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Volume 72, Issue 1
Displaying 1-7 of 7 articles from this issue
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Original articles
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Sohei KOBAYASHI, Satoru NAKANISHI, Kunihiko AMANO2011 Volume 72 Issue 1 Pages 1-18
Published: 2011
Released on J-STAGE: April 28, 2012
JOURNAL FREE ACCESSWe investigated the biomass and community structure of benthic macroinvertebrates in the lower reach of Kurobe Dam, where bedrock exposures on streambeds have recently been increasing, and in the upper reach without bedrock exposure, to better understand the impact of channel degradation on a macroinvertebrate community in a mountain gravel-bed river. Based on quantitative samplings at 4 stations (a total of 6 sampling reaches) in the upper and lower reaches, major contrasts in the macroinvertebrate community among habitats (riffles, runs, and pools) were evident, with the macroinvertebrate biomass being greatest in riffles (4.6-fold greater than in runs and 8.6-fold greater than in pools). The macroinvertebrate community differed between the upper and lower reaches, though the differences were not as large as those among habitats. Further samplings of riffles in the lower reach revealed that the macroinvertebrate biomass was greater in large-cobble than in small-cobble (with fewer sedentary taxa) and boulder riffles (with fewer taxa encountering underneath the cobbles). Macroinvertebrates were usually scarce in bedrock riffles except for blackflies that inhabited the substrate surface, while community compositions at small gravel clusters (gravel patches) in bedrock riffles were similar to those in gravel-bed riffles. Based on the difference in the amount and composition of habitats and bed-substrates between the upper and lower reaches of the dam, we estimated that the channel degradation potentially reduced the macroinvertebrate biomass up to 1/6 at an entire reach through alterations in habitats and bed characteristics.View full abstractDownload PDF (1225K) -
Hisanori KAGAWA, Ryuichi OMOTO, Misato ASHIKARI, Masayoshi MORI, Hiros ...2011 Volume 72 Issue 1 Pages 19-40
Published: 2011
Released on J-STAGE: April 28, 2012
JOURNAL FREE ACCESSOn the upper reaches of the Ishite River, Ehime Prefecture, Japan, long-term changes in the water quality were investigated to clarify the effects of acid rain on the chemistry of streams flowing out of a moderately acid-tolerant catchment of brown forest soil over coarse-grained granodiorite. The chemical composition of bulk rainwater was determined in the catchment over two time periods, 1986-1987 and 1997-1998, in which the annual mean pH was c. 4.6. From January 1978 to December 2003, several sets of surveys were carried out at three sampling stations along the main stream, i. e., W1 (214 m a. m. s. l., 56.3 km2 in the catchment area), W2 (445 m) above which there was no village or arable land, and W3 (530 m). A monthly survey of pH at W1 (n = 312) indicated that pH decreased gradually from c. 8.4 in 1978 to c. 7.5 in 1991, then gradually rose to c. 8.1 in 2003. Similar trends were found at W2 and W3. Another survey series that was carried out every three months from February 1985 to November 2003 at W1 (n = 76) indicated that among strong acid anions (SO42-, Cl- and NO3-), SO42- concentrations decreased gradually throughout the survey period. Base cations (Ca2+, Mg2+, Na+ and K+) and dissolved silica indicated no clear long-term increase or decrease. A similar situation was found at W3. The third survey series, i. e., a monthly survey at W1 from February 1993 to December 2003 (n = 131) covering HCO3- concentrations and the partial pressure of CO2 gas (Pco2) indicated that HCO3- and surplus base cations over strong acid anions resulted in the weakly alkaline water. A factor analysis showed that pH levels fluctuated depending on Pco2 rather than HCO3- concentrations, which were c. 105 times greater than H+ concentrations. An increase or decrease in Pco2 seemed to have greater effects on pH than on HCO3- concentrations, due to the changes in the same amount of H+ and HCO3- through the dissociation of H2CO3. Based on the literature, concentrations of base cations at W1 in the 1980s and 1990s were greater than those between 1949 and 1950, and were accompanied with increases in both SO42- and NO3- presumably supplied by acid rain. The acid rain appeared to hasten the velocity of mineral weathering in the catchment soil. From 1950 to the 1980s-1990s, almost no increase in HCO3- concentration and only a slight increase in pH were observed. In an outline, hypothetical changes in CO2 production in the soil depending on the stand age of the forest agreed with changes in the stream pH.View full abstractDownload PDF (1077K) -
Yuichi MIYABARA, Kazuyoshi ASAI, Masamichi YAMAMOTO2011 Volume 72 Issue 1 Pages 41-55
Published: 2011
Released on J-STAGE: April 28, 2012
