Mississippi River Delta study reveals which human actions contribute to land loss

Published in Nature Sustainability, the study compares the impacts of different human actions on land loss and explains historical trends. Until now, scientists have been unsure about which human-related factors are the most consequential, and why the most rapid land loss in the Mississippi River Delta occurred between the 1960s and 1990s and since has slowed down.

"What we found was really surprising," said Doug Edmonds, the Malcolm and Sylvia Boyce Chair in the IU Bloomington College of Arts and Sciences' Department of Earth and Atmospheric Sciences. "It is tempting to link the land loss crisis to dam building in the Mississippi River Basin -- after all, dams have reduced the sediment in the Mississippi River substantially. But in the end, building levees and extracting subsurface resources have created more land loss and, according to our research, building dams has not had that big of an effect."

The current Mississippi River Delta formed over the past 7,000 years through sediment deposition from the river near the Gulf Coast. But due to human efforts to harness the river and protect communities, the delta is no longer accumulating sediment. As a result, coastal Louisiana has lost about 1,900 square miles of land since the 1930s, according to the Louisiana Coastal Protection and Restoration Authority.

There is no one cause of the crisis, Edmonds said. But many researchers believe it is the result of different human interventions in the delta, including dam building, flood control levee installation and subsurface resource extraction.

The study found that only about 20% of the land loss is due to dam building, while levee building and extracting subsurface resources like oil and gas each account for about 40% of the Mississippi River Delta land loss. The study also suggests that the most rapid land loss and the recent deceleration might be related to the reduction of subsurface resource extraction.

Additional leaders on the study were Robert R. Twilley, Samuel J. Bentley, Kehui Xu and Chris Siverd at LSU.

To conduct their study, researchers re-created the land loss for an area in the Mississippi River Delta called the Barataria Basin. They used a model that describes the sediment budget, which is the balance between sediment flowing in and out of a coastal system. Using that model, they quantified the impact that building dams and levees and extracting subsurface resources had on land loss.

"This study emphasizes the importance of doing a broad systems analysis of complex problems, so we really can have confidence in the solutions we're proposing to reverse land loss and protect our land and people," said Twilley, professor of oceanography and coastal sciences at LSU. "There's a possibility river diversions might have more impact in building wetlands than we anticipated."

The 2023 Coastal Master Plan for Louisiana prioritizes restoring the processes that naturally build land in the delta. The Mid-Barataria Sediment Diversion, which is the largest coastal land restoration project in Louisiana at more than $2 billion, will release sediment and water from the Mississippi River into the adjacent Barataria Basin.

"Our work suggests the Mid-Barataria Sediment Diversion is the right tool for the job to counter land loss due to subsidence and sea level rise," said Bentley, professor and the Billy and Ann Harrison Chair in Sedimentary Geology at LSU. "Overall, this study offers perhaps a rosier outlook than some other analyses on our ability to engineer with nature to reverse land loss."