To characterize dissolved nitrogen (DN) export from a forested area, we analyzed relations between DN concentration and stream discharge (C-Q relations) during rainfall-derived and snowmelt-derived runoff in a headwater catchment, the central Chugoku Mountains, based on mixing processes of runoff water components. C-Q relations during each rainfall-derived runoff showed strong correlations, and the slopes of regression lines were strongly correlated with initial discharge of runoff, implying that the C-Q relations depended on the mixing rain water and soil water with groundwater. Although the C-Q relation during snowmelt-derived runoff was uncorrelated, very high DN concentration was observed in early phase of the snowmelt period. Eventually, we proposed the estimation method for DN export loading based on initial concentration, initial discharge and variable discharge during rainfall-derived runoff, and pointed out the importance of frequent sampling in early phase of snowmelt period for the load estimation.
