Modelling of soil nitrogen dynamics within the decision support system DANUBIA

Within the GLOWA-Danube project, the integrated decision support system DANUBIA was developed to address effects of global change on water resources of the Upper Danube watershed (∼80,000 km2). Key components of DANUBIA in respect to water quality and plant growth modelling are nitrogen turnover, nitrogen fluxes and storages. This paper discusses an approach to model soil nitrogen dynamics in a mesoscale watershed. Within the model, the soil column is represented by three soil layers. The model components for water fluxes, nitrogen uptake and nitrogen transformation are process-based. To validate the model, field data from four locations were used. Nitrogen modelling results are in good agreement with measured data. Statistical analysis for soil nitrogen and water content resulted in satisfactory indices of agreement. The study demonstrated that the coupled soil moisture and soil nitrogen transformation model is suitable to simulate the fate of mineral nitrogen within the soil profile on the field scale. Sensitivity studies indicate that the model quality for large scale modelling depends particularly upon the appropriate representation of sandy soils, the accurate parameterization of the saturated hydraulic conductivity and the precise initialization of soil mineral nitrogen content.