Assessing the transport of rare earth elements in runoff in a small watershed developed on a coarse-grained granite area in southern China

The transport of rare earth elements (REEs) in surface runoff could have adverse ecological and public health impacts in some regions. In this study, the transport of REEs in a small watershed developed on coarse-grained granite in southern China (the Zhuxi Watershed) was analyzed using a Soil and Water Assessment Tool (SWAT) model and an artificial rainfall experiment. The SWAT model was used to simulate the runoff and sediment generation in the Zhuxi Watershed. Moreover, an artificial rainfall experiment was conducted for determining the mass and distribution of REEs transported from the erosion of soils on a slope in the watershed. The results showed that the average annual runoff volume and amount of sediment in the Zhuxi Watershed from 2013 to 2017 were 4.793 × 10¹⁰ L and 1.037 × 10⁷ kg, respectively. Additionally, the content of REEs in the runoff and sediment were 10.91 μg L⁻¹ and 2.282 × 10⁵ μg kg⁻¹, respectively. The SWAT model indicated that the average annual amounts of REEs transported in runoff and sediment in the Zhuxi Watershed from 2013 to 2017 were 1554 ± 239 and 2367 ± 307 kg a⁻¹. Further investigations should be conducted in the area to determine the most effective methods of reducing sediment export from the watershed to limit the potential for adverse environmental and public health impacts through exposure to REEs in areas receiving discharge.