Hurricane Ida caused marsh loss equivalent to 32 years of coastal erosion without hurricanes in the Barataria Basin when it made landfall in 2021.
Oceanography and coastal sciences associate professors Giulio Mariotti and Tracy Quirk found that not all marshes are equally susceptible to hurricane damage.
The two professors published a paper on their findings last month. According to their research, 82% of the marshes lost during Hurricane Ida had intermediate salinities, meaning that they were surrounded by brackish water. Those marshes were also dominated by the plant Spartina patens.
Mariotti explained that the intermediate marshes dominated by this plant have weak soil and contain semi-floating blocks, which means the marshes’ root systems and vegetation mats are not firmly rooted in the ground but are floating on water. This flimsy internal structure makes it easy for hurricane storm surges to uproot plants in these marshes.
Mariotti clarified that Spartina patens is not an inherently weak plant.
He explained that, in the brackish marshes destroyed by Hurricane Ida, Spartina patens plants were positioned low in the marshes and submerged underwater. The plants’ disadvantageous position restricted their access to oxygen, making them weak.
In some parts of the country, Mariotti added, this same plant grows strong and healthy. The intense storm surges coastal Louisiana experiences might contribute to the weakness of the plants in the region’s marshes.
Mariotti emphasized that marshes in Louisiana are not growing as fast as the sea level is rising, causing marsh plants to be submerged and stressed.
“This is not something you would extrapolate to every marsh in the U.S. That being said, Louisiana has a very large portion of the overall marshes in the U.S., and there is a very large rate of loss,” he said. “Even though this process only happens in the Mississippi Delta, it is still very significant even at the national level.”
Mariotti explained that saltier marshes were more resistant to storm surges because they tended to have more sediments, helping their plants bind firmly to their roots. Freshwater marshes were also resilient because even though they had less sediments, their root systems are more cohesive than those in brackish marshes.
Mariotti said now that he and Quirk have identified which marshes are weak, scientists can focus on making them stronger.
Still, exactly what measures scientists should take to strengthen marshes remains unclear. He mentioned proposals like putting sediment on top of the marshes to make them heavier, but he said he does not know what will actually work.
Quirk said that prior to Ida, she and Mariotti had already been studying Spartina patens. While this plant species is growing healthy in some parts of the country, Quirk said that it has also suffered losses in marshes in New England and the Mid-Atlantic.
“When Hurricane Ida happened and we saw this marsh loss, it sort of coincided with some of the other research that we were doing,” Quirk said.
Quirk said that a potential solution is to create marshes with large amounts of mineral sediment material. She said those would be more resistant to storm surges because their vegetation mats are less organic and are attached rather than floating.
“I know managers are interested in how the created marshes compare with natural marshes in terms of erodibility or vulnerability to storm impacts, and our study definitely speaks to that,” Quirk said.
