page_title: Wetlands of Louisiana
section_title: Loss of the wetlands
hierarchical_section_title: Wetlands of Louisiana / Loss of the wetlands
caption_attribution_description: English: maps of a section of southern Louisiana showing wetland lose through out time; the images of human activities on the area; the changes of subsidence, biodiversity, vegetation coverage and sediments.
context_page_description: The wetlands of Louisiana are water-saturated coastal and swamp regions of southern Louisiana.
  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." Different wetland types arise due to a few key factors, primarily: water levels, fertility, natural disturbance and salinity. 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.
  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.
context_section_description: 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, water filtration and enhanced disagreement over the relative importance of these factors, although it is probably safe to say that the two major factors now acting 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. A brief explanation of various causes follows.
  Subsidence of the coast is certainly occurring. Some people blame the direct effects of oil and gas extraction.  The logic is that 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.  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. Another factor is rising sea levels estimated to be about 2mm per year associated with global warming.
  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.
  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) 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 apparent 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.
  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 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
caption: Diorama picturing wetland loss in coastal Louisiana as attributed to human activities
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