Along Earth’s coastlines, grassy wetlands flooded by seawater, called salt marshes, trap and store carbon at rates roughly 40 times higher than forests on land. As salt marshes have expanded in some regions, scientists were hopeful their carbon stores might have largely recovered as well, but a new study found that’s not the case. Researchers measuring carbon storage in salt marsh soil found that destruction of the world’s salt marshes resulted in a net loss of roughly half a million metric tons of surface soil organic carbon (SOC) between 2002 and 2019 — the equivalent of the emissions from 6,600 passenger cars over the same period. Most of that was from mature salt marshes that stored much more carbon than newly established marshes. “The most surprising finding … is the paradox that salt marsh area is recovering globally, yet soil organic carbon is undergoing a net loss,” study co-author Xinxin Wang, a wetland ecologist at Fudan University in China, told Mongabay. The southern U.S. is a global hotspot for SOC loss from marshes, the study notes, with Louisiana’s Gulf Coast ground zero. Hurricanes Katrina and Rita hit the region in 2005, causing immediate damage to rich marshlands. Louisiana’s salt marshes have suffered from decades of industrialization, including more than 75,000 oil and gas recovery wells and nutrient runoff from agriculture. The weakened salt marshes were torn apart by the storms and largely transformed into open mudflats. Nearly 200,000 barrels of oil and other petrochemicals were spilled during Hurricane Katrina. The…This article was originally published on Mongabay

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