Distribution characteristics and driving factors of potentially toxic elements in the soil of Hippophae rhamnoides forests in the reclaimed coal - mine areas of ordos

Abstract

To investigate the distribution characteristics and driving factors of soil potentially toxic elements after land reclamation in a mining area, this study focused on the soil potentially toxic elements distribution in a Hippophae rhamnoides plantation within the Juxinlong Coal Mine reclamation area in Ordos, Inner Mongolia. Soil sampling gradients were established at distances of 1/8 (0.25 m), 1/4 (0.5 m), and 1/2 (1 m) of the inter-tree distance from the standard tree. Abandoned grassland was used as a control group. The contents and distribution characteristics of potentially toxic elements including Cadmium (Cd), Copper (Cu), Lead (Pb), Chromium (Cr), and Arsenic (As) in the soil were analyzed to assessed their potential ecological risks, and identified the driving factors. The results showed that the contents of Pb, Cu, Cr, Cd, and As in the study area increased as the distance from the tree trunk decreased. The contents of Pb, Cu, Cr, and Cd in the abandoned grassland were generally higher than those in the Hippophae rhamnoides treatment groups, while As showed significant enrichment at the 1/8 plant spacing distance, with its content increasing from 4.03 mg·kg⁻¹ to 9.35 mg·kg⁻¹.The comprehensive potential ecological risk index (RI) increased as the distance decreased, reaching an extremely high-risk level near the standard trees (1/8 plant spacing), with RI values ranging from 434.58 to 581.17, and Cr was identified as the key risk factor. Soil moisture indicators (field water-holding capacity, CWC; saturated water content, SW) were the core driving factors regulating the contents of As, Cd, and Cu, exerting significant negative direct effects (with path coefficients of -0.84, -0.80, and -0.50, respectively). Furthermore, soil moisture indirectly influenced potentially toxic elements distribution by affecting soil pH, available potassium, organic matter, and bacterial community diversity. This study elucidates the distribution pattern of soil potentially toxic elements and their main influencing factors in a coal mine reclamation area, providing a theoretical basis for risk identification and precise management in mining area ecological restoration.