Hydric Soils

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Introduction
Criteria
Field Indicators of Hydric Soils in the United States
National Technical Committee for Hydric Soils (NTCHS)
Hydric Soils Technical Notes
Procedure for Submitting Comments

Introduction

Definition

The definition of a hydric soil is a soil that formed under conditions of saturation, flooding or ponding long enough during the growing season to develop anaerobic conditions in the upper part.
 

Field Indicators

Field Indicators are soil characteristics which are documented to be strictly associated only with hydric soils. Field Indicators are an efficient on-site means to confirm the presence of hydric soil. The Field Indicators are designed to identify soils which meet the hydric soil definition without further data collection. Some hydric soils exist for which no Field Indicators have yet been recorded and documented, and to identify these soils as hydric, evidence must be gathered to demonstrate that the definition is met. Additional Field Indicators are being developed and tested.
 

Concept

The concept of hydric soils includes soils developed under sufficiently wet conditions to support the growth and regeneration of hydrophytic vegetation. Soils that are sufficiently wet because of artificial measures are included in the concept of hydric soils. Also, soils in which the hydrology has been artificially modified are hydric if the soil, in an unaltered state, was hydric. Some series, designated as hydric, have phases that are not hydric depending on water table, flooding, and ponding characteristics.
 

Hydric Soils Lists

The lists of hydric soils were created by using National Soil Information System (NASIS) database selection criteria that were developed by the National Technical Committee for Hydric Soils. These criteria are selected soil properties that are documented in Soil Taxonomy (Soil Survey Staff , 1999) and were designed primarily to generate a list of potentially hydric soils from the National Soil Information System (NASIS) database.

Hydric soil lists have a number of agricultural and nonagricultural applications. These include assistance in land-use planning, conservation planning, and assessment of potential wildlife habitat. A combination of the hydric soil, hydrophytic vegetation, and hydrology properties define wetlands as described in the National Food Security Act Manual (Soil Conservation Service, 1994) and the Corps of Engineers (COE) Wetlands Delineation Manual (Environmental Laboratory, 1987) and COE Regional Supplements. Therefore, an area that meets the hydric soil definition must also meet the hydrophytic vegetation and wetland hydrology definitions in order for it to be correctly classified as a jurisdictional wetland.

Criteria

New NASIS Database Selection Criteria

Federal Register Doc. 2012-4733 Filed 2-28-12

The NTCHS has updated the criteria to select map units components for the hydric soils list. The former database selection criteria created to select soils that may meet the definition of hydric soils did not cover the full extent of what is included in the hydric soils definition.

Due to issues with database population, it was easier for a soil scientist to individually populate a field that identified those soil map unit components that meet the definition of hydric soils and which criterion or criteria the soil met rather than to auto-populate using the developed query. The list has evolved from a national list of hydric soil series that may be hydric to a comprehensive list of all map units that have at least one map unit component that is hydric. The list also provides information on what component is at least in part hydric and where it is located on the landscape. Since map unit components may consist of soil series that cross the hydric/nonhydric boundary, a map unit component listed as hydric may also include portions that are non-hydric.

The updated criteria are as follows:

1. All Histels except Folistels and Histosols except Folists; or
        
2. Map unit components in Aquic suborders, great groups, or subgroups, Albolls suborder, Historthels great group, Histoturbels great group, or Andic, Cumulic, Pachic, or Vitrandic subgroups that:
   • Based on the range of characteristics for the soil series, will at least in part meet one or more Field Indicators of Hydric Soils in the United States, or
   • Show evidence that the soil meets the definition of a hydric soil;
      
3. Map unit components that are frequently ponded for long duration or very long duration during the growing season that:
   • Based on the range of characteristics for the soil series, will at least in part meet one or more Field Indicators of Hydric Soils in the United States, or
   • Show evidence that the soil meets the definition of a hydric soil; or
      
4. Map unit components that are frequently flooded for long duration or very long duration during the growing season that:
   • Based on the range of characteristics for the soil series, will at least in part meet one or more Field Indicators of Hydric Soils in the United States, or
   • Show evidence that the soils meet the definition of a hydric soil.
      

Glossary of Terms Used in Hydric Soils Criteria

Anaerobic means a situation in which molecular oxygen is virtually absent from the environment.

Artificial hydric soil means a soil that meets the definition of a hydric soil as a result of an artificially induced hydrologic regime and did not meet the definition before the artificial measures were applied.

Drained means a condition in which ground or surface water has been removed by artificial means.

