EFFECTS OF WATER FLOW PATHS IN A HILLSLOPE ON RELATIONSHIPS BETWEEN DISSOLVED ORGANIC CARBON CONCENTRATION AND DISCHARGE IN A HEADWATER STREAM

Abstract

We investigated effects of water flow paths on relationships between dissolved organic carbon (DOC) concentration and discharge, i.e., C-Q relationships in a headwater stream and discussed the estimation approach for DOC concentration. We found a strong positive C-Q relationship when the saturated overland flow (SOF) generated from the bottom of hillslope was the dominant flow path. On the other hand, we also found a weak positive C-Q relationship when the saturated subsurface flow (SSF) derived from the upslope area was the dominant flow path, but the slope of regression line was much smaller than that of SOF-dominated period (4%). The shift of dominant flow path from the SOF to SSF during a same storm event resulted in lower stream DOC concentration than expected value based on the regression line of the SOF dominated-period. In conclusion, we interpreted that occurrence of SSF had a dilution effect for stream DOC concentration. Moreover, we pointed out that analysis of flow path-based C-Q relationships can be helpful to estimation of stream DOC concentration.