Multiple Faces of Podzolization on the Coastal Plain of the Southeastern United States.

Podzolic horizons (Bh and B’h) occur extensively on the Coastal Plain of the SE United States. Their occurrence across landforms reflects hydrologic-geomorphic interactions, is central to carbon cycling, and is fundamental to soil interpretations through space and time. Podzolic horizons are most prevalent, and most extensively studied, in the top two meters of “flatwoods” landforms, characterized by fluctuating water tables and seasonal near-surface saturation. These hydrologic conditions foster podzolization by achieving biogeochemical thresholds to initiate organo-metal complexation and translocation that lead to Aquod formation. Transitions from Aquods to better-drained soils are marked by diminished expression and ultimate disappearance of these near surface podzolic horizons. The Coastal Plain also contains massive pools of deep podzolic C (DPC) that transgress near-surface drainage gradients and extend well below two meters, commonly escaping routine soil observations. DPC is strongly associated with landforms derived from relict marine shorelines where it occurs subjacent to Spodosols and Entisols. It is similar in composition to Aquod Bh horizons, but tends to be much thicker and to have upper boundaries that darken gradually rather than abruptly with depth. These morphological distinctions suggests differences in mode of formation as influenced by shallower versus deeper hydrologic conditions. A distinct subset of soils with subjacent DPC, classifying as Entisols, have an extremely well expressed podzolic E horizon that extends from the soil surface to the upper DPC boundary. Finally, many former terrestrial landforms that accumulated podzolic C have been truncated or drowned by rising sea level in areas along the Gulf and Atlantic coasts of Florida. The fate of podzolic C exposed to coastal subaqueous conditions is uncertain.