Chemical and Morphological Distinctions between Vertical and Lateral Podzolization at Hubbard Brook

Classical podzolization studies assumed vertical percolation and pedon‐scale horizon development. However, hillslope‐scale lateral podzolization also occurs where lateral subsurface water flux predominates. In this hydropedologic study, 99 podzols were observed in Watershed 3, Hubbard Brook Experimental Forest, New Hampshire. Soil horizon samples were extracted with citrate–dithionite (d) and acid ammonium oxalate (o) to quantify Fe d , Mn d , Al o , and Fe o . Optical density of oxalate extract (ODOE) was measured to assess spodic C. Amorphous organometallic complexes (AOC) were observed in thin section, for which Al, Fe, Mn, and C were quantified using scanning electron microscopy–energy dispersive X‐ray spectroscopy. Porosity and AOC/mineral ratio were calculated for thin section images using ImageJ. Laterally developed spodic horizons were twice as thick as vertically developed spodic horizons and contained higher concentrations of Al and Mn but lower Fe and C. Vertically developed spodic horizons had crumb microstructure with higher porosity, while laterally developed spodic horizons were more infilled. Aluminum + 0.5Fe and ODOE in the surface of laterally developed podzols were high and lacked contrast with the spodic horizon, making Spodosol classification problematic. Vertically developed spodic horizons form by solutional translocation and precipitation of AOC under unsaturated conditions. However, laterally developed spodic horizons could form via lateral translocation of solutes or physical transport and deposition of colloidal AOC with unsaturated or saturated flow. This study demonstrates the importance of lateral podzolization in producing soils with distinctive morphology, composition, and classification. Future studies or mapping efforts in podzolized catchments should incorporate these different pedogenic processes.