Natural trace elements baselines and dissolved loads in groundwater from carbonate aquifers of central Italy

In this work, the natural baselines of several trace and ultra-trace elements dissolved in groundwater of the carbonate aquifers of central Italy are defined based on a probabilistic approach. The concentration of minor and trace elements is showed as cumulative frequency distribution diagrams, and the mean value and the confidence interval for each element are estimated. Most of the elements considered in this study are characterised by a polymodal distribution. The differences between the various populations are mainly related to natural geological causes and, to a lesser extent, to local contamination. Most of the data are below the European standards for drinking water. The highest concentration of trace and ultra-trace species is generally representative of deep circulation in carbonate–evaporite aquifer, while the lower concentration is relative to shallower circulation into the carbonate aquifer. The estimated dissolved load of groundwater from carbonate–evaporite aquifers is about 1.4 × 10 6 ton yr −1 that represents 25–30% of the annual dissolved transport of the main river of the region (Tiber River), and the elemental fluxes discharged by the whole Umbrian carbonate aquifer give an important contribution to the composition of the surface water of the region.