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30-491: It is one of the five largest freshwater lakes in all of China, covering approximately 2,339 km. In years with high precipitation, the normally exit−less endorheic lake may overflow at its northern shore, and the water will meet the Argun River (Ergune) after about 30 kilometres (19 mi). The lake is not far from Manzhouli , which is on a major passenger rail-line. Although there are several villages nearby, Manzhouli

60-531: A sink lake or terminal lake ) is a collection of water within an endorheic basin , or sink, with no evident outlet. Endorheic lakes are generally saline as a result of being unable to get rid of solutes left in the lake by evaporation . These lakes can be used as indicators of anthropogenic change, such as irrigation or climate change , in the areas surrounding them. Lakes with subsurface drainage are considered cryptorheic . The two main ways that endorheic lakes accumulate water are through river flow into

90-647: A country have become erodible. For example, on the Madagascar high central plateau , which constitutes approximately ten percent of that country's land area, most of the land area is devegetated, and gullies have eroded into the underlying soil to form distinctive gulleys called lavakas . These are typically 40 meters (130 ft) wide, 80 meters (260 ft) long and 15 meters (49 ft) deep. Some areas have as many as 150 lavakas/square kilometer, and lavakas may account for 84% of all sediments carried off by rivers. This siltation results in discoloration of rivers to

120-465: A dark red brown color and leads to fish kills. In addition, sedimentation of river basins implies sediment management and siltation costs.The cost of removing an estimated 135 million m of accumulated sediments due to water erosion only is likely exceeding 2.3 billion euro (€) annually in the EU and UK, with large regional differences between countries. Erosion is also an issue in areas of modern farming, where

150-432: A grain, such as pits, fractures, ridges, and scratches. These are most commonly evaluated on quartz grains, because these retain their surface markings for long periods of time. Surface texture varies from polished to frosted, and can reveal the history of transport of the grain; for example, frosted grains are particularly characteristic of aeolian sediments, transported by wind. Evaluation of these features often requires

180-458: A higher density and viscosity . In typical rivers the largest carried sediment is of sand and gravel size, but larger floods can carry cobbles and even boulders . Wind results in the transportation of fine sediment and the formation of sand dune fields and soils from airborne dust. Glaciers carry a wide range of sediment sizes, and deposit it in moraines . The overall balance between sediment in transport and sediment being deposited on

210-426: A hydrodynamic sorting process within the marine environment leading to a seaward fining of sediment grain size. One cause of high sediment loads is slash and burn and shifting cultivation of tropical forests. When the ground surface is stripped of vegetation and then seared of all living organisms, the upper soils are vulnerable to both wind and water erosion. In a number of regions of the earth, entire sectors of

240-470: A result, can cause exposed sediment to become more susceptible to erosion and delivery to the marine environment during rainfall events. Sediment can negatively affect corals in many ways, such as by physically smothering them, abrading their surfaces, causing corals to expend energy during sediment removal, and causing algal blooms that can ultimately lead to less space on the seafloor where juvenile corals (polyps) can settle. When sediments are introduced into

270-515: A spring, a tributary, or flooding), the temporal result of a lake in a sink may change. The lake could be a persistent lake , an intermittent lake , a playa lake (temporarily covered with water), or an ephemeral lake, which completely disappears (e. g. by evaporation) before reappearing in wetter seasons. These terms (playa, ephemeral lake, etc.) are sometimes used interchangeably, but there has been activity tending towards defining meanings for each term. This change would mean less confusion over

300-541: Is expected to be delivered to the outlet of the river. The sediment transfer and deposition can be modelled with sediment distribution models such as WaTEM/SEDEM. In Europe, according to WaTEM/SEDEM model estimates the Sediment Delivery Ratio is about 15%. Watershed development near coral reefs is a primary cause of sediment-related coral stress. The stripping of natural vegetation in the watershed for development exposes soil to increased wind and rainfall and, as

330-581: Is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder". The shape of particles can be defined in terms of three parameters. The form is the overall shape of the particle, with common descriptions being spherical, platy, or rodlike. The roundness is a measure of how sharp grain corners are. This varies from well-rounded grains with smooth corners and edges to poorly rounded grains with sharp corners and edges. Finally, surface texture describes small-scale features such as scratches, pits, or ridges on

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360-538: Is the nearest city of notable size. As of 1995 annual fish production was about 7,000 tons, 100 tons of shrimp , 4 kilograms of pearls , 1.5 million crayfish . Hulun Lake is also one of the key reed production areas in China. Hulun Lake and its wetlands are a Biosphere reserve and a Ramsar site of China, Dalai Lake National Nature Reserve . [REDACTED] Media related to Hulun Lake at Wikimedia Commons Endorheic lake An endorheic lake (also called

390-488: The Aralkum Desert . Endorheic lakes, because of the closed nature of their systems, are sensitive to new conditions. Records of previous environmental change are preserved in lake sediments in endorheic lakes that are being affected by climate change ; these natural records can give information about past climates and conditions of the lake. Research on these lake sediments could lead to these lakes becoming archives of

420-399: The effects of climate change . There is early evidence that in regions affected by irrigation the majority of endorheic lake area may have already been lost. Sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion , and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on

450-596: The bed is given by the Exner equation . This expression states that the rate of increase in bed elevation due to deposition is proportional to the amount of sediment that falls out of the flow. This equation is important in that changes in the power of the flow change the ability of the flow to carry sediment, and this is reflected in the patterns of erosion and deposition observed throughout a stream. This can be localized, and simply due to small obstacles; examples are scour holes behind boulders, where flow accelerates, and deposition on

