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

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.