Seasonality of Radium Isotopes in an Intertidal Aquifer

The presence of radium activity variation within the lower intertidal aquifer introduces substantial uncertainties in the estimation of submarine groundwater discharge (SGD) and associated chemical fluxes. This study presents findings on the seasonal variation of radium isotopes in a two-dimensional cross-section of an intertidal aquifer. The research demonstrates that the variability in vertical and temporal dimensions is considerably greater than lateral variation, which is due to different flow regimes and mixing with different water sources. Numerical modeling demonstrates that groundwater dynamics strongly influence the seasonal variation of radium isotopes by controlling the groundwater residence time and amount of mixing with infiltrated seawater from the beach boundary. Hydrochemical properties such as salinity and pH play a minor role in the seasonal variation of radium isotopes in the lower intertidal zone. This study provides valuable insights into the seasonal fluctuations of radium isotopes and emphasizes the importance of accounting for variations in multiple dimensions when analyzing SGD in different timescales.