| সংক্ষিপ্ত: | Submarine groundwater discharge (SGD) consists of fresh submarine groundwater discharge (FSGD) and recirculated submarine groundwater discharge (RSGD). In this study, we conducted simultaneous 25-hour time-series measurements of short-lived <sup>222</sup>Rn and <sup>224</sup>Ra activities at two sites with differing SGD rates in the central Seto Inland Sea of Japan to evaluate SGD rates and their constituents. At both sites, we also quantified the total SGD, FSGD, and RSGD using a seepage meter to verify the water fluxes estimated with <sup>222</sup>Rn and <sup>224</sup>Ra. SGD rates estimated using <sup>222</sup>Rn and <sup>224</sup>Ra at the site with significant SGD approximated the total SGD and RSGD measured by the seepage meter. However, SGD rates derived using <sup>222</sup>Rn at the site with minor SGD were overestimated, since <sup>222</sup>Rn activity at the nearshore mooring site was lower than that in the offshore area. These results suggest that the coupling of short-lived <sup>222</sup>Rn and <sup>224</sup>Ra is a powerful tool for quantification of FSGD and RSGD, although it is important to confirm that tracer activities in coastal areas are higher than those in offshore.
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