Flooded means a condition in which the soil surface is temporarily covered with flowing water from any source, such as streams overflowing their banks, runoff from adjacent or surrounding slopes, inflow from the high tides, or any combination of sources.

Frequently flooded, ponded, saturated: a frequency class in which flooding, ponding, or saturation is likely to occur often under usual weather conditions (more than 50 percent chance in any year, or more than 50 times in 100 years).

Hydric soil means a soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part. This definition includes soils that developed under anaerobic conditions in the upper part but no longer experience these conditions due to hydrologic alteration such as those hydric soils that have been artificially drained or protected (e.g., ditches or levees).

Long duration means a duration class in which inundation for a single event ranges from 7 days to 1 month.

Map unit means a collection of areas defined and named the same in terms of their soil components or miscellaneous areas or both.

Map unit components means the collection of soils and miscellaneous areas found within a map unit.

Phase, map unit means a subdivision of a map unit based on features that affect its use and management (e.g., slope, surface texture, stoniness, and thickness).

Ponded means a condition in which water stands in a closed depression. The water is removed only by percolation, evaporation, or transpiration.

Very long duration means a duration class in which inundation for a single event is greater than 1 month.

National Technical Committee for Hydric Soils (NTCHS)

1. Provide continuing technical leadership in the formulation, evaluation, and application of hydric soil definition, criteria, indicators, and the glossary.
    
2. Annually update and distribute a national list of hydric soils, as necessary.
    
3. Refine and maintain the Field Indicators of Hydric Soils in the United States. Changes to the Field Indicators will be recommended by the sub-committee to the entire NTCHS, and must be reviewed and approved before adopting.
    
4. Communicate and respond to public comment regarding suggested changes in hydric soil definition, criteria, lists and field indicators.
    
5. Determine soil, hydrologic, and climatic data necessary to more accurately define and determine hydric soils (technical methodology and standards).

Minutes of Annual Meetings (link to Box)

Hydric Soils Technical Notes

Hydric Soils Technical Notes contain National Technical Committee for Hydric Soils (NTCHS) updates, insights, and clarifications of the publication “Field Indicators of Hydric Soils in the United States” (USDA, NRCS, 1996 and 1998). Comments and suggestions for additional notes are encouraged. Each note has the name of the compiler and an email address to send comments.

Hydric Soils Technical Notes (link to Box)

Procedure for Submitting Comments

List of Hydric Soils or Criteria

If you have comments on the criteria for hydric soils or if soils should be removed from or added to the list of hydric soils, gather supporting data to make your case and either:

Submit the documentation and the proposed changes in the criteria along with your supporting data to Lenore Vasilas, Chair, National Technical Committee for Hydric Soils (NTCHS) or to your NRCS State Office with copies to Lenore Vasilas.

Supporting documentation must include information on the geographic area (soil survey area) and hydrology, vegetation, and soil characteristics that support changing the definition of the soil series. A written response will be given to inquiries within a reasonable time.
 

Field Indicators

Guidelines for requesting changes to field indicators are as follows:

1. Adding indicators or changing existing indicators: Minimally, the following should accompany all requests for additions and changes to existing hydric soil indicators in Field Indicators of Hydric Soils in the United States:
   • Detailed pedon descriptions of at least three pedons that document the addition or change and detailed pedon descriptions of the neighboring non hydric pedons.
   • Detailed vegetative data collected to represent the vegetation of the six pedons.
   • Saturation (inundation) data and Eh data for a duration that captures the saturation cycle (dry-wet-dry) of, at least, one of the hydric pedons and one of the non hydric pedons. Precipitation and in-situ soil-water pH data from the same sites should also be provided.
         
2. Adding a Test Indicator: Minimally, the following should accompany all requests for adding a test indicator to Field Indicators of Hydric Soils in the United States:
   • Detailed pedon descriptions of at least three pedons that document the test indicator and detailed pedon descriptions of the neighboring non hydric pedons.
   • Detailed vegetative data collected to represent the vegetation of the six pedons.
      
3. All requests involving 1 and 2 above, additionally require a short written plan that:
   • Identifies the problem,
   • Explains the rationale for the request, and
   • Provides the following:
     • person responsible and point of contact (e-mail, mail addresses, and phone number)
     • timeline for supporting data and final report to be delivered to NTCHS
     • timeline needed for final NTCHS decision
     • partners involved in the project

Requests, plans, and data should be sent to Lenore Vasilas, Chair, National Technical Committee for Hydric Soils (NTCHS).