The wetlands of Louisiana are water-saturated coastal and swamp regions of southern Louisiana, often called bayous.
The Louisiana coastal zone stretches from the border of Texas to the Mississippi line and comprises two wetland-dominated ecosystems, the Deltaic Plain of the Mississippi River (unit 1, 2, and 3) and the closely linked Chenier Plain (unit 4). The Deltaic Plain contains numerous barrier islands and headlands, such as the Chandeleur Islands, Barataria Basin Barrier Islands, and Terrebonne Basin Barrier Islands. The Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) program, through the NOAA Habitat Conservation National Marine Fisheries Service funded $102 million in construction for deteriorated wetlands and barrier island habitats.
Geography The Environmental Protection Agency defines wetlands as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration water to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions (e.g. swamps, bogs, fens, marshes, and estuaries)." Different wetland types arise due to a few key factors, primarily: water levels, fertility, natural disturbance and salinity.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Around Lake Pontchartrain, for example, these few factors produce wetlands including bottomland hardwoods, cypress swamp, freshwater marsh and brackish marsh. High levels of flooding reduce the abundance of trees, leaving four principal marsh types: saline, brackish, intermediate and fresh.Chabreck, R. H. 1972. Vegetation, Water and Soil Characteristics of the Louisiana Coastal Region. Louisiana State University, Agricultural Experiment Station Bulletin No. 664
Although these areas make up a very small percentage of the total land found in the United States, southern Louisiana contains 40 to 45 percent of the wetlands found in the lower states. This is because Louisiana is the drainage gateway to the Gulf of Mexico for the Lower Mississippi Regional Watershed. The Lower Mississippi Regional Watershed drains more than 24 million acres (97,000 km2) in seven states from southern Illinois to the Gulf of Mexico. Hence the wetlands of this area are important at the national scale.Gosselink, J. G., J. M. Coleman, and R. E. Stewart, Jr. 1998. Coastal Louisiana. pp. 385–436. In M. J. Mac, P. A. Opler, C. E. Puckett Haecker, and P. D. Doran 1998. Status and Trends of the Nation's Biological Resources, 2 Vols. Reston: U.S. Department of the Interior, U.S. Geological Survey.
On the east side of Louisiana, coastal wetlands intergrade with long leaf pine savannas, which support many rare and unusual species such as pitcher plants and gopher tortoises.Keddy, P.A. 2008. Water, Earth, Fire: Louisiana's Natural Heritage. Xlibris, Philadelphia. 229 p. On the western side, they intergrade with wet prairies, an ecosystem type that was once vast, and now has been all but eliminated. The larger vertebrate fauna such as wolves and bison was exterminated. The eastern coastline of Louisiana is much more susceptible to erosion than the western coastline because much of the eastern coastline was created by silt deposits from the Mississippi River. This natural process of sediment deposition has been blocked by an extensive levee system that directs flood water past wetlands.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Figure 2.25, p. 73. The western coastline is marshy, but the marshes only extend inland by at the most, then the elevation begins to increase and the marshes fade into solid grounded prairies. Therefore, rising sea levels due to global warming and coastal erosion, may not affect the western coastline as profoundly as it will the eastern half, which may be replaced in open water over substantial areas.
Loss of the wetlands
The wide range of benefits provided by the wetlands of this region were not recognized by a majority of policy makers in the early 20th century. Wetlands provide vital ecological services including flood control, fisheries production, carbon storage, and water filtration The two major factors are subsidence, mostly from lack of sediment, and salt water intrusion from canals dredged to service oil and gas wells and facilitate oil and gas exploration. Further wetland loss is attributed to the construction of the now-closed Mississippi River Gulf Outlet, which introduced salt water into freshwater and intermediate marshes and facilitated significant erosion.
