Environmental Engineering Reference
In-Depth Information
by the interactions of climate, relief, and living organisms over time. Commonly,
soil grades at its lower boundary to hard rock or to earthy materials virtually devoid
of animals, roots, or other marks of biological activity. For purposes of classifica-
tion, the lower boundary of soil is arbitrarily set at 200 cm (~6.5 ft.) (Soil Survey
Staff
1999
).
The term
hydric soil
was first published in
Classification of Wetlands and
Deepwater Habitats
(Cowardin et al.
1979
). The initial purpose of the definition
was to define a class of soils that were closely correlated with hydrophytic vegeta-
tion and to produce a list of soils that could be used with soil surveys to facilitate the
development of National Wetland Inventory (NWI) maps. Conceptually, hydric
soils are soils that developed under hydrologic conditions associated with wetlands.
Because of the role of hydric soil identification in jurisdictional determinations of
wetlands, very specific criteria/definitions are applied to distinguish hydric soils
from non-hydric soils.
4.2.2 Hydric Soils and Wetland Regulation
Identification of soils as
hydric
is critical to the protection of wetlands under the
Clean Water Act (CWA) (Federal Water Pollution Control
2008
) and for conserva-
tion compliance under the Farm Bill. According to the
US Army Corps of Engineers
Wetlands Delineation Manual
(hereafter referred to as the
Delineation Manual
)
(Environmental Laboratory
1987
), the presence of a hydric soil is one of three
factors that must be met in order for an area to meet the definition of a jurisdictional
wetland. The other two are the presence of hydrophytic vegetation and wetland
hydrology. The use of the Delineation Manual and Regional Supplements
(U.S. Army COE
2012
) is required for all federal agencies involved in identification
of wetlands that may be jurisdictional, as well as for most states that have environ-
mental programs to protect wetlands.
A hydric soil as defined by the National Technical Committee for Hydric Soils
(NTCHS) is
a soil that formed under conditions of saturation
,
ponding
,
or flooding
long enough during the growing season to develop anaerobic conditions in the
upper part
(Federal Register, July 13,
1994
). For a soil to qualify as a hydric soil for
regulatory purposes, it must meet the definition of a hydric soil. It is important to
note that a soil meets the definition if it developed under the stated hydrologic
conditions. If those hydrologic conditions are altered through drainage or protection
(levees), the soil is still considered to be hydric
if the soil in its undisturbed state
developed as a hydric soil
.
A hydric soil is defined in the National Food Security Act (USDA, FSA
1985
)as
a soil that
,
in its undrained condition
,
is saturated
,
flooded
,
or ponded long enough
during the growing season to develop an anaerobic condition that supports the
growth and regeneration of hydrophytic vegetation
. While the definition is slightly
different than the definition developed by the NTCHS, the methods (hydric soils
