Geochemical Distribution Characteristics of Rare Earth Elements in Different Soil Profiles in Mun River Basin, Northeast Thailand

Abstract

Exploring the distributions of rare earth elements (REEs) in soil profiles is essential to understanding how natural and anthropogenic factors influence the geochemical behaviors of REEs. This study aimed to learn about the distribution characteristics of REEs in soils, including their fractionation and enrichment, and to explore the influence of soil pH and soil organic carbon (SOC) on REEs. One hundred and three samples were collected from six soil profiles under different land uses (paddy field: T1, T3; forest land: T2, T6; wasteland: T4; building site: T5) in the Mun River Basin, Northeast Thailand. The average total REE contents (∑REE) are much lower (<80 mg kg−1) than that of Earth’s crust (153.80 mg kg−1) in soil profiles T2, T3, T4, and T6. The contents of REEs tend to increase slightly with depth in all soil profiles. The ratios of (La/Yb)N range from 0.35 to 0.96 in most samples, indicating that the enrichment of heavy REEs (HREEs) relative to light REEs (LREEs) is the main fractionation pattern. Samples from profile T2 show relatively obvious negative Ce anomalies (0.55–0.78) and positive Eu anomalies (1.41–1.56), but there are almost no anomalies of Ce and Eu in other soil profiles. Enrichment factors of LREEs (EFLREEs) range from 0.23 to 1.54 and EFHREEs range from 0.34 to 2.27, which demonstrates that all soil samples show no LREE enrichment and only parts of samples show minor HREE enrichment. Soil organic carbon (SOC) contents positively correlate with the enrichment factors of REEs (EFREE) in soil profiles T1 (R = 0.56, p < 0.01) and T6 (R = 0.71), while soil pH values correlate well with EFREE in soil profiles T2 (R = 0.75) and T4 (R = −0.66, p < 0.01), indicating the important influence of soil pH and SOC on the mobility of REEs in some soil profiles.

Distribution, fractionation and sources of rare earth elements in suspended particulate matter in a tropical agricultural catchment, northeast Thailand

“…The data of REE in soils quoted from the previous study, and the information of six soil profile location and REE analysis can be found in Zhou et al (2020) . The dissolved organic carbon (DOC) concentrations of river water quoted from Liu et al (2019) .…”

“…The Mun River drains in extensively cultivated areas, where few studies have reported the concentrations and behaviors of REE in different natural materials, except several recent studies focusing on soils and basalts ( Yuan et al, 2019 ; Zhou et al, 2020 ). Moreover, REE geochemistry in the tropical agricultural watershed systems have rarely been reported, especially to examine the impact factors of REE in SPM ( Comte et al, 2012 ; Davis et al, 2017 ).…”

Geochemical Behaviors of Rare Earth Elements (REEs) in Karst Soils under Different Land-Use Types: A Case in Yinjiang Karst Catchment, Southwest China

“…The δCe values can be used to reflect the soil redox environment. Generally, Ce 3+ is easily oxidized to Ce 4+ and absorbed by hydroxide, Mn-oxide, and Fe-oxide [ 72 , 73 , 74 ]. A large amount of REEs is released into soils during the rock weathering processes while Ce 4+ remains in the regolith, resulting in the depletion of Ce in soils.…”

Occurrence and Contamination of Rare Earth Elements in Urban Mangroves of Shenzhen, South China

“…Generally speaking, the distribution of REEs in sediment cores records the historical changes of REE deposition [13,47]. As for deposition of individual REEs in urban mangrove sediments (Table S2), the main composition of REEs (including Ce, La, Nd, and Y) demonstrated reducing trends with increasing depth, except for Y in XXM, and Nd and Y in SJM.…”