Compositional and mineralogical (primary silicate minerals, volcanic glass, secondary minerals) properties of weathered basaltic ash soil ("Andisol") derived from Mt. Fuji, central Japan, with an age of ca. 6,000 y.B.P. to 240 y.B.P. were studied. X-ray fluorescence analysis indicates that the order of relative elemental mobilities during the weathering is Na, Ca > K > Mg > P > Si > Ti, Fe > Al > Mn. The trends of soil water chemistry (H4SiO4 concentration) with depth were calculated based on a dissolution (volcanic glass)-precipitation (allophane) kinetics-fluid flow coupling model. In order to calculate the trends, the data on present-day annual rainfall, solubility of basalt glass, porosity and specific gravity of the soil, deposition rate of volcanic ash and grain size of volcanic glass were used. The calculated results were compared with analytical trends of soil water chemistry. From this comparison, the dissolution rate constant of basalt glass was estimated to be 10-10.2±0.5 (mole Si m-2s-1). This value is consistent with previously determined experimental long-term dissolution rate constant of basalt glass reported in the literature (Berger et al., 1994).

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Dissolution rates of silicate minerals in aqueous solution : a comparison of experimental and field results and interpretation of groundwater chemistry by a coupled fluid flow-dissolution kinetics model

An estimate of dissolution rate constant of volcanic glass in volcanic ash soil from the Mt. Fuji area, central Japan

As mountainous areas provide abundant water resources to lower elevations, and alpine zones are major recharge areas for water resources, it is important to understand water storage and discharge processes in these zones. Regarding water storage, sedimentary structures (e.g., talus and moraines) in alpine zones function as aquifers. However, the functions of vegetation, thought to contribute to water recharge and storage in forested watersheds, have rarely been investigated. Accordingly, we evaluated the influence of alpine vegetation on water storage processes in alpine zones. Two intensive field surveys were conducted on August 17 and October 5, 2019, in the alpine headwaters of Mt. Norikura in the Northern Japan Alps. Chemical analyses were conducted of rainwater, snowmelt water, and runoff water from bare and vegetated catchments. From the results, a two-component separation was conducted to calculate the contributions of precipitation and groundwater components to runoff water. Our results implied that runoff water from vegetated catchments was in contact with the regolith for longer, with the contribution of groundwater being higher in this runoff water. Moreover, the groundwater component contribution tended to increase as the ratio of vegetation area to bare area in each catchment increased, suggesting a higher water storage function for vegetated areas. In other words, the subsurface water flow should be slower in vegetated areas due to the presence of vegetated soils compared to bare areas where coarse-grained sediments are dominant. Accordingly, the alpine vegetated area has a higher water storage function than the alpine bare area. 

Dissolution rates of silicate minerals in aqueous solution : a comparison of experimental and field results and interpretation of groundwater chemistry by a coupled fluid flow-dissolution kinetics model

Citations

An estimate of dissolution rate constant of volcanic glass in volcanic ash soil from the Mt. Fuji area, central Japan

Influence of alpine vegetation on water storage and discharge functions in an alpine headwater of Northern Japan Alps

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