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Volume 51, Issue 3
Displaying 1-8 of 8 articles from this issue
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Seasonal Variation of Nitrate NitrogenYasushi SEIKE, Kunio KONDO, Hiroshi HASHITANI, Minoru OKUMURA, Kaoru F ...1990 Volume 51 Issue 3 Pages 137-147
Published: July 24, 1990
Released on J-STAGE: October 19, 2009
JOURNAL FREE ACCESSThe seasonal variation of nitrate in the upper layer in the brackish Lake Nakanoumi has been investigated by the analysis of the data collected monthly during the period of 1976-1986. Upward trends in nitrate concentration were found in the colder season (January to March), and also in the rainy season (July). In contrast to nitrate, chlorinity decreased at the same time.
A significant negative correlation between nitrate concentration and chlorinity in the surface water in Lake Nakanoumi was found in January, February, March and July. In addition, from the analysis of the correlation between the increment of nitrate concentration in the surface water and cumulative rainfall, it was concluded that the accumulation of nitrate in the upper layer is mainly caused by discharge from the rivers into the lake through rainfall and melted snow.View full abstractDownload PDF (1431K) -
Yoshio SUGAYA, Masayuki YASUNO, Takanori YANAI1990 Volume 51 Issue 3 Pages 149-153
Published: July 24, 1990
Released on J-STAGE: October 19, 2009
JOURNAL FREE ACCESSThe lethal dosage of an extract of a toxic strain of Microcystis viridis or purified toxin, microcystin RR was determined against goldfish. The LD50 values of microcystin RR obtained by intraperitoneal injection into goldfish were just above 2 mg·kg-1 which was about 26 times higher than the known values for mice.
Death of goldfish occurred rather slowly until 5th day, when the observation was terminated following injection of extract. The liver tissue was most severely affected by the intraperitoneal injection of toxin, and hemorrhage, swelling and finally blood pooling in the tissue were observed.
Oral administration of Microcystis viridis as pellets mixed with the algae for 28 d did not cause any mortality but a few fish showed a slight liver damage.View full abstractDownload PDF (791K) -
Shin-ichi NAKANO, Masayuki SETO1990 Volume 51 Issue 3 Pages 155-161
Published: July 24, 1990
Released on J-STAGE: October 19, 2009
JOURNAL FREE ACCESSThe relationships between the degradation of 2, 4-dichlorophenol (DCP) and the changes in the density of DCP-degraders were examined in water samples from aquatic enviroments. In most of the water samples, the rapid degradation of 1 μg DCP-C·ml-1 or 0.1, μg DCP-C·ml-1 was observed, after a lag period lasting for more than a week, when DCP-degraders had increased to 104-105 cells·ml-1 or 103-104 cells·ml-1, respectively. However, in the water sample from the spring Masugata-no-ike, the degradation of 0.1 μg DCP-C·ml-1 was not observed for 42 day incubation, although DCP-degraders had increased to 104 cells·ml-1 at 35-day incubation. When both nitrogen and phosphorus were added to the water sample, the rapid degradation of DCP was observed. These results suggested that the sufficient increase in the density of DCP-degraders was a prerequisite condition for the degradation of DCP, but ecological factors such as mineral nutrients might limit the expression of the ability of DCP-degraders even when their densities were high.View full abstractDownload PDF (1111K) -
Muneoki YOH, Akihiko YAGI, Hisayoshi TERAI1990 Volume 51 Issue 3 Pages 163-171
Published: July 24, 1990
Released on J-STAGE: October 19, 2009
JOURNAL FREE ACCESSDenitrifying and nitrifying activities were determined to elucidate the mechanism of N2O accumulation in the oxygen depleted zone of Lake Kizaki. Both activities were detected without any substrate enrichments in a zone of low-oxygen content (0.03-0.14 ml·-1), where N2O and NO2-were accumulated. The determined nitrifying activity approximately coincided with the NH4+ utilization estimated from the NH4+ budget in this zone during the observation interval. On the basis of these activities and the change in N2O concentation, it was suggested that the observed N2O accumulation had dual origins of nitrification and denitirification and that these productions were in a dynamic equilibrium with further reduction of N2O to N2. The low-oxygen zone was found to be an active site for nitrogen cycling and was characterized by the presence of dissolved Mn and the absences of dissolved Fe and sulfide.View full abstractDownload PDF (1266K) -
