Field Indicators of Hydric Soils in the

United States

Version 7.0 and errata and all info on hydric soils can be downloaded from the NTCHS website at http://soils.usda.gov/use/hydric/.

Field Indicators

Field indicators are soil morphological features used to identify hydric soils

The features result from soil genesis in the presence of “anaerobic conditions”

They are used for on-site verification

Development of Field Indicators

Continuous process On-going since mid-80’s

Inter-agency Including universities, private sector,

federal, state, and local agencies Multi-disciplinary

Soil scientists, hydrologists, botonists

Hydromorphic Processes

Reduction, translocation, and precipitation of iron and manganese

Accumulation and differential translocation of organic matter

Reduction of sulfur

Hydric Soil Indicators Indicators are not

intended to replace or relieve the requirements contained in the Hydric Soil Definition

Indicators are used to identify the hydric soil component of wetlands; however, there are some hydric soils that lack one of the currently listed indicators

Biogeochemical Processes Used as Indicators

Iron

Many indicators are based on iron reduction, transformation, and differential accumulation.

Carbon

Many indicators are based on carbon accumulation and differential decomposition

Carbon and Iron

Some indicators are based on carbon accumulation and differential decomposition and iron reduction, translocation, and differential accumulation.

Carbon and/or Iron

One indicator is based on carbon accumulation and differential decomposition and/or iron reduction, translocation, and differential accumulation: S6 Stripped Matrix.

Carbon and Iron/Manganese

One indicator is based on carbon accumulation and differential decomposition and iron/manganese reduction, translocation, and differential accumulation: F16 High Plains

Depression

Iron/Manganese

One indicator is based on iron/manganese reduction, transformation, and differential accumulation: F12 Iron-

Manganese Masses

Sulfur

One indicator is based on sulfur reduction: A4 Hydrogen

Sulfide

Algae

One indicator is based on precipitation of calcium carbonate by algae: F10 Marl

Chroma 2 or less

Not all indicators require a chroma 2 or less F8 Redox

Depressions F19 Piedmont

Flood Plain Soils F20 Anomalous

Bright Loamy Soils

Field Indicators of Hydric Soils in the United States

Refinement of the 1987 indicators Low chroma colors, mottles Gleyed colors “High” organic matter content Organic streaking Histosol, histic epipedon Sulfidic material

Address problem soils and situations

Important Concepts and Terminology

Proof positive

If it meets a Field Indicator it is a hydric soil

If it does not meet a Field Indicator it may still be a hydric soil if it meets the definition of a hydric soil

Regional

Listed by Land Resource Region

Addresses “Problem” soils Mollisols and

vertisols Sandy soils Flooded and

ponded soils Red parent

material

Control Sections or Zones

Layers with: High value, low chroma or; Redoximorphic features or; Organic matter accumulations

At at depth Of a certain thickness

Field Indicators Glossary

An * indicates a definition in the glossary that is different from other references such as Soil Taxonomy, Soil Survey Manual, National Soils Handbook, and Field Book for Describing and Sampling Soils.

Important Definition

Depleted matrix Gleyed matrix Organic soil material (muck, mucky

peat, and peat) Mucky mineral

Depleted Matrix

Value Chroma Redox concentrations

≥5 1 Not required

≥6 ≤2 Not required

4 or 5 2 Required

4 1 Required

Moist Color

All color requirements are for moist color.

Features are usually more readily identifiable in moist state; they may be hard to see or missing if the soil is too wet, or too dry.

Depleted Matrix

The range in colors for the depleted matrix is value 4 or more and chroma 1 or 2; however, colors of value 4 and chroma 1 or 2 and value 5 and chroma 2 must have redox concentrations.

A, E, and Calcic Horizons

A, E, and calcic horizons are excluded from the concept of a depleted matrix unless common or many, distinct or prominent redox concentrations as soft masses or pore linings are present.

