Onzekerheidsanalyse van stikstofberekeningen met het NPKRUN model

Abstract

One of the aspects in the Environmental Reports produced regularly by the RIVM is the contents of nutrients in small surface waters. As part of quality assurance of models used in these reports an uncertainty analysis has been carried out for the nitrogen calculations performed with the NPKRUN (Nitrogen-Phosphor-Potassium) model. It appeared that there certainly is no amplification in sensitivity on the way from individual input parameters to model outcomes. In sandy areas the uncertainty in the aquifer thickness is observed to be the most influential factor. Second is the uncertainty in historical nitrogen contents of ground water flows which affects the concentration in (part of) the base flow. Furthermore, in specific situations the uncertainty in the exact origen of surface water recharge comes into play. Accurate information on the contributions of surface runoff, interflow (including tile drainage) and base flow could then be of importance. Particularly in clay soils or peaty areas in the lowlands reliable estimates of the flows of the former two drainage components are necessary. This especially holds for surface runoff in the winter and for interflow in the summer period. The limited extent of observed uncertainties makes model based statements on exceeding critical values rather robust for nitrogen compounds.<br>