ORIGINAL PAPER Contribution of groundwater discharge and associated contaminants input to Dongting Lake, Central China, using multiple tracers ( 222 Rn, 18 O, Cl 2 ) Xiaoliang Sun . Yao Du . Yamin Deng . Hongchen Fan . Yanqiu Tao . Teng Ma Received: 31 January 2020 / Accepted: 30 July 2020 Ó Springer Nature B.V. 2020 Abstract Lacustrine groundwater discharge (LGD) can play an important role in water and contaminant mass balance of lakes. Dongting Lake is the second largest fresh lake in China which is connected to Yangtze River and has quite prominent ecological status and function within Yangtze River basin. However, the effect of groundwater discharge on the balance of water and contaminant in Dongting Lake has long been overlooked. This study estimated the groundwater discharge and associated contaminants input into Dongting Lake during the dry season using multiple tracers ( 222 Rn, 18 O, Cl - ). After sensitivity analysis of different models, it is found that the result of 222 Rn mass balance model is the most reliable. Based on the 222 Rn mass balance model, the ground- water discharge rate is estimated to be 73.94 mm/d and the contribution of LGD to water balance is 10.94%. As the main nutrient components, NH 3 -N, P and Si from groundwater input account for 23.65%, 5.12% and 30.15% % of the total input, respectively. As the main heavy metal components, Fe, Mn and As from groundwater input all account for more than 50% of the total input. Although the LGD rate is relatively small, the contaminant input from LGD is significant enough, which may be a potential threat to the ecological stability of Dongting Lake. In this study, the mass balance models of multiple tracers were integrated to understand the role of groundwater in maintaining the water balance and pollution status of Dongting Lake, which has certain reference signifi- cance for the LGD study in plain lakes or reservoirs with complex water systems in humid regions. Keywords Groundwater discharge  Dongting Lake  222 Rn  Mass balance Introduction As an important wetland ecosystem, lake has the functions of regulating water resources in a watershed, retarding environmental pollutants and providing biological habitats (Harvey and Rudolph Harvey et al. 2000). The assessment on water and pollutant balance of lakes is crucial to the management and protection of lakes. Lacustrine groundwater discharge (LGD) can be a key component that plays an important role in water and pollutant balance of lakes. For example, Gurrieri and Furniss (2004) found that X. Sun Geological Survey, China University of Geosciences, Wuhan 430074, China Y. Du (&)  Y. Deng  H. Fan  Y. Tao  T. Ma School of Environmental Studies, China University of Geosciences, Lumo Road 388, Wuhan 430074, China e-mail: yaodu@cug.edu.cn Y. Du  Y. Deng  H. Fan  Y. Tao  T. Ma State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China 123 Environ Geochem Health https://doi.org/10.1007/s10653-020-00687-z