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{{Short description|Type of land area that is flooded or saturated with water}}
{{Other uses|Wetland (disambiguation)}}
<noinclude>{{multiple image |perrow=2 |total_width=400 |image1=USGS_image_cropped.jpg |alt1=Upland vs. wetland vs. lacustrine zones |image2=Freshwater swamp forest in Gowainghat Sylhet Bangladesh photo taken in July 2016.jpg |alt2=Freshwater [[swamp]] forest in [[Bangladesh]] |image3=Tourbière 03 - Parc de Frontenac - Juillet 2008.jpg |alt3= [[Peat bogs]] are freshwater wetlands that develop in areas with [[standing water]] and low [[soil fertility]]. |image4= Remediated wetlands at the Mount Polley mine.jpg |alt4 = Mount Polley wetlands in [[British Columbia]], Canada |footer= Wetlands come in different sizes and types. From top left: Upland vs. wetland vs. lacustrine zones; freshwater [[swamp]] forest in [[Bangladesh]]; [[peat bogs]] are freshwater wetlands that develop in areas with [[standing water]] and low [[soil fertility]]; a freshwater cattail (''[[Typha]]'') marsh that develops with standing water and high soil fertility.}}</noinclude>
A '''wetland''' is a distinct [[semi-aquatic]] [[ecosystem]] whose [[groundcover]]s are [[flooded]] or [[soil saturation|saturated]] in [[water]], either permanently, for years or decades, or only seasonally.  Flooding results in [[oxygen]]-poor ([[anoxic waters|anoxic]]) processes taking place, especially in the [[soil]]s.<ref name=Keddy2010>{{cite book |last=Keddy |first=P.A. |url=https://books.google.com/books?id=eVeaSqFy2VgC |title=Wetland ecology: principles and conservation |date=2010 |publisher=Cambridge University Press |isbn=978-0521519403 |edition=2nd |location=New York |access-date=2020-06-03 |archive-date=2023-03-17 |archive-url=https://web.archive.org/web/20230317201346/https://books.google.com/books?id=eVeaSqFy2VgC |url-status=dead }}</ref> Wetlands form a transitional zone between [[waterbodies]] and [[dry land]]s, and are different from other [[terrestrial ecosystem|terrestrial]] or [[aquatic ecosystem]]s due to their [[vegetation]]'s [[root]]s having adapted to oxygen-poor [[hydric soil|waterlogged soils]].<ref name=ramsar>{{cite web|title=Official page of the Ramsar Convention|url=http://www.ramsar.org/cda/en/ramsar-pubs/main/ramsar/1-30_4000_0__|access-date=2011-09-25}}</ref> They are considered among the most [[biologically diverse]] of all ecosystems, serving as [[habitat]]s to a wide range of aquatic and semi-aquatic [[plant]]s and [[animal]]s, with often improved [[water quality]] due to plant removal of [[nutrient pollution|excess nutrients]] such as [[nitrate]]s and [[phosphorus]].
Wetlands exist on every [[continent]], except [[Antarctica]].<ref name=Davidson2014>{{cite journal |author=Davidson, N.C. |year=2014 |title=How much wetland has the world lost? Long-term and recent trends in global wetland area |journal=Marine and Freshwater Research |volume=65 |issue=10|pages=934–941|doi=10.1071/MF14173|s2cid=85617334}}</ref> The water in wetlands is either [[freshwater]], [[brackish]] or [[seawater|saltwater]].<ref name=ramsar/> The main types of wetland are defined based on the dominant [[plant]]s and the source of the water. For example, ''[[marsh]]es'' are wetlands dominated by [[aquatic plant#Emergent|emergent]] [[herbaceous vegetation]] such as [[reed (plant)|reed]]s, [[cattail]]s and [[sedge]]s. ''[[Swamp]]s'' are dominated by [[woody vegetation]] such as [[tree]]s and [[shrub]]s (although [[reedswamp|reed swamps]] in Europe are dominated by reeds, not trees). [[Mangrove forest]] are wetlands with [[mangrove]]s, [[halophytic]] woody plants that have evolved to tolerate [[salty water]].
Examples of wetlands classified by the sources of water include ''[[tidal wetland]]s'', where the water source is [[ocean tides]]); ''[[estuaries]]'', water source is mixed tidal and river waters; ''[[floodplain]]s'', water source is excess water from overflowed rivers or lakes; and ''[[bog]]s'' and ''[[vernal pond]]s'', water source is [[rainfall]] or [[meltwater]].<ref name=Keddy2010/><ref name="water">{{cite web |date=2015 |title=US EPA|url=http://water.epa.gov/type/wetlands/what.cfm|access-date=2011-09-25}}</ref> The world's largest wetlands include the [[Amazon River basin]], the [[West Siberian Plain]],<ref name="FraserKeddy">{{cite book |url=https://books.google.com/books?id=tYeccNT_AsQC&pg=PP1 |title=The World's Largest Wetlands: Their Ecology and Conservation |date=2005 |publisher=Cambridge University Press |isbn=978-0521834049 |editor-last=Fraser |editor-first=L. |location=Cambridge, UK |editor2-last=Keddy |editor2-first=P.A.}}</ref> the [[Pantanal]] in South America,<ref name=":1">{{cite web |title=WWF Pantanal Programme |url=http://wwf.panda.org/who_we_are/wwf_offices/bolivia/our_work/pantanal_programme/ |access-date=2011-09-25}}</ref> and the [[Sundarbans]] in the [[Ganges]]-[[Brahmaputra]] delta.<ref name=":2">{{cite journal |author=Giri, C. |author2=Pengra, B. |author3=Zhu, Z. |author4=Singh, A. |author5=Tieszen, L.L. |year=2007 |title=Monitoring mangrove forest dynamics of the Sundarbans in Bangladesh and India using multi-temporal satellite data from 1973 to 2000 |journal=Estuarine, Coastal and Shelf Science |volume=73 |issue=1–2 |pages=91–100 |bibcode=2007ECSS...73...91G |doi=10.1016/j.ecss.2006.12.019}}</ref>
Wetlands contribute many [[ecosystem service]]s that benefit people. These include for example [[water purification]], stabilization of shorelines, storm protection and [[flood control]]. In addition, wetlands also process and condense [[carbon]] (in processes called [[carbon fixation]] and [[carbon sequestration|sequestration]]), and other nutrients and [[water pollution|water pollutants]]. Wetlands can act as a [[carbon sink|sink]] or a [[carbon source|source]] of carbon, depending on the specific wetland. If they function as a carbon sink, they can help with [[climate change mitigation]]. However, wetlands can also be a significant [[greenhouse gas emissions from wetlands|source of methane emissions]] due to [[anaerobic decomposition]] of soaked [[detritus]], and some are also emitters of [[nitrous oxide]].<ref name=":4">{{Cite journal|last=Bange|first=H. W.|date=2006 |title=Nitrous oxide and methane in European coastal waters |url=https://linkinghub.elsevier.com/retrieve/pii/S0272771406002496|journal=Estuarine, Coastal and Shelf Science |volume=70 |issue=3 |pages=361–374 |doi=10.1016/j.ecss.2006.05.042 |bibcode=2006ECSS...70..361B}}</ref><ref name=":3">{{cite journal |last1=Thompson |first1=A. J. |last2=Giannopoulos |first2=G. |last3=Pretty |first3=J. |last4=Baggs |first4=E. M. |last5=Richardson |first5=D. J. |date=2012 |title=Biological sources and sinks of nitrous oxide and strategies to mitigate emissions |journal=Philosophical Transactions of the Royal Society B |volume=367 |issue=1593 |pages=1157–1168 |doi=10.1098/rstb.2011.0415 |pmc=3306631 |pmid=22451101}}</ref>
Humans are disturbing and damaging wetlands in many ways, including [[oil and gas extraction]], building infrastructure, [[overgrazing]] of [[livestock]], [[overfishing]], alteration of wetlands including [[dredging]] and draining, [[nutrient pollution]], and [[water pollution]].<ref name="clewell2013" /><ref name="mitsch2007" /> Wetlands are more threatened by [[environmental degradation]] than any other [[ecosystem]] on Earth, according to the [[Millennium Ecosystem Assessment]] from 2005.<ref>{{cite book |last1=Davidson |first1=N.C. |url=https://www.millenniumassessment.org/documents/document.358.aspx.pdf |title=Ecosystems and Human Well-being: Wetlands and Water Synthesis: a report of the Millennium Ecosystem Assessment |last2=D'Cruz |first2=R. |last3=Finlayson |first3=C.M. |date=2005 |publisher=World Resources Institute |isbn=978-1-56973-597-8 |location=Washington, DC |name-list-style=amp}}</ref> Methods exist for assessing wetland [[ecological health]]. These methods have contributed to [[wetland conservation]] by raising public awareness of the functions that wetlands can provide.<ref name="ACADEMIC PRESS">{{Cite book |title=Wetland and Stream Rapid Assessments: Development, Validation, and Application|date=2018|publisher=Academic Press|isbn=978-0-12-805091-0|editor-last=Dorney |editor-first=J. |location=London; San Diego, CA |oclc=1017607532|editor-last2=Savage |editor-first2=R.|editor-last3=Adamus |editor-first3=P.|editor-last4=Tiner |editor-first4=R.}}</ref> Since 1971, work under an international treaty seeks to identify and protect "[[wetlands of international importance]]."
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==Definitions and terminology==
[[File:A somewhat smoggy Midtown Manhattan skyline as seen from Jamaica Bay - panoramio (cropped).jpg|thumb|300px|[[Marshlands]] are often noted within wetlands, as seen here at the [[Jamaica Bay Wildlife Refuge]] in [[New York City]].]]
===Technical definitions===
A simplified definition of wetland is "an area of land that is usually saturated with water".<ref>{{Cite web |title=Home: Oxford English Dictionary |url=https://www.oed.com/ |access-date=2022-07-08 |website=www.oed.com |language=en}}</ref> More precisely, wetlands are areas where "water covers the [[soil]], or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season".<ref name=":5" /> A patch of land that develops pools of water after a [[rain storm]] would not necessarily be considered a "wetland", even though the land is wet. Wetlands have unique characteristics: they are generally distinguished from other [[water bodies]] or [[landform]]s based on their [[water level]] and on the types of [[plant]]s that live within them. Specifically, wetlands are characterized as having a [[water table]] that stands at or near the [[land surface]] for a long enough period each year to support [[aquatic plants]].<ref>{{cite web |title=Glossary of Terms |url=http://www.cvwd.net/water_glossary.htm |archive-url=https://web.archive.org/web/20120425163056/http://www.cvwd.net/water_glossary.htm |archive-date=April 25, 2012 |access-date=2012-05-23 |publisher=Carpinteria Valley Water District}}</ref><ref>{{cite web |title=Glossary |url=http://mapping2.orr.noaa.gov/portal/calcasieu/calc_html/resources/glossary.html |archive-url=https://web.archive.org/web/20120425163041/http://mapping2.orr.noaa.gov/portal/calcasieu/calc_html/resources/glossary.html |archive-date=2012-04-25 |access-date=2012-05-23 |publisher=Mapping2.orr.noaa.gov}}</ref>
A more concise definition is a community composed of [[hydric soil]] and [[hydrophytes]].<ref name="Keddy2010" />
Wetlands have also been described as [[ecotone]]s, providing a transition between dry land and water bodies.<ref>{{cite web |title=Glossary |url=http://www.alabamapower.com/hydro/glossary.asp |archive-url=https://web.archive.org/web/20120321233304/http://www.alabamapower.com/hydro/glossary.asp |archive-date=2012-03-21 |access-date=2012-05-23 |publisher=Alabama Power}}</ref> Wetlands exist "...at the interface between truly [[terrestrial ecoregion|terrestrial]] ecosystems and [[aquatic habitat|aquatic]] systems, making them inherently different from each other, yet highly dependent on both."<ref name="mitsch2007">{{cite book |last1=Mitsch |first1=William J. |url=https://books.google.com/books?id=1cSKeTCi894C |title=Wetlands |last2=Gosselink |first2=James G. |date=2007-08-24 |publisher=John Wiley & Sons |isbn=978-0-471-69967-5 |edition=4th |location=New York, NY}}</ref>
In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions.
