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  • Artikel: DFG Deutsche Nationallizenzen  (4)
  • 2000-2004  (4)
  • Key words Brackish Lake Obuchi  (2)
  • Key words Urea decomposition  (2)
  • 14-labden-8,13-diol
  • [abr] B.I.; Brinkman index
Datenquelle
  • Artikel: DFG Deutsche Nationallizenzen  (4)
Materialart
Erscheinungszeitraum
  • 2000-2004  (4)
Jahr
Schlagwörter
  • 1
    ISSN: 1439-863X
    Schlagwort(e): Key words Urea decomposition ; Diel variation ; Lake Nakaumi
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Diel variations in urea decomposing activity in the euphotic zone of brackish Lake Nakaumi were measured under fixed light intensity. The decomposition rate of urea was 17 to 44 μ mol urea m−3 h−1 in the light and 10 to 27 μ mol urea m−3 h−1 in the dark. Higher decomposition rates were obtained in the upper euphotic zone. A clear diel periodicity in the urea decomposition rate was observed, with high rates from 1200 to 1600 and low rates from 0000 to 0400. Chlorophyll a specific decomposing activity ranged from 12 to 21 μg urea C mg chl.a −1 h−1 in the light and 7 to 13 μg urea C mg chl.a −1 h−1 in the dark. In the light, high values were obtained from 1600 to 2000 and low values from 0400 to 0800. The diel change in specific decomposing activity exhibited a similar pattern to that of the photosynthetic assimilation number, following the diel change in photosynthetic activity.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1439-863X
    Schlagwort(e): Key words Brackish Lake Obuchi ; Uranium ; Sediment ; Physicochemical form ; Sequential extraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Limnology 1 (2000), S. 57-62 
    ISSN: 1439-863X
    Schlagwort(e): Key words Brackish Lake Obuchi ; Salinity ; Water quality ; Density gradient
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 1439-863X
    Schlagwort(e): Key words Urea decomposition ; Size fraction ; Phytoplankton ; Lake Nakaumi
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The influence of brackish phytoplankton cell classes upon the response of urea decomposition was investigated in Lake Nakaumi. The urea decomposition rate was 5 to 350 μmol urea m−3 h−1 in the light and 3 to 137 μmol urea m−3 h−1 in the dark. The urea decomposition rates in the light were obviously higher than in the dark. An extremely high rate (350 μmol urea m−3 h−1) was observed in Yonago Bay. The rate in the smaller fraction (〈5 μm) exceeded that in the middle (5–25 μm) and larger fractions (〉25 μm). The chlorophyll- and photosynthesis-specific rates for urea decomposition in the light were 0.5 to 3.9 μmol urea mg chl.a −1 h−1 and 0.3 to 1.3 μmol urea mg photo.C−1. The specific urea decomposing activities were higher in the smaller fraction than in the other two fractions. The present results suggest that in brackish waters urea decomposition occurred with coupling to the standing crop and photosynthetic activity of phytoplankton.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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