Identifying watershed-scale spatiotemporal groundwater and surface water mixing function in the Yiluo River, Middle of China

Researching the watershed-scale spatiotemporal groundwater and surface water mixing function, groundwater recharge heights and age can provide important information to watershed water sources management and water pollution controlling. In this study, 20 groundwater samples, 6 precipitation samples, and 40 surface water samples in the Yiluo River watershed in middle China were collected, and the mixing function between groundwater and surface water, recharge height, and age of groundwater was studied by using hydrochemistry (Cl, DO, EC, pH), radioactive isotopes ( 14 C), and stable isotopes ( 13 C, 18 O, 15 N). The results showed that river and shallow groundwater had frequent interaction. Evaporation function played a major role in the groundwater recharging process. Groundwater age displayed spatial and seasonal variations, and the age ranged from 660 to 2800 years (dry season) and 560 to 1800 years (wet season) in downstream and midstream, while the age range from 12,025 to 143,600 years (dry season) and 10,560 to 12,650 years (wet season) in upstream. The average recharge height of downstream and midstream both in dry and wet seasons is about 576.00 to 908.70 m. While in upstream, both, in the dry and wet seasons, ranged from 1285 to 2680 m. The mixing function between groundwater and surface water displayed spatiotemporal variety. These results of this study can provide useful information for the watershed-scale water resources management.