Lagoon

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Balos coastal lagoon of northwestern Crete. The shallow lagoon is separated from the Mediterranean sea by narrow shoals connecting to a small, rocky mountain. BalosLagoonCreta.jpg
Balos coastal lagoon of northwestern Crete. The shallow lagoon is separated from the Mediterranean sea by narrow shoals connecting to a small, rocky mountain.
Garabogaz-Gol lagoon in Turkmenistan Kara-Bogaz Gol from space, September 1995.jpg
Garabogaz-Göl lagoon in Turkmenistan
Venice Lagoon Venice Lagoon December 9 2001.jpg
Venice Lagoon

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Contents

Definition

Lagoon vs. estuary

Lagoons are shallow, often elongated bodies of water separated from a larger body of water by a shallow or exposed shoal, coral reef, or similar feature. Some authorities include fresh water bodies in the definition of "lagoon", while others explicitly restrict "lagoon" to bodies of water with some degree of salinity. The distinction between "lagoon" and "estuary" also varies between authorities. Richard A. Davis Jr. restricts "lagoon" to bodies of water with little or no fresh water inflow, and little or no tidal flow, and calls any bay that receives a regular flow of fresh water an "estuary". Davis does state that the terms "lagoon" and "estuary" are "often loosely applied, even in scientific literature." [1] Timothy M. Kusky characterizes lagoons as normally being elongated parallel to the coast, while estuaries are usually drowned river valleys, elongated perpendicular to the coast. [1] [2] [3] [4] [5]

When used within the context of a distinctive portion of coral reef ecosystems, the term "lagoon" is synonymous with the term "back reef" or "backreef", which is more commonly used by coral reef scientists to refer to the same area. [6] Coastal lagoons are classified as inland bodies of water. [7] [8]

Names

Many lagoons do not include "lagoon" in their common names. Albemarle and Pamlico sounds in North Carolina, [9] Great South Bay between Long Island and the barrier beaches of Fire Island in New York, [10] Isle of Wight Bay, which separates Ocean City, Maryland from the rest of Worcester County, Maryland, [11] Banana River in Florida, [12] Lake Illawarra in New South Wales, [13] Montrose Basin in Scotland, [14] and Broad Water in Wales have all been classified as lagoons, despite their names. In England, The Fleet at Chesil Beach has also been described as a lagoon.

In some languages the word for a lagoon is simply a type of lake: In Turkish, a lake is göl, a lagoon is gölcük. Similarly, in Chinese a lake is hu (湖), a lagoon is xihu. (潟湖)

Contrariwise, several other languages have specific words for such bodies of water. In  Spanish, coastal lagoons generically are laguna costera, but those on the Mediterranean coast are specifically called albufera (es): In Russian and Ukrainian those on the Black Sea are liman (лиман), while the generic word is laguna (Лагуна). Similarly, in the Baltic, Danish has the specific Nor (da), and German the specifics Bodden and Haff (de), as well as generic terms derived from laguna. In New Zealand the Maori word hapua refers to a coastal lagoon formed at the mouth of a braided river where there is mixed sand and gravel beaches, while the word waituna is the more general term.

Some languages differentiate between coastal and atoll lagoons: In French, lagon(fr) refers specifically to an atoll lagoon, while coastal lagoons are described as etang(fr), the generic word for a still lake or pond. In Vietnamese, Đầm san hô refers to an atoll lagoon, whilst Đầm phá is coastal.

Latin American laguna

In Latin America, the term laguna in Spanish, which lagoon translates to, may be used for a small fresh water lake in a similar way a creek is considered a small river. However, sometimes it is popularly used to describe a full-sized lake, such as Laguna Catemaco in Mexico, which is actually the third largest lake by area in the country. The brackish water lagoon may be thus explicitly identified as a "coastal lagoon" (laguna costera). In Portuguese the same usage is found: lagoa may be a body of shallow sea water, or a small freshwater lake not linked to the sea.

Etymology

Lagoon is derived from the Italian laguna, which refers to the waters around Venice, the Lagoon of Venice. Laguna is attested in English by at least 1612, and had been Anglicized to "lagune" by 1673. In 1697 William Dampier referred to a "Lagune or Lake of Salt water" on the coast of Mexico. Captain James Cook described an island "of Oval form with a Lagoon in the middle" in 1769. [15]

Atoll lagoons

Satellite picture of the Atafu atoll in Tokelau in the Pacific Ocean Atafutrim.jpg
Satellite picture of the Atafu atoll in Tokelau in the Pacific Ocean

Atoll lagoons form as coral reefs grow upwards while the islands that the reefs surround subside, until eventually only the reefs remain above sea level. Unlike the lagoons that form shoreward of fringing reefs, atoll lagoons often contain some deep (>20m) portions.

