A new study looks at human contributions to Mississippi River Delta land loss and hints at possible solutions.
Published March 6, 2023 03:18PM EST
A dying cypress swamp seen under stormy skies, Venice, Louisiana.
Matthew D White / Getty Images
No American river is as iconic as the mighty Mississippi. The country’s second longest river, it winds its way through 10 states and drains 41 percent of the continental United States. The river and its floodplain support more than 400 different species of wildlife, while 40% of North America’s waterfowl migrate along its flyway. The basin provides critical habitat for more than 300 candidate species of rare, threatened, or endangered plants and animals listed by state or federal agencies. Not to mention the cultural significance and the services it provides to humans along its course.
Yet, in a tragic twist of fate that has befallen a number of American rivers, she’s in trouble. While Native Americans have had a harmonious relationship with the Mississippi River since at least the 4th millennium BCE—including the Choctaw, Chickasaw, Quapaw, Osage, Caddo, Natchez, and Tunica in the Lower Mississippi, and the Sioux, Sac and Fox, Ojibwe, Pottawatomie, Illini, Menominee, and Winnebago in the Upper Mississippi—human interference in the last century has proven devastating, especially for the Delta.
Levees and subsurface extracting for resources such as oil and gas each account for about 40% of the Delta’s land loss.
As the authors of a new study on the Delta’s land loss note, “due to human efforts to harness the river and protect communities, sediment accumulation is no longer sufficient to sustain the Delta. As a result, coastal Louisiana has lost about 1,900 square miles of land since the 1930s.
The research comes from scientists at Louisiana State University (LSU) and Indiana University who looked into the role humans have played in the Delta’s dramatic land loss, information that is crucial to understand if we are to find solutions to this creeping disaster.
Until this research, scientists haven’t understood which human-related factors have had the most impact. That the most rapid land loss happened between the 1960s and 1990s—and has slowed down in the 21st century—has also been a mystery.
What the researchers uncovered was unexpected.
“What we found was surprising,” said Doug Edmonds, lead author of the study and an associate professor of Earth and atmospheric sciences at Indiana University Bloomington. “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.”
In the early decades of the 20th century, significant efforts were made to tame the river. As the river-conservation non-profit America Rivers explains: “Following the monumental flood of 1927, an era of federally funded levees, dredging, and diking ensued. In man’s attempt to control the river, we have leveed more than 2,000 miles of the Mississippi watershed, isolating it from its floodplain.”
While the dams do have consequences for land loss—the study found that about 20 percent of the land loss is due to dam building—levee building and extracting subsurface resources play a much larger role. Levees and subsurface extracting for resources such as oil and gas, each account for about 40% of the Delta’s land loss.
The study also suggests that the rapid land loss and deceleration between the 1960s and 1990s might be related to the reduction of subsurface resource extraction.
“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 study author Robert R. Twilley, an LSU professor of oceanography and coastal sciences. “There’s a possibility river diversions might have more impact in building wetlands than we anticipated.”
The study, “Land loss due to human-altered sediment budget in the Mississippi River Delta,” was published in Nature Sustainability.
Coastal Louisiana is one of the most important ecosystems in the United States. The vast wetlands provide protection from hurricanes and other severe weather, create habitats for wildlife, and support a thriving seafood industry. Unfortunately, over the past century the area has lost more than 1,900 square miles of land due to a variety of causes.
Coastal erosion, which has been exacerbated by climate change and rising sea levels, plays an especially important role in the region’s land loss. Waves erode beaches and shorelines and reduce the stability of the of land in these areas, leading to “headward erosion” or a gradual retreat of the shoreline. This process is made worse by coastal land subsidence, a term that describes the sinking of land due to natural and human-driven processes. The combination of the two processes can seriously affect the Louisiana Coast, leading to the loss of land.
Oil and gas activities, such as canal dredging and the construction of oil rigs and pipelines, have also had a major impact on coastal erosion in the region. Often, canals are cut across wetlands to facilitate navigation for oil and gas vessels, and the displaced sediment contributes to coastal erosion. Oil rigs and pipelines can erode the surrounding land from the pressure of their drilling. Though the industry has played an important role in providing economic growth for the area, it has also been an immense contributor to land loss in the region, as it accounts for more than two-thirds of all wetland losses in Louisiana.
The effects of coastal erosion and subsidence, along with oil and gas development, have been intensified by man-made projects such as the Mississippi River levee system. The construction of levees along the Mississippi aimed to reduce the risk of flooding, but they have done the opposite in some areas of the coast, actually exacerbating land loss due to their trapping of sediment behind them.
The widespread loss of land in Louisiana has had serious ecological and economic consequences, including a decrease in the state’s natural ability to protect itself against hurricanes and a decrease in the productivity of its fisheries. To address this crisis, the state has taken various steps to protect its coastline, including restoring coastal wetlands and providing funding for coastal restoration and protection projects.
The serious loss of land in Louisiana must be addressed. To ensure the future success of the region, efforts must be made to restore the land and protect it from further degradation. Through a combination of restorative projects, improved regulation and enforcement of oil and gas developments, and more sustainable management of the coastline, there is hope that Louisiana’s coast can be better protected.