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{{short description|Coastal wetlands where sediments have been deposited by tides or rivers}}
[[Image:Tidal flat general sketch.png|upright=1.5|thumb|General sketch-map of a tidal plain, showing the typical tripartition in [[supratidal zone|supratidal]], [[intertidal]] and [[subtidal]] zones. The most apparent character of the area is the development of tidal channels, affecting mainly the [[intertidal zone]]. In this case, the tidal flat is protected seaward by a [[shoal|beach barrier]], but in many cases (low-energy [[water waves|waves]] and [[longshore currents]]) the tidal flats may directly pass into a shallow marine environment.]]

'''Mudflats''' or '''mud flats''', also known as '''tidal flats''' or, in Ireland, '''slob''' or '''slobs''',<ref>{{Cite web|url=http://www.askaboutireland.ie/enfo/irelands-environment/county-focus/wexford/wexford-sloblands/|title=Sloblands|website=www.askaboutireland.ie}}</ref><ref>{{Cite web|url=https://www.irishtimes.com/news/celebrating-the-slobs-1.48177|title=Celebrating the Slobs|first=Richard|last=Roche|website=The Irish Times}}</ref> are [[coastal wetland]]s that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal flat ecosystems are as extensive globally as [[mangrove]]s, covering at least {{convert|127,921|km2|mi2|abbr=on}} of the Earth's surface.<ref name=Murray>
{{Citation | last1 = Murray | first1 = N.J. | last2 = Phinn | first2 = S.R. | last3 = DeWitt | first3 = M. | last4 = Ferrari | first4 = R. | last5 = Johnston | first5 = R. | last6 = Lyons| first6 = M.B. |last7 = Clinton | first7 = N. |last8 = Thau| first8 = D. | last9 = Fuller | first9 = R.A. | year = 2019 |title = The global distribution and trajectory of tidal flats | journal = Nature | volume = 565 | issue = 7738 | pages = 222–225 | doi = 10.1038/s41586-018-0805-8 | pmid = 30568300 | bibcode = 2019Natur.565..222M }}/</ref> They are found in sheltered areas such as [[bay]]s, [[bayou]]s, [[lagoon]]s, and [[Estuary|estuaries]]; they are also seen in [[freshwater]] [[lake]]s and [[salt lake|salty lakes]] (or inland seas) alike, wherein many rivers and creeks end.<ref>Swamps and marshes (with thick and deep mud beneath surfaces in hot season) are either freshwater, salty, or brackish.</ref> Mudflats may be viewed [[geology|geologically]] as exposed layers of [[bay mud]], resulting from deposition of [[estuarine]] [[silt]]s, [[clay]]s and aquatic animal [[detritus]]. Most of the sediment within a mudflat is within the [[intertidal zone]], and thus the flat is submerged and exposed approximately twice daily.

A recent global remote sensing analysis estimated that approximately 50% of the global extent of tidal flats occurs within eight countries ([[Indonesia]], [[China]], [[Australia]], [[United States]], [[Canada]], [[India]], [[Brazil]], and [[Myanmar]]) and that 44% of the world's tidal flats occur within Asia ({{convert|56,051|km2|mi2|disp=or|abbr=on}}).<ref name=Murray/>

In the past tidal flats were considered unhealthy, economically unimportant areas and were often dredged and developed into agricultural land.<ref>{{Cite web|url=http://www.mrcirl.org/marker/marker1701/0701.html|title=Dredging Indian River Lagoon Wetlands 1920 - 1950s}}</ref> Several especially shallow mudflat areas, such as the [[Wadden Sea]], are now popular among those practising the sport of [[mudflat hiking]].

On the [[Baltic Sea]] coast of [[Germany]] in places, mudflats are exposed not by tidal action, but by wind-action driving water away from the shallows into the sea. This kind of wind-affected mudflat is called ''[[Windwatt]]'' in German.

