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Global beach erosion threatens protected marine areas

A new survey based on satellite data from NASA Goddard and the United States Geological Survey has revealed that the world’s beach shorelines have slightly increased on a global scale over the last three decades. In marine protected areas, however, shorelines have decreased in size due to erosion.

The findings of the study, which is the first of its kind, suggest that plant and animal species are threatened along the 50,000 miles of coastline where erosion was observed.

Researchers were able to gain a more accurate assessment of beaches using the data collected from space. They found that 31 percent of all ice-free shorelines are comprised of sand or gravel. Africa has the highest proportion of sandy beaches at 66 percent, while Europe has the lowest at 22 percent.

Using machine learning, a team of experts from the Netherlands trained software to accurately identify sandy beaches from images taken by Landsat satellites. This approach enabled the researchers to rapidly determine how many of the world’s beaches are sandy and how these beaches have changed over the last 30 years.

Study co-author Arjen Luijendijk is a coastal development expert at Deltares, an independent research institute with studies focused on deltas, river basins, and coasts.

“It only took about two months’ calculation time to generate this data set of annual shorelines between 1984 and 2016 for the entire world,” said Luijendijk. “The alternative of taking aerial images, placing the images in world coordinates, and sometimes manually detecting shorelines, takes weeks or months to capture a coast longer than 50 miles.”

The scientists found that many of the world’s non-protected beaches are transforming, but in different ways. They determined that about 24 percent of Earth’s sandy beaches are eroding, and 27 percent are expanding.

Furthermore, about 16 percent of all beaches are eroding at rates which are classified as “intense” or “extreme,” while 18 percent are growing at similar rates. Overall, there has been a small increase in the total amount of sandy beaches across the globe.

Because protected marine areas are not as influenced by human activities, these regions provide experts with insight on how natural processes may affect shorelines.

There are over 1,200 marine protected areas in the United States including sanctuaries and reserves, national parks, wildlife refuges, and national monuments. Many of these sites were designated to protect vulnerable plant and animal species, and losing land could disrupt the balance of the ecosystems and threaten their future.

“At this point we think the continental differences in beach erosion and accretion are largely influenced by human interventions along the coast,” said Luijendijk. “Our next steps will focus on distinguishing the human impact from the natural dynamics and trends.”

The research is published by Springer Nature.

By Chrissy Sexton, Staff Writer

Image Credit: NASA Earth Observatory, Spencer Kennard

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