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Volume 53, Issue 2
Displaying 1-7 of 7 articles from this issue
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Naoshi C. WATANABE1992 Volume 53 Issue 2 Pages 125-131
Published: April 26, 1992
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSEggs of Potamanthus formosus were kept at constant temperature (range 4.8-30°C) in the laboratory. The percentage of eggs hatched was 34-53% over a mean temperature range of 15-30°C, peaking at ca. 20°C, but dropping abruptly below 15°C to almost zero at ca. 13°C. The developmental time (Y) was inversely related to the water temperature, and the relationship was well described by a hyperbolic equation. The threshold temperature for egg development was calculated to be 10.5°C for 50% hatch based on the relationship between the rate of development (1/Y) and temperature. This suggests that the threshold temperature for egg development may differ from that for egg hatching. The calculated values of the summation of effective degree-days were 222.2 above 10.5°C for 50% hatch. Extrapolating the results to a natural stream, eggs must be laid until late in September to hatch by the time water temperature decreases to 15°C. The above estimation suggests that eggs laid late in the emergence period from June to October would not hatch before winter. These eggs may overwinter and hatch in spring. This conjecture is supported by the fact that the number of tiny nymphs evidently increased in April and May.View full abstractDownload PDF (367K) -
Toshihiro MIYAJIMA1992 Volume 53 Issue 2 Pages 133-138
Published: April 26, 1992
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSDuring aerobic decomposition of a natural assemblage of particulate organic matter collected by a 70μm-mesh nylon net from the north basin of Lake Biwa, a rapid regeneration of both ammonia and phosphate occurred in association with the proliferation of bacteria and heterotrophic microflagellates. Although ammonia was liberated during the growth periods of both bacteria and microflagellates, phosphate was mainly regenerated in parallel with the proliferation of microflagellates. This suggests the enhancing effect of microflagellate activity on the regeneration of phosphorus from indigenous particulate organic matter.View full abstractDownload PDF (306K) -
Yasuhiko TEZUKA1992 Volume 53 Issue 2 Pages 139-144
Published: April 26, 1992
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSAlthough the north (main) basin of Lake Biwa has become progressively eutrophicated since the beginning of this century, its eutrophication was not so marked for the last 24 years from the standpoints of such physical and chemical parameters indicating trophic status as transparency, minimum dissolved oxygen concentration in the hypolimnion and total phosphorus concentration of the water body.
In spite of the above facts, the external phosphorus loading in Lake Biwa has been high enough to bring about its rapid eutrophication with reference to VOLLENWEIDER's (1976) prediction model. Mass balance of phosphorus for Lake Biwa was examined to explain the above discrepancy. As a result, it was suggested that phosphorus sedimentation plays a decisive role in the delay of the eutrophication of Lake Biwa (north basin).View full abstractDownload PDF (308K) -
Shin-ichi NAKANO1992 Volume 53 Issue 2 Pages 145-149
Published: April 26, 1992
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSProduction of bacterioplankton was studied together with phytoplankton composition at a pelagic site in the north basin of Lake Biwa from 19 February to 7 June 1990. During the investigation period, two species of phytoplankton predominated: Asterionella formosa (Bacillariophyceae) from 19 February to 18 April (the early period) and Uroglena americana (Chrysophyceae) from 9 May to 7 June (the late period). Bacterioplankton production estimated by the frequency of dividing cells method remained at a high level during the early period, ranging from 7.4 to 33μgC⋅l-1⋅d-1. During the late period, bacterioplankton production was low, ranging from 4.1 to 18μgC⋅l-1⋅d-1. The change in bacterioplankton production appeared to relate to the change in phytoplankton composition.View full abstractDownload PDF (287K) -
Hiromi KOFUJI, Yu ISOBE, Teizi KAWAI1992 Volume 53 Issue 2 Pages 151-156
Published: April 26, 1992
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSWe studied the mandible shapes of aquatic insects, and analyzed correlations between the wet body weight and the size of mandibles and other parts of six orders, 15 families commonly found in the Takami and Shigou Rivers in Higashiyoshino, Nara Prefecture. Highly significant correlations between the size of mandible and wet body weight of insects were obtained in all families studied. Since the mandibles of aquatic insects usually remain in the feces of the birds and the stomachs of fishes, and are easily identified by family name, the regression lines obtained in this study would be useful in estimating the amount of prey taken by animals.View full abstractDownload PDF (305K) -
Masaru AMEMIYA1992 Volume 53 Issue 2 Pages 157-166
Published: April 26, 1992
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe Zenpukuji River is a small river that originates from and flows through a residential area of the western region of Tokyo. The river was highly polluted, but it has recovered following the completion of a sewerage system. Conservation of water from the groundwater is the most important factor in discussing this river's environment. Discharge from groundwater, dilution of water quality, and their inter -relation were investigated. The results are as follows:
1) The source of river water is groundwater in the basin and from the Musashino Aquifer. The discharge is related to rainfall amount.
2) Concentrations of BOD and SS are clearly reduced in the lower reaches by dilution and self-purification. The rate of the reduction is related to the river discharge, i. e., groundwater discharge.
3) The effects of dilution on Cl- and electric conductance (EC) are not observed, since groundwater of the region shows high concentrations of Cl- and EC.View full abstractDownload PDF (644K) -
Kazuko MORIKAWA, Toshihiro SUGITATE1992 Volume 53 Issue 2 Pages 167-172
Published: April 26, 1992
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe numbers of bacteria in river water and the epilithon of the river bed were enumerated using color image-analyzed epifluorescence microscopy. Bacteria stained by acridine orange (AO) are known to show fluorescent green or red-orange colors. The two colors of stained particles were separated and counted independently by an image analyzer (nexusQube), and the area of each stained particle displayed on the microscope field was measured. Bacterial communities in the river water and river epilithon were composed of two subcommunities which were stained red-orange or green. The bacterial particles stained fluorescent green were small in area, but the red-orange ones were composed of various sizes of stained particles. Judging from the particle area and color, no differences were observed in the composition of bacterial communities between the river water and the epilithon at the Koremasa site of the Tamagawa River.View full abstractDownload PDF (1713K)
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