Discharge and environmental isotope behaviours of adjacent fractured and porous aquifers

The combined use of hydrogeological and hydrogeochemical methods can provide relevant information about the characteristics of aquifers in studies focused on groundwater protection and management. In the present study, spring discharge monitoring coupled with stable and unstable water isotopes was used to compare the behaviour of adjacent fractured and porous aquifers hosted in a 4.5 km2 area along the same slope in the northern Apennines, Italy. Based on stable isotope analyses of four springs, a plausible local meteoric water line and a local vertical isotopic gradient were identified. Additionally, tritium contents revealed a recent meteoric origin for groundwater via infiltration in the area. The results of monthly stable isotope monitoring, hourly spring discharge monitoring, hourly rainfall monitoring, and statistical analyses (time series analysis) suggested that although the adjacent aquifers exhibited pronounced geological and hydrogeological differences, few discrepancies were observed regarding groundwater infiltration and release processes. Notably, they exhibited similar temporal delays associated with the response to precipitation events due to the roles of macro-fractures and macro-porosity. Groundwater circulation was characterized by piston and memory effects in both the fractured and porous aquifers, and these effects reflect the roles of micro-fractures/fissures and micro-porosity. The study highlights the relevant contributions of isotopes in studies that focus on spring vulnerability and aquifer processes. Moreover, results obtained in the Pietra di Bismantova site are useful to increase hydrological knowledge on the quite relevant aquifers hosted in Epi-ligurian rock slabs and the surrounding slope deposits in the northern Apennines of Italy.