Isotopic features of precipitation and groundwater from the Eastern Alps of Italy: results from the Mt. Tinisa hydrogeological system

This study analyses water stable isotopes data collected from precipitation (one rain gauge) and groundwater outlets (seven occurrences and two springs) at Mt. Tinisa, in the Eastern Alps of Italy. Limestones and dolostones outcrop in the mountain relief, making up a single aquifer which feeds the monitored outlets with almost steady discharges. Lack of runoff in the streambeds throughout the whole year means that all meteoric water can be considered as recharging the aquifer. Sampling was undertaken during the periods 2005-2010 (precipitation) and 2014-2015 (groundwater) via monthly and two/three-monthly field-activities, respectively, which allowed a total of 138 water samples to be gathered and analysed. Results highlighted the presence of apparent isotopic anomalies in groundwater in comparison with meteoric water. The study demonstrates that the assessment of groundwater residence time and estimates of the mean monthly isotopic content in rainwater have been necessary to correctly compare the two isotopic datasets and relate the anomaly to the recharge time-window, occurring in the late autumn.