480-579: The body of water. Terrigenous material is often supplied by nearby rivers and streams or reworked marine sediment (e.g. sand ). In the mid-ocean, the exoskeletons of dead organisms are primarily responsible for sediment accumulation. Deposited sediments are the source of sedimentary rocks , which can contain fossils of the inhabitants of the body of water that were, upon death, covered by accumulating sediment. Lake bed sediments that have not solidified into rock can be used to determine past climatic conditions. The major areas for deposition of sediments in

510-417: The coastal regions of the ocean, the proportion of land, marine, and organic-derived sediment that characterizes the seafloor near sources of sediment output is altered. In addition, because the source of sediment (i.e., land, ocean, or organically) is often correlated with how coarse or fine sediment grain sizes that characterize an area are on average, grain size distribution of sediment will shift according to

540-519: The designations of different types of endorheic lakes. Many endorheic lakes exist in arid or semi-arid climates. Because these climates have limited rainfall, but also a high possibility of evaporation, endorheic lakes in these regions often experience flux in their water levels. This flux can be aggravated by anthropogenic intrusions (e.g. global warming ). In Central Asia , a large percentage of water for farming comes from surface water, like endorheic lakes, rather than precipitation. Because of

570-422: The edges and corners of particle are. Complex mathematical formulas have been devised for its precise measurement, but these are difficult to apply, and most geologists estimate roundness from comparison charts. Common descriptive terms range from very angular to angular to subangular to subrounded to rounded to very rounded, with increasing degree of roundness. Surface texture describes the small-scale features of

600-510: The flow. In geography and geology , fluvial sediment processes or fluvial sediment transport are associated with rivers and streams and the deposits and landforms created by sediments. It can result in the formation of ripples and dunes , in fractal -shaped patterns of erosion, in complex patterns of natural river systems, and in the development of floodplains and the occurrence of flash floods . Sediment moved by water can be larger than sediment moved by air because water has both

630-539: The inside of meander bends. Erosion and deposition can also be regional; erosion can occur due to dam removal and base level fall. Deposition can occur due to dam emplacement that causes the river to pool and deposit its entire load, or due to base level rise. Seas, oceans, and lakes accumulate sediment over time. The sediment can consist of terrigenous material, which originates on land, but may be deposited in either terrestrial, marine, or lacustrine (lake) environments, or of sediments (often biological) originating in

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660-541: The lake (discharge) and precipitation falling into the lake. The collected water of the lake, instead of discharging , can only be lost due to either evapotranspiration or percolation (water sinking underground, e.g., to become groundwater in an aquifer ). Because of this lack of an outlet, endorheic lakes are mostly salt water rather than fresh water. The salinity in the lake gradually builds up through years as water evaporates and leaves its solutes behind. Depending on water losses, precipitation, and inflow (e.g.,

690-406: The long, intermediate, and short axis lengths of the particle. The form ψ l {\displaystyle \psi _{l}} varies from 1 for a perfectly spherical particle to very small values for a platelike or rodlike particle. An alternate measure was proposed by Sneed and Folk: which, again, varies from 0 to 1 with increasing sphericity. Roundness describes how sharp

720-435: The marine environment include: One other depositional environment which is a mixture of fluvial and marine is the turbidite system, which is a major source of sediment to the deep sedimentary and abyssal basins as well as the deep oceanic trenches . Any depression in a marine environment where sediments accumulate over time is known as a sediment trap . The null point theory explains how sediment deposition undergoes

750-414: The overall lack of precipitation, farming in this area can only be sustained by irrigation. Massive amounts of irrigation in agrarian Central Asia have led to the reduction in size of endorheic lakes. The Aral Sea was once the second largest endorheic lake in the world, but anthropogenic effects such as bad irrigation practices have led to this lake's drastic decrease in size and turn into a desert named

780-824: The particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation ; if buried, they may eventually become sandstone and siltstone ( sedimentary rocks ) through lithification . Sediments are most often transported by water ( fluvial processes ), but also wind ( aeolian processes ) and glaciers . Beach sands and river channel deposits are examples of fluvial transport and deposition , though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments. Sediment can be classified based on its grain size , grain shape, and composition. Sediment size

810-491: The relative input of land (typically fine), marine (typically coarse), and organically-derived (variable with age) sediment. These alterations in marine sediment characterize the amount of sediment suspended in the water column at any given time and sediment-related coral stress. In July 2020, marine biologists reported that aerobic microorganisms (mainly), in " quasi-suspended animation ", were found in organically-poor sediments, up to 101.5 million years old, 250 feet below

840-473: The removal of native vegetation for the cultivation and harvesting of a single type of crop has left the soil unsupported. Many of these regions are near rivers and drainages. Loss of soil due to erosion removes useful farmland, adds to sediment loads, and can help transport anthropogenic fertilizers into the river system, which leads to eutrophication . The Sediment Delivery Ratio (SDR) is fraction of gross erosion (interill, rill, gully and stream erosion) that

870-445: The surface of the grain. Form (also called sphericity ) is determined by measuring the size of the particle on its major axes. William C. Krumbein proposed formulas for converting these numbers to a single measure of form, such as where D L {\displaystyle D_{L}} , D I {\displaystyle D_{I}} , and D S {\displaystyle D_{S}} are

900-494: The use of a scanning electron microscope . Composition of sediment can be measured in terms of: This leads to an ambiguity in which clay can be used as both a size-range and a composition (see clay minerals ). Sediment is transported based on the strength of the flow that carries it and its own size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, while larger or denser particles will be more likely to fall through

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