Balos coastal lagoon of northwesternCrete. The shallow lagoon is separated from the Mediterranean Sea by narrow shoals connecting to a small, rocky mountain.Garabogazköl lagoon inTurkmenistanVenetian Lagoon
Alagoon is a shallowbody of water separated from a larger body of water by a narrowlandform, such asreefs,barrier islands, barrier peninsulas, oristhmuses. Lagoons are commonly divided intocoastal lagoons (orbarrier lagoons) andatoll 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 asestuaries. Lagoons are common coastal features around many parts of the world.
Lagoons are shallow, often elongated bodies of water separated from a larger body of water by a shallow or exposedshoal,coral reef, or similar feature. Some authorities includefresh water bodies in the definition of "lagoon", while others explicitly restrict "lagoon" to bodies of water with some degree ofsalinity. 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 notidal flow, and calls anybay 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]
In some languages the word for a lagoon is simply a type of lake: In Chinese a lake ishu (湖), and a lagoon isxihu (潟湖). In theFrench Mediterranean several lagoons are calledétang ("lake"). Contrariwise, several other languages have specific words for such bodies of water. In Spanish, coastal lagoons generically arelaguna costera, but those on the Mediterranean coast are specifically calledalbufera. In Russian and Ukrainian, those on theBlack Sea areliman (лиман), while the generic word islaguna (Лагуна). Similarly, in theBaltic, Danish has the specificNor [da], and German the specificsBodden andHaff, as well as generic terms derived fromlaguna. In Poland these lagoons are calledzalew ("bay"), and in Lithuaniamarios ("lagoon, reservoir"). InJutland several lagoons are known asfjord. InNew Zealand theMāori wordhapua refers to a coastal lagoon formed at the mouth of abraided river where there are mixed sand and gravel beaches, whilewaituna, anephemeral 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 asétang [fr], the generic word for a still lake or pond.In Vietnamese,Đầm san hô refers to an atoll lagoon, whilstĐầm phá is coastal.
In Latin America, the termlaguna in Spanish, which lagoon translates to, may be used for a small fresh waterlake in a similar way acreek is considered a small river. However, sometimes it is popularly used to describe a full-sizedlake, such asLaguna Catemaco in Mexico, which is actually the third-largest lake by area in the country. Thebrackish 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.
Lagoon is derived from theItalianlaguna, which refers to the waters aroundVenice, theVenetian Lagoon.Laguna is attested in English by at least 1612, and had beenAnglicized to "lagune" by 1673. In 1697William 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 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 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, orsubsidence 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 theEastern andGulf Coasts.[3][4]
Coastal lagoons can be classified as leaky, restricted, or choked.[17]Coastal lagoons are usually connected to the open ocean byinlets 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 asLake St. Lucia, inSouth Africa, may become highly saline. Lagoons with no connection to the open ocean and significant inflow of fresh water, such as theLake 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 theWadden 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 andmarsh plants can facilitate the accumulation of sediment in a lagoon.Benthic organisms may stabilize or destabilize sediments.[3][4]
^abcNybakken, James W., ed. (2003). "Lagoon".Interdisciplinary Encyclopedia of Marine Sciences. Vol. 2 G-O. Danbury, Connecticut: Grolier Academic Reference. pp. 189–90.ISBN0-7172-5946-3.
^Kirk, R.M. and Lauder, G.A (2000).Significant coastal lagoon systems in the South Island, New Zealand: coastal processes and lagoon mouth closure. Wellington, N.Z.:Department of Conservation.ISBN0-478-21947-4.{{cite book}}: CS1 maint: multiple names: authors list (link)
^"Lagoon".Oxford English Dictionary. Vol. I A-O (Compact ed.). Oxford, England: Oxford University Press. 1971. p. 1560.
^Smith, Ned P. (Summer 2001). "Tides of Biscayne Bay, Card Sound, Little Card Sound, Barnes Sound, and Manatee Bay, Florida".Florida Scientist.64: 224.JSTOR24321024.
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