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.

中文翻译：

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泰国东北部热带农业流域悬浮颗粒物中稀土元素的分布，分馏和来源

从泰国东北部的芒河及其与湄公河的交界处收集了48个悬浮颗粒物（SPM）样品，以研究SPM中稀土元素（REE）的分布与流域土壤之间的关系。门河SPM中的总REE含量（∑REE）为78.5至377.8 mg / kg，平均为189.3 mg / kg，低于湄公河的∑REE 222.3 mg / kg（1个样品为交界处）。Post Archean Australia页岩（PAAS）标准化的轻稀土（LREE），中稀土（MREE）和重稀土（HREE）的平均值平均为1.0、1.3和1.0，表明MREE明显富集。简而言之，沿着门河，SPM中的REE含量正在下降，并且PAAS归一化模式显示REE逐渐平坦。SPM和土壤中的REE含量在上游流域最高，表明土壤/基岩是SPM中最重要的REE来源。另外，SPM中较高的Ca含量会增强Eu的正异常（R = 0.45），这可能是由于用Ca和Eu代替Ca的长石或碳酸盐含量更高而引起的。研究结果显示了芒河SPM的REE行为以及SPM中REE与土壤/基岩之间的关系，这一发现可能支持流域风化的其他研究。