Salt marshes could disappear by the end of the century

The Cape Cod coastline is a patchwork of wetlands. One in every four hectares is estimated to be either a swamp, bog or marsh. To date, however, 36 per cent of the cape's historical salt marshes have been lost or severely degraded. Now it looks as though they’ll soon disappear for good.

More than 90 per cent of all the world's salt marshes are likely to be underwater by 2100, according to scientists at the Marine Biological Laboratory (MBL), who caution that this figure is based on conservative estimates of future sea-level rise. ‘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,’ says Ivan Valiela, a senior research scientist at MBL.

Salt marshes are among the most productive ecosystems on Earth. They serve as critical habitat for a wide range of different species, including fish, shellfish and birds, and buffer the coast from storms. They also act as coastal filters, removing excess nitrogen from the ocean, and are important carbon sinks. ‘There are a great number of reasons for being concerned about losing these valuable habitats,’ says Valiela, ‘and we’re on our way to doing just that I’m afraid.’

When change happens slowly enough, these coastal ecosystems are often able to adapt. Some species, such as saltgrass, act like ecosystem engineers – as they decompose, the accumulation of plant material raises the overall height of the marsh. But sea-level rise will outpace this process, leaving the plants too submerged to survive. Their only option is to migrate further inland. But more often than not, there will be barriers to this. More than 600 million people worldwide live in low-elevation coastal zones, a number that may grow to a billion by 2060. Even in areas that have not yet been built on, cliffs and other geographical features prevent salt marshes migrating to higher ground.

Change is now happening rapidly on Cape Cod. Valiela says that recently, he didn't visit his local salt marshes for a year and a half. ‘When I went back, a year or so ago, I was startled by all the changes that I could see. Things are changing in ways that we didn't predict.’

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Despite conservation efforts to restore these wetlands in many parts of the globe, he isn't optimistic. ‘People have put forward a multiplicity of solutions,’ he says. ‘Unfortunately, we have tried to read through all of that stuff and, at best, they’re just going to slow these changes down rather than stop them. The only real solution is to get rid of fossil fuels.’

The scientists at MBL aren't the first to highlight the serious risk that sea-level rise poses to salt marsh ecosystems. In 2018, researchers at Durham University found that more than 80 per cent of British salt marshes could retreat by 2100; in the South East, they could disappear as early as 2040. The new findings from MBL, which reveal the global extent of the problem, come as a result of a 50-year study in Great Sippewissett Marsh in Falmouth, on the western coast of Cape Cod. Valiela, who has worked on the study since its inception in 1971, points to the benefits of long-term datasets like this one. If you study an ecosystem for long enough, he says, all sorts of revelations may emerge.

Filed Under: Science & Environment Tagged With: June 23, Worldwatch