東亞島弧不同地區蛇紋岩土壤鉻與鎳在化育過程中的動態及有效性評估

蛇紋岩土壤的特徵為偏低的鈣/鎂比、高鉻、鎳背景含量等，但受到母質來源及化育條件的不同，全球各地的蛇紋岩土壤在鉻、鎳型態分布與其潛在有效性上可能會有差異。本論文採集東亞島弧的日本、臺灣與菲律賓蛇紋岩土壤，以及越南紅河斷裂帶之蛇紋岩土壤，共七個剖面，分析土壤物化性質與元素全量，並以BCR序列萃取與單一化學試劑萃取，評估鉻、鎳型態分布與潛在有效性。王水消化全量結果顯示，不同地區蛇紋岩土壤的組成元素含量差異大，其中鉻全量為684.9-3410 mg/kg，鎳全量為288.8-15746 mg/kg，另外以PCA (Principal Component Analysis) 分析元素 (鈣、鎂、鉀、鐵、鋁、錳、鉻、鎳、鈷) 全量可知，這些元素組成可區別不同地區蛇紋岩土壤，其中鎂、鎳是主要的影響元素。序列萃取發現殘餘態為鉻與鎳最高比例的結合型態，在越南土樣中，有大量鎳與鐵氧化物型態結合，且在化育過程會隨著鐵氧化物從表層洗入至裏土層；但在日本土樣中，鎳與鉻則較傾向和有機質結合而非鐵氧化物，且比例隨著深度遞減。單一化學試劑萃取結果顯示，除了日本土樣以外，所有土樣中鎳的潛在有效性皆高於鉻。此外，X光繞射分析顯示這些地區的土壤母質礦物組成在綠泥石、蛇紋石與鉻鐵礦等比例不同，支持了PCA所分析在元素含量上的差異。總結而言，受到古南海板塊碰撞影響的臺灣、菲律賓及越南蛇紋岩土壤性質相似，而位於東北亞的日本土樣與其他土樣有明顯差異，可能是因板塊運動的不同造成，導致土壤元素組成、鉻與鎳型態分布與其潛在有效性以及礦物組成皆有所不同。

關鍵字

蛇紋岩土壤；土壤化育；母質； BCR序列萃取；單一化學試劑萃取

並列摘要

Serpentine soils usually contain unique properties, etc. low Ca to Mg raio and high heavy metal contents, compared with other non-serpentine soils. However, these soils could have different dynamics and potential availability of Cr and Ni due to different parent materials and pedogenetic factors. Soils were collected from Japan, Taiwan and Philippines along the Eastern Asia island arc as well as Red River fault zone in Vietnam. Totally, seven pedons were collected and analyzed by physio-chemical properties and total element contents. Cr and Ni distribution and potential availability were evaluated by BCR sequential extraction and single stage extraction. According to total content digested by aqua-regia, Cr content ranged in 684.9-3410 mg/kg, while Ni content was among 288.8-15746 mg/kg. After analyzed by principal component analysis, element composition (Ca, Mg, K, Fe, Al, Mn, Cr, Ni, Co) was shown to lead to the main difference among these serpentine soils. On the other hand, Ni was one of the dominant elements. On average, residual Cr and Ni had the highest ratio in soils. Nevertheless, Ni in Vietnam soils were greatly associated with Fe-oxides, and appeared to illuviate into B horizon with Fe-oxides. On the contrary, Ni and Cr in Japan soils tended to combine with organic matter, and the aomunt decreased with depth. The results of single stage extraction indicated that Ni had much higher potential availability than Cr in all pedons except for OY1. In addition, powder XRD (X-Ray Diffraction) analysis showed that these soils had different chlorite, serpentine and chromite composition, which identified the outcome of PCA analysis. All in all, Taiwan, Philippines and Vietnam serpentine soils, which were influenced by south China sea plate, had similar properties, while element composition, Cr and Ni distribution and potential availability, and mineral composition of Japan serpentine soils were apparently different from other soils, probably due to different tectonic activities.