If you were to choose a name for one of the world’s most important types of habitat, you would probably not choose ‘wetlands’.  It conjures up images of soggy wastelands, bogs, swamps and other generally unloved (by humans at least) environments.  A motley collection of water-dominated habitats that have traditionally been regarded by many ‘modern’ humas, as a waste of space – to be drained and reclaimed so they can be put towards more ‘productive’ purposes.

But as so often with the natural world, our perception is – at best – inaccurate and short-sighted, ignorant of the vital role these areas play in our planet’s ecosystem.  Belatedly, wetlands are now recognized as absolutely vital.  Some experts call them the “kidneys of the earth” because of their high and long-term capacity to filter pollutants from the water that flows through them.

Even from a human perspective, the World Wildlife Fund (WWF) estimates that somewhere between 300-400 million people live close to, and depend upon, wetlands which also support the cultivation of crops such as rice, a staple in the diet of half the world’s population.  They also provide flood control, clean water, shoreline and storm protection, materials, medicines, and vital habitat.

For many years, the habitat on which most of our efforts to protect the environment were focused were forests, particularly rainforests, such as the Congo and the Amazon.  Yet wetlands can be even more effective carbon sinks than forests.  Research suggests that mangroves and coastal wetlands sequester carbon ten times faster than mature tropical forests.  They also store three to five times more carbon per equivalent area than tropical forests.  Unfortunately, wetlands, from marshes to swamps to coral reefs, are disappearing at a rate some three times faster than the forests we are always talking about.

Over 80% of wetlands have been ‘degraded’ in some manner, since the 18th Century, while 35% have been lost since 1970.  Not so coincidentally, there has been a staggering 83% collapse in freshwater species’ populations since then[1].

Yet all is not lost.  Recent decades have seen growing international recognition at both grass roots and policy maker levels, that this is a critical issue that requires urgent action.

What is a wetland?

The working definition of a wetland is “an area of inland or coastal land partly covered, or saturated by, water”, though there are more formal descriptions such as the one used by the US Fish & Wildlife Service (USFWS)[2], of “…lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water….”  Which are necessary to enforce legal protection.




They come in many forms, with examples are found across all continents and some are among the most well-known regions of the world, places such as the Florida Everglades, Australia’s Great Barrier Reef, and the Amazon Basin.

Very broadly speaking, there are several  major categories of wetlands[3][4]:

  • Marshes: are wetlands that are permanently flooded or flooded during high water periods at the edges of rivers, streams, lakes, or ponds. Marshes may be dominated by submersed, floating-leaved, or emergent vegetation.  According to whether they are inland or coastal and fed by rivers or oceans, marshes can be either fresh or salt water.  Depending on tides, currents and seasons, water levels in these regions often fluctuate.
    • Emergent marshes are found around shorelines out to relatively shallow water, and generally characterized by emergent plant species up to 100%.
    • Hemi-marsh is found in deeper water and characterized by a mix of emergent and/or floating-leaved vegetation intermingled with a submersed plant community.
  • Sedge meadows (or wet meadows): are wetlands with permanently or near-permanently saturated soils often forming a transitional zone between marshes and other wetlands with less-saturated soils, or in wet depressions or around groundwater discharge zones. The meadows are wet grasslands often dominated by sedges and grasses with few broad-leaved flowering plants.
  • Fens and seeps: are fed by groundwater ‘seeping’ to the surface. The vegetation found here depends on the water chemistry and acidity.
    • Fens: typically, are alkaline with groundwater emerging from calcareous, dolomitic soils or bedrock, and contain peat layer from dead plant material, typically with herbaceous vegetation.
    • Seeps are found along the base of slopes or glacial deposits where water emerges from saturated soils or a spring.
  • Bogs: are freshwater basin wetlands where precipitation is the only water source so are not fed by surfacing groundwater or streams. They are generally of spongy terrain, dominated by a mat of mosses and are prevalent in the cooler climates of Europe, Asia, North America, and the Arctic regions.  The mosses acidify the water to levels as low as 3.0 pH, comparable to acid rain, with a micro-climate, very low oxygen levels and are nutrient poor.  They commonly evolve from lakes that have been filled with plant debris.  Over time, this debris partially decomposes to form peat and is a major source of carbon storage.
  • Swamps: are either fresh or saltwater wetlands dominated by woody vegetation that typically have standing water during certain times of the year and are often in low-elevation floodplains along rivers or slow-moving streams. Unlike bogs, they offer a nutrient-rich environment.
    • Forested swamps are dominated by water-tolerant trees such as mangroves or cypress.
    • Shrub swamps, sometimes also known as scrub-shrub wetlands, are dominated by short, shrubby.

