Field Indicators of Hydric Soils in the United States - ITC

Field Indicators of Hydric SoilsRedox depletions. Bodies of low chroma (2 or less)having value 4 or more where Fe/Mn oxideshave been stripped or where both iron andmanganese oxides and clay have been stripped.Redox deletions contrast distinctly or prominentlywith the matrix. See Vepraskas (1994) forcomplete description.Redoximorphic features. Features formed by theprocesses of reduction, translocation, or oxidationof Fe and Mn oxides. Formerly calledmottles and low chroma colors (fig. 38). SeeVepraskas (1994) for complete description.Reduced matrix. Soil matrices that have low chromaand high value, but whose color changes in hue orchroma when exposed to air. See Vepraskas(1994) for complete description.*Reduction. For the purpose of the Indicators, whenthe redox potential (Eh) is below the ferric/ferrous iron threshold as adjusted for pH. Inhydric soils, this is the point when the transformationof ferric iron (Fe+++) to ferrous iron(Fe++) occurs (fig. 39).Relict features. Soil morphological features that donot reflect recent hydrologic conditions ofsaturation and anaerobiosis (fig. 40). SeeVepraskas (1994) for complete description.*Sapric. See Muck.Saturation. When the soil water pressure is zero orpositive, most all the soil pores are filled withwater.Sharp boundary. Used to describe redoximorphicfeatures that grade sharply from one color toanother. The color grade is commonly less than0.1 millimeter wide (fig. 40).Figure 38. Redoximorphic features as required in many ofthe Indicators. These redox concentrationsoccur as pore linings along root channels andped faces.Soft masses. Redox concentrations that are nothard, frequently within the matrix, and whoseshape is variable.Soil texture. The weight proportion of the soilseparates for particles less than 2 mm.Figure 39. Reduction would probably occur in this saltmarsh throughout the year. The Indicator A4Hydrogen Sulfide would most likely occur here.Figure 40. Sharp boundaries, such as those shown here,may indicate these redoximorphic features arerelict.(430, FIHS, Ver. 5.01, March 2003) 29