北京西山大气降水中D和^(18)O组成变化及水汽来源

The Variations of Hydrogen and Oxygen Compositions and Moisture Sources in the Precipitation in Western Mountain Areas of Beijing

论文利用北京西山鹫峰地区2011年7月—2012年7月观测站点内大气降水δD和δ18O数据,研究了北京西山山前丘陵区降水稳定同位素的变化特征。结果表明:研究区的大气降雨δD和δ18O的平均值要低于中国和全球降水同位素的平均值,并与北京地区的降水同位素组成平均值之间显示出较大的差异,且同一个月份内降水的同位素特征也具有较大的变化范围。由于季风气候以及局地水汽循环的共同影响,使得夏季降水中的δD和δ18O值较小,并且在4—7月随着月降水量的增加和温度的升高,在温度效应和降雨量效应的交互作用中,降雨量效应此时起主导作用,月均δD和δ18O值呈现减小的趋势,而在7—9月,温度效应呈现出主导作用,δD和δ18O值呈现增加的趋势,而冬季来自偏北风的大陆性气团形成的降水δD和δ18O值较大。同时局地水汽循环过程中降水的二次蒸发,也导致在典型长历时场降水过程中δD和δ18O值呈现出分段波动式下降的特征。研究区大气降水线方程为δD=7.17δ18O+1.46,斜率和截距小于全球和中国大气降水线方程,而与北京地区大气降水线方程的对比发现,斜率差异较小而截距差异明显,说明海洋水汽不是研究区唯一的水汽来源,同时受到大陆性气团以及局地较强的水汽循环和北京地区近年的干旱化过程的影响。而氘盈余的年内变化的无规律则间接反映了研究区水汽来源的复杂性。

Stable isotopes of δD and δ18O in precipitation are investigated in western mountains of Beijing from July 2011 to July 2012. The results show that the mean values of δD and δ18O in precipitation in the study area were lower than those in global and in China, and had great difference to those in Beijing, and the isotope values of precipitation within the same month showed great variations. Because of the mutual influence of monsoon climate and atmospheric water vapor cycle, the stable isotopes of δD and δ18O in summer precipitation were less. The isotopic values decreased with the increase of monthly precipitation and temperature from April to July since the rainfall played the leading role in the interaction process of temperature and rainfall. The isotopic values increased from July to September when the temperature took the leading role. There are more stable isotopes of δD and δ18O in winter precipitation since the precipitation was formed in the continental air masses from the northerly winds. The second evaporation after the rainfall in the process of atmospheric water vapor cycle also causes the piecewise fluctuated decline of δD and δ18O in a typical long duration of rain. The meteoric water line equation of the study areas was δD=7.17δ18O＋1.46（R2=0.934 2）, and the slope and intercept were lower than those in the national and global atmospheric precipitation line equations. When compared to the meteoric water line equation of Beijing, the slope of the equation was similar and the intercept was obviously different, which indicated that the ocean water vapor was not the only source of water vapor in the study area, the values of isotopes in the precipitation in this area were also influenced by the continental air masses, local strong water vapor cycle and the drying process in recent years. The irregularity of deuterium excess indirectly reflected the complexity of water source in the study area.