is a dynamic landscape, formed by sediments deposited by the Mississippi River in several delta lobes. Historically, the river switched course approximately every thousand years.
The currently active delta of the Mississippi - the birdfoot delta - is artificially held in place by massive levees that line the river almost to its mouth. However, two small active deltas of the Atchafalaya River, a major distributary of the Mississippi River, exist: the Atchafalaya and Wax Lake deltas.
These two deltas receive sediments and are the main areas of land gain on the Louisiana coast. All other coastal wetlands east of the Atchafalaya River are currently in the degrading phase of the delta cycle because they do not receive sediments.
This region erodes primarily due to the geologic forces of compaction and subsidence. However, erosion rates are increased by a variety of other factors, including a large population of nutria that graze the marsh.
A nutria nibbles on aquatic vegetation.
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Grazing leads to erosion because it reduces the number of plants that can bind the soil together and also because some grazers dig holes to eat roots and tubers. Tubers are special roots that some plants use to store food, similar to a potato. One of the first indications that grazing was a significant factor in marsh degradation came from the Atchafalaya Delta.
A group of researchers from the Louisiana State University Coastal Ecology Institute first demonstrated the enormous impact of grazing on the marsh vegetation in the Atchafalaya Delta. They initially set up small plots protected by chicken-wire fences that
showed more and larger plants than unprotected plots had.
Due to the small size of these plots, it was not possible to determine which of the
grazers present on the island -- nutria or waterfowl -- were responsible for the grazing
phenomenon. So a bigger experiment was started with four different types of plots.
One plot was unprotected and grazed by both nutria and ducks. The second plot was protected from grazing by nutria with a fence embedded in the soil; the area was large enough, however, for ducks to land in. The third plot was small, with a fence that was
raised six inches above the marsh surface so nutria could crawl in. The fourth plot was
small, with a normal fence that protected the plants from both nutria and ducks.
After one year, there was a dramatic difference between the protected and unprotected plots. This experiment showed that both waterfowl and nutria significantly reduced the vegetation and that grazing by both at the same time was devastating. Only those plants not eaten by nutria and ducks water-willow and elephants ear survived.
Since 1986, the mud flats of the Atchafalaya Delta have been almost bare of emergent vegetation. LSU researchers started another experiment there to test if plants could develop naturally and/or artificially when protected from grazing.
Additional plots protected from grazing by both nutria and waterfowl were installed, and half of them were planted with arrowhead and deltaduckpotato; the others were left empty. Some plants were also planted in unprotected plots to see if they would survive.
