降水による地下水水質の変動

抄録

Groundwater samples were collected from three drilled wells situated in a forest area, after ordinary and heavy precipitation events. Two patterns of concentration change of dissolved species were observed after ordinary precipitation event. One, examplified by the behavior of Ca²⁺ and alkalinity, represents a simple dilution of ground-water by penetrating rainwater. The other, characteristic of NO₃^- and silica, indicates a temporary increase in concentrations of these species. The nitrate was derived from dissolution of dry fallout, and the silica from dissolution of amorphous aluminosilicates formed by weathering of silicate rocks. After a heavy precipitation, the pattern of concentration change can be explained by a strong dilution of groundwater by rainwater. Only silica concentration remained virtually unchanged, thus supporting leaching of silica from aluminosilicates by descending rainwater.