长武塬区大气降水中氢氧同位素特征分析

Characteristics of Hydrogen and Oxygen Isotopes in Precipitation on Changwu Tableland

通过测定长武塬区2005年降水水样的氢氧同位素组成,分析了该区降水氢氧同位素组成的基本特征。结果表明,长武塬区大气降水线方程为δD=7.44δ^(18)O+1.69,其斜率和截距与全球以及我国大气降水线相比均偏小,这与研究区地理位置和气候条件有关;降水氘盈余d值4—6月份较大,大于或接近10,7—10月份则小于10;以天为时间单位采集的次降水,其氢氧同位素组成的温度效应和降水量效应均不显著,而连续2 d长历时降水的雨量效应极显著;降水氢氧同位素组成季节变化明显,春季降水的氢氧同位素值较高,夏季同位素值降低,秋季同位素值最小,这在以次降水量为权重的加权平均值中表现得更加明显。

Precipitation is the most important component of water cycle process. Hydrogen and oxygen isotopic compositions of precipitation are closely related to the source of vapor and the meteorologic process of rainfall formation. The isotopic compositions of precipitation over the Changwu tableland in 2005 are stud- ied. Local meteoric water line is fitted as δD= 7. 44 δ^18O＋1.69. Its slope and intercept are lower than those of global meteoric water line and Chinese meteoric water line, which are related to the geographical and meteorological characteristics in the area. Deuterium excess shows seasonal variation. The values of deuterium excess are higher than or about 10 from April to June and less than 10 from July to October. Both temperature and rainfall amount have no significant effect on the isotopic compositions of individual rainfall events with one-day-period. For the 2-day-period rainfall events, rainfall amount have significant effect on them. Moreover, the isotopic compositions of precipitation have seasonal variation. The 8D and δ^180 values are higher in spring, lower in summer, and much lower in autumn, which is more remarkable in the average of δD and δ^18O when the individual rainfall amount is assigned as a weight.