Abstract
Soil samples from eight soil profiles under different land-use types were collected at the Puding Karst Critical Zone Observatory, Southwest China, to investigate the distribution, fractionation, and controlling factors of rare earth elements (REEs). The total REEs contents in topsoil ranged from 149.97 to 247.74 mg kg−1, the contents in most topsoil were higher than local soil background value (202.60 mg kg−1), and the highest content was observed in topsoil under cropland. The REEs contents in surface soils from lower slopes sites were higher than that of middle and upper slope sites, and the highest contents were observed in cropland. The PAAS-normalized REEs pattern in soils showed MREEs significantly enriched relative to LREEs and HREEs, and HREEs were enriched relative to LREEs. The results showed that clay content, pH, soil organic carbon, total phosphorus, and Fe content were the main factors influencing the distribution of REEs in karst soils, and soil organic carbon (SOC), Fe content showed better linear relationship with REEs.
Highlights
Rare earth elements (REEs) include a series of lanthanide elements, and they have similar electronic structures and chemical properties
Aubert et al revealed that the proportion of REEs bound to organic matters increased with soil depth and the migration was more obvious for heavy rare earth elements (HREEs) than for light rare earth elements (LREEs) [8]
The ΣREEs in surface soils ranged from 145 to 248 mg kg−1, and the contents in most surface soils were higher than local soil background value (BV) (ΣREEs = 203 mg kg−1)
Summary
Rare earth elements (REEs) include a series of lanthanide elements, and they have similar electronic structures and chemical properties. Two to three groups of REEs are generally distinguished into light rare earth elements (LREEs), heavy rare earth elements (HREEs), and sometimes middle rare earth elements (MREEs) based on their atomic mass and effective ion radius [1,2]. REEs contents in soils are largely influenced by the bedrocks and its physical/chemical properties [5]. The soil properties such as clay mineralogy, organic matter, pH and presence of carbonate influence the distribution and migration of REEs [5,7]. Aubert et al revealed that the proportion of REEs bound to organic matters increased with soil depth and the migration was more obvious for HREEs than for LREEs [8]. A.J.; Boutton, T.W. Soil carbonate decomposition by acid has little effect on δ 13C of organic matter.
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