Stream water chemistry in a steep headwater basin with high relief

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. Concentra tions of Cl-, NO3-, Na+, K+, Mg2+ and SiO2 of hillslope soil water are almo st the same as those of spring water and stream water, whereas concentratio ns of Ca2+, SO42- and HCO3- in spring water and stream water are considerab ly higher than those in hillslope soil water. Clear negative correlations a re observed between Ca2+, Mg2+, Na+, SO42-, HCO3- and SiO2 concentrations a nd discharge rate for spring and stream waters. These results suggest that stream water chemistry in this basin is influenced by subsurface water flow ing through bedrock. Dilute, short residence subsurface flow through bedroc k contributes to the stream during high flow periods, and concentrated, lon g residence subsurface flow contributes to the stream during low flow perio ds. The SiO2 data in spring and stream waters indicate that the residence t ime of subsurface water flowing through the bedrock is relatively short in this basin compared with that observed in previous studies of other basins. Copyright (C) 2001 John Wiley & Sons, Ltd.