Environmental Engineering Reference
In-Depth Information
Table 4.1 Upper thresholds
for faint contrast. Any
feature above the upper
threshold for faint features
would be considered either
distinct or prominent
Upper thresholds for faint contrast
Δ
Hue
Value
Chroma
Δ
Δ
0
2
1
1
1
1
2
0
0
Hue
Value
Chroma
Any
3
2
4.5.4.5 Type of Redoximorphic Features
Four classes of redoximorphic features are recognized as defined below. On the
data sheet under the category
Type
, they should be noted by their abbreviation.
Examples of redox concentrations and depletions are shown in Fig.
4.6
.
1. Concentration (C): Bodies of apparent accumulation of Fe-Mn oxides.
2. Depletion (D): Bodies of low chroma (less than or equal to) having values of 4 or
more where Fe-Mn oxides alone have been stripped out or where both Fe-Mn
oxides and clay have been stripped out.
3. Reduced Matrix (RM): Soil matrices that have a low chroma color
in situ
because of the presence of Fe
2+
, but whose color changes in hue or chroma
when exposed to air as the Fe
2+
is oxidized to Fe
3+
. The change in color occurs
within 30 min or less after the sample is exposed to air.
4. Masked Sand Grains (CS): This applies to particles masked with coats of organic
material.
4.5.4.6 Location of Redoximorphic Features
When noting “Location” there are two categories, which are defined below:
1. Pore Lining (PL): Zones of accumulation are either coatings on a ped or pore
surface or impregnations of the matrix adjacent to the pore or ped.
2. Matrix (M): Zones of accumulation that are impregnations within the matrix.
4.6 Soil Texture
Soil texture, or particle size distribution, is the numerical proportion of the mineral
particles
2 mm (in.) in size (sand, silt, and clay) and is expressed as percent by
weight. These mineral size classes are distinguished by size: sand, 0.05-2 mm; silt,
0.002-0.05 mm; and clay,
<
0.002 mm. Figure
4.7
shows the relative sizes of sand,
silt, and clay. Almost everyone knows what sand and clay feel like, either from
playing in a sandbox or sculpting with clay in an art class. Silt feels similar to
talcum powder or flour. Typically, a sample of soil will contain all three
components in various ratios. Therefore, soil textural classes were created to
designate the ratios (Fig.
4.8
). For example, a sandy clay contains 35-55 % clay,
<
