A three-component end-member analysis of streamwater hydrochemistry in a small Japanese forested headwater catchment

Intensive water sampling in conjunction with hydrological observations was conducted during three different rainstorms in order to understand the effects of rainfall events on the temporal variation of streamwater chemistry in a small headwater forest catchment. Concentrations of Na+ and SO42- decreased as the discharge rate increased. Hydrograph separation of the components was made using the three-component model based on the end-members mixing analysis (EMMA). The three end-members were: 1. the groundwater in the saturated zone that prescribes the chemistry of the baseflow; 2. the throughfall that dilutes the streamwater; 3. the groundwater in the transient saturated zone prescribed, which was dependent on the groundwater level. When the groundwater level was lower, only the two components, groundwater in the saturated zone and throughfall, affected the streamwater chemistry. When the groundwater level rose and the saturated zone spread, the groundwater in the transient saturated zone became the third component. When the groundwater in the transient saturated zone contributed to the discharge, this component became the dominant source and the streamwater chemistry was affected by the groundwater chemistry in the transient saturated zone. When this component was discharged as the saturation overland flow, the streamwater chemistry was greatly affected by this component. Copyright (C) 2001 John Wiley & Sons, Ltd.