Difference between revisions of "Estuary"

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{{Definition|title= estuary
 
{{Definition|title= estuary
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|definition= A semi-enclosed littoral basin (embayment) of the coast in which fresh river water entering at its head mixes with saline water entering from the ocean. Fully developed estuarine systems consist of complex dynamic interactions between channels, tidal flats, middle ground shoals and salt marshes.
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|definition= A semi-enclosed embayment of the coast in which fresh run-off water mixes with saline water entering from the ocean. }}
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This is the definition given by Cameron and Pritchard (1963) <ref> Cameron, W. M. and D. W. Pritchard (1963) Estuaries. In M. N. Hill (editor), The Sea, Vol. 2. John Wiley & Sons, New York, pp. 306–324</ref>. However, it excludes the tidal river upstream of the seawater intrusion limit, where tidal motion can still have important consequences for ecosystem, water quality and morphology – for example: import of marine sediments and organisms, generation of a high turbidity zone, sedimentation/erosion of intertidal wetlands. 
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Estuaries are characterized by the presence of tides and a prominent system of channels and shoals (open bays and enclosed coastal seas such as the Bohai Sea or North Sea therefore do not qualify as estuaries). According to this characteristic, estuaries can also be defined as
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{{Definition|title= estuary
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|definition= Semi-enclosed inlet system where the tide propagates along channels.<br>
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The part of the estuary upstream of the seawater intrusion limit, but subject to tidal motion, is usually referred to as 'tidal river'.}}
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According to the first, more common definition, the tidal river is excluded from the estuary, but included according to the second definition. The second definition, which is closer to the etymological origin of the word estuary, includes tidal inlet systems without significant fresh water inflow, for example:
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* drowned coastal valleys;
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* tidal lagoons – drowned coastal plains semi-closed by a barrier system;
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* inverse estuaries – estuaries where evaporation exceeds fresh water inflow.
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From a morphological or ecological viewpoint, such inlet systems can be very similar to estuaries with small fresh water inflow according to the first definition.
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[[Image:DebenEstuary.JPG|thumb|700px|center|Mudflat in the Deben estuary, UK. Photo credit: Bescoe]]
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Estuaries are widely diverse and can be classified according to different criteria:<br>
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'''tidal range'''
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: microtidal: tidal range < 2 m;
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: mesotidal: tidal range 2-4 m;
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: macrotidal: tidal range > 4 m.<br>
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'''salinity <math>\delta = \Delta s / s</math>''' (ratio of bottom-surface salinity difference and sea salinity)
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:well-mixed:  <math>\delta < 0.05</math> (see [[Seawater intrusion and mixing in estuaries]])
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:partially mixed: <math>0.05 < \delta < 0.25</math> (see [[Estuarine circulation]])
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:stratified: <math>\delta > 0.25</math> (see [[Salt wedge estuaries]]) <br>
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'''morphology''' (see [[Morphology of estuaries]])
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:river-dominated: delta-shoal system;
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:tide-dominated: funnel-shape channel system;
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:wave-dominated: coastal barrier system.
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Estuaries generally offer a great diversity of habitats consisting of subtidal and intertidal areas with different bed structures, different sediment composition and different salinity regimes. Typical estuarine habitats are intertidal mudflats and [[salt marshes]]. They host unique ecosystems with essential spawning and nursery functions for adjacent marine and fluvial ecosystems. They also provide important natural ecosystem services such as living resources, water quality regulation and flood protection (see also [[Estuarine ecosystems]]).
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==Articles on estuaries==
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* [[Estuarine ecosystems]]
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* [[Seawater intrusion and mixing in estuaries]]
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* [[Estuarine circulation]]
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* [[Salt wedge estuaries]]
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* [[Morphology of estuaries]]
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* [[Tidal asymmetry and tidal inlet morphodynamics]]
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* [[Estuarine turbidity maximum]]
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* [[Estuarine morphological modelling]]
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* [[Physical processes and morphology of synchronous estuaries]]
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* [[Coastal and marine sediments]]
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* [[Estuarine dispersion: dye experiments in the Eastern Scheldt scale model]]
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* [[US National Estuary Program]]
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* [[Heavy metal content of mussels in the Western Scheldt estuary]]
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==Reference==
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<references/>
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{{author
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|AuthorID=120
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|AuthorFullName=Job Dronkers
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|AuthorName=Dronkers J}}
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Estuaries are of particular ecological value and significance because they provide important natural values concerning, for example, fish and wildlife habitat, flood protection, and maintenance of water quality. }}
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[[Category:Physical coastal and marine processes]]
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[[Category:Estuaries and tidal rivers]]