==Ecology==
[[Image:Stewart Island Oban Mudflats.jpg|thumb|Mudflats near [[Oban, New Zealand|Oban]] on [[Stewart Island/Rakiura|Stewart Island]], [[New Zealand]]]]

Tidal flats, along with intertidal [[salt marsh]]es and [[mangrove]] forests, are important [[ecosystem]]s.<ref>{{Cite web|url=https://irlspecies.org/index.php|title=Indian River Lagoon Species Inventory Home|website=irlspecies.org}}</ref> They usually support a large population of wildlife, and are a key habitat that allows tens of millions of migratory [[shorebirds]] to migrate from breeding sites in the northern hemisphere to non-breeding areas in the southern hemisphere. They are often of vital importance to [[migratory bird]]s, as well as certain species of [[crab]]s,<ref>Triño, A. T., & Rodriguez, E. M. (2000). Mud crab (Scylla serrata) culture in tidal flats with existing mangroves. In J. H. Primavera, M. T. Castaños, & M. B. Surtida (Eds.), ''Mangrove-Friendly Aquaculture: Proceedings of the Workshop on Mangrove-Friendly Aquaculture organized by the SEAFDEC Aquaculture Department, January 11–15, 1999, Iloilo City, Philippines'' (pp. 171–176). Aquaculture Department, Southeast Asian Fisheries Development Center. https://repository.seafdec.org.ph/handle/10862/454</ref> [[mollusk]]s and [[fish]].<ref>{{Cite web|url=http://www.env.go.jp/en/nature/npr/ramsar_wetland/pamph/manko_34.pdf|title=Manko - Tidal Flat, Mangrove Forest}}</ref> In the [[United Kingdom]] mudflats have been classified as a [[Biodiversity Action Plan]] priority habitat.

The maintenance of mudflats is important in preventing coastal erosion. However, mudflats worldwide are under threat from predicted [[sea level rise]]s, land claims for development, [[Dredge|dredging]] due to shipping purposes, and [[soil contamination|chemical pollution]].<ref name=Murray/> In some parts of the world, such as East and South-East Asia, mudflats have been reclaimed for [[aquaculture]], [[agriculture]], and industrial development. For example, around the [[Yellow Sea]] region of East Asia, more than 65% of mudflats present in the early 1950s had been destroyed by the late 2000s.<ref>{{ Citation | first1 = J. | last1 = MacKinnon | first2 = Y.I. | last2 = Verkuil | first3 = N.J. | last3 = Murray | year = 2012 | title = IUCN situation analysis on East and Southeast Asian intertidal habitats, with particular reference to the Yellow Sea (including the Bohai Sea)| series = Occasional Paper of the IUCN Species Survival Commission No. 47 | pages = 70 | publisher = IUCN | place = Gland, Switzerland and Cambridge, UK | isbn = 9782831712550 | url = http://www.iucn.org/asiancoastalwetlands/}}</ref><ref>
{{Citation | last1 = Murray | first1 = N.J. | last2 = Clemens | first2 = R.S. | last3 = Phinn | first3 = S.R. | last4 = Possingham | first4 = H.P. | last5 = Fuller | first5 = R.A. | year = 2014 |title = Tracking the rapid loss of tidal wetlands in the Yellow Sea| journal = Frontiers in Ecology and the Environment | volume = 12 | issue = 5 | pages = 267–272 | doi = 10.1890/130260 | url = https://researchonline.jcu.edu.au/60169/1/130260.pdf }}/</ref> It is estimated that up to 16% of the world tidal flats have disappeared since the mid-1980s.<ref name=Murray/>

Mudflat sediment deposits are focused into the [[intertidal zone]] which is composed of a barren zone and marshes. Within these areas are various ratios of sand and mud that make up the sedimentary layers.<ref name=Reineck>Reineck, H.E, and I.B Singh, ''Depositional Sedimentary Environments,'' 2nd Ed. New York: Springer-Verlag Berlin Heidelberg, 1980, pp. 418-428</ref> The associated growth of coastal sediment deposits can be attributed to rates of subsidence along with rates of deposition (example: silt transported via river) and changes in sea level.<ref name=Reineck/>

Barren zones extend from the lowest portion of the intertidal zone to the marsh areas. Beginning in close proximity to the tidal bars, sand dominated layers are prominent and become increasingly muddy throughout the tidal channels. Common bedding types include laminated sand, ripple bedding, and bay mud. [[Bioturbation]] also has a strong presence in barren zones.