Under the [[Ramsar Convention|Ramsar international wetland conservation treaty]], wetlands are defined as follows:<ref>{{cite web|title=The Ramsar 40th Anniversary Message for November| publisher = Ramsar| access-date = 2011-10-10 | url = http://www.ramsar.org/cda/en/ramsar-home/main/ramsar/1_4000_0__}}</ref>
* Article 1.1: "...wetlands are areas of marsh, [[fen]], [[peatland]] or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, [[fresh water|fresh]], [[brackish water|brackish]] or [[saline water|salt]], including areas of marine water the depth of which at low tide does not exceed six meters."
* Article 2.1: "[Wetlands] may incorporate [[riparian]] and coastal zones adjacent to the wetlands, and [[island]]s or bodies of marine water deeper than six meters at [[low tide]] lying within the wetlands."
An ecological definition of a wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota, particularly rooted plants, to adapt to flooding".<ref name="Keddy2010" />
Sometimes a precise legal definition of a wetland is required. The definition used for regulation by the United States government is: 'The term "wetlands" means those areas that are inundated or saturated by surface or ground water at a frequency and duration to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally included swamps, marshes, bogs, and similar areas.'<ref>Environmental Laboratory. (1987). Corps of Engineers wetlands delineation manual. ''Tech. Rep. Y‐87–1''.</ref>
For each of these definitions and others, regardless of the purpose, hydrology is emphasized (shallow waters, water-logged soils). The soil characteristics and the plants and animals controlled by the wetland hydrology are often additional components of the definitions.<ref>{{cite book |last1=Sharitz |first1=Rebecca R. |chapter=Ecology of Freshwater and Estuarine Wetlands: An Introduction |date=2019-12-31 |title=Ecology of Freshwater and Estuarine Wetlands |pages=1–22 |location=Berkeley |publisher=University of California Press |language=en |doi=10.1525/9780520959118-003 |isbn=978-0-520-95911-8 |last2=Batzer |first2=Darold P. |last3=Pennings |first3=Steven C. |s2cid=198427881}}</ref>
=== Types ===
[[File:Sunrise at viru bog.jpg|thumb|upright=1.5|Sunrise at Viru Bog, Estonia]]
{{Main|Classification of wetlands}}
Wetlands can be [[Tide|tidal]] (inundated by tides) or non-tidal.<ref name=":5"/> The water in wetlands is either [[freshwater]], [[brackish water|brackish]], [[Saline water|saline]], or [[alkali]]ne.<ref name="ramsar" /> There are four main kinds of wetlands&nbsp;– [[marsh]], [[swamp]], [[bog]], and [[fen]] (bogs and fens being types of peatlands or [[mire]]s). Some experts also recognize [[wet meadow]]s and [[aquatic ecosystem]]s as additional wetland types.<ref name="Keddy2010" /> Sub-types include [[mangrove swamp|mangrove forests]], [[Carr (landform)|carrs]], [[pocosin]]s, [[floodplain]]s,<ref name="Keddy2010" /> peatlands, [[vernal pool]]s, [[Sink (geography)|sinks]], and many others.<ref name=":0">{{Cite web|url=https://dec.vermont.gov/watershed/wetlands/what/types|title = Wetland Types &#124; Department of Environmental Conservation}}</ref>
The following three groups are used within [[Australia]] to classify wetland by type: Marine and coastal zone wetlands, inland wetlands and human-made wetlands.<ref>{{cite book|date=2001|title=A Directory of Important Wetlands in Australia: Third edition, Chapter 2: Wetland classification system, Criteria for inclusion and Data presentation|url=http://www.environment.gov.au/water/publications/environmental/wetlands/directory.html |access-date=30 March 2021|publisher=Australian Department of the Environment}}</ref> In the US, the best known classifications are the [[Cowardin classification system]]<ref>{{Cite web|title=NPWRC :: Classification of Wetlands and Deepwater Habitats of the United States|url=https://www.fws.gov/wetlands/documents/classwet/index.html|access-date=2018-07-28|website=www.fws.gov|archive-date=2014-01-21|archive-url=https://web.archive.org/web/20140121073314/http://www.fws.gov/wetlands/Documents/classwet/index.html}}</ref> and the hydrogeomorphic (HGM) classification system. The Cowardin system includes five main types of wetlands: [[Marine habitats|marine]] (ocean-associated), [[Estuary|estuarine]] (mixed ocean- and river-associated), [[riverine]] (within river channels), [[lacustrine]] (lake-associated) and [[palustrine]] (inland nontidal habitats).
==== Peatlands ====
[[Mire|Peatlands]] are a unique kind of wetland where lush plant growth and slow decay of dead plants (under anoxic conditions) results in organic peat accumulating; bogs, fens, and mires are different names for peatlands.
=== Wetland names ===
Variations of names for wetland systems:
{{Div col|colwidth=22em}}
* [[Bayou]]
* [[Flooded grasslands and savannas]]
* [[Marsh]]
** [[Brackish marsh]]
** [[Freshwater marsh]]
* [[Mire]]
** [[Fen]]
** [[Bog]]
* [[Riparian zone]]
* [[Swamp]]
** [[Freshwater swamp forest]]
**[[Tidal Freshwater forest]]
** [[Coniferous swamp]]
** [[Peat swamp forest]]
** [[Mangrove swamp]]
* [[Vernal pool]]
{{Div col end}}
Some wetlands have localized names unique to a region such as the prairie potholes of North America's northern plain, [[pocosin]]s, [[Carolina bay]]s and [[baygall]]s<ref name="Watson (2006)">{{cite book |author=Watson, G. E. |title=Big Thicket Plant Ecology: An Introduction |publisher=University of North Texas Press |year=2006 |isbn=978-1574412147 |edition=Third |series=Temple Big Thicket Series #5 |location=Denton, Texas}}</ref><ref name="Texas P&W">{{Cite web |work=Texas Parks and Wildlife. Ecological Mapping systems of Texas |url=https://tpwd.texas.gov/landwater/land/programs/landscape-ecology/ems/emst/woody-wetlands-and-riparian/west-gulf-coastal-plain-seepage-swamp-and-baygall |title=West Gulf Coastal Plain Seepage Swamp and Baygall |archive-url=https://web.archive.org/web/20200710060502/https://tpwd.texas.gov/landwater/land/programs/landscape-ecology/ems/emst/woody-wetlands-and-riparian/west-gulf-coastal-plain-seepage-swamp-and-baygall |archive-date=2020-07-10 |access-date=7 July 2020}}</ref> of the Southeastern US, mallines of Argentina, Mediterranean seasonal ponds of Europe and California, [[Turlough (lake)|turloughs]] of Ireland, [[billabong]]s of Australia, among many others.
=== Locations ===
==== By temperature zone ====
[[File:MiddleSpring.JPG|thumb|Wetlands contrast the hot, arid landscape around Middle Spring, [[Fish Springs National Wildlife Refuge]], [[Utah]].]]
Wetlands are found throughout the world in different climates.<ref name=":5">{{Cite web |last=US EPA |first=OW |date=2015-09-18 |title=What is a Wetland? |url=https://www.epa.gov/wetlands/what-wetland |access-date=2022-07-08 |website=US EPA |language=en}}</ref> Temperatures vary greatly depending on the location of the wetland. Many of the world's wetlands are in the [[temperate zone]]s, midway between the North or South Poles and the equator. In these zones, summers are warm and winters are cold, but temperatures are not extreme. In subtropical zone wetlands, such as along the [[Gulf of Mexico]], average temperatures might be {{convert|11|C|F}}. Wetlands in the [[tropics]] are subjected to much higher temperatures for a large portion of the year. Temperatures for wetlands on the [[Arabian Peninsula]] can exceed {{convert|50|C|F}} and these habitats would therefore be subject to rapid evaporation. In northeastern [[Siberia]], which has a polar climate, wetland temperatures can be as low as {{convert|−50|C|F}}. [[Peatland]]s in arctic and subarctic regions insulate the [[permafrost]], thus delaying or preventing its thawing during summer, as well as inducing its formation.<ref>{{Cite web|url=https://www.ramsar.org/document/peatlands-climate-change-mitigation-biodiversity-conservation|title=Peatlands, climate change mitigation and biodiversity conservation &#124; The Convention on Wetlands, The Convention on Wetlands|website=www.ramsar.org}}</ref>
==== By precipitation amount ====
The amount of precipitation a wetland receives varies widely according to its area. Wetlands in [[Wales]], [[Scotland]], and western [[Ireland]] typically receive about {{convert|1500|mm|in|abbr=on}} per year.{{citation needed|date=December 2022}} In some places in [[Southeast Asia]], where heavy rains occur, they can receive up to {{convert|10000|mm|in|abbr=on}}.{{citation needed|date=December 2022}} In some drier regions, wetlands exist where as little as {{convert|180|mm|in|abbr=on}} precipitation occurs each year.{{citation needed|date=February 2017}}
Temporal variation:<ref>{{Cite web|url=http://www.ramsar.org/cda/en/ramsar-pubs-reports/main/ramsar/1-30-99_4000_0__|title=Ramsar Convention Technical Reports}}</ref>
* [[Perennial]] systems
* [[Seasonal]] systems
* Episodic (periodic or intermittent) systems
* [[Ephemeral]] (short-lived) systems
Surface flow may occur in some segments, with subsurface flow in other segments.
==Processes==
Wetlands vary widely due to local and regional differences in [[topography]], [[hydrology]], [[vegetation]], and other factors, including human involvement. Other important factors include fertility, natural disturbance, competition, [[herbivory]], burial and salinity.<ref name="Keddy2010" /> When [[peat]] accumulates, [[bog]]s and [[fen]]s arise.
===Hydrology===
[[File:Wetlands Cape May New Jersey.jpg|thumb|300px|The wetlands of [[Cape May]], [[New Jersey]], in the [[United States]] comprise an extensive hydrological network that makes them an [[ornithology|ornithologically]] important location to study the many birds which use the preserve as a place to [[nest]].]]
[[File:Mallows Bay Park wetlands.PNG|300px|thumb|A wetland in the [[Chesapeake Bay]] [[drainage basin]] in Mallows Bay Park in [[Charles County, Maryland|Charles County]], [[Maryland]], in the United States.]]
The most important factor producing wetlands is hydrology, or [[flooding]]. The duration of flooding or prolonged soil saturation by [[groundwater]] determines whether the resulting wetland has aquatic, [[marsh]] or [[swamp]] [[vegetation]]. Other important factors include soil fertility, natural disturbance, competition, [[herbivory]], burial, and salinity.<ref name="Keddy2010" /> When [[peat]] from dead plants accumulates, [[bog]]s and [[fen]]s develop.
Wetland hydrology is associated with the spatial and temporal dispersion, flow, and physio-chemical attributes of surface and ground waters. Sources of hydrological flows into wetlands are predominantly [[precipitation]], surface water (saltwater or freshwater), and groundwater. Water flows out of wetlands by [[evapotranspiration]], surface flows and [[tide]]s, and subsurface water outflow. [[Hydrodynamics]] (the movement of water through and from a wetland) affects hydro-periods (temporal fluctuations in water levels) by controlling the water balance and water storage within a wetland.<ref>{{cite book|last1=Richardson|first1=J. L.|last2=Arndt|first2=J. L.|last3=Montgomery|first3=J. A.|date=2001|contribution=Hydrology of wetland and related soils|editor1-first=J. L.|editor1-last=Richardson|editor2-first=M. J.|editor2-last=Vepraskas|title=Wetland Soils|publisher=Lewis Publishers|location=Boca Raton, FL}}</ref>
Landscape characteristics control wetland hydrology and water chemistry. The [[oxygen|O<sub>2</sub>]] and [[carbon dioxide|CO<sub>2</sub>]] concentrations of water depend upon [[temperature]], [[atmospheric pressure]] and mixing with the air (from winds or water flows). Water chemistry within wetlands is determined by the [[pH]], [[salinity]], nutrients, [[Electrical conductivity|conductivity]], soil composition, [[Water hardness|hardness]], and the sources of water. Water chemistry varies across landscapes and climatic regions. Wetlands are generally [[minerotrophic]] (waters contain dissolved materials from soils) with the exception of [[ombrotrophic]] bogs that are fed only by water from precipitation.
Because bogs receive most of their water from precipitation and humidity from the [[atmosphere]], their water usually has low [[mineral]] ionic composition. In contrast, wetlands fed by groundwater or tides have a higher [[concentration]] of dissolved nutrients and minerals.