Latest revision as of 12:40, 20 January 2024

Definition of estuary:
A semi-enclosed embayment of the coast in which fresh run-off water mixes with saline water entering from the ocean.
This is the common definition for estuary, other definitions can be discussed in the article


This is the definition given by Cameron and Pritchard (1963) [1]. However, it excludes the tidal river upstream of the seawater intrusion limit, where tidal motion can still have important consequences for ecosystem, water quality and morphology – for example: import of marine sediments and organisms, generation of a high turbidity zone, sedimentation/erosion of intertidal wetlands.

Estuaries are characterized by the presence of tides and a prominent system of channels and shoals (open bays and enclosed coastal seas such as the Bohai Sea or North Sea therefore do not qualify as estuaries). According to this characteristic, estuaries can also be defined as


Definition of estuary:
Semi-enclosed inlet system where the tide propagates along channels.
The part of the estuary upstream of the seawater intrusion limit, but subject to tidal motion, is usually referred to as 'tidal river'.
This is the common definition for estuary, other definitions can be discussed in the article


According to the first, more common definition, the tidal river is excluded from the estuary, but included according to the second definition. The second definition, which is closer to the etymological origin of the word estuary, includes tidal inlet systems without significant fresh water inflow, for example:

  • drowned coastal valleys;
  • tidal lagoons – drowned coastal plains semi-closed by a barrier system;
  • inverse estuaries – estuaries where evaporation exceeds fresh water inflow.

From a morphological or ecological viewpoint, such inlet systems can be very similar to estuaries with small fresh water inflow according to the first definition.


Mudflat in the Deben estuary, UK. Photo credit: Bescoe

Estuaries are widely diverse and can be classified according to different criteria:
tidal range

microtidal: tidal range < 2 m;
mesotidal: tidal range 2-4 m;
macrotidal: tidal range > 4 m.

salinity [math]\delta = \Delta s / s[/math] (ratio of bottom-surface salinity difference and sea salinity)

well-mixed: [math]\delta \lt 0.05[/math] (see Seawater intrusion and mixing in estuaries)
partially mixed: [math]0.05 \lt \delta \lt 0.25[/math] (see Estuarine circulation)
stratified: [math]\delta \gt 0.25[/math] (see Salt wedge estuaries)

morphology (see Morphology of estuaries)

river-dominated: delta-shoal system;
tide-dominated: funnel-shape channel system;
wave-dominated: coastal barrier system.

Estuaries generally offer a great diversity of habitats consisting of subtidal and intertidal areas with different bed structures, different sediment composition and different salinity regimes. Typical estuarine habitats are intertidal mudflats and salt marshes. They host unique ecosystems with essential spawning and nursery functions for adjacent marine and fluvial ecosystems. They also provide important natural ecosystem services such as living resources, water quality regulation and flood protection (see also Estuarine ecosystems).


Articles on estuaries


Reference

  1. ↑ Cameron, W. M. and D. W. Pritchard (1963) Estuaries. In M. N. Hill (editor), The Sea, Vol. 2. John Wiley & Sons, New York, pp. 306–324


The main author of this article is Job Dronkers
Please note that others may also have edited the contents of this article.
Citation: Job Dronkers (2024): Estuary. Available from http://www.coastalwiki.org/wiki/Estuary [accessed on 25-11-2024]
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