Japanese Journal of Limnology (Rikusuigaku Zasshi)
Online ISSN : 1882-4897
Print ISSN : 0021-5104
ISSN-L : 0021-5104
Volume 58, Issue 2
Displaying 1-6 of 6 articles from this issue
  • Koichiro KAWAI, Shiro KASUYA, Tetsuo MURAKAMI, Hiromichi IMABAYASHI
    1997 Volume 58 Issue 2 Pages 145-156
    Published: June 01, 1997
    Released on J-STAGE: June 12, 2009
    JOURNAL FREE ACCESS
    The chironomid fauna of the lower reaches of the Nagara River was investigated on the basis of male adults emerging from bottom samples and those collected by light sampling. As a result, a total of 547 males representing 72 species were collected. For bottom samples, one occurrence peak was observed from May to June. The number of species increased remarkably with the distance from the rivermouth.For light samples, two peaks of species richness were observed, one in June and another from September to November. Larval distribution ranges differed considerably with species. Cryptochironomus albofasciatus was recorded from all the sites. Fourteen out of 18 major species were collected only at the upper reaches of more than 20 km from the rivermouth. This suggests the existence of a salinity barrier for freshwater species between 15 km and 20 km. Clear differences in the seasonal occurrence of larvae were observed among species. For example, Polypedilum masudai and P. cultellatum occurred only from spring to summer and summer to autumn, respectively. Paratendipes albimanus was collected only by bottom sampling, suggesting the weak phototaxis of male adults of the species. In contrast, Smittia aterrima was collected only by light sampling, probably due to the terrestrial nature of the species.
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  • Michiko SHIMODA
    1997 Volume 58 Issue 2 Pages 157-172
    Published: June 01, 1997
    Released on J-STAGE: June 12, 2009
    JOURNAL FREE ACCESS
    Vegetation and environmental conditions of irrigation ponds in the Saijo Basin, Hiroshima Prefecture, were studied to show the differences among aquatic plant communities in ponds with differing environments. The following three communities were found from mountain ponds to ponds in agricultural land : Brasenia schreberi-Nymphaea tetragona community, Trapa japonica-Brasenia schreberi community, and Trapa japonica community. Species-rich ponds were small and had low electric conductivity values ranging from 17.1-50.6 μS cm-1. Nuphar oguraense var. akiense, Brasenia schreberi and Trapa japonica occurred in the ponds with a wide range of conductivity. Most of the other species were restricted to water with low conductivity values. The temporal vegetation changes in a pond following surrounding land-use change was similar to the spatial distribution pattern of aquatic plant communities. Plant distribution seems to be influenced not only by water quality but also by other factors such as accidental species dispersal, interspecific competition, allelopathy, aquatic animals, substrate types and pond history. To conserve pond life, both the ponds themselves and the catchment areas must be protected.
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  • Studies of Submerged Macrophyte Communities in Lake Biwa (3)
    Etsuji HAMABATA
    1997 Volume 58 Issue 2 Pages 173-190
    Published: June 01, 1997
    Released on J-STAGE: June 12, 2009
    JOURNAL FREE ACCESS
    The areal distribution, stand structure and biomass of pure stands of Elodea nuttallii, an alien species of water weed invading Lake Biwa since 1961, were studied with emphasis on the remarkable yearly fluctuation in its biomass. The total area covered by the Elodea community was estimated at 895 ha, based on a complete lake survey in 1990 using sonar detection along a number of line transects. Underwater biomass samplings were carried out at two different depths in the northernmost part of the lake during two successive years, representing a light crop year (1988) and a heavy crop year (1989). The maximum biomass and stem density at the shallower site (depth 3 m) in 1989 amounted to 723g dry wt. m-2 and 4, 960 stems m-2, respectively. Those in 1988 were only 68% and 60% of the corresponding values of 1989. Both biomass and stem density decreased at the deeper sites (depth 5m), with the latter remaining fairly constant in both years. A comparison of environmental factors between light and heavy crop years indicated that a mild winter with a minimum monthly temperature above 8°C combined with sufficient sunshine in early spring favored the growth of overwintering plants from which new shoots were produced vegetatively. This resulted in greater biomass production in the following season.
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  • Takayoshi TSUCHIYA, Wataru TANAKA, Isao IKUSIMA
    1997 Volume 58 Issue 2 Pages 191-196
    Published: June 01, 1997
    Released on J-STAGE: June 12, 2009
    JOURNAL FREE ACCESS
    Gas exchange was measured for leaves of an emergent plant, Zizania latifolia (GRISEB.) TURCZ grown at an experimental pond. Net photosynthesis per unit leaf area at above light saturation was rather small. Vapor pressure differences between the intercellular spaces in the leaf and the atmosphere (VPD) affected leaf conductance at photosynthetic photon flux densities saturating net photosynthesis. However, VPD did little to impede net photosynthesis in a surplus of light, which is different from certain emergent plants with high photosynthetic activity per unit leaf area such as Oryza sativa L. and Cyperus papyrus L.
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  • Yasuro KADONO, Toshiyuki NAKAMURA, Takeshi SUZUKI
    1997 Volume 58 Issue 2 Pages 197-203
    Published: June 01, 1997
    Released on J-STAGE: June 12, 2009
    JOURNAL FREE ACCESS
    Genetic variation in two plants introduced into Japan, Egeria densa and Elodea nuttallii, was investigated by enzyme electrophoresis. As a result, no polymorphism in allozyme patterns was found among 44 and 26 populations, respectively, of Egeria densa and Elodea nuttalii naturalized in Japan. This result suggests that the populations of the two species are rametes of the same clone which have spread by vegetative means from a single source, though the possibility of multiple introduction is not excluded. The ecological implication of genetic uniformity was briefly discussed in relation to the cause of decline in the population after the peak of abundance.
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  • Shiori YAMASAKI
    1997 Volume 58 Issue 2 Pages 205-214
    Published: June 01, 1997
    Released on J-STAGE: June 12, 2009
    JOURNAL FREE ACCESS
    Based on the assumption that the oxygen supply to underground organs is by diffusion from aerial shoots to the lower boundary of Zizania latifolia (GRISEB.) STAPF, a model was constructed to determine whether buds from the presumed largest rhizomes can emerge in water 40 cm in depth such as occurs in the spring. A tank experiment was also carried out to determine the rates of bud emergence in spring from different-sized rhizomes transplanted the previous fall. Larger rhizomes had a higher rate of bud emergence. Seventy-six percent of buds from rhizomes larger than 40 cm3 in volume emerged. Dry weight of whole shoots and maximum dry weight of individual shoots that emerged from a rhizome were 8.1% and 2.1%, respectively, of the estimated initial dry weight of the rhizomes. About 24% of the dry weight of the rhizomes was lost during the winter. These results suggest that Z. latifolia grown in deep sediment where the oxygen concentration of the inner basal stem is 8.2% can produce rhizomes large enough for bud emergence in the spring when the water depth is 40 cm.
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