General information

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

MLRA notes

Major Land Resource Area (MLRA): 131A–Southern Mississippi River Alluvium

MLRA 131A, Southern Mississippi River Alluvium, is in Louisiana (32 percent), Arkansas (26 percent), Mississippi (26 percent), Missouri (12 percent), Tennessee (3 percent), and Kentucky (1 percent). A small part of Illinois also is in the area. This MLRA makes up about 29,555 square miles (76,585 square kilometers). It includes the towns or cities of Lake Providence, Morgan City, and Houma, Louisiana; Greenville, Yazoo City, and Clarksville, Mississippi; Eudora, Helena, and West Memphis, Arkansas; Caruthersville, Kennett, and Sikeston, Missouri; and the west edge of Memphis, Tennessee. The cities of Baton Rouge and New Orleans, Louisiana, are just outside this area. This area makes up most of the Mississippi Alluvial Plain Section of the Coastal Plain Province of the Atlantic Plain. It is on the alluvial plain along the lower Mississippi River, south of its confluence with the Ohio River. The landforms in the area are level or depressional to very gently undulating alluvial plains, backswamps, oxbows, natural levees, and terraces.

The Mississippi River has the third largest drainage basin in the world, exceeded in size only by the watersheds of the Amazon and Congo Rivers. It drains 41 percent of the 48 contiguous states of the United States. The basin covers more than 1,245,000 square miles, includes all or parts of 31 states and two Canadian provinces, and roughly resembles a funnel which has its spout at the Gulf of Mexico. Waters from as far east as New York and as far west as Montana contribute to flows in the lower river.

For the purpose of Ecological Site Concepts the MLRA was separated by the Technical team into 6 Sub-regions based on various assemblages of data reviewed. The sub-region where this site is delineated extends from the confluence of the Mississippi the Arkansas Rivers and continues south to the Red River, where the Old River Control Structures regulates the flows of the Mississippi, Red and Atchafalaya Rivers of MLRA 131A in Arkansas and Louisiana.

Classification relationships

Major Land Resource Area (MLRA) and Land Resource Unit (LRU) (USDA-Natural Resources Conservation Service, 2006)

EPA Level IV Ecoregion

The Natural Communities of Louisiana - (Louisiana Natural Heritage Program - Louisiana Department of Wildlife and Fisheries)

2011; Foti, ETAL; Potential Natural Vegetation of the Mississippi Alluvial Valley Tensas Basin - Not a direct one to one relationship between concepts and PNV Classification, however PNV concepts are very useful in informing the site concepts.

Ecological site concept

Bottomland Forests of this site are better drained and are found above the regular flooding frequency, although formed in alluvium therefore has a potential for flooding. The soils of this site are lighter textured which improves the internal drainage and will provide opportunities for species that will favor better drainage to thrive. This site is typically a runoff site, however at high stream flows may receive run-on water from offsite. Slopes on this site range from 0 - 2 percent generally around 1/2 %.

Hydrology is a major drive of this site concept, as with all alluvial sites which received parent material soil from flooding, however it has been disconnected from the Mississippi River influence. There may be significant inflow into this site from local waterways and backwater flooding may occur as part of the hydrologic regime due to potential connectivity to other rivers within the Mississippi River alluvial Plain. Absent catastrophic failure of the protection levee system this site will no longer receive direct inflows from the MS River.

Areas are on Flood Plains in portions of level IV EPA Ecoregions 73a - Northern Holocene Meander Belts, 73d - Northern Backswamps, 73i - Arkansas/Ouachita River Backswamps, 73m - Southern Backswamps and 73K Southern Holocene Meander Belts, of the Southern Mississippi River Alluvium Major Land Resource Area. Within the central western portion of the MLRA in the Tensas Basin which extends from approximately where the Arkansas River influence begins within the MLRA and to the Red River to the south. This concept is described for location outside of the constructed protection levees of the MS River.

Of note, this site occurs on the “protected” side of the extensive Mississippi River levee system and is distinguished from similar landforms within the “batture lands” (i.e., the alluvial land between the river channel and the constructed levee system).

Table 1. Dominant plant species