Runoff load estimation model for dissolved organic carbon that considers soil and hydrologic processes in forested watersheds

Abstract

Estimation of dissolved organic carbon (DOC) runoff load in forested watersheds is important for the assessment of the global carbon cycle as well as for the local water quality control. A few process-based models previously proposed exhibited difficulties with the availability of input data and applicability to short time-scale rainfall-runoff processes in the Asian monsoon area. With the four years' data from two nested study areas in Yamanashi, Japan, this study developed a new numerical model that consists of two processes for determining DOC loads. For the hydrologic process, a semi-distributed hydrological model (modified TOPMODEL) was installed. For the soil process, a wet-dry cycle was successfully simulated by an advection-diffusion and dissolution formulation. Finally, cumulative DOC loads were also successfully estimated during baseflow and stormflow periods separately, showing reasonable matching between the simulations and the observations for both study sites. Considering the storm periods, from 27% to 47% of high flows contributed to 50% of the total DOC load at the two monitoring areas, respectively. In essence, the proposed model was expected to identify and evaluate the importance of DOC production potentially linked with internal processes within forested river systems.