The Distribution and "Problematic" Nature of F21 (Red Parent Material) Hydric Soils.

It has long been recognized that soils derived from certain red parent materials (RPM) fail to develop hydric features typical of wetlands, creating problematic situations for wetland delineators. To address this issue, the National Technical Committee for Hydric Soils approved Field Indicator F21 (Red Parent Material) to identify these areas. For red soils to qualify as problematic, they must have Color Change Propensity Index (CCPI) values below 30. Based on CCPI analyses of more than a thousand soil samples collected from around the country, a national draft map has been compiled to identify areas that are likely to contain soils derived from problematic RPM. Although progress has been made in recognizing the geographical extent of these problem soils, the cause of their problematic nature remains uncertain. We have observed that problematic RPM soils occur in association with sedimentary, hematite-rich “red bed” deposits, and the alluvial and glacial materials derived from them. Several mineralogical and pedological hypotheses have been identified as possible causes of the “problematic” nature of F21 RPM soils that are mostly related to the hematitic mineralogy of the associated iron oxides. A variety of methods have been employed to evaluate these hypotheses, and preliminary results from mineralogical investigations will be presented and discussed.