VILLANOVA, PA — As global temperatures increase, the threat of sea level rise continues to impact coastal wetlands in the United States. Climate change has already altered the composition of these wetlands, but according to a new study published by a team of scientists led by Samantha Chapman, PhD, and Adam Langley, PhD, professors of Biology in Villanova University’s College of Liberal Arts and Sciences (CLAS) and the Center for Biodiversity and Ecosystem Stewardship (CBEST), the invasion of mangrove trees in saltwater marshes could protect these ecosystems against modest sea level rise. The results were published by the American Geophysical Union (AGU) Journal on April 10, 2023.
Dr. Chapman and Dr. Langley worked alongside a team of scientists on the WETFEET Project from the National Park Service, The Smithsonian Institution, the University of South Carolina and the Guana Tolomato Mantanzas National Estuarie Research Reserve on the study, which was supported by the National Science Foundation Division of Environmental Biology. The WETFEET Project examines how coastal wetlands are responding to rising temperatures, seas, and nutrient loads.
Data were collected from three sites in northeast Florida at the Guana Tolomato Matanzas National Estuarine Research Reserve and used to build a mathematical model to forecast how the wetland would perform in the future. The model projected that invading mangrove trees would build soil elevation at a rate four times greater than saltmarshes at the same sites.
“These findings have some profound implications for climate change mitigation and adaptation,” Langley said. “We have long-term control over how much sea level rise we experience, and we have some short-term control over which plants grow where, so we can possibly help keep our wetlands from drowning.”
The study also concluded that mangroves collapse rapidly under high rates of sea level rise. Neither mangrove trees nor saltmarshes can survive a 100-centimeter rise in sea level (about the length of a yardstick) over the course of a century, which is the level of rise humans could experience if there is no further action to slow climate change.
“These results show that we need to do everything we can to slow future sea level rise because our wetlands can’t keep up the higher rates we could encounter in the future,” Langley said.
The paper also questions how coastal wetlands should be optimally managed. Mangrove trees serve as a layer of protection against climate change by reducing coastal erosion and absorbing storm surge impacts, but marshes also provide this service in climactic zones where they naturally occur. Previous work by this research team showed that mangroves are moving into marshes as freeze events are reduced but future freeze events could again move them back southward into warmer climates. More work needs to be done to slow the rate of sea level rise to allow for both types of natural barricades to function properly.
“We have a real opportunity to restore green barriers of plants along our coastlines to help protect us and mitigate further climate change,” Chapman said. “Our results help guide these efforts by increasing knowledge on what rate of sea level rise plants can keep pace with along our seaboard.”
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