The podzol hydrosequence of Itaguare (Sao Paulo, Brazil). 1. Geomorphology and interpretation of profile morphology

A continuous section of hydromorphic to well-drained podzols in a Late Pleistocene marine terrace of southeastern Brazil offers a unique opportunity for a detailed interpretation of podzol morphology. The soils show very deep and homogeneously colored B horizons in the most hydromorphic members, where the predominant water movement in the B horizon appears to be lateral. Upon improving drainage, the effect of roots becomes evident by the increase in root-related E-horizon tongues, while the B horizon becomes shallower and shows a more pronounced accumulation of organic matter at its top. Only where the groundwater does not periodically reach into the B horizon, a homogeneous distribution of Fe is found in the Bs horizon. The sequence shows clear effects of decomposition of the B horizon through growth of the E horizon, sometimes leading to isolated remnants of the B horizon, on the fringes of which organic matter may accumulate. Especially the hydromorphic profiles show large mottles with roughly concentric structures in the B horizon where organic matter has been depleted. In the poorly drained members of the sequence, the effect of improved drainage by erosion of the cliff is visible in black instead of brown colors of the upper B horizon. In all profiles, the conversion of the former B horizon into an E horizon is accompanied by strong biological activity in the form of burrows.