Fen peatlands receive water both from precipitation and ground water in varying amounts so their water chemistry ranges from acidic with low levels of dissolved minerals to alkaline with high accumulation of [[calcium]] and [[magnesium]].<ref>{{cite journal|last1=Vitt|first1=D. H.|last2=Chee|first2=W|date=1990|title=The relationships of vegetation to surface water chemistry and peat chemistry in fens of Alberta, Canada|journal=Plant Ecology|volume=89|issue=2|pages=87–106|doi=10.1007/bf00032163|s2cid=25071105}}</ref>
===Role of salinity===
Salinity has a strong influence on wetland water chemistry, particularly in coastal wetlands<ref name="Keddy2010" /><ref>{{cite book|editor1-first=B. R.|editor1-last=Silliman|editor2-first=E. D.|editor2-last=Grosholz|editor3-first=M. D.|editor3-last=Bertness|date=2009|title=Human Impacts on Salt Marshes: A Global Perspective|publisher=University of California Press|location=Berkeley, CA}}</ref> and in arid and semiarid regions with large precipitation deficits. Natural salinity is regulated by interactions between ground and surface water, which may be influenced by human activity.<ref>{{cite journal|last1=Smith|first1=M. J.|last2=Schreiber|first2=E. S. G.|last3=Kohout|first3=M.|last4=Ough|first4=K.|last5=Lennie|first5=R.|last6=Turnbull|first6=D.|last7=Jin|first7=C.|last8=Clancy|first8=T.|date=2007|title=Wetlands as landscape units: spatial patterns in salinity and water chemistry|journal=Wetlands, Ecology & Management|volume=15|issue=2|pages=95–103|doi=10.1007/s11273-006-9015-5|bibcode=2007WetEM..15...95S |s2cid=20196854}}</ref>
===Soil===
[[Carbon]] is the major [[nutrient cycle]]d within wetlands. Most nutrients, such as [[sulfur]], [[phosphorus]], [[carbon]], and [[nitrogen]] are found within the soil of wetlands. [[Anaerobic respiration|Anaerobic]] and [[aerobic respiration]] in the soil influences the [[nutrient cycling]] of carbon, hydrogen, oxygen, and nitrogen,<ref>{{cite journal|last=Ponnamperuma|first=F. N.|date=1972|title=The chemistry of submerged soils|journal=Advances in Agronomy|volume=24|pages=29–96|doi=10.1016/S0065-2113(08)60633-1|isbn=9780120007240}}</ref> and the solubility of phosphorus<ref>{{cite journal|last1=Moore|first1=P. A. Jr.|last2=Reddy|first2=K. R.|date=1994|title=Role of Eh and pH on phosphorus geochemistry in sediments of Lake Okeechobee, Florida|journal=Journal of Environmental Quality|volume=23|issue=5|pages=955–964|doi=10.2134/jeq1994.00472425002300050016x|pmid=34872208|bibcode=1994JEnvQ..23..955M }}</ref> thus contributing to the chemical variations in its water. Wetlands with low pH and saline conductivity may reflect the presence of acid [[sulfate]]s<ref>{{cite journal|last1=Minh|first1=L. Q.|last2=Tuong|first2=T. P.|last3=van Mensvoort|first3=M. E. F.|last4=Bouma|first4=J.|date=1998|title=Soil and water table management effects on aluminum dynamics in an acid sulphate soil in Vietnam|journal=Agriculture, Ecosystems & Environment|volume=68|issue=3|pages=255–262|doi=10.1016/s0167-8809(97)00158-8|bibcode=1998AgEE...68..255M }}</ref> and wetlands with average salinity levels can be heavily influenced by calcium or magnesium. [[Biogeochemistry|Biogeochemical processes]] in wetlands are determined by soils with low [[redox]] potential.<ref>{{cite book|last=Schlesinger|first=W. A.|date=1997|title=Biogeochemistry: An Analysis of Global Change|url=https://archive.org/details/isbn_9780126251555|url-access=registration|edition=2nd|publisher=Academic Press|location=San Diego, CA|isbn=9780126251555}}</ref>
== Biology ==
The life forms of a wetland system includes its plants ([[flora]]) and animals ([[fauna]]) and [[Microorganism|microbes]] (bacteria, fungi). The most important factor is the wetland's duration of flooding.<ref name="Keddy2010" /> Other important factors include fertility and salinity of the water or soils. The chemistry of water flowing into wetlands depends on the source of water, the geological material that it flows through<ref>{{cite journal|last=Bedford|first=B. L.|date=1996|title=The need to define hydrologic equivalence at the landscape scale for freshwater wetland mitigation|journal=Ecological Applications|volume=6|issue=1|pages=57–68|doi=10.2307/2269552|jstor=2269552|bibcode=1996EcoAp...6...57B }}</ref> and the nutrients discharged from organic matter in the soils and plants at higher elevations.<ref>{{cite journal|last1=Nelson|first1=M. L.|last2=Rhoades|first2=C. C.|last3=Dwire|first3=K. A.|date=2011|title=Influences of Bedrock Geology on Water Chemistry of Slope Wetlands and Headwaters Streams in the Southern Rocky Mountains|journal=Wetlands|volume=31|issue=2|pages=251–261|doi=10.1007/s13157-011-0157-8|bibcode=2011Wetl...31..251N |s2cid=14521026}}</ref> Plants and animals may vary within a wetland seasonally or in response to flood regimes.
[[File:Temperate wetlands in Pennsylvania.jpg|thumb|Humid wetland in Pennsylvania before a rain]]
=== Flora ===
[[File:Nelumbo nucifera LOTUS bud.jpg|thumb|upright|Bud of water lotus (''[[Nelumbo nucifera]]''), an aquatic plant]]
There are four main groups of [[hydrophyte]]s that are found in wetland systems throughout the world.<ref>{{cite web|title=Blacktown Council wetlands |access-date=2011-09-25 |url=http://www.blacktown.nsw.gov.au/environment/educational-resources/wetlands/animals-plants-and-algae-in-wetlands.cfm |archive-url=https://web.archive.org/web/20110410125002/http://www.blacktown.nsw.gov.au/environment/educational-resources/wetlands/animals-plants-and-algae-in-wetlands.cfm |archive-date=2011-04-10}}</ref>
[[Submergent plant|Submerged]] wetland vegetation can grow in saline and fresh-water conditions. Some species have underwater flowers, while others have long stems to allow the flowers to reach the surface.<ref>{{cite book|last1=Hutchinson|first1=G. E.|date=1975|title=A Treatise on Limnology. Vol. 3: Limnological Botany|location=New York, NY|publisher=John Wiley}}</ref> Submerged species provide a food source for native fauna, habitat for invertebrates, and also possess filtration capabilities. Examples include [[seagrasses]] and [[Vallisneria|eelgrass]].
Floating water plants or floating vegetation are usually small, like those in the [[Lemnoideae]] subfamily (duckweeds).
Emergent vegetation like the cattails (''[[Typha]]'' spp.), sedges (''[[Carex]]'' spp.) and arrow arum (''[[Peltandra virginica]]'') rise above the surface of the water.
When trees and shrubs comprise much of the plant cover in saturated soils, those areas in most cases are called [[swamp]]s.<ref name="Keddy2010" /> The upland boundary of swamps is determined partly by water levels. This can be affected by dams<ref>{{cite book|editor-last=Hughes|editor-first=F. M. R.|date=2003|title=The Flooded Forest: Guidance for policy makers and river managers in Europe on the restoration of floodplain forests|series=FLOBAR2, Department of Geography, University of Cambridge, Cambridge, UK}}</ref> Some swamps can be dominated by a single species, such as [[silver maple]] swamps around the [[Great Lakes]].<ref>{{cite book|last1=Wilcox|first1=D. A|last2=Thompson|first2=T. A.|last3=Booth|first3=R. K.|last4=Nicholas|first4=J. R.|date=2007|title=Lake-level variability and water availability in the Great Lakes|series=USGS Circular 1311}}</ref> Others, like those of the [[Amazon basin]], have large numbers of different tree species.<ref>{{cite book|last=Goulding|first=M.|date=1980|title=The Fishes and the Forest: Explorations in Amazonian Natural History|location=Berkeley, CA|publisher=University of California Press}}</ref> Other examples include cypress (''[[Taxodium]]'') and [[mangrove]] swamps.
=== Fauna ===
[[File:Northern Leopard Frog (Lithobates pipiens).jpg|thumb|upright|Many species of [[frog]]s live in wetlands, while others visit them each year to lay eggs.]]
[[File:Snapping turtle 3 md.jpg|thumb|[[Snapping turtle]]s are one of the many kinds of turtles found in wetlands.]]
Many species of [[fish]] are highly dependent on wetland ecosystems.<ref>{{Cite journal |last1=Colvin |first1=S. A. R. |last2=Sullivan |first2=S. M. P. |last3=Shirey |first3=P. D. |last4=Colvin |first4=R. W. |last5=Winemiller |first5=K. O. |last6=Hughes |first6=R. M. |last7=Fausch |first7=K. D. |last8=Infante |first8=D. M. |last9=Olden |first9=J. D. |last10=Bestgen |first10=K. R. |last11=Danehy |first11=R. J. |last12=Eby |first12=L. |date=2019 |title=Headwater Streams and Wetlands are Critical for Sustaining Fish, Fisheries, and Ecosystem Services |journal=Fisheries |language=en |volume=44 |issue=2 |pages=73–91 |doi=10.1002/fsh.10229|bibcode=2019Fish...44...73C |s2cid=92052162}}</ref><ref>{{Cite journal |last1=Sievers |first1=M. |last2=Brown |first2=C. J. |last3=Tulloch |first3=V. J. D. |last4=Pearson |first4=R. M. |last5=Haig |first5=J. A. |last6=Turschwell |first6=M. P. |last7=Connolly |first7=R. M. |date=2019 |title=The Role of Vegetated Coastal Wetlands for Marine Megafauna Conservation |journal=Trends in Ecology & Evolution |language=English |volume=34 |issue=9 |pages=807–817 |doi=10.1016/j.tree.2019.04.004 |pmid=31126633 |bibcode=2019TEcoE..34..807S |hdl=10072/391960 |s2cid=164219103 |hdl-access=free}}</ref> Seventy-five percent of the United States' commercial fish and shellfish stocks depend solely on [[Estuary|estuaries]] to survive.<ref name="ramsar_a">{{cite web |title=Ramsar Convention Ecosystem Services Benefit Factsheets| access-date = 2011-09-25 | url = http://www.ramsar.org/cda/en/ramsar-pubs-info-ecosystem-services/main/ramsar/1-30-103%5E24258_4000_0__}}</ref>
[[Amphibian]]s such as [[frog]]s and [[salamander]]s need both terrestrial and aquatic habitats in which to reproduce and feed. Because amphibians often inhabit depressional wetlands like prairie potholes and Carolina bays, the connectivity among these isolated wetlands is an important control of regional populations.<ref>{{Cite journal |last1=Zamberletti |first1=P. |last2=Zaffaroni |first2=M. |last3=Accatino |first3=F. |last4=Creed |first4=I. F. |last5=De Michele |first5=C. |date=2018 |title=Connectivity among wetlands matters for vulnerable amphibian populations in wetlandscapes |journal=Ecological Modelling |language=en |volume=384 |pages=119–127 |doi=10.1016/j.ecolmodel.2018.05.008 |bibcode=2018EcMod.384..119Z |s2cid=90384249|url=https://hal.inrae.fr/hal-02626276/file/Zamberletti_2018_preprint.pdf }}</ref> While tadpoles feed on algae, adult frogs forage on insects. Frogs are sometimes used as an indicator of [[ecosystem health]] because their thin skin permits absorption of nutrients and toxins from the surrounding environment resulting in increased extinction rates in unfavorable and polluted environmental conditions.<ref>{{cite web|url=http://www.savethefrogs.com/why-frogs/ |title=Frogs {{!}} Bioindicators |website=Savethefrogs.com |date=2011 |access-date=2014-01-21}}</ref>
