Wetlands: The World’s Most Productive Ecosystems

Wetlands are among the planet’s most remarkable yet undervalued ecosystems. These water-saturated landscapes-where aquatic and terrestrial environments meet-function as biodiversity hotspots, climate regulators, and natural water treatment facilities. Despite covering only about 6 percent of Earth’s land surface, wetlands support an extraordinary 40 percent of all plant and animal species. They are, quite simply, essential for both ecological balance and human survival.

What exactly are wetlands? 🔗

Wetlands are ecosystems where water is the primary factor controlling the environment and the associated plant and animal life. According to the U.S. Environmental Protection Agency, these landscapes are characterised by saturated soils during the growing season and standing water during certain times of the year. The presence of water-whether permanent, seasonal, or fluctuating-shapes everything from soil composition to the species that call these areas home.

The Ramsar Convention, an international treaty for wetland conservation, defines wetlands broadly as areas of marsh, fen, peatland, or water-whether natural or artificial, permanent or temporary-with water that is static or flowing, fresh, brackish, or salt. This definition encompasses an extraordinary range of habitats, from coastal mangroves and coral reefs to inland swamps and human-made rice paddies.

Major types of wetlands 🔗

Scientists classify wetlands into several major categories based on their location, water source, and dominant vegetation. The three broad groupings recognised internationally are marine and coastal wetlands, inland wetlands, and human-made wetlands.

Marshes are wetlands frequently or continually inundated with water, dominated by soft-stemmed emergent vegetation like cattails, reeds, and bulrushes. They occur in both freshwater and saltwater environments and are considered one of the most productive ecosystems on earth due to their high nutrient levels.

Swamps differ from marshes primarily in their vegetation-they are dominated by woody plants rather than grasses. Forested swamps support water-tolerant trees like cypress and tupelo, while shrub swamps feature buttonbush, willow, and dogwood. The nutrient-rich soils in swamps support highly diverse biological communities.

Bogs are distinctive wetlands characterised by spongy peat deposits, acidic waters, and a thick carpet of sphagnum moss. Unlike other wetlands, bogs receive most of their water from precipitation rather than groundwater or streams, resulting in nutrient-poor conditions that support specialised plants like carnivorous sundews and pitcher plants.

Fens are peat-forming wetlands that receive nutrients from groundwater and surrounding mineral soils, making them less acidic and more biologically diverse than bogs. Coastal wetlands include salt marshes, mangrove forests, and tidal flats that form crucial transition zones between land and sea.

The significance of wetlands for our planet 🔗

Wetlands play an outsized role in maintaining global ecological balance relative to their geographic extent. Their significance spans climate regulation, water management, and biodiversity conservation-functions that are increasingly critical as climate change accelerates.

Carbon storage powerhouses 🔗

Wetlands are remarkable carbon sinks. Although they cover just 5-8 percent of Earth’s land surface, wetlands store an estimated 20-30 percent of terrestrial organic carbon, representing a crucial component of global climate regulation. This carbon storage capacity stems from their unique anaerobic (oxygen-poor) soil conditions, which dramatically slow decomposition and allow organic matter to accumulate over centuries or even millennia.

Peatlands are particularly significant carbon reservoirs. The U.S. Global Change Research Program estimates that freshwater inland wetlands hold nearly ten times more carbon than tidal coastal wetlands, with peatlands in forested regions accounting for almost half of all wetland carbon storage in the United States. This accumulated carbon represents thousands of years of plant growth locked away from the atmosphere.

Coastal wetlands-including mangroves, salt marshes, and seagrass beds-also sequester carbon at impressive rates. These “blue carbon” ecosystems capture and store carbon dioxide while simultaneously buffering coastlines against rising sea levels and storm surges. The Global Wetland Outlook emphasises that restoring and protecting these ecosystems represents a powerful nature-based approach to climate change mitigation and adaptation.

