Nearly all of the world’s salt marshes may be underwater by 2100

Salt marshes are some of the most biologically productive ecosystems on Earth, playing a crucial role in nitrogen cycling, protecting coastal development from storm surges, providing critical habitats and nurseries for a variety of fish, shellfish, and coastal bird species, and acting as major carbon sinks. Unfortunately, according to a new study led by the Marine Biological Laboratory (MBL), over 90 percent of the world’s salt marshes are estimated to be underwater by the end of this century due to sea-level rise.

Since 1971, scientists have mapped vegetative cover in experimental plots in the Great Sippewissett Marsh in Falmouth, Massachusetts to examine how increasing levels of nitrogen may impact several species of marsh grass. However, due to the length of the study, they also managed to detect the effects of climate change on this ecosystem, including those driven by accelerating sea-level rise.

“Places like Great Sippewissett Marsh will likely become shallow inlets by the turn of the century,” said study lead author Ivan Valiela, a senior research scientist at MBL. “Even under conservative sea level estimates, more than 90 percent of the salt marshes of the world will likely be submerged and disappear or be diminished by the end of the century.”

“This is not a prediction from isolated scientists worried about little details. Major changes are going to be taking place on the surface of the Earth that will change the nature of coastal environments.”

The researchers found that, when changes in sea level occur slowly enough, salt marshes plants that usually grow at lower elevations can migrate upward, adapting and thriving in new environments. However, considering the fast pace with which sea-level currently rises – and its probable further acceleration in the near future – soon there will be no more room for low marsh plants. 

This problem is exacerbated by the fact that marshes around the world face what the scientists call a “coastal squeeze,” where sea-level rise pushes from one direction and human development from another. For instance, seawalls constructed to protect human communities from flooding will most likely prevent the migration of a marsh upward.

“These barriers, whether they be geographic like a hill or a cliff, or people building along the edges of the ecosystem, constrain the potential for landward marsh migration,” said co-author Kelsey Chenoweth, a research assistant at MBL. “On top of that, sea-level rise is accelerating and marshes are having a hard time keeping up.”

“Sea level rise is the most important threat to salt marshes. We really need to figure out what’s going to happen to these ecosystems and learn how to prevent some of the losses from happening or try to adapt to them, so marshes can continue to play these important roles for nature as well as humans,” concluded co-author Javier Lloret, a research scientist at the same institution.

The study is published in the journal Science of the Total Environment.

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By Andrei Ionescu, Earth.com Staff Writer

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