Kunio KONDO, Yasushi SEIKE, Yoshio DATE1990 Volume 51 Issue 3 Pages 173-184
Published: July 24, 1990
Released on J-STAGE: October 19, 2009
JOURNAL FREE ACCESSThe relationships between the occurrence of phytoplankton and salinity or water temperature have been investigated for 8 years from 1979 to 1986 in brackish Lake Nakanoumi. Fourteen species such as Skeletonema costatum, Prorocentrum minimum and Cyclotella nana were dominant in this lake. Five among the 14 species bloomed in conditions of water temperature less than optimal for their growth, whereas every species bloomed in optimum salinity conditions. This fact indicates that the occurrence of dominant species in the lake is more strongly controlled by salinity than water temperature.
The result of comparison of weighted mean value of water temperature and salinity for the two periods of 1974-1978 and 1979-1986 also indicated the greater importance of salinity than water temperature.View full abstractDownload PDF (1663K) -
Masami NAKANISHI, Osamu MITAMURA, Takeshi MATSUBARA1990 Volume 51 Issue 3 Pages 185-189
Published: July 24, 1990
Released on J-STAGE: October 19, 2009
JOURNAL FREE ACCESSTo estimate seasonal change in the nutritional state of phytoplankton in the south basin of Lake Biwa, surveys for the determination of sestonic C : N : P ratios were conducted at five stations from May 1987 to May 1988. The sestonic C : N : P ratios indicated the possibility that phytoplankton were exposed frequently to moderate or severe phosphorus deficiency from May to October 1987 but little therafter until May 1988, whereas they were not in the state of severe nitrogen deficiency except for a given time in November of 1987.View full abstractDownload PDF (824K) -
Kunio KONDO, Yasushi SEIKE, Yoshio DATE1990 Volume 51 Issue 3 Pages 191-197
Published: July 24, 1990
Released on J-STAGE: October 19, 2009
JOURNAL FREE ACCESSMonthly surveys of phytoplankton occurrence were conducted from 1974 to 1986 at six stations in the brackish lake Nakanoumi. Both the numbers of phytoplankton cells and species tended to increase during the period when T-N concentration sharply increased, and decreased during the period when T-N concentration remained at the same level or gradually decreased.
Among the four diversity indices for the phytoplankton community (i.e., Fatten, Shannon, Simpson and Margalef), only the Margalef index showed a highly positive correlation (coefficient > 0.7) with the yearly changes of the nutrient (T-P or T-N) concentration at some stations.View full abstractDownload PDF (958K) -
Fumio HAYASHI1990 Volume 51 Issue 3 Pages 199-215
Published: July 24, 1990
Released on J-STAGE: February 05, 2010
JOURNAL FREE ACCESSBody size at maturation of aquatic insects differs individually or between populations. In this review, variations in the body size at maturity (a total of 112 examples) are classified into six categories ; intra-cohort, seasonal, annual, inter-habitat, and geographic variations, and those observed under experimental conditions. Individuals exposed to lower temperature tend to mature at a larger size, but in some cases, the inverse relationship is observed. Larger adults are always obtained in conditions of increased food availability or high quality of food. Body size at maturity decreases with increasing population density in all examples dealing with the density effect on adult body size. Predation pressure, photoperiod and competition may be other important factors changing the adult body size, but there have only been a few studies in this area. Finally, the adaptive significance of the size at maturation is discussed in relation to various aspects of the life history of aquatic insects.View full abstractDownload PDF (2906K)
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