In situ underwater gamma-ray spectrometry as a tool to study groundwater–seawater interactions

A new technology based on in situ underwater gamma-ray spectrometry of radon daughter products in water has been applied for groundwater–seawater interaction studies in the coastal regions of SE Sicily (offshore Donnalucata) and SE Brazil (offshore Ubatuba). The continuous monitoring carried out at the Donnalucata (and Ubatuba) site have revealed an inverse correlation between the Rn concentration versus the tides and salinity, as Rn concentrations in seawater varied from 2 kBq m (1 kBq m) during high tide to 5 kBq m (5 kBq m) during low tide. The observed variations in Rn concentrations are likely caused by sea level changes, as tidal effects induce variations of hydraulic gradient, which can increase Rn concentrations during a falling tide, while during a high tide, Rn concentrations decrease.