See also: Estuary (homonymy)

The estuary is the portion of the mouth of a Fleuve where the effect of the Mer or Océan in which it is thrown is perceptible. This definition leads to a controversy. Thus some defend the idea that the estuary of a Fleuve is all the portion where the Eau is salted, or brackish only. For the others, it is the dynamic effect of the Marée on river water which must be taken into account. Sometimes separation between the maritime zone and river has various definitions, conflict and variable according to the times. The estuary is a moving écotone whose limits are of delicate appreciation. They are generally appreciated on the analysis of the movement of the water masses fresh and salted, on the basis of principal and/or average flood of the tide. By convention, one does not speak about estuaries for the rivers which throw in closed seas (Black Sea, for example).

Each estuary is a dynamic and single system physical and ecological, including wetlands, meanders and/or deltas unceasingly reorganized with the liking of the currents, suspended matter loads brought by the river, and according to the nature of the geological context and the Bassin pouring, the climate, the winds and the historical and contemporary human interventions. The estuary is also the place where the force of the river is slowed down. Certain pollutants form a deposit there preferentially and can concentrate there.

For needs commercial, military, maritime, agricultural, halieutics or sedentary, since thousand-year-old or secular times, ports, channels, channels, adjustments of stabilizations, drainage and draining, alluvial deposits or installation conchylaceous or huntings modified volumes and the profiles of them transversely and longitudinally.

The Man sought to control the estuaries by fixing some the banks and the channels, by building there expensive dams, sometimes immersed. With this intention it mobilized sciences naturalists, like mathematics (modeling) and physics (dynamics of the fluids and materials). For a few decades, social sciences and economic have been also called by the developers, in particular to solve the conflicts of uses there (drives out, fishing, tourism, walk, leisures, water sport, deep-sea diving, fishing with foot, port activities, etc).

It is only the ecosystem where the altimetric modification of the twice-daily watermark varies in time and space, at the same time as the Salinité and the Turbidité. One finds there species marine, fresh water species and endemic species with the estuaries. When pollution and surpêche do not overexploit it, the biomass produced there is exceptionally important. The estuaries are in the beginning many food chains, and are an irreplaceable zone of reproduction and nourrissage for many species. Sometimes, the sedimentary rich person deltas were dedicated to the culture (Delta of the Nile, Bengladesh, the Camargue in France…)

All alteration work downstream or upstream can have an impact differed in space and time, on flows, the currents, the Vasière S, the Sédimentation, the movement and the importance or the quality of the muddy stopper and sometimes on the safety of the users.

Etymology

Resulting from Latin aestuare , the word appears in France as of the 15th century at least, but it appears in the dictionaries only in the 18th century. The Spanish word estuario resulted not in estuary but by “ bars” (word indicating the wave created by the meeting of the wave of the downward river and the tide).

Lat. aestuarium, of aestus, flow of the sea: place where flow penetrates, but also term of Roman antiquity: maritime pond where fish was nourished. HTTP: /colet.uchicago.edu/cgi-bin/dico1look.pl?strippedhw=estuaire

Muddy stopper

Zone of maximum turbidity (maximum turbidity zone or MTZ for the Anglo-Saxons) which appears in the systems estuariens, the muddy stopper is created by the meeting of fresh water charged with suspended matter and nutrients in solution and of salted marine water. It migrates at the rate/rhythm of the tides, but its size and its position evolve/move according to hydrological conditions clean with the estuary (temperature, sunning, flows, cycles of tide, pollution), but also according to the human practices or of the natural evolution of the catchment area, very upstream (snow melts, rains intense, renaturation or on the contrary proofing and/or husbandries erosive and forest (ploughings, weeding, close-cropped cuts…), pollution, work of clearing out… which exacerbate the content of water of nutrients, matter organic, suspended matter, etc).

The muddy stopper constitutes one (éco) completely particular system, often seriously disturbed by the human activities, because of an excessive quantity of eutrophisant S, matter organic, Pesticide S and other pollutants adsorbed on the suspended particles or solubilized in water, to some extent protected from a fast decomposition by the light or the native oxygen produced by the Phytoplancton.

The muddy stopper was studied little until in the years 1980, but since, of many studies showed that it was naturally important for the biological productivity of the estuaries, very high, but that because of human disturbances in particular, it can become a degraded zone and contribute to the marine dead zones, and become a very important source of emission of CO2 and CH4, two gases with greenhouse effect of major importance.

