• International research findings help better explain the causes and impacts of global wetland losses, and inform protection and restoration of wetlands
• Study finds global wetlands losses have likely been overestimated, but equal at least an area about the size of Western Australia and New South Wales combined
• The findings give governments and agencies a second chance to take action against further declines, and the results provide a guide for prioritising conservation and restoration

Charles Sturt University researchers have contributed to an international study that found that although wetlands remain threatened in many parts of the world, including Australia, global losses of wetlands have likely been overestimated.

Adjunct Professor Max Finlayson (pictured, inset) and Adjunct Professor Nick Davidson are researchers in the Charles Sturt Gulbali Institute of Agriculture, Water and Environment and are co-authors of the new Stanford University-led study.

The study, ‘Extensive global wetland loss over the past three centuries’, is published in the science journal Nature, and found the US accounts for more wetlands losses than any other country.

“The findings help to better explain the causes and impacts of wetland loss, enabling more informed plans to protect or restore wetlands ecosystems crucial for human health and livelihoods,” Professor Finlayson said.

“Despite the good news that our results might imply, it remains urgent to halt and reverse the conversion and degradation of wetlands.

“The geographic disparities in losses are critical to consider because the forgone local benefits from drained wetlands cannot be replaced by wetlands elsewhere.”

Professor Finlayson said being able to accurately estimate the extent, distribution and timing of wetland loss is key to understanding their role in natural processes and the impact of wetland drainage on the water and carbon cycles.

“A lack of historical data has hindered the effort, forcing scientists to make estimates based on incomplete collections of regional data on wetland loss,” he said.

“Wetlands are now understood to be vital sources of water purification, groundwater recharge, and carbon storage, where once they were long-seen as unproductive areas teeming with disease-bearing insects and good only for draining to grow crops or harvest peat for fuel and fertilizer.

“Unrelenting drainage for conversion to human land uses, such as farmland and urban areas, in addition to alteration by fires and groundwater extraction, has made wetlands among the most threatened ecosystems in the world.

“Wetlands purify our water, prevent flooding, and are biodiversity superheroes, and we need the best data possible to save what we have and know what we’ve lost.”

Professor Finlayson explained the findings were the result of a first-of-its-kind historical reconstruction in which the researchers combed through thousands of records of wetland drainage and land-use changes in 154 countries.

They mapped the distribution of drained and converted wetlands onto maps of present-day wetlands to get a picture of what the original wetland area might have looked like in 1700.

The researchers found that the area of wetland ecosystems has declined 21-35 per cent since 1700 due to human intervention - which is far less than the 50-87 per cent losses estimated by previous studies.

Nevertheless, the authors estimate that at least 1.3 million square miles of wetlands have been lost globally  ̶  an area about the size of Western Australia and New South Wales combined.

“These new results allow us to better quantify changes in wetlands’ sequestration of carbon from the atmosphere and the emission of methane, another powerful greenhouse gas,” Professor Finlayson said.

The low estimate is likely the result of the study’s focus beyond regions with historically high wetland losses, and its avoidance of large extrapolations – characteristics of many previous estimates. For instance, using wetland loss rates observed in the US or Europe would not likely apply to loss rates in the tropics or Arctic.

Moreover, grouping all wetlands together hides vast differences among distinct wetland types that provide different benefits and are under different levels of pressure. For instance, temperate river floodplains have been highly impacted while remote arctic peatlands have been comparatively unharmed.

The researchers note their estimate of losses is likely conservative because they constrained their analysis to available data, which is scarce for the years before 1850.

Despite what may seem to be good news, the researchers emphasize that wetland losses have been dramatically high in some regions, such as the US, which is estimated to have lost 40 per cent of its wetlands since 1700 and accounts for more than 15 per cent of all global losses during the duration of the study.

Although wetland conversion and degradation has slowed globally, it continues apace in some regions, such as Indonesia, where farmers and corporations continue to clear large swathes of land for oil palm plantations and other agricultural uses.

“We need to improve our capacity to map current wetlands extents and monitor their status using satellites in order to know whether we are making progress toward conservation goals,” Professor Finlayson said.

“Discovering that fewer wetlands have been lost than we previously thought gives us a second chance to take action against further declines, and these results provide a guide for prioritising conservation and restoration.”