水の流出経路が森林河川の溶存有機炭素濃度に及ぼす影響

Abstract

Here, we qualitatively discuss the effects of flow paths on dissolved organic carbon (DOC) concentrations in a headwater stream during a nonstorm flow (NF) period on the basis of hydrometric measurements at a hillslope and a riparian zone and the DOC concentrations of hillslope runoff water. In the analysis, the NF period in which dominant runoff water was derived from the upslope area in a hillslope (hillslope-NF period) was distinguished from the other NF period (normal-NF period). For hillslope runoff water, DOC concentrations during the hillslope-NF period were very low compared with those during the normal-NF period. For stream water, at a few measurement points, DOC concentrations during the hillslope-NF period were also very low (< 10th percentile of concentrations during normal-NF period), but at most measurement points the concentrations were slightly lower than those during the normal-NF period (at least 25th percentile). At sampling points with a relatively large catchment area (≥ 36 ha), the difference in DOC concentration between the hillslope- and normal-NF periods was small and nearly constant. It was inferred that stream DOC concentrations during NF periods were determined by the balance between the decreasing effects of hillslope water and the increasing effects of riparian water. Moreover, these results suggest that considering the balance is important for models estimating DOC concentrations in headwater streams.