Depleted Matrices

Gleyed Matrix

All colors found on the gleyed pages with value ≥ 4.

The range of colors for the gleyed matrix is value 4 or more on either of the two color charts.

Gleyed Matrix

Reduced Matrix

Soils that have high value and low chroma in situ but color changes when exposed to air Reduced iron is

present Iron is oxidized

upon exposure

Organic Soil Material

Color of organic soil material may be important Muck – sapric

material Mucky peat –

hemic material Peat – fibric

material

Mucky Modified Textures

Mucky modified mineral soil has 0% clay and between 5 and 12% organic carbon, 60% clay and between 12% and 18% organic carbon, or intermediate amounts of clay and intermediate amounts of organic carbon.

Three Major Divisions

All soils Use regardless of texture Mostly organic based indicators

Sandy soils Loamy soils

Use sandy indicators in sandy layers, and loamy indicators in loamy layers

Indicators Format

1. Alpha numeric symbol2. Short name3. Applicable Land Resource Region4. Description of the indicator5. User notes

Example

Rules for Field Indicator Use

A chroma of 2 or less means that the chroma cannot be higher than 2

Except for F8, F12, F19, F20, and F21 all mineral Field Indicators must have less then 15 cm (6 in) of a chroma > 2 above the indicator.

Soil Surface

The soil surface for Field Indicators A1, A2, A3, S2, and S3 begins at the actual surface.

In LRRs W, X and Y for all other Field Indicators measurements begin at the mineral soil surface.

For all other LRRs all other Field Indicators the measurements should start at the muck or mineral surface.

Combining Indicators

It is permissible to combine certain hydric soil indicators if all requirements of the indicators are met except thickness

The most restrictive requirements for thickness of layers in any indicators used must be met

Minimum Thickness Requirements for

Commonly Combined Indicators S5 – Sandy Redox 4 in. (10 cm) thick starting

within 6 in. (15 cm) of the soil surface S7 – Dark Surface 4 in. (10 cm) thick starting

within 6 in. (15 cm) of the soil surface F1 – Loamy Mucky Mineral 4 in. (10 cm) thick

starting within 6 in. (15 cm) of the soil surface F3 – Depleted Matrix 6 in. (15 cm) thick starting

within 10 in. (25 cm) of the soil surface F6 – Redox Dark Surface 4 in. (10 cm) thick

entirely within the upper 12 in. (30 cm) F7 – Depleted Dark Surface 4 in. (10 cm) thick

entirely within the upper 12 in. (30 cm)

Example of a Soil That is Hydric Based on a

Combination of Indicators

• 3-6 inches meets F6 Redox Dark Surface, but thickness requirement is 4 inches

• 6 to 10 inches meets F3 Depleted Matrix requirements, but thickness requirement is 6 inches

• Add the 3-6 inch and 6 to 10 inch layer thicknesses together to get 7 inches which is thicker than the most restrictive requirement of 6 inches

Example of a Soil That is Hydric Based on a

Combination of Indicators

• 0 to 3 inches meets F6 Redox Dark Surface, but thickness requirement is 4 inches

• 3 to 6 inches meets S5 Sandy Redox, but thickness requirement is also 4 inches

• Combine the thickness of the 2 layers to get 6 inches

Key to Soils that Lack Field Indicators

Dig a hole to 6 in. Do organic soil materials or mucky modified

layers exist? Does chroma ≤ 2 exist? Are there any distinct or prominent redox

concentrations as soft masses or pore linings? Is there a hydrogen sulfide odor? Do stripped zones in a sandy layer exist? Are you in red parent material, a depression,

on a floodplain, or within 200 m of an estuarine marsh and 1 m of mean high water?

If answer is no to all questions, the soil will not meet an indicator.

Summary

Field Indicators are soil morphological features used to identify hydric soils

It is important to understand some of the terminology, concepts, and rules in order to use the Field Indicators of Hydric Soils in the United States