What is known about the rate of habitat conversion, and ultimately land loss in the coastal areas of the Barataria and Terrebonne basins, is that it is alarmingly high. Studies through 1978 showed that over 11,500 acres of land a year were being lost as it slowly converted to open water due to subsidence or other factors. The rate in 1990 was estimated at almost 13,500 acres per year. Scientists have calculated that over 294,000 acres of marsh converted to open water between 1956 and 1978.
The rate of land loss currently shows a decline. With over 33 percent of the coastal area of the state, the Barataria and Terrebonne basins are experiencing between 50 and 61 percent of the land loss for the entire state. At the current rate, it is predicted that residents of coastal communities throughout Louisiana will be forced to move within the next 15 years as land under their homes is replaced by water. Conservative estimates are that an additional 163,000 acres of land will be lost by the year 2010.
Land loss is not evenly distributed across Barataria-Terrebonne. Hot spots of land loss can be seen at the southernmost tip of the basins near the mouth of the Mississippi River in the Barataria basin, moving northward in a narrow band following the river and extending westward to Bayou Perot and Rigolettes. A second hot spot occurs along western Barataria Bay to the Gulf. In Terrebonne, the area of greatest marsh loss occurs in the marshes north of Terrebonne Bay, extending south along the western edge of Terrebonne Bay.
Habitat loss can occur due to many activities. As noted earlier, sediment loss, in conjunction with the natural sinking of marsh, is by far the most significant problem in the estuary. Sea level rise and erosion also contribute to the problem, as can human activities, such as canal dredging and construction of navigation channels. Additionally, overgrazing by mammals, such as nutria, destroys plant communities that hold soil in place. Studies have indicated that hurricane damage is increased in marshes that have been heavily grazed by nutria.
Storm surges and winds associated with severe tropical storms and winter fronts are additional natural forces that account for significant habitat alteration and land loss in the estuary. During storms or periods of floods, habitats are subjected to changes in water chemistry and extended periods in which they are totally submerged. When a wetland plant experiences sustained and deep flooding, growth suffers. If the flooding stress is sufficient, the plant dies. In the case of saltwater intrusion from the Gulf, some plant species have adapted and exclude salt from their tissues, but their tolerance of salt varies widely. Most fresh marsh species, however, are unable to survive exposure to high salinity waters. When fresh marsh plants die quickly from salt water exposure, their roots can no longer hold the soil, and massive soil loss can occur before the area can be colonized by salt tolerant plants.
- Hydrological modifications and wetland subsidence resulting in saltwater intrusion
- Spoil banks and diking or leveeing of wetlands resulting isolation, submergence, and mortality of wetlands
- Wetland erosion and internal fragmentation
- Shoreline erosion by commercial and recreational boat wakes
- Filling of wetlands for agriculture and other development
- Decreases in sport and commercial fish and shellfish populations
- Changes in fur-bearing and waterfowl populations with sport and commercial value
- Reduced recreation and commercial value of wetlands and estuaries
- Decreased acreage available to treat pollution inputs resulting in increased levels of eutrophication, pathogen contamination, and toxic substances
- Decreased capacity to buffer storm energy
- Decreased habitat for neotropical migratory birds and other species such as the black bear