Publications
Linking magnetic susceptibility with chromium and nickel pedogeochemistry in ultramafic soils: A nexus perspective
Authors: Yang,C.Y., A. Nakao, Z.Y. Hseu
Catena • 2026
Soil magnetic susceptibility (κ) provides a sensitive record of soil evolution because it often increases as non-magnetic Fe-bearing silicates transform into fine-grained ferrimagnetic oxides during pedogenesis. However, this pattern does not always apply to ultramafic soils, where abundant inherited spinel-group minerals such as magnetite and chromite markedly elevate κ independent of pedogenic formation. Since both spinels and pedogenic Fe oxides are one of the hosts for chromium (Cr) and nickel (Ni), variations in κ may also reflect the redistribution of these elements during weathering—a linkage that remains poorly constrained. To explore this relationship, eight pedons representing Entisols, Inceptisols, Alfisols, and Ultisols were examined as representative soil profiles from ophiolite complexes in eastern Taiwan. The soil κ was determined for individual soil horizons, alongside selective Fe extractions and geochemical analyses. Across the profiles, κ ranged from 1.54 to 30.3 × 10−3 SI, showing irregular depth trends driven by the preservation of inherited spinels and attenuation through pedogenic alteration and carbonate dilution. The κ was predominantly governed by inherited ferrimagnets since only structural Fe but not pedogenic Fe oxides displayed a significant positive correlation with κ. Significant and positive correlations between κ, Cr, and Ni revealed that κ can serve as a proxy for Crsingle bondNi abundance and redistribution within ultramafic profiles. Multivariate analyses further indicated secondary influences from soil texture and carbonate content. Collectively, these findings highlighted a mechanistic linkage between magnetic and geochemical properties in Cr/Ni-rich soils and emphasized the need for broader climatic comparisons to generalize this relationship.
Genesis and mass balance of basaltic soils along a lava plateau chronosequence in Penghu Islands, Taiwan
Authors: Yang,C.Y., C.Y. Huang, Z.Y. Hseu
Soil Science and Plant Nutrition • 2025
Basalt-derived soils are important to global biogeochemical cycles due to their extensive distribution and rapid weathering. The Penghu Islands, located in the Taiwan Strait, provide an ideal setting to investigate the effects of time on pedogenesis within a basaltic chronosequence under humid tropical conditions. Four pedons – PH1, PH2, PH3, and PH4—developed on basaltic lava with stratigraphic ages of 8.5, 9.3, 10.6, and 12 Ma, respectively, were collected. The morphological, physio-chemical, and mineralogical properties of soils were analyzed. A geochemical mass balance approach was conducted to obtain the τj, w value of each element for evaluating the gain and loss of elements. A progressive increase in solum thickness, clay accumulation, and rubification with stratigraphic age were identified, highlighting long-term pedogenic transformations. Younger soils (PH1, PH2), classified as Typic Ustorthents, exhibited minimal horizon development, while older soils (PH3, PH4), classified as Typic Haplustalfs, were characterized by well-developed Bt horizons and high crystallinity of secondary Fe oxides. Mass balance analysis revealed significant elemental depletion, particularly for Si, Al, and Fe, consistent with progressive weathering. However, the τj, w values of Ca and Mg implied net accumulation, suggesting sustained external inputs from marine-derived carbonates and eolian deposition. The τj, w values of trace metals, including Cr and Ni, displayed irregular trends with depth and stratigraphic age, indicating complex interactions between primary mineral dissolution and secondary mineral adsorption. Despite its utility in quantifying element fluxes, mass balance analysis proved inadequate for fully capturing the effect of time on pedogenesis in an open-system environment influenced by external inputs. The lack of a significant correlation between element depletion patterns and plateau age suggested that processes such as eolian deposition, marine carbonate addition, and hydrological influenced variability that cannot be resolved through mass balance alone. This study disentangled in situ weathering from allochthonous contributions, providing a more comprehensive understanding of basaltic soil evolution in dynamic coastal landscapes.
Pedogenic fractionation of rare earth elements in chromium- and nickel-enriched ultramafic soils
Authors: Yang,C.Y., Z.C. Zhang, Z.Y. Hseu
Catena • 2025
The geochemical behaviors of chromium (Cr) and nickel (Ni) associated with rare earth elements (REEs) have received limited attention in ultramafic soils. This study hypothesized that ultramafic soils originating from distinct ophiolite complexes exhibit varying amounts of Cr and Ni, with REEs fractionation serving as a fingerprint in these soils. A total of 39 horizon samples from eight pedons, including Entisols, Inceptisols and Alfisols, were collected at different landscape positions from three ophiolite complexes in eastern Taiwan. The total concentrations of major elements, Cr, Ni and REEs were determined. Linear correlation and principal component analysis (PCA) were then used to assess variations in the signatures of REEs corresponding to soil properties, Cr, and Ni. The soils from different ophiolite complexes exhibited various Cr and Ni abundance, and signatures of REEs. REEs remained immobile as their concentrations increased during pedogenesis. The ratio between light REEs (LREEs) and heavy REEs (HREEs) of the soils indicated an enrichment of LREEs compared to HREEs. A common minerals origin of REEs and Cr existed. Thus, REEs and Cr underwent similar geochemical processes in the soils. Additionally, Ce anomaly (δCe) increased along with REEs, Cr, and Ni, corresponding to the formation of secondary iron oxides. Differentiation in ΣREEs, Cr, Ni, ΣLREEs/ΣHREEs, (La/Sm)N, (La/Yb)N, (Gd/Yb)N, and δCe by the PCA can be used to separate the soils from various ophiolite complexes, identifying the origins of these soils in Taiwan. However, further validation with additional data from diverse pedoclimate regions is required for future studies.
Geochemical signatures and contamination levels of rare earth elements in soil profiles controlled by parent rock and soil properties
Authors: Wu,C.Y., Yang,C.Y., M.D. Cascante, W.A. Liao, H.Z. Hum, J.Y. Wu, K.F. Huang, Z.Y. Hseu
Environmental Science and Pollution Research • 2025
Rare earth elements (REEs) are emerging contaminants rendering potential risks in soils to environmental quality and human health. The causation between their geochemical signatures and contamination levels with parent rocks and soil properties are critical for REEs risk assessments, which are urgently needed globally. Thus, this study aimed to elucidate cause-and-effect among hydrofluoric-acid-digested total and ethylenediaminetetraacetic acid extracted bioavailable soil REEs and their contamination degree evaluated by pollution indices in 268 soil layer (horizon) samples from 50 soil profiles derived from felsic, intermediate, mafic, ultramafic, and sedimentary rocks in Taiwan. The total REEs was 133 ± 61.9 mg/kg and all individual REEs were classified as minimal contamination by the enrichment factor. The highest total soil REEs was from granite, followed by sandstone and shale, mafic rocks, andesite, and ultramafic rocks. All soils were ranked as significantly pollution risk by the pollution loading index. Furthermore, REEs were accumulated in all subsoils due to the co-translocation with soil colloids during the intensive leaching, corresponding with their higher geoaccumulation index value than those in surface soils. The contamination degree and bioavailable REEs significantly increased with the increasing total REEs. However, the stronger sequestration of clay and free Fe oxides for heavy REEs (HREEs) over light REEs (LREEs) mitigated their bioavailability, especially in the highly weathered soils like Ultisols and Oxisols. This study highlighted the dominance of soil properties in REEs fractionation, where the preferential fixation of soil colloids for HREEs throughout soil profiles reduced their uptake risk for biome even under the rising contamination potential.