Environmental Engineering Reference
In-Depth Information
Fig. 4.5 The dominant color
of this soil is
gray
. Therefore,
the matrix color of this soil
would be considered
gray
while the other splotches of
color would be considered
mottles. In this soil, the
mottles are due to wetness in
the soil and are a type of
mottle called redoximorphic
features
4.5.4.2 Mottling Versus Redoximorphic Features
Secondary zones of color less dominant in surface area to the matrix are referred to as
mottles. Redoximorphic (redox) features are a type of mottling that is associated with
wetness and form as a result of saturation and reduction of Fe and manganese (Mn).
4.5.4.3 Percentages
When assessing a soil layer with multiple colors care should be taken to accurately
document percentages as they are critical to many of the Field Indicators. Some of
these require a minimum percentage of the matrix and/or redoximorphic features.
One example would be A11 Depleted Below Dark Surface, which requires a matrix
color that has
2 starting within 30 cm (12 in.)
of the soil surface. Another would be F6 Redox Dark Surface, which requires
60 % of the layer with a chroma of
2%
distinct or prominent redox concentrations (F6a) or
5 % distinct or prominent
redox concentrations (F6b).
4.5.4.4 Contrast
Contrast refers to the degree of visual distinction that is evident between associated
colors. Three categories of contrast are recognized as faint, distinct, and prominent.
Contrast is an important consideration when using the Field Indicators as most
indicators require redox concentrations to be either distinct or prominent. Note that
currently the only Field Indicator to allow faint contrast is S6 Stripped Matrix. The
upper threshold for faint contrast is presented in Table
4.1
.
