Mobility of iron-oxide associated elements in pseudogley soils; influence of parent material age and land use

Abstract

Pseudogleys, a colloquial term for some Retisol-classified soils, are subjected to periodic water stagnation beneath their surface resulting in a spatially and temporally heterogeneous redox environment, which produces patterns from the dissolution and precipitation of Fe (oxy)hydroxide minerals. This study investigates the mobility and redistribution of other soil elements, namely metals, associated with reducible Fe (oxy)hydroxide minerals (extracted by citrate-bicarbonate-dithionite) in four Danish pseudogley profiles under forest or agricultural land use and with Saalian-age or Weichselian-age parent material. Of the analyzed elements, a depletion of Fe and Mn was observed in the upper horizons, while Co, Cr, Cu, Ni, and V showed mobility in the matrix of pseudogley profiles, influenced by redox activity, podsolization, and clay illuviation soil forming processes. Further, Cr and V showed horizontal redistribution in the argic horizon, likely due to an Fe (oxy)hydroxide-influenced precipitation gradient along the macropore structures. The influence of agricultural land use suggests reduced mobility of Fe, Cr, and V but not Mn, Co, Cu, or Ni compared to forested land use, which supports greater acidification and podsolization processes. Older, Saalian-age parent material led to more mottled retic properties while younger, Weichselian-age parent material produced glossic and retic properties. The findings of this study conclude that not only Fe and Mn are influenced and mobilized by the redox conditions of pseudogley soils, but that some elemental redistribution may also be influenced directly by an Fe-controlled gradient along the macropore structures.