A new distributed hydrologic and water quality model for nonpoint source pollution assessment

This paper shows a new hydrologic and water quality model development and field application. The model has been developed to evaluate nitrate and ammonium nitrogen sources in catchments. The model is based upon a spatial splitting of the territory into elementary square cells and schematises the main hydrological processes of degradation and transport of nutrients, performed on a control volume built on the single cell. For evaluating the local generation of surface, sub-surface and groundwater runoff a WetSpa (Yongbo and De Smedt, 2000) distributed hydrologic model evolution, performed by Manfreda et al. (2001), has been used. The model operates on a daily time step and predicts the export of non-point sources soluble nitrate-nitrogen and ammonium-nitrogen from catchments. The model uses reaction kinetic equations to allow the simulation of the nutrient cycling processes, such as mineralization, fixation, nitrification, denitrification, plant uptake, etc. Sources of nitrogen can be atmospheric depositions, from the terrestrial environment (e.g. agriculture, leakage from forest systems, etc.), or from direct discharges via sewage or intensive farm units. The model, applied to the larger sub-catchment of the 1500 km2 Basento river basin in Southern Italy, has offered a good prediction of daily nitrate-nitrogen and ammonium-nitrogen concentration against observed data.