Aerial view of Wallasea Island, Essex

Why the world needs wetlands

Image credit: Jeff Kew

We’ve spent hundreds of years trying to protect ourselves from the Earth’s waters. So why, in the 21st century, are wetlands being restored and how can they help us cope with global warming?

The UK’s biggest wetlands restoration project was completed last year. It took almost a decade, and now thousands of sea birds and waders congregate on Wallasea Island – avocet, black-headed gulls, golden plovers, teal, redshank and lapwing, and soon, hopefully, rare spoonbills, black-winged stilts and Kentish plover.

Wallasea, situated between the estuaries of the rivers Crouch and Roach in Essex, is Britain’s biggest wetland habitat and twice the size of the city of London. Chris Tyas, who led the project for the Royal Society for the Protection of Birds (RSPB), explains that when a sea wall like the one at Wallasea is breached, seawater and silt move inland, over time creating marshes, mudflats, lagoons and other inter-tidal habitats.

“Invertebrates and seeds from the nearby estuary colonise the new habitats,” Tyas says. “Within three years, you’ve got equivalent habitat to the adjacent estuary and all the right saltmarsh plants.”

More birds on Wallasea Island is great for bird-watchers, the RSPB and, of course, the birds themselves. The EU directive on the Conservation of Wild Birds says that member nations have to safeguard the habitats of migratory birds and certain threatened birds within designated special protection areas. However, the restoration of Wallasea Island cost £70m. Thinking like a bean counter, that’s a lot of money for a few birds.

Similarly, last November, the US National Fish and Wildlife Foundation approved $48m for wetlands conservation and restoration along the Alabama coastline. The recently completed Lost Lake restoration project in Louisiana cost $36m. The Australian government spent $180m to buy the Nimmie-Caira wetlands in New South Wales.

Then there’s the ongoing Everglades restoration project, which over 35 years will cost an estimated $10bn. However much they love their cypress trees and alligators down there, for authorities to spend that sort of money they must think that wetland restoration has some serious benefits for human society.

Wetland – swamp, marsh, bog, fen and some peatland – covers 12.1 million square kilometres of the Earth’s surface. That’s a larger area than Canada, the world’s second-largest country, but it’s only a fraction of the wetland we used to have, before so much of it was drained and otherwise modified for large-scale urban and agricultural development.

Since 1700, the world has lost 87 per cent of its wetlands according to the Ramsar Convention on Wetlands in its 2018 Global Wetland Outlook (GWO). That’s three times the rate of loss of our rainforests. In the technological age, the rate of loss is even greater – 35 per cent since 1970.

The Wetlands Convention also says that wetlands provide food and livelihood for more than one billion people. And that 40 per cent of the world’s plant and animal species live and breed in wetlands. Some of the animals are commercially important species like fish, crab and shrimp, which use inter-tidal coastal habitats as nursery areas.

Wetlands are also known to regulate nutrient and trace metal cycles in water systems, filtering out pollutants from human habitation, industry and agriculture before they reach rivers. “Excess phosphorus and nitrogen pollution is a particular problem,” says Dr Matthew Simpson, associate director and president of the Society of Wetland Scientists, Europe.

This has all long been known, though, and hasn’t stopped authorities around the world from continuing to drain and redirect their wetland habitats. What is now increasingly being realised, however, is that wetlands, rather than making human settlements susceptible to floods, provide us with natural protection from fast-rising waters.

Wetlands can trap, store, regulate and slowly release excess water flows caused by high rainfall and storm surges. When these environments are modified, they can lose their capacity to absorb the excess waters. This is what many believe happened last August, when floods devastated Kerala in southern India after a particularly intense monsoon. Mountain rivers dumped their excess water into lowland backwaters; over 500 people died and a quarter of a million were evacuated. The Kerala backwaters had previously been modified to create, among other things, paddy fields and tourist lodges.

John Lehrter, a marine scientist from the University of South Alabama, says that in Louisiana funds are being directed towards reconnecting rivers and sediment loads to marshes. Louisiana was designated a Federal Disaster area after floods in 2016 caused more than $10bn of damages. The Mississippi River, he explains, had previously been engineered for transportation purposes with levees and channels so sediments were forced to flow out into the Gulf of Mexico.

As the Earth warms, seas rise and floods affect wider areas and more people, this function of wetlands will become increasingly important. All over the world, authorities will have to think more about what might happen should existing flood defences fail. And some of these defences are very old indeed.

