Human Environment Interaction
Case Study
Wetland Loss in the Mississippi Delta
CLASS SET – ANSWER ON YOUR OWN PAPER
Create a Venn diagram of Human-Environment Interaction:
Environment
(Nature)
Human
Interaction
Louisiana Coastal Land Loss
Create a T chart with Human causes of land loss on one side, and natural causes on the other
Graphs:
1. Write a sentence that compares the pre- and post- dam sediment load of the Mississippi. Which river brought
the most sediment into the Mississippi before dams?
2. In which era did the most places lose land: 1956-78, or 1978-90?
NOLA Times-Picayune animation
3. Where was New Orleans 6000 years ago?
4. How did the Chandeleur islands develop?
5. How did early residents of New Orleans keep the yearly spring floods out of the city?
6. What is subsidence? Why is it a problem along the coast?
7. How have invasive species damaged the marsh?
8. One acre of land is lost every 45 minutes. About how big is an acre?
WRITE YOUR ESSAY IN 3rd PERSON – no I, You, Me, Our
Write a brief summary of what is happening to the delta, why it’s happening, and propose a workable solution. Explain
what groups would be opposed to your solution, and why.
Louisiana Coastal Land Loss
By Clare Davis-Wheeler
The loss of Louisiana’s coastal wetlands is one of the most serious environmental problems facing the country
today. Louisiana boasts more than 4 million acres of wetlands, representing 40% of the nation’s total. These wetlands are
among the world’s most diverse and productive ecosystems.
Presently, Louisiana's wetlands are in a state of rapid degradation. 80% of the nation’s coastal land loss occurs in
Louisiana. The state loses 25-35 square miles, or 25,000 acres, per year, the equivalent of one football field every 15
minutes. These losses are not only environmental and aesthetic, but commercial. Projected losses to the fishing industry
by the year 2050 as a result of coastal land loss are a staggering $37 billion.
Natural Deltaic Cycles
The natural processes of coastal land formation are based on the sedimentary load delivered by the Mississippi
River. Deposits of sand, silt, and clay made at the mouth of the river form the basis of coastal land and marshes. The
sediments accumulate through flood overtopping and overbank sedimentation. These natural forces, known as accretion,
lead to a net gain of 1-2 square miles per year in coastal land area.
There are many forms of natural disturbance that contribute to coastal land loss. Catastrophic disturbance from
hurricanes erode marshes and introduce excess saltwater into the system. Natural rises in sea level, mostly associated
with the advance and retreat of glaciers, are also responsible for dramatic decreases in wetland area. During the last major
glacial retreat 15,000 years ago, 40-50% of the existing wetlands were lost. The natural processes of the deltaic life cycle
also include the breakdown of abandoned deltas and the subsequent loss of coastal land. Another form of natural
disturbance to wetlands is subsidence. This is the general term for the gradual sinking of coastal land into the
ocean. Subsidence is primarily due to the geological movement of deposits along tectonic fault lines and the compaction
of loosely deposited sediments. Subsidence is one of the largest causes of coastal land loss, but cannot even begin to rival
the human impact in either the amount of coastal land destroyed or the rate of its destruction.
Human Disturbance
Human disturbance has had a massive impact on the balance of wetland growth and decline. Since the colonization of
America, over half of the original wetlands have been lost. In modern times and with the increase in available technology,
this loss has accelerated geometrically. In the past 100 years, Louisiana has lost 20% of its wetlands, representing an
acceleration of 10 times the natural rate.
The main forms of human disturbance are the river-control structures such as dams and levees, the dredging of canals,
and draining and filling. Beginning in the 1920’s, large scale river-control structures, such as the Old River Control
Structure, which diverts 30% of the Mississippi Rover water into the Atchafalaya River system, were built to ease
flooding problems along the banks. These control structures led to a dramatic decrease in the sedimentary load which
reached the mouth of the river and formed the basis of new coastal land.
The construction of levees similarly affected coastal land. A large part of the sediment gathered by existing marshes is
accumulated during seasonal flooding. Flood overtopping and overbank sedimentation, both vital to the survival of
existing marshes, were dramatically reduced as large areas ceased to be flooded. River water also helped to reduce marsh
salinity and provide nutrients, and its loss has resulted in the breakup and dispersal of large amounts of nutrient-starved
marshlands.
