Environmental Engineering Reference
In-Depth Information
list, Field Indicators, and Hydric Soil Technical Standard) that can be used to
identify a hydric soil are the same.
Important concepts in the definition to note are:
1.
in its undrained condition
means that the soil formed under wet conditions and
the absence of a water table would not preclude the soil from still being
considered hydric. In other words, it may be currently in the dry part of the
season when it is being observed or it may have been artificially or naturally
drained but if the soil formed when the water table saturated the upper part of the
soil it is still hydric;
2.
saturated
,
flooded
,
or ponded
means that the soil must have water in an unlined
bore hole in the upper part of the soil or the water must rise above the surface of
the soil;
3.
during the growing season
means that the water must be present during the
growing season as determined by the use of the Hydric Soil Technical Standard
(NTCHS
2007
);
4.
anaerobic condition
means the soil lacks oxygen and is a reducing environment.
If the soil meets all the above mentioned concepts, then it will support the
growth and regeneration of hydrophytic vegetation. Hydrophytic vegetation, as
defined in the FSA Manual means a plant growing in (A) water; or (B) a
substrate
that is at least periodically deficient in oxygen during a growing season as a result
of excessive water content
[16 U.S.C. 3801(a)(13)].
4.2.3 Hydric Soil Indicators
Nearly all hydric soils exhibit characteristic morphologies that result from repeated
periods of saturation or inundation for more than a few days. Saturation or inunda-
tion, when combined with microbial activity in the soil, causes the depletion of free
oxygen (O
2
). This anaerobiosis (without O
2
) promotes certain biogeochemical
processes, such as the accumulation of organic matter and the reduction, transloca-
tion, or accumulation of iron (Fe) and other reducible elements. These processes
result in distinctive characteristics that persist in the soil during both wet and dry
periods, making them particularly useful for identifying hydric soils in the field.
Hydric soils are routinely identified in the field through use of the Field
Indicators. Most hydric soils are readily identified by observing either a predomi-
nance of gray color with redoximorphic concentrations (formerly called “high
chroma mottles”) near the surface or an accumulation of organically enriched
material on the surface. These features indicate that the soil has been chemically
reduced and fits the standard saturated soil/wet soil morphology paradigm. These
readily observable soil morphologies resulting from oxidation-reduction of princi-
pally Fe near the surface and accumulation of organic matter comprise the primary
Field Indicators used for jurisdictional determinations of wetlands. The presence
of one indicator is evidence that the soil meets the definition of a hydric soil.
