安庆地区大气降水氢氧同位素特征及水汽来源

摘要

[Objective] It is critical to examine the characteristics of hydrogen (δD) and oxygen (δ 18O) stable isotopes in the precipitation as well as the source and migration process of regional atmospheric precipitation in Anqing that help reveal the mechanism of the hydrological cycle in the forest ecosystem of Anhui Province along the Yangtze River in response to climate change.[Method] Using a stable isotope technique,we analyzed the compositions of δD and δ 18O in 155 precipitation samples between June 2015 and June 2017 in Anqing,and examined the local meteoric water line.To analyze whether and how the climatic factor affects the compositions of δD and δ 18O in the precipitation,we established the relationships of δD (δ 18O) to the precipitation and temperature.We traced the sources of atmospheric water in Anqing by calculating the D-excess (d) in the precipitation,and verified the results of the sources through HYSPLIT model.[Result] The relationship between δD and δ 18O in the precipitation in Anqing was δD =(8.08 ± 0.06)δ 18O + (10.84 ±0.48) (R2 =0.99,n =155).The stable isotopes δD and δ 18O were significantly negatively associated with temperature (P ＜ 0.01),while no significant correlation was found between the stable isotopes and the precipitation (P ＞ 0.05).The D-excess(d) was close to the global average (10‰),suggesting that the precipitation in the area was mainly affected by the ocean monsoon.The results of air mass back trajectories of the precipitation were calculated by the HYSPLIT model and showed that there were different sources of atmospheric vapor in Anqing.In spring,the atmospheric vapor was affected by the local evaporation and continental air mass from north and south China,and was likely influenced by the Pacific southeast monsoon when rainfall was heavy.In other seasons,atmospheric vapor sources were mainly impacted by the South China Sea air mass,Pacific southeast monsoon,and southwest monsoon of India Ocean.[Conclusion] In this study,the precipitation in Anqing was primarily influenced by atmospheric vapor from the ocean.Differing from the traditional stable isotopes theory of temperature effect,a opposite temperature effect was found in the precipitation in Anqing,this is probably attributable to the latitudes of Anqing,suggesting that different geographical locations probably influenced the composition of δD and δ 18O in the precipitation.Therefore,further studies understand the influences are needed.%[目的]研究安庆地区大气降水氢氧同位素特征、水汽来源和运移过程,为揭示安徽沿江地区森林生态系统水循环过程对气候变化的响应机制提供科学依据.[方法]运用氢氧稳定同位素技术测定安庆地区2015年6月至2017年6月(25个月)共155个大气降水样品的氢氧同位素组成,得出大气降水线方程;建立安庆地区大气降水中氢氧稳定同位素值与气温、日降水量相关关系,分析影响该地区降水中氢氧同位素组成变化的主要因素;计算大气降水过量氘值用以示踪水汽来源,并运用HYSPLIT气团轨迹模型进一步验证水汽来源结果的可靠性.[结果]安庆地区大气降水氢同位素(δD)与氧同位素(δ18O)关系为δD=(8.08±0.06)δ18O+(10.84±0.48)(R2 =0.99,n=154);降水δD和δ18O均与气温显著负相关(P＜0.01),与日降水量无显著相关关系;大气降水过量氘值接近全球平均值(10‰),表明该地区水汽主要受海洋季风的影响;HYSPLIT气团轨迹模型结果进一步表明,安庆地区春季的水汽主要来源于我国华北、华南地区的大陆性气团及局地蒸发水汽,降雨量较大时也会受到太平洋东南季风的影响,而夏、秋、冬季的水汽主要受我国南海气团、印度洋西南季风及太平洋东南季风的影响.[结论]安庆地区大气降水由海洋水汽主导;不同于经典大气降水稳定同位素理论中的温度效应,安庆地区大气降水稳定同位素呈现显著的反温度效应,这可能与其所处纬度有关,表明不同地理位置会对大气降水的氢氧稳定同位素组成产生影响,今后研究中需加以区分.