Nutrient emission models in environmental policy evaluation at different scales-experience from the Netherlands

A nutrient emission modelling system, called STONE, has been developed for the Netherlands. The approach of STONE and its use in evaluating environmental policies in the Netherlands are discussed. This specific approach is then compared with that of other nutrient emission modelling systems. Emphasis is put on both the scientific-technical aspects and on the applications in quantifying environmental effects of policy interventions at different scales. Results from STONE show, for example, the areas in the Netherlands where maximally acceptable nitrate concentrations in groundwater may be exceeded in the future, the effectiveness of implemented or intended policy measures on nutrient emissions, and the advantage of its mechanistic, spatially distributed approach. Such a detailed modelling approach is shown to be required to take into account the strong and complex interacting effects of, e.g. nutrient supply, groundwater level and management on nutrient emissions.