Salt Marsh Erosion Driven By Regular Weather, Not Sporadic Violent Storms

Contrary to common belief, large hurricanes are not the leading cause of coastal wetland erosion. In a recent study, researchers from Boston University (BU) and the United States Geological Survey (USGS) investigated why these vulnerable environments are retreating at an alarming rate and discovered normal weather conditions are responsible.

"Waves are very powerful because they attack the marsh in its weakest part," Nicoletta Leonardi, lead author and Ph.D. candidate at BU's Department of Earth and Environment, said in a news release. "Generally, the more a salt marsh is exposed to waves, the faster it is eroding."

Salt marshes nourish many different types of wildlife, which means their deterioration is cause for concern. After examining eight salt marsh locations in Australia, Italy and the U.S., researchers found there was a constant relationship between wave energy and the speed of marsh erosion. While the occasional hurricane or violent storm contributes less than one percent of salt marsh deterioration, regular moderate northeast storms that hit every few months cause far more damage. Researchers say this is because salt marshes have learned how to cope against hurricane waves and are more susceptible to erosion from land use, higher sea levels and loss of sediment from upstream dams.

"While hurricanes are catastrophic events, the salt marsh doesn't respond catastrophically," Neil Kamal Ganju, co-author and research oceanographer with USGS, explained, adding that because a hurricane's surge brings up water level so high over a marsh, waves have relatively little effect.

Therefore, researchers suggest salt marshes could be preserved as "living shorelines" that act as buffers between coastal communities and the ocean. Such efforts were initiated in New Jersey and New York after Hurricane Sandy in 2012, and in salt marshes surrounding New Orleans after Hurricane Katrina in 2005, according to the release.

"You can take the geography of a salt marsh and the estuary around it, and if you understand the wind climate and the wave climate, using historical data, you now can predict the marsh erosion," Ganju added in BU's news release.

Their study, recently published in Proceedings of the National Academy of Sciences, has implications for better wetland management and restoration, as well as modeling carbon storage as it relates to climate change.

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