[[Reptile]]s such as [[snake]]s, [[lizard]]s, [[turtle]]s, [[alligator]]s and [[crocodile]]s are common in wetlands of some regions. In freshwater wetlands of the Southeastern US, alligators are common and a freshwater species of crocodile occurs in South Florida. The Florida [[Everglades]] is the only place in the world where both crocodiles and alligators coexist.<ref>{{cite journal |author=Mazzotti, F.J. |author2=Best, G.R. |author3=Brandt, L.A. |author4=Cherkiss, M.S. |author5=Jeffery, B.M. |author6=Rice, K.G. |year=2009 |title=Alligators and crocodiles as indicators for restoration of Everglades ecosystems |journal=Ecological Indicators  |volume=9 |issue=6 |page=S137−S149|doi=10.1016/j.ecolind.2008.06.008 |bibcode=2009EcInd...9.S137M}}</ref> The [[saltwater crocodile]] inhabits estuaries and mangroves.<ref>{{cite book |author=Messel, H. |year=1981 |title=Surveys of tidal river systems in the Northern Territory of Australia and their crocodile populations |volume=1 |publisher=Pergamon Press}}</ref> [[Snapping turtle]]s also inhabit wetlands.<ref>{{Cite journal |last1=Piczak |first1=M. L. |last2=Chow-Fraser |first2=P. |date=2019 |title=Assessment of critical habitat for common snapping turtles (''Chelydra serpentina'') in an urbanized coastal wetland |journal=Urban Ecosystems |volume=22 |issue=3 |pages=525–537 |doi=10.1007/s11252-019-00841-1 |bibcode=2019UrbEc..22..525P |s2cid=78091420}}</ref>
[[Bird]]s, particularly [[waterfowl]] and [[wader]]s use wetlands extensively.<ref>{{Cite book |title=Wetland birds: habitat resources and conservation implications |last=Milton |first=W. |date=1999 |publisher=Cambridge University Press |isbn=978-0511011368 |location=Cambridge |oclc=50984660}}</ref>
[[Mammal]]s of wetlands include numerous small and medium-sized species such as [[vole]]s, [[bat]]s,<ref>{{Cite journal |last1=Mas |first1=M. |last2=Flaquer |first2=C. |last3=Rebelo |first3=H. |last4=López-Baucells |first4=A. |date=2021 |title=Bats and wetlands: synthesising gaps in current knowledge and future opportunities for conservation |journal=Mammal Review |volume=51 |issue=3 |pages=369–384 |doi=10.1111/mam.12243 |s2cid=233974999}}</ref> [[muskrat]]s<ref>{{Cite journal |last1=Bomske |first1=C. M. |last2=Ahlers |first2=A. A. |date=2021 |title=How do muskrats ''Ondatra zibethicus'' affect ecosystems? A review of evidence |journal=Mammal Review |volume=51 |issue=1 |pages=40–50 |doi=10.1111/mam.12218 |s2cid=224916636}}</ref> and [[platypus]] in addition to large herbivorous and [[apex predator]] species such as the [[beaver]]s,<ref>{{Cite journal |last1=Rosell |first1=F. |last2=Bozser |first2=O. |last3=Collen |first3=P. |last4=Parker |first4=H. |date=2005 |title=Ecological impact of beavers ''Castor fiber'' and ''Castor canadensis'' and their ability to modify ecosystems |journal=Mammal Review |volume=35 |issue=3–4 |pages=248–276 |doi=10.1111/j.1365-2907.2005.00067.x |hdl=11250/2438080 |issn=0305-1838|hdl-access=free}}</ref> [[coypu]], [[swamp rabbit]], [[Florida panther]],<ref>{{Cite journal |last1=Kerk |first1=M. |last2=Onorato |first2=D. P. |last3=Hostetler |first3=J. A. |last4=Bolker |first4=B. M. |last5=Oli |first5=M. K. |date=2019 |title=Dynamics, Persistence, and Genetic Management of the Endangered Florida Panther Population |journal=Wildlife Monographs |volume=203 |issue=1 |pages=3–35 |doi=10.1002/wmon.1041 |bibcode=2019WildM.203....3V |s2cid=199641325 |doi-access=free }}</ref> [[jaguar]],<ref>{{Cite journal |last1=Figel |first1=J. J. |last2=Botero-Cañola |first2=S. |last3=Forero-Medina |first3=G. |last4=Sánchez-Londoño |first4=J. D. |last5=Valenzuela |first5=L. |last6=Noss |first6=R. F.|date=2019 |title=Wetlands are keystone habitats for jaguars in an intercontinental biodiversity hotspot |journal=PLOS ONE |volume=14 |issue=9 |pages=e0221705 |doi=10.1371/journal.pone.0221705 |doi-access=free|pmid=31509559 |pmc=6738587 |bibcode=2019PLoSO..1421705F }}</ref> and [[moose]]. Wetlands attract many mammals due to abundant seeds, berries, and other vegetation as food for herbivores, as well as abundant populations of invertebrates, small reptiles and amphibians as prey for predators.<ref>{{cite web |url=https://www.environment.nsw.gov.au/topics/water/wetlands/plants-and-animals-in-wetlands/mammals |title=Mammals in Wetlands |work=NSW Environment, Energy and Science |publisher=Department of Planning, Industry and Environment |date=2020 |access-date=2021-10-11}}</ref>
[[Invertebrate]]s of wetlands include aquatic insects such as [[dragonflies]], aquatic bugs and [[beetle]]s, midges, [[mosquito]]s, [[crustacean]]s such as crabs, crayfish, shrimps, microcrustaceans, mollusks like clams, mussels, snails and worms. Invertebrates comprise more than half of the known animal species in wetlands, and are considered the primary food web link between plants and higher animals (such as fish and birds).<ref>{{Cite book |title=Invertebrates in freshwater wetlands of North America: ecology and management |date=1999 |publisher=Wiley |last1=Batzer |first1=D. P. |last2=Rader |first2=R. Ben. |last3=Wissinger |first3=S. A. |isbn=978-0471292586 |location=New York |oclc= 39747651}}</ref>
== Ecosystem services ==
{{Further|Ecosystem service}}
Depending on a wetland's geographic and topographic location,<ref>Adamus, P.R. and L.T. Stockwell. 1983. ''A Method for Wetland Functional Assessment.'' Vol. I. Critical Review and Evaluation Concepts. FHWA-IP-82-23. Federal Highway Admin., Washington, DC.</ref> the functions it performs can support multiple [[ecosystem services]], values, or benefits. [[Millennium Ecosystem Assessment|United Nations Millennium Ecosystem Assessment]] and [[Ramsar Convention]] described wetlands as a whole to be of [[biosphere]] significance and societal importance in the following areas:<ref>{{Cite book |title=Ecosystems and human well-being: wetlands and water synthesis: a report of the Millennium Ecosystem Assessment |date=2005 |publisher=World Resources Institute |author=Millennium Ecosystem Assessment |isbn=1-56973-597-2 |location=Washington, DC |oclc=62172810}}</ref>
* [[Flood control|Water storage (flood control)]]
* Groundwater replenishment
* Shoreline stabilization and storm protection
* [[Water purification]]
* [[Wastewater treatment]] (in [[constructed wetland]]s)
* Reservoirs of [[biodiversity]]
* Pollination
* Wetland products
* Cultural values
* Recreation and [[Eco tourism|tourism]]
* [[Climate change mitigation]] and [[Climate change adaptation|adaptation]]
According to the Ramsar Convention:{{citation needed|date=December 2022}}
<blockquote>The economic worth of the ecosystem services provided to society by intact, naturally functioning wetlands is frequently much greater than the perceived benefits of converting them to 'more valuable' intensive land use – particularly as the profits from unsustainable use often go to relatively few individuals or corporations, rather than being shared by society as a whole.</blockquote>
To replace these wetland [[ecosystem services]], enormous amounts of money would need to be spent on [[water purification]] plants, dams, levees, and other hard infrastructure, and many of the services are impossible to replace.
=== Storage reservoirs and flood protection ===
Floodplains and closed-depression wetlands can provide the functions of storage reservoirs and flood protection. The wetland system of [[floodplains]] is formed from major rivers downstream from their [[headwaters]]. "The floodplains of major rivers act as natural storage reservoirs, enabling excess water to spread out over a wide area, which reduces its depth and speed. Wetlands close to the headwaters of streams and rivers can slow down rainwater runoff and spring snowmelt so that it does not run straight off the land into water courses. This can help prevent sudden, damaging floods downstream."<ref name="ramsar_a" />
Notable river systems that produce wide floodplains include the [[Nile River]], the Niger river inland delta, the Zambezi River flood plain, the Okavango River inland delta, the Kafue River flood plain, the Lake Bangweulu flood plain (Africa), [[Mississippi River]] (US), [[Amazon River]] (South America), [[Yangtze River]] (China), [[Danube River]] (Central Europe) and [[Murray-Darling]] River (Australia).
===Groundwater replenishment===
Groundwater replenishment can be achieved for example by [[marsh]], [[swamp]], and subterranean [[karst]] and cave hydrological systems. The [[surface water]] visibly seen in wetlands only represents a portion of the overall water cycle, which also includes atmospheric water (precipitation) and [[groundwater]]. Many wetlands are directly linked to groundwater and they can be a crucial regulator of both the quantity and [[water quality|quality of water]] found below the ground. Wetlands that have [[Permeability (earth sciences)|permeable]] substrates like [[limestone]] or occur in areas with highly variable and fluctuating water tables have especially important roles in [[groundwater replenishment]] or water recharge.<ref>{{Cite journal |last1=van der Kamp |first1=Garth |last2=Hayashi |first2=Masaki |date=2009-02-01 |title=Groundwater-wetland ecosystem interaction in the semiarid glaciated plains of North America |journal=Hydrogeology Journal |language=en |volume=17 |issue=1 |pages=203–214 |doi=10.1007/s10040-008-0367-1 |bibcode=2009HydJ...17..203V |s2cid=129332187 |issn=1435-0157}}</ref>
Substrates that are [[porous]] allow water to filter down through the soil and underlying rock into [[aquifers]] which are the source of much of the world's [[drinking water]]. Wetlands can also act as recharge areas when the surrounding water table is low and as a discharge zone when it is high.
===Shoreline stabilization and storm protection===
{{Main|Integrated coastal zone management}}
[[Mangrove]]s, [[coral reef]]s, [[salt marsh]] can help with shoreline stabilization and storm protection. Tidal and inter-tidal wetland systems protect and stabilize coastal zones.<ref>{{Cite journal |last1=Costanza |first1=Robert |last2=Anderson |first2=Sharolyn J. |last3=Sutton |first3=Paul |last4=Mulder |first4=Kenneth |last5=Mulder |first5=Obadiah |last6=Kubiszewski |first6=Ida |last7=Wang |first7=Xuantong |last8=Liu |first8=Xin |last9=Pérez-Maqueo |first9=Octavio |last10=Luisa Martinez |first10=M. |last11=Jarvis |first11=Diane |last12=Dee |first12=Greg |date=2021-09-01 |title=The global value of coastal wetlands for storm protection |journal=Global Environmental Change |language=en |volume=70 |pages=102328 |doi=10.1016/j.gloenvcha.2021.102328 |issn=0959-3780|doi-access=free |bibcode=2021GEC....7002328C |hdl=1885/296695 |hdl-access=free }}</ref> [[Coral reefs]] provide a protective barrier to coastal shoreline. [[Mangrove]]s stabilize the coastal zone from the interior and will migrate with the shoreline to remain adjacent to the boundary of the water. The main conservation benefit these systems have against storms and [[storm surge]]s is the ability to reduce the speed and height of waves and floodwaters.
