Stream water chemistry in a steep headwater basin with high relief

Abstract

Soil water, spring water and stream water were monitored to investigate the behaviour of dissolved loads in relation to subsurface flow processes in a steep, high‐relief mountainous headwater basin in central Japan. Concentrations of Cl⁻, NO₃⁻, Na⁺, K⁺, Mg²⁺ and SiO₂ of hillslope soil water are almost the same as those of spring water and stream water, whereas concentrations of Ca²⁺, SO₄²⁻ and HCO₃⁻ in spring water and stream water are considerably higher than those in hillslope soil water. Clear negative correlations are observed between Ca²⁺, Mg²⁺, Na⁺, SO₄²⁻, HCO₃⁻ and SiO₂ concentrations and discharge rate for spring and stream waters. These results suggest that stream water chemistry in this basin is influenced by subsurface water flowing through bedrock. Dilute, short residence subsurface flow through bedrock contributes to the stream during high flow periods, and concentrated, long residence subsurface flow contributes to the stream during low flow periods. The SiO₂ data in spring and stream waters indicate that the residence time of subsurface water flowing through the bedrock is relatively short in this basin compared with that observed in previous studies of other basins. Copyright © 2001 John Wiley & Sons, Ltd.