Environmental Engineering Reference
In-Depth Information
dark surface layer. Partially decomposed organic material may accumulate in
saturated soils resulting in thick organic surfaces. These thick organic surfaces
are one of the features that can be used to identify a hydric soil.
4.3.2.2 Losses
Most losses occur by leaching. Water moving through the soil dissolves certain
minerals and transports them into deeper layers. Some materials, especially sodium
salts, gypsum, and calcium carbonate, are relatively soluble. They are removed
early in the soil's formation. As a result, soil in humid regions generally does not
have carbonates in the upper horizons. Quartz, aluminum, Fe oxide, and kaolinitic
clay weather slowly. They remain in the soil and become the main components of
highly weathered soil.
4.3.2.3 Translocations
Translocation means movement from one place to another. In low rainfall areas,
leaching often is incomplete. Water starts moving down through the soil, dissolving
soluble minerals such as calcium carbonate as it goes. Saturation promotes the
reduction of Fe which helps bridge clay particles together. Reduced Fe and
the associated clays will move with the water. When the water stops moving
these materials are deposited. Soil layers enriched with clays, calcium carbonate
or other salts form this way. Translocation upward and lateral movement is also
possible. Translocation is most apparent in seasonally saturated soils as minerals
and clay move up and down with the water table.
4.3.2.4 Transformations
Transformations are biogeochemical changes that take place in the soil.
Microorganisms that live in the soil feed on fresh organic matter and change it
into humus. For example, ferric Fe (Fe +3 ) commonly present in Fe oxides under
aerobic conditions and is readily reduced to soluble ferrous Fe (Fe +2 ) which is quite
easily removed from the soil by leaching. The patterns in the soil as a result of Fe
transformations is the most common feature used to identify hydric soils.
4.4 Soil Horizons
The factors of soil formation do not have a consistent impact with depth. For
example, plant roots may not extend throughout the entire depth of the soil. Some
soils contain more than one type of parent material. Anthropogenic disturbance
(such as plowing) is usually restricted to the upper part of the soil. Soil moisture
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