What it is
Salt marshes protect coastlines by attenuating wind waves with their raised marsh platform and the vegetation above ground. Confidence that this service will persist as the climate changes requires knowing how extreme storms damage the platform and the vegetation, and a comprehensive, quantified understanding of how salt marshes and waves interact during extreme events has been lacking. The authors transferred intact salt marsh to one of the world's largest wave flumes and exposed it to increasingly higher waves, reaching up to 2 m significant wave height. The marsh substrate persisted with negligible erosion despite the cumulative wave exposure. The vegetation, by contrast, was progressively damaged as exposure continued, gradually reducing the wave attenuation it provided. Vegetation was most effective at attenuating waves on low-energy marsh coasts, with waves up to 1 m, where attenuation exceeded 10%, reaching up to 50%, whereas on high-energy marsh coasts, with waves above 1 m, attenuation does not exceed 10%. A global assessment by the authors supports this distinction between low- and high-energy conditions drawn from the flume experiment. Their results suggest that the marsh platform remains stable under extreme wave events, and that substantial wave attenuation by marsh vegetation is limited to low-energy marsh coasts.
Why it matters
In a giant wave flume, a salt marsh's soil barely eroded under waves of up to 2 m significant height, but its plants were progressively damaged and damped waves less and less. Salt marshes protect coasts with their raised platform and their vegetation, and a quantified understanding of how both fare in extreme storms had been lacking. Vegetation damped waves most on low-energy coasts, with waves up to 1 m, where attenuation exceeded 10%, reaching up to 50%; on high-energy coasts it did not exceed 10%, a distinction the authors' global assessment supports. Their results suggest the marsh platform stays stable under extreme waves, while substantial attenuation by vegetation is limited to low-energy coasts.
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Filed underCoastal wetland ecosystem dynamics, Coastal and Marine Dynamics, Aeolian processes and effects