Hydric Soils - 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. 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 (from http://soils.usda.gov/use/hydric/intro.html).


A list of Dane County hydric soils was developed using the National Hydric Soils Criteria.  It lists map units in the soil survey area which contain hydric components or contain hydric inclusions.  The hydric list is updated whenever additional hydric components or inclusions are identified by field investigations, or there are changes in the National Hydric Soils Criteria (USDA Natural Resources Conservation Service-Wisconsin Technical Guide Section II, March 1996).


Hydric Soils Criteria Codes and Definitions

From "Hydric Soils of the United States" (USDA Miscellaneous Publication No. 1491, June, 1991, as revised in the Federal Register, Vol. 60, No. 37, February 24, 1995)


1. All Histosols, except Folists, or

2. Soils in Aquic suborders, great groups, or subgroups, Albolls suborder, Aquisalids, Pachic subgoups, 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) A 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) A 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/hr in all layers within 20 in, or


(3) A 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/hr in any layer within 20 in, or


3. Soils that are frequently ponded for long or very long duration during the growing season, or

4. Soils that are frequently flooded for long or very long duration during the growing season.


More information:


Hydric Table Creation – Dane County
April 3, 2006

At this time there is no hydric table with a 1:1: correlation between the mapunit and the hydric definition (neither from the Federal NRCS or State NRCS), for both hydric soils and non-hydric soils likely to contain hydric inclusions.  Therefore, Dane County created their own hydric soils table based on values in tables from NRCS.  If NRCS creates such a table in the future, the Dane County table will be replaced.
Process Step:
1.  Tabular soil data was downloaded in 2006 from the soil data mart:

1.  The resultant Access .mdb was opened, and all the map units were selected.  The Hydric Soils report was run, include minor components

2.  Open, Query, Report – Hydric Soils (view the report to assign hydric values to soil map units)

The following is information provided by Carl Wacker, Assistant State Soil Scientist, WI NRCS. 
Possible hydric classifications of soil map units if NRCS NASIS soil data is aggregated:
ALL = all components are hydric
MOST = all components included in the mapunit name are hydric, some unnamed components are not
PART = map unit contains both hydric and non-hydric named components
INCL = all named components are non-hydric, some unnamed components are hydric
NONE = no components are hydric
UN = hydric class not determined

The soils that have one hydric component which is 100% of the mapunit are all hydric or “hydric” (ex. Ad Adrian Muck).  DeA has 2 hydric components (which are both inclusions) so the map unit is “non hydric but likely to contain hydric inclusions”.  Note that if there was a soil that has 2 major components (one hydric and one not), these mapunits would be “partially hydric”; however, Dane County does not have any soil map units like this.  Map units not listed in the table are “not hydric”.

3.  Using the above information (with the Hydric Soils table) the Dane County soil map units with 100% are hydric and the other ones are non hydric but likely to contain hydric inclusions.

4.   Finally, Dane County implemented one change from the NRCS Hydric Soil table.  For the miscellaneous land use type GP (gravel pit), NRCS called this hydric.  Per discussion with former NRCS Resource Soil Scientist, Dave Roberts, he said that it was “extremely unlikely that there is a hydric soil, or any other soil, that will be found in a gravel pit.”  Therefore, we classified this soil map unit type as not hydric.