The [[United Kingdom]] has begun the concept of managed coastal realignment. This management technique provides shoreline protection through restoration of natural wetlands rather than through applied engineering. In East Asia, reclamation of coastal wetlands has resulted in widespread transformation of the coastal zone, and up to 65% of coastal wetlands have been destroyed by coastal development.<ref>{{Citation | first1 = J. | last1 = MacKinnon | first2 = Y. I. | last2 = Verkuil | first3 = N. J. | last3 = Murray | date = 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 | page = 70 | publisher = IUCN | place = Gland, Switzerland and Cambridge, UK | isbn = 9782831712550 | url = http://www.iucn.org/asiancoastalwetlands/ | archive-url = https://archive.today/20140624015227/http://www.iucn.org/asiancoastalwetlands/ | archive-date = 2014-06-24 }}</ref><ref>{{cite journal | 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. | date = 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 | bibcode = 2014FrEE...12..267M | url = http://espace.library.uq.edu.au/view/UQ:331832/UQ331832_OA.pdf }}</ref> One analysis using the impact of hurricanes versus storm protection provided naturally by wetlands projected the value of this service at US$33,000/hectare/year.<ref>{{cite web|url=http://www.fao.org/figis/servlet/static?dom=root&xml=index.xml|title=FAO|archive-url=https://web.archive.org/web/20070909042747/http://www.fao.org/figis/servlet/static?dom=root&xml=index.xml|archive-date=2007-09-09|access-date=2011-09-25}}</ref>
===Water purification===
[[Water purification]] can be provided by floodplains, closed-depression wetlands, [[mudflat]], [[freshwater marsh]], [[salt marsh]], mangroves. Wetlands cycle both sediments and nutrients, sometimes serving as buffers between [[Terrestrial ecoregion|terrestrial]] and [[aquatic ecosystems]]. A natural function of wetland vegetation is the up-take, storage, and (for nitrate) the removal of nutrients found in [[Surface runoff|runoff]] water from the surrounding landscapes.<ref>{{cite web|url=http://www.wild.org/blog/letting-nature-do-the-job|title=Letting Nature Do the Job|date=2008-08-01|website=Wild.org|archive-url=https://archive.today/20130113192135/http://www.wild.org/blog/letting-nature-do-the-job|archive-date=2013-01-13|access-date=2012-05-23}}</ref>
Precipitation and surface runoff induces [[soil erosion]], transporting sediment in suspension into and through waterways. All types of sediments whether composed of clay, silt, sand or gravel and rock can be carried into wetland systems through erosion. Wetland vegetation acts as a physical barrier to slow water flow and then trap sediment for both short or long periods of time. Suspended sediment can contain heavy metals that are also retained when wetlands trap the sediment.
The ability of wetland systems to store or remove nutrients and trap sediment is highly efficient and effective but each system has a threshold. An overabundance of nutrient input from fertilizer run-off, sewage effluent, or non-point pollution will cause [[eutrophication]]. Upstream erosion from [[deforestation]] can overwhelm wetlands making them shrink in size and cause dramatic [[biodiversity loss]] through excessive sedimentation load.
===Wastewater treatment===
Constructed wetlands are built for wastewater treatment. An example of how a natural wetland is used to provide some degree of [[sewage treatment]] is the [[East Kolkata Wetlands]] in [[Kolkata, India]]. The wetlands cover {{convert|125|km2|sqmi}}, and are used to treat Kolkata's sewage. The nutrients contained in the wastewater sustain fish farms and agriculture.
{{Excerpt|Constructed wetland|paragraphs=1,2}}
===Reservoirs of biodiversity===
Wetland systems' rich [[biodiversity]] has become a focal point catalysed by the [[Ramsar Convention]] and [[World Wildlife Fund]].<ref>{{Cite web |title=What is a wetland? And eight other wetland facts |url=https://www.worldwildlife.org/stories/what-is-a-wetland-and-8-other-wetland-facts |access-date=2022-11-18 |website=World Wildlife Fund |language=en}}</ref> The impact of maintaining biodiversity is seen at the local level through job creation, sustainability, and community productivity. A good example is the Lower Mekong basin which runs through Cambodia, Laos, and Vietnam, supporting over 55&nbsp;million people.
A key fish species which is overfished,<ref>{{Cite journal |last1=Prestes |first1=Luiza |last2=Barthem |first2=Ronaldo |last3=Mello-Filho |first3=Adauto |last4=Anderson |first4=Elizabeth |last5=Correa |first5=Sandra B. |last6=Couto |first6=Thiago Belisario D'Araujo |last7=Venticinque |first7=Eduardo |last8=Forsberg |first8=Bruce |last9=Cañas |first9=Carlos |last10=Bentes |first10=Bianca |last11=Goulding |first11=Michael |date=2022-03-02 |editor-last=Aguirre |editor-first=Windsor E. |title=Proactively averting the collapse of Amazon fisheries based on three migratory flagship species |journal=PLOS ONE |language=en |volume=17 |issue=3 |pages=e0264490 |doi=10.1371/journal.pone.0264490 |pmid=35235610 |pmc=8890642 |bibcode=2022PLoSO..1764490P |issn=1932-6203|doi-access=free }}</ref> the Piramutaba catfish, ''[[Brachyplatystoma vaillantii]]'', migrates more than {{convert|3300|km|mi|abbr=on}} from its nursery grounds near the mouth of the Amazon River to its spawning grounds in Andean tributaries, {{convert|400|m|ft|abbr=on}} above sea level, distributing plant seeds along the route.
Intertidal mudflats have a level of productivity similar to that of some wetlands even while possessing a low number of species. The abundant [[invertebrates]] found within the mud are a food source for [[migratory waterfowl]].<ref>{{Cite journal |last1=Jing |first1=Zhu |last2=Kai |first2=Jing |last3=Xiaojing |first3=Gan |last4=Zhijun |first4=Ma |date=2007 |title=Food supply in intertidal area for shorebirds during stopover at Chongming Dongtan, China |url=https://linkinghub.elsevier.com/retrieve/pii/S1872203207600456 |journal=Acta Ecologica Sinica |language=en |volume=27 |issue=6 |pages=2149–2159 |doi=10.1016/S1872-2032(07)60045-6|bibcode=2007AcEcS..27.2149J }}</ref>
Mudflats, saltmarshes, mangroves, and seagrass beds have high levels of both species richness and productivity, and are home to important nursery areas for many commercial fish stocks.
Populations of many species are confined geographically to only one or a few wetland systems, often due to the long period of time that the wetlands have been physically isolated from other aquatic sources. For example, the number of [[endemic species]] in the Selenga River Delta of [[Lake Baikal]] in Russia classifies it as a hotspot for biodiversity and one of the most biodiverse wetlands in the entire world.<ref>{{Cite journal |last1=Lane |first1=Charles R. |last2=Anenkhonov |first2=Oleg |last3=Liu |first3=Hongxing |last4=Autrey |first4=Bradley C. |last5=Chepinoga |first5=Victor |date=2015 |title=Classification and inventory of freshwater wetlands and aquatic habitats in the Selenga River Delta of Lake Baikal, Russia, using high-resolution satellite imagery |url=http://link.springer.com/10.1007/s11273-014-9369-z |journal=Wetlands Ecology and Management |language=en |volume=23 |issue=2 |pages=195–214 |doi=10.1007/s11273-014-9369-z |bibcode=2015WetEM..23..195L |s2cid=16980247 |issn=0923-4861}}</ref>
===Wetland products===
[[File:Broadmoor Wildlife Sanctuary marsh.jpg|thumb|Wetland at the Broadmoor Wildlife Sanctuary in Massachusetts, United States, in February]]
Wetlands naturally produce an array of vegetation and other ecological products that can be harvested for personal and commercial use.<ref>{{Cite book |title=Waterlogged wealth: why waste the world's wet places? |last=Maltby |first=E. |date=1986 |publisher=International Institute for Environment and Development |others=Earthscan |isbn=978-0905347639 |location=London |url-access=registration |url=https://archive.org/details/waterloggedwealt0000malt}}</ref> Many fishes have all or part of their life-cycle occurring within a wetland system. Fresh and saltwater fish are the main source of protein for about one billion people<ref>{{Cite journal |last1=Tidwell |first1=James H |last2=Allan |first2=Geoff L |date=2001 |title=Fish as food: aquaculture's contribution: Ecological and economic impacts and contributions of fish farming and capture fisheries  |journal=EMBO Reports |language=en |volume=2 |issue=11 |pages=958–963 |doi=10.1093/embo-reports/kve236 |issn=1469-221X |pmc=1084135 |pmid=11713181}}</ref> and comprise 15% of an additional 3.5&nbsp;billion people's protein intake.<ref>{{Cite journal |last1=Béné |first1=Christophe |last2=Barange |first2=Manuel |last3=Subasinghe |first3=Rohana |last4=Pinstrup-Andersen |first4=Per |last5=Merino |first5=Gorka |last6=Hemre |first6=Gro-Ingunn |last7=Williams |first7=Meryl |date=2015-04-01 |title=Feeding 9 billion by 2050 – Putting fish back on the menu |journal=Food Security |language=en |volume=7 |issue=2 |pages=261–274 |doi=10.1007/s12571-015-0427-z |s2cid=18671617 |issn=1876-4525|doi-access=free }}</ref> Another food staple found in wetland systems is rice, a popular grain that is consumed at the rate of one fifth of the total global calorie count. In Bangladesh, Cambodia and Vietnam, where rice paddies are predominant on the landscape, rice consumption reach 70%.<ref name="ramsar b">{{cite web|url=http://www.ramsar.org/cda/en/ramsar-documents-info/main/ramsar/1-31-59_4000_0__|title=The Ramsar Information Sheet on Wetlands of International Importance|date=September 18, 2009|access-date=November 19, 2011}}</ref> Some native wetland plants in the Caribbean and Australia are harvested sustainably for medicinal compounds; these include the red mangrove (''[[Rhizophora mangle]]'') which possesses antibacterial, wound-healing, anti-ulcer effects, and antioxidant properties.<ref name="ramsar b" />
Other mangrove-derived products include fuelwood, salt (produced by evaporating seawater), animal fodder, traditional medicines (e.g. from mangrove bark), fibers for textiles and dyes and tannins.<ref>{{Cite book |last=Hogarth |first=Peter J. |title=The biology of mangroves and seagrasses |date=2015 |isbn=978-0-19-102590-7 |edition=Third |location=Oxford |oclc=907773290}}</ref>
=== Additional services and uses of wetlands ===
Some types of wetlands can serve as fire breaks that help slow the spread of minor wildfires. Larger wetland systems can influence local precipitation patterns. Some boreal wetland systems in catchment headwaters may help extend the period of flow and maintain water temperature in connected downstream waters.<ref>{{Cite journal |last1=Leibowitz |first1=Scott G. |last2=Wigington |first2=Parker J. |last3=Schofield |first3=Kate A. |last4=Alexander |first4=Laurie C. |last5=Vanderhoof |first5=Melanie K. |last6=Golden |first6=Heather E. |date=2018 |title=Connectivity of Streams and Wetlands to Downstream Waters: An Integrated Systems Framework |journal=JAWRA Journal of the American Water Resources Association |language=en |volume=54 |issue=2 |pages=298–322 |doi=10.1111/1752-1688.12631 |pmc=6071435 |pmid=30078985|bibcode=2018JAWRA..54..298L }}</ref> Pollination services are supported by many wetlands which may provide the only suitable habitat for pollinating insects, birds, and mammals in highly developed areas.<ref>{{Citation |last=McInnes |first=Robert J. |title=Managing Wetlands for Pollination |date=2016 |work=The Wetland Book |pages=1–4 |editor-last=Finlayson |editor-first=C. Max |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-007-6172-8_226-1 |isbn=978-94-007-6172-8 |editor2-last=Everard |editor2-first=Mark |editor3-last=Irvine |editor3-first=Kenneth |editor4-last=McInnes |editor4-first=Robert J.|doi-access=free }}</ref>
== Disturbances and human impacts ==
{{See also|Human impacts on the environment}}
Wetlands, the functions and services they provide as well as their flora and fauna, can be affected by several types of disturbances.<ref>{{Cite journal |last1=Swindles |first1=Graeme T. |last2=Morris |first2=Paul J. |last3=Mullan |first3=Donal J. |last4=Payne |first4=Richard J. |last5=Roland |first5=Thomas P. |last6=Amesbury |first6=Matthew J. |last7=Lamentowicz |first7=Mariusz |last8=Turner |first8=T. Edward |last9=Gallego-Sala |first9=Angela |last10=Sim |first10=Thomas |last11=Barr |first11=Iestyn D. |date=2019-10-21 |title=Widespread drying of European peatlands in recent centuries |url=https://www.nature.com/articles/s41561-019-0462-z |journal=Nature Geoscience |language=en |volume=12 |issue=11 |pages=922–928 |bibcode=2019NatGe..12..922S |doi=10.1038/s41561-019-0462-z |issn=1752-0908 |s2cid=202908362 |hdl-access=free |hdl=10871/39305}} [http://eprints.whiterose.ac.uk/151050/ Alt URL] {{Webarchive|url=https://web.archive.org/web/20200727010653/http://eprints.whiterose.ac.uk/151050/|date=2020-07-27}}</ref> The disturbances (sometimes termed stressors or alterations) can be human-associated or natural, direct or indirect, reversible or not, and isolated or cumulative.
