Abstract
Forty-eight suspended particulate matter (SPM) samples were collected from the Mun River, northeast Thailand and its junction with the Mekong River, to investigate the relationship between the distribution of rare earth elements (REE) in SPM and the soils in the watershed. The total REE contents (∑REE) in SPM in the Mun River ranged from 78.5 to 377.8 mg/kg with the average of 189.3 mg/kg, which was lower than ∑REE of 222.3 mg/kg at the Mekong River (one sample at junction). The Post Archean Australia Shale (PAAS)-normalized ratios of light REE (LREE), middle REE (MREE) and heavy REE (HREE) were averaged to 1.0, 1.3 and 1.0, which showed a clear enrichment in MREE. In short, along the Mun River, the REE contents in SPM were decreasing, and the PAAS-normalized patterns of REE showed gradually flat. The REE content in SPM and soils are highest in the upper catchment, indicating that soil/bedrock is the most important source of REE in SPM. Additionally, the positive Eu anomaly was enhanced by the higher Ca content in SPM (R = 0.45), which may be caused by more feldspars or carbonates with Ca and Eu substituting Ca. The results present the REE behaviors of SPM in the Mun River and relationship between REE in SPM and soil/bedrock, the findings may support the other studies in catchment weathering.
Highlights
The rare earth elements (REE) are a collection of fifteen trace elements: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu (i.e., “the lanthanides”), all of which be found together in the geological materials
Normalized REE to post archean Australia shale and soil Comparing different parts of the Mun River in Table 1, it can be found that the lowest light REE (LREE)/heavy REE (HREE) fractionation was recorded in the tributaries of the upper reaches
The REE contents in suspended particulate matter (SPM) were higher in the tributaries that drain granites and basalt rocks than sediment rocks
Summary
The rare earth elements (REE) are a collection of fifteen trace elements: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu (i.e., “the lanthanides”), all of which (except Pm) be found together in the geological materials. The REE are usually divided into three groups as light REE (LREE) (La–Nd), middle REE (MREE) (Sm–Dy) and heavy REE (HREE) (Ho–Yb). The REE have common trivalent oxidation state so they are an extremely coherent group in aspect of chemical behaviors, for which REE have been used to investigate the weathering processes and water-rock or water-particle interactions (Han & Liu, 2007). How to cite this article Yang K, Han G, Zeng J, Zhou W. Distribution, fractionation and sources of rare earth elements in suspended particulate matter in a tropical agricultural catchment, northeast Thailand.
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