Dutch settlers built the Wallasea sea wall in the 15th century to drain the land for farming. Before that, Wallasea was five separate saltmarsh islands. Parts of the wall needed rebuilding after the infamous North Sea flood in 1953, but when, in the 1990s, the landowner applied for funding to repair the wall, he was turned down. In 2009, the RSPB bought the land.

“We knew that if the sea wall was left, sooner or later it would have failed,” RSPB’s Tyas says. This, he explains, would have caused much of the island, which is below sea-level, to flood, which in turn would have caused problems in the estuary.

In 2015, the RSPB’s engineering contractors breached the sea wall in three places. The aim, according to Tyas, was to allow the tide to spread naturally over the landscape in a controlled way. Paul Eaves, principal geotechnical engineer with Aecom, another Wallasea contractor, adds that to protect the estuary and maintain the tidal prism they had to make sure the right amount of water came on and off during each tidal cycle.

Phil McLoughlin, principal engineer with Wallasea contractor Jacobs, explains that an unmanaged breach in the sea wall would have put flood defences at risk further inland, along the Crouch and the Roach. “All that water is no longer going up and down the estuary, you’d end up getting erosion and sediment where you don’t want it,” he says.

This is why the Society of Wetland Scientists’ Simpson thinks it’s so important to restore a river’s connection to its flood plain in the upper catchment. “To reduce flooding risk downstream, we need to make sure rivers behave in a more natural way in upland areas,” he says.

If left alone, wetland habitats are created naturally over time as water flows on and off the land. The type of habitat created depends on the amount and frequency of flooding and the debris deposited. To create the desired variety of wetland habitats on Wallasea, engineers had to find a way to raise the height of the land above sea level in various places. These areas would flood only when the tide was particularly high, while other parts would flood more often.

To do this, RSPB did a deal with Crossrail. Digging tunnels across London had left Crossrail with a lot of debris. RSPB decided to buy six million tonnes of it. “On average we raised the land by a metre and a half,” Tyas says.

Unfortunately, part of the way through the project, Crossrail discovered that some of their material was too wet to ship out to Wallasea. “The shortfall was about one-third of the material we needed, so we had to adapt our plans with part of the island already built,” says Aecom’s Eaves.

To restore the last part of the island meant switching to a different strategy – regulated tidal exchange; a process by which sluices and other artificial devices restrict the flow of water on and off. The Wallasea engineers also took earth from earlier structures that were above high tide and used it to raise other areas above sea-level.

“We dug ditches and channels planned for aquatic mammals, earlier than anticpated, to free up more material,” Eaves says. “We also set pools below tide level, so the first time the water came in the pools filled up. Then, during subsequent tides, that water doesn’t go in or out.”

Jacobs’ McLoughlin adds that without the pools, more water would come on to the island than could be dissipated, leaving the landscape permanently wet.

And all this just to return Wallasea to something like the state it was in before humans started messing around with it in the first place. It’s the same elsewhere.

Marine scientist Lehrter says that sediment stuck in shipping channels off the Alabama coast could be used to build up the coastal wetlands. “Before the channels were dug to allow big ships into port, sediment used to deposit naturally on the shoreline,” he says. “Now, the sediment is dumped out into the gulf and, as a result, marshes have sunk and we have erosion problems on the east end of Dauphin Island.”

To do this, however, requires more than just putting the right amount of sediment on the right bit of land. Lehrter explains that marsh is made of very organic, fine silt sediment. “Sand from the shore is too heavy, the marsh soil can’t support the weight,” he says, before suggesting using thin layer sediment dispersal: “If you fluidise fine sediments and spray the material over the marsh, the sediment is then deposited in thin layers, which, over time, build up the right kind of sediments and aren’t going to collapse the marsh.”

Simpson would like to see more land developers make use of natural wetland systems rather than build expensive new flood defences. Lehrter believes that doing this not only protects the local environment, but allows it to be a functioning habitat. He is also in favour of ecologically friendly engineering tools and more scientific research to test out which designs are most beneficial to wetland ecosystems.

Geoff Sweaney, director of UK company Wetland Engineering, adds that in areas where wetlands have historically been drained and used for industry, it is important to remove top soil and, with it, any residual pollutants prior to introducing water. “If not, the water is likely to transport these contaminants over a wider area,” he says.

Wetlands are not static environments; they are prone to change over time, depending on prevailing conditions. Because of this, Lehrter thinks that adaptive engineering approaches would work best, approaches that would enable experts to monitor wetlands over future decades and modify initial designs as needed.