Hydrological regulators 🔗

Wetlands function as natural sponges within the hydrological cycle. They absorb excess water during heavy rainfall and release it slowly during dry periods, effectively moderating both floods and droughts. The Washington State Department of Ecology notes that the cumulative presence of wetlands and lakes in a watershed can significantly reduce flood flows during major storm events.

This water storage capacity becomes increasingly valuable as climate change produces more extreme weather patterns. Wetlands also recharge groundwater aquifers, maintaining water supplies for surrounding ecosystems and human communities during dry seasons. For coastal areas, tidal marshes and mangroves provide additional protection by absorbing wave energy and reducing the impact of storm surges.

Biodiversity hotspots 🔗

The biological productivity of wetlands is extraordinary. Wetlands International reports that an estimated 40 percent of the world’s biodiversity is found in wetlands-from inland lakes and river floodplains to coastal mangroves and coral reefs. More than a million threatened plant and animal species depend on wetlands for their survival.

These ecosystems serve as critical connecting habitats, linking different environments and facilitating species movement. Hundreds of millions of migratory birds rely on networks of wetlands for feeding and resting along their intercontinental flyways. Over 1,000 migratory fish species depend on rivers and their associated ecosystems. Wetlands also provide nursery habitat for countless fish species that support both commercial and recreational fisheries.

Ecosystem services: what wetlands provide to humanity 🔗

The benefits that wetlands provide to human communities are vast and varied. Scientists categorise these as provisioning, regulating, and cultural ecosystem services-each representing tangible value for human wellbeing and economic activity.

Provisioning services 🔗

Wetlands directly supply resources essential for human survival and livelihoods. More than a billion people globally depend on wetlands for their livelihoods-approximately one in eight people on Earth. These ecosystems provide freshwater for drinking and irrigation, fish and shellfish for food, timber and plant materials for construction, and medicinal plants.

Rice paddies-a type of human-made wetland-produce the staple food for over half the world’s population. Coastal wetlands support commercial fishing industries worth billions of dollars annually. In many developing regions, wetlands provide the primary source of protein and income for local communities.

Regulating services 🔗

The regulating functions of wetlands protect communities and infrastructure from natural hazards while maintaining environmental quality. These services include flood mitigation through water storage and slow release, water purification through natural filtration processes, climate regulation through carbon sequestration, and shoreline stabilisation through vegetation that reduces erosion.

Wetlands have been called “kidneys of the landscape” because they function as downstream receivers of water and waste, filtering pollutants and excess nutrients before they reach rivers, lakes, and oceans. This natural water treatment reduces the need for costly engineered solutions while protecting drinking water supplies and aquatic ecosystems.

Cultural services 🔗

Beyond their ecological and economic functions, wetlands provide cultural, recreational, and spiritual value. They offer spaces for fishing, hunting, birdwatching, and nature tourism. Many wetlands hold deep cultural significance for indigenous communities, serving as sites for traditional practices, ceremonies, and storytelling passed down through generations.

Research increasingly recognises the mental health benefits of wetland landscapes. Access to these natural environments reduces stress, promotes physical activity, and enhances overall wellbeing. The aesthetic and educational value of wetlands also contributes to environmental awareness and conservation efforts.

Threats facing wetland ecosystems 🔗

Despite their immense value, wetlands are among Earth’s most threatened ecosystems. The United Nations reports that wetlands are disappearing three times faster than forests. In just 50 years since 1970, approximately 35 percent of the world’s wetlands have been lost-a staggering rate of decline that continues today.

Historical and ongoing losses 🔗

In the United States, a 2024 report from the U.S. Fish and Wildlife Service revealed that wetlands covered less than 6 percent of the lower 48 states as of 2019-half the area they covered since the 1780s. Loss rates have increased by 50 percent since 2009, with vegetated wetlands like marshes and swamps particularly affected. Between 2009 and 2019, the country lost approximately 670,000 acres of vegetated wetlands-an area roughly equal to Rhode Island.

Globally, the picture is similarly concerning. The Global Wetland Outlook reports that around 25 percent of remaining wetlands are in poor ecological condition, with this proportion increasing across all regions. Degradation now rivals outright loss as a threat to wetland ecosystems.

