闽江河口区水体中镭的分布特征及河水与海水的混合速率

入海河口中河水与海水的混合是海洋学中一个重要的界面过程，两者混合尺度和混合速率关系到河流携带物质的扩散范围和归宿，采用天然示踪剂²²⁴Ra和²²⁶Ra计算河水与海水的混合速率。2010年8月28日，采集了闽江河口区地下水样20个、河水样13个、河水与海水的混合水样12个，分别测量了每个水样的盐度、²²⁴Ra活度和²²⁶Ra活度。结果表明：地下水中²²⁴Ra、²²⁶Ra活度普遍高于河水；所有水体中的²²⁴Ra活度普遍都高于²²⁶Ra活度；河水遇到海水后，²²⁴Ra活度出现较大幅度的增加，而²²⁶Ra活度的增加并不明显。基于²²⁴Ra与²²⁶Ra半衰期的差异，在只有河水与海水发生涡流混合的情况下，计算获得河水与海水的混合速率为140.2~142.5 m/h。

Distribution Characteristics of Radium and Determination of Transport Rate in the Min River Estuary Mixing Zone

The mixing between river water and seawater is a key interface process in the estuary.The mixing scale and rate concern the dispersion range and fate of the material transported by river. The aim of this paper is to calculate the transport rate of river plume in the estuary by using naturally occurring tracer ²²⁴Ra and ²²⁶Ra. In August 2010, we collected twenty groundwater samples, thirteen river water samples and twelve mixing samples in the estuary to measure the salinity,²²⁴Ra and ²²⁶Ra activities. The results showed that，1)²²⁴Ra and ²²⁶Ra activities in the groundwater samples were generally higher than those in the river water samples; 2)²²⁴Ra activity was generally higher than ²²⁶Ra activity in every sample; 3)²²⁴Ra activity largely increased when river water mixed with seawater, however,²²⁶Ra activity increased slightly. Based on the differences of radioactive half-life between ²²⁴Ra and ²²⁶Ra, and only eddy diffusion mixture occurring between river water and seawater, the transport rate for river plume in the estuary was calculated to be 140.2-142.5 m/h.