_____________ 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.

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.

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.

___________________ 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.

_________________: 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.

_________________: subsidence, as the result of movements of the crust. –____________________

___________: 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.

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.

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.

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.

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.

_______________ 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 _________.

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.

___________________ 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.

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.

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 ________.

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.

Spartina sp., wrack Outwelling

Salicornia sp., succulent

Oyster beds mussel beds seagrass beds