The Louisiana delta wetland is in the southeast corner of Louisiana as shown in Figure 1. Beginning about 100 years ago, the Mississippi River has been diverted in various locations both within and outside of Louisiana for the purposes of fresh water supplies, flood protection, and recreational use. This has strongly affected the amount and character of sediment carried by the river to the delta. The subject wetland is an estuarine wetland with bidirectional waterflow from the Mississippi River (downstream) and the Gulf of Mexico (upstream) (CWPPRA, n.d.).
Hydrology
The dominant source of hydrology for the Louisiana delta wetland is the Mississippi River. Over thousands of years, the river has changed course as the lobes of its delta have changed as seen in Figure 2. The current lobe has formed the uncommon bird’s foot-shaped delta (see Figure 2). However, it is important to note that for approximately a century the normal hydrologic processes have not been allowed to operate in these wetlands due to diversions of the rivers. These diversions can serve multiple purposes, including the provision of canals for oil and gas production, protection of cities from frequent flooding, and creation of recreational areas. Today, about one-third of the Mississippi’s water (and the silt that travels with it) is diverted into Atchafalaya Bay (CWPPRA, n.d.).
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Rivers that empty into the Mississippi River or the delta itself include the Atchafalaya, Red, Black, Yazoo, and Homochito. Many of these rivers are diverted before they reach their outlets, thus reducing the flow of fresh water and sediment. These rivers, along with groundwater and precipitation, form the downstream flow in the wetlands. Tides from the Gulf of Mexico flow upstream, mixing with fresh water in the estuaries (Snedden et al., 2015).
Water takes the path of least resistance; therefore, it is more likely to flow along lower areas rather than higher areas. Sandy or loamy soil is more likely to be eroded but it may also slow the water flow by absorbing it, while clay soil does not absorb water easily. Rock does not absorb the water.
Plants
The subject wetland is estuarine and features several dominant plant communities according to the salinity and other characteristics of a given area. In the Louisiana delta, categories of salinity include fresh marsh, intermediate marsh, brackish marsh, and saline marsh. All four categories have been decreasing as the wetland shrinks, but especially fresh and brackish marshes. This causes death of plants which require lower levels of salinity; for example, the population of Live Oak trees (Quercus virginiana) within the delta is diminishing because it cannot survive in the increasing salinity. Dominant plants in the mesohaline and oligohaline regions include Spartina patens, Spartina alterniflora, and Sagittaria lancifolia. Their relative contributions depend on the precise salinity of the water as well as its stability regarding fresh and salt water inputs (Visser et al., 1998).
Historic Use of the Wetland and Current Conditions
The subject wetland has been used historically for fishing, shrimp farming, and leisure pursuits. The discovery of oil and gas deposits within the wetland has prompted changes such as dredging of canals that make it easier to acquire and transport these products. Population increases have led to pumping of wetland areas to create new land and building levees to prevent flooding. These factors, along with diversions of hydrology, have resulted in a net loss of wetlands to open water. As tides come in, they erode the coastline, and if it is not replenished by silt carried by the river, the land is eventually submerged. This process is occurring in many locations across the Louisiana delta area. Hurricanes Katrina and Rita were also very destructive, especially in the lower “bird’s foot” area of the delta. Several programs aim to restore the Louisiana delta wetlands. One involves the diversion of the river back to the current delta, while another suggests moving sediment from the Atchafalaya Bay, which contains far too much, to areas of the delta that need it (Snedden et al., 2007).
- Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA). (n.d.). The Mississippi River Delta Basin. Retrieved from https://lacoast.gov/new/About/Basin_data/mr/
- Snedden, G. A., Cable, J. E., Swarzenski, C., & Swenson, E. (2007). Sediment discharge into a subsiding Louisiana deltaic estuary through a Mississippi River diversion. Estuarine, Coastal and Shelf Science, 71(1-2), 181-193.
- Snedden, G. A., Cretini, K., & Patton, B. (2015). Inundation and salinity impacts to above-and belowground productivity in Spartina patens and Spartina alterniflora in the Mississippi River deltaic plain: Implications for using river diversions as restoration tools. Ecological Engineering, 81, 133-139.
- Visser, J. M., Sasser, C. E., Chabreck, R. H., & Linscombe, R. G. (1998). Marsh vegetation types of the Mississippi River deltaic plain. Estuaries, 21(4), 818-828.
