One-fifth of wetlands worldwide have been lost in the last 320 years

Human activity has seen the loss of one-fifth of the world’s wetlands since 1700 according to a new study published in Nature.

The loss equates to an estimated 3.4 million square kilometres, about 21 percent, of wetland habitat in the 320 years up to 2020. This loss equates to about half the size of the Australian mainland or two percent of the Earth’s total land surface area.

To get their result, the team combined 3,320 records of wetland drainage and land conversion from 154 countries. Much of the loss of wetlands occurred in Europe, China and the US. The most common cause behind the destruction of these habitats have been conversion to crops and urban development.

It is no easy task to adequately map wetland loss on a global scale. Previous attempts have given wildly varying estimates.

Prior to the latest study, research has placed wetland loss at between 28 and 87 percent since 1700. Other research has suggested at least 50 percent of wetlands have been lost since 1900. These studies have often extrapolated globally local wetland loss history. The authors of the Nature paper argue that such disparities in the results have undermined attempts to compare wetland loss rates with those of other ecosystems such as forests.

“A rigorous estimation of wetland loss has been hindered by the paucity of historical data, requiring the unification of data and modelling approaches,” they add.

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The team, which included researchers from Australia’s James Cook and Charles Sturt universities, combined their historical data with models calibrated to give regional estimates of percentage change in wetland area.

They focused on inland wetlands – ignoring permanently inundated areas such as river channels and lakes, and coastal wetlands like you would find at a river delta.

Such wetlands have high biodiversity, have supported human communities around the world for thousands of years, and play a key role in improving soil and water quality as well as storing floodwaters and maintain surface water flow during arid periods.

In the same issue of Nature, James Cook University senior lecturer in Global Ecology and Conservation Dr Nicholas Murray (who is not an author of the paper) writes in an editorial that the new study’s authors “put considerable effort into developing a database to support their analyses.”

Murray says that many patterns missing in older research on wetland loss are crucial “for purposes including wetland management, planning conservation and restoration activities, assessing progress towards global conservation targets and understanding the various drivers of wetland loss.”

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In his article, Murray also notes that changing rainfall patterns and restoration efforts are actually seeing wetland gains in some parts of the world. This is something not considered in the recent research.

While Murray believes the new analysis is a step in the right direction in highlighting “the ongoing need to protect and restore the world’s remaining wetland ecosystems,” he says further research is needed.

“Wetland gains should be addressed in future studies as the rate of losses continues to decelerate and meaningful actions to restore the world’s wetlands grow. Knowledge about the types of wetland that have disappeared would also enable a better understanding of lost ecosystem services and historical changes in wetland biota, leading to a better understanding of the global status of the world’s freshwater ecosystems,” Murray writes.