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Volume 65, Issue 1
Displaying 1-5 of 5 articles from this issue
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Yukimi KATAGAMI, Toshiyuki TANAKA, Takamitsu HONMA, Atsushi YOKOYAMA, ...2004 Volume 65 Issue 1 Pages 1-12
Published: April 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe upstream region of the Tenryu River (the outflow river of the hypertrophic lake Lake Suwa) has the world's largest population of the net-spinning caddisfly, Stenopsyche marmorata. The river water often contains huge amounts of the toxic cyanobacteria Microcystis and hepatotoxin microcystin that originate from the lake during spring- to -autumn blooms. The seasonal changes in microcystin concentrations in S. marmorata larvae from the river and the bioaccumulation and depuration of microcystin in S. marmorata were investigated. The toxic contents of the larvae correlated with the toxicity of volatile suspended solids in the river water. The younger larvae of S. marmorata contained higher concentrations of microcystin than the older ones. This tendency is probably caused by the differences in their food preferences. The prepupae, pupae and adults of S. marmorata showed only low levels of microcystin. Furthermore, the results of excretion experiments suggested that microcystin remained in S. marmorata tissues throughout the experimental period. These findings indicate that S. marmorata is a vector of microcystin in the river ecosystem, and that there is the potential for a transition of the cyanobacterial toxin to higher levels in the aquatic food chain and terrestrial habitat.View full abstractDownload PDF (934K) -
Taisuke OHTSUKA, Yasunori KUWABARA, Hiroki HAGA2004 Volume 65 Issue 1 Pages 13-20
Published: April 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSWe estimated the distribution and biomass of a submerged macrophyte community in the Lake Biwa's South Basin using an echo-sounder. Echograms corresponding to GPS locations were obtained during a cruise along 14 latitudinal transects at 1-km intervals. Based on the echograms, we drew a distribution map of the submerged macrophyte community. We also made a model to estimate its biomass from the echograms. The submerged macrophyte community was estimated to have a biomass of 7.1×104t in dry weight; the estimated macrophyte area was 32 km2 and accounted for 58% of the whole basin. These quantities were approximately equal to or grater than those before the 1960s, the time when the community decline became apparent. We compared the distribution map to an inferred submerged macrophyte area from transparency. In 1994, the macrophyte community was absent from many part of the euphotic zone where it would thrive. In contrast, the macrophyte community was present in most part of the euphotic zone in 2001. The submerged macrophyte community is considered to have gradually expanded to the empty bottom where sufficient light was available after 1994.View full abstractDownload PDF (678K) -
Yasuhiko KONNO2004 Volume 65 Issue 1 Pages 21-26
Published: April 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe author investigated the lotic aquatic insects in the Azusa River, in the Kamikochi Valley of Chubu Sangaku National Park. Among the 35 taxa collected, Baetis thermicus (Ephemeroptera), Cinygmula spp. (Ephemeroptera), and Epeorus aesculus (Ephemeroptera) were dominant.View full abstractDownload PDF (266K) -
Shinji UEDA, Kunio KONDO, Yuki CHIKUCHI, Yasushi SEIKE, Osamu MITAMURA2004 Volume 65 Issue 1 Pages 27-35
Published: April 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIn order to elucidate the species composition of phytoplankton and its characterization in brackish Lake Obuchi, located virtually in the center of the Shimokita Peninsula in Aomori Prefecture, observations were made of phytoplankton and water quality from April 2001 to March 2003. Mean cell density of the phytoplankton at the freshwater river estuary and the central point in lake reached 4.3×106 and 5.4×106 cells L-1, respectively. There was no significant difference in density between the stations. Phytoplankton identified in the present study totaled were 97 species, the most dominant of which in this lake were Skeletonema costatum, Cyclotella spp., Melosira juergensii, Nitzschia pungens, Chaetoceros sp. and Prorocentrum minimum. It was clarified that the dominant species of phytoplankton occurring in Lake Obuchi enjoyed optimum conditions for salinity (5 to 30 psu) and water temperature (< 15°C).View full abstractDownload PDF (628K) -
Shin-ichi NAKANO, Kentaro NOZAKI, Yuichi HAYAMI, Koji NAKAYAMA, Hirosh ...2004 Volume 65 Issue 1 Pages 37-44
Published: April 20, 2004
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSDownload PDF (693K)
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