Isotopic signatures of precipitation, surface water, and groundwater interactions, Poyang Lake Basin, China

Poyang Lake, whose hydrological characteristics are impacted by the operation of the Three Gorges Dam, is the largest freshwater lake in China. However, water cycle mechanisms in the Poyang Lake Basin remain poorly understood. In this study, stable isotopes (δD and δ18O) of water samples (taken in April, July, and November 2013) and hydrological data are used to investigate the interactions between precipitation, river water, lake water, and shallow groundwater in the Poyang Lake region. The isotopic results show seasonal variations in precipitation, surface water, and groundwater, which provides a set of tools to identify waters that have different histories. The similar isotopic compositions of river water and groundwater suggest a close hydrological connection. Hydrological data present a positive correlation between river run-off and precipitation; however, isotopic results show that rivers in the Poyang Lake Basin in different seasons are primarily recharged by subsurface run-off with different proportion between base flow and near-surface quick flow, rather than by surface run-off directly formed by concurrent rainfall. Due to the geological characteristics of stratum in the Poyang Lake Basin, it is easier for precipitation to infiltrate into soil and recharge groundwater than to form direct surface flow that feeds rivers. The groundwater system is like a huge reservoir which can effectively impound rainfall water, playing an important role in restraining floodwater during the flood season and in ensuring river run-off supply during the dry season.