Determining the sources of stormflow from the fluorescence properties of dissolved organic carbon in a forested headwater catchment

Concentrations of SiO2 and dissolved organic carbon, as well as the fluorescence properties of the latter were used as tracers of stormflow sources in a forested headwater catchment in Japan. Separate analyses were made of throughfall and of groundwater in the saturated and transient saturated zones, using three-dimensional fluorescence spectrometry. Groundwater in the saturated zone showed almost no fluorescence, whereas groundwater from the transient saturated zone showed fluorescence patterns characteristic of fulvic acid. Throughfall showed fluorescence of a non-fulvic character. Stormflow water showed fulvic-type fluorescence, showing that groundwater from the transient saturated zone contributed 62.7% of the total discharge. The source area for transient saturated zone groundwater accounted for less than 1% of the catchment area during the storm event. The contribution of the riparian zone to the storm runoff was important, although its source area was also very small.