利用^(223)Ra和^(224)Ra对冬季三亚河口海底地下水排放通量估算研究

Estimation of submarine groundwater discharge into the Sanya River estuary in the winter using ^(223)Ra and ^(224)Ra as tracers

对三亚河口两种短半衰期溶解态镭同位素(223 Ra和224 Ra)活度随盐度的分布进行了调查,并估计了其源汇项。调查发现,三亚河口中溶解态223 Ra和224 Ra的分布范围分别是:1~8dpm/100L和13~281dpm/100L。在低盐度区,223 Ra和224 Ra的活度都随着盐度的增大而增大,至中盐度时达到最大值,之后随盐度的继续增加而逐渐减小。其活度主要受控于放射性衰变、涨潮退潮、颗粒物解吸、沉积物扩散和海底地下水排放。利用同位素比值法和质量平衡模型计算得到三亚河口水体的平均近似水龄为4d,河口中68%的镭来自于海底地下水排放的贡献,海底地下水排放流量为1.14×106 m3/d,是三亚河流量的2倍。

We investigated distributions of the two short-lived radium isotopes in the dissolved phase in the Sanya River estuary.The activities of 223 Ra and 224 Ra were in the range of 1to 8dpm/100Land 13to 281dpm/100L,respectively.Their activities increased with salinity rising in the low salinity zone,and reached the maxima in the mid salinity zone;however,the activities decreased with the salinity getting even higher.In the estuary the activity of radium is controlled by such factors as radioactive decay,tide input and output,desorption from suspended particles,sediments diffusion and submarine groundwater discharge.Using the activity ratio of the two isotopes and the mass-balance model,the average apparent age in the Sanya River estuary was estimated to be 4d.More than 68% of radium sources were contributed by submarine groundwater discharge.The submarine groundwater discharge flux into the Sanya River estuary was 1.14×106 m3/d,about two times of the Sanya River discharge.