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Estuary
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An estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. They are affected by both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. As a result they may contain many biological niches within a small area, and so are associated with high biological diversity.
Estuaries are typically the tidal mouths of rivers (aestus is Latin for tide), and they are often characterized by sedimentation or silt carried in from terrestrial runoff and, frequently, from offshore.
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Encyclopedia
An estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. They are affected by both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. As a result they may contain many biological niches within a small area, and so are associated with high biological diversity.
Estuaries are typically the tidal mouths of rivers (aestus is Latin for tide), and they are often characterized by sedimentation or silt carried in from terrestrial runoff and, frequently, from offshore. They are made up of brackish water. Estuaries are often given names like bay, sound, fjord, etc. The terms are not mutually exclusive.
As ecosystems, many estuaries are under threat from human activities such as pollution and overfishing.
Estuary circulation
Estuaries are marine environments whose pH, salinity, and water levels vary, depending on the river that feeds the estuary and the ocean from which it derives its salinity (oceans and seas have different salinity levels). The time it takes an estuary to completely cycle is called its flushing time.
- Estuarine circulation is common in estuaries; this occurs when fresh or brackish water flows out near the surface, while denser saline water flows inward near the bottom.
- Anti-estuarine flow is its opposite, in which dense water flows out near the bottom and less dense water circulates inward at the surface.
These two terms, however, have a broader oceanographic application that extends beyond estuaries proper, such as in describing the circulation of nearly-closed ocean basins.
Estuaries are more likely to occur on submerged coasts, where the sea level has risen in relation to the land; this process floods valleys to form rias and fjords. These can become estuaries if there is a stream or river flowing into them.
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