青海湖西部镭同位素分布特征及环境意义

Radium Isotope Distribution in Western Qinghai Lake and Its Environmental Significance

通过对2011~2014年采集的青海湖及周边水体样品（岩层间隙水、井水、泉水、河流水、降水和湖表水）镭同位素活度及离子含量测定,得到镭同位素的空间分布特征。223Ra的活度范围是0~2.30 dpm/100L,224Ra的活度范围是0~97.49 dpm/100L,226Ra的活度范围是33.30~126.70 dpm/100L,228Ra的活度范围是22.50~209.40 dpm/100L。降水只有半衰期最长的226Ra有活度,其余镭同位素皆低于检测值。无论是长半衰期还是短半衰期,间隙水和井水都拥有比较高的活度值,河水和湖表水则比较低。短半衰期镭同位素的分布特征呈现由湖岸向湖中心快速降低的规律,无地表径流注入的湖岸距离5~6 km就检测不到其活度,证明在这个距离短半衰期镭同位素基本衰变完毕;5号采样点活度是平均活度值的一倍,接近18 dpm/100L,可能有深层地下水的渗出。12号与13号采样点由于靠近布哈河口,受到水平涡动扩散的影响,所以矿化度有所下降,短半衰期的活度值有所上升,除此之外短半衰期的镭同位素的变化趋势基本与矿化度呈负相关;除12号、13号采样点受到布哈河的影响外,228Ra的活度的变化基本与Ca2＋、HCO-3、Mg2＋、K＋呈现正相关,与NO-3基本呈负相关。

By analyzing the activity of more than 50 Ra isotopes samples collected from interstitial water, well water, rock springs, river, precipitation and lake surface water in 2011 -2014, the authors got a distribution character of Ra isotopes and mineralization. The activity range of 223Ra is 0 -2. 30 dpm/100L, 224Ra 0 -97. 49 dpm/100 L, 226Ra 33.30 - 126. 70 dpm/100 L, and 228Ra 22. 50 -209. 40 dpm/100 L re- spectively. Only the longest half-life 226Rb Can be detected in the precipitation, the other Ra sotopes are lower than the deleetion limits. Interstitial water and well water have high activity of Ra both in short half - life or long half - life, while river and lake surface water are in low activity. The activity of short - life Ra isotopes declines from the lakeshore to the center of the lake quickly and neither exist when the dis- tance is 5 km far than lakeshore, proving that the activity of Ra isotopes basically decay out. The activity of sample 5 is 18 dpm/100 L, double than the average activity, that is probably because of the under- ground water seepage. Sample 12 and Sample 13 are influenced by Buha river, so that their activity comes a little higher and salinity comes lower. Above that, the change tendency of short half -life Ra isotopes is negatively correlated with salinity. Underground water discharge of Qinghai lake is not so large, more samples are needed to quantitative the amount of underground water discharge, and the change tendency of 22SRa is positively correlated with Ca2＋ , HCO3- , Mg2＋ , K＋ , and negatively correlated with NO3-.