What Went Wrong
The Mississippi River Delta is disappearing at an astonishing rate: A football field of wetlands vanishes into open water almost every hour.
Since the 1930s, Louisiana has lost nearly 1,900 square miles of land, an area roughly equivalent in size to the state of Delaware.
Many factors have led to the delta's collapse. One of the most significant is that the lower Mississippi River has been straitjacketed with huge levees as part of a national program to "control" the Mississippi River and protect communities, economic infrastructure and croplands from river flooding. But the delta's wetlands are built and sustained by sediment delivered by the river. Cutting the river off from its delta with levees doomed existing wetlands and largely stopped the cycle of new wetlands growth. Without land-building deposits from the river, the delta is doomed to continue sinking beneath the water, endangering people, wildlife and jobs.
Exacerbating the problem are a vast network of shipping channels – including the Mississippi River-Gulf Outlet, the Houma Navigational Canal and the Freshwater Bayou Canal. Thousands of miles of oil and gas canals have been dug to accommodate energy infrastructure and extraction. These channels and canals alter the natural hydrology and allow saltwater to penetrate deep into the wetlands, disrupting the salinity balance and killing the vegetation of freshwater wetlands, causing them to subside underwater.
In addition to these land loss issues, the delta has in recent years suffered through additional catastrophes. In 2005, Hurricanes Katrina and Rita wrecked coastal communities. The damage they wrought, in the form of flooding and storm surge, was made worse by the previous loss of miles of protective wetlands. Then, in 2010, devastation came again in the form of the BP oil disaster, when millions of barrels of oil spewed from the Deepwater Horizon oil rig only to wash up on Louisiana shorelines. Both of these catastrophes were crushing blows to an already degraded region. Their effects add increased urgency to the need for long-term, large-scale restoration of the Mississippi River Delta.
Causes of the Delta's collapse
Oil and Gas Infrastructure: Louisiana is America’s Energy Coast. There are thousands of offshore oil rigs and onshore wells in coastal Louisiana, significant refinery capacity and thousands of miles of pipelines connecting it all. Over the decades, these activities have directly impacted thousands of acres of coastal wetlands and modified the coastal hydrology, speeding up erosion.
Dams Upriver: Valuable land-building sediments are trapped behind locks and dams on the Missouri, Mississippi and Ohio Rivers. Since 1850, the amount of sediment in the Lower Mississippi River has decreased by more than 70 percent.
Subsidence: Land formed by river sediments naturally subsides and sinks over time. Historically, sediment deposition and accretion by plant growth outpaced the natural subsidence, resulting in coastal land gain. Without land-building deposits from the river, subsidence dominates and massive areas of land are sinking below sea level and disappearing.
Sea level rise: Scientists say that the level of the world’s oceans will rise from one to three feet over the next century. Rising seas combined with subsiding land (called “relative sea level rise”) makes the threat of submergence even greater for the Mississippi Delta. When wetlands receive sufficient sediment from the river, they can stay above the rising seas.
Hurricanes: Storm surge from Hurricanes Katrina and Rita destroyed hundreds of square miles of coastal wetlands. The continued loss of wetlands will make coastal communities such as New Orleans even more vulnerable to storms.
Oil spill: The BP Macondo well spewed 206 million gallons of oil into the Gulf, affecting hundreds of miles of delicate shoreline, thousands of acres of coastal marsh, and disrupting the communities, economy and wildlife of the coast. The spill's long-term effects will continue to impact the coast and its inhabitants for decades to come.
Invasive species: Though several harmful invasive species exist in the delta, two stand out. Nutria, fast breeding, voracious rodents were introduced into Louisiana for the fur trade, but their impact on coastal wetlands has been disastrous. They burrow into the ground, eat the roots of marsh plants and devour cypress seedlings, harming wetlands as they go. In recent years, feral hogs have become a problem. Like nutria, they destroy wetlands through aggressive foraging.
- U.S. Geological Survey, "Land Area Change in Coastal Louisiana." (video)