Carbon storage, hurricanes and history: The importance of preserving coastal wetlands

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Louisiana wetlands continue to disappear, threatening to displace coastal communities and release stored carbon into the atmosphere 

By Nicole Nguyen

BATON ROUGE, LA – Louisiana native Jack Green’s family grew up in Lake Charles, and their history is rooted in the state and its natural landscape.  

“People tie their culture to Louisiana and all these different cultures that are so endemic to the coastline, and I think that’s all tied to the land and appreciation of natural wildlife,” Green said. 

But many of the wetlands Green’s family grew up around had eroded by the time he was born. 

“When my parents were growing up, they would tell me stories of what it used to look like prior to now,” Green said. “There’s still a little bit of natural wetlands left to be appreciated, though I do understand that there used to be a lot more when my parents were younger.” 

In addition to the cultural value of wetlands, these ecosystems provide communities important services like water purification, protection against storms for coastal cities and reservoirs of biodiversity containing various plant and fish species. They also act as carbon sinks, storing vast amounts of carbon dioxide.  

In Louisiana, a sinking coastline combined with rising seas threatens to shift these ecosystems from carbon sinks into carbon sources.  

Climate Change, Hurricanes and Flooding

The soils and plant biomass in wetlands store carbon dioxide, the predominant greenhouse gas warming the planet, from the atmosphere. The carbon captured and stored in coastal systems for long periods is known as blue carbon. 

Wetland erosion releases this blue carbon into the atmosphere, leading to further warming of the planet, according to a 2017 study published in the Journal of Environmental Management.

“While these systems only take up about 2% of the planet’s land, their per-square ability in capturing carbon is high,” said Tracy Quirk, Louisiana State University wetland researcher. 

Coastal wetlands also act as barriers, or sponges, by absorbing storm surges from hurricanes and protecting coastal communities from flooding. Wetlands farther inland, like the freshwater marshes and swamps along the Mississippi River in Louisiana, help reduce flooding by soaking up rain.  

A 2017 study published in Scientific Reports estimates that coastal wetlands prevented $625 million in property damage by reducing flood heights across 12 coastal states affected by Hurricane Sandy in 2012.  

History and Culture

Combinations of ethnic groups along Louisiana’s coast have created a region unlike any other in the country. The wetlands gave these populations a variety of natural resources.  

French, Spanish, African, German, Anglo-American and Acadian settlers joined Native Americans in South Louisiana during the 18th century, according to a paper in the Journal of Coastal Research. These groups were followed by Yugoslavs, Haitians, Irish, Chinese, Italians, Filipinos and Vietnamese.   

But the state’s coast looks much different today. More than 2,000 square miles of Louisiana’s coastal wetlands have been lost since the early 20th century due to subsidence and erosion, according to the United States Geological Survey.  

Louisiana is home to the first American climate refugees from Isle de Jean Charles, a community that was resettled using $48 million provided by the Department of Housing and Urban Development in 2016.  

Officials decided that there was no realistic path for the community to protect what little land was left from coastal erosion. Most of the resettled residents belong to the Biloxi-Chitimacha-Choctaw tribe.  

“We’re going to lose all our heritage, all our culture,” Chief Albert Naquin of the Biloxi-Chitimacha-Choctaw said in an interview with the New York Times. “It’s all going to be history.”  

A Sinking Coast

Louisiana wetlands are formed by sediment deposits from flowing bodies of water. 

Development and industrialization in Louisiana allowed many people to settle along Louisiana’s coast. To permanently settle in these hurricane-prone areas, residents had to build levees to control the flow of rivers and prevent flooding in their communities. 

But the levees prevented sediment carried by the Mississippi River from being deposited in the areas that needed it. As a result, Louisiana began to experience high rates of wetland and coastal loss.   

A young Spartina alterniflora clone colonizing a newly created marsh in Sabine National Wildlife Refuge, Hackberry, Chenier Plain, Louisiana. Graduate Student Kate Abbott ponders where to collect a sediment core to evaluate soil carbon and microbial community development. Photo courtesy of Tracy Quirk.

Rising seas certainly don’t help the Louisiana coast’s fate. Climate-induced sea level rise caused by thermal expansion and the melting of ice sheets and glaciers will have a larger effect in the future if left uncontrolled.    

Vertical accretion, a process explained by LSU Renewable Natural Resources professor John Nyman, is the accumulation of sediment in wetlands. It increases wetland elevation and provides stability for the land.  

Sea-level rise will eventually outmatch vertical accretion and inundate much of our wetlands, speeding up degradation and loss, Nyman said.  

Uncertainty surrounding how much wetland loss is caused by sea-level rise versus other factors makes implementing policy to thwart continued sinking difficult.  

“Despite that certainty, there’s tremendous uncertainty,” Nyman said. “That makes it very inefficient to try to know when you’re spending money restoring something that is done within five years—or one.”  

Louisiana has a $50 billion Coastal Master Plan aimed at holding on to as much land as possible, but officials agree further land loss is inevitable.  

“I feel obligated to keep the wetlands going as long as it’s profitable to do so, and not profitable only in the economic sense,” Nyman said. “I like to compare the wetlands to my 2000 Dodge pickup truck. It’d be ridiculous to stop changing the oil and tires on my truck, just as it’d be ridiculous to not manage the wetlands so we can get more life, water quality and carbon storage out of it. It would be very inefficient to abandon them right now.” 

Green said the communities along Louisiana’s coast should be at the forefront of the conversation around saving wetlands.  

“Listen to the people,” he said. “The people are really important and their stories and culture are important. To me, people are the reason why wetlands are worth saving.”

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