Sensitivity Analysis of the MONERIS Model for Scenarios Construction

THE MONERIS model (Modelling Nutrient Emission in River Systems) was developed in order to estimate the nutrient fluxes into river basins from point emission sources (i.e., waste water treatment plants, direct industrial discharge into rivers) and various diffuse pathways (atm dep, erosion, tile drainage, surface runoff, groundwater and paved urban areas). Along the pathway from the source of the emission to the river substances are influenced by different processes of transformation, retention and loss. Knowledge of these processes is necessary in order to quantify the nutrient emissions into the rivers. These processes are influenced by different chemical and physical parameters analysed in the sensitivity analysis conducted in the present study. The sensitivity analysis study has been undertaken using different procedures: local sensitivity analysis (that employs partial derivatives to quantify the influence of parameters on a limited range of variations) and global sensitivity analysis (that links the output sensitivity to its causes). In particular, the overall goal of the MONERIS sensitivity analysis was to study the outcome of the model when changing parameters which influence the sub-division of the nutrient fluxes into different pathways, highlighting the more sensitive. Moreover, the variations of these parameters with different transformation processes, with associated retention and loss, determine a variation in a specific pathway flux and/or the global nutrient flux. The intercomparison of the experimental data with the sensitivity analysis of the model is necessary in order to predict future scenarios for nutrient emissions.