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

Abstract

The geochemical characteristics of rare earth elements (REEs) can be employed to identify the anthropogenic and natural influence on the distributions of REEs in soils. A total of 47 soil samples from the three soil profiles of the secondary forest land, abandoned cropland, and shrubland in the Yinjiang county of Guizhou province, southwest China, were collected to determine the contents and distribution of REEs in the soil environment. The total REEs (ΣREE) contents in different soil profiles are in the following sequence: secondary forest land (mean: 204.59 mg·kg−1) > abandoned cropland (mean: 186.67 mg·kg−1) > shrubland (mean: 139.50 mg·kg−1). The ratios of (La/Gd)N and (Gd/Yb)N ranged from 0.62 to 1.00 and 1.18 to 2.16, which indicated that the enrichment of the medium rare earth elements (MREEs) was more obvious than that of the light rare earth elements (LREEs) and the heavy rare earth elements (HREEs). The phenomenon could be attributed to the preferential absorption of MREEs by fine particles and the substitution of Ca2+ by MREEs. Most soil samples were characterized by the negative Ce anomalies (anomalies values: 0.30–1.10) and positive Eu anomalies (anomalies values: 0.43–2.90). The contents of REEs in the profiles of secondary forest land and shrubland were mainly regulated by soil pH and Fe contents while clay content and agricultural activities were the main controlling factors in the soil profile of abandoned cropland. This study highlights the role of agricultural activities in affecting the distributions of REEs in karst soils, which could provide some insights for the protection of the soil environment.

Spatial distribution and ecological risk assessment of heavy metals in karst soils from the Yinjiang County, Southwest China

“…The variations of soil properties in all profiles are summarized in Table 4 . The values of soil pH T1 profile: 7.1–7.9, T2 profile: 4.8–5.2 and T3 profile: 6.3–7.0) in the three profiles have been reported by Han & Xu (2021) . Soil silt particle accounted for the largest portion (mean: 85.87% in T1profile; 75.12% in T2 profile; 85.25% in T3 profile), and the second largest was clay (mean: 12.96% in T1profile; 15.50% in T2 profile; 12.09% in T3 profile) in all profiles ( Han & Xu, 2021 ).…”

“…The values of soil pH T1 profile: 7.1–7.9, T2 profile: 4.8–5.2 and T3 profile: 6.3–7.0) in the three profiles have been reported by Han & Xu (2021) . Soil silt particle accounted for the largest portion (mean: 85.87% in T1profile; 75.12% in T2 profile; 85.25% in T3 profile), and the second largest was clay (mean: 12.96% in T1profile; 15.50% in T2 profile; 12.09% in T3 profile) in all profiles ( Han & Xu, 2021 ). The contents of soil SOC in three profiles ranged from 0.38% to 4.2% in T1 profile, 0.51% to 1.7% in T2 profile and 0.76% to 10.8% in T3 profile.…”

Rare Earth Elements Transfer from Soil to Vegetables and Health Risks Associated with Vegetable Consumption in a Former Mining Area

“…Rare earth elements (REEs) have chemical properties that change gradually across the series from La to Lu [1,2]. Generally, REEs occur collectively in various minerals and are trivalent except for Ce 3+ , which can be oxidized to Ce 4+ under typical surface conditions, and Eu 3+ , which can be reduced to Eu 2+ under extremely reducing conditions and/or high temperature [3,4]. REEs have similar physicochemical properties and multiple applications, some of them being considered critical elements [2,5].…”

Feature Paper in Environmental Chemistry and Technology

“…Among the main processes of interaction, agricultural activity is certainly one that has influenced and modified the morphology of the land. A study conducted in China, in Guizhou's Yinjiang County [5], showed that the REE content in secondary forest land and shrub profiles was mainly regulated by the soil pH and Fe content, while the clay content and agricultural activities were the main controlling factors in the soil profile of abandoned farmland. This study highlights the role of agricultural activities in influencing the distribution of REEs in karst soils, which could provide some insights into protecting the soil environment.…”