Disturbances include [[Exogeny|exogenous]] factors such as flooding or drought.<ref name="clewell2013" /> Humans are disturbing and damaging wetlands for example by [[oil and gas extraction]], building infrastructure, [[overgrazing]] of [[livestock]], [[overfishing]], alteration of wetlands including [[dredging]] and draining, [[nutrient pollution]] and [[water pollution]].<ref name="clewell2013" /><ref name="mitsch2007" /> Disturbance puts different levels of stress on an environment depending on the type and duration of disturbance.<ref name="clewell2013" />
Predominant disturbances of wetlands include:<ref>{{Cite web |author=Office of Research & Development |title=Impacts on quality of inland wetlands of the United States: A survey of indicators, techniques, and applications of community-level biomonitoring data |url=https://cfpub.epa.gov/si/si_public_record_Report.cfm?dirEntryID=39147 |access-date=2018-07-27 |website=cfpub.epa.gov}}</ref><ref>{{Cite book |last1=Adamus |first1=Paul |url=https://www.researchgate.net/publication/323993409 |title=Indicators for Monitoring Biological Integrity of Inland Freshwater Wetlands: A Survey of North American Technical Literature (1990–2000) |last2=J. Danielson |first2=Thomas |last3=Gonyaw |first3=Alex |date=2001-03-24 |publisher=13214 |doi=10.13140/rg.2.2.22371.86566}}</ref>
{{Div col|colwidth=22em}}
* Enrichment/[[eutrophication]]
* Organic loading and reduced dissolved oxygen
* Contaminant [[toxicity]]
* [[Freshwater acidification|Acidification]]
* [[Salinity|Salinization]]
* [[Sedimentation]]
* Altered solar input ([[turbidity]]/shade)
* Vegetation removal
* Thermal alteration
* Drying/[[aridification]]
* Inundation/flooding
* [[Habitat fragmentation]]
* Other human impacts
{{Div col end}}
Disturbances can be further categorized as follows:
* Minor disturbance: Stress that maintains ecosystem integrity.<ref name="clewell2013" />
* Moderate disturbance: Ecosystem integrity is damaged but can recover in time without assistance.<ref name="clewell2013" />
* Impairment or severe disturbance: Human intervention may be needed in order for ecosystem to recover.<ref name="clewell2013" />
[[Nutrient pollution]] comes from nitrogen inputs to aquatic systems and have drastically effected the dissolved nitrogen content of wetlands, introducing higher nutrient availability which leads to [[eutrophication]].<ref>{{Cite journal |last1=Finlay |first1=Jacques C. |last2=Efi Foufoula-Georgiou |author-link2=Efi Foufoula-Georgiou |last3=Dolph |first3=Christine L. |last4=Hansen |first4=Amy T. |date=February 2018 |title=Contribution of wetlands to nitrate removal at the watershed scale |journal=Nature Geoscience |volume=11 |issue=2 |pages=127–132 |bibcode=2018NatGe..11..127H |doi=10.1038/s41561-017-0056-6 |issn=1752-0908 |s2cid=46656300}}</ref>
[[Biodiversity loss]] occurs in wetland systems through [[land use change]]s, [[habitat destruction]], pollution, exploitation of resources, and [[invasive species]]. For example, the introduction of [[water hyacinth]], a native plant of South America into [[Lake Victoria]] in East Africa as well as [[duckweed]] into non-native areas of [[Queensland]], Australia, have overtaken entire wetland systems overwhelming the habitats and reducing the diversity of native plants and animals.{{citation needed|date=August 2024}}
=== Conversion to dry land ===
To increase economic productivity, wetlands are often converted into dry land with [[Ditch|dykes]] and [[Drainage|drains]] and used for agricultural purposes. The construction of dykes, and dams, has negative consequences for individual wetlands and entire watersheds.<ref name="Keddy2010" />{{rp|497}} Their proximity to lakes and rivers means that they are often developed for human settlement.<ref name="Alexander">{{cite book |last=Alexander |first=David E. |title=Encyclopedia of Environmental Science |date=1 May 1999 |publisher=[[Springer Science+Business Media|Springer]] |isbn=0-412-74050-8}}</ref> Once settlements are constructed and protected by dykes, the settlements then become vulnerable to land subsidence and ever increasing risk of flooding.<ref name="Keddy2010" />{{rp|497}} The Mississippi River Delta around New Orleans, Louisiana is a well-known example;<ref>{{Cite journal |last1=Keddy |first1=P.A. |last2=Campbell |first2=D. |last3=McFalls |first3=T. |last4=Shaffer |first4=G.P. |last5=Moreau |first5=R. |last6=Dranguet |first6=C. |last7=Heleniak |first7=R. |date=2007 |title=The Wetlands of Lakes Pontchartrain and Maurepas: Past, Present and Future |url=http://www.nrcresearchpress.com/doi/10.1139/a06-008 |journal=Environmental Reviews |language=en |volume=15 |issue=NA |pages=43–77 |doi=10.1139/a06-008 |issn=1181-8700}}</ref> the Danube Delta in Europe is another.<ref>Gastescu, P. (1993). The Danube Delta: geographical characteristics and ecological recovery. Earth and Environmental Science, 29, 57–67.</ref>
=== Drainage of floodplains ===
[[Drainage]] of [[floodplain]]s or development activities that narrow floodplain corridors (such as the construction of [[levee]]s) reduces the ability of coupled river-floodplain systems to control flood damage. That is because modified and less expansive systems must still manage the same amount of precipitation, causing flood peaks to be higher or deeper and floodwaters to travel faster.
Water management engineering developments in the past century have degraded floodplain wetlands through the construction of artificial embankments such as [[Levee|dykes]], bunds, [[levees]], [[weirs]], barrages and [[dams]]. All concentrate water into a main channel and waters that historically spread slowly over a large, shallow area are concentrated. Loss of wetland floodplains results in more severe and damaging flooding. Catastrophic human impact in the Mississippi River floodplains was seen in death of several hundred individuals during a [[2005 levee failures in Greater New Orleans|levee breach in New Orleans caused by Hurricane Katrina]]. Human-made embankments along the Yangtze River floodplains have caused the main channel of the river to become prone to more frequent and damaging flooding.<ref>{{Cite journal |last1=Li |first1=Luqian |last2=Lu |first2=XiXi |last3=Chen |first3=Zhongyuan |date=2007 |title=River channel change during the last 50 years in the middle Yangtze River, the Jianli reach |url=https://linkinghub.elsevier.com/retrieve/pii/S0169555X06003151 |journal=Geomorphology |language=en |volume=85 |issue=3–4 |pages=185–196 |bibcode=2007Geomo..85..185L |doi=10.1016/j.geomorph.2006.03.035}}</ref> Some of these events include the loss of [[riparian vegetation]], a 30% loss of the vegetation cover throughout the river's basin, a doubling of the percentage of the land affected by soil erosion, and a reduction in reservoir capacity through [[siltation]] build-up in floodplain lakes.<ref name="ramsar_a" />
=== Overfishing ===
[[Overfishing]] is a major problem for sustainable use of wetlands. Concerns are developing over certain aspects of farm fishing, which uses natural wetlands and waterways to harvest fish for human consumption. [[Aquaculture]] is continuing to develop rapidly throughout the Asia-Pacific region especially in China where 90% of the total number of aquaculture farms occur, contributing 80% of global value.<ref name="ramsar b" /> Some aquaculture has eliminated massive areas of wetland through practices such as the [[shrimp farming]] industry's destruction of mangroves. Even though the damaging impact of large-scale shrimp farming on the coastal ecosystem in many Asian countries has been widely recognized for quite some time now, it has proved difficult to mitigate since other employment avenues for people are lacking. Also burgeoning demand for shrimp globally has provided a large and ready market.<ref>{{Cite web |title=Shrimp Market Size, Share & Growth Analysis Report, 2030 |url=https://www.grandviewresearch.com/industry-analysis/shrimp-market-report |access-date=2022-11-19 |website=www.grandviewresearch.com |language=en}}</ref>
== Conservation ==
{{main|Wetland conservation}}
[[File:Hommik Mukri rabas.jpg|thumb|upright=1.25|Fog rising over the Mukri bog near [[Mukri, Estonia]]. The bog has an area of {{convert|2147|ha}} and has been protected since 1992.]]
Wetlands have historically subjected to large draining efforts for development ([[Real estate development|real estate]] or agriculture), and [[flooding]] to create recreational [[lake]]s or generate [[hydropower]]. Some of the world's most important agricultural areas were wetlands that have been converted to farmland.<ref>{{cite book|first=G. P.|last=Van de Ven|date=2004|title=Man-Made Lowlands: History of water management and land reclamation in the Netherlands|location=Utrecht|publisher=Uitgeverij Matrijs}}</ref><ref>{{cite book|last=Wells|first=Samuel A.|date=1830|title=A History of the Drainage of the Great Level of the Fens called Bedford Level 2|url=https://archive.org/details/historydrainage00wellgoog|location=London|publisher=R. Pheney}}</ref><ref>{{cite web|first1=Thomas E.|last1=Dahl|first2=Gregory J.|last2=Allord|title=History of Wetlands in the Conterminous United States|url=https://water.usgs.gov/nwsum/WSP2425/history.html}}</ref><ref>{{cite journal|first=Brian|last=Lander|title=State Management of River Dikes in Early China: New Sources on the Environmental History of the Central Yangzi Region|journal=T'oung Pao|volume=100|issue=4–5|date=2014|pages=325–362|doi=10.1163/15685322-10045p02}}</ref> Since the 1970s, more focus has been put on preserving wetlands for their natural functions. Since 1900, 65–70% of the world's wetlands have been lost.<ref>{{Cite journal |last=Davidson |first=Nick C. |date=2014 |title=How much wetland has the world lost? Long-term and recent trends in global wetland area |url=http://www.publish.csiro.au/?paper=MF14173 |journal=Marine and Freshwater Research |language=en |volume=65 |issue=10 |pages=934 |doi=10.1071/MF14173 |issn=1323-1650}}</ref> In order to maintain wetlands and sustain their functions, alterations and disturbances that are outside the normal range of variation should be minimized.
===Balancing wetland conservation with the needs of people===
Wetlands are vital ecosystems that enhance the livelihoods for the millions of people who live in and around them. Studies have shown that it is possible to conserve wetlands while improving the livelihoods of people living among them. Case studies conducted in Malawi and Zambia looked at how [[dambo]]s – wet, grassy valleys or depressions where water seeps to the surface – can be farmed sustainably. Project outcomes included a high yield of crops, development of [[Sustainable agriculture|sustainable farming]] techniques, and water management strategies that generate enough water for irrigation.<ref>{{cite web |date=2008-12-01 |title=Good practices and lessons learned in integrating ecosystem conservation and poverty reduction objectives in wetlands |url=https://www.ramsar.org/news/linking-wetland-management-and-poverty-reduction |access-date=10 May 2022 |publisher=The Ramsar Convention on Wetlands}}</ref>
===Ramsar Convention===
{{Main|Ramsar Convention|List of Ramsar wetlands of international importance}}
The [[Ramsar Convention]] (full title: ''Convention on Wetlands of International Importance, especially as Waterfowl Habitat''), is an international [[treaty]] designed to address global concerns regarding wetland loss and degradation. The primary purposes of the treaty are to list wetlands of international importance and to promote their wise use, with the ultimate goal of preserving the world's wetlands. Methods include restricting access to some wetland areas, as well as educating the public to combat the misconception that wetlands are wastelands. The Convention works closely with five International Organisation Partners (IOPs). These are: [[Birdlife International]], the [[IUCN]], the [[International Water Management Institute]], [[Wetlands International]] and the [[World Wide Fund for Nature]]. The partners provide technical expertise, help conduct or facilitate field studies and provide financial support.
==Restoration==
Restoration and [[Restoration ecology|restoration ecologists]] intend to return wetlands to their natural trajectory by aiding directly with the natural processes of the ecosystem.<ref name="clewell2013">{{cite book|last1=Clewell|first1=AF|last2=Aronson|first2=J|title=Ecological restoration|date=2013|publisher=Island Press|location=Washington, DC|edition=2nd}}</ref> These direct methods vary with respect to the degree of physical manipulation of the natural environment and each are associated with different levels of restoration.<ref name="clewell2013" /> Restoration is needed after disturbance or [[Disturbance (ecology)|perturbation]] of a wetland.<ref name="clewell2013" /> There is no one way to restore a wetland and the level of restoration required will be based on the level of disturbance although, each method of restoration does require preparation and administration.<ref name="clewell2013" />
===Levels of restoration===
Factors influencing selected approach may include<ref name="clewell2013" /> budget, time scale limitations, project goals, level of disturbance, landscape and ecological constraints, political and administrative agendas and socioeconomic priorities.
