Preliminary Data on the Groundwater Geochemistry of Su Bentu Cave (Sardinia, Italy)

The Su Bentu Cave has been recently investigated to determine the geochemical features of its groundwater. The analyses have shown a low mineralization with calcium bicarbonate character. Its main composition is explained by calcite dissolution and mainly reflects both cave lithology and rainwater input. A slight increase in sodium and sulphate contents is the only exception to this pattern that may be related to the weathering of the sediments filling the cave conduits. These preliminary results have been compared with the available data on Su Gologone spring, the main karst outlet of the Supramonte aquifer (Sardinia, Italy) to whose the cave is tributary. The same alkaline-earth bicarbonate character is also observed in the spring water, but the salinity and the concentration of main ions generally increase due to longer residence time. Moreover, for the discharge point, major magnesium content indicates a dominant circulation in Jurassic dolomites outcropping nearby.