An innovative method to determine springs recharge areas by using water isotopes: intuitions from mountain hydrogeological studies in central Italy

Over the years the scientific community underlined several problems related to the use of isotopic hydrology techniques in areas characterized by a complex orography, usually occurring in mountain areas, or in those cases where the hydrological setting is complicated by contacts between different aquifers (Nanni et al., 2013).

In this study, an innovative isotopic model, able to identify the most probable recharge area for several springs exploited for drinking purposes, has been developed and applied to the Nera catchment in the Sibillini Mountain National Park (central Italy). The isotopic investigation consists of a preliminary definition of a new δ¹⁸O - elevation relationship, considering the morphological and meteorological heterogeneities within the area and their possible influences on the precipitation isotope values (e.g., shaded areas, snow drift effect, etc.). Second, an advanced δ¹⁸O distribution model, supported by statistical and GIS-based procedures, has been implemented by clipping the precipitation δ¹⁸O values (depicted from the δ¹⁸O – elevation relationship) over an upstream area for each analyzed spring. The new isotopic modeling approach can be conveniently applied if the infiltration rate of the meteoric water is fast enough to avoid fractionation processes that may alter the isotopic signal of the precipitation input within the aquifer, and if peculiar meteoric recharge phenomena, altering the springs' isotopic signal, are treated as outliers.

This research highlights if the most used isotopic approach based on the determination of groundwater recharge areas starting from δ¹⁸O - elevation gradient (Jeelani et al., 2010; Jasechko, 2019) applied to a selected spring isotopic data agrees with the hydrogeological setting of the spring recharge area which is often complicated by the topography and the contacts between different aquifers both for stratigraphic and tectonic reasons.

The ultimate goal of this study is to quantify the aquifers recharge under the impact of drought to improve the water resources management operations in the area.