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  • 1
    ISSN: 1439-863X
    Keywords: Key words Brackish Lake Obuchi ; Salinity ; Water quality ; Density gradient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fluctuations in the salinity and physicochemical characteristics of water quality were surveyed in brackish Lake Obuchi on the Shimokita Peninsula in Aomori, Japan. The mean salinity in the surface layer in all regions of Lake Obuchi was about 10 psu, whereas in the basin region at depths of greater than 3 m it was 20 psu. Furthermore, all the year round the halocline was formed at depths of 1–4 m. The maximum density gradient along a vertical axis in the center of the lake was observed at depths of 1–2 m in summer and 2–4 m in spring and fall. The depth of the maximum density gradient fluctuated with the seasons. In summer the water in the bottom layer was anoxic, and Fe, Mn, PO4 3−-P, and NH4 +-N supplied from the bottom sediment accumulated at high concentrations below the halocline. Thus, it was observed that the transfer of substances between the layers above and below the barrier formed by the halocline is suppressed. Although Lake Obuchi is small and shallow, the inflowing seawater easily resides, and a stable halocline readily forms because of the shape of its basin, which suddenly deepens on the Pacific Ocean side.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1439-863X
    Keywords: Key words Brackish Lake Obuchi ; Uranium ; Sediment ; Physicochemical form ; Sequential extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The physicochemical form of uranium (238U) in the sediment of brackish Lake Obuchi was investigated using the standard procedures of sequential extraction. Approximately 60% to 70% of 238U was composed of the form bound to carbonates and iron (Fe)-manganese (Mn) oxides in silty sediments, whereas more than 50% of 238U existed in the minerals of sandy sediments. The proportions of 238U bound to carbonates in the sediments of brackish Lake Obuchi were larger than those in fresh-water lake sediments. Most of the uranium in the brackish lake sediment was considered to be mainly influenced by UO2(CO3)3 4− in seawater, judging from the fact that the 234U/ 238U activity ratios (1.13 to 1.16) of silty sediments were very close to that of seawater (1.14). The high correlation found between the 238U concentration in the sediment and the amount of organic matter demonstrated that organic matter acts as a scavenger for 238U accumulation on the lake bottom.
    Type of Medium: Electronic Resource
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