Eaves explains that, for this reason, the new Wallasea flood wall was built 800mm higher than currently needed to allow for sea level rise over the next 50 years. McLoughlin adds that control structures can be adjusted as tide levels change. “If more material became available, the rest of Wallasea Island could be built up to higher levels,” he says.

Despite all this, the Ramsar GWO2018 complains that policymakers in parts of the world still underestimate the value of their wetlands. The report estimates that by 2050, one-third of the global population will likely be exposed to water with excessive nitrogen and phosphorus. It wants more wetlands to be protected under the UN Convention, and additional research conducted, so policymakers might better understand the value of these ecosystems.

The University of Santa Cruz researchers have recommended introducing financial incentives for wetland conservation and restoration.

McLoughlin argues that restoring wetlands on a larger scale, rather than the piecemeal restoration normally favoured, would save money in the long run.

Wetland Engineering’s Sweaney thinks that decisions about what to do with the natural environment should be determined by what’s best for society, not the needs of individual farmers and landowners.

It helps when the Insurance Bureau of Canada announces, as it did in September 2018, that wetlands provide flood protection more effectively and more cheaply than dams, levees or other manmade solutions.

A few months earlier, researchers from Colorado State University had claimed that the global insurance industry could save $52bn a year by increasing protected coastal wetlands. The previous year, a University of Santa Cruz study found that coastal wetlands prevented more than $625m-worth of direct property damage during 2012’s Hurricane Sandy alone. The researchers also found that in some parts of Barnegat Bay, New Jersey, the presence of wetlands reduced flood losses by 70 per cent.

Saving money motivates the authorities, obviously. But there’s another global environmental benefit to restoring wetlands which will become more compelling as the effects of climate change are increasingly felt over the coming decades.

Wetland plants take carbon out of the atmosphere and store it as plant tissue and eventually soil, unlike on dry land where plants die, break down and release the carbon back into the air. However, according to a November 2018 Florida International University report, a wetland can only perform this function if it is healthy and intact. “Draining or disturbing wetlands can actually release the stored carbon into the atmosphere very quickly,” Lehrter adds.

Last year, researchers from Tufts University in the USA went as far as to suggest that without wetlands and forests taking carbon out of the atmosphere, carbon dioxide from human activities would increase by 28 per cent each year.

A Royal Academy of Engineering report, published last September, said restoring wetlands could reduce greenhouse gases and help the UK to be carbon-neutral by 2050, something that decision-makers throughout the world, struggling to meet their climate change targets, will be pleased to hear.

While all this might shift the environmental cost analysis away from building dams and towards restoring wetlands, it must also be remembered that 400 years of human interference and damage to the natural environment is not easily undone.

Facts and figures


■ Global inland and coastal wetlands cover an area of 12.1 million km2, with 54 per cent permanently inundated and 46 per cent seasonally inundated.
■ Regional distribution of wetlands 2018: Asia 31.8 per cent, North America 27.1 per cent, Latin America and Caribbean 15.8 per cent, Europe 12.5 per cent, Africa 9.9 per cent, Oceania 2.9 per cent.
■ Around 93 per cent of wetlands are inland systems, with 7 per cent being marine and coastal.
■ Of the inland wetlands, rivers and streams account for 6 per cent, natural lakes 29 per cent, non-forested peatlands 27 per cent, forested peatlands 6 per cent, marshes and swamps 22 per cent, forested wetlands 10 per cent.
■ Up to 87 per cent of the global wetland resource has been lost since 1700 in places where data exist.
■ Between 1970 and 2015, inland and marine/coastal wetlands both declined by approximately 35 per cent.
■ Natural wetland has been lost at an average of -0.78 per cent a year between 1990 and 2015, according to the Wetland Extent Trends (WET) Index, with the rate increasing since 2000.
■ Human-made wetlands, largely rice paddy (20 per cent) and reservoirs (20 per cent), almost doubled since 1970, now forming 12 per cent of wetlands.
■ Since 1970, 81 per cent of inland wetland species populations and 36 per cent of coastal and marine species have declined.
■ By 2050, one-third of the global population is likely to be exposed to water with excessive nitrogen and phosphorus, leading to rapid algal growth and decay that can kill fish and other species.
■ There are now 2,300 internationally important wetlands designated as Ramsar Sites, which marks them out for conservation.

Source: Ramsar Convention Global World Outlook 2018.

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