A statistical method for source apportionment of riverine nitrogen loads

This study describes a source apportionment methodology for riverine nitrogen transport. A statistical model was developed relating stream nitrogen load to spatially referenced nitrogen sources and basin characteristics. It is able to estimate the nitrogen load on the basis of only three parameters. It considers applied fertiliser, atmospheric deposition and point discharges as sources and rainfall, topography and water flow as basin characteristics. The model was calibrated on three European watersheds, the Wash (UK), the Zelivka (Czech Republic) and the Vilaine (France) river basins in order to represent a range of different climatic characteristics and nitrogen input pressures. Based on model predictions, the spatial and temporal variations of diffuse nitrogen emission were described, identifying critical areas more prone to nitrogen loss. The model makes it possible to estimate the contribution of each nitrogen sources (point and diffuse) to the total river load. Finally, scenarios of different nitrogen input pressure were analysed. The model was shown to be a suitable tool for understanding the fate of the actual nitrogen input pressure and evaluating the impact of alternative management strategies with a limited data requirement.