US Army Corps of Engineers
Wetlands Delineation Manual
Please Note that hydric soil field indicators developed by NRCS are updated at Hydric Soil Field Indicators. Revisions to hydric soil field indicators may not apply to wetland delineations provided to the Corps.
1. This appendix consists of two sections. Section 1 describes the basic procedure for digging a soil pit and examining for hydric soil indicators. Section 2 is a list of hydric soils of the United States. [Note: Not included here - contact local NRCS field office]
Digging a soil pit
2. Apply the following procedure: Circumscribe a 1-ft-diameter area, preferably with a tile spade (sharpshooter). Extend the blade vertically downward, cut all roots to the depth of the blade, and lift the soil from the hole. This should provide approximately 16 inches of the soil profile for examination. Note: Observations are usually made immediately below the A-horizon or 10 inches (whichever is shallower). In many cases, a soil auger or probe can be used instead of a spade. If so, remove successive cores until 16 inches of the soil profile have been removed. Place successive cores in the same sequence as removed from the hole. Note: An auger or probe cannot be effectively used when the soil profile is loose, rocky, or contains a large volume of water (e.g. peraquic moisture regime).
Examining the soil
3. Examine the soil for hydric soils indicators (paragraphs 44 and/or 45 of main text (for sandy soils)). Note: It may not be necessary to conduct a classical characterization (e.g. texture, structure, etc.) of the soil. Consider the hydric soil indicators in the following sequence (Note: THE SOIL EXAMINATION CAN BE TERMINATED WHEN A POSITIVE HYDRIC SOIL INDICATOR IS FOUND):
a. Determine whether an organic soil is present (see paragraph 44 of the main text). If so, the soil is hydric.
b. Determine whether the soil has a histic epipedon (see paragraph 44 of the main text). Record the thickness of the histic epipedon on DATA FORM 1.
c. Determine whether sulfidic materials are present by smelling the soil. The presence of a "rotten egg" odor is indicative of hydrogen sulfide, which forms only under extreme reducing conditions associated with prolonged inundation/soil saturation.
d. Determine whether the soil has an aquic or peraquic moisture regime (see paragraph 44 of the main text). If so, the soil is hydric.
e. Conduct a ferrous iron test. A calorimetric field test kit has been developed for this purpose. A reducing soil environment is present when the soil extract turns pink upon addition of a-a-dipyridil.
f. Determine the color(s) of the matrix and any mottles that may be present. Soil color is characterized by three features: hue, value, and chroma. Hue refers to the soil color in relation to red, yellow, blue, etc. Value refers to the lightness of the hue. Chroma refers to the strength of the color (or departure from a neutral of the same lightness). Soil colors are determined by use of a Munsell Color Book (Munsell Color 1975). Each Munsell Color Book has color charts of different hues, ranging from 10R to 5Y. Each page of hue has color chips that show values and chromas. Values are shown in columns down the page from as low as 0 to as much as 8, and chromas are shown in rows across the page from as low as 0 to as much as 8. In writing Munsell color notations, the sequence is always hue, value, and chroma (e.g. 10YR5/2). To determine soil color, place a small portion of soil (moistened) in the openings behind the color page and match the soil color to the appropriate color chip. Note: Match the soil to the nearest color chip. Record on DATA FORM 1 the hue, value, and chroma of the best matching color chip. CAUTION: Never place soil on the face or front of the color page because this might smear the color chips. Mineral hydric soils usually have one of the following color features immediately below the A-horizon or 10 inches (whichever is shallower):
(1) Gleyed soil.
Determine whether the soil is gleyed. If the matrix color best fits a color chip found on the gley page of the Munsell soil color charts, the soil is gleyed. This indicates prolonged soil saturation, and the soil is highly reduced.
(2) Nongleyed soil.
(a) Matrix chroma of 2 or less in mottled soils. (moistened)
(b) Matrix chroma of 1 or less in unmottled soils. (moistened)
(c) Gray mottles within 10 inches of the soil surface in dark (black) mineral soils (e.g., Mollisols) that do not have characteristics of (a) or (b) above.
Soils having the above color characteristics are normally saturated for significant duration during the growing season. However, hydric soils with significant coloration due to the nature of the parent material (e.g. red soils of the Red River Valley) may not exhibit chromas within the range indicated above. In such cases, this indicator cannot be used.
g. Determine whether the mapped soil series or phase is on the national list of hydric soils (Section 2). CAUTION: It will often be necessary to compare the profile description of the soil with that of the soil series or phase indicated on the soil map to verify that the soil was correctly mapped. This is especially true when the soil survey indicates the presence of inclusions or when the soil is mapped as an association of two or more soil series.
h. Look for iron and manganese concretions. Look for small (>0.08-inch) aggregates within 3 inches of the soil surface. These are usually black or dark brown and reflect prolonged saturation near the soil surface.
Look for one of the following indicators in sandy soils:
a. A layer of organic material above the mineral surface or high organic matter content in the surface horizon (see paragraph 45a of the main text). This is evidenced by a darker color of the surface layer due to organic matter interspersed among or adhering to the sand particles. This is not observed in upland soils due to associated aerobic conditions.
h. Streaking of subsurface horizons (see paragraph 45c of the main text). Look for dark vertical streaks in subsurface horizons. These streaks represent organic matter being moved downward in the profile. When soil is rubbed between the fingers, the organic matter will leave a dark stain on the fingers.
c. Organic pans (see paragraph 45b of the main text). This is evidenced by a thin layer of hardened soil at a depth of 12 to 30 inches below the mineral surface.
Section 2. Hydric Soils of the United States
[Note: Current lists are available from local NRCS offices.]