Environmental Engineering Reference
In-Depth Information
The hydric soil indicators are “proof positive,” i.e., the presence of an indicator is
proof that the soil is hydric. The absence of an indicator does not prove that the soil
is not hydric (“proof negative”). It is important to remember that a soil that does not
contain a hydric soil indicator may in fact be hydric if it meets the definition of a
hydric soil. In general, soil morphology reflects long-term hydrologic conditions,
which is the basis for the Field Indicators. For a myriad of reasons, some of which
are still poorly understood, there are some relatively small but significant areas that
are, or appear to be, anomalies to the standard saturated soil/wet soil morphology
paradigm. That is, not all hydric soils develop diagnostic redoximorphic features,
and some soils have colors that suggest that the soils formed under saturated
conditions when, in fact, they did not. It is these anomalous soil morphologies
that are so difficult to interpret and are easily misinterpreted by the layperson that
have become known collectively as
problem soils
.
Hydric soil lists, Field Indicators, and the Hydric Soil Technical Standard were
all created to help identify those soils that meet the definition. If a soil meets the
definition of a hydric soil, then it is hydric regardless of whether or not it is a soil
series on a hydric soils list or meets an approved Field Indicator.
Currently there are not Field Indicators or soil series mapped that fit every hydric
soil condition. These soils are considered problem soils for the purpose of hydric soil
identification. Chapter 5 of the Regional Supplements has some suggested methods to
assist in making hydric soils determinations in problem soils where Field Indicators
may not adequately identify hydric soils. Ultimately, the Hydric Soil Technical
Standard may need to be applied to collect data to make a hydric soils determination
and/or to develop a field indicator that will work in a problem soil situation.
4.3 Soil Formation
4.3.1 Factors of Soil Formation
Soils develop as a result of the interactions of climate, living organisms, and
landscape position as they influence parent material decomposition over time (the
five soil-forming factors). Each of these five soil-forming factors also influence
the development of morphological patterns on which the Field Indicators are based.
4.3.1.1 Parent Material
Parent material refers to the great variety of unconsolidated organic matter and
mineral material in which soil formation begins. Certain parent materials such as
red parent material or parent material that weathers to soils with high pH can be
problematic because the hydric soils that develop in these parent materials often
lack characteristic hydric soil morphologies.
