Hydrologic export of dissolved organic carbon (DOC) and particulate organic carbon (POC) has often been overlooked in quantifying soil C pools and fluxes. Recent studies have suggested that rapid responses of hydrologic carbon export to extreme rainfall events can result in a substantial, but often unrecognized, soil carbon loss, particularly in mountainous terrain. To evaluate the relative importance of DOC and POC as a source of soil carbon loss in a changing monsoon climate, hydro-biogeochemical responses of DOC and POC to storm events of varying intensity and duration were compared for two years at a forest stream and a downstream agricultural stream in a mountainous watershed in Korea using a biweekly routine water sampling combined with intensive storm sampling.

Results/Conclusions

Biweekly biogeochemical monitoring conducted at the forested subcatchment and two streams showed generally higher concentrations of DOC than POC in throughfall, forest floor leachates, and both streams. Monsoon storm samplings, however, exhibited stronger, nonlinear increases in POC concentrations in both streamwaters in response to moderate to extreme events. Real-time monitoring of DOC and POC concentrations in the forest stream using a spectroscopy-based probe during the second summer season corroborated differential hydrologic response of DOC and POC, with lower concentrations and fluxes of POC under base- to low-flow conditions but stronger responses to intense rainfalls. While DOC export during seven storm events accounted for 58% of the total DOC export over the monitoring period from July 17 to September 3, the storm export of POC represented 75% of the total POC export, with one extreme event (210 mm for 1 d) accounting for 68% of the total export. The results suggest that hydrologic carbon export, in the form of both DOC and POC, should be taken into account in predicting changes in soil carbon storage in response to changing monsoon hydroclimates, because very rapid responses of hydrologic carbon export during extreme rainfall events can account for a large fraction of annual soil carbon fluxes in mountainous watersheds.