- 期刊
臺灣森林土壤中鐵氧化物與鋁層間蛭石之生成機制
Formation of Iron Oxide and Hydroxy-Interlayered Vermiculite in Forest Soils of Taiwan
摘要
本文就臺灣五個森林土壤體，探討其氧化鐵（Fe oxides）與粘土之組成，及氧化鐵分布相對於土壤深度。自E化育層到B層，結晶性氧化鐵含量劇增。由示差性X-射線繞射儀（differential X-ray diffraction，DXRD）所鑑定B（含薄膠層placic）化育層之帶磁性粘粒部份含有纖鐵礦（lepidocrocite），針鐵礦（goethite）及蛭石。此等土體在X-射線繞射圖並未顯現赤鐵礦（hematite）之存在。氫氧化鋁層間蛭石（hydroxy-interlayered vermiculite，HIV）也可藉助鉀飽和粘粒加熱至350˚C而鑑定之。X-射線繞射（X-ray diffraction，XRD）之粘粒層間距離為1.42 nm，加熱至350˚C則收縮至1.0 nm；鎂飽和甘油蒸氣處理後，則其1.42 nm之繞射峰更為增強。纖鐵礦、針鐵礦及氫氧化鋁層間蛭石在森林土壤之B化育層（B horizons）中含量相當佔優勢。鐵、鋁及粘粒聚積於森林土壤之底土層（subsoil），乃由於酸性，排水不良，濕潤與溫和的土壤環境所促成。此等土壤樣體以酸性草酸銨法所萃取而獲致之資料，顯示鐵，鋁由淋洗（leached）而聚積於B層。充份的有機碳含量促進鋁之移動（transport），亦即螫合作用（chelation）所促成。有機酸對纖鐵礦、針鐵礦及氫氧化鋁層間蛭石在B化育層生成大有助益。
並列摘要
Five pedons from forest soils of Taiwan were examined for Fe oxides, clay minerals and Fe oxides distribution as a function of soil depth. The crystalline Fe oxides sharply increased from the E to B horizons. Only lepidocrocite and goethite were identified by differential X-ray diffraction (DXRD) analysis in magnetic clay fractions of the B (or placic) horizons. There were no substantial hematite peaks appearing in the X-ray diffraction (XRD) patterns of any pedons. Hydroxy-interlayered vermiculite (HIV) was also characterized by the K-saturated clay which was heated from 25˚C to 350˚C. The XRD d-spacing of the 1.4 nm peak collapsed to 1.0 nm. Lepidocrocite, goethite and HIV were dominant in the B horizons (below E) of forest soils under acidic conditions, poorly drained soil environments, in udic and mesic soil climates. Acid ammonium oxalate extractable data in these pedons indicate accumulation of leached Al and Fe in the B horizons. Abundant organic C may contribute to Al transport i.e., chelation. Organic acids were conducive to the in-situ formation of lepidocrocite association with goethite and HIV in the B horizons of forest soils.
延伸閱讀
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