Improvement of evaluation of water age and submarine groundwater discharge: a case study in Daya Bay, China

•Radium-based model should include all sources and sinks to improve water age accuracy.•RSGD and open sea water end-member significantly affect the water age in Daya Bay.•SGD-derived material fluxes were significantly higher than those from local rivers.•SGD has important effect on coastal ecosystems by promoting primary production.