Havens of biodiversity

Wetlands punch well above their weight in terms of biodiversity.  Though they cover only a small portion of the Earth’s land surface, 40% of all plant and animal species – including 30% of all known fish species – live or breed in wetlands[5].  More than 100,000 freshwater species have been identified in wetlands so far, with 200 new ones discovered annually.

They are home to many threatened amphibians and reptiles, host migratory and resident water birds, and nurture thousands of plant species.  Coastal wetlands, like mangroves and coral reefs, are among the most biologically diverse places on Earth, while many endemic species are only found in a specific wetland area.  Unfortunately, a quarter of these species are threatened by extinction.  For instance, in New South Wales, Australia, there are 71 known frog species, 47 of which depend on wetlands[6].  When these wetlands are under threat, so are the local frogs – up to 18 frog species.  To combat this, the state government in New South Wales has enacted a number of policies to protect wetlands, most recently 2016’s Biodiversity Conservation Act, and the region has added 200,000 hectares of wetlands to its protected reserves since 2005.

Sunrise in Pantanal, Brazil. Pantanal is the world’s largest wetland

Boosting carbon reduction

Wetlands are able to store much more carbon than they release, which makes them one of the world’s most important ‘carbon sinks.’  Research suggests that, despite amounting to less than 5% of global land area and less than 2% of the ocean, they store roughly 50% of all carbon buried in ocean sediments.[7]  As such, they are crucial to achieving the Paris Agreement target of limiting “the increase in the global average temperature to well below 2°C above pre-industrial levels”, with a target of 1.5oC.

The capacity of wetlands to capture and store carbon depends on a number of factors.  A crucial element is the wet, low-oxygen conditions of tidally influenced and submerged soils common in coastal wetlands, conditions which naturally slow the decay of plant and other organic material.  During photosynthesis, plants absorb carbon dioxide from the air and water and use it to support their growth.  When the plants die or shed old leaves or roots, the carbon in the decaying organic matter becomes locked in the soils, preventing it from being released into the atmosphere and contributing to climate change.

When wetlands degrade, however – by being drained for example – stored carbon is released into the atmosphere in the form of three major greenhouse gases: carbon dioxide, methane, and nitrous oxide.  It’s estimated that around 450 million metric tons of carbon dioxide is emitted from the destruction of coastal wetlands each year.[8]

Wetlands Carbon Sequention

Natural water filters

As their “kidneys of the earth” title suggests, wetlands are also extraordinarily effective at purifying water.  As sediment-containing water passes through wetlands, the water flow slows down so the sediment drops out of the water and become part of the ground layer[9].  In this way, the water becomes clearer, and sediment is removed which would otherwise create cloudy water conditions.  This is particularly useful in dealing with agricultural runoff and sewage effluent which contain high levels of nutrients such as phosphorous and nitrogen.

Wetlands can stop these nutrients from reaching toxic levels in the groundwater used for drinking and reduce eutrophication, the process by which they cause a massive boost in algal growth, depleting oxygen and blocking out the light that other aquatic plants and animals need to survive.

Removing sediments benefits humans, plants and animals because sediments often contain toxins and, in wetlands, these contaminants are sequestered within the sediment layer.  Provided that this layer remains undisturbed, these pollutants are effectively trapped and rendered harmless, while the clearer water enables organisms that filter water for food, such as clams, to flourish.

Even the plants that inhabit the wetlands have their role to play in purifying water.  Many of them can remove toxic substances from pesticides, industrial discharges and mining activities[10].  For instance, the tissues of some floating plants, especially Eichhornia crassipes (water hyacinth), Lemna (duckweed) and Azolla (water fern) are able to absorb and ‘store’ heavy metals – such as iron and copper – contained in wastewater.  The quantity of heavy metals taken up by plants depends on a whole variety of factors such as speed of water, climate and type of plants – but levels are commonly many times higher in plant stems, leaves and roots than in the wastewater being treated.

These principles have been successfully applied – at scale – to one of the world’s most crowded cities.  Originally built to house one million people, Kolkata (Calcutta) in India is now home to more than 10 million, many living in slums.

East Kolkata Wetlands
The 8,000-hectare East Kolkata Wetlands site. Photo Credit © East Kolkata Wetlands Management Authority

But the 8,000-hectare East Kolkata Wetlands site[11] – and the 20,000 people that work there – is able to re-purpose one-third of the city’s sewage and most of its domestic refuse to support toxin-free fish and fresh vegetables.

