Explain briefly about delta
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Deltas are wetlands that form as rivers empty their water and sediment into another body of water, such as an ocean, lake, or another river. Deltas can also empty into land, although this is less common.
A river moves more slowly as it nears its mouth, or end. This causes sediment, solid material carrieddownstream by currents, to fall to the river bottom.
The slowing velocity of the river and the build-up of sediment allows the river to break from its singlechannel as it nears its mouth. Under the right conditions, a river forms adeltaic lobe. A mature deltaic lobe includes adistributary network—a series of smaller, shallower channels, called distributaries, that branch off from the mainstem of the river.
In a deltaic lobe, heavier,coarser material settles first. Smaller, finer sediment is carried farther downstream. The finest material is deposited beyond the river's mouth. This material is called alluvium or silt. Silt is rich in nutrients that helpmicrobes and plants—the producers in the food web—grow.
As silt builds up, new land is formed. This is the delta. A delta extends a river's mouth into the body of of water into which it is emptying.
A delta is sometimes divided into two parts: subaqueous and subaerial. The subaqueous part of a delta is underwater. This is the most steeply sloping part of the delta, and contains the finest silt. The newest part of the subaqueous delta, furthest from the mouth of the river, is called the prodelta.
The subaerial part of a delta is above water. The subaerial region most influenced by waves and tides is called thelower delta. The region most influenced by the river's flow is called the upper delta.
This nutrient-rich wetland of the upper and lower delta can be an extension of the river bank, or a series of narrow islands between the river's distributary network.
Like most wetlands, deltas are incredibly diverse and ecologically importantecosystems. Deltas absorbrunoff from both floods (from rivers) and storms (from lakes or the ocean). Deltas also filter water as it slowly makes its way through the delta's distributary network. This can reduce the impact ofpollution flowing from upstream.
Deltas are also important wetland habitats. Plants such as lilies and hibiscus grow in deltas, as well asherbs such as worts, which are used in traditional medicines.
Many, many animals areindigenous to the shallow, shifting waters of a delta. Fish, crustaceans such as oysters, birds, insects, and even apex predators such as tigers and bears can be part of a delta's ecosystem.
Not all rivers form deltas. For a delta to form, the flow of a river must be slow and steady enough for silt to be deposited and build up. The Ok Tedi, in Papua New Guinea is one of the fastest-flowing rivers in the world. It does not form a delta as it becomes a tributary of the Fly River. (The Fly, on the other hand, does form a rich delta as it empties into the Gulf of Papua, part of the Pacific Ocean.)
A river will also not form a delta if exposed to powerfulwaves. The Columbia River in Canada and the United States, for instance, deposits enormous amounts of sediment into the Pacific Ocean, but strong waves and currents sweep the material away as soon as it is deposited.
Tides also limit where deltas can form. The Amazon, the largest river in the world, is without a delta. The tides of the Atlantic Ocean are too strong to allow silt to create a delta on the Amazon.
A river moves more slowly as it nears its mouth, or end. This causes sediment, solid material carrieddownstream by currents, to fall to the river bottom.
The slowing velocity of the river and the build-up of sediment allows the river to break from its singlechannel as it nears its mouth. Under the right conditions, a river forms adeltaic lobe. A mature deltaic lobe includes adistributary network—a series of smaller, shallower channels, called distributaries, that branch off from the mainstem of the river.
In a deltaic lobe, heavier,coarser material settles first. Smaller, finer sediment is carried farther downstream. The finest material is deposited beyond the river's mouth. This material is called alluvium or silt. Silt is rich in nutrients that helpmicrobes and plants—the producers in the food web—grow.
As silt builds up, new land is formed. This is the delta. A delta extends a river's mouth into the body of of water into which it is emptying.
A delta is sometimes divided into two parts: subaqueous and subaerial. The subaqueous part of a delta is underwater. This is the most steeply sloping part of the delta, and contains the finest silt. The newest part of the subaqueous delta, furthest from the mouth of the river, is called the prodelta.
The subaerial part of a delta is above water. The subaerial region most influenced by waves and tides is called thelower delta. The region most influenced by the river's flow is called the upper delta.
This nutrient-rich wetland of the upper and lower delta can be an extension of the river bank, or a series of narrow islands between the river's distributary network.
Like most wetlands, deltas are incredibly diverse and ecologically importantecosystems. Deltas absorbrunoff from both floods (from rivers) and storms (from lakes or the ocean). Deltas also filter water as it slowly makes its way through the delta's distributary network. This can reduce the impact ofpollution flowing from upstream.
Deltas are also important wetland habitats. Plants such as lilies and hibiscus grow in deltas, as well asherbs such as worts, which are used in traditional medicines.
Many, many animals areindigenous to the shallow, shifting waters of a delta. Fish, crustaceans such as oysters, birds, insects, and even apex predators such as tigers and bears can be part of a delta's ecosystem.
Not all rivers form deltas. For a delta to form, the flow of a river must be slow and steady enough for silt to be deposited and build up. The Ok Tedi, in Papua New Guinea is one of the fastest-flowing rivers in the world. It does not form a delta as it becomes a tributary of the Fly River. (The Fly, on the other hand, does form a rich delta as it empties into the Gulf of Papua, part of the Pacific Ocean.)
A river will also not form a delta if exposed to powerfulwaves. The Columbia River in Canada and the United States, for instance, deposits enormous amounts of sediment into the Pacific Ocean, but strong waves and currents sweep the material away as soon as it is deposited.
Tides also limit where deltas can form. The Amazon, the largest river in the world, is without a delta. The tides of the Atlantic Ocean are too strong to allow silt to create a delta on the Amazon.
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