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Satellite images reveal global losses of tidal wetlands

Published : Wednesday, 18 May, 2022 at 12:00 AM  Count : 815

Research had been using satellite data to monitor three types of tidal ecosystems - tidal flats, tidal marshes and mangroves - from 1999 to 2019.
It found that a total of 13,700km2 of tidal wetlands were lost from 1999 to 2019, largely as a result of human activities, including aquaculture, agriculture and urban expansion. Indirect factors also played a role, the study says, including sea-level rise and coastal processes such as erosion.
However, during the same time frame, both human-led and natural restoration led to the creation of 9,700km2 of new tidal wetlands - offsetting 71 per cent of the loss.
The study's findings could "allow us to finally scale up local measurements of carbon accumulation to estimate the size of the coastal carbon sink", a scientist not involved in the study tells.
The new study, published in Science, takes a look at how the global area of tidal wetlands has changed over the past two decades and what reasons led to these changes.
According to the research, "tidal wetlands" consist of Earth's three intertidal ecosystems: tidal flats, tidal marshes and mangroves.
Tidal flats are shallow, muddy areas that are covered and uncovered by the rise and fall of the tide. Tidal marshes are wet, vegetated areas found along coasts and rivers that are regularly flooded. Mangroves are densely covered, swampy forests surrounded by saltwater in a coastal area.
These ecosystems "are of immense importance to humanity", the scientists say, providing benefits such as carbon storage, flood protection and habitat for commercial fish stocks.
Dr Mark Spalding - a marine scientist at the University of Cambridge and co-author of the study said "Wetlands are among the only ecosystems on the planet that are effectively going to sequester carbon in perpetuity - and, unlike freshwater wetlands, they don't emit methane. They also protect us from storms, can grow vertically to track rising seas and generate vast volumes of fish." The study is the first to monitor all three tidal ecosystems simultaneously, adds Dr Nicholas Murray, study lead author and a research scientist focused on environmental management and conservation from James Cook University in Queensland.
"Our results indicate that over the last two decades around 13,600km2 of tidal wetlands were lost due to a range of different drivers, including rapid coastal development. However, we also found that about 9,600km2 of new tidal wetlands were detected in places where they did not occur in 1999. The 'net change' of tidal wetlands (-4,000km2) is overwhelmingly still in the negative."
Using the satellite images, the study estimates that the total area of tidal wetlands in 2019 was at least 354,600km2 - larger than previous estimates had suggested.
It adds that the largest remaining single tidal wetlands are located in the Amazon delta, the northern Bay of Bengal, New Guinea, and the Niger delta.
The researchers also used the images to produce the first estimate for the size of tidal marshes globally, which they say covers 90,800km2.











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