Estuaries - Estuaries Estuaries are semi-enclosed coastal...

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Estuaries are semi-enclosed coastal embayments where freshwater rivers meet and mix with the sea, creating unique and complex ecosystems. More than one third of Americans live within the drainage basins of our 100 or so estuaries. Estuaries
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CO 12
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Types of Estuaries Estuaries are classified both by their modes of formation and by their patterns of water circulation: Coastal plain estuaries ( drown river valleys ) Chesapeake Bay, Columbia River Bar-built estuaries Formed as near shore deposits of sand and mud transported by coastal wave action to build an obstruction (barrier island) in front of a coastal river or stream. Deltas ( large fan shaped deposits of upstream sediment) Tectonic estuaries (land sank due to crustal movements). Coastal lagoons ( no source of freshwater but like bar-built estuaries) .
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(a) (b) two coastal-plain estuaries (drowned river valleys) bar-built estuaries
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Delta
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Fjord Tectonic Estuary San Francisco Bay
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Estuarine Circulation Salinity in estuaries typically increases from the surface downward and from the estuary head downstream to its mouth (seaward) Because of the higher density of seawater, incoming tides move along the floor of the estuary and riverine inputs exit along its surface.
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The general pattern of fresh water and sea water mixing in an estuary. Estuaries can be defined according to their circulation patterns
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Estuarine Circulation -Vertically Mixed A shallow, low volume estuary where salinity at any point is the same at whatever depth. The seawater and freshwater are well-mixed vertically. -Slightly Stratified A deeper estuary with two distinct water layers separated by a MIXING ZONE. Salinity increases with depth . -Highly Stratified A deep estuary where a less dense upper layer floats over a deep water layer towards the mouth. These estuaries have strong haloclines. -Salt Wedge Fresh water is undermined by a wedge of salty water from the ocean. Surface water is of the same salinity, no horizontal salinity gradient (i.e. fresh water). However salinity increases with depth.
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Salt Wedge e.g. Columbia River in Washington and Oregon, the Hudson River in New York, and the Mississippi River in Louisiana
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Salt Wedge – High Tide
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Salt Wedge – Low Tide Organisms in a salt wedge environment may be exposed to major changes in salinity (2x a day for a diurnal tide, 4x a day for a semi diurnal tide)
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Cross-sections of (top) a well-mixed ( e.g. large, shallow estuaries, such as Delaware Bay ) and (bottom) slightly stratified estuary ( e.g. Very deep estuaries, such as Puget Sound in Washington State and San Francisco Bay in California)
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Estuarine Currents As many estuaries are long and narrow, the tide may rush in, forming strong tidal currents . In some places so much water enters the estuary a
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Estuaries - Estuaries Estuaries are semi-enclosed coastal...

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