Coastal lagoons

Anzali Lagoon in southwestern Caspian Sea coast, Iran Anzali lagoon Barry Kent.jpg
Anzali Lagoon in southwestern Caspian Sea coast, Iran
Coastal lagoon landscapes around the island of Hiddensee near Stralsund, Germany. Many similar coastal lagoons can be found around the Western Pomerania Lagoon Area National Park. Hiddensee (2011-05-21).JPG
Coastal lagoon landscapes around the island of Hiddensee near Stralsund, Germany. Many similar coastal lagoons can be found around the Western Pomerania Lagoon Area National Park.

Coastal lagoons form along gently sloping coasts where barrier islands or reefs can develop off-shore, and the sea-level is rising relative to the land along the shore (either because of an intrinsic rise in sea-level, or subsidence of the land along the coast). Coastal lagoons do not form along steep or rocky coasts, or if the range of tides is more than 4 metres (13 ft). Due to the gentle slope of the coast, coastal lagoons are shallow. A relative drop in sea level may leave a lagoon largely dry, while a rise in sea level may let the sea breach or destroy barrier islands, and leave reefs too deep under water to protect the lagoon. Coastal lagoons are young and dynamic, and may be short-lived in geological terms. Coastal lagoons are common, occurring along nearly 15 percent of the world's shorelines. In the United States, lagoons are found along more than 75 percent of the Eastern and Gulf coasts. [3] [4]

Coastal lagoons are usually connected to the open ocean by inlets between barrier islands. The number and size of the inlets, precipitation, evaporation, and inflow of fresh water all affect the nature of the lagoon. Lagoons with little or no interchange with the open ocean, little or no inflow of fresh water, and high evaporation rates, such as Lake St. Lucia, in South Africa, may become highly saline. Lagoons with no connection to the open ocean and significant inflow of fresh water, such as the Lake Worth Lagoon in Florida in the middle of the 19th century, may be entirely fresh. On the other hand, lagoons with many wide inlets, such as the Wadden Sea, have strong tidal currents and mixing. Coastal lagoons tend to accumulate sediments from inflowing rivers, from runoff from the shores of the lagoon, and from sediment carried into the lagoon through inlets by the tide. Large quantities of sediment may be occasionally be deposited in a lagoon when storm waves overwash barrier islands. Mangroves and marsh plants can facilitate the accumulation of sediment in a lagoon. Benthic organisms may stabilize or destabilize sediments. [3] [4]

Images

See also

Related Research Articles

Atoll Ring-shaped coral reef

An atoll, sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. The coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the water. The lagoon forms over the volcanic crater or caldera while the higher rim remains above water or at shallow depths that permit the coral to grow and form the reefs. For the atoll to persist, continued erosion or subsidence must be at a rate slow enough to permit reef growth upward and outward to replace the lost height.

Estuary Partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea

An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.

Coral reef Outcrop of rock in the sea formed by the growth and deposit of stony coral skeletons

A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.

Reef A bar of rock, sand, coral or similar material, lying beneath the surface of water

A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, etc.—but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae.

Shoal A natural landform that rises from the bed of a body of water to near the surface and is covered by unconsolidated material

In oceanography, geomorphology, and earth sciences, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water to near the surface. Often it refers to those submerged ridges, banks, or bars that rise near enough to the surface of a body of water as to constitute a danger to navigation. Shoals are also known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex.

Barrier island A coastal dune landform that forms by wave and tidal action parallel to the mainland coast

Barrier islands are coastal landforms and a type of dune system that are exceptionally flat or lumpy areas of sand that form by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen. They are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. A barrier chain may extend uninterrupted for over a hundred kilometers, excepting the tidal inlets that separate the islands, the longest and widest being Padre Island of Texas. The length and width of barriers and overall morphology of barrier coasts are related to parameters including tidal range, wave energy, sediment supply, sea-level trends, and basement controls. The amount of vegetation on the barrier has a large impact on the height and evolution of the island.

Inlet An indentation of a shoreline that often leads to an enclosed body of salt water, such as a sound, bay, lagoon, or marsh

An inlet is an indentation of a shoreline, usually long and narrow, such as a small bay or arm, that often leads to an enclosed body of salt water, such as a sound, bay, lagoon, or marsh.

