_____________

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