upright=1.45|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 beach barrier, but in many cases (low-energy waves and longshore currents) the tidal flats may directly pass into a shallow marine environment.]]

alt=Aerial photograph showing shallow turquoise water and scattered rocky outcrops forming tidal flats near Roscoff in Brittany, France.|thumb|Aerial view of rocky tidal flats off the coast of [[Roscoff, Brittany, France]]

Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands 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 mangroves, covering at least of the Earth's surface. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries; they are also seen in freshwater lakes and salty lakes (or inland seas) alike, wherein many rivers and creeks end. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays 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 ().

In the past tidal flats were considered unhealthy, economically unimportant areas and were often dredged and developed into agricultural land. Some mudflats can be extremely treacherous to walk on. For example, the mudflats surrounding Anchorage, Alaska, are made from fine glacial-silt which does not easily separate out its water, and, although seemingly solid, can quickly gel and become like quicksand when disturbed by stepping on it. Four people are known to have become stuck up to their waists and drowned when the tide came in, and many others are rescued from the Anchorage mudflats each year.

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

thumb|Mudflats near [[Oban, New Zealand|Oban on Stewart Island, New Zealand]]

Tidal flats, along with intertidal salt marshes and mangrove forests, are important ecosystems. They 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 birds, as well as certain species of crabs, mollusks and fish. 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 rises, land claims for development, dredging due to shipping purposes, and chemical pollution. It is estimated that up to 16% of the world tidal flats have disappeared since the mid-1980s. 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. Intergenerational practices of tidal flat gleaning and fishing are central to tidal flat-dependent communities. Hence, enabling cultural preservation and identity for the coastal communities, which are intricately linked with the tidal flats ecosystem.

Selected example areas

  • Arcachon Bay, France
  • Banc d'Arguin, Mauritania
  • Chamiza Wetland, Chile
  • Great Rann of Kutch, India
  • 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 Island, England, United Kingdom
  • Minas Basin, Nova Scotia, Canada
  • Moreton Bay, Queensland, Australia
  • North Slob, Wexford, Ireland
  • Kneiss Archipelago, Tunisia
  • Padilla Bay, Washington, United States
  • Plymouth Bay, Massachusetts, United States
  • Skagit Bay, Washington, United States
  • Snettisham, Norfolk England, United Kingdom
  • Wadden Sea: Netherlands, Germany, Denmark
  • West coast of Andros Island, Bahamas
  • Yellow Sea: China, North Korea, South Korea (Getbol)

See also

  • Getbol
  • Herringbone cross beds

References

  • Tidal Flats
  • Tidal Flats Field Sites
  • Intertidal Change Explorer