Environmental Engineering Reference
In-Depth Information
than.” Water table depths for a given time period are impacted not only by
precipitation during that timeframe but also by precipitation in the preceding
months; therefore, any evaluation of rainfall data for a given time period should
also include consideration of the precipitation patterns prior to the time period of
interest. For example, the NTCHS recommends the evaluation of precipitation data
for the 3 months prior to the period when the soil in question is most saturated and
reduced (NTCHS
2007
).
4.13 Other Uses for Soil Morphology Information
4.13.1 Monitoring and Interpreting Wetland Hydrology
4.13.1.1 Field Indicators of Hydric Soils
All wetlands by definition experience saturation in the upper part of the soil for at
least part of the year in a majority of years. However, wetlands display a wide range
in hydroperiods, from peraquic moisture regimes (continuously saturated) such as
tidal marshes to seasonally saturated wetlands such as many mineral soil flats.
Some wetlands are inundated for extended periods in most years, others are rarely
inundated. In addition, some wetlands such as groundwater driven slope wetlands
display a static water table with a consistent depth. Others, such as precipitation
driven mineral soil flats display a wide range in water table depths and multiple
fluctuations in depth each year.
Soil morphology typically reflects long term hydrologic conditions. Field
Indicators were developed to identify soils that developed under hydrologic
conditions associated with wetlands. Hydric soils are as diverse as wetlands.
Therefore, the Field Indicators represent a range in hydrologic conditions and
individual indicators represent a more limited range in hydrologic conditions.
Soil scientists recognize this relationship and associate specific indicators with
certain hydroperiods. For example, F3 Depleted Matrix is based on the reduction
and translocation of Fe, not the accumulation of organic matter. Conversely, A3
Black Histic is based on the accumulation of organic matter. Development of a
histic epipedon or Histisols requires longer periods of saturation than the reduction
and translocation of iron. For example, A3 Black Histic is found in wetlands that are
inundated for extensive periods; whereas, F3 Depleted Matrix is found in wetlands
that are rarely inundated and have a very dynamic water table. Therefore, the Field
Indicators can be used not only to identify a hydric soil, but also to characterize
wetland hydroperiods.
Soil colors can be used to distinguish between episaturation and endosaturation.
By definition, episaturation is characterized by two layers of saturated soil
separated by an unsaturated zone. Horizons that are saturated for extended periods
are typically characterized by low chroma colors. In a peraquic moisture regime,
