What are wetlands, and why are they so critical for life on Earth?

This ecosystem by many names—bogs, swamps, bayous, marshes, billabongs, fens, vernal pools, lagoons and other waterlogged fields and forests all fall under the broad wetland category. If water, salty or fresh, is present on top of or just below the soil, it’s a wetland. You’ll know you’re in a wetland when your shoe prints turn muddy and wet.

They make up just 6 percent of Earth’s surface. Despite their small footprint, wetlands have important jobs, providing fresh water and habitats, and fighting climate change. 

Wetlands were historically considered wastelands. Many have been drained and filled in with sediment to become solid ground for structures like homes, highways, and businesses. But protecting these misunderstood environments can help wildlife thrive and protect us from a changing climate.

What are wetlands?

These diverse ecosystems are found on every continent except for Antarctica.

Generally, they’re divided into two categories: coastal or inland. Coastal wetlands are a mix of fresh and saltwater, a combination called brackish water. Wetlands here look like grassy salt marshes and mangrove forests. 

Inland wetlands consist of vernal pools, woodland swamps, bogs, or waterlogged, grassy stretches near rivers and lakes. While many inland wetlands contain freshwater, some are salty, like this salt marsh in Nebraska that was once a prehistoric ocean. They occur as a result of rainy climates or groundwater gurgling up toward the surface. Some are seasonal, appearing only during rainy periods. 

Protecting against floods and purifying water 

Perpetually in limbo, wetlands are “transition zones” between dry land and water. During floods, they sponge up excess rainwater that would otherwise cause flooding and damage homes. One acre of wetland can store over one million gallons of flood water.

Since the 18th century, over 64 million acres of wetlands have been destroyed in the Upper Mississippi River Basin as a result of agricultural and urban development. The environmental loss contributed to the billion-dollar flood disaster that occurred in the region in 1993.

But wetland protection in the form of city parks and green spaces along the Charles River in Boston has prevented an estimated $17 million in potential flood damage, according to research done by the U.S. Army Corps of Engineers. 

On the coast, wetlands help buffer the onslaught of storm surge pushed onto land by powerful storms like hurricanes. 

When runoff contains pollutants like fertilizer sprayed on agriculture fields, wetlands are natural water filters that absorb these nutrients and prevent them from reaching lakes and rivers. Chemicals stuck to soil particles are slowed by wetland plants, suspended, and pollutants are locked in place by wetland plant roots. 

The Congaree Bottomland Hardwood Swamp in South Carolina filters so much pollution every year, it would take a $5 million-dollar water filtration plant to filter the same amount, according to the EPA.

Supporting life 

Well-known animal and plant species such as alligators, turtles, and snakes live in wetlands around the world. In North America, migratory birds use these habitats as pit-stops on their cross-country journeys. Of the 12 million waterfowl in the U.S., as many as two thirds reproduce in Midwestern wetlands. 

These ecosystems are important for humans, too. Their calm waters are breeding grounds for valuable fish and shellfish species like bass and oysters. Wetlands play a role in the life cycle of 75 percent of these commercially harvested species in the U.S. 

Globally, two-thirds of all the fish we eat spend at least part of their life in a wetland. An estimated one billion people around the world depend on wetlands to support their livelihoods through activities such as fishing, rice farming, hunting, or tourism. 

Fighting climate change

Once released, most greenhouse gasses stay in the atmosphere, warming the planet. But about 26 percent is absorbed by plants growing on land. These types of ecosystems are called carbon sinks, and they absorb millions of tons of carbon every year. 

Wetlands are carbon sinks that, when destroyed, can become a major source of greenhouse gas emissions. Altogether, wetlands contain about a third of the world’s carbon, and when they’re degraded, the emissions locked in their soils are released.

Peatlands in particular are important to conserve if we want to prevent wetlands from becoming a source of atmospheric pollution. They occupy only 3 percent of Earth’s surface, but their waterlogged soils store twice as much carbon as the world’s forests—about 30 percent of all the carbon locked in the world’s soils. To degrade them would be to set off what some scientists have described as a “carbon bomb.”

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What threats do wetlands face? 

While wetlands are increasingly being recognized as important ecosystems, draining them for development is a practice that still continues today. In the U.S. alone about 80,000 acres of wetland are lost every year. Louisiana loses about a football field’s worth of marshland every hour.

In countries like Scotland and Argentina where peatlands are common, wetlands are destroyed when peat is dug up and burned for energy.

Invasive plant and animal species can also destroy wetland habitats. Beavers and nutria, a type of invasive rodent, damage wetlands by devouring plants that hold wetland soil together.

Wetlands in court 

This year, the Supreme Court will rule on a case called Sackett v. EPA that could have profound consequences for how wetland protection is regulated in the U.S. In 2007, the EPA stopped the Sackett family from building their home because the agency said the property included a wetland that fed a nearby lake over which they have jurisdiction. To build their home, the family had to fill the land with sediment. The Sacketts sued the EPA in 2008, claiming their property was not wet enough to constitute a wetland.

The decision will be decided based on whether the Sackett's property included a wetland that significantly affected nearby federal waters. Wetlands that are more obviously connected to rivers, lakes, and coastlines tend to have more protections than those whose connections to navigable waters are less obvious—often wetlands that are not adjacent to a body of water or are seasonal.

Lawyers at EarthJustice, a law firm dedicated to environmental protection, say the Court’s decision could dramatically reduce how many wetlands are protected by the Clean Water Act.

What are we doing to protect them?

In 1971, world leaders met in the Iranian city of Ramsar to create a global treaty to protect wetlands—the Ramsar Convention on Wetlands. Currently, 171 countries have signed the treaty, but since it was signed into effect in 1971, more than a third of the world’s wetlands have been destroyed. 

(In the Philippines, this tropical marsh is slipping away.)

In 2021, scientists published a paper arguing that wetlands should be granted legal rights because of their role in supporting life on Earth.

Private companies are also looking at wetlands as a source for carbon offsets, which allow individuals and businesses to theoretically “offset” their carbon emissions by contributing to the conservation or restoration of ecosystems that absorb their equivalent emissions. 

Where wetlands are already destroyed, there are some ambitious projects hoping to bring them back to life. 

The swampy mangrove forests of Miami Beach were destroyed 100 years ago, but the city plans to restore this ecosystem to limit shoreline erosion and prevent flooding. And in Louisiana, the state has an ambitious plan to allow rivers to retake their natural shape and dump river sediment into their southern marshes, helping rebuild the wetland coastline.

A report published by the Ramsar Convention says the world’s wetlands are still being lost at an alarming rate, but restoration and conservation projects offer hope that these ecosystems can be saved.