Hydric Soils - NASIS Database Selection Criteria

The following National Soil Information System (NASIS) database selection criteria reflect those soils that may meet the definition of hydric soils. Criteria 1, 3, and 4 serve as both database criteria and as field indicators for identification of hydric soils; however, proof of anaerobic conditions is also required with criteria 1, 3, and 4. Criterion 2 serves only to retrieve soils from the database. In addition, the wording of criteria 1 and 2 were changed in 2000 to incorporate recent changes in Soil Taxonomy (Soil Survey Staff, 1999). Please note that these changes did not cause any soils to be added or deleted from the list.

1. All Histels except Folistels and Histosols except Folists, or
    

2. Soils in Aquic suborders, great groups, or subgroups, Albolls suborder, Historthels great group, Histoturbels great group, Andic, Vitrandic, and Pachic subgroups, or Cumulic subgroups that are:

   a. Somewhat poorly drained with a water table^* equal to 0.0 foot (ft) from the surface during the growing season, or

   b. poorly drained or very poorly drained and have either:
    
   1. water table^* equal to 0.0 ft during the growing season if textures are coarse sand, sand, or fine sand in all layers within 20 inches (in),
      
      or for other soils
       
   2. water table^* at less than or equal to 0.5 ft from the surface during the growing season if permeability is equal to or greater than 6.0 in/hour (h) in all layers within 20 in,
      
      or
       
   3. water table^* at less than or equal to 1.0 ft from the surface during the growing season if permeability is less than 6.0 in/h in any layer within 20 in, or
       
3. Soils that are frequently ponded for long duration or very long duration during the growing season, or
    
4. Soils that are frequently flooded for long duration or very long duration during the growing season.

Glossary

anaerobic: a situation in which molecular oxygen is virtually absent from the environment.

artificial hydric soil: 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.

biologic zero: the soil temperature, at a depth of 50 cm (19.7"), below which the growth and function of locally adapted plants are negligible.

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

flooded: 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).

growing season: the portion of the year when soil temperatures are above biologic zero at 50 cm (19.7"). The following growing season months are assumed for each of the soil temperature regimes of Soil Taxonomy:

hydrophytic vegetation: plant life growing in water or on a substrate that is at least periodically deficient in oxygen as a result of excessive water content.

long duration: a duration class in which innundation for a single event ranges from 7 days to 1 month.

permeability: the ease with which water passes through a bulk mass of soil or a layer of soil. In the Map Unit Interpretation Record (MUIR) database, permeability is expressed as the number of inches per hour that water moves downward through the saturated soil.

phase, soil: a subdivision of a soil series based on features that affect its use and management (e.g. slope, surface texture, stoniness, and thickness).

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

poorly drained: water is removed from the soil so slowly that the soil is saturated periodically during the growing season or remains wet for long periods.

saturated: a condition in which all voids (pores) between soil particles are filled with water.

soil series: a group of soils having horizons similar in differentiating characteristics and arrangements in the soil profile, except for texture of the surface layer.

somewhat poorly drained: water is removed slowly enough that the soil is wet for significant periods during the growing season.

very long duration: a duration class in which innundation for a single event is greater than 1 month.

very poorly drained: water is removed from the soil so slowly that free water remains at or on the surface during most of the growing season.

^*water table: the upper surface of ground water where the water is at atmospheric pressure. In the Map Unit Interpretation Record (MUIR) database, entries are made for the zone of saturation at the highest average depth during the wettest season. It is at least six inches thick and persists in the soil for more than a few weeks. In other databases, saturation, as defined in Soil Taxonomy (Soil Survey Staff. 1999), is used to identify conditions that refer to water table in Criteria 2.