An integrated and physically based nitrogen cycle catchment model

This paper presents a modelling approach where the entire land-based hydrological and nitrogen cycle from field to river outlet was included. This approach is based on a combination of a physically based root zone model (DAISY) and a physically based distributed catchment model (MIKE SHE/MIKE11). Large amounts of data available from statistical databases and surface maps were used for determination of land use and management practises to predict leaching within the catchment. The modelling approach included a description of nitrate transformations in the root zone, denitrification in the saturated zone, wetland areas and the river system within the catchment. The modelling approach was applied for the Odense Fjord catchment which constitutes one of the pilot river basins for implementation of the European Water Framework Directive. The model simulated overall nitrogen fluxes in the river system consistent with the observed values but showed some discrepancies between simulated and observed daily discharge values The results showed significant differences of denitrification capacities between larger areas such as sub-catchments. This approach has great potential for optimal planning of the establishment of wetlands and further land use legislation with respect to high denitrification rates.