Ecology of the Mississippi River Delta Region
SOILS
(the definitions and descriptions below were taken from various publications of the local U.S. Soil Conservation Service).
The following are some terms that help define and understand soils. See also the adjacent figure
from Strahler, A.N. 1975. Physical Geography. 4th ed. Wiley. P. 371.
25.6 mm = 1 in
1000 microns = 1 mm
- Alluvium - Material, such as sand, silt, or clay, deposited on land by streams.
- Association, soil - A group of soils geographically associated in a characteristic repeating fashion.
- Calcareous soil - A soil containing enough calcium carbonate to effervesce visibly when treated with cold, dilute hydrochloric acid.
- Clay - As a soil separate, the mineral soil particle less than 0.004 mm in diameter. As a soil textural class, soil material that is 40% or more clay, less than 45% sand, and less than 40% silt.
- Gleyed soils - Soils that formed under poor drainage, resulting in the reduction of iron and other elements in the profile and in gray colors and mottles.
- Hemic soil material (=mucky peat) - Organic soil material intermediate in degree of decomposition between the less decomposed fibric and the more decomposed sapric material.
- Horizon, soil - A layer of soil, approximately parallel to the surface, having distinct characteristics produced in soil-forming processes.
- Humus - The well decomposed, more or less stable part of the organic matter in mineral soils.
- Leaching - The removal of soluble material from soil or other material by percolating water.
- Loam - Soil material that is 7-27% clay particles, 28-50% silt particles, and less than 52% sand particles.
- Muck (=sapric soil material) - Organic soil material in an advanced stage of decomposition making it impossible to identify plant parts with the unaided eye. Muck has the least amount of plant fiber, the highest bulk density, and the lowest water content at saturation of all organic soil material.
- Peat (=fibric soil material) - Unconsolidated material, largely undecomposed organic matter, that has accumulated under excess moisture.
- Profile, soil - A vertical section of the soil extending through all its horizons and into the parent material.
- Sand- As a soil separate, individual rock or mineral fragments from 0.0625-2.0 mm in diameter. Most sand grains consist of quartz. As a soil texture class, a soil that is 85% or more sand and not more than 10% clay.
- Series, soil - A group of soils that have profiles that are almost alike, except for differences in texture of the surface layer or of the underlying material. All the soils of a series have horizons that are similar in composition, thickness, and arrangement.
- Silt - As a soil separate, individual mineral particles that range in diameter from 0.004-0.0625 mm. As a soil textural class, soil that is 80% or more silt and less than 12% clay.
The following are definitions of colloquial soil terminology:
- Gumbo - wet clays.
- Buckshot - high clay content. When wet, it gets sticky. When dry, it can be crumbled into dry, angular pieces the size of buckshot.
- Coffee grounds - soil from former freshwater marshes that has been dry for 50 yr or more. It has decomposed as far as it can, is
inert, has lost its elasticity, is black and grandular (and remains grandular when wet).
- Floatant (Carlin peat) - very poorly drained soil that occurs in large areas in the floating marshes. The surface layer is strongly acid to neutral and is very dark grayish brown mucky peat about 12 in thick. The lower layer is more alkaline. The fibrous peat layer floats on a layer of water that is greater than 50 in to the mineral layers. Small areas of other soils with different properties may be included with this soil.
The following is a synopsis of soil associations that are common in the Mississippi River Delta. It is important to note that they are at least partially defined by where they exist.
- Soils on natural levees protected from flooding:
- Sharkey-Commerce - level, poorly (Sharkey) to somewhat poorly (Commerce) drained; have a clayey or loamy surface layer and clayey subsoil or may be loamy throughout. Sharkey occurs lower on the levees than Commerce.
- Vacherie - gently undulating; occurs in levee cuts; basically loamy top to the cut in Sharkey-Commerce soils.
- Soils in marshes and swamps that are frequently flooded or impounded:
- Barbary - in swamps (with logs and stumps), level, very poorly drained, thin mucky surface layer, clayey underlying material.
- Kenner-Allemands - in freshwater marshes, level, very poorly drained, moderately thick mucky surface layer, mucky and clayey underlying materials; Kenner much more permeable than Allemands.
- Larose - in freshwater marshes, same as Kenner-Allemands but thin layer of muck on surface; Larose exists as a very minor component.
- Lafitte-Clovelly - in brackish marshes, level, very poorly drained, thick (Lafitte) or moderately thick (Clovelly) mucky surface layer, clayey underlying material.
- Timbalier-Scatlake - in salt marshes, level, very poorly drained, thick (Timbalier) or thin (Scatlake) mucky surface, clayey underlying material, semifluid mineral (Scatlake) or organic (Timbalier).
- Soils in former swamps and marshes that are drained
- Drained-Kenner-drained-Allemands - in drained freshwater marshes, otherwise as Kenner-Allemands
- Westwego-Harahan - in drained swamps, clayey surface layer and subsoil, mineral (Harahan) or organic (Westwego).
- Soils of sandy ridges that are occasionally flooded
- Felicity - in old and current beaches, gently undulating, somewhat poorly drained, sandy throughout.
- Soils of spoil from canal construction
- Ijam - on spoil banks, level, poorly drained, mineral soils (firm clay over semifluid clay).