Uncertainty and Spatial Analysis of Groundwater Nitrate Concentrations in the Po River: A Stochastic Approach

Within EUROCAT a large database that includes temporal trends of physical, ecological and socio-economic data was developed in order to support the nutrient fluxes modeling for different socio-economic scenarios at catchment and coastal zone level of the Po Basin with reference to Water Quality Objectives (WQOs) reported in the Framework Water Directive and Italian legislation as well. Emission data derived from different sources at national, regional and local levels are referred to point and non-point sources. While non-point (diffuse) sources are simply integrated into nutrient flux model, point sources are irregularly distributed. Moreover the intensive farming activities in the Po valley is one of the main Pressure factor Driving the groundwater pollution in the catchment, therefore understanding the spatial and temporal variability of groundwater nitrate concentrations is a critical issue to be considered in developing a Water Quality Management Plan. Therefore in order to use the point sources data as input in our biogeochemical and transport models the data have been spatially interpolated by using geostatistical techniques. This study reports on spatial analysis of groundwater nitrate concentrations and discusses the uncertainty associated by using a probabilistic approach. Our approach is based on geostatistic technique used to yield a series of stochastic images characterised by equal probable spatial distributions of the nitrate concentration across the area. Post-processing of many simulations allowed the mapping of contaminated and uncontaminated areas and assessing the uncertainty in nitrate concentrations.