‘A living laboratory’: An accidental delta taught Louisiana scientists how to rebuild wetlands

ST. MARY PARISH, LA. — Amid the rapid erosion of Louisiana’s coast, something hopeful is happening where the Atchafalaya River meets the Gulf. A flow of sediment from a decades-old river diversion has accidentally given birth to new wetlands.

While that small delta is dwarfed by what’s washing away all around it, researchers have gained knowledge from Wax Lake Delta that could help save the rest of Louisiana’s coast and contribute to a better understanding of wetland science across the globe.

“We have sea level rise, we have storms, but yet … the Wax Lake Delta remains and continues to grow and reach out into the Atchafalaya Basin,” said Alisha Renfro, a coastal scientist with the National Wildlife Federation.

Researchers at Louisiana State University’s Coastal Systems Ecology Lab, led by wetland scientist and professor Robert Twilley, take regular trips to Wax Lake to study what makes a healthy wetland. They monitor soil chemistry and study the way water moves throughout the delta, depositing sediment and building land as it flows.

“Wax Lake has this beautiful, long history of researchers that literally wrote the textbook on what is a delta based on that region,” Twilley said.

Rather than having to rely on computer modeling for their research, Wax Lake is known as a “living laboratory,” said Renfro, describing it as the perfect place to study what makes a healthy wetland.

During a research trip on a bright February morning, alligators meandered through the marshy channels of the Wax Lake Delta, part of the Atchafalaya Wildlife Management Area. The scientists were happy to see them. The presence of so many apex predators in the muddy water is a testament to the health of the ecosystem, said Jessica Richardson, a data manager working with Twilley at LSU in the Coastal Sciences department.

“You’ve got different wildlife nesting, laying eggs, such as alligators … and birds that fly, that come in during different seasons and nest,” Twilley said.

Deltas are formed from sediment that collects at the end of a river, like the Mississippi or Atchafalaya. Over time, this sediment builds, creating new land and using nutrients carried by the river to grow vegetation, the roots of which stabilize the new soil and keep it from eroding.

Deltaic wetlands are uniquely diverse and ecologically valuable. When a river flows into the delta, “it’s not just water,” said Ivan Vargas-Lopez, a wetland scientist and researcher with the Coastal Systems Ecology Lab.

“It’s bringing a lot of nutrients, a lot of sediment, a lot of particles, a lot of material,” he said. “When the water recedes, a lot of that material stays.”

This process can happen naturally over thousands of years, but the new land built from Wax Lake happened by mistake.

The U.S. Army Corps of Engineers dug a channel in 1941 to try to reduce flooding in nearby Morgan City, redirecting the flow of water from the Atchafalaya. This started the process of sediment buildup, noticed only after a massive flood in 1973 flushed a torrent of dirt down the river.

At Wax Lake, land is built through flooding. Floods bring in great heaps of sediment, spreading it out across the floodplain in a lobelike shape at the end of the river.

“Under that water, you’re building a delta, and all of a sudden it sort of … pops up,” Twilley said.

Over time, the process forms the wetlands so important to the integrity of Louisiana’s coast.

Subsidence, or the slow sinking of land, paired with ongoing oil and gas development and sea level rise caused by climate change, are erasing Louisiana’s coastal wetlands — and fast. These wetlands are some of the most vulnerable in the world, with much of the coast washing away at a rate of about a football field every 100 minutes, endangering cities, towns and livelihoods all along the coast.

Meselhe used data from Wax Lake Delta in his work on the Mid-Barataria sediment diversion project, which would redirect the Mississippi River into the Barataria Basin to reverse land loss in coastal parishes. The diversion has been highly controversial due to its impact on fisheries, and it’s facing delays and legal challenges.

The Wax Lake Delta data helped him to understand how the interaction between water flow, sediment buildup and plant growth worked to build land. He also looked at how land is being built by another diversion called West Bay and at the Bonnet Carré spillway to see how the diversion would affect the river itself. Then he used that information to calibrate models to help explain how Mid-Barataria would work.

 “Wax Lake, West Bay and Bonnet Carré served as examples because they had data and measurements and maps over a number of years that helped us to have confidence and trust in the models we ended up using for the Mid-Barataria area,” he said.

The LSU Center for River Studies houses a massive model of the Mississippi River in its Baton Rouge facility, built using data including water velocity and sediment concentrations observed at Wax Lake and other Louisiana deltas. Researchers and students use it to test how sediment moves with the Mississippi River and where it’s deposited.

Physical models are useful and necessary; the Army Corps has used them since the early 20th century. But Twilley said field observations like those done at Wax Lake are crucial.

As scientists study how Wax Lake builds land, they can also better understand the benefits of healthy wetlands, such as natural carbon storage and nutrient reduction.

Because Wax Lake has been building wetlands for decades, Twilley’s lab can compare older and newer areas of marsh.

“The older delta does a much better job at holding the soil and serving as a hurricane protection system than the younger,” he said.

Mature wetlands also store huge amounts of carbon in organic matter, found in dead plants. Buried in the marsh, they keep microorganisms from eating the carbon and releasing it as planet-warming CO2. Wetlands also filter excess nitrogen out of the water, sequestering it before it reaches the Gulf and contributes to harmful algal blooms and the “dead zone.”

That’s one of the reasons it’s important to protect existing wetlands, Twilley said. Their systems are already established and don’t have to catch up.

While the science is clear — wetlands have lots of benefits and we know how to build more of them — the future is not. America’s wetlands are under increased threat. After hundreds of years of draining them for agriculture and housing — and historic efforts to protect them — regulations are now being rolled back.

The U.S. Fish and Wildlife Service estimated that wetlands covered about 6% of the lower 48 states as of 2019 — about half the amount of wetlands that existed around 1780.

The report also found that the rate of wetland loss increased 50% during the latest study period. Wetlands are now being lost faster than ever, from a combination of drainage for agriculture, development and the effects of climate change.

Louisiana’s coastal wetlands make up about 40% of all coastal marshes in the United States, according to a series of reports from the U.S. Geological Survey conducted throughout the 1980s and finished in 1996, which found that “wetlands once covered more than one-half of the area that is now Louisiana, but wetland acreage has declined to less than one-third of the State’s land surface over the last 200 years.”

Changes at the federal level could also increase risk of continued wetland loss.

The fate of the Mississippi River’s precious wetlands hangs in the balance.

Research on Wax Lake Delta illustrates that wetlands are more important than ever. Renfro said that’s why it’s critical to take these lessons and use them to build more wetlands.

“At the end of the day, reconnecting the river with those wetlands it once built is kind of the consistent way to build robust, healthy coastal ecosystems that continue to grow.”