Modelling nitrogen dynamics in an agricultural-forested catchment

A spatially distributed nitrogen simulation (DNS) model has been developed to simulate daily nitrogen concentration variation in an agricultural- forested catchment. The model can simulate hydrological processes and various nitrogen processes at the grid cell level, continuously considering plant uptake, atmospheric wet deposition, fertilizer application, mineralization, nitrification and denitrification. The hydrological component is based on the distributed Xinanjiang (DXAJ) rainfall-runoff model, and the nitrogen component simulates key sources and sinks using a series of first-order kinetic equations. In particular, plant growth indices for land-use classes are incorporated to simulate plant uptake variation in accordance with seasonal vegetation cover variations. Model calibrations showed that there is a reasonable agreement between simulated and observed stream nitrate-nitrogen concentration. Sensitivity analysis showed that plant uptake is the key nitrogen sink, whereas agricultural fertilizer application is the key source of nitrogen.