Cores 11 through 26 by Gary B. Dr - University of Illinois at Urbana ...

For most cores, the Rb content was greatest in the upper part of the B horizon. Cores 16, 17, 22, and 25were exceptions to this observation. In core 26, the Rb content increased with depth through the core. Theminimum Rb content was 37 mg/kg and the maximum was 191 mg/kg.Strontium Strontium generally is associated with soil organic matter, but may also precipitate, underalkaline conditions, as strontianite (SrCO 3), and is commonly associated with calcium geochemically.Strontium is easily mobilized during weathering of soils, especially in acidic oxidizing environments, butit is quickly incorporated in clay minerals and strongly bound by soil organic matter (Kabata-Pendias,2001).The Sr contents of these cores did not vary appreciably, falling in the range of 69 to 255 mg/kg. In general,the Sr content was in the range of 100 to 200 mg/kg. Even though the statistical correlation of Sr with Cain these cores was very low, the shapes of the Ca depth trends were reflected in the Sr depth trends. The Srtrends, however, lacked the degree of change from sample to sample exhibited by the Ca trends.Vanadium During weathering vanadium can be mobile, depending on the host minerals. Once freed byweathering, V tends to be incorporated in clay minerals or iron oxides (Butler, 1953, 1954). Vanadiumalso may form complex compounds with soil organic matter, for example in porphyrin-type compounds(Kabata-Pendias, 2001). In addition to the rocks in the parent materials, V can be contributed to soils byindustrial processes such as smelting or combustion of coal or oil.The V content in the soil (range from 37 to 172 mg/kg) generally was greatest in the upper B horizon. Thetrend of V content with depth paralleled that of Zn and/or Rb in all but four (16, 17, 22, and 25) of thesixteen cores.Zinc Zinc is strongly adsorbed by clay minerals and soil organic matter, and, therefore, is commonlypresent in higher concentrations in surface horizons than at deeper positions in the soil profile (Kabata-Pendias, 2001). The atmospheric input of Zn from industrial fallout may be higher than its loss from thesoil profile by leaching (Kabata-Pendias, 2001). This lack of balance between input and output resultsin an accumulation of Zn in the surface horizon. Zinc is tightly bound by clay minerals and soil organicmatter (Lindsay, 1972) and by iron oxyhydroxides (White, 1957). Therefore, the availability of Zn toplants is low.In these 16 cores the zinc content (range from 33 to 139 mg/kg) was generally greatest in the B horizon. Intwo cores (25 and 26), however, the Zn content increased through the depth of the cores.Zirconium Zirconium generally occurs in soil as the very stable mineral zircon (ZrSiO 4). Zircon is veryresistant to weathering and zirconium is only very slightly mobile in soils. The Zr content of soils isgenerally inherited from the parent materials (Kabata-Pendias, 2001).The minimum Zr content was 98 mg/kg and the maximum was 489 mg/kg. The Zr content in 13 of the 16cores was greater in the upper one or two samples than in those from deeper positions in the soil profiles,which suggests a greater degree of weathering of minerals other than zircon at the surface of the soil thanlower in the profile. The content of Zr in the surface samples would also be elevated if Zr-containingmineral particles were carried to and deposited on the soil surface by wind.Carbon Most carbon in the samples was combined in organic residues from biological material. Plantresidues are typically plowed into the upper portions of the soil column after harvest each year. Burrowing23