Hydrogeochemical features of the Sardinian rivers

The physical-chemical parameters and contents of the main dissolved components, together with some minor elements, were determined in 35 waters from rivers flowing in Sardinia (Italy). Dominant Na-Cl, low salinity (<0.5 g/L) and high SiO2 concentrations are observed in waters draining silicate environments, and dominant Na-Ca-Cl- HCO3 and higher salinity (0.6 to 1.2 g/L) occur in waters from sedimentary environments. Waters draining areas that host Pb-Zn ores show higher SO4 due to the oxidation of sulphide minerals. The main chemical composition does not change when waters are sampled at different climatic conditions; however, salinity and concentrations of the main ions increase at low-flow condition in the summer season. At high-flow condition, i.e. when the rivers have a high rainwater component, a decrease in many chemical species is observed due to dilution processes, but at the same time, an increase in the concentration of soluble species, such as nitrate, may occur.