Ring maps applied to hydrogeological and environmental studies in alluvial aquifers, central Italy

Analysis of hydrogeological data of aquifers requires assessment of multiple variables and this is difficult to visualise in a single map with commonly used techniques. Ring maps are presented in this paper as a useful option to overcome this limitation. Four alluvial aquifers from Central Italy were assessed and are presented as case studies, evaluating the hydrogeological setting, the groundwater chemistry and the distribution of representative contaminants (Boron, Iron, Manganese and Nitrates). The final result is a graphical representation showing the ring maps, which simultaneously depict 12 numerical variables and two other variables: the geographical position and the main lithological properties of the aquifers. The research indicates that coastal alluvial aquifers show higher contamination when compared to the intramontane alluvial aquifers. Boron is exclusively present in the coastal alluvial aquifers where maximum concentrations are associated with the uprising of deeper saline groundwater with a chloride-sodium chemistry. Iron and manganese are generally associated and their presence is inversely correlated to that of nitrates. The presence of Nitrates is less common in the intramontane aquifers. The ring maps presented in this paper have been effectively used as a geovisualisation tool for multivariate hydrogeological and environmental data. The technique simultaneously and clearly shows several variables in one single graphical representation.