洞庭湖湖区降水-地表水-地下水同位素特征

Characteristics of stable isotopes in precipitation,surface water and groundwater in the Dongting Lake region

为探明洞庭湖湖区水体稳定同位素时间和空间上的变化规律,弄清各水体间的相互关系,分别在2012年4月和8月对区域内具有代表性的采样点进行了地表水和地下水的采样。通过对样品进行D、18O同位素分析,结合全球大气降水同位素监测网(GNIP)公布的1988—1992年间长沙降水同位素数据,发现湖区年内受不同盛行风影响,降水及地表水的同位素存在较大的季节性差异,4月份同位素富集,8月份贫化。此外,河水、湖水同位素也呈现明显的空间差异。两个时期地表水的水线斜率均小于当地降水线,地表水在两个时期均存在蒸发作用。虽然地表水和地下水的来源均为大气降水,但与地表水相比,地下水同位素季节变化较小,地下水接受地表水补给是一个较为长期的过程。

In order to perform a detailed investigation of the characteristics of temporal and spatial isotopic variation in the Dongting Lake region and to understand the interrelations of different water bodies in the same area, samples of surface water and groundwater were taken in April and August 2012, respectively. The hydrogen and oxygen isotopic compositions of all the samples were analysed and by combining them with isotopic data obtained from precipitation in Changsha from 1988 to 1992, published by the global network of isotopes in precipitation （GNIP）, we find that this region is influenced by different monsoons throughout the year. Consequently, the isotopic compositions of precipitation and surface water demonstrate significant seasonal differences： Enriched in April and depleted in August. Additionally, the isotopic composition of surface water displays great spatial variation. The slopes of the surface water lines in April and August are all smaller than that of the local meteoric water line, which indicates the existence of evaporation of surface water. Even though the original source of both surface water and groundwater is precipitation, groundwater exhibits little seasonal variation compared with surface water, because groundwater recharge by surface water is a long-term process.