Canal dredging has had one of the most dramatic effects on wetland growth and regeneration. In addition to directly
destroying marshes in the path of the canal, the plants are unable to recolonize, and thus the marsh is unable to regenerate
itself. Once canals are dredged, most grow larger as the sustainable areas of marsh subsequently decrease. The largest
and most destructive example of this dredging is the Mississippi River Gulf Outlet (MRGO). Created in the 1960’s to
facilitate the passage of ships to the Gulf of Mexico, the canal destroyed over 23,000 acres of wetland. The MRGO has
now grown to 2 ½ times its original size and costs the government $7.6 million a year to maintain. Experts say that canals
now account for 6.8% of Louisiana’s wetland area.
Eutrophication is another major problem facing Louisiana’s wetlands. Caused by chemical and industrial pollutants,
human waste and agricultural runoff, eutrophication literally means “overnourishing.” The excess chemicals present
cause the wetland plants to die, breaking the marsh apart. In addition to these more indirect effects, human effect the
wetlands by draining and filling them, destroying them for commercial use, and dumping pollutants directly into them.
Proposed Solutions
Fortunately, many have realized the plight of the wetlands and have mobilized against further destruction. Many
preventative measures and replacement strategies have been conceived and implemented. One idea that has been put to
extensive use in wetland restoration is that of river diversions. These function by pumping river water into ailing marshes,
increasing sediment load and reducing salinity. Many of these diversion structures are currently in use, and an even larger
structure has been proposed. The Bohemia Diversion would divert 30% of the Mississippi River into Breton Sound,
creating 89,000 acres of new marshes over the next 50 years. Another proposed solution is the closing of the MRGO. An
alternative canal would be formed through the Plaquemines Parish marsh and all sediment retention structures along the
river would be removed. This solution would allow the mouth of the river to silt up and new wetlands to form. More
creative solutions have also been proposed. One of the most practical proposals is vegetative planting, which places
native plants in threatened systems, and allows the root systems to form a more solid basis for soil.
In response to the problem of coastal land loss, both the federal and Louisiana state governments have met to propose
legislation. The Breaux Act, passed in 1990, was designed to increase public awareness of the problem, and created a
committee to investigate and recommend solutions to Congress. The state legislature has identified oil production as a
major threat to coastal wetlands, with the dredging of canals for ships and pipelines and direct pollution posing
problems. Many steps have been taken to limit the industry’s toll on the environment. According to current Louisiana
law, if an action threatens even ½ acre of wetland an alternative solution must be investigated.
Coast 2050 Plan
The state government met in 1998 to devise a comprehensive plan for coastal land rehabilitation and
conservation. The result of the session was the Coast 2050 plan, which addresses the culture, industry, and environment
of coastal Louisiana. The plans operates by soliciting public opinion and recommendations and attempting to resolve
conflicts between restoration goals and coastal zone development and infrastructure. It seeks to develop a scientifically
and technically sound plan with special attention to ecological and economic resources.
One facet of the plan already in effect is the Caernarvon Diversion project, which pumps river water into the marshes of
Breton Sound and will preserve 16,000 acres of wetlands per year. So far, the effected area has experienced a net yearly
increase of 5.9%. The plan also includes other projects such as the Davis Pond diversion, while promoting legislation to
close MRGO and reverse other such harmful trends.
Despite these efforts, coastal land loss in Louisiana remains a major problem. Losses due to human activity might soon
become irreplaceable. One harrowing estimate projects that the projected land loss by the year 2050 would form a onefoot-wide strip of land that would reach from the earth to the moon and back 11 times. Louisiana’s wetlands are
vanishing. Without significant action, they could soon disappear forever.
Further Reading
Coastal Louisiana: Here Today, Gone Tomorrow? Coalition to Restore Coastal Louisiana. 1989.
Coleman, James M., Harry H. Roberts, Robert Spence Tye. Causes of Louisiana Coastal Land Loss: A Report Prepared for
the Louisiana Mid-Continent Oil and Gas Association. 1985.
Craig, N.J., and J.W. Day, Jr. Cumulative impact studies in the Louisiana coastal zone: eutrophication and land loss. 1977.
“Coast 2050: Toward a Sustainable Coastal Louisiana.” The Louisiana Coastal Wetlands Conservation and Restoration Task
Force and the Wetlands Conservation and Restoration Authority. 1999.
http://www.tulane.edu/~bfleury/envirobio/enviroweb/LandLoss/LandLoss.htm
http://lacoast.gov/new/Pubs/Report_data/NWRC-OFR94.aspx
Barras, J.A., P.E. Bourgeois, and L.R. Handley. 1994. Land loss in coastal Louisiana 1956-90.
National Biological Survey, National Wetlands Research Center Open File Report 94-01. 4 pp. 10
color plates
Delta Animation from The New Orleans Times-Picayune
http://www.nola.com/speced/lastchance/multimedia/flash.ssf?flashlandloss1.swf