map units lists identify all map units that are either 

 named by a hydric soil or that have a potential of 

 having hydric soil inclusions. The lists provide the 

 map unit symbol, the name of the hydric soil part 

 or parts of the map unit, information on the hydric 

 soil composition of the map unit, and probable 

 landscape position of hydric soils in the map unit 

 delineation. The county lists also include map units 

 named by miscellaneous land types or higher levels 

 in "Soil Taxonomy" that meet hydric soil criteria. 



Soil Surveys 



3.23. The SCS publishes county soil surveys for 

 areas where soil mapping is completed. Soil sur- 

 veys that meet standards of the National Coopera- 

 tive Soil Survey (NCSS) are used to identify delin- 

 eations of hydric soils. These soil surveys may be 

 published (completed) or unpublished (on file at lo- 

 cal SCS district offices). Published soil surveys of 

 an area may be obtained from the local SCS district 

 office or the Agricultural Extension Service office. 

 Unpublished maps may be obtained from the local 

 SCS district office. 



3.24. The NCSS maps four kind of map units: (1) 

 consociations, (2) complexes, (3) associations, and 

 (4) undifferentiated groups. Consociations are soil 

 map units named for a single kind of soil (taxon) or 

 miscellaneous area. Seventy-five percent of the 

 area is similar to the taxon for which the unit is 

 named. When named by a hydric soil, the map unit 

 is considered a hydric soil map unit for wedand de- 

 terminations. However, small areas within these 

 map units may not be hydric and should be exclud- 

 ed in delineating wedands. 



3.25. Complexes and associations are soil map 

 units named by two or more kinds of soils (taxa) or 

 miscellaneous areas. If all taxa for which these map 

 units are named are hydric, the soil map unit may 

 be considered a hydric soil map unit for wetland 

 determinations. If only pan of the map unit is made 

 up of hydric soils, only those portions of the map 

 unit that are hydric are considered in wetland deter- 

 minations. 



3.26. Undifferentiated groups are soil map units 

 named by two or more kinds of soils or miscellane- 

 ous areas. These units are distinguished from the 

 others in that "and" is used as a conjunction in the 

 name, while dashes are used for complexes and as- 

 sociations. If all components are hydric, the map 



unit may be considered a hydric soil map unit. If 

 one or more of the soils for which the unit is 

 named are nonhydric, each area must be examined 

 for the presence of hydric soils. 



Use of the Hydric Soils List and 

 Soil Surveys 



3.27. The hydric soils list and county soil surveys 

 may be used to help determine if the hydric soil cri- 

 terion is met in a given area. When making a wet- 

 land determination, one should first locate the area 

 of concern on a soil survey map and identify the 

 soil map units for the area. The list of hydric soils 

 should be consulted to determine whether the soil 

 map units are hydric. If hydric soil map units are 

 noted, then one should examine the soil in the field 

 and compare its morphology with the correspond- 

 ing hydric soil description in the soil survey report. 

 If the soil's characteristics match those described 

 for hydric soil, then the hydric soil criterion is met, 

 unless the soil has been effectively drained (see 

 disturbed areas section, p. 50). In the absence of 

 site-specific information, hydric soils also may be 

 recognized by field indicators. 



Field Indicators 



3.28. Several field indicators are available for de- 

 termining whether a given soil meets the definidon 

 and criteria for hydric soils. Other factors to con- 

 sider in recognizing hydric soils include obligate 

 wetland plants, topography, observed or recorded 

 inundation or soil saturation, and evidence of hu- 

 man alterations, e.g., drainage and fiUing. Any one 

 of the following may indicate that hydric soils are 

 present: 



1) Organic Soils - Various peats and mucks are 

 easily recognized as hydric soils. Organic soils that 

 are cropped are often drained, yet the water table is 

 closely managed to minimize oxidation of organic 

 matter. These soils often retain their hydric soil 

 characteristics and, if so, meet the wedand hydrol- 

 ogy criterion. 



2) Histic epipedons - A histic epipedon (organ- 

 ic surface layer) is an 8- to 16-inch organic layer at 

 or near the surface of a hydric mineral soil that is 

 saturated with water for 30 consecutive days or 

 more in most years. It contains a minimum of 20 

 percent organic matter when no clay is present or a 



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