Effects of topography and soil properties on the distribution and fractionation of REEs in topsoil: A case study in Sichuan Basin, China.

In order to investigate how topographic factors and soil physicochemical properties influenced the distribution and fractionation of rare earth elements (REEs) in soil, Jiangjin district of Sichuan Basin, an area with mountainous topography, was selected as a study area. The concentration of REEs, pH and organic matter (OM) and major elements in 156 topsoil samples were measured and analyzed. The topographic factors considered were elevation, slope, and topographic wetness index (TWI), which were extracted by using the digital elevation model (DEM). The median concentration of total REEs in topsoil of the study area was 147 mg/kg, lower than the Chinese soil background value (164 mg/kg). The concentration of LREEs and HREEs, and the ratio of LREEs/HREEs and La/Yb indicated that the distribution and fractionation patterns of REEs in topsoil were LREEs-enriched. Significant Eu negative anomalies and weak Ce negative anomalies were observed in topsoil according to the median values of δEu (0.57) and δCe (0.89). The coefficient of weathering and eluviation (BA), an important factor affecting the distribution and fractionation of REEs, was substantially correlated with δEu (r = 0.344, p < 0.01), δCe (r = -0.252, p < 0.01), ∑REEs (r = 0.135, p < 0.01), and LREEs/HREEs (r = -0.281, p < 0.01) in topsoil. Soil pH and OM had some influence on the distribution and fractionation of REEs. Under the geographical environment of the study area, Ce was positive anomaly with the elevation and slope increasing. The enrichment of LREEs was more significant than HREEs as elevation increased. The findings revealed that topographical attributes and soil physicochemical properties integratedly influenced the distribution and fractionation of REEs in topsoil.