periodic disturbances from flooding to prevent ecological succession to more vegetated riparian habitat.
Many of the threats to ERS act to:
Other threats operate over smaller scales, such as livestock trampling. [5]
A braided river consists of a network of river channels separated by small, often temporary, islands called braid bars or, in British English usage, aits or eyots.
Iniidae is a family of river dolphins containing one living genus, Inia, and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.
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The Dytiscidae – based on the Greek dytikos (δυτικός), "able to dive" – are the predaceous diving beetles, a family of water beetles. They occur in virtually any freshwater habitat around the world, but a few species live among leaf litter. The adults of most are between 1 and 2.5 cm (0.4–1.0 in) long, though much variation is seen between species. The European Dytiscus latissimus and Brazilian Megadytes ducalis are the largest, reaching up to 4.5 and 4.75 cm respectively. In contrast, the smallest is likely the Australian Limbodessus atypicali of subterranean waters, which only is about 0.9 mm (0.035 in) long. Most are dark brown, blackish, or dark olive in color with golden highlights in some subfamilies. The larvae are commonly known as water tigers due to their voracious appetite. They have short, but sharp mandibles and immediately upon biting, they deliver digestive enzymes into prey to suck their liquefied remains. The family includes more than 4,000 described species in numerous genera.
The riverine rabbit, also known as the bushman rabbit or bushman hare, is a rabbit with an extremely limited distribution area, found only in the central and southern regions of the Karoo Desert of South Africa's Northern Cape Province. It is the only member of the genus Bunolagus because of unique traits that separate it from the other leporids. It is one of the most endangered mammals in the world, with only around 500 living adults, and 1500 overall.
The greater horseshoe bat is an insectivorous bat of the genus Rhinolophus. Its distribution covers Europe, Northern Africa, Central Asia and Eastern Asia. It is the largest of the horseshoe bats in Europe and is thus easily distinguished from other species. The species is sedentary, typically travelling up to 30 kilometres (19 mi) between the winter and summer roosts, with the longest recorded movement being 180 km (110 mi). The frequencies used by this bat species for echolocation lie between 69–83 kHz, have most energy at 81 kHz and have an average duration of 37.4 ms.
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Manas National Park is a national park, Project Tiger reserve, and an elephant reserve in Assam, India. Located in the Himalayan foothills, it borders the Royal Manas National Park in Bhutan. The park is known for its rare and endangered endemic wildlife such as the Assam roofed turtle, hispid hare, golden langur and pygmy hog. It also hosts the only known population of pygmy hogs in the world. Manas is also famous for its population of the wild water buffalo. Because of its exceptional biodiversity, scenery, and variety of habitats, Manas National Park is a biosphere reserve and a UNESCO World Heritage Site.
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Washdyke Lagoon is a brackish shallow coastal lagoon approximately 1 kilometre (0.62 mi) north of Timaru, South Canterbury, New Zealand. The lagoon has drastically reduced in size since 1881 when it was approximately 253 hectares, now it is less than 48 hectares (0.48 km2) in area. It is enclosed by a barrier beach that is 3 kilometres (1.9 mi) long and 3 metres (9.8 ft) above high tide at its largest point. The reduced lagoon size is due to the construction of the Timaru Port breakwater which is preventing coarse sediments from reaching and replenishing Washdyke Barrier. This is important as the lagoon and the surrounding 250 hectares are classified as a wildlife refuge and it demonstrates the role human structures have on coastline evolution.
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The Molteno Formation is a geological formation found in several localities in Lesotho and South Africa. It lies mainly south of Maseru, near Burgersdorp, Aliwal North, Dordrecht, Molteno, and Elliot. It extends as far north as Matatiele in the Eastern Cape. The formation's localities lie along the Drakensberg Mountains in Kwazulu-Natal, and near Ladybrand in the Free State of South Africa. The Molteno Formation is the lowermost of the three formations in the Stormberg Group of the greater Karoo Supergroup. The Molteno Formation represents the initial phase of preserved sedimentation of the Stormberg Group.
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