Simulation of water-induced erosion and transport of particulate elements in a catchment by extending the CNMM-DNDC model

Water-induced erosion is one of the most widely distributed and severely impaired types of soil and water loss in China. Particulate carbon (C), nitrogen (N), and phosphorus (P) losses associated with soil erosion has led to several environmental problems, such as a decline in soil fertility and eutrophication of rivers and lakes. Quantitative assessment of soil erosion intensity and the identification of soil erosion spatial distribution characteristics are of great significance for control of soil and water loss and prevention of non-point source pollution. In this study, based on a well-applied soil erosion physical model of ROSE, we extended several modules of simulating the soil erosion loss and particulate C/N/P enrichments in a catchment-scale hydrology and biogeochemistry coupled model of CNMM-DNDC to simulate soil erosion and particulate C/N/P losses at a high spatiotemporal resolution on the scales of plots and catchments. For instance, the Jieliu catchment in Yanting County, Sichuan Province was used for model verification and application. The results indicated that the CNMM-DNDC with soil erosion extension performed well in simulating the seasonal dynamics of sediment yield (R²=0.83, RMSE=32.0%) and particulate N loss (R²=0.85, RMSE=88.0%) in the runoff plot with a maize-wheat rotation in the Jieliu Catchment. Therefore, the extended CNMM-DNDC model was able to simulate and evaluate the spatial distribution of soil erosion and particulate C/N/P loss intensity in the catchment. The soil erosion and particulate C/N/P loss intensity caused by land surface runoff are related to land use types and topographical features of the catchment, where severe soil erosion and high particulate C/N/P loss came from sloping cultivated lands and residential areas. From 2004 to 2006, the simulated soil erosions in the Jieliu Catchment were 400, 701, and 1550 t∙km⁻²∙a⁻¹, respectively, and were classified as the low erosion category. Meanwhile, the simulated annual particulate C losses caused by the water-induced erosion in Jieliu in 2004, 2005 and 2006 were 63.9, 107.2, and 200.2 kg(C)∙hm⁻²∙a⁻¹, respectively. Consequently, the simulated annual particulate N losses from 2004 to 2006 were 6.3, 10.5, and 19.5 kg(N)∙hm⁻²∙a⁻¹, respectively; and the simulated annual particulate P losses were 0.9, 1.5, and 2.8 kg(P)∙hm⁻²∙a⁻¹, respectively. This study extended the erosion functionality of the CNMM-DNDC model in terms of simulating soil sediment yield and particulate C/N/P loss and can provide useful supporting tools for the research and control of soil erosion and non-point source pollution.