Estimation of coastal residence time of submarine groundwater discharge using radium progenies

A methodology based on gamma-spectrometry measurements of untreated coastal water samples is proposed for the direct estimation of coastal residence time of submarine discharged groundwater. The method was applied to a submarine spring at Stoupa Bay covering all seasons. The estimated residence time exhibited an annual mean of 4.6 +/- 1.7 d. An additional measurement using the in situ underwater gamma-spectrometry technique was performed, in the same site. The in situ method yielded a value of 2.8 +/- 0.2 d that was found consistent with the corresponding value derived using the developed lab-based method (3.4 +/- 2.0 d) for the same period.