==== Prescribed natural or assisted regeneration ====
For this strategy, there is no biophysical manipulation and the ecosystem is left to recover based on the process of [[Ecological succession|succession]] alone.<ref name="clewell2013" /> The focus is to eliminate and prevent further disturbance from occurring and for this type of restoration requires prior research to understand the probability that the wetland will recover naturally. This is likely to be the first method of approach since it is the least intrusive and least expensive although some biophysical non-intrusive manipulation may be required to enhance the rate of succession to an acceptable level.<ref name="clewell2013" /> Example methods include prescribed burns to small areas, promotion of site specific soil [[microbiota]] and plant growth using nucleation planting whereby plants radiate from an initial planting site,<ref>{{cite journal|last1=Corbin|first1=JD|last2=Holl|first2=KD|title=Applied nucleation as a forest restoration strategy|journal=Forest Ecology and Management|date=2012|volume=256|pages=37–46|doi=10.1016/j.foreco.2011.10.013|bibcode=2012ForEM.265...37C }}</ref> and promotion of niche diversity or increasing the range of niches to promote use by a variety of different species.<ref name="clewell2013" /> These methods can make it easier for the natural species to flourish by removing environmental impediments and can speed up the process of succession.
==== Partial reconstruction ====
For this strategy, a mixture of natural regeneration and manipulated environmental control is used. This may require some engineering, and more intensive biophysical manipulations including ripping of [[subsoil]], [[Agrochemical|agrichemical]] applications of herbicides or insecticides, laying of [[mulch]], mechanical seed dispersal, and tree planting on a large scale.<ref name="clewell2013" /> In these circumstances the wetland is impaired and without human assistance it would not recover within an acceptable period of time as determined by ecologists. Methods of restoration used will have to be determined on a site by site basis as each location will require a different approach based on levels of disturbance and the local ecosystem dynamics.<ref name="clewell2013" />
==== Complete reconstruction ====
{{further|Constructed wetland}}
This most expensive and intrusive method of reconstruction requires engineering and ground up reconstruction. Because there is a redesign of the entire ecosystem it is important that the natural trajectory of the ecosystem be considered and that the plant species promoted will eventually return the ecosystem towards its natural trajectory.<ref name="clewell2013" />
In many cases constructed wetlands are often designed to treat stormwater/wastewater runoff. They can be used in developments as part of [[water-sensitive urban design]] systems and have benefits such as flood mitigation, removing pollutants, carbon sequestration, providing habitat for wildlife and biodiversity in often highly urbanised and fragmented landscapes.<ref>{{cite book |title=Functional assessment of wetlands: towards evaluation of ecosystem services |date=2009 |publisher=Woodhead Publ. [u.a.] |location=Cambridge |isbn=978-1-84569-516-3}}</ref>
====Traditional knowledge====
The ideas from [[traditional ecological knowledge]] can be applied as a holistic approach to the restoration of wetlands.<ref>{{Cite book |last=Inglis, J. T. |url=https://books.google.com/books?id=J2CNS64AFvsC&pg=PR4 |title=Traditional Ecological Knowledge: Concepts and Cases |date=1993 |publisher=International Program on Traditional Ecological and International Development Research Centre |isbn=978-0-88936-683-1 |place=Ottawa, Canada}}</ref> These ideas focus more on responding to the observations detected from the environment considering that each part of a wetland ecosystem is interconnected. Applying these practices on specific locations of wetlands increase productivity, biodiversity, and improve its resilience. These practices include monitoring wetland resources, planting propagules, and addition of key species in order to create a self-sustaining wetland ecosystem.<ref>{{Cite book |last=Craft |first=Christopher |url=https://books.google.com/books?id=DNhOEAAAQBAJ&dq=Creating+and+Restoring+Wetlands+From+Theory+to+Practice&pg=PP1 |title=Creating and Restoring Wetlands: From Theory to Practice |date=2022-05-12 |publisher=Elsevier |isbn=978-0-12-823982-7 |language=en}}</ref>
== Climate change aspects ==
=== Greenhouse gas emissions ===
In Southeast Asia, [[peat swamp forest]]s and soils are being drained, burnt, mined, and overgrazed, contributing to [[climate change]].<ref name="wetlands">{{cite web |title=Wetlands International works to sustain and restore wetlands for people and biodiversity |url=http://www.wetlands.org/ |access-date=2014-01-21 |publisher=Wetlands International}}</ref> As a result of peat drainage, the organic carbon that had built up over thousands of years and is normally under water is suddenly exposed to the air. The peat decomposes and is converted into [[carbon dioxide]] (CO<sub>2</sub>), which is then released into the atmosphere. Peat fires cause the same process to occur rapidly and in addition create enormous clouds of smoke that cross international borders, which now happens almost yearly in Southeast Asia. While peatlands constitute only 3% of the world's land area, their degradation produces 7% of all CO<sub>2</sub> emissions.{{excerpt|Wetland methane emissions}}
===Climate change mitigation===
{{Further|Climate change mitigation#Wetlands|Carbon sequestration#Wetlands||Blue carbon}}
Studies have favorably identified the potential for coastal wetlands (also called [[blue carbon]] ecosystems) to provide some degree of [[climate change mitigation]] in two ways: by conservation, reducing the greenhouse gas emissions arising from the loss and degradation of such habitats, and by restoration, to increase carbon dioxide drawdown and its long-term storage.<ref name=":6">{{Cite journal |last1=Williamson |first1=Phillip |last2=Gattuso |first2=Jean-Pierre |date=2022 |title=Carbon Removal Using Coastal Blue Carbon Ecosystems Is Uncertain and Unreliable, With Questionable Climatic Cost-Effectiveness |journal=Frontiers in Climate |volume=4 |pages=853666 |doi=10.3389/fclim.2022.853666 |issn=2624-9553|doi-access=free}} [[File:CC-BY icon.svg|50px]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/  Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=2017-10-16 }}</ref> However, CO<sub>2</sub> removal using coastal blue carbon restoration has questionable cost-effectiveness when considered only as a climate mitigation action, either for [[Carbon offset|carbon-offsetting]] or for inclusion in [[Nationally determined contribution|Nationally Determined Contributions]].<ref name=":6" />
When wetlands are restored they have mitigation effects through their ability to [[Carbon sink|sink carbon]], converting a greenhouse gas ([[carbon dioxide]]) to solid plant material through the process of [[photosynthesis]], and also through their ability to store and regulate water.<ref>{{cite book |title=Synthesis of Adaptation Options for Coastal Areas |date=2009 |publisher=US Environmental Protection Agency |series=Climate Ready Estuaries Program, EPA 430-F-08-024 |location=Washington, DC}}</ref><ref>{{Cite web |date=2020-02-06 |title=Coastal Wetland Protection |url=https://drawdown.org/solutions/coastal-wetland-protection |access-date=2020-09-13 |website=Project Drawdown |language=en}}</ref>
Wetlands store approximately 44.6 million tonnes of carbon per year globally (estimate from 2003).<ref name="Chmura, G. L. 2003">{{cite journal |last1=Chmura |first1=G. L. |date=2003 |title=Global carbon sequestration in tidal, saline wetland soils |journal=Global Biogeochemical Cycles |volume=17 |issue=4 |pages=1111 |bibcode=2003GBioC..17.1111C |doi=10.1029/2002GB001917 |doi-access=free |s2cid=36119878}}{{page needed|date=January 2017}}</ref> In [[salt marsh]]es and mangrove swamps in particular, the average [[carbon sequestration]] rate is {{nowrap|210 g CO<sub>2</sub> m<sup>−2</sup> y<sup>−1</sup>}} while [[peatlands]] sequester approximately {{nowrap|20–30 g CO<sub>2</sub> m<sup>−2</sup> y<sup>−1</sup>}}.<ref name="Chmura, G. L. 2003" /><ref>{{cite journal |last=Roulet |first=N. T. |date=2000 |title=Peatlands, Carbon Storage, Greenhouse Gases, And The Kyoto Protocol: Prospects And Significance For Canada |journal=Wetlands |volume=20 |issue=4 |pages=605–615 |doi=10.1672/0277-5212(2000)020[0605:pcsgga]2.0.co;2 |s2cid=7490212}}</ref>
Coastal wetlands, such as tropical [[mangrove]]s and some temperate [[salt marshes]], are known to be sinks for carbon that otherwise contribute to [[climate change]] in its gaseous forms (carbon dioxide and methane).<ref>{{Cite journal |last1=Ouyang |first1=Xiaoguang |last2=Lee |first2=Shing Yip |date=2020-01-16 |title=Improved estimates on global carbon stock and carbon pools in tidal wetlands |journal=Nature Communications |language=en |volume=11 |issue=1 |pages=317 |bibcode=2020NatCo..11..317O |doi=10.1038/s41467-019-14120-2 |issn=2041-1723 |pmc=6965625 |pmid=31949151 |doi-access=free}}</ref> The ability of many tidal wetlands to store carbon and minimize methane flux from tidal sediments has led to sponsorship of [[blue carbon]] initiatives that are intended to enhance those processes.<ref>{{Cite web|url=https://earthtimes.org/blogs/climate/blue-carbon|title=Blue Carbon|website=Earth Times}}</ref><ref>{{Cite journal |last=Wang |first=F. |date=2021 |title=Global blue carbon accumulation in tidal wetlands increases with climate change |journal=National Science Review |volume=8 |issue=9 |pages=nwaa296 |doi=10.1093/nsr/nwaa296 |pmid=34691731|pmc=8433083 }}</ref>
=== Climate change adaptation ===
{{Further|Climate change adaptation}}
The restoration of coastal blue carbon ecosystems is highly advantageous for [[climate change adaptation]], coastal protection, food provision and biodiversity conservation.<ref name=":6" />
Since the middle of the 20th century, human-caused [[climate change]] has resulted in observable changes in the global [[water cycle]].<ref name=":8">Arias, P.A., N. Bellouin, E. Coppola, R.G. Jones, G. Krinner, J. Marotzke, V. Naik, M.D. Palmer, G.-K. Plattner, J. Rogelj, M. Rojas, J. Sillmann, T. Storelvmo, P.W. Thorne, B. Trewin, K. Achuta Rao, B. Adhikary, R.P. Allan, K. Armour, G. Bala, R. Barimalala, S. Berger, J.G. Canadell, C. Cassou, A. Cherchi, W. Collins, W.D. Collins, S.L. Connors, S. Corti, F. Cruz, F.J. Dentener, C. Dereczynski, A. Di Luca, A. Diongue Niang, F.J. Doblas-Reyes, A. Dosio, H. Douville, F. Engelbrecht, V.  Eyring, E. Fischer, P. Forster, B. Fox-Kemper, J.S. Fuglestvedt, J.C. Fyfe, et al., 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf Technical Summary] {{Webarchive|url=https://web.archive.org/web/20220721021347/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |date=2022-07-21 }}. In [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] {{Webarchive|url=https://web.archive.org/web/20210809131444/https://www.ipcc.ch/report/ar6/wg1/ |date=2021-08-09 }} [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 33–144. doi:10.1017/9781009157896.002.</ref>{{rp|85}} A warming climate makes extremely wet and very dry occurrences more severe, causing more severe floods and droughts. For this reason, some of the ecosystem services that wetlands provide (e.g. water storage and flood control, groundwater replenishment, shoreline stabilization and storm protection) are important for climate change adaptation measures.<ref name=":52">{{Cite web |title=Fact Sheet: Blue Carbon |url=https://www.american.edu/sis/centers/carbon-removal/fact-sheet-blue-carbon.cfm |url-status=live |archive-url=https://web.archive.org/web/20210428062528/https://www.american.edu/sis/centers/carbon-removal/fact-sheet-blue-carbon.cfm |archive-date=April 28, 2021 |access-date=2021-04-28 |website=American University |language=en}}</ref> In most parts of the world and under all [[Climate change scenario#Emissions scenarios|emission scenarios]], water cycle variability and accompanying extremes are anticipated to rise more quickly than the changes of average values.<ref name=":8"/>{{rp|85}}
== Valuation ==
The value of a wetland to local communities typically involves first mapping a region's wetlands, then assessing the functions and ecosystem services the wetlands provide individually and cumulatively, and finally evaluating that information to prioritize or rank individual wetlands or wetland types for conservation, management, restoration, or development.<ref>{{Citation |last=Emerton |first=Lucy |title=Economic Valuation of Wetlands: Total Economic Value |date=2016 |work=The Wetland Book |pages=1–6 |editor-last=Finlayson |editor-first=C. Max |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-007-6172-8_301-1 |isbn=978-94-007-6172-8 |editor2-last=Everard |editor2-first=Mark |editor3-last=Irvine |editor3-first=Kenneth |editor4-last=McInnes |editor4-first=Robert J.|doi-access=free }}</ref> Over the longer term, it requires keeping inventories<ref>{{Cite web |title=A new toolkit for National Wetlands Inventories {{!}} Convention on Wetlands |url=https://www.ramsar.org/news/a-new-toolkit-for-national-wetlands-inventories |access-date=2022-11-28 |website=www.ramsar.org}}</ref> of known wetlands and monitoring a representative sample of the wetlands to determine changes due to both natural and human factors.