[[Marshes]] contain an abundance of [[herbaceous plant]]s while the sediment layers consist of thin sand and mud layers. [[Mudcrack]]s are a common as well as wavy bedding planes.<ref name=Reineck/> Marshes are also the origins of coal/peat layers because of the abundant decaying plant life.<ref name=Reineck/>

[[Salt pan (geology)|Salt pans]] can be distinguished in that they contain thinly laminated layers of clayey silt. The main source of the silt comes from rivers. Dried up mud along with wind erosion forms silt dunes. When flooding, rain or tides come in, the dried sediment is then re-distributed.<ref name=Reineck/>

[[Image:brewster mudflat.jpg|thumb|Mudflats in [[Brewster, Massachusetts]], [[United States]], extending hundreds of yards offshore at the low tide. The line of [[Wrack (seaweed)|wrack]] and seashells in the foreground indicates the [[tide|high-water mark]].]]
[[File:Skagit_Bay_6308.JPG|thumb|Gulls feeding on mudflats in [[Skagit Bay]], [[Washington (state)|Washington]].]]

==Selected example areas==

* [[Arcachon Bay]], [[France]]
* [[Banc d'Arguin]], [[Mauritania]]
* [[Great Rann of Kutch]], [[India]]
* [[Belhaven, Scotland|Belhaven]], [[East Lothian]] [[Scotland]], [[United Kingdom]]
* [[Bridgwater Bay]] and [[Morecambe Bay]], [[United Kingdom]]
* [[Cape Cod Bay]], [[Massachusetts]], [[United States]]
* [[Cook Inlet]], [[Alaska]], [[United States]]
* [[Lindisfarne|Lindisfarne Island]], [[England]], [[United Kingdom]]
* [[Minas Basin]], [[Nova Scotia]], [[Canada]]
* [[Moreton Bay]], [[Queensland]], [[Australia]]
* [[North Slob]], [[Wexford]], [[Ireland]]
* [[Padilla Bay]], [[Washington (state)|Washington]], [[United States]]
* [[Plymouth Bay]], [[Massachusetts]], [[United States]]
* [[Port of Tacoma]], [[Washington (state)|Washington]], [[United States]]
* [[Port Susan]], [[Warm Beach]], [[Washington (state)|Washington]], [[United States]]
* [[Skagit Bay]], [[Washington (state)|Washington]]
* [[Snettisham]] [[Norfolk]] [[England]], [[United Kingdom]]
* [[Wadden Sea]]: [[Netherlands]], [[Germany]], [[Denmark]]
* West coast of [[Andros, Bahamas|Andros Island, Bahamas]]
* [[Yellow Sea|West Sea]] : [[South Korea]]

== See also ==
{{Portal|Wetlands}}
* [[Herringbone cross bed]]s

==References==
{{Reflist}}

==External links==
{{Commons category|Mudflats}}
*[https://web.archive.org/web/20110605124633/http://www.cbbep.org/projects/molliebeattie/flatlinksvaluable.htm Tidal Flats]
*[https://web.archive.org/web/20130718151050/http://tidalflats.org/ Tidal Flats Field Sites]
*[http://intertidal.app Intertidal Change Explorer]

{{Coastal geography|state=expanded}}
{{aquatic ecosystem topics|expanded=none}}
{{Wetlands}}

{{Authority control}}

[[Category:Landforms]]
[[Category:Wetlands]]
[[Category:Coastal geography]]

Mudflat - Revision history

Robertoson: added references

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