Section 2.5 Other Human Impacts on Land Loss in Southeast Louisiana
The Gulf Coast of Louisiana is now one of the most heavily human-modified landscapes on earth. Some of these modifications have taken place to prevent coastal flooding and to protect human settlements and economic activities along the coast. Other human alterations of the landscape and the environment have been aimed at other goals and have had serious negative consequences for coastal land loss.
In addition to the Mississippi River levee system, much of the coast of Louisiana is now lined with coastal levees designed to prevent coastal flooding during periodic sea level rise events, especially storm surges and flooding from tropical storms. The construction of coastal levees began in the late 19th century and has been instrumental in protecting coastal communities from destructive coastal flooding. At the same time, coastal levees have been controversial in terms of their separation of land areas protected within their boundaries and the unprotected areas beyond them, sometimes referred to using the Cajun/Creole term batture. This division has had profound economic consequences for residents affected by it and it has again tended to be entangled with constructs of race and class.
The coastal levee system has also had negative consequences for wetlands in preventing the flow of freshwater, sediment, and organic materials through the smaller streams and bayous on the interior of the coast. Coastal levees, in a sense, arbitrarily divided the freshwater and saltwater ecosystems and landscapes of the coast, which accelerates the erosion of wetland land surfaces outside the levees. While this is a tradeoff that many coastal residents have been willing to make, it clearly played a major role in disrupting the delicate interplay between water flow, sedimentation, the growth of vegetation communities, and the erosion of the coastline.
Finally, coastal levees have also experienced problems during major storm surge events given that they now completely restrict the flow of water inland. As with flood control levees along the Mississippi, storm surge waters with no place to go simply rise against the coastal levees, increasing the pressure on them and making them more prone to catastrophic failures. Several examples of such catastrophic failures occurred in 2005 during Hurricane Katrina. During that storm, storm surges entered Lake Pontchartain from the Gulf of Mexico, driving water levels higher against the levees along the shore of the lake and the various canals that enter it. Failures in these levees were responsible for the horrific flooding that occurred in New Orleans during Hurricane Katrina.
Human economic activities along the coast have also had serious consequences for coastal erosion. The earliest of these was logging, which focused on valuable species of hardwood, such as bald cypress, that inhabited coastal wetland ecosystems. Logging in Louisiana increased dramatically during the late 19th century thanks to the growth of the industrial economy in the U.S. and the development of shipping methods to move lumber to mechanized mills in the North. In the decades spanning the late 19th and early 20th century, huge tracts of cypress forest wetlands along the coast were wiped out by logging activities. One estimate puts the destruction of wetland forest at 4.3 million acres (Earley, 2004)—nearly 13% of the land area of the state of Louisiana. The removal of old-growth cypress trees and the destruction of coastal wetland habitat caused great problems in terms of coastal erosion. Once again, this had the effect of removing vegetation and increasing the salinity of these wetlands, which removed plant communities that were buffering the effects of coastal erosion.
In addition, large-scale mechanized forestry operations constructed networks of canals into remote wetland areas. These canals promoted the flow of saltwater from the Gulf of Mexico into freshwater wetland ecosystems, which increased salinity and accelerated coastal erosion.
The construction of canals by the forestry industry foreshadowed the much larger-scale modification of wetland landscape by the petrochemical industry in the 20th and 21st centuries. Major oil deposits were discovered in Louisiana at the beginning of the 20th century and, with the economic boom following World War II, oil extraction activities expanded into many remote wetlands and offshore areas along the Gulf Coast. This surge in drilling activities necessitated the construction of a vast network of access canals, as well as a great number of oil and natural gas pipelines. These canals and pipelines are perhaps coastal Louisana’s most problematic and enduring industrial legacy in speeding the transition of freshwater wetlands to saltwater, and in increasing erosion from storm surges and saltwater intrusion from the Gulf of Mexico.
While the petrochemical industry in Louisiana has improved its environmental impact significantly in recent decades, we should bear in mind that any human activity that degrades the ecosystems of our coastal wetland should be considered an existential threat to the coastline. In this respect, the 2010 B.P./Deepwater Horizon oil spill, and other recent human-made environmental disasters, have done serious harm in their impacts on the environmental dynamics involved in coastal erosion. For this reason, we must be aware of the issues involved in balancing the economic interests that hinge on the petrochemical industry, as well as other industries that may have environmental impacts on coastal wetlands.
Go to: Section 2.6: Exercises