Abstract: Submarine groundwater discharge (SGD) represents an essential part of the global water cycle and one of the vital ways to transport various chemical substances such as nutrients to the ocean.The influences of recirculated seawater (RSGD) on water body refresh time, SGD, and the flux of nitrogen and phosphorus nutrients in Yingkou sea area in the eastern part of Liaodong Bay were investigated by establishing and improving the radium mass balance model with natural radium isotopes (²²⁴Ra and ²²⁸Ra) as tracers.The water refresh time calculated by the radium mass balance model is 9 days while by the improved radium mass balance model 14.35-18.11 days.The SGD flux in the traditional model is (3.01-3.51)×10⁸ m³/d while in the improved model (3.55-4.39)×10⁸ m³/d.The water refresh time and SGD calculated by the improved model increased by 59.44%-101.22% and 17.94%-25.07%, respectively, compared with those by the traditional model.Moreover, the nitrogen and phosphorus nutrient fluxes from groundwater to the sea are 1.73×10⁸ mol/d and 1.52×10⁹ mol/d, respectively, in consideration of RSGD.In conclusion, RSGD has a remarkable impact on SGD and nutrient fluxes.

Key words: submarine groundwater discharge, radium isotopes, improved radium mass balance model, nitrogen and phosphorus nutrients, Yingkou sea area