Effects of Different Erosion Intensities on Rare Earth Elements Migration and Control in Benggang

Benggang is vividly called "ecological ulcer" in the south red soil area. The purpose of this study is to clarify the characteristics of rare earth elements (REEs) in collapsed hillocks (Benggang) with different soil erosion intensities in extremely degraded ecosystems and to explore the ecological restoration measures in controlling REEs migration. Taking 3 Benggang samples in Huangnikeng, Zhuotian Town, Changting County of Fujian Province representing 3 different erosion intensities (mild, intense, and extremely intense) as the study cases, the effects of different soil erosion intensities on contents characteristics and horizontal migration of REEs in Bengbang system were analyzed. The results show that the highest content of REEs in Benggang with intense erosion occurred in the gully area, while the highest content of REEs in Benggang with mild and intense erosion occurred in the colluvial area. Under the same soil erosion intensity, the REE contents in the soil of different parts of the slope of Benggang and the control slope were significantly different (P < 0.05). The exchangeable and residual forms of REEs were dominant among the rare earth binding forms additionally, exchangeable REEs content in Benggang systems was significantly higher than that of non-collapsed slope. The average content of bioavailable forms in non-rhizosphere soil of Dicranopteris dichotoma was 214.90 mg·kg^-1, while in rhizosphere soil was 231.78 mg·kg^-1. The research results show that with the intensification of soil erosion in Benggang, the migration capacity of REEs to the downstream was enhanced. Therefore, the ecological restoration and management of Benggang system in the extremely degraded ecosystem should be strengthened to reduce the loss of surface soil and prevent and control horizontal migration of REEs. The ecological restoration measure of rare earth hyper-accumulated plants will be beneficial to prevent and control the REEs horizontal migration in the degraded Benggang ecosystem. Consequently, the distribution of Dicranopteris dichotoma, one of the REEs accumulation plants, showed that the available REEs can migrate from the original soil to the Dicranopteris dichotoma, which can be beneficial to control REEs migration and reduce the potential ecological risk. The results can provide a theoretical basis for expanding the ecological restoration fields of REEs control in Benggang.