DNA and fluorescein tracer tests to study the recharge, groundwater flowpath and hydraulic contact of aquifers in the Umbria-Marche limestone ridge (central Apennines, Italy)

The purpose of this paper is to highlight the hydrogeological contact among aquifers in karst and fissured systems and study the different flowpaths present in said aquifers; given the complex hydrogeological and tectonics settings, detailed surveys in the Umbria-Marche limestone ridges and tracer field tests were used to achieve this goal. DNA and fluorescent tracers were injected into a sinkhole and thereafter recovered at different points, allowing both for the identification of contact among aquifers, as well as the main and secondary directions of groundwater. The tracer tests have shown that the majority of the groundwater flow is directed towards the axis of the tectonic structures, emerging in more depressed areas. In addition, they have confirmed the influence of karstification on the recharge, which allows for a more detailed characterisation of water circulation in the unsaturated zone of the Maiolica and the Calcare Massiccio limestone aquifers thus offering confirmation of the hydrogeological survey results, and providing additional information that was previously unknown. Furthermore, the DNA tracer provided good results in the field especially in the karst systems and fissured rocks, thus confirming its appropriacy for flowpath investigations and vulnerability analyses of springs. In particular, DNA is suitable for very large amounts of groundwater owing to its very low detection limit. Further investigations and studies are, however, required to assess its validity also for the evaluation of hydrogeological parameters.