Japanese Journal of Limnology (Rikusuigaku Zasshi)
Online ISSN : 1882-4897
Print ISSN : 0021-5104
ISSN-L : 0021-5104
Volume 78, Issue 3
Displaying 1-2 of 2 articles from this issue
Original article
  • Masaru YAMANAKA
    2017 Volume 78 Issue 3 Pages 217-230
    Published: September 30, 2017
    Released on J-STAGE: September 30, 2018
    JOURNAL FREE ACCESS

     A combination of carbon stable isotopic compositions (δ13CDIC) and chemical compositions of the water in Lake Haruna (LH) was used to investigate origins and supply processes of dissolved inorganic carbon (DIC) during the summer stagnant period in LH, located in the central part of Gunma Prefecture. The temperature depth profile illustrated that the lake water could be divided into two main layers: an epilimnion and a hypolimnion, and the boundary was 7 to 8 m deep as thermocrine. Higher values of pH and dissolved oxygen (DO) were observed to be associated with lower values of DIC, partial CO2 pressure (logPCO2), and δ13CDIC in the epilimnion than those in the hypolimnion. This can be attributed to photosynthesis occurring in the epilimnion, since it is the euphotic zone. A Rayleigh model with -16.6‰ as the isotopic enrichment factor (ε) demonstrated that a photosynthesis process, which consumed up to approximately 30% of DIC, sufficiently accounts for the decreases in the DIC concentrations and the increases in the δ13CDIC values, upon moving upwards from the hypolimnion to the epilimnion. Moreover, δ13C value for the CO2 gas, which initially equilibrated with DIC in LH, was calculated to be approximately -21‰, which indicated that DIC in LH originated entirely from the decomposition of organic materials through a respiration process and was not likely to be derived from atmospheric CO2.

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  • Shigeaki TAMURA, Takashi KAGAYA
    2017 Volume 78 Issue 3 Pages 231-235
    Published: September 30, 2017
    Released on J-STAGE: September 30, 2018
    JOURNAL FREE ACCESS

     We evaluated the distribution of the late instar larvae of the stone-living mayfly Drunella trispina (Uéno) in fine substrate. In a mountain stream of the Tamagawa River system, the presence or absence of larvae was investigated on stones with different abundances of fine substrate under or around the stone. The occurrence probability of the larvae was high when the stone had a high proportion of fine substrate; larvae occurred only on stones with fine substrate covering > 75% of the area under the stone. Thus, fine substrate may be important for the microhabitat structure of macroinvertebrate species that inhabits stony riffles and does not directly utilize gravel or sand.

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