Determining recharge distribution in fractured carbonate aquifers in central Italy using environmental isotopes. Snowpack cover as an indicator for future availability of groundwater resources

Environmental isotopes were used to determine the source and to understand the physical–chemical processes involved ingroundwater movement along a flowpath. This study applies groundwater stable isotopes to assess snow-cover influence onthe recharge processes of some regional carbonate aquifers of central Italy. Starting with extensively investigated aquifers, 17springs were selected and sampled (June–October 2016) for isotope analyses. The δ18O–δD results follow the local meteoricwater line; the low mismatch between the 2016 sampling surveys suggests that those springs are not influenced by seasonalvariability. Nevertheless, the average elevations of recharge areas calculated using the vertical isotope gradient were highercompared to those obtained with hypsographic profiles. This means that the relevant contribution to recharge comes fromhigher elevation areas; hence, snowpack coverage and snowpack persistence over time on recharge areas were analysed usingsatellite images. Four different relationships between the snowpack characteristics and the elevation of recharge areas havebeen identified. These offer relevant information about the different degrees of dependence of the regional aquifers of centralItaly on the recharge due to high-elevation subbasins where the snowpack cover is significant. A possible correlation emergesbetween computed isotope recharge elevation and mean snow cover elevation, revealing how snowmelt is a primary sourcefor aquifer recharge. Consequently, to evaluate the risk of groundwater resource depletion in a climate-change scenario, thereis discussion on how a potential snow-cover reduction would affect the recharge rate of mountainous aquifers.