Extreme weather protection

One of the great benefits of the wetlands habitat for anyone living nearby is that it acts as a defense against many different natural hazards.  It forms a barrier to flooding from the coast, as it intercepts high tides and distribute the force of incoming water over flood plains.  It stores up water to strengthen water security during drought.  It can help to regulate coastal climates.  And it can lower the risk of flooding by absorbing heavy rains into the porous ground beneath the wetland surface.

This is because wetlands contain water-loving soils called histosols[12], which comprise 20% to 30% organic matter and develop in areas that are poorly drained, causing decomposing plant or animal material to become part of the soil.  Histosols can absorb great quantities of water – a single acre of wetlands can absorb up to 1.5 million gallons of water.

The protective power of wetlands was demonstrated in 2012 by Hurricane Sandy, one of the worst storms to hit the US East Coast[13].  Across the four states with the most wetland coverage, flood damage was reduced by 20%-30% compared to unprotected areas.  In New Jersey alone, where wetlands cover 10% of the floodplain, it is estimated the state saved nearly US$ 430 million in flood damage.

Insurance companies took note.  Now Zurich Canada, along with another 14 insurers, is collaborating with environmental non-profit Ducks Unlimited Canada to form Nature Force.  Using modeling tools, Nature Force will identify urban areas across Canada that are susceptible to flooding and then develop projects to restore or manage wetlands to provide flood resilience.

Under attack

If wetlands are such important sites of biodiversity, not to mention carbon sequestration, why were they drained in the first place?  The answer, as it so often is, is a combination of short-term thinking and ignorance.  Draining the Pontine Marshes in Italy, for example, seemed a good idea at the time as they sheltered the malaria-bearing mosquitos that plagued Rome[14].   In Iraq, Saddam Hussein drained the Mesopotamian marshes in the 1980s to deny shelter to his opponents.  But much of the wetlands that have been lost in recent centuries has been due to agriculture and commercial priorities.

Linked to this is the long-held belief that wetlands are just wasteland; unproductive land that could be put to much better use once it has been drained or filled.  In the Mekong Delta in China, for example, the UN’s Indo-Burma Wetland Outlook 2022 warns that “natural wetlands have been been filled-in and ‘reclaimed’ for infrastructure development as urban sprawl continues to swallow up surrounding floodplains.”[15]

Progress towards protection

Thankfully, there has been growing global recognition over the past few years of the critical contribution wetlands make to the environmental sustainability of our planet, and of the need to preserve and reinstate them, rather than drain them.

The fight to protect wetlands first kicked off with the wildlife charities such as the World Wildlife Fund (WWF), which as far back as 1963 bought land in the Coto Doñana, Spain, a crucially important stopover wetland for migratory birds[16].  It has continued to work with governments and other charities to buy and safeguard millions of hectares of wetland.  For example, in 2000 it cooperated with the governments of Bulgaria, Romania, Ukraine and Moldova to set up a protected green corridor along the lower reaches of the Danube, a scheme now covering 1.4 million hectares of wetland.

Yet the WWF’s biggest contribution may be its work towards establishing the Ramsar Convention in 1971.[17]  Named after the Iranian city in which it was drawn up, the Ramsar Convention on Wetlands is the only global treaty to focus on a single ecosystem and the number of countries signed up to it has grown from the original seven to 170[18], nearly 90% of all UN members.  These signatories commit to:

  • Designate wetlands of high value on the list of Wetlands of International Importance (Ramsar sites)
  • Use all wetlands wisely and cooperate on transboundary issues.

Today there are around 2,500 designated Ramsar sites, in countries as diverse as Austria, Kazakhstan, UAE and Zimbabwe, covering a total surface area of more than 250 million hectares (an area slightly larger than Algeria).

One of the first multilateral environmental agreements, the Convention on Wetlands works alongside the six other major global biodiversity-related conventions[19], such as the Convention on Biological Diversity (CBD) and the World Heritage Convention (WHC).  Global Wetlands outlook A further breakthrough came in 2015 with the establishment of the UN Sustainable Development Goals (SDGs), aimed at achieving a “better and more sustainable future for all” by 2030.  Many of the individual SDGs can only be achieved by a concerted focus on preserving and protecting wetlands, as the Ramsar Convention makes clear in its 2018 report on wetlands and the SDGs.[20]

More has followed.  In 2022, at the UN Biodiversity Conference[21], countries reached a landmark agreement to protect nature, a deal that included a provision to restore at least 30% of degraded inland water bodies and conserve healthy freshwater ecosystems in an equitable way.  At the UN Water Conference in 2023, the ‘Freshwater Challenge’ was unveiled.  This is an ambitious initiative led by a coalition of governments, including Colombia, DR Congo, Ecuador, Gabon, Mexico, and Zambia, that aims to revitalize 300,000 km of rivers and restore 350 million hectares of wetlands (an area larger than India) by the year 2030.

