Can Sewage Save Wetlands? One Louisiana City Decided To Find Out
St. Bernard Parish is considering a new marsh creation project: adding partially-treated sewage to Bayou Bienvenue, east of New Orleans. The idea is to build up vegetation—and spur marsh creation—by tapping the natural fertilizer that humans around the world create daily.
As unappetizing as that might sound, there are projects like it all over the world. Sewage is full of nutrients that can enhance plant growth, and with proper treatment and disinfection, it can be completely safe. Southeast Louisiana currently has twelve “wetland assimilation” projects, as the technique is known. All are permitted by the Louisiana Department of Environmental Quality.
For the most part, the wetland assimilation projects have gone off without a hitch. But the city of Hammond’s project has perhaps gone awry—and stirred up not only local controversy, but questions about the safety of the whole technique.
Hammond launched their wetland assimilation project in 2006. But the marsh they chose to “assimilate” their sewage wasn’t in Hammond itself—it was just south, outside of Ponchatoula.
If you want to tour a marsh full of disinfected sewage, you can’t ask for a better guide than Albert Poche. He put four kids through college trapping this very marsh for nutria, mink, muskrat, otter and raccoon. He knows it well, as does Poche’s friend Ed Bodker. Bodker is 70 years old, and grew up nearby. His grandfather was a fur buyer, and the first time Ed came in this marsh he was nine years old.
Officially, the marsh—part of the Joyce Wildlife Management Area—is called the Four-Mile Marsh. But locals have a different name for it now, according to Bodker.
“Some people call it the poop pond,” he says. “And some people call it Lake Commode.”
The pond used to be solid wetland, but now it’s open water. The marsh grasses are mostly gone, except for a few uprooted patches floating by. And because of all the water, two invasive species have taken over: water hyacinth and salvinia.
There’s so much hyacinth that Bodker can barely push through it in his pirogue. And the water has changed the wildlife in the marsh as well. Poche says that Four-Mile Marsh isn’t “productive” anymore. And he blames the sewage coming down from Hammond.
“They took a once vibrant, green, productive marsh and they’ve converted it to open water,” says Poche. “It was well-intentioned people that tried this project. They meant well, but it just absolutely didn’t work.”
Bodker lives less than two miles away. In fact, one of the creeks that feeds Four-Mile Marsh touches his property. His complaint isn't just due to having sewage in his backyard, though. For 27 years, Bodker managed environmental testing for the Louisiana Department of Transportation—monitoring compliance for about 100 state-owned sewage treatment plants. He says that though he sometimes wished he didn’t, he knows from sewage.
Yet putting treated sewage into wetlands is a proven technique. In Louisiana, one of the first people to study it was John Day, Professor Emeritus in Oceanography and Coastal Science at Louisiana State University.
Day has been researching wetland assimilation since the 1980s, and the adoption of the technique in Louisiana was in large part borne of his research. Beyond the scientific, Day also has a business interest in wetland assimilation: his company, Comite Resources, designed six of Louisiana’s currently-active assimilation projects, and they are paid to monitor the sites and deliver reports to the Department of Environmental Quality.
“We’ll probably bid on [the St. Bernard assimilation project,]” says Day.
Day explains that assimilation projects are supposed to have two big benefits. First, cities save money on sewage treatment. When sewage is discharged into rivers and streams, it requires an advanced—and expensive—level of treatment. Wetlands can clean sewage that passes through them, which obviates the need for that advanced level of treatment. Second, the nutrients in treated sewage can act as fertilizer to build up vegetation and spur marsh creation.
And at first, that’s exactly what happened at Four-Mile Marsh. “There was a very significant increase in the growth rate of the marsh vegetation,” says Day. Unfortunately, soon after that, the marsh started to degrade. Day says this degradation has not happened at any other sites.
And Day has an explanation for why the Hammond vegetation disappeared: nutria. He’s co-authored a peer-reviewed paper concluding that the increased vegetation drew an increased population of hungry nutria, which quickly ate away the renewed wetland.
This is where the controversy takes hold. Local resident Ed Bodker claims that there are no more nutria than before, and that the problem is the sewage itself—it’s too full of nutrients and is frying the marsh. And Bodker has published his own peer-reviewed paper to support his conclusion. He’s not an LSU professor, but his co-author Gene Turner is. In fact, Turner is in the very same department as John Day—the School of Oceanography and Coastal Sciences.
“[Four-Mile Marsh] is clearly decomposing from below-ground,” says Turner. “It doesn’t have the attachment necessary for high water—it floats away.” Turner says this is not an unexpected conclusion: it happens to marshes around the world. But Day contends that marshes around the world receive the same level of nutrient without degrading.
But both scientists agree that the assimilation project at Four-Mile Marsh has one big difference. Many such projects are built with a mechanism for controlling the level of water in the marsh, whether by draining it or moving it around. Four-Mile Marsh lacks this feature.
“Under natural conditions these wetlands would flood and drain, flood and drain,” says Day. The “drain” half of the natural cycle has been disrupted at Four-Mile Marsh. Turner claims that this is one of the primary causes of the marsh degradation, and that it’s now just getting worse. For his part, Day agrees that going forward, all wetland assimilation projects should have a water-control mechanism built in. The scientists hope to convene a panel of independent reviewers who can assess the problems at Four-Mile Marsh, put an end to the debate about what caused the project to fail, and recommend a way forward.
In the meantime, Albert Poche and Ed Bodker continue to watch the marsh they grew up in deteriorate. And they feel that their first-hand knowledge of Four-Mile Marsh is invaluable.
“The first time I came in this marsh I was nine years old,” Bodker says. “And I’m 70 years old now. So I feel like I can see backwards in time to where things were and how they have come to change. Most people don’t spend enough time out here to really observe that closely.”
Turner echoes the sentiment. “Being at home, or being at your office, is different from being actually out there. You cannot understand the natural environment unless you go out there and see things happen. And not for 30 minutes, and not for a one-time sampling, but over a long—many, many, many years.”
This tension between expert science and local knowledge plays out all over Louisiana’s planning and restoration projects. Turner says one lesson is that sometimes, neither one can paint a complete picture. Wetland ecosystems are complicated, and engineering projects often come with unintended consequences.
Bodker has been watching warily as St. Bernard Parish considers a wetland assimilation project of its own. Now, he’s submitted a 14-page public comment against it. Having seen the technology fail in his backyard, he feels like it needs a lot more study before it’s worth the risk.