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_____________
An ________ is a partially _________ body of water of variable salinity,
– with a freshwater ________ at one end and seawater introduced by __________ at the other.
Estuaries rank among the environments most _________ by humans.
• Estuaries are natural ___________, and many of the world’s largest cities have developed along them.
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The consequences of human intrusion in estuaries has been ____________.
– Estuaries are _______________ and transformed into marinas, seaports, industrial parks, cities and __________________.
– Many have been obliterated, and most surviving are endangered.
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The dominant features of an estuary include:• ______________• tidal action• a _______________ or interface between salt
and fresh water• often large areas of shallow, _____________
overlying mud flats and salt marshes.
Why protect them?• Estuaries are vital ___________________
grounds for many birds, fishes and other animals.
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___________________
• Many estuaries were formed when sea level rose at end of last ice age (about ____________ years ago).
• Drowned river valleys or ____________ estuaries.– probably the most _________ type of
estuary.• Examples = _____________ Bay and
the mouths of the Delaware and St. Lawrence rivers.
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_________________: are semienclosed bay or lagoon.
Sediments accumulate along the coast and build up ____________ and barrier islands that act as a wall between the ocean and fresh water from rivers.
Sandbars build up ____________ to the coastline,– a shallow lagoon forms behind bar and
collects the freshwater discharge from the land.
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• _________________: subsidence, as the result of movements of the crust.
– ____________________
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___________: were created when retreating glaciers cut ___________ along the coast.
Fjords are characterized by a __________ at the mouth that greatly restricts water exchange between the deeper waters of the fjord and the sea.
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Estuarine circulation
In general, seawater mixes with freshwater discharged by a river.
Freshwater flows along the estuary on the _________, mixing with salt water as it goes out to sea.
A deep, ______________ from the ocean enters the estuary along the bottom.
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Salinity
The salinity of estuaries _____________dramatically.
Seawater averaging about ____0/00 mixes with freshwater of nearly __0/00, salinity somewhere in between.
Depends on the __________________, salinity decreases moving upriver.
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More saline water is more dense and ______.
The denser saline water flows in along the bottom in what is called the ____________,
– while the less dense freshwater flows out on the surface.
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Estuarine circulation makes an estuary rich in _____________.
The _________________, drawn from deep offshore water, usually contains many nutrients.
The _______ input to an estuary also adds nutrients.
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_______________
Rivers carry large amounts of sediment and other material, including ______________.
Sand and other course material settle out near the river mouth when the _________________.
The _______ muddy particles, are carried out into the main body of the estuary, and eventually settle out when the current slows even more.
The substrate of most estuaries is _________.
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Substrate
Mud is a combination of silt and clay, and is rich in _______________.
Respiration by ________________ depletes the interstitial water of oxygen.
Sediments below several cm are _________. (black)
– ___________ bacteria continue decomposition.
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___________________
Exposed at low tide and extensive in estuaries where there is a large difference in water height between high and low tide.
Diatoms & bacteria =_________________ of mud flat.
Most organisms are ___________,
– deposit and _____________ feeders.
• Birds and fishes are important predators in the mud flat community.
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Estuaries are important _______________ and wintering areas for many species of _______________ birds.
Common wading shorebirds: willet, godwit, dowitchers, knots, plovers, oystercatchers and sandpipers (feed on polychaetes, ghost shrimp, small crusatceans, clams and mud snails.
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Salt marshes
Estuaries in temperate and subarctic regions are usually bordered by extensive ____________ that extend inland from the mud flats.
Partially ____________ at high tide– known as _____ or tidal marshes.
• ______ creeks and freshwater streams frequently cut through the marsh.
• Optimal conditions on our coast. (broad estuaries, ___________________).
• Muddy substrate held together by ________.
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Zonation pattern: from the tidal creek to the _________________ with true land plants.
The lowest zone at the ___________________, the Spartina alterniflora (cordgrass) zone, then ____________ patens and Juncus (rush) zone, Salicornia zone (pickelweed) zone.
Cord grass have ____________, pickelweed accumulate _______________ of water to dilute salts.
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Spartina sp., wrack
Outwelling
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Salicornia sp., succulent
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Oyster beds
mussel beds
seagrass beds
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