Field Indicators of Hydric Soils in the United States - ITC

Field Indicators of Hydric Soils inthe United StatesIntroductionField Indicators of Hydric Soils in the UnitedStates (hereafter referred to as Indicators) is a guideto help identify and delineate hydric soils in the field(fig. 1). Indicators are not intended to replace orrelieve the requirements contained in the definitionof a hydric soil. The list of Indicators is considered tobe dynamic; changes and additions are anticipatedannually. The section To Comment on the Indicatorsprovides guidance to recommend changes, deletions,and additions. Any modifications to the Indicatorsmust be approved by NRCS and the National TechnicalCommittee for Hydric Soils. To properly use theIndicators, a basic knowledge of soil landscaperelationships and soil survey procedures is necessary.The indicators are designed to be regionally specific.Each indicator provides the Land Resource Regions(LRRs) or the Major Land Resource Areas (MLRAs)in which it can be used. The geographic extent ofLRRs (fig. 2) and MLRAs are defined in USDA AgricultureHandbook 296 (USDA, SCS, 1981). LRR specificIndicators are listed in appendix A and describedin section Field Indicators of Hydric Soils.The indicators are used to identify the hydric soilcomponent of wetlands; however, some hydric soilsdo not have any of the currently listed indicators.Therefore, the absence of any listed indicator doesnot exclude the soil from being classed as hydric.Such soils should be studied and their characteristicmorphologies identified for inclusion in this guide.days. Saturation or inundation when combined withmicrobial activity in the soil causes a depletion ofoxygen. This anaerobiosis promotes biogeochemicalprocesses, such as the accumulation of organicmatter and the reduction, translocation, and/oraccumulation of iron and other reducible elements.These processes result in characteristic morphologiesthat persist in the soil during both wet and dryperiods, making them particularly useful for identifyinghydric soils.Figure 1.The field indicators are to be used to delineatehydric soils. The soil on the right is hydric thathas the Indicator S6 Stripped Matrix starting ata depth of about 14 cm, and the soil on the leftis nonhydric with the Stripped Matrix starting ata depth of about 18 cm.ConceptHydric soils are defined as soils that formed underconditions of saturation, flooding, or ponding longenough during the growing season to develop anaerobicconditions in the upper part of the soil (FederalRegister, July 13, 1994).Nearly all hydric soils exhibit characteristic morphologiesthat result from repeated periods of saturationor inundation, or both, for more than a few(430, FIHS, Ver. 5.01, March 2003) 1