Organic carbon efflux from a deciduous forest catchment in Korea

Abstract. Soil infiltration and surface discharge of precipitation are critical processes that affect the efflux of Dissolved Organic Carbon (DOC) and Particulate Organic Carbon (POC) in forested catchments. Concentrations of DOC and POC can be very high in the soil surface in most forest ecosystems and their efflux may not be negligible particularly under the monsoon climate. In East Asia, however, there are little data available to evaluate the role of such processes in forest carbon budget. In this paper, we address two basic questions: (1) how does stream discharge respond to storm events in a forest catchment? and (2) how much DOC and POC are exported from the catchment particularly during the summer monsoon period? To answer these questions, we collected hydrological data (e.g., precipitation, soil moisture, runoff discharge, groundwater level) and conducted hydrochemical analyses (including DOC, POC, and six tracers) in a deciduous forest catchment in Gwangneung National Arboretum in west-central Korea. Based on the end-member mixing analysis of the six storm events during the summer monsoon in 2005, the surface discharge was estimated as 30 to 80% of the total runoff discharge. The stream discharge responded to precipitation within 12 h during these storm events. The annual efflux of DOC and POC from the catchment was estimated as 0.04 and 0.05 t C ha⁻¹ yr⁻¹, respectively. Approximately 70% of the annual organic carbon efflux occurred during the summer monsoon period. Overall, the annual efflux of organic carbon was estimated to be about 10% of the Net Ecosystem carbon Exchange (NEE) obtained by eddy covariance measurement at the same site. Considering the current trends of increasing intensity and amount of summer rainfall and the large interannual variability in NEE, ignoring the organic carbon efflux from forest catchments would result in an inaccurate estimation of the carbon sink strength of forest ecosystems in the monsoon East Asia.