LOUISIANA WETLANDS

Wetland Land Loss

Historical Land Loss in Coastal Louisiana -
Louisiana has lost 1,900 square miles of land since the 1930's (Barras et al. 1994, Barras et al. 2003, Dunbar et al. 1992). Currently Louisiana has 30% of the total coastal marsh and accounts for 90% of the coastal marsh loss in the lower 48 states (Dahl 2000, Field et al. 1991, USGS 2003).

Current Rate of Coastal Land Loss -
Between 1990 and 2000 wetland loss was approximately 24 square miles per year, that is one football field lost every 38 minutes. The loss over the next 50 years with current restoration efforts is expected to be 500
square miles (Barras et al. 2003).

For further information on the Breaux Act or Restoration Projects in Louisiana,
contact the Breaux Act home page (http://www.lacoast.gov),
the OCRM home page (http://www.savelawetlands.org),
the Coast 2050 home page (http://www.coast2050.gov)

Causes of Wetland Loss
Despite all the benefits provided by wetlands, the United States loses about 60,000 acres of wetlands each year. It is also estimated that more than 220 million acres of wetlands are thought to have existed in the lower 48 states in the 1600's. Since that time, extensive losses have occurred, and more than half of our original wetlands have been drained and converted to other uses. The mid-1950's to the mid-1970's were a time of major national wetland loss. The very runoff that wetlands help to clean can overload and contaminate these fragile ecosystems. In addition, non-native species of plants and climate changes contribute to wetland loss and degradation.

Human activities cause wetland degradation and loss by changing water quality, quantity, or flow rates; increasing pollution and change the make-up of species within a habitat. These changes occur when wetland ecosystems are disturbed and/or non-native species are introduced to a habitat.

Hydrologic Alterations
A wetland's characteristics evolve when the soil is saturated with water for a period of time each year. Any change in this process can dramatically impact the soil, plants, and animals that live there. Here are some common human causes of hydrologic changes to wetlands.

  • Depositing fill materials (such as mud) for land development

  • Draining wetlands of water in order to develop the land for housing or commercial use, for farming or for mosquito control

  • Damming wetlands to create ponds or lakes, or creating levees that cut off wetland water flow
  • Diverting the flow of water to or from wetlands

  • Adding man-made surfaces like cement which increases runoff pollution into wetlands

  • Pollution
    Although wetlands do reduce runoff by absorbing some pollutants from surface water, there is a limit to how much they can take in. The main pollutants that cause damage to wetlands are sediment, fertilizer, human sewage, animal waste, road salts, pesticides, heavy metals, and selenium. Pollutants can come from a variety of sources, including:
    • Runoff from cities and towns, farms, and forestry and mining areas
    • Air pollution from cars, factories and power plants
    • Older landfills and dumps that can leak toxic substances
    • Marinas where boats can increase turbulence in the water and kick up more pollutants from the bottom

  • Vegetation Damage
    Wetland plants can suffer as a result of both pollution and hydrologic changes. Some other ways wetland plants can be damaged are:
    • Cattle and other livestock grazing
    • Introduction of non-native plants that compete with native plants
    • Removal of plants in order to use land for other purposes

Natural Causes for Wetland Loss
Not everything that can damage or diminish wetlands is the result of human actions. Natural processes can sometimes impact wetlands. Here are some natural events that can damage or reduce wetlands:
  • Hurricanes, storms, strong winds can cause storm surges that can erode wetlands

  • Disintegration of barrier islands
    These islands, which act as a buffer, and reduce the impact of ocean waves and currents on estuaries and wetlands, can be eroded away by these same waves and currents, or by storms. As the islands diminish, the shelter they afford the wetlands is reduced, and wetlands can become more exposed to the full force of open ocean processes such as wave action, saltwater intrusion, storm surges, tidal currents, and sediment. All of these things combine to speed-up wetlands deterioration.

  • Major shifts in a river's course
    The Mississippi River delta and all of its wetlands and barrier islands are produced by the continual build-up of sediments deposited by the river. Periodically in geologic time, the river's course has changed, and the sediments were moved and began building up in another area. This shift also caused the deltas that had lost their flow of sediment from the river to erode and degrade. Marine coastal processes eroded and shaped the margins of the deltas that ran along the sea and formed sandy headlands and barrier beaches. As this process continued, barrier islands were formed, and were gradually separated from the mainland coast by bays and lagoons.

content from the Environmental Protection Agency

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See the Wetland Land Cover MAPS of Cocodrie, LA

Plot Line: Land Converts to Water
Mapping Out the Story

While conservation practices help in slowing the rate of loss, Louisiana continues to lose an alarming amount of land. Even if the Mississippi River were immediately to commence building land at its historic rate, it would take centuries to regain the land lost over the past 50 years.

Land Mass, Terrebonne Area, 1932

Land Mass, Terrebonne Area, 2000

Courtesy of USGS

Maps illustrate land changes that have occurred as well as those likely to occur during the next 50 years. Over the past several decades, the subprovince composed primarily of Terrebonne Parish has suffered the most dramatic loss, over 10 percent of its area converting to water since 1978. Projections indicate it is likely to lose another 11 percent (229 square miles) by 2050.

How much land has Louisiana lost?

Traveling at 60 mph it would take 2 hours to circumnavigate an equivalent area

The lost area is

  • about the size of Delaware
  • 31 times the size of the District of Columbia
  • the size of New York, Chicago, Los Angeles, San Diego, and Houston combined

On average, Louisiana has lost an area the size of

  • an executive desk top every second
  • a tennis court every 13 seconds
  • a small cottage every minute

In the next 50 years, the rate of loss will approximate

  • one coat closet every second
  • one office cubicle every 10 seconds
  • one large conference room every minute

In the time it has taken you to read this chart, a chunk of Louisiana 50 times the size of your easy chair has converted from land to water.

 

Courtesy U.S. Geological Survey
Marine and Coastal Geology Program

See the Wetland Land Cover MAPS of Cocodrie, LA