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Volume 65, Issue 2
Displaying 1-8 of 8 articles from this issue
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Kenji KATO, Toshiyuki GODO, Akihiko KAGEYAMA, Ryo ASHIYA, Koji MISHIMA ...2004 Volume 65 Issue 2 Pages 69-82
Published: August 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSFrequent water quality monitoring, identification of phytoplankton species, and measurement of C:N:P ratios were conducted to clarify the time series in the occurrence of a red tide by a dinoflagellate, Prorocentrum minimum, in Lake Nakaumi, a coastal lagoon with a two-layered structure.
In late autumn 1996, when vertical mixing by seasonal winds started, a red tide from P. minimum occurred after a supply of NO3-N due to a freshet in an upper layer where PO4-P had excessively accumulated. That red tide continued throughout the winter, strengthened in spring, and disappeared in mid-May 1997 when fluxes of inorganic nitrogen and phosphorus to the upper layer decreased. During the period from autumn 1996 to spring 1997, the C:N:P ratio of suspended material gradually increased from 130:14:1 to 300:30:1.
Compared with the early 1980s, the concentration of PO4-P in the central lake increased in the lower layer during the warmer seasons. Consequently, water quality in the upper layer changed from P to N deficiency in late autumn. P. minimum was dominant enough to absorb the supplied NO3-N under excess phosphorus conditions. The change toward N deficiency in the water quality was considered to be the reason why almost all red tides recently formed were due to P. minimum rather than to the diatom, Skeletonema costatum.View full abstractDownload PDF (1029K) -
Kunimitsu INOUCHI, Hideki YASUTOMI2004 Volume 65 Issue 2 Pages 83-92
Published: August 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSSalt water intrusion into groundwater occurred in connection with a construction project in progress near a tidal river. The groundwater level needed to be lowered during the digging of a drain pipe ditch. The well-point method (one of the groundwater level lowering methods used in construction) was adopted. The construction lasted one year and six months. A high concentration of salt in a local well near the digging operation was observed during the latter half of construction, making us concerned about the possibility of accidentally salinizing the surrounding groundwater. A numerical analysis using a three-dimensional unsteady hydrodynamic dispersion model was carried out, enabling us to reproduce the salinization level and to investigate its cause. Our results suggest that, although the amount of pumping was an important factor in the salinization, the positional relation between the site of the pumping well and that of the local wells supplying water was also important. Furthermore, it was also forward that the dispersivity and groundwater recharge in the field can be estimated using our observations of the results of salinization.View full abstractDownload PDF (698K) -
Shiho KAGEYAMA, Takeshi SUMINO, Nobuhisa MOROOKA2004 Volume 65 Issue 2 Pages 93-98
Published: August 20, 2004
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSIn order to clarify the effect of anthropogenic contamination on the water quality of Lake Oze, we investigated the water quality in the surrounding Oze wetland at 10 sampling stations (including Lake Oze) between 1999 and 2002. We found that the eutrophication of the lake was accelerated by elevated levels of NO3--N and PO43--P, and that the Nushiri River was contaminated with total coliforms. Both contaminations were caused by drainage from septic tanks in the Oze area. The contamination from organic matter, indicated as COD or BOD, was detected during cold weather, probably due to the impaired efficiency of septic tanks under low temperature. By contrast, during warm weather, it is suggested that nutrients such as DIN are released through the decomposition and remineralization of organic matter in the tanks. Thus the eutrophication in Lake Oze is attributable to the these loading of the released nutrients.View full abstractDownload PDF (475K) -
Shunichi YOSHIKAWA, Kazuko TAZAKI, Shozo OKUDA, Kazuko NAKAGAWA, Kozo ...2004 Volume 65 Issue 2 Pages 99-108
Published: August 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSWater quality was monitored in Sawanoike Pond, Kyoto from 1993 to 2003. The averages of pH and alkalinity in the pond during the monitoring period were 5.53 and 16μeq L-1, respectively. These values belonged to the lowest levels investigated for the effects of acid rain on the aquatic ecosystems in Japanese lakes. Neither increasing nor decreasing trends were found for these variables during the period of this study. However, H+ concentrations in the pond showed a tendency to fluctuate in inverse proportion to the water level (γ=-0.652 ) and in proportion to the SO42- ion concentrations (r=0.632). On the other hand, the correlation coefficients between H+ ion and water temperature as well as chlorophyll-a concentrations were low (γ=-0.143, γ=0.006 ), which suggest that the fluctuations in pH did not result from changes in either water temperature or photosynthesis activity. The monitoring results included the unusual case of a pH decline during October and November 2000, indicating the effect of the eruption of Miyake-jima Island on the water quality of the pond. In summer, dissolved oxygen concentrations in the bottom layer of the pond decreased (min.: 1.9 mg L-1), resulting in an increase in alkalinity (max.: 52μeq L-1) and reserved pH (max: 6.5) in the bottom layer.View full abstractDownload PDF (728K) -
Yasuhiko KONNO, Shunsuke WATANABE2004 Volume 65 Issue 2 Pages 109-114
Published: August 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIn order to elucidate the species composition of aquatic insects in the lower reaches of the Hirose River, Miyagi Prefecture, aquatic insects were monitored once a month from April 2001 to January 2002 at two stations (St.1: Hirosebashi, and St.2: Sendai-ohashi). The two sites were approximately 1.5 km apart, and St.1 was located upstream. A total of 2, 862 aquatic insects from 43 taxa belonging 25 families were collected at the two stations. Among the 43 taxa collected, Drunella basalis (Ephemeroptera), Hydropsyche orientalis (Trichoptera) and Cincticostella (Cincticostella) elongatula (Ephemeroptera) were dominant in number, and D. basalis, Stenopsyche marmorata (Trichoptera) and C. (C.) elongatula were dominant in the standing crop. Although the taxon richness and total standing crop did not differ significantly between the two sites, total number of individuals was significantly lower in St.2 (p<0.01) as determinrd by unreplicated two-way ANOVA.View full abstractDownload PDF (321K) -
2004 Volume 65 Issue 2 Pages 115
Published: August 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSDownload PDF (68K) -
G. Allen Burton Jr.2004 Volume 65 Issue 2 Pages 117-134
Published: August 20, 2004
Released on J-STAGE: June 12, 2009
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2004 Volume 65 Issue 2 Pages 161
Published: 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSDownload PDF (24K)
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