Regional-scale assessment of factors affecting non-point sources pollution: nitrate in groundwater

Natural and anthropogenic factors influencing the occurrence of high nitrate concentrations in groundwater in a sector of the Po Plain (Northern Italy) have been analyzed. The methodology combines measurements of nitrate concentrations (response variable) with spatial data representing both categorical and numerical variables (explanatory variables or predictors). The statistical model was developed by first testing each single explanatory variable in a logistic-regression model to determine the most significant factors. Then, factors were tested in a probabilistic-based model (Weights of Evidence Modeling Technique). The statistical model outlined: the overall influence each variable and each variable class have on the presence/absence of nitrate; the range of their values mostly influencing this presence/absence; the most and least critical combination of factor classes existing in each specific zone. Results provide a useful tool to evaluate the potential effect of development on groundwater quality for future planning of land use.