http://staffwww.fullcoll.edu/tmorris/elements_of_ecology/images/estuary_salinity.jpg
For other uses, see Estuary (disambiguation).
Estuary of Klamath River

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.[1] Estuaries are often associated with high levels of 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.

Contents

Estuary circulation

River Exe estuary
River Nith estuary
Estuary mouth located in Darwin, Northern Territory, Australia
Estuary mouth
Río de la Plata estuary

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.[2]

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.

Large estuaries, like Chesapeake Bay and the Gulf of St. Lawrence, often have many streams flowing into them and can have complex shapes. Where an enormous volume of river water enters the sea (as, for example, from the Amazon into the South Atlantic) its estuary could be considered to extend well beyond the coast.

Types of estuary

Estuaries can be grouped by circulation.

Grouped by structure rather than circulation, there are other types of estuaries.

Human impacts

Of the 32 largest cities in the world, 22 are located on estuaries.[5] For example, New York is located at the mouth of the Hudson River estuary.[6]

As ecosystems, estuaries are under threat from human activities such as pollution and overfishing. Estuaries are impacted by events far upstream, and concentrate materials such as pollutants and sediments[7]. Land run-off and industrial, agricultural, and domestic waste enter rivers and are discharged into estuaries. Contaminants can be introduced which do not disintegrate rapidly in the marine environment, such as plastics, pesticides, furans, dioxins, phenols and heavy metals.

Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation. They also accumulate in benthic environments, such as estuaries and bay muds: a geological record of human activities of the last century.

For example, Chinese and Russian industrial pollution, such as phenols and heavy metals, in the Amur River have devastated fish stocks and damaged its estuary soil.[8]

Estuaries tend to be naturally eutrophic because land runoff discharges nutrients into estuaries. With human activities, land run-off also now includes the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. Excess oxygen depleting chemicals in the water can lead to hypoxia and the creation of dead zones.[9] It can result in reductions in water quality, fish, and other animal populations.

Over fishing also occurs. Chesapeake Bay, North America's second largest estuary, once had a flourishing oyster population which has been almost wiped out by overfishing. Historically the oysters filtered the estuary's entire water volume of excess nutrients every three or four days. Today that process takes almost a year,[10] and sediment, nutrients, and algae can cause problems in local waters. Oysters filter these pollutants, and either eat them or shape them into small packets that are deposited on the bottom where they are harmless.

See also

Sister project Wikimedia Commons has media related to: Estuaries
Sister project Look up estuary in
Wiktionary, the free dictionary.
The Moore River estuary, a seasonally closed estuary in Western Australia

Notes

  1. ^ Pritchard, D. W. (1967) What is an estuary: physical viewpoint. p. 3–5 in: G. H. Lauf (ed.) Estuaries, A.A.A.S. Publ. No. 83, Washington, D.C.
  2. ^ Tomczak, M (2000) Oceanography Notes Ch. 15: The flushing time. Retrieved 17 August 2008.
  3. ^ Tomczak, M (2000) 'Oceanography Notes Ch. 12: Estuaries. Retrieved 30 November 2006.
  4. ^ 'Types of Estuaries: Based on Geology'[dead link] . Retrieved on 1 December 2006.
  5. ^ Ross (1995)
  6. ^ NOAA Estuaries tutorial Revised March 25, 2008
  7. ^ G.Branch, Estuarine vulnerability and ecological impacts, TREE vol. 14, no. 12 Dec. 1999
  8. ^ 'Indigenous Peoples of the Russian North, Siberia and Far East: Nivkh' by Arctic Network for the Support of the Indigenous Peoples of the Russian Arctic]
  9. ^ Gerlach: Marine Pollution, Springer, Berlin (1975)
  10. ^ 'Oyster Reefs: Ecological importance'. US National Oceanic and Atmospheric Administration. Retrieved on 2008-01-16.

References

v • d • e
Aquatic ecosystems
Marine ecosystem
Freshwater ecology
v • d • e
Subfields of physical geography
Retrieved from 'http://en.wikipedia.org/Estuary'

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CAPE MAY: Third Delaware Estuary Science and Environmental Summit to be held this weekend (Daily Journal)The Partnership for the Delaware Estuary will host its third Delaware Estuary Science and Environmental Summit from Jan. 11 to 14, at the Grand Hotel in Cape May.
Murrells Inlet 2007 sets up agenda with playsite (The Myrtle Beach Sun News)The Murrells Inlet 2007 community revitalization group is looking toward adding an educational playsite for children at Morse Park, adding diversity to its board of directors and working on declaring the creek an estuary under the federal government's National Estuary Protection Program.
Nature Conservancy backs Delta canal, with conditions (The Sacramento Bee) One of the nation's largest environmental groups has decided to support building a controversial new water canal around the Sacramento-San Joaquin Delta. In a statement expected today, the Nature Conservancy calls a canal diverting the Sacramento River around the Delta an "essential component" to restore the estuary and protect water supplies. It thus becomes the first major environmental ...
Big freeze hits Barnstaple (North Devon Gazette & Advertiser)THE big freeze drew scores of photographers onto the banks of the river Taw this morning (Wednesday) as overnight temperatures lower than minus seven began to freeze the estuary for the first time this century.
Storm decimates estuary fish (Pretoria News)Hundreds of fish have died in the Isipingo estuary outside Durban after a thunderstorm. On Tuesday, swollen fish, some with bulging eyes and bellies which had burst open, were floating on the surface of the water.
Group sues to force EPA to clean up Chesapeake Bay (AP via Yahoo! News) A conservation group is suing to force the U.S. Environmental Protection Agency to enforce the law and clean up the polluted Chesapeake Bay, citing 25 years of failure to restore the nation's largest estuary.
Plan a Peninsula parlay to make most of visit to Sportsmen's Expo (San Francisco Chronicle)With the Sportsmen's Expo in town, there is no better chance for a two-for-one, to parlay a morning adventure with a trip to the show in the afternoon. Here are five getaways within close range of the San Mateo Event Center: Coyote Point Recreation Area: For...
Free food to promote ecotourism (Thaipr.net)It sustains life and it is certainly a pleasure very few can deny so it kind of makes sense to celebrate the simple task of eating. Villagers in La Un district, some 80 km northeast of Ranong provinc
‘First Mondays’ discusses obstacles facing Everglades restoration, U.S. Sugar purchase (Captiva Current)During the Sanibel-Captiva Conservation Foundation’s “First Mondays: Policy at SCCF” presentation for the month of January, SCCF Natural Resource Policy Director Rae Ann Wessel continued her series on the essentials for the restoration of South Florida’s rivers, lakes and the Everglades by focusing the discussion how to remove obstacles in order to restore flow in the Everglades and how the U.S. ...
Cumberland, Salem area need $19 million environmental fix (Press of Atlantic City)STOW CREEK TOWNSHIP - State officials want to spend more than $19 million to restore and create wetlands and grasslands near the Stow Creek to compensate for ecological damages from a 2004 oil spill.

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