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Volume 57, Issue 3
Displaying 1-7 of 7 articles from this issue
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Hiroki HAGA, Toshi NAGATA, Mitsuru SAKAMOTO1996 Volume 57 Issue 3 Pages 213-223
Published: September 01, 1996
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSWe conducted 15NH4+ dilution experiments to examine temporal variations in NH4+ regeneration and uptake in the pelagic environments of mesotrophic Lakes Kizaki and Biwa. In Lake Kizaki, both NH4+ regeneration and uptake rates showed no apparent diurnal periodicity during summer (July and August), and the regeneration: uptake ratio was close to one over the course of the day, suggesting that regeneration and uptake were tightly coupled regardless of light conditions. Size fractionation experiments showed that bacterial NH4+ regeneration was substrantial throughout the day, suggesting that a microbial loop was responsible for the rapid turnover of NH4+. Seasonal measurements revealed that NH4+ regeneration and uptake rates were highest in summer in both lakes. Correlation analyses indicated that temperature, nutrients and chlorophyll-α concentrations had little effect on the uptake rates. The regeneration : uptake ratio was close to one (0.95±0.31, n=18) despite large variations in nutrients and biological conditions, suggesting that phytoplankton usually take up regenerated NH4+ as rapidly as they can. Our data provide direct evidence that biological regeneration in the euphotic zone is the dominant process in NH4+ supply to phytoplankton in pelagic environments of mesotrophic lakes.View full abstractDownload PDF (654K) -
Kumiko YAJIMA1996 Volume 57 Issue 3 Pages 225-233
Published: September 01, 1996
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSPrincipal component analysis (PCA) was applied to evaluate some of the potential factors contributing to Secchi depth (SD) in the oligotrophic alpine Lake Oze-Numa, using seven water quality parameters obtained during 1990-1992. The data on SD, water temperature (WT), chemical oxygen demand (COD), total nitrogen (TN), suspended solids (SS), total phosphorus (TP), and chlorophyl-α (CHL) were examined. The first component had large loadings on SD, WT, SS, TP, and CHL attributable to phytoplankton population. COD and TN correlated with the second component, showing natural contributions. SD was revealed to be a reliable indicator of eutrophication in the lake, as it was predicted successfully by multiple linear regression analysis using SS, TP, and CHL as independent variables. A time-series analysis of the SD records was applied to a simple estimation of the eutrophication rate of the lake. SD has decreased for the past 25 years (1965-1990) at a rate of 0.065 m⋅yr-1 or 1.2%⋅yr-1. The SD trend was partly explained by the increase in TP concentration attributable to tourists.View full abstractDownload PDF (530K) -
Seiichi NOHARA1996 Volume 57 Issue 3 Pages 235-243
Published: September 01, 1996
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSThe growth of Nelumbo nucifera GAERTN. was investigated at an artificial stand in outdoor concrete ponds. The ratio of above- to below-ground biomass (T/R ratio) ranged from 0.3 to 3. Although N. nucifera is a perennial, the reproductive organ (tuber) begins to form later in the growing period than in annual plants; in addition, the life span of the tuber is less than one year. Maximum relative growth rate was 0.037 g⋅g-1⋅day-1 in July.The leaf area index of floating leaves did not exceed 1 m2⋅m-2.
