Groundwater–Surface Water Interaction: Process Understanding, Conceptualization and Modelling (Proceedings of Symposium HS1002 at IUGG2007, Perugia, July 2007). IAHS Publ. 321, 2008, 158-163.

Analysis of nutrient losses and parameter uncertainties in soils and surface water systems at the catchment scale

P. Groenendijk¹, R. Bijlsma², D. J. J. Walvoort¹ & L. V. Renaud¹

1 Alterra, Wageningen University and Research Centre, PO Box 47, 6700 AA, Wageningen, The Netherlands

piet.groenendijk@wur.nl

2 Department for Water Engineering & Management, University of Twente, PO Box 217, 7500 AE, Enschede,
The Netherlands

Abstract The NL-Cat modelling system has been developed to enable the assessment of the relation between agricultural land use and surface water quality at the catchment scale in a mechanistic way. The modelling system comprises of specialized modules for spatial discretization, data processing, and process simulation. The tool can assist in the process of defining the sources of nutrient pollution and the magnitude of relevant pathways and, in this study, has been applied to the Regge catchment in the eastern part of The Netherlands. It has been widely recognized that risk assessment is a crucial part of the water management process. Uncertainties in the quantification tools can be addressed, but are often complicated to deal with. Therefore, an uncertainty analysis was also included in this study. The objective of this case study is to predict surface water concentrations and its associated uncertainty due to variability in parameters and input data. It was found that uncertainties with respect to land use data, fertilizer and manure application rates and meteorological variation affects the variability of the results most. The uncertainty associated with nitrogen concentrations reduces with the reduction of future N-surpluses. However, the uncertainty associated with phosphorus concentrations increases in time, despite the reduction of P-surpluses.

Key words catchment; modelling; prediction; nutrient losses; surface water quality; uncertainty