银川平原承压水氢氧同位素组成与~(14)C年龄分布特征

利用地下水氢氧同位素(2H、3H和18O)和碳同位素(14C)方法,分析银川平原承压水的补给更新能力。在平原区采集承压水氢、氧、碳同位素样品45组,测试其氢氧同位素含量和14C年龄。据测试结果分析,地下水氢、氧、碳环境同位素分布特征存在较好的一致性,揭示了该区承压水的补给、流动的区域规律和局部变化特征。地下水14C测年结果显示,承压水年龄大多介于3000~22290 a之间,同时采用Tamers和Gonfiantinie模型对14C年龄校正进行了对比分析。沿同位素水文地质剖面计算得出:银川以北贺兰山前向平原中部地下水的流动速率为2.22~0.63 m/a,呈现由南向北递减的特征;从青铜峡冲洪积区向平原中部地下水由每年流动十余米减少至2 m。综合分析认为,银川平原承压水流动缓慢,水交替循环时间长,局部与潜水水力联系较密切,在承压水开采区,潜水越流补给量可达45%,适量开采存在一定程度的可更新性。

Distribution Characteristics of Hydrogen and Oxygen Isotopic Compositions and 14C Ages in Confined Water of Yinchuan Plain

With the application of hydrogen and oxygen isotopes(2H,3H and 18O) and carbon isotope(14C),the recharge and renewability of confined water in Yinchuan Plain have been analyzed.Forty five groups of confined water samples have been collected in the plain for isotope analysis.The analysis results show that the distribution characteristics of hydrogen and oxygen isotopes(2H,3H and 18O) and carbon(14C) possess very good consistency,revealing the regional regularities of recharge and flow,and local change features of confined water in the study area.14C dating results indicate that the age of confined water is within the range of 3,000 to 22,290 a.Correcting 14C age has been calibrated by Tamers and Gonfiantinie models,and the results have been compared.Along the isotope hydrogeological profile,it is calculated that the flow rate of groundwater from Helan mountain piedmont in the north to the middle part of Yinchuan Plain is from 2.22 to 0.63 m/a,showing the decreasing characteristics from south to north;the flow rate of groundwater from Qingtongxia alluvial-diluvial area to middle part of Yinchuan Plain is from more than 10 to 2 m.It is concluded that the flow rate of confined groundwater in Yinchuan Plain is slow and the water exchange takes longer time.Confined water has hydraulic connection with locally phreatic water.The leakage recharge of phreatic water can amount to 45%,so that the appropriate exploitation of confined water can be conducted for renewability of confined water to a certain degree.