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.
Garabogazkol lagoon in Turkmenistan Kara-Bogaz Gol from space, September 1995.jpg
Garabogazköl lagoon in Turkmenistan
Venetian Lagoon Venice Lagoon December 9 2001.jpg
Venetian Lagoon

A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into coastal lagoons (or barrier 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.

Definition and terminology

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] Coastal lagoons are classified as inland bodies of water. [6] [7]

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. [8]

Many lagoons do not include "lagoon" in their common names. Currituck, 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, US, [12] Lake Illawarra in New South Wales, Australia, [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 Chinese a lake is hu (), and a lagoon is xihu (潟湖). In the French Mediterranean several lagoons are called étang ("lake"). 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 . 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 , as well as generic terms derived from laguna. In Poland these lagoons are called zalew ("bay"), in Lithuania marios ("lagoon, reservoir"). In Jutland several lagoons are known as fjord . In New Zealand the Māori word hapua refers to a coastal lagoon formed at the mouth of a braided river where there are mixed sand and gravel beaches, while waituna , an ephemeral coastal waterbody, is neither a true lagoon, lake nor estuary. [15]

Some languages differentiate between coastal and atoll lagoons. In French, lagon  [ fr ] refers specifically to an atoll lagoon, while coastal lagoons are described as étang  [ 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.

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, a similar usage is found: lagoa may be a body of shallow seawater, 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 Venetian Lagoon. 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. [16]

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 (>20 m (66 ft)) portions.

Coastal lagoons

Anzali Lagoon in southwestern Caspian Sea coast, Iran Caspian Sea covered with plants near Bandar-e Anzali - 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 offshore, 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 underwater 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] Lake Chilika is the largest brackish water lagoon in Asia and the second largest coastal lagoon in the world.

Largest coastal lagoons

Lagoonsquare kilometerCountry
New Caledonian lagoon 24,000 km2 (9,300 sq mi)Flags of New Caledonia.svg  New Caledonia
Garabogazköl 18,000 km2 (6,900 sq mi)Flag of Turkmenistan.svg  Turkmenistan
Lake Maracaibo 13,512 km2 (5,217 sq mi)Flag of Venezuela.svg  Venezuela
Lagoa dos Patos 10,100 km2 (4,000 sq mi)Flag of Brazil.svg  Brazil
Albemarle-Pamlico sound system7,800 km2 (3,000 sq mi)Flag of the United States.svg  United States
Lagos Lagoon 6,354.7 km2 (2,453.6 sq mi)Flag of Nigeria.svg  Nigeria
Curonian lagoon 1,619 km2 (625 sq mi)Flag of Lithuania.svg  Lithuania /Flag of Russia.svg  Russia
Mayotte lagoon ~1,500 km2 (600 sq mi)Flag of France.svg  France
Rangiroa lagoon 1,446 km2 (600 sq mi)Flag of French Polynesia.svg  French Polynesia
Chilika Lake 1,165 km2 (450 sq mi) during monsoon season, 906 km2 (350 sq mi) during dry seasonFlag of India.svg  India
Indian River Lagoon 910 km2 (353 sq mi) [17] Flag of the United States.svg  United States
Vistula lagoon 838 km2 (324 sq mi)Flag of Russia.svg  Russia /Flag of Poland.svg  Poland
Biscayne Bay System
—Biscayne Bay (traditional)
703 km2 (271 sq mi) [18]
572 km2 (221 sq mi) [19]
Flag of the United States.svg  United States
Marovo lagoon 700 km2 (270 sq mi)Flag of the Solomon Islands.svg  Solomon Islands
Szczecin Lagoon 689 km2 (266 sq mi)Flag of Germany.svg  Germany / Flag of Poland.svg  Poland
Venetian lagoon 550 km2 (210 sq mi)Flag of Italy.svg  Italy

Images

See also

Related Research Articles

<span class="mw-page-title-main">Fjord</span> Long, narrow inlet with steep sides or cliffs, created by glacial activity

In physical geography, a fjord or fiord is a long, narrow sea inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Antarctica, the Arctic, and surrounding landmasses of the northern and southern hemispheres. Norway's coastline is estimated to be 29,000 km (18,000 mi) long with its nearly 1,200 fjords, but only 2,500 km (1,600 mi) long excluding the fjords.

<span class="mw-page-title-main">Estuary</span> Partially enclosed coastal body of brackish water

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. Estuaries form a transition zone between river environments and maritime environments and are an example of an ecotone. Estuaries are subject both to marine influences such as tides, waves, and the influx of saline water, and to fluvial influences such as flows of freshwater and sediment. The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.

<span class="mw-page-title-main">Coral reef</span> 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.

<span class="mw-page-title-main">Shoal</span> Natural submerged sandbank that rises from a body of water to near the surface

In oceanography, geomorphology, and geoscience, 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 close to the surface or above it, which poses 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.

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<span class="mw-page-title-main">Spit (landform)</span> Coastal bar or beach landform deposited by longshore drift

A spit or sandspit is a deposition bar or beach landform off coasts or lake shores. It develops in places where re-entrance occurs, such as at a cove's headlands, by the process of longshore drift by longshore currents. The drift occurs due to waves meeting the beach at an oblique angle, moving sediment down the beach in a zigzag pattern. This is complemented by longshore currents, which further transport sediment through the water alongside the beach. These currents are caused by the same waves that cause the drift.

<span class="mw-page-title-main">Barrier island</span> Coastal dune landform that forms by wave and tidal action parallel to the mainland coast

Barrier islands are a coastal landform, a type of dune system and sand island, where an area of sand has been formed 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 for hundreds of kilometers, with islands periodically separated by tidal inlets. The largest barrier island in the world is Padre Island of Texas, United States, at 113 miles (182 km) long. Sometimes an important inlet may close permanently, transforming an island into a peninsula, thus creating a barrier peninsula, often including a beach, barrier beach. Though many are long and narrow, 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.

<span class="mw-page-title-main">Inlet</span> Indentation of a shoreline

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<span class="mw-page-title-main">Biscayne Bay</span> Florida lagoon

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<span class="mw-page-title-main">Gulf of Honduras</span> A large inlet of the Caribbean Sea, indenting the coasts of Belize, Guatemala, and Honduras.

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<span class="mw-page-title-main">Lake Worth Lagoon</span> Lagoon in Florida, US

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References

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