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How muddy, mouldy ponds help fight climate change

A lotus pond in Hong Kong. (Flickr/Richard Mortel)

Aside from being breeding grounds for blood-thirsty mosquitoes, ponds, swamps and other wetlands are important hotspots for biodiversity and play a key role in protecting us from the effects of climate change. But they are also incredibly fragile ecosystems in dire need of protection.

Like every year, the second day of February went by without much fuss, despite World Wetland Day marking the anniversary of one of the oldest environmental conventions.

But these ecosystems, which have been under enormous pressure from human activity for centuries and now from global warming, provide crucial services for humans, such as improving the quality of our drinking water, says Tobias Salathe, senior regional advisor of the Geneva-based secretariat of the Ramsar Convention on Wetlands.

“If wetlands cease to exist, the ecosystem functions that they deliver to humanity may simply not exist either,” he says.

Why they matter. Wetlands are areas covered by water which are not very deep, such as swamps, ponds, lakes, rivers and mangroves. Initially spearheaded by ornithologists worried by the decline of migratory bird populations, the Ramsar Convention watches over the conservation and "wise use" of these unique aquatic ecosystems. 

Since its entry into force in 1975, 171 States have ratified the treaty and submitted over 2,400 wetlands to the list of protected sites. While wetlands only make up six per cent of the Earth's surface, they excel in keeping the planet from heating up.

Research has found that all ponds combined can store as much carbon as the world’s oceans. This is because the rate at which organic material is buried can be as much as 20 to 50 times faster. 

They can also keep carbon locked up for long periods of time. Unlike other terrestrial vegetation such as leaves and branches, which release the emissions back into the atmosphere once they fall to the ground and break down, water plants get trapped in water covered soils, along with the carbon they have absorbed, and can remain like that for hundreds of years, as long as it does not dry out.

Wetlands also help reduce the impact of climate-related events. Floodplains and swamps act as sponges and retain excess rainfall, preventing flood surges but also providing wildlife and humans with water during periods of drought. Coastal wetlands, such as mangroves, salt marshes, seagrass beds and coral reefs shield coastlines from the shock of tsunamis and storms.

When wetlands fade away. The world's wetlands have declined by a third since the convention came into effect. This is mainly because of human activity. Around 15 per cent of the world's peatlands have been drained for agriculture, a number as high as 48 per cent when it comes to Europe and 95 per cent in certain countries like Germany, Salathe says.

The situation in Switzerland is also worrisome. "In the past 200 years, Switzerland has lost 90 per cent of its wetlands, mainly due to urbanisation and agriculture," says Beat Oertli, professor at the Haute école du paysage, d'ingénierie et d'architecture de Genève, who specialises in small stagnant water bodies. This has contributed to loss of biodiversity but also to more flooding, he notes.

Rising global temperatures are also putting enormous pressure on these water bodies, he adds. "Climate change is happening too rapidly and biodiversity is not able to adapt that fast."

As these inland water bodies continue to disappear, this triggers domino-like negative effects. When they dry out, the organic material stored by the soil begins to decompose, releasing methane, one of the gases with the strongest greenhouse effects. The surrounding ecosystem, which depends on these water bodies, can also be at risk of collapsing. 

Dried out peatlands, which represent only 0.5 per cent of the Earth's surface, emit as much as five per cent of total greenhouse gases, Salathe notes. Ponderful, a six million euros EU-funded project in which Oertli is taking part, will be measuring the efficiency of small stagnant water bodies to trap carbon but also how much methane they would release if they were to become dry.

More restoration and protection needed. Oertli argues that while Switzerland does a good job on keeping track of its wetlands, more needs to be done to restore them, especially natural ones.

"Currently, many of the wetlands that are being created are artificial, for example when a pit is dug to extract gravel for the building industry. These new wetlands are becoming more and more present in our landscape, but they do not compensate for the 90 per cent that we have lost," Oertli warns, adding that artificial ponds only bring half of the biodiversity compared to natural ponds.

The Lac des Vernes in Meyrin is a good example of what can be done, he notes. Opened to the public in 2017, the 2.5-hectare near-natural lake was built to collect the excess water from rainfall and prevent flooding. At the same time, it has brought a splash of green and many other colours that the inhabitants of the Geneva commune can enjoy.

These types of projects make economic sense, according to Salathe, but have a hard time gathering support. "The real comparative economic analysis is seldom done to show that it may indeed be much cheaper in the long run to maintain or to revert a natural wetland, rather than build a dam for electricity production, or for water irrigation," he says.

Salathe does feel that progress has been made in the 45 years since the convention and that there is a growing recognition of the services that these ecosystems provide, but time is running out, he warns. As climate change accelerates and populations continue to grow, wetlands only become more fragile.