Dredging can manage tidal marshes

An eroded marsh with vegetation recovery on the neighboring tidal flat. Credit: Zhenchang Zhu at NIOZ

Salt marshes are under threat as sea levels rise, making the coastlines more vulnerable to stronger wave attacks. Those also erode the marsh edge and hinder plant regrowth on tidal flats, an international research team, led by the Royal Netherlands Institute for Sea Research (NIOZ), has found in its study published in the journal Limnology and Oceanography.

The study, titled Vegetation Recovery on Neighbouring Tidal Flats Forms an Achilles’ Heel of Saltmarsh Resilience to Sea Level Rise, has found that marsh loss takes place when waves erode the seaward marsh edge. The rise in sea levels is expected to increase this erosion as stronger waves will block the recovery of the marsh by washing away seed implantation.

The paper found that the best way to improve the health of the marshes under threat is by managing and elevating the neighbouring tidal flats, as they can directly protect the coast and salt marshes against wave attacks.

Dredged materials can be used to maintain high elevation or by restoring reef ecosystems, such as mussel beds and oyster reefs, which will limit the wave formation on the tidal flat. “This research teaches us that with good management of our tidal flats, we can preserve wide wave-attenuating marshes,” said Zhu.

“A few centimetre increase of wave height can double the time needed for vegetation recovery on the tidal flats,” said Zhenchang Zhu, lead author of the paper. “This is problematic as sea level rise may speed up marsh erosion, meanwhile limiting its recovery. In the long run, this can cause big loss in marsh extent and key ecosystems services humans rely on, such as coastal defence.”