To elucidate the properties of pedogenic Cr and Ni in serpentine soils in terms of mobilization, three pedons on the shoulder (Entisol), backslope (Inceptisol). and footslope (Alfisol) along a toposequence in eastern Taiwan were examined for metal partitioning and their geochemical origins. The analysis combined bulk soil analysis by selective sequential extraction (SSE) with mineralogical methods, including x-ray diffraction (XRD) and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX) analyses. Experimental results showed that Cr and Ni were mainly concentrated in chromites and silicates, respectively, and were gradually exposed by weathering of the parent materials. The SEM/EDX analysis indicated that chemical modification of the chromites was more prevalent near the soil surface and that the chemical modification increased as available Cr content increased from the shoulder to the footslope. Landscape position was the most important factor in controlling the trends in Ni and Cr fractions. The footslope accumulated more total Cr and Ni than the shoulder and backslope. Additionally the soil on the footslope received more effective precipitation as run-on water from upslope and was potentially more leached than the soils on the other landscape positions. The accumulation of clay and dithionite-citrate-bicarbonate (DCB) extractable Fe (Fej) and the increase of exchangeable Ca/Mg ratio correlated with the increased total labile pools of Cr and Ni in the soil from the shoulder and backslope to the footslope. However, the concentrations of acid soluble, reducible, and oxidizable fractions (total labile pool) of Ni were higher than those of Cr, indicating diat Ni was more available than Cr in all soils tested by the SSE procedures.Abbreviations: BCR.European Community Bureau of Rcferenc; BSE. back-scattered electron; BSP, base saturation percentage; CEC, cation-exchange capacity; DCB, ditbionite-citrate-bicarbonate ; EDX, energy dispersive x-ray spectroscopy; FAAS.flame atomic absorption spectrophotometer; OC. organic carbon; SEM. scanning electron microscopy: SSE. selective sequential extraction: XRD. x-ray diffraction; XRF, x-ray fluorescence.

The vertical distribution of 14 geochemical elements (Si, Al, Ti, K, Na, Ca, Mg, Fe, Mn, Cu, Cr, Ni, Pb, and Zn) in nine serpentine pedons for three ophiolite complexes was investigated. The pedons are located at Wu-Mau, Tong-An, and Shih-Tao mountains in the Coastal Range, eastern Taiwan. The objective of this study was to discriminate the parent material inheritance and pedogenic factors by comparison of the element concentrations based on principal component (PC) analysis. From the experimental results, the relative abundance of major elements was as follows: Si 9 Fe 9 Mg 9 Al, with lesser concentrations of Ti, K, Na, and Ca. In addition, Cr, Mn, and Ni contents in these soils were higher than in soils formed from other parent materials, with considerable variation between pedons on different landscapes, which reflected the ophiolite differences and degrees in chemical weathering of the associative serpentinitic rocks. The contents of pairs of Si-Fe, Si-Mn, Si-Pb, and Si-Zn showed significantly (P G 0.05) positive correlations. The close relations among contents of Fe, Mn, Cr, and Ni were observed herein. According to the eigenvalue in PC analysis, the elements most responsible for separation along the PC-1 axis were Si, Fe, Mn, Zn, Mg, and Ca, whereas Cr and Ni were the trace metals responsible for separation along the PC-2 axis. This result reflected the parent material differences in igneous rock composition and the degree of serpentinization between ophiolite complexes.

Liuchiu Island is an uplifted coral-reef island located off southwestern Taiwan. A total of four soil pedons, labeled as LC-1 and LC-2 from the Holocene terraces and LC-3 and LC-4 from the Pleistocene terraces, were sampled on the island for this work. These soils were siliceous, and were characterized by enrichment of clay and free iron (Fe d ). According to Soil Taxonomy, pedons LC-3 and LC-4 were classified as Paleudults and pedons LC-1 and LC-2 were Dystrudepts. The soil properties showed progressive changes from pedon LC-1 to pedon LC-4 in morphology, physical and chemical properties, and clay mineralogy. The contents of total Fe and dithionite-citrate-bicarbonate extractable Fe were significantly higher in pedons LC-3 and LC-4 with high weathering degree than in pedons of LC-1 and LC-2 with less weathering degree. Enrichment of kaolinite and gibbsite in pedons LC-3 and LC-4 also suggested high chemical weathering degree of the soils. The estimated soil ages for all studied pedons were consistent with their degrees in pedogenesis, where pedons LC-3 and LC-4 were located at older terraces and pedons LC-1 and LC-2 were located at younger terraces. Namely, it complied with the geologic interpretation of the continuous and simultaneous uplift and tilt of the island over time. Instead of the in situ weathering from the underlying coral reef limestone, all soils developed from siliceous parent materials deposited onto the surfaces. The SiO 2 /Al 2 O 3 ratios of soils indicated a component of loess may have been incorporated from continental China as part of the parent material, which confirmed a climate change of strong monsoons or severe dust storms occurred before the Holocene. However, soil development increased by the subsequent warm and humid climates of the interglacial stage over time.