The Wetland Biome: Earth's Most Productive and Most Threatened Ecosystems

Wetlands — ecosystems where water saturation dominates and determines soil, vegetation, and animal communities — cover approximately 6% of Earth's land surface in a diversity of forms: marshes, swamps, bogs, fens, floodplains, mangroves, and peatlands. Despite their modest area, wetlands provide ecosystem services worth approximately $47 trillion annually — purifying water, regulating flooding, sequestering carbon, sustaining fisheries, and supporting extraordinary biodiversity. The world has lost approximately 35% of its wetland area since 1970 — at a rate three times faster than forests — driven by drainage for agriculture, urban development, and water extraction. Restoring and protecting wetlands is increasingly recognised as one of the most cost-effective strategies for simultaneously addressing biodiversity loss, climate change, and water security.

Peatlands — The Carbon Giants

Peatlands — wetlands where waterlogged conditions prevent full decomposition, allowing plant material to accumulate as peat — store approximately 30% of the world's soil carbon on just 3% of its land. The Siberian peat bogs, the Congo Basin peatlands (discovered to be far larger than previously known in 2017), and the tropical peat forests of Southeast Asia collectively store more carbon than all tropical forests. Peat accumulates at approximately 1 millimetre per year, meaning 10-metre deposits represent 10,000 years of carbon storage. Draining or burning peatlands releases this stored carbon rapidly: Southeast Asian peatland drainage for palm oil generates carbon emissions equivalent to burning 100 million tonnes of coal annually.

Mangroves — Coastal Carbon Stores

Mangrove forests colonising tropical and subtropical coastlines between the intertidal zone are among the most ecologically and economically important coastal ecosystems. They protect coastlines from storm surge and erosion, sequester carbon at rates up to 10 times higher per unit area than tropical forests — primarily in their deep, waterlogged soils — provide nursery habitat for a large proportion of commercial fish species, and support unique communities adapted to tidal inundation and saline conditions. Approximately 35% of global mangrove cover has been lost since 1980, primarily to aquaculture and coastal development. Restoration of mangroves is increasingly valued for its climate, biodiversity, and coastal protection co-benefits.

Wetland Birds — The Most Threatened Vertebrate Group

Waterbirds — species dependent on wetlands for breeding, feeding, or both — have declined by an average of 81% since 1970, making them the most severely affected vertebrate group of the global biodiversity crisis. The drivers are multiple and interacting: loss of wetland habitat through drainage, water abstraction, and development; degradation of remaining wetlands by eutrophication, salinisation, and invasive species; hunting pressure on migratory species along flyways where regulations are absent or unenforced; and climate change altering the timing of seasonal flooding that triggers breeding and migration. Long-distance migratory waterbirds — shorebirds that breed in the Arctic and winter in tropical coastal wetlands — are among the most vulnerable, facing threats at every stop along migration routes that may span 15,000 kilometres, as well as the desynchronisation of their arrival at breeding grounds with the peak of food availability driven by warming-induced phenological mismatch.

Wetland Restoration — Rewetting for Climate and Nature

The restoration of degraded wetlands — rewetting drained peatlands, removing levees to restore floodplain inundation, recreating coastal marshes on reclaimed land — is increasingly recognised as one of the most cost-effective nature-based climate solutions available. Rewetted peatlands rapidly cease emitting CO₂ from the oxidation of drained peat, and over timescales of decades to centuries, re-establish the waterlogged, anoxic conditions that allow peat to re-accumulate. The reduction in greenhouse gas emissions from rewetting drained European peatlands alone — currently the source of approximately 5% of the EU's total greenhouse gas emissions, more than all of the EU's aviation — would represent a major climate contribution. The costs of peatland rewetting (purchasing land, removing drainage infrastructure, compensating farmers) are typically less than €50 per tonne of CO₂ equivalent reduced — making rewetting one of the cheapest climate mitigation options in the agricultural and land use sector.

Freshwater Biodiversity — The Most Threatened on Earth

Freshwater ecosystems — rivers, lakes, ponds, and wetlands — cover less than 1% of Earth's surface but support approximately 10% of all species and a disproportionate share of vertebrate diversity. Yet freshwater species are experiencing extinction rates estimated at 3-4 times higher than terrestrial or marine species — making freshwater biodiversity the most threatened on Earth. The Living Planet Index for freshwater vertebrates shows an average population decline of 83% between 1970 and 2018 — far exceeding the 69% average across all vertebrates. Freshwater megafauna (large-bodied species including river dolphins, large fish, large turtles, and hippos) have declined by 88% on average — proportionally greater than any other vertebrate group. The primary drivers are dam construction (which blocks fish migration, alters flow regimes, and fragments river ecosystems), water extraction (reducing flows below biological minimums), pollution (agricultural runoff, sewage, industrial discharge), and invasive species.

Wetland restoration — the re-establishment of natural hydrological regimes, native vegetation, and ecological function in degraded or converted wetlands — is increasingly recognised as one of the most cost-effective ecosystem restoration strategies available. Restored wetlands can filter agricultural pollutants from water, reducing eutrophication in downstream lakes and coastal zones; store floodwaters, reducing downstream flood peaks; sequester carbon in waterlogged soils; and recover biodiversity at rates exceeding any other ecosystem type. The restoration of the Florida Everglades — the world's largest wetland restoration project, with a planned investment of $16 billion over 30 years — is already producing measurable improvements in water quality, wading bird abundance, and Florida panther population recovery, demonstrating that even severely degraded large-scale wetland systems can recover with appropriate investment and political commitment.