Morphologic and hydrologic distinctions between shallow and deep podzolized carbon in the southeastern United States Coastal Plain

Podzolization imparts soils and landforms of the southeastern United States Coastal Plain with two distinct pools of organic carbon (C), referred to as shallow podzolized C (SPC) and deep podzolized C (DPC). We evaluate podzolization across two catenas, and across the state of Florida, to establish that SPC and DPC are morphologically and hydrologically distinct. We demonstrate that SPC lightens downward (i.e. a Bh horizon with a darker top than bottom) and accumulates below low chroma material, while DPC darkens downward and accumulates below higher chroma material. We interpret these distinct morphologies to be manifestations of separate podzolization processes that are controlled by unique components of soil hydrology. Our analyses support existing notions that SPC is a product of vadose zone hydrology; formed within a pronounced eluvial-illuvial system where C, metals (predominately aluminum), and clay-sized particles are mobilized and immobilized together when near surface saturation thresholds are met. Our work however also identifies DPC to be a product of phreatic zone hydrology; part of an eluvial-illuvial system where C is translocated without metals or clays and immobilized when subsoil saturation thresholds are met. Recognizing the morphologic and hydrologic differences between SPC and DPC not only provides insights into interactions between soil hydrology and terrestrial C cycling in low-relief landforms, but also by incorporating these differences into field-based assessments soil scientists can improve their interpretations and communication of the hydropedology and podzolization.