Modelling instream nitrogen variability in the Dee catchment, NE Scotland

The Integrated Nitrogen in CAtchments model (INCA) was applied to the River Dee, Aberdeenshire, NE Scotland. To a first approximation the model was able to simulate the annual mean streamwater NO3-N concentrations observed along the length of the main channel. This provided the basis for using INCA to subsequently explore the effects of N deposition and land use management on streamwater NO3-N concentrations and loads. On an annual timescale, the model predictions suggest that NO3-N concentrations will decrease by 5% following a 20% reduction in fertiliser application. Furthermore, model results also suggest that a 50% increase in N deposition will cause a 15% increase in the streamwater NO3-N concentrations. The utility of INCA as a tool for catchment management is discussed, current limitations are highlighted and possible improvements are suggested.