Submarine groundwater discharge investigations in Sicilian and Brazilian coastal waters using an underwater gamma-ray spectrometer

摘要

Submarine groundwater discharge (SGD) in coastal zones was monitored using in situ underwater gamma-ray spec-trometry of radon decay products (~(214)Bi). Several sites were visited during the IAEA'2002 expedition to southeastern Sicily, where SGD variations were observed in the Donnalucata boat basin. The continuous monitoring carried out for 3 days at the site closest to the coast revealed an anticorrelation dependence of ~(222)Rn concentration with tide and salinity. The ~(222)Rn activity concentrations in seawater varied from 2.3 kBq m~(-3) (during high tides) to 4.8 kBq m~(-3) (during low tides). In situ gamma-ray spectrometric measurements were also carried out during the IAEA-UNESCO'2003 expedition to Ubatuba (Brazil). The results obtained during 5 days of continuous monitoring in Flamengo Bay confirmed an anticorrelation between the ~(222)Rn activity concentration in seawater (which varied between 1.5 and 5.2 kBq m~(-3)) and tide/salinity, however, the relationship seems to be more complicated than was observed off Donnalucata. It was confirmed that at both Donnalucata and Ubatuba sites the variations in Rn concentrations were caused by sea level changes, as tide effects induce variations of hydraulic gradients, which increase ~(222)Rn concentrations during decreasing sea level, and conversly, during high tides the ~(222)Rn concentrations are decreasing.