Lake Illawarra lake in New South Wales, Australia

Lake Illawarra, an open and trained intermediate wave dominated barrier estuary or large coastal lagoon, is located in the Illawarra region of New South Wales, situated about 100 kilometres (62 mi) south of Sydney, Australia.

Gulf of Honduras A large inlet of the Caribbean Sea, indenting the coasts of Belize, Guatemala, and Honduras.

The Gulf or Bay of Honduras is a large inlet of the Caribbean Sea, indenting the coasts of Belize, Guatemala, and Honduras. From north to south, it runs for approximately 200 km from Dangriga, Belize, to La Ceiba, Honduras.

Body of water Any significant accumulation of water, generally on a planets surface

A body of water or waterbody is any significant accumulation of water, generally on a planet's surface. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such as ponds, wetlands, or more rarely, puddles. A body of water does not have to be still or contained; rivers, streams, canals, and other geographical features where water moves from one place to another are also considered bodies of water.

Bombetoka Bay

Bombetoka Bay is a bay on the northwestern coast of Madagascar near the city of Mahajanga, where the Betsiboka River flows into the Mozambique Channel. Numerous islands and sandbars have formed in the estuary from the large amount of sediment carried in by the Betsiboka River and have been shaped by the flow of the river and the push and pull of tides

Marine ecosystem Ecosystem in saltwater environment

Marine ecosystems are the largest of Earth's aquatic ecosystems and are distinguished by waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Marine ecosystems include nearshore systems, such as the salt marshes, mudflats, seagrass meadows, mangroves, rocky intertidal systems and coral reefs. They also extend outwards from the coast to include offshore systems, such as the surface ocean, pelagic ocean waters, the deep sea, oceanic hydrothermal vents, and the sea floor. Marine ecosystems are characterized by the biological community of organisms that they are associated with and their physical environment.

Fringing reef Type of coral reef

A fringing reef is one of the three main types of coral reef recognized by most coral reef scientists. It is distinguished from the other main types in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows directly from the shoreline the reef flat extends right to the beach and there is no backreef. In other cases, fringing reefs may grow hundreds of yards from shore and contain extensive backreef areas with numerous seagrass meadows and patch reefs.

Coastal fish

Coastal fish, also called inshore fish or neritic fish, inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than 200 metres deep, it follows that pelagic coastal fish are generally epipelagic fish, inhabiting the sunlit epipelagic zone. Coastal fish can be contrasted with oceanic fish or offshore fish, which inhabit the deep seas beyond the continental shelves.

A tidal prism is the volume of water in an estuary or inlet between mean high tide and mean low tide, or the volume of water leaving an estuary at ebb tide.

Marine habitats A habitat that supports marine life

Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea. A habitat is an ecological or environmental area inhabited by one or more living species. The marine environment supports many kinds of these habitats.

Estuaries of Australia are features of the Australian coastline. They are linked to tides, river mouths and coastal features and conditions. In many cases the features of estuaries are also named inlets.

Estuaries of Texas Estuaries on the Gulf coast of Texas

The U.S. state of Texas has a series of estuaries along its coast on the Gulf of Mexico, most of them bounded by the Texas barrier islands. Estuaries are coastal bodies of water in which freshwater from rivers mixes with saltwater from the sea. Twenty-one drainage basins terminate along the Texas coastline, forming a chain of seven major and five minor estuaries: listed from southwest to northeast, these are the Rio Grande Estuary, Laguna Madre, the Nueces Estuary, the Mission–Aransas Estuary, the Guadalupe Estuary, the Colorado–Lavaca Estuary, East Matagorda Bay, the San Bernard River and Cedar Lakes Estuary, the Brazos River Estuary, Christmas Bay, the Trinity–San Jacinto Estuary, and the Sabine–Neches Estuary. Each estuary is named for its one or two chief contributing rivers, excepting Laguna Madre, East Matagorda Bay, and Christmas Bay, which have no major river sources. The estuaries are also sometimes referred to by the names of their respective primary or central water bodies, though each also includes smaller secondary bays, inlets, or other marginal water bodies.

References

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  11. "Total Maximum Daily Loads for the North and Central Indian River Lagoon and Banana river Lagoon, Florida" (PDF). United States Environmental Protection Agency. Retrieved 24 March 2012.
  12. "Proposed Swimming Enclosure Net, Entrance Lagoon, Lake Illawarra" (PDF). Lake Illawarra Authority. Archived from the original (PDF) on 28 February 2011. Retrieved 24 March 2012.
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