Louisiana’s wetlands form an expansive ecosystem located at the mouth of the Mississippi River, characterized by water-saturated coastal and swamp regions. These diverse landscapes, often referred to as “Bayou,” encompass freshwater swamps, brackish, and salt marshes. The state contains approximately 25 percent of the United States’ coastal wetlands and 40 percent of its salt marshes. This vast system holds immense ecological and economic value, supporting a wide array of plant and animal life and contributing to the state’s economy. However, these wetlands face significant vulnerability and rapid changes.
The Critical Role of Wetlands
Louisiana’s wetlands provide storm surge protection for coastal communities and infrastructure. These natural barriers dissipate wave energy and absorb floodwaters, reducing the impact of hurricanes and tropical storms on populated areas and vital facilities. This protective function safeguards coastal development infrastructure, valued in billions of dollars, including nationally significant oil and gas facilities and major federal navigation channels.
These wetlands serve as habitat for a diverse array of wildlife, including migratory birds, fish, and shellfish. They function as nurseries for many aquatic species, supporting rich food webs and high biological productivity. This biodiversity underpins industries like commercial fishing, trapping, and nature-based tourism.
Beyond habitat and storm protection, Louisiana’s wetlands act as filters, improving water quality by absorbing nutrients, sediments, and contaminants from runoff. This filtration process maintains healthier aquatic environments downstream. The wetlands also store and convey floodwaters, regulating the region’s hydrology. These combined functions contribute to the environmental health and economic well-being of Louisiana.
Drivers of Wetland Loss
The disappearance of Louisiana’s wetlands stems from a complex interplay of natural processes and human modifications to the landscape. Natural processes contribute to wetland loss, notably through subsidence, the sinking of land due to the compaction of underlying sediments. Louisiana’s deltaic plain experiences some of the highest subsidence rates globally, averaging around 9 ± 1 millimeters per year in many areas, though rates can vary significantly across the coast. This sinking, combined with global sea level rise, results in relative sea level rise (RSLR). Studies indicate that RSLR in parts of coastal Louisiana has accelerated, reaching over 10 millimeters per year since 2010, causing wetlands to lose elevation.
Hurricanes also play a role in wetland degradation. Powerful winds, storm surges, and erosion can destroy large areas of marshland. Hurricanes Katrina and Rita, for instance, caused substantial wetland loss by reshaping marshes, creating new channels, and introducing saltwater into freshwater environments, which can kill sensitive vegetation. The physical forces of these storms can break down marsh mats and redistribute sediment, sometimes creating permanent open water areas.
Human activities have accelerated these natural processes. The construction of levees along the Mississippi River is a primary factor. These levees, built to prevent flooding and facilitate navigation, have disconnected the river from its deltaic wetlands. Historically, the river’s annual floods deposited sediment, which built and maintained the wetlands, counteracting subsidence. Now, this sediment is channeled directly into the deep waters of the Gulf of Mexico, depriving the wetlands of the material needed for replenishment and vertical accretion.
Dredging navigation canals and access channels for oil and gas exploration and production has also caused damage. These canals convert wetlands to open water and alter natural hydrology. They act as conduits for saltwater intrusion, allowing saline water from the Gulf to penetrate deep into freshwater and intermediate marshes, stressing and killing vegetation not adapted to such conditions. This saltwater intrusion, along with wave action within the canals, contributes to increased erosion of marsh edges.
Nutrient runoff from agricultural lands and urban areas in the Mississippi River basin contributes to environmental stress. Excess nitrogen and phosphorus flow downriver, fueling algal blooms in the Gulf of Mexico. When these algae die and decompose, they deplete oxygen in the water, creating “dead zones” that harm marine life and impact the broader ecosystem, including species that rely on the wetlands. While not a direct cause of land loss, this pollution impacts the health and resilience of the aquatic system supporting the wetlands.