Ion solubilization in surface soil layers of montane region with heavy snowfall

Abstract

Although eluvial (E) horizons of podzols typically form on sandy soils, they can also form in acidic clayey soils. Two non-exclusive hypotheses for E-horizon formation in clayey soils are podzolization and the reductive dissolution of iron (Fe). To analyze the effects of redox reactions on Fe solubilization in montane soils in regions with heavy snowfall, we measured the redox potential (Eh), pH, and Fe2+ concentration in soil solutions sampled from the Midagahara peatland of Mt. Tateyama and Mt. Naeba. We also conducted continual in situ Eh monitoring of soils under snow cover in a beech forest on Mt. Naeba. In the Midagahara peatland, Eh decreased with increasing clay content and was lowest in E horizons. A mineral stability diagram of the soil solution data, in which (pH + 3pe) was expressed as a function of log [Fe2+], suggests that ferrihydrite dissolution from the E horizons and precipitation of the other Fe oxides (lepidocrocite or goethite) in the B horizons are ongoing processes. A combination of low pH and reducing conditions in clayey soils can increase the loss of Fe oxides to form impermeable E horizons. Continual monitoring of Eh in the soil of Mt. Naeba revealed a sharp drop in Eh under heavy snow cover during winter. The reducing conditions in winter, along with consistently low pH, are favorable for the formation of E horizons in clayey soils, which lead to poor drainage and summer flooding. The combination of clayey E horizons and flooding with snowmelt are required for peat accumulation in the Midagahara peatland.