Temporal and spatial characteristics of radium isotope in phreatic water in the Pearl River Estuary and their influence on the calculation of submarine groundwater discharge fluxes
Accurate selection of representative groundwater end-members is critical for quantifying submarine groundwater discharge(SGD)fluxes using radium isotope tracers.This study analyzed temporal and spatial distribution characteristics of 224Ra and 223Ra in the phreatic water of the Pearl River Delta,and assessed its impact on SGD fluxe calculation.The results showed that from the near end to the far end of the intertidal zone,both the salinity and radium activity of the intertidal phreatic water tended to firstly decrease and then increase.Under similar salinity,there is no order of magnitude difference in the activity of radium in the intertidal phreatic water of different tidal flats,and only a slight difference in the trend of change with increasing salinity.The maximum difference of 224Ra activity in the intertidal phreatic water inside and outside the estuary is(1986.8±94.5)dpm/100L,leading to an SGD variance of up to(25.2±9.6)×108 m3/d.Taking sandy tidal flat as an example,the calculated difference of SGD flux in dry season and rainy season is as high as(2.3±1.6)×108 m3/d.Sensitivity analysis of SGD flux on phreatic water end-member selection showed that salinity has the greatest impact,followed by seasonality,and tidal flat properties have the least impact.Therefore,it is more reasonable to choose high salinity intertidal phreatic water that is close to reaching the radium desorption equilibrium as the representative phreatic water end-member for SGD flux calculation.
radium isotopesradium mass balance modelsalinityphreatic water end-memberintertidal phreatic water
万方数据
维普
