Using 223Ra and 224Ra to estimate discharges of groundwater and associated nutrients into southeast of Qinghai Lake, in Qinghai–Tibet Plateau

With its important geographical location and status as the largest saltwater body in China, Qinghai Lake plays a vital role in the ecological environment of the northeastern part of the Qinghai-Tibet Plateau. Due to climate change and the subsequent adjustment of Qinghai Lake’s tourism policy, it is necessary to understand groundwater discharges in southeast of Qinghai lake both for ecological protection and risk prevention. This study used radium isotopes 223Ra and 224Ra to trace groundwater discharges and nutrients carried into the lake. The spatial characteristics of Ra isotopes with greater activity in the upper and bottom layers in the lake indicated that they were influenced by inputs of shallow groundwater and diffusion from sediments. The average 224Ra diffusion flux of the sediments in the Lake was 33.54 dpm m−2 d−1. Based on the 224Ra mass balance model, the discharge flux of shallow groundwater in this region was estimated to be 3.49 × 106 ∼ 3.68 × 106m3d−1. The PO43− and SiO2 fluxes carried into the southeastern of the lake by groundwater were 1.78 × 1011 ∼ 1.88 × 1011 mg/y and 2.22 × 1012 ∼ 2.34 × 1012 mg/y, respectively. It is thus essential to monitor shallow groundwater discharge into Qinghai Lake for the protection of the water environment and prevention of potential ecological risks.