Salt marshes to persist despite rising seas: Study

Salt marshes - the coastal wetlands that are flooded and drained by salt water brought in by the tides - are expected to grow vertically and migrate landward even as sea-level rises across the world, says a study.

According to lead author Matt Kirwan, professor at the Virginia Institute of Marine Science, traditional assessment models used by researchers greatly underestimate marsh resilience as they don't fully account for processes that allow the marshes to adapt to sea-level increase.

"Catastrophic predictions of marsh loss appear alarming, but they stem from simple models that don't simulate the dynamic feedbacks that allow marshes to adapt not only to present rates of sea-level rise but the accelerated rates predicted for coming decades," explained Kirwan.

"Marsh soils actually build much faster as marshes become more flooded," he added.

The study, published in the journal Nature Climate Change, found that more frequent flooding carries more mud into the marsh and also encourages the growth of several common marsh plants. Together, these processes raise the marsh soil in concert with rising waters.

Kirwan's team conducted their study by compiling and re-analysing 179 previously published records of change in marsh elevation from sites in North America and Europe.

"Our study shows that soil accretion rates more than double as marshes become more flooded, suggesting a strong ability for marshes to survive accelerations in sea-level rise," Kirwan noted.

But marsh migration is not possible where obstructed by coastal cliffs or human barriers, the researchers found.

The study could help ecosystem managers assess marsh vulnerability more accurately.

Healthy marshes buffer coasts from storms, improve water quality, provide habitat for commercial fisheries, and help fight global warming by trapping carbon.