Résumé
Since 15 years numerous works have shown the influence of submarine groundwater discharge (SGD) on the water budget of lagoons, bays or open coastal areas [1]. In particular the high concentrations in nutrients of discharging groundwater may result in very productive ecosystems [2]. A radon-radium study was coupled with nutrients in semi-arid South-Eastern Spain. Mar Menor lagoon (135 km (super 2) ) is bordered by a Quaternary sedimentary aquifer extending over 1200 km (super 2) . (super 222) Rn and (super 224) Ra activities in groundwaters along the coast range between 2200 to 17500 and 16 to 120 Bq/m (super 3) respectively. In the lagoon, (super 222) Rn and (super 224) Ra activities varied from 10 to 100 and 4 to 8 Bq/m (super 3) respectively. The increase of both nuclides is localized and synchronous with a peak in NO (sub 3) (super -) and chlorophyll, revealing groundwater input. In the same area, changes observed in coastal vegetation could be related. Further measurements will refine the SGD flux to Mar Menor and its ecological impact.