How many wetlands worldwide have been lost in last 320 years?

Wetlands are areas that remain in flooded conditions or with soil saturated with water for considerable periods of time. A fifth of Earth's wetlands has been destroyed by humans since 1700 according to a new study published in Nature found.

Wetlands lost worldwide

The loss equates to an estimated 3.4 million square kilometres, around 21 per cent, of wetland habitat in the 320 years to 2020. This loss is equivalent to roughly half the size of the Australian continent or two per cent of the total land area of the Earth.

The water can come from the sea, rivers, rain or groundwater. Wetlands are also distinguished by the particular characteristics of their soils and by the presence of plants and animals adapted to flood conditions or alternating periods of flooding and drought. 

In this way, wetlands are not necessarily transitions between aquatic and terrestrial systems, but rather have their own structural and functional characteristics that differentiate them from each other.

The amount of Earth's precious wetlands that have been lost since 1700 has recently been addressed by a major new study published in Nature. Previously, it was feared that up to 50% of our wetlands had been wiped out. However, the latest research suggests the figure is actually closer to 21% - an area the size of India.

Some countries have seen much greater losses, with Ireland losing over 90% of its wetlands. The main reason for these global losses has been the drainage of wetlands for growing crops.

The findings of the large-scale study, published this week in the journal Nature, are substantially lower than previous estimates, some of which were based on extrapolating regional wetland loss. Previous evaluations varied so dramatically, between 28% and 87%, that they left the subject under a cloud of confusion for years.

The new study looks only at inland wetlands and not permanently flooded areas, coastal tidal zones, or near-shore marine wetlands.

An organic tonic

Losing a few acres of wetland may not seem like much on a global or even national scale, but it is very serious for the nearby town which now floods when it rains and is catastrophic for specialized animals and plants such as curlews and swallowtail butterflies, to live here.

Fortunately, countries and international organizations are beginning to understand just how important wetlands are locally and globally, with some adopting “no net loss” policies that force developers to restore any habitat they destroy. The UK has promised to ban the sale of peat-based compost to hobby growers by 2024.

Wetland habitats are being conserved around the world, often at enormous cost. More than $10 billion (£8.2 billion) has been spent on a 35-year plan to restore Florida's Everglades, a unique network of subtropical wetlands, making it the largest and most expensive ecological restoration project in the world.

The creation of new wetlands is also underway in many places. The reintroduction of beavers into enclosures in Great Britain is expected to increase the country's wetland coverage, bringing with it all the advantages of these habitats.

Beaver dams and the wetlands they create reduce the effects of flooding by up to 60% and can encourage wildlife in the area. One study showed that the number of local mammal species skyrocketed by 86% thanks to these furry engineers.

Another chance to act on wetland loss

"Wetlands, in their natural state, are among the most important ecosystems for regulating our water resources, benefiting both humans and the environment," adds co-author Bernhard Lehner, a global hydrologist at McGill University.

“Finding that fewer wetlands have historically been lost than previously thought gives us a second chance to take action to ensure that wetland coverage does not decline further.

As part of that, we need to improve our ability to map its past and current extents and monitor their status using satellites. This will allow us to set meaningful conservation targets and restoration targets.

“Wetlands, and particularly peatlands, can absorb carbon dioxide from the atmosphere and store it as soil carbon for millennia, but wetlands are also emitters of methane, another greenhouse gas. Drainage of these waterlogged unique ecosystems alters their greenhouse gas budgets and their impact on the climate.

Our new results will help quantify how drained wetlands influenced Earth's climate in the past," said study co-author Avni Malhotra, a senior scientist at the University of Zurich and a McGill geography PhD graduate.

Why is it important to keep them?

Wetlands make a crucial contribution to human well-being by performing functions from which multiple benefits are derived.

• Biological diversity. Many species of wild flora and fauna are completely dependent on wetlands. They are extremely important habitats for migratory species such as birds and shelter endangered species. Some have a high proportion of endemic species, meaning they are not found anywhere else in the world.

• Flood damping. Wetlands play an important role in flood control. They can act like sponges, absorbing rainwater and river floodwater, allowing it to percolate more slowly through soil and vegetation, thereby reducing the speed and volume of water flowing downstream.

• Mitigation and adaptation to climate change. Wetlands play critical roles in mitigating global warming. On the one hand, they are important carbon sinks and, therefore, their destruction releases greenhouse gases, while their restoration and creation results in the retention of more greenhouse gases. Wetlands play a fundamental role in adaptation to climate change, since they cushion the effect of storms and floods.

• Water supply. Wetlands retain and store water, available for human consumption, production, and sustaining wildlife. When wetlands are situated over permeable sediments and rocks, the water they retain seeps through the soil and recharges aquifers. 

• Cultural values. As providers of water and many other goods and services, the population has historically settled in wetland areas, from the original peoples to the present day, developing a rich and diverse cultural heritage. Many wetlands are sites of great archaeological and historical relevance.

• Provision of food, materials and medicines. Wetlands produce a wide variety of plant, animal and mineral products that are used by people around the world. Products from wetlands range from staple foods such as fish, to construction timber, firewood, vegetable oil, salt, medicinal plants, stems and leaves for textile manufacture, and animal fodder. 

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