东江下游大气降水氢氧同位素特征及水汽来源

The hydrogen and oxygen isotope characteristics of precipitation and water vapor sources in the lower Dongjiang River reaches, Guangdong Province

大气降水是水循环系统的主要输入源,其氢、氧稳定同位素组成(δD、δ18 O)受区域气象、地理等因素变化影响较大,可以对环境变化做出快速、及时的响应,是研究全球和局地水循环特征的重要技术手段。东江流域地处我国珠江三角洲,季风环流通过影响水汽输送场的分布控制降水的时空分配。为研究区域降水成因及机理,本文采集并测定东江流域下游地区2017年逐日降水样品中δD、δ18 O,以月为研究时间尺度,分析其与气温、降水量之间的关系;利用HYSPLIT后向轨迹模式追踪降水气团的传输路径,进一步探讨区域降水的水汽来源及输送状况。结果表明,研究期间降水样品中δD的变化范围为-105.10‰^+9.98‰,雨量加权平均值为-57.88‰;δ18 O的变化范围为-14.80‰^-0.55‰,雨量加权平均值为-8.61‰,局地大气降水线为δD=8.60δ18 O+16.15(R 2=0.99)。月尺度下δ18 O最高值出现在1月份,为-3.47‰,最低值出现在8月份,为-10.17‰。δ18 O与气温、降水量均呈显著负相关关系,表现“反温度效应”和“降水量效应”。太平洋水汽带来的降水δ18 O、δD偏高,印度洋水汽带来的降水δ18 O、δD偏低,而南海降水气团中δ18 O、δD则随季节的不同而改变,表现为夏、秋两季明显较春季贫化,存在明显“降水同位素环流效应”。

Atmospheric precipitation is the main input source of the water cycle system,and the stable isotope compositions(δD,δ18 O)are greatly influenced by regional meteorological and geographical factors and are very sensitive to environmental changes.Stable oxygen and hydrogen isotope technique is widely used to study the characteristics of the global and local water circulation.The Dongjiang River Basin is located in the Pearl River Delta,China.The monsoon circulation controls the time and space distributions of precipitation by affecting the distribution of water vapor transport field.The lower reaches of the Dongjiang River was taken as the research object to study the mechanism of regional precipitation.Daily precipitation samples were collected in 2017,δD andδ18 O were measured and the relationships betweenδD,δ18 O and temperature,precipitation were analyzed.The HYSPLIT backward trajectory model was used to trace water vapor sources and the transport of regional precipitation.The results show that theδD andδ18 O values ranged from-105.10‰to+9.98‰and-14.80‰to-0.55‰,respectively,and the annual weighted mean values were-57.88‰and-8.61‰.Regional Meteoric Water Line wasδD=8.60δ18 O+16.51(R 2=0.99).The maximumδ18 O appeared in January,which was-3.47‰,and the minimum value appeared in August,which was-10.17‰.In the monthly scale,δ18 O shows“anti-temperature effect”and“quantity effect”.TheδD andδ18 O in precipitation which caused by water vapor in the Pacific Ocean were higher than those in the Indian Ocean.However,theδD andδ18 O in precipitation caused by the air masses from the South China Sea changed with the seasons,which weres significantly lower in summer and autumn than those in spring.There was obvious circulation effect of isotope in atmospheric precipitation.