Estimation of groundwater discharge and associated chemical fluxes into Poyang Lake, China: approaches using stable isotopes (δD and δ 18 O) and radon

Poyang Lake is the largest freshwater lake in China and is well known for its ecological and economic importance. Understanding the contribution of groundwater to Poyang Lake is important for the lake’s protection and management. In this study, stable isotopes (δD and δ 18 O), 222 Rn measurements, and corresponding models ( 222 Rn and 18 O mass balance models) were employed to evaluate the groundwater discharge and associated chemical inputs to Poyang Lake. The results showed that the distribution of δ 18 O in the lake water reflects the groundwater discharge into the lake. The groundwater discharge estimated using the 222 Rn mass balance model was in reasonable agreement with the groundwater discharge derived from the 18 O mass balance model. The 222 Rn mass balance model showed that the groundwater discharge rate was 24.18 ± 6.85 mm/d with a groundwater discharge flux of (2.24 ± 0.63) × 10 7 m 3 /d, which accounts for 6.52–11.14% of river-water input in the Poyang Lake area. The groundwater discharge flux estimated using the 18 O mass balance model was 3.17 × 10 7 m 3 /d, and the average groundwater discharge rate was 26.62 mm/d. The estimated groundwater discharge was used to estimate the associated chemical fluxes. It was found that groundwater-derived heavy metals such as iron and manganese are potential threats to the lake ecological system because of their large inputs from groundwater discharge.