Particular ecosystems

The estuariens mediums characterized by important Marling S, currents sometimes violent one are nevertheless rich in biomass (ex: up to 1 million larvae of hulls per m ² in Bay of Somme) and a total productivity estimated at least 30 tons/hectare for the small estuaries in moderate climate. They can be subjected to various pollution which degrades these resources (pesticides, heavy metals or nitrates for example).

The protection of the estuaries implies a quantitative and qualitative management of water on a basin whole slopes scale. Certain activities were prohibited (example there: the pétardage of the Chemical weapons, not-exploded or stored of the two First World Wars). Several tens of small European estuaries are concerned with the proximity of old deposits of immersed ammunition likely to pollute them by nitrates, mercury, lead, copper, etc, if it is not of the poisons of war of the Ypérite type, chloropicrin.

The intertidal mediums are écotone S private individuals, whose Slikke and Schorre is the two main components in continental zone, replaced by the Mangrove in tropical zone.

  • the Slikke is the stage low: exposed to the sea, muddy zone immersed with each tide, apparently poor, it shelters an intense life, primarily macro-invertebrates and micro-organisms. The lowone, mouthful of water, accommodates plants Phanérogame S rare (reduced to the Zostère S). The highone, it, is covered with Salicorne S and Spartine S (graminaceous hard resistant to salt).

  • the Schorre is submerged only with the spring tides and at the time of the storms, but it is exposed to the spray. It shelters Graminée S constituting the salted Prés and a vegetation all the more varied since the fresh water is present.

the low-salt meadow is a medium of transition still accommodating species from high the slikke which mix with the glycery and to the maritime Aster.
the means-salt meadow accommodates the false-pourpier obione (sub-shrub with the persistent sheets) evolving/moving to the top salt meadow enriched by maritime statice (lavender of sea), maritime Plantain, with still the maritime aster and the glycery. Coleopter S, Dipterous, Collembole S supplements the fauna of the Crustacé S of the edges of slikke, which nourish many birds (Laridés (gulls and seagulls), Limicole S, geese Bernache S, ducks, Héron S with low tide and plunger birds piscivorous (grèbes) or malacophages (Eider S, Macreuse S) with high tide.

The estuaries are places of laying or enlargement for unquestionable fish (Sole and Plie). The majority of the Amphibien S flee the salted zones, except in Europe the punctuated Pélodyte and the Crapaud calamite.

Estuaries and Greenhouse effect

One thought formerly because of their rich person productivity (> 30 T/ha/an) that the estuaries were carbon wells, but when the estuary is eutrophized or dystrophe, of the emissions of CO2 and CH4 can take place, in very large quantities starting from the Sédiment S and of the muddy Bouchon, the night in particular, like showed it a series of study having carried on more than 30 European estuaries. But the Protocole of Kyoto did not take into account these emissions which could however correspond for Europe to 8% of the total of the emissions of Gaz to greenhouse effect of this area of the world.

Particular legal entities

The estuaries, which in are crossed mediums (salted water and, air and grounds, rivers and seas), are concerned with many policies and regulations: maritime and halieutic, harbor, of transport, town and country planning, the littoral, environment, in particular.

Biogeographic or administrative limits?

According to the criteria selected (geomorphological, biological, landscape or of navigability…) and their update, the limits of the estuaries differ. This presents complex legal problems, for example for the regulation of the fishing or the definition of the zones concerned with the Loi littoral or Natura 2000.

Longitudinally, the estuary can extend to the zone from influence from the Marée S (maximum or average tide). Transversely, the estuary as an ecological and landscape entity integrates the adjacent mediums, of which generally wetlands, and, according to the contexts, a more or less significant part of the major beds and historical and geological minor beds, even the whole of the Bassin pouring when it is small.

