A SEMIDISTRIBUTED INTEGRATED NITROGEN MODEL FOR MULTIPLE SOURCE ASSESSMENT IN CATCHMENTS (INCA) - PART I - MODEL STRUCTURE AND PROCESS EQUATIONS

A new model has been developed for assessing multiple sources of nitro gen in catchments. The model (INCA) is process based and uses reaction kinetic equations to simulate the principal mechanisms operating. The model allows for plant uptake, surface and sub-surface pathways and c an simulate up to six land uses simultaneously. The model can be appli ed to catchment as a semi-distributed simulation and has an inbuilt mu lti-reach structure for river systems. Sources of nitrogen can be from atmospheric deposition, from the terrestrial environment (e.g. agricu lture, leakage from forest systems etc.), from urban areas or from dir ect discharges via sewage or intensive farm units. The model is a dail y simulation model and can provide information in the form of time ser ies at key sites, or as profiles down river systems or as statistical distributions. The process model is described and in a companion paper the model is applied to the River Tywi catchment in South Wales and t he Great Ouse in Bedfordshire. (C) 1998 Elsevier Science B.V.