All this activity augurs well. In a report by the Southern University of Science Technology in China[22], researchers calculated that restoring dried-out wetlands could avoid emissions equivalent to more than 100 billion tons of carbon dioxide by the end of the century, about a tenth of all expected human-caused emissions over the same period[23].  The same study also concluded that preventing degradation of intact wetlands would avoid an additional 150 to 650 billion tons of emissions by the end of the century.  Regions with the greatest potential for emissions reductions include Siberia, Canada, the Congo, Brazil and Indonesia.

New technologies

Addressing the global challenge of climate change requires significant efforts to reduce greenhouse gas emissions.  Immediate, short-term measures can also provide tangible benefits.

Strategies include increasing the size of wetlands by adding fresh sediment.  There are also cutting-edge methods being explored, such as “smart gates” that control tidal flows to protect coastal wetland.  Such gates prevent seawater from rising too much, and they’ve seen promising results in places like Hunter Wetlands National Park in Australia[24].

Hope not hype

From the first formal recognition of their importance at Ramsar more than 50 years ago to the present day, the world is increasingly recognizing the immense value and potential of wetlands.  These complex ecosystems not only serve as crucial carbon sinks and natural purifiers, but also provide a frontline defense against the adverse impacts of climate change.

More crucially, the pace of change is stepping up – and it must do, because we might be on the right track, but we are playing catch-up.  Reforestation and coastal wetlands restoration must accelerate threefold to meet the Paris Agreement targets for 2030, according to the World Resources Institute[25].  Nevertheless, the signs are positive, and progress is unmistakable.  Wetlands are recognized as a vital natural asset, essential for the environmental, social and commercial sustainability of our plant.  If we look after them, we will all benefit.  If we do not, our hopes for a more sustainable future could disappear beneath the rising waters of our oceans.

[1] https://www.unep.org/news-and-stories/press-release/largest-river-and-wetland-restoration-initiative-history-launched-un

[2] https://pondinformer.com/wetland-types/

[3] https://www.greenpeace.org.uk/news/wetlands-biodiversity-climate-change

[4] https://www.wetlands-initiative.org/what-is-a-wetland

[5] https://www.un.org/en/observances/world-wetlands-day

[6] https://www.zurich.com/en/media/magazine/2022/why-we-should-care-about-and-protect-our-wetlands

[7] https://bg.copernicus.org/articles/2/1/2005/

[8] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0043542

[9] https://sciencing.com/do-wetlands-filter-water-6398284.html

[10] https://www.ramsar.org/sites/default/files/documents/library/services_05_e.pdf

[11] https://www.ramsar.org/sites/default/files/documents/library/services_05_e.pdf

[12] https://www.zurich.com/en/media/magazine/2022/why-we-should-care-about-and-protect-our-wetlands

[13] https://www.zurich.com/en/media/magazine/2022/why-we-should-care-about-and-protect-our-wetlands

[14] https://pubmed.ncbi.nlm.nih.gov/20812795

[15] https://www.iucn.org/sites/default/files/2022-11/indo-burma-wetland-outlook-2022_v4.5_pages-compressed.pdf

[16] https://wwfint.awsassets.panda.org/downloads/wwf_50_years_ddd__lrsm_1.pdf

[17] https://www.ramsar.org/

[18] https://www.ramsar.org/sites/default/files/documents/library/services_05_e.pdf

[19] https://www.ramsar.org/about/partnerships/partnerships-other-conventions

[20] https://www.ramsar.org/sites/default/files/documents/library/wetlands_sdgs_e.pdf

[21] https://www.unep.org/un-biodiversity-conference-cop-15

[22] https://www.newscientist.com/article/2335373-rewetting-dried-wetlands-could-stop-100-billion-tons-of-co2-emissions

[23] https://www.newscientist.com/article/2335373-rewetting-dried-wetlands-could-stop-100-billion-tons-of-co2-emissions

[24] https://www.wrc.unsw.edu.au/news/turning-the-tide-on-the-hunter-wetlands

[25] https://www.wri.org/insights/climate-action-progress-indicators-2030-2050-targets