US East Coast marshlands under threat

Sea level rise caused by global warming is threatening to engulf the coastal wetlands of the east coast of the United States of America, which are essential for coastal food webs, carbon sequestration and capturing sediments.

The research, published by the American Geophysical Union, examines the coastal marshlands in Chesapeake and Delaware Bays using satellite data from 1993, updated with recent aerial photography and field surveys. Widespread disappearance of the marshes could severely affect food webs and the biogeochemical cycles of littoral ecosystems. According to the researchers, their degradation could also have serious implications for estuarine water quality through the massive export of particulates into nearshore waters from eroding marshes.

Coastal marshes may also be important carbon sinks. This means that “the potential collapse of hundreds of thousands of hectares of coastal marsh over the next few decades could also have a significant impact on the overall North American carbon budget,” say the researchers.

The research revealed that marshlands in the middle and lower reaches of estuaries of the two bays were found to have been more degraded over recent years than those in the upper reaches. “Generally, depending on what rate of sea level rise you assume could ultimately occur, the marshes furthest upstream could survive because [they] get mineral sediment from the river,” Professor Michael Kearney from the University of Maryland, and lead author of the research, said to edie.

What proportion of coastal marshlands are at risk is hard to predict as there are no good estimates of how far salty water penetrates upstream, Kearney explained. “Moreover, as sea level rises, what today would be river-dominated marsh will change. However, since almost all the largest marshes in Chesapeake Bay are not upstream in location, it is likely that none of these systems will survive if global sea levels rise at the high rates suggested by the Intergovernmental Panel on Climate Change.”

In addition to this, man-made impoundments, limiting stream flow into Delaware Bay from New Jersey, have resulted in increased degradation of marshes. Between 1984 and 1993, the proportion of marshes that were degraded in the bay increased from 25% to 54% of the total marshland, especially on the New Jersey shore. Currently, around 70% of the marshland has been affected, according to the researchers.

Another area of concern is southern Louisiana, where the Mississippi Delta – which once had 40% of North America’s coastal wetlands – has been losing marshland for a long time. “It’s probably going elsewhere as well,” said Kearney. “In fact, we mapped the whole Atlantic coast, but were only able to validate it for the Mid-Atlantic.”

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