Coastal erosion in Louisiana facts for kids
Coastal Erosion in Louisiana is the process of steady depletion of wetlands along the state's coastline in marshes, swamps, and barrier islands, particularly affecting the alluvial basin surrounding the mouth of the Mississippi River at the foot of the Gulf of Mexico on the Eastern half of the state's coast. In the last century, Southeast Louisiana has lost a large portion of its wetlands and is expected to lose more in the coming years, with some estimates claiming wetland losses equivalent to up to 1 football field per hour. One consequence of coastal erosion is an increased vulnerability to hurricane storm surges, which affects the New Orleans metropolitan area and other communities in the region. The state has outlined a comprehensive master plan for coastal restoration and has begun to implement various restoration projects such as fresh water diversions, but certain zones will have to be prioritized and targeted for restoration efforts, as it is unlikely that all depleted wetlands can be rehabilitated.
The process of coastal erosion is the result of various factors, including sea level rise, the loss of deposition of sediments to the Mississippi River delta, and the consequent permanent flooding of marshes, wetlands, and neighboring areas along the Louisiana coast of the Gulf of Mexico. Contributing factors include the blockage of traditionally occurring deposits of fresh water and silt from the river caused by man-made levees which have been built up and down most of the river over the last century, which now impede the river's ability to replenish its southernmost alluvial plains which are constantly dependent on the infusion of the river's once plentiful deposits which usually occurred during annual high stage floods in the springtime, the kind of which the river-levees now serve to buffer against for the protection of residents, livestock, and property residing in regions adjacent to the river throughout the Mississippi River valley. The deterioration results in the death of fresh and brackish water plants historically part of the ecosystem, which are not only a vital feature of the wetlands' topography, but also serve to capture silt, and thus are needed to build up and sustain marsh structures. As fresh and brackish water plant habitats recede, salt water from the Gulf of Mexico further encroaches, killing off more non-saltwater plants, thus further eroding pre-existing mud formations that these plants had once supported.
Other factors exacerbating coastal erosion in Southeast Louisiana include the presence of canals and navigational routes dug through marshes and swamps, often to accommodate logistical needs of the petrochemical industry, as well as the previous practice of logging, all of which have allowed the incursion of saltwater (saline) from the Gulf into previously fresh and brackish water plant habitats. While land subsidence is dominated by Glacial Isostatic Adjustment (GIA), sediment compression is next factor further compounding the problem. Sea-level rise attributed to global warming, though not a root cause, is also considered a contributing factor and future concern.
Causes and factors
Man-made levees, which were designed to protect residents and property adjacent to the river, block spring flood water that would otherwise bring fresh water and sediment to marshes. Swamps have been extensively logged, leaving canals and ditches that allow saline water to move inland. Canals dug for the oil and gas industry also allow storms to move sea water inland, where it damages swamps and marshes. Rising sea levels attributed to global warming have exacerbated the problem. Some researchers estimate that the state is losing a land mass equivalent to 30 football fields every day.
An extensive levee system aided by locks and dams has been developed in the waterways of the lower Mississippi River. The levees, designed to prevent flooding along the waterways, on one hand, prevent silt from draining into the river yet also from being distributed into the marshes downriver. With no new accretion and with steady subsidence, the wetlands slowly are replaced by encroaching saltwater form the Gulf. As a result of this apparent dilmma, large areas of marsh are being lost to the ocean. Since 1930 water has consumed more than 1,900 square miles (4,900 km2) of the state's land. This loss equates to the disappearance of 25 square miles (65 km2) of wetlands each year or a football field sized area every 30 minutes. This loss can be reversed, at least in some areas, but only with large scale restoration, including the removal of levees to allow the Mississippi River to carry silt into these areas.
Prior to the building of levees on the Mississippi River, the wetlands were kept in balance by occasional floods, which fill the area with sediment, and subsidence, the sinking of land. After the levees were built, however, flood sediment flowed directly into the Gulf of Mexico. This subsidence along with the recent sea level rise tipped the balance toward subsidence rather than marsh growth. This, along with the canals built in the area, caused decline of the wetlands and also caused less weakening of and less protection from recent hurricanes such as Hurricane Katrina. The Lake Pontchartrain Basin Foundation has developed a comprehensive management plan for the eastern regions of the Louisiana coast, placing emphasis upon restoration of riverine habitats, cypress swamps and fringing marsh. This could be a model applied to other coastal regions.
Subsidence may be due to other factors as well. Some observers blame the direct effects of oil and gas extraction. They contend that, as billions of barrels of oil and saltwater and as trillions of cubic feet of gas were removed from the subterranean structures in which they had accumulated over millions of years, these structures lost their ability to support the weight of the earth above. As these structures slowly collapsed, the soil above gradually subsided. The wetlands on the surface began to sink into the gulf waters. Others argue that subsidence is a natural process in deltas, as sediments compress, and that the real problem is the lack of flood waters that would normally deposit new layers of sediment. The role of hurricanes is also a matter of disagreement; some studies show that hurricanes actually build elevation in marshes. A new and important factor is rising sea levels associated with global warming.
