Environmental Engineering Reference
In-Depth Information
Soil morphology refers to field observable soil characteristics that can be
assessed visually or by touch. Morphological characteristics addressed in this
chapter include horizonation or layers, color, texture, and structure. Soil morphol-
ogy typically reflects long term hydrologic conditions. Therefore, the ability to
identify, document, and interpret soil morphology is critical to many wetland
investigations. Expertise in soil morphology and the interpretation of soil morphol-
ogy assists in (1) determinations and delineation of wetlands subject to federal
jurisdiction, (2) assessment of current or past wetland hydrology, and (3) assessment
of changes to wetland condition.
Of particular importance for wetland determinations is the ability to apply Field
Indicators of Hydric Soils in the United States (hereafter referred to as
Field
Indicators
) properly. Hydric soils are routinely identified in the field through
hydric soil indicators, which are sets of morphological patterns that are correlated
with soils that formed under hydrologic conditions associated with wetlands.
Hydric soils are one of three factors needed to identify an area as wetlands
subject to federal jurisdiction under the Clean Water Act and Food Security Act.
In this chapter, we present soil morphological concepts that are used in the
application of the Field Indicators. These same concepts can be used to further
characterize site-specific hydrology with respect to hydroperiod (the seasonal
pattern of water table depth) and hydrodynamics (the direction and energy of
hydrologic inputs).
The goal of this chapter is not to turn the reader into a soil scientist, but to give
the individual enough expertise in soil science to allow for routine wetland
determinations and delineations, as well as hydrologic assessment. Knowledge of
soil morphology also allows the wetlands practitioner to identify difficult situations
where a soil scientist should be called in for assistance.
4.2 Overview of Hydric Soils
4.2.1 What Is a Hydric Soil?
Soil is a natural body comprised of solids (minerals and organic matter), liquid, and
gases that occurs on the land surface, occupies space, and is characterized by one or
both of the following: horizons, or layers, that are distinguishable from the initial
material as a result of additions, losses, transfers, and transformations of energy and
matter, or the ability to support rooted plants in a natural environment. The upper
limit of soil is the boundary between soil and air, shallow water, live plants, or plant
materials that have not begun to decompose. Areas are not considered to have soil if
the surface is permanently covered by water too deep (typically more than 2.5 m
[~8 ft.]) for the growth of rooted plants. The lower boundary that separates soil from
the nonsoil underneath is most difficult to define. Soil consists of horizons near the
Earth's surface that, in contrast to the underlying parent material, have been altered
