From Texas to Maine, coastal wetlands and marshes are releasing more than 1.45 billion pounds (660,000 metric tons) of carbon into the ocean each year, according to new research supported by NASA.
Coastal marshes, like forests and tundra, store large amounts of carbon in their plants and soil, but changes caused by storms, rising seas and human development can affect how that carbon is stored and transported.
The authors of the new study analyzed Landsat imagery along with lidar elevation data from the U.S. Geological Survey to track marsh loss along the Gulf Coast and Eastern seaboard between 1985 and 2022. They estimate that while some of the carbon released by erosion is offset by new marsh growth, the net loss is still around 800 million pounds (380,000 metric tons) of carbon every year.
The amount of erosion varied across regions and time periods. The authors identified increases in coast erosion in the Mississippi River Delta following hurricanes Katrina in 2005 and Ida in 2021, both of which uprooted and submerged miles of coastal vegetation. Home to the nation’s largest marshland by area, the region moved more coastal carbon than the entire Eastern seaboard.
Most of the carbon displaced by marsh erosion isn’t emitted directly into the atmosphere but enters the ocean. This air-land-ocean exchange is traditionally hard to model because of the complexity of shoreline environments, which change continually, sculpted by rising sea levels, wind, tides and marine life. To better simulate the process, new models are being developed at NASA’s Goddard Institute for Space Studies. Improved understanding of how carbon moves from land to sea along our coastlines can help scientists construct a more accurate picture of Earth’s carbon cycle overall.
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