Sediment is some solid material - whether heavy or light - that is moved by some force and deposited in a new location. The general term used to refer to the force that moves sediment is erosion. This erosion is described as the removal and transportation of sediment. Sediment varies drastically in size, and can be as small as a grain of sand or as large as a boulder. Generally, sediment is composed of rocks, minerals, and the remains of plants and animals.
Sediment in water is generally small, and is present in nearly every body of water. When sediment in water is floating it is known as suspended sediment. Conversely, sediment that settles on the bottom of a waterway is known as bedded sediment.
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The process of moving sediment from one place to another through a variety of different mechanisms is known as sediment transport. Transport of sediment in moderate amounts is important for diverse ecosystems to exist. Generally speaking, the greater the flow the more sediment that is moved. Another name for sediment transport is sediment load.
Wind is one mechanism by which sediment can be moved. During a dust or sandstorm, wind can move dirt across a plane. Sand dunes are created when rocky sediment is worn down by wind and the sediment is deposited in one place.
Glaciers can move extremely large pieces of sediment by freezing them into the glacier and depositing them elsewhere as the ice sheet moves across the landscape or melts. Sediment from glaciers is called moraine.
Water can wash medium or small sediment from a river into a delta. Generally, the stronger the flow of the water the more sediment it will be able to move. If flow is strong enough, the motion of the water can suspend particles in the water as they move downstream or simply push them along the bottom of the waterway.
A certain amount of sediment movement is necessary for a healthy, evolving ecosystem. The movement of sediment from one place to another enriches ecosystems with new nutrients and shapes landscapes of other areas. The supplementation of nutrients through sediment movement results in areas that are very diverse - such as river deltas.
Although important, too much sediment in a body of water can be harmful. The presence of too much sediment in a body of water is known as sediment pollution. Although some sediment is introduced into water by a process of natural erosion, the majority of sediment enters through accelerated erosion as a result of human activities, particularly construction activities. Sediment pollution degrades water quality and clarity. Decreased water clarity can make it difficult for animals to see their food in the water an prevents vegetation from growing in water. Too much sediment in stream beds disrupts the natural food chain by destroying the habitat of extremely small stream organisms - this in turn decreases fish populations. As well, although some introduction of nutrients through sediment is important, too many nutrients can result in harmful extreme algal blooms and eutrophication.