Primary drivers of wetland destruction 🔗

Agricultural expansion has historically been the leading cause of wetland loss. Drainage for cropland conversion eliminates wetland hydrology and destroys habitat. Runoff carrying fertilisers, pesticides, and sediment degrades water quality in remaining wetlands, while water extraction for irrigation reduces flows into wetland systems.

Urban development poses increasing threats as global populations grow and cities expand. Wetlands are frequently drained, filled, or built over to accommodate infrastructure and housing. The Maine Department of Environmental Protection notes that although modern legislation has slowed wetland loss, the United States continues to lose almost 60,000 acres annually, with ecological health threatened by habitat fragmentation in rapidly urbanising areas.

Pollution from industrial discharge, municipal sewage, and agricultural runoff introduces contaminants that exceed wetlands’ natural filtering capacity. Heavy metals, excess nutrients, and toxic chemicals accumulate in wetland sediments, harming plants, animals, and the microbial communities essential for ecosystem function.

Climate change compounds these pressures through rising sea levels, altered precipitation patterns, increased temperatures, and more frequent extreme weather events. Coastal wetlands face inundation and saltwater intrusion, while inland wetlands experience changes in water availability that disrupt plant and animal communities. When wetlands are disturbed or warmed, they can shift from carbon sinks to carbon sources, releasing stored greenhouse gases and accelerating climate change in a destructive feedback loop.

Invasive species introduced through human activity can outcompete native plants and animals, fundamentally altering wetland ecosystems. Once established, invasive species are extremely difficult to control and can permanently change community structure and ecosystem function.

Conservation and restoration: a path forward 🔗

Protecting remaining wetlands and restoring degraded ones is essential for maintaining biodiversity, regulating climate, and supporting human communities. International frameworks like the Ramsar Convention have designated over 2,500 wetlands of international importance, covering more than 2.5 million square kilometres globally.

The Kunming-Montreal Global Biodiversity Framework, adopted at the 2022 UN Biodiversity Conference, explicitly includes wetlands in its restoration and protected area targets. This framework aims to halt and reverse biodiversity loss by 2030, providing new opportunities for upscaling wetland conservation across all countries.

Restoration efforts are showing that degraded wetlands can recover significant ecosystem functions when appropriate hydrological conditions are re-established. Created wetlands tend to have carbon accumulation rates higher than natural wetlands, suggesting that active restoration can meaningfully contribute to climate mitigation. However, research indicates that only about 21 percent of restored wetlands achieve ecologically equivalent natural functions, highlighting the importance of protecting existing wetlands rather than relying solely on restoration.

Individual actions also matter. Reducing fertiliser and pesticide use, supporting wetland conservation organisations, and advocating for protective policies can all contribute to wetland preservation. Understanding the value of these ecosystems-rather than viewing them as wastelands-is the essential first step toward ensuring their survival.

What do you think? Have you visited a wetland ecosystem in your area? How might changing public perception of wetlands-from “swamps” to be drained to valuable ecosystems to be protected-influence conservation outcomes in your community?

References

1. https://www.un.org/en/observances/world-wetlands-day
2. https://www.epa.gov/wetlands/classification-and-types-wetlands
3. https://www.ramsar.org/
4. https://link.springer.com/article/10.1007/s13157-018-1023-8
5. https://bwsr.state.mn.us/carbon-sequestration-wetlands
6. https://www.global-wetland-outlook.ramsar.org/
7. https://ecology.wa.gov/water-shorelines/wetlands/tools-resources/wetlands-climate-change
8. https://www.wetlands.org/biodiversity/
9. https://www.tandfonline.com/doi/full/10.1080/21513732.2015.1006250
10. https://www.fws.gov/press-release/2024-03/continued-decline-wetlands-documented-new-us-fish-and-wildlife-service-report
11. https://www.maine.gov/dep/water/wetlands/threats.htm
12. https://carbon2018.globalchange.gov/chapter/13/