WHAT'S CAUSING THE CRISIS?
By the 1700’s the Mississippi River had shifted paths back and forth several times - spreading sediment and creating land at the end of an ever-changing delta. The Pontchartrain Basin stretches out into the Gulf of Mexico as a 10,000 square mile watershed from the Mississippi River to the Pearl River and includes 16 Louisiana Parishes and 4 Mississippi Counties.
The southern part of the Pontchartrain Basin was built 5,000 thousand years ago. Benefiting our nation since the founding of New Orleans, today the region provides approximately 30% of our nation’s fisheries, and 30% of the nation’s oil and gas supply. The coast that protects these valuable resources must be saved!
In 1718 the need for a port city to transport materials up the Mississippi River and back out into the Gulf of Mexico to other ports resulted in the founding of New Orleans. The river had produced 6,000 square miles of land with slightly raised ridges on which the original towns were built. It wasn’t until 1904 when Baldwin Wood invented huge drainage pumps that New Orleans had the ability to drain the surrounding wetlands. The city grew rapidly and to this day the Port of New Orleans is one of our nation’s largest.
After the 1927 massive flood of the Mississippi River, huge levees were erected along the river. This was a good news – bad news story. Good news, the land will never flood, homes can be built safely on the ground. Bad news, the land will never flood, so no new sediment will be added as natural subsidence occurs.
In the 1930’s logging of cypress trees in the coastal swamps for their valuable wood resulted in saltwater intrusion which prevented new cypress from growing. Ultimately the loss of the cypress destroyed the buffer against storms that the coastal swamps provided the urban areas.
As the century continued, oil and gas became prominent economic drivers and critical resources for our nation. Access to these was provided by navigation canals and pipelines which crisscrossed South Louisiana marshes. Unfortunately, in the process the coastal marshes were lost when spoil banks were left randomly throughout the area, disastrously altering the natural hydrology of the region. Saltwater intrusion increased and more land was lost.
In the 1940’s nutria, an invasive species of rodent brought in from South America, added to the coastal woes. A voracious eater of wetland vegetation roots, the nutria has annihilated miles of protective marshland.
On August 29, 2005 the lives of over a million people changed in a day when Hurricane Katrina came across the Pontchartrain Basin. Without a robust coast to help protect the area, winds over 130 miles per hour and storm surges of 15-25 feet, floodwalls and levees were overtopped and breached. Over 80% of the urban area flooded. Three weeks later Hurricane Rita again flooded the region. Because of the hurricane season of 2005, 79 square miles of the Pontchartrain Basin and 217 square miles of Louisiana coast had been lost.
Looking back through the 20th Century, the country has to face the challenges to the coast that man unknowingly created in the name of progress. To a large degree, the reduced coastal hurricane protection for South Louisiana was the result of poor decisions made in the 1900’s.
The Natural Process:
Erosion is when wind, water, and ice take away sediments of land. Sediment is made of rocks, dirt, and earth. Erosion by wind action occurs mostly on beaches and in deserts, because there is no continuous vegetation or plants. Wave erosion, which occurs along beaches and coasts, is caused by the impact of breaking waves on the land.
Coastal erosion occurs along beaches and shorelines. Both wind action and water action have important parts in this process and constantly change the boundary between land and water. Coastal erosion takes land away forever from one area to deposit it someplace else.
The beach is constantly pounded by waves which eventually break fragments of ground and rock into sand. How hard a beach is hit by waves depends on lunar tides and differences in water density.
There is no continuous groundcover on the beach, so sand dunes form easily. Wind blows sand particles from side to side. People sometimes build fences to keep sand from shifting so much. Eventually, the sand is blown away and water takes its' place. The land is gone.
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.
At first glance, there are many forms of natural disturbance that contribute to coastal land loss:
1. Catastrophic disturbance from hurricanes erode marshes and introduce excess saltwater into the system.
2. 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.
3. The natural processes of the deltaic life cycle also include the breakdown of abandoned deltas and the subsequent loss of coastal land.
4. 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 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.
Coast in Crisis:
-The Hurricanes of 2005 changed the “Status-Quo”
-Louisiana has lost 2,300 mi.2 of land loss since the 1930’s
-Between 1990 and 2000, wetland loss was approx. 24 mi.2 per year
-Hurricanes Katrina and Rita transformed 382 mi.2 of marsh to open water in Coastal Louisiana
-The Master Plan – the State makes long term commitment to integrated coastal protection and coastal ecosystem restoration.
Below is a before and after map image, taken from satelite, of the Mississippi River Delta. Located at the southernmost region of Louisiana and extending far into the Gulf of Mexico, the sediments that once built this dynamic wetland habitat are now being leached away from where they are needed and where nature intended them to be. What has caused so much land to just vanish from our coast in less than 70 years? Why is the Mississippi River receding back in to the continental United States? What is happening to our precious coast?
In general terms, wetland loss has resulted from alteration in hydrology leading to changes in salinity and soil inundation (Penland et al. 1996). These changes typically cause a dieback of vegetation and eventually lead to a collapse of marsh substrate, turning coastal wetlands into open water.
Natural forces which can be detrimental to the health of coastal wetlands include tropical storm and hurricane impacts, subsidence, and global sea-level rise. Not only do storms erode marsh (including fragile, floating marsh), but storm surges also push salt water into fresh marshes, killing vegetation (LCWCRTF and WCRA, 1998).
Subsidence, the compaction and sinking of the soil, is variable from one part of the state to another, but it was historically counteracted with the accretion of sediments brought to the coastal marshes through annual flooding of the Mississippi River and organic accumulation through continued growth and deposition of vegetated material.
Rise in Global Sea Level
Compounding the problem of subsidence is the gradual rise in sea level which may be a result of a rise in global temperatures from elevated atmospheric carbon dioxide levels or damage to the ozone layer.
In the 19th and 20th centuries, Louisiana's wetlands provided sustenance to many communities. As communities settled in the wetlands, conflicts with nature began. wetlands were drained for agriculture, levees were constructed for flood protection, canals were dredged for ease of navigation, wetland forests were harvested for building materials, and in the early to mid-20th century, oil and gas exploration activities increased the dredging of canals.
Herbivory on wetland plants by nutria (Myocastor coypus) is also a major cause of wetland loss in coastal Louisiana. Nutria were accidentally introduced to Louisiana from the escape of a captive population during a hurricane in the 1930’s. These herbivores thrive in the Louisiana marsh and graze heavily on marsh vegetation.
When one considers the human cost, the risks to infrastructure, and the danger to wildlife and landscape, it is clear that we must take bold action. Significant upgrades to our hurricane protection systems are clearly in order, but levees alone can not do the job. A sustainable coastal ecosystem will help storm protection projects diffuse flooding while safeguarding the infrastructure, fisheries, and communities that are integral to our state and national security. In addition, wiser land use practices must govern the way we live in this dynamic landscape if we are to make our communities safer and ensure that they continue to thrive over the long-term.
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