Applying radium isotopes to estimate groundwater discharge into Poyang Lake, the largest freshwater lake in China

Abstract Understanding groundwater discharge into Poyang Lake is important for maintaining the lake’s ecological status and water resource management. This study applied radium isotopes to estimate groundwater discharge into Poyang Lake in light of the characteristics of radium isotopes in groundwater and lake water. It was found that the activities of radium isotopes in most of groundwater samples were higher than those in lake water and river water samples in the Poyang Lake area. The investigations along a flow profile in Poyang Lake indicated radium activities in lake water were affected by groundwater input and the groundwater with high activities of radium isotopes predominantly discharged into this lake. Assuming that the radium activities in Poyang Lake were mainly dominated by the sources and sinks, this study employed the 226Ra and 228Ra mass balance models to estimate groundwater discharge flux into the lake, which was (2.99–3.99) × 107 m3/d. Meanwhile, in order to avoid the estimated result’s errors from the radium activities of groundwater endmember, this study proposed a simple but maybe useful method based on the observed correlation between 226Ra and 228Ra activities in groundwater in the Poyang Lake area. Coupling this regression equation with Ra isotope mass balance models, the groundwater discharge flux could be estimated without using a specific value of radium activity of “groundwater endmember”. The study also found that potentially polluted groundwater from the mountainous areas may have discharged into the lake and posed a threat to its water quality. Thus, future studies may need to focus more on the groundwater discharge from mountainous areas for the protection and management of Poyang Lake.