Soil sulfur content and its spatial distribution in a small catchment covered by volcanic soil in the montane zone of central Japan

Abstract High concentrations of organic C and Al/Fe oxides, and low bulk density are responsible for the accumulation of large amounts of S compounds in volcanic soils. The purpose of our study was to clarify the spatial distribution of S compounds and determine the factors governing that distribution within the Katsura Headwater Catchment, a small drainage basin covered by volcanic soil in a mountainous area of the North Kanto district, central Japan. Geostatistical analysis revealed a strong spatial dependence of total S concentration throughout the catchment area. Total S concentrations were higher on upper slopes than on lower slopes, and higher in deeper soils (20–50 cm depth) than in surface soils (0–20 cm depth). Our analyses also revealed similar spatial variations of the characteristic pedogenic volcanic minerals properties (i.e., concentrations of oxalate extractable Al, Fe, and Si), total C concentrations, and bulk density. The strong relationships of total S with the pedogenic mineral properties indicate that the accumulation of S in the soils is governed predominantly by the abundance of those pedogenic minerals, and that the influence of volcanic ash as a parent material is reflected more strongly in residual soils than in colluvial soils. Because the total S concentrations of the residual and colluvial soils differ, so too do the S pools in the uppermost 50 cm of these soils: residual soils retain larger amounts of S (2030 ± 590 kg S ha –1 on average) than colluvial soils (1400 ± 590 kg S ha –1 on average). Our results indicate that volcanic ash that remains in situ on the upper slopes of the small Katsura Headwater Catchment contributes strongly to the accumulation and spatial variation of S. Total C inputs from plant communities might also influence S accumulation, particularly in surface soils.