The dynamics of DOC in the hydrological process in a forested watershed

Abstract

The purpose of this study was to clarify the dynamics of dissolved organic carbon (DOC) in the Kiryu Experimental Forest. The concentration of DOC and the UV absorbance: DOC ratio were measured along the flow path from precipitation to stream water via soil solution and groundwater. The DOC concentration and the UV absorbance: DOC ratio decreased with depth. There was a vertical variation in the rate of the decrease in DOC concentration, which we postulated as resulting from the occurence of two different mechanisms in the infiltration process. In the upper soil layer, the relationships between DOC and A1 and Fe indicated that organically-complexed A1 and Fe contributed to decreasing the DOC concentration. In the lower soil layer, no fluctuation in DOC concentration was seen, although the DOC adsorption efficiency seemed to be homogeneous from the upper soil layer to the lower. We postulated that the easily adsorbed DOC fraction had been removed, and that decomposition contributed to decreasing the DOC concentration in the lower soil layer. The DOC concentrations of stream water and groundwater were almost the same, suggesting that the DOC concentration of stream water during the period of baseflow is determined mainly in the unsaturated zone.