Generally, the principal administrative limits are transverse limits, with for example in France:

  • transverse limit of the sea (LTM, cf decree n°2004-309 of March 29th, 2004 in French right): it is sometimes a geographical and/or cultural limit clearly identified on charts and by fixed physical reference marks (headlight, course, top.). It is sometimes an arbitrary limit, without physical or socio-economic base, selected because of a complex or moving cutting of the coasts. It is sometimes fixed rather far inside estuaire.
    La LTM thus distinguishes in France the maritime Public domain and the river Public domain or the private field from the residents if the river is not domanial. It is also used as reference to determine the bordering communes of the sea within the meaning of the law littoral;
  • limit of salinity of water (Them), often used to regulate maritime fishing and hunting and in France (Law littoral of 1986) for the delimitation of the estuariennes communes and the field of intervention of the Conservatory of littoral space and the lake shores.
    En France, decree 75-293 regulates the exploitation of hunting on the maritime Public domain and the part of the domanial river located at the downstream of the limit of salinity of water. It is thus a lawful limit concerning the management of the alive species;
  • limit of the maritime inscription : it corresponds (in France) to the first physical obstacle with sea transport on the river. With its upstream, navigation is river . It is downstream maritime . This limit merges for certain rivers with the limit of their mouth (LTM). It tallies with certain regulations of sea and river transport or with the exercise and the statute of fishing in estuary;
  • limit of the face of salinity : defined by the zone where average salinity on the surface is higher or equal to 1 ‰.
    Cette notion results in France of the law on the water from 1992 which imposes a procedure of authorization or declaration for the installations, works, work or activities having an important influence on the aquatic environment (ex: dredgings, at sea or in zone estuarienne with the downstream of the face of salinity);
  • limiting of the water masses: these limits are defined by the Parent directive on the water (DCE), which defines a typology of the masses of continental”, “coastal”, “of transition”, “strongly modified” and “artificial” water “. The state of these water masses will have to be qualified in France in the Master development plans and of management of water (SDAGE) and, if it them ecological state is not satisfactory, of the plans of reconquest will have to be defined. This Directive can impose new limits which are not superimposed obligatorily with those, administrative, of the sea, the salinity of water, the face of salinity!

Remark : The wave front and of salinity is driven with the tides and varies according to their coefficients and the flow of the river (it is a moving écotone in space and time, which confers particular ecological characteristics to him). The Limite of the influence of the tides does not have an administrative value and can be very upstream limit of the maritime inscription. It however has a value for the developer, the resident or the ecologist.

There exist also longitudinal limits “ ” of the watery part of the estuaries or their wetlands (useful for the application of the texts which prohibits hunting for the Lead shot (cf source of Saturnisme of the water birds), only in or towards the wetlands in France).

Upstream of the transverse limit of the sea, they are the limits of the domanial rivers which count, materialized in France “by the height of water running on full board before overflowing”.

The rivers were often used as administrative borders. This is why it is current that estuaries are located on two countries, different areas, departments, cantons or districts (it is the case of the estuaries of the the Seine and the the Gironde in France which are on several departments and on two areas). This makes their management even more complex, with sometimes divergent or contradictory regulations on the two banks.

In France, the Loi littoral of 1986 defines the limit between the parts watery and terrestrial of the estuary while regarding as littoral communes, “ the bordering communes of the estuaries and the deltas when they are located downstream from the limit of salinity of water and take part in the economic equilibrium and ecological littoral ”. The decree n°2004-311 of March 19th, 2004 fixes a list of 98 bordering communes of estuaries downstream from the transverse limit of the sea, and 87 located upstream this limit and downstream from the limit of the salinity of water.

Various legal tools applicable to the estuaries

  • International conventions, of which OSPAR, Agreement on the conservation of the migrating water birds of Africa-Eurasia (AEWA),
  • EU law, of which Natura 2000 (60 estuaries approximately concerned in France) and Parent directive on water,
  • National legislations, whose Parks or communal, national or regional natural reserves,
  • More than three hundred Directives or Payments European relate to the environment, of which many can particularly relate to the estuaries.

In France :

A decree on enforcement of a law should in 2006 reform the Schéma of development of the sea (SMVM), making it possible to create a shutter SMVM in the SCOT, for an integrated approach “ground/sea/river” of the documents of territorial planning.
  • SDAGE, WISE and Conservatory contract of river
  • of the littoral and the lake shores
  • step of “Management integrated of the coastal areas” (GIZC), intended to solve or control conflicts

List principal estuaries of France

Other estuaries

See too

estuary

Bibliographical references

  • Attrill, M.J and S.D. Rundle. 2002. Ecotone gold ecocline: ecological boundaries in estuaries. Estuarine, Coastal, and Shelf Science 55:929 - 936.

Internal bonds

External bonds

  • French administrative Report/ratio on the management of the estuaries, 72 pages, May 2006
  • Acts (pdf) of the seminar of work " Estuariens" indicators; June 19th and 20th 2006 in Rouen

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