Riparian control of stream-water chemistry: implications for hydrochemicalbasin models

End-member mixing analysis has been used to determine the hydrological stru cture for basin hydrochemical models at several catchments. Implicit in thi s use is the assumption that controlling end members have been identified, and that these end members represent distinct landscape locations. At the P anola Mountain Research Watershed, the choice of controlling end members wa s supported when a large change in the calcium and sulphate concentration o f one of the end members was reflected in the stream water. More extensive sampling of groundwater and soil water indicated, however, that the geograp hic extent of the contributing end members was limited to the riparian zone . Hillslope solutions were chemically distinct from the riparian solutions and did not appear to make a large contribution to streamflow. The dominant control of the riparian zone on stream-water chemistry suggests that hydro logical flow paths cannot be inferred from stream-water chemical dynamics.