Subsidence of the coast can be from the effects of oil and gas extraction. As billions of barrels of oil and saltwater and as trillions of cubic feet of gas were removed from the reservoirs in which they had accumulated over millions of years, these reservoirs lost their ability to support the weight of the rocks above.E.P. Mallman and M.D. Zoback (2007), Subsidence in the Louisiana coastal zone due to hydrocarbon production. In: Lemckert, C. (ed.), International Coastal Symposium (ICS) 2007 Proceedings (Gold Coast, Queensland, Australia). Journal of Coastal Research, Special Issue No. 50, pp. 443–448. As these structures slowly collapsed, the soil above gradually subsided. The wetlands on the surface began to sink into the gulf waters. Subsidence is also a natural process in deltas, as sediments compress, and flood waters that would normally deposit new layers of sediment are lacking.Boesch, D. F., Josselyn, M. N., Mehta, A. J., Morris, J. T., Nuttle, W. K., Simenstad, C. A., and Swift, D. P. J. (1994). Scientific assessment of coastal wetland loss, restoration and management in Louisiana. Journal of Coastal Research, Special Issue No. 20. The role of hurricanes is also a matter of disagreement; some studies show that hurricanes actually build elevation in marshes.Liu, K. and Fearn, M. L. (2000). Holocene history of catastrophic hurricane landfalls along the Gulf of Mexico coast reconstructed from coastal lake and marsh sediments. In Current Stresses and Potential Vulnerabilities: Implications of Global Change for the Gulf Coast Region of the United States, eds. Z. H. Ning and K. K. Abdollhai, pp. 38–47. Baton Rouge, LA: Franklin Press for Gulf Coast Regional Climate Change Council. Another factor is rising sea levels estimated to be about 2mm per year associated with global warming.Ricardo A. Olea and James L Coleman., Jr. (2014), A synoptic examination of causes of land loss in southern Louisiana as they relate to the exploitation of subsurface geologic resources. Journal of Coastal Research, v. 30, no. 5, p. 1025−1044.
Sediment compaction is also a significant source of wetland loss. Compaction rates have been conservatively estimated at 5mm to 10mm or more per year for the organic-rich Holocene sediment (peat) that predominates the Mississippi River Delta environment. Given the ubiquity of this compaction-prone sediment in southern Louisiana, coastal restoration project managers (see: Louisiana Coastal Protection and Restoration Authority) must consider the underlying geology of their regions prior to development as to not exacerbate rates of compaction.Törnqvist, Torbjörn E., et al. "Mississippi Delta subsidence primarily caused by compaction of Holocene strata." Nature Geoscience 1.3 (2008): 173-176.
An extensive levee system aided by locks and dams has been developed in the waterways of the lower Mississippi River.Reuss, M. (1998). Designing the Bayous: The Control of Water in the Atchafalaya Basin 1800–1995. Alexandria, VA: U.S. Army Corps of Engineers Office of History. The levees (designed to prevent flooding along the waterways) prevent needed sediment from being distributed into the marshes downriver. With no new accretion and with steady subsidence, the wetlands slowly are replaced by encroaching saltwater from the Gulf. As a result of this engineering dilemma, 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 sediment into these areas.Turner, R. E. and Streever, B. 2002. Approaches to Coastal Wetland Restoration: Northern Gulf of Mexico. The Hague, the Netherlands: SPB Academic Publishing.
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".Keddy, P.A. 2008. Water, Earth, Fire: Louisiana's Natural Heritage. Xlibris, Philadelphia. 229 p. P. 122. 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.
The introduction of nutria from South America in the 1930s provided an entirely new species of grazing mammal. Although only a few escaped, there are now millions.Keddy, P.A. 2008. Water, Earth, Fire: Louisiana's Natural Heritage. Xlibris, Philadelphia. 229 p. P. 148-150. 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 marshKeddy, P.A. 2000. Wetland Ecology: Principles and Conservation. Cambridge University Press, Cambridge, UK. 614 p. P. 163-165. 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.Keddy, P.A., L. Gough, J.A. Nyman, T. McFalls, J. Carter and J. Siegrist. 2009. Alligator hunters, pelt traders, and runaway consumption of Gulf coast marshes: A trophic cascade perspective on coastal wetland losses. p. 115-133 in B.R. Silliman, E.D. Grosholz, and M.D. Bertness (eds.) Human Impacts on Salt Marshes. A Global Perspective. University of California Press, Berkeley, CA.