In addition to subsidence is the presence of canals which were dug through the marshes and swamps to service oil and gas wells to facilitate oil and gas exploration, which have enabled salt water intrusion from the Gulf of Mexico. In similar fashion, the construction of the now-closed Mississippi River Gulf Outlet (MRGO) introduced salt water into freshwater and intermediate marshes in St. Bernard Parish, which is adjacent to New Orleans, and facilitated significant erosion.
Another factor that damaged wetlands was large scale logging, particularly the extensive logging of cypress forests in the early 1900s. One early logger described it this way: "We just use the old method of going in and cutting down the swamp and tearing it up and bringing the cypress out. When a man's in here with all the heavy equipment, he might as well cut everything he can make a board foot out of; we're not ever coming back in here again" This logging often required construction of canals, which, once the logging was finished, allowed salt water to enter the wetlands and prevent regeneration of the cypress.
As if these problems were not enough, the introduction of nutria an invasive species from South America in the 1930s provided an entirely new species of grazing mammal. Although only a few escaped, there are now millions. Natural grazing by muskrat was now accelerated by grazing from nutria. By removing plants, nutria both cause loss of vegetation, and, perhaps more seriously, a loss of dead organic matter which would otherwise accumulate as peat and raise the level of the marsh One of the most important natural controls on nutria is large alligators, which may provide a useful tool for biological control of nutria, and therefore for reduced impacts of grazing.
Consequences
The many benefits of the wetlands found in this region were not recognized by a majority of policy makers early in the 20th century. Wetlands provide many important ecological services including, fisheries production, resting areas for migratory species, carbon storage, water filtration and enhanced disagreement over the relative importance of these factors, not to mention flood control.
Southeastern Louisiana's disappearing wetlands have a broad impact ranging from cultural to economic. Commercial fishing in Louisiana accounts for more than 300 million dollars of the state's economy. More than 70% of that amount stems from species such as shrimp, oysters and blue crabs that count on the coastal wetlands as a nursery for their young. Annually Louisiana sells more than 330,000 hunting licenses and 900,000 fishing licenses to men and women who depend on the wetlands as a habitat for their game. Additional recreational activities such as boating, swimming, camping, hiking, birding, photography and painting are abundant in wetland areas. Wetlands host a variety of trees such as the bald cypress, tupelo gum and cottonwood. Other plants such as the dwarf palmetto and wax myrtle and submerged aquatic plants such as Vallisneria and Ruppia are native to Louisiana wetlands. Wetland plants act as natural filters, helping to remove heavy metals, sewage, and pesticides from polluted water before reaching the Gulf of Mexico. Animal species native to these areas include osprey, herons, egrets, alligators, and beavers. Although there are several naturally occurring forces that adversely affect the wetland regions of Louisiana, many believe it is human intervention that has caused the majority of the decline.
As the wetlands disappear, more and more people are leaving wetland areas. Since the coastal wetlands support an economically important coastal fishery, the loss of wetlands is adversely affecting this industry.
Proposed and attempted solutions
There are several projects and proposals to save coastal areas by reducing human damage, some of which have been attempted, including restoring natural floods from the Mississippi. Without such restoration, coastal communities will continue to disappear. One of the primary methods that has been developed are freshwater diversions, which extract water from Mississippi River at strategic locations and transport fresh water and silt from the river through aqueducts and then pump and distribute them into nearby estuaries. This process invigorates freshwater plant life and re-introduces silt into the estuaries. Freshwater diversions have not been without controversy and have encountered some opposition, primarily from oyster harvesters who believe that the current high level salinity is needed in their state-licensed zones in order to maintain healthy production. Another method of coastal restoration is the direct planting of new marsh grasses and other forms of sustainable plant life into affected areas. There is the practice of seeding, which may be turn out to be more productive than direct planting, which often entails the dropping large amounts of seeds from crop-dusters intended to grow into freshwater plants. Mangrove seeds have been tried because when grown they have the benefit of reducing marsh water salinity. Transporting already-dredged material from the Mississippi river to marshes, swamps, and barrier islands is also an option. Some have proposed the removal of river levees in certain low-populated areas to allow fresh water and silt dispersion into marshes, though this method is controversial and has yet to be attempted.
The Louisiana State Coastal Restoration Authority has developed a master plan which outlines the state's strategy for achieving future coastal restoration as well as flood protection. Current Louisiana law stipulates that all oil and gas revenue royalties collected by the state go towards coastal restoration. However, under present arrangement with the Federal government Louisiana, is only able to receive a small percentage of royalties and that the rest go to the Federal government. However, starting in 2018 Louisiana will be able to receive 37.5 from all new leases, though pre-existing leases will still fall under the prior state/federal revenue sharing arrangement. Proceeds from part of the BP oil spill lawsuits and federal fines will also go towards coastal restoration.
