Abstract
On the basis of hydrological processes in a well-characterized hillslope (0.65 ha), we analyzed the effects of flow paths on dissolved organic carbon (DOC) concentrations in a headwater stream (catchment area, 103 ha) during storm flow periods. In the hillslope, our previous findings of water flow paths and an analysis of the relationship between soil pore water pressure and hillslope discharge enabled us to classify the hillslope discharge representing water flow paths. During storm flow periods, the occurrence of upslope-derived water had the effect of keeping the stream DOC concentration low, reflecting that the DOC concentration of the upslope-derived water was very low. However, this effect was not observed during nonstorm flow periods, when the stream DOC concentration was nearly constant regardless of the occurrence of upslope-derived water. We inferred that the major reason that the effects of upslope-derived water on stream DOC concentration were different between storm and nonstorm flow periods was the difference in the timing of DOC export from a riparian area. We concluded that information on hydrological processes in hillslopes is helpful for elucidating the formation mechanism of stream DOC concentration in forested headwater catchments.