===Assessment===
Rapid assessment methods are used to score, rank, rate, or categorize various functions, [[ecosystem services]], species, communities, levels of disturbance, and/or [[ecological health]] of a wetland or group of wetlands.<ref>{{Cite journal |last1=McInnes |first1=R.J. |last2=Everard |first2=M. |date=2017 |title=Rapid Assessment of Wetland Ecosystem Services (RAWES): An example from Colombo, Sri Lanka |url=https://linkinghub.elsevier.com/retrieve/pii/S221204161630417X |journal=Ecosystem Services |language=en |volume=25 |pages=89–105 |doi=10.1016/j.ecoser.2017.03.024|bibcode=2017EcoSv..25...89M |s2cid=56403914 }}</ref> This is often done to prioritize particular wetlands for conservation (avoidance) or to determine the degree to which loss or alteration of wetland functions should be compensated, such as by restoring degraded wetlands elsewhere or providing additional protections to existing wetlands. Rapid assessment methods are also applied before and after a wetland has been restored or altered, to help monitor or predict the effects of those actions on various wetland functions and the services they provide. Assessments are typically considered to be "rapid" when they require only a single visit to the wetland lasting less than one day, which in some cases may include interpretation of aerial imagery and [[geographic information system]] (GIS) analyses of existing spatial data, but not detailed post-visit laboratory analyses of water or biological samples.
To achieve consistency among persons doing the assessment, rapid methods present indicator variables as questions or checklists on standardized data forms, and most methods standardize the scoring or rating procedure that is used to combine question responses into estimates of the levels of specified functions relative to the levels estimated in other wetlands ("calibration sites") assessed previously in a region.<ref>{{Cite web |last=Adamus |first=P. |date=2016 |title=Manual for the Wetland Ecosystem Services Protocol (WESP) |url=http://people.oregonstate.edu/~adamusp/WESP/Manual_WESP1.3_13Oct2016_Adamus.pdf |archive-url=https://web.archive.org/web/20180728191340/http://people.oregonstate.edu/~adamusp/WESP/Manual_WESP1.3_13Oct2016_Adamus.pdf |archive-date=2018-07-28 |url-status=live |access-date=July 28, 2018 |website=Oregon State University}}</ref> Rapid assessment methods, partly because they often use dozens of indicators pertaining to conditions surrounding a wetland as well as within the wetland itself, aim to provide estimates of wetland functions and services that are more accurate and repeatable than simply describing a wetland's class type.<ref name="ACADEMIC PRESS" /> A need for wetland assessments to be rapid arises mostly when government agencies set deadlines for decisions affecting a wetland, or when the number of wetlands needing information on their functions or condition is large.
===Inventory===
Although developing a global inventory of wetlands has proven to be a large and difficult undertaking, many efforts at more local scales have been successful.<ref>{{Cite web |title=Home {{!}} Ramsar Sites Information Service |url=https://rsis.ramsar.org/ |access-date=2022-11-28 |website=rsis.ramsar.org}}</ref> Current efforts are based on available data, but both classification and spatial resolution have sometimes proven to be inadequate for regional or site-specific environmental management decision making. It is difficult to identify small, long, and narrow wetlands within the landscape. Many of today's [[remote sensing]] satellites do not have sufficient spatial and spectral resolution to monitor wetland conditions, although multispectral IKONOS<ref>{{Cite journal |last1=Wei |first1=Anhua |last2=Chow-Fraser |first2=Patricia |date=2007 |title=Use of IKONOS Imagery to Map Coastal Wetlands of Georgian Bay |url=http://doi.wiley.com/10.1577/1548-8446(2007)32[167:UOIITM]2.0.CO;2 |journal=Fisheries |language=en |volume=32 |issue=4 |pages=167–173 |doi=10.1577/1548-8446(2007)32[167:UOIITM]2.0.CO;2 |issn=0363-2415}}</ref> and QuickBird<ref>{{Cite journal |last1=Cook |first1=Bruce D. |last2=Bolstad |first2=Paul V. |last3=Næsset |first3=Erik |last4=Anderson |first4=Ryan S. |last5=Garrigues |first5=Sebastian |last6=Morisette |first6=Jeffrey T. |last7=Nickeson |first7=Jaime |last8=Davis |first8=Kenneth J. |date=2009-11-16 |title=Using LiDAR and quickbird data to model plant production and quantify uncertainties associated with wetland detection and land cover generalizations |url=https://linkinghub.elsevier.com/retrieve/pii/S0034425709002119 |journal=Remote Sensing of Environment |language=en |volume=113 |issue=11 |pages=2366–2379 |doi=10.1016/j.rse.2009.06.017|bibcode=2009RSEnv.113.2366C }}</ref> data may offer improved spatial resolutions once it is 4&nbsp;m or higher. Majority of the pixels are just mixtures of several plant species or vegetation types and are difficult to isolate which translates into an inability to classify the vegetation that defines the wetland. The growing availability of 3D vegetation and topography data from LiDAR has partially addressed the limitation of traditional multispectral imagery, as demonstrated in some case studies across the world.<ref name="xu2022">{{cite journal |last1=Xu |first1=Haiqing |last2=Toman |first2=Elizabeth |last3=Zhao |first3=Kaiguang |last4=Baird |first4=John |title=Fusion of Lidar and Aerial Imagery to Map Wetlands and Channels via Deep Convolutional Neural Network |journal=Transportation Research Record |date=2022 |volume=2676 |issue=12 |pages=374–381 |doi=10.1177/03611981221095522 |s2cid=251780248 |url=https://journals.sagepub.com/doi/10.1177/03611981221095522}}</ref>
===Monitoring and mapping===
A wetland needs to be monitored<ref>{{Cite journal |last1=Stephenson |first1=P. J. |last2=Ntiamoa-Baidu |first2=Yaa |last3=Simaika |first3=John P. |date=2020 |title=The Use of Traditional and Modern Tools for Monitoring Wetlands Biodiversity in Africa: Challenges and Opportunities |journal=Frontiers in Environmental Science |volume=8 |doi=10.3389/fenvs.2020.00061 |issn=2296-665X|doi-access=free }}</ref> over time to assess whether it is functioning at an ecologically sustainable level or whether it is becoming degraded.<ref>{{Cite journal |last1=Bhatnagar |first1=Saheba |last2=Gill |first2=Laurence |last3=Regan |first3=Shane |last4=Waldren |first4=Stephen |last5=Ghosh |first5=Bidisha |date=2021-04-01 |title=A nested drone-satellite approach to monitoring the ecological conditions of wetlands |journal=ISPRS Journal of Photogrammetry and Remote Sensing |language=en |volume=174 |pages=151–165 |doi=10.1016/j.isprsjprs.2021.01.012 |bibcode=2021JPRS..174..151B |s2cid=233522024 |issn=0924-2716|doi-access=free }}</ref> Degraded wetlands will suffer a loss in water quality, loss of sensitive species, and aberrant functioning of soil geochemical processes.
Practically, many natural wetlands are difficult to monitor from the ground as they quite often are difficult to access and may require exposure to dangerous plants and animals as well as diseases borne by insects or other invertebrates. Remote sensing such as aerial imagery and satellite imaging<ref>{{Cite journal |last1=Munizaga |first1=Juan |last2=García |first2=Mariano |last3=Ureta |first3=Fernando |last4=Novoa |first4=Vanessa |last5=Rojas |first5=Octavio |last6=Rojas |first6=Carolina |date=2022 |title=Mapping Coastal Wetlands Using Satellite Imagery and Machine Learning in a Highly Urbanized Landscape |journal=Sustainability |language=en |volume=14 |issue=9 |pages=5700 |doi=10.3390/su14095700 |issn=2071-1050|doi-access=free }}</ref> provides effective tools to map and monitor wetlands across large geographic regions and over time. Many remote sensing methods can be used to map wetlands. The integration of multi-sourced data such as [[LiDAR]] and aerial photos proves more effective at mapping wetlands than the use of aerial photos alone,<ref name="xu2022" /> especially with the aid of modern machine learning methods (e.g., deep learning). Overall, using digital data provides a standardized data-collection procedure and an opportunity for data integration within a [[geographic information system]].
== Legislation ==
=== International efforts ===
{{excerpt|Ramsar Convention}}
=== National efforts ===
====United States====
Each country and region tends to have a codified definition of wetlands for legal purposes. In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas".<ref>{{cite web|date=March 2015|title=EPA Regulations listed at 40 CFR 230.3(t)|url=http://water.epa.gov/lawsregs/guidance/wetlands/definitions.cfm|access-date=2014-02-18|publisher=US Environmental Protection Agency}}</ref> This definition has been used in the enforcement of the [[Clean Water Act]]. Some US states, such as [[Massachusetts]] and [[New York (state)|New York]], have separate definitions that may differ from the federal government's.
In the [[United States Code]], the term wetland is defined "as land that (A) has a predominance of hydric soils, (B) is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation typically adapted for life in saturated soil conditions and (C) under normal circumstances supports a prevalence of such vegetation." Related to these legal definitions, "normal circumstances" are expected to occur during the wet portion of the growing season under normal climatic conditions (not unusually dry or unusually wet) and in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Still, under normal environmental conditions, the soils will be inundated to the surface, creating anaerobic conditions persisting through the wet portion of the growing season.<ref>US Government Publishing Office. (2011) [https://www.law.cornell.edu/uscode/text/16/3801 16 U.S. Code Chapter 58 Subchapter I, § 3801 – Definitions] {{Webarchive|url=https://web.archive.org/web/20170206000118/https://www.law.cornell.edu/uscode/text/16/3801 |date=2017-02-06 }}. Legal Information Institute,  Cornell Law School, Ithaca.</ref>
==== Canada ====
* [[Wetlands and wetland policies in Canada]]<ref name=rubec2009>{{cite journal |last1=Rubec |first1=C. D.A. |last2=Hanson|first2=A. R|title=Wetland mitigation and compensation: Canadian experience |journal=Wetlands Ecol Manage |date=2009|volume=17|issue=1 |pages=3–14 |doi=10.1007/s11273-008-9078-6 |bibcode=2009WetEM..17....3R |s2cid=32876048}}</ref>
* Other Individual Provincial and Territorial Based Policies<ref name=rubec2009/>
== Examples ==
{{See also|List of Ramsar Wetlands of International Importance|Mediterranean wetlands|List of Ramsar wetland sites in Pakistan|List of Ramsar sites in Australia}}
The world's largest wetlands include the swamp forests of the [[Amazon River basin]], the peatlands of the [[West Siberian Plain]],<ref name="FraserKeddy" /> the [[Pantanal]] in South America,<ref name=":1" /> and the [[Sundarbans]] in the [[Ganges]]-[[Brahmaputra]] delta.<ref name=":2" />
==See also==
{{Portal|Wetlands|Environment|Ecology|Water}}
* {{annotated link|List of wetland plants}}
* {{in title|wetland}}
==References==
{{Reflist|24em}}
==External links==
* {{commons-inline}}
{{Wetlands}}
{{Aquatic ecosystem topics}}
{{Biomes}}
{{Authority control}}
[[Category:Wetlands| ]]
[[Category:Aquatic ecology]]<!---saline--->
[[Category:Environmental terminology]]
[[Category:Freshwater ecology]]
[[Category:Habitat]]
[[Category:Terrestrial biomes]]
[[Category:Bodies of water]]
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