The influence of initial tuber density on the foliage structure and below-ground biomass of N. nucifera were investigated. The initial death rate at the time of lamina rolling increased with leaf density. Control of the density of floating leaves was done twice ; once at the early stage of lamina rolling, and again at the late stage of the fully expanded leaf. The below-ground biomass in the following spring did not correlate with initial tuber size. When the tuber biomass was under about 400 g dry weight⋅m-2, net production of below-ground biomass of the N. nucifera stand seems to have attained a plus value. N. nucifera exhibited typical pioneer characteristics in an environment of frequent disturbances such as flooding, i.e., a high T/R ratio, high vegetative propagation by stolons and a short life span of the tuber.View full abstractDownload PDF (554K) -
Noriko TAKAMURA, Yasushi ISHIKAWA, Hidetoshi MIKAMI, Hajime MIKAMI, Yu ...1996 Volume 57 Issue 3 Pages 245-259
Published: September 01, 1996
Released on J-STAGE: March 04, 2010
JOURNAL FREE ACCESSRelationships of bacterial, picocyanobacterial, eucaryotic picoplankton, nano-flagellate and ciliate abundances to each other and to chlorophyll α (Chl.α) (total and > 10, 2-10 and <2 μm fractions), total phosphorus (TP), total nitrogen (TN) and TN : TP ratio in 34 epilimnetic waters during the warm season in 1994 were investigated. Linear regressions on TP and Chl.α accounted for 51% and 34% of the variability in bacterial and ciliate abundances, respectively. The abundance of heterotrophic nanoflagellates was not correlated with that of bacteria. For occasions when the abundance of picocyanobacteria was greater than 104 cells⋅ml-1, the maximum abundance of picocyanobacteria in each lake was positively correlated with TP (γ=0.40, n=32, P=0.021), but negatively correlated with the TN : TP ratio (γ=-0.51, n=32, P=0.003). Eucaryotic picoplankton (spherical chlorococcales) were not observed in oligotrophic lakes with less than 7 mg⋅m-3 TP. The Chl.α contents in the <2, 2-10 and >10 μm fractions were linearly regressed on TP. Among these regressions, that for the <2 μm Chl.α fraction had the lowest slope and the highest Y intercept, indicating that the <2 μm Chl.α was larger in clear waters, but did not increase as sharply as did larger size fractions with increasing nutrient levels. The reason why the <2 μm Chl.α fraction was not correlated with picophytoplankton abundance was discussed.View full abstractDownload PDF (1017K) -
Taisuke OHTSUKA, Keiji IWASAKI, Akio KUMAGAI, Tamito KONISHI1996 Volume 57 Issue 3 Pages 261-266
Published: September 01, 1996
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSRecent changes in the emergent macrophyte zone along the eastern shore of Lake Biwa's South Basin were investigated by field surveys in 1987 and 1995. Phragmites australis was the most dominant species at most sites. Comparison with the published literature revealed that the decline of emergent macrophyte zone had started since about 1981. The area had decreased from 62.6 ha in 1981, to 24.6 ha in 1995. This rapid decline was mainly caused by the destruction of habitats by an embankment along the shoreline. Other enviromental stresses associated with changes in water quality and large water level fluctuations were considered to be potential causes of the decline.View full abstractDownload PDF (414K) -
Kazuya HIRAMATSU1996 Volume 57 Issue 3 Pages 267-272
Published: September 01, 1996
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSHere, I present a simple field method to estimate the larval size of a net-spinning caddis, Hydropsyche orientalis MARTYNOV, without serious disturbance to the larvae. I measured the retreat length to the nearest of 0.1 mm with an underwater watching box and a caliper. There were significant correlations between the retreat lengths and the wet weights of 4th and 5th (final) instar larvae, particulaly for the 5th instars. For 3rd instar larvae, however, there was no significant correlation between length and weight. However, instars could not be identified by retreat length alone, so the correlation between average retreat length at intervals of 1 mm and wet weight was examined. There was highly significant correlation between them. This method provides reliable estimations of larval weight from retreat length data, permitting the individual growth of net-spinning caddis larvae to be monitored in situ.View full abstractDownload PDF (297K) -
Masumi YAMAMURO, Jun-ichi HIRATSUKA, Toshiki KOSHIKAWA, Hiromichi KUWA ...1996 Volume 57 Issue 3 Pages 273-281
Published: September 01, 1996
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe change in the fish assemblage in an estuarine lagoon, Lake Shinji, Japan, was surveyed with a set net monthly from October 1994 to September 1995. Although abundantly caught by net, the brackish water fishes, Konosirus punctatus and Sardinella zunasi, were not commercially utilized. Abnormally high water temperature and salinity in the summer of 1994 seemed to affect the fish fauna of Lake Shinji during the winter. Juveniles (total length = 32 ± 3.4 mm) of a commercial marine fish, Lateolabrax japonicus, entered L. Shinji in May, which was earlier than previously believed. They had grown 165±6.8 mm in total length by September. One of L. japonicus prey fish, Acanthogobius flavimanus, also entered L. Shinji in May with a length 32±2.1 mm, and grew 114±16 mm by September. These facts suggest that L. Shinji plays an important role in the growth of L. japonicus during its early life stages.View full abstractDownload PDF (514K)
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