JOURNAL FREE ACCESSConcentrations of chlorofluorocarbons (CFCs) in lake waters of Japan were determined for the first time. A high concentration of CFC-113 not explained by its atmospheric partial pressure was detected in Lake Suwa. That might be due to the prior industrial use of CFC-113, which polluted the soil and grondwater in the area, thus releasing CFC-113 form water of Lake Suwa into the atmosphere. On the other hand, the concentration of CFCs in the water of Lake Kizaki was explained by the gas liquid equilibrium. Vertical distributions of both CFCs and major ions in the lake water reflected the thermal stratification of Lake Kizaki. It was confirmed that CFCs acted as useful chemical tracers for determining the mixing and circulation of lake water.View full abstractDownload PDF (905K)
Notes
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Yoshihiro YAMADA, Yugo MITO2011 Volume 72 Issue 1 Pages 57-64
Published: 2011
Released on J-STAGE: April 28, 2012
JOURNAL FREE ACCESSNitrogen and phosphorus concentrations and temporal variations were investigated in the Shin and the Kasuga rivers, Shikoku Island, Japan. For effective water-use, many irrigation ponds were located in these river basins, and many weirs were established in the rivers themselves. Our investigation was carried out in waters dammed up by river mouth weirs in both rivers. TN and TP concentrations were high, reaching values of 7.35 mg L-1 and 0.505 mg L-1, respectively. TN concentrations were comparatively low from spring to autumn during the irrigation period. In this season, the dilution effect of irrigation water with a low TN concentration from the Yoshino River had to be considered. The proportions of organic nitrogen and phosphorus in both TN and TP were high in both rivers. The organic nitrogen and phosphorus especially increased in winter during low water temperatures. Precipitation and the water supply from the Kagawa water canal were low in this period, and the volume of river water markedly decreased. It was indicated that the organic substance production rose by the increase in the residence time of the water. In addition, the inflow of organic material to the river by the draining of pond water for pond bottom improvement was also considered as a factor in high levels of organic material in the river.View full abstractDownload PDF (708K) -
Maiko KAGAMI, Junko ISHINABE2011 Volume 72 Issue 1 Pages 65-70
Published: 2011
Released on J-STAGE: April 28, 2012
JOURNAL FREE ACCESSLake Inba is one of Japan’s most eutrophic lakes. Few studies have examined its plankton dynamics, including bacteria. To investigate the factors affecting the bacterial abundance in Lake Inba, data were collected weekly from April to October 2009. That abundance ranged from 1.8 to 9.5×106cells mL-1, with its highest in late April. Multiple regression analysis revealed that the bacterial abundance was significantly correlated with particulate phosphorus concentrations and heterotrophic nanoflagellates (HNF), but not with water temperature, nutrient concentrations or chlorophyll a. A significant relationship with particulate phosphorus, but not with chlorophyll a concentration, indicated that organic substrates including allochthonous input were an important source for bacterial growth in the lake. That also implied that phosphorus might limit bacterial growth, although no relationship was found with SRP due to its extremely low concentrations. Negative relationships with HNF indicated that HNF reduced the bacterial abundance through grazing. These results indicate that bacterial abundance in the eutrophic Lake Inba was regulated not only by top-down factors, that is grazing by HNF, but also by bottom-up factors including organic sources and phosphorus.View full abstractDownload PDF (600K) -
Masami Kanao KOSHIKAWA, Mirai WATANABE, Takejiro TAKAMATSU, Seiji HAYA ...2011 Volume 72 Issue 1 Pages 71-80
Published: 2011
Released on J-STAGE: April 28, 2012
JOURNAL FREE ACCESSStream water chemistry was investigated in relation to watershed geology and topography (area, mean elevation, and mean slope) in the Miomote River System, which is comprised of many small watersheds with different geologies and which has been largely unaffected by human activities such as sewage or acid deposition. Representative geologies of the watersheds included Jurassic sediments, granites, acidic tuffs, and andesites. Concentrations of NO3-, non-sea-salt (nss-) SO42-, nss-K, nss-Mg, nss-Ca, Si and Al were measured in stream waters from 62 watersheds during baseflow periods. Stream water chemistry under the influence of rain events was also investigated for 31 watersheds. Primary component analysis (PCA) performed on stream water chemistry data extracted two significant factors explaining 57.2 % of the total variance among the watersheds; the first component was related with the fractional area of acidic tuffs, while the second component was related to the mean elevation of watersheds. Factor loadings suggested as follows: nss-K and Al rose and nss-Mg and nss-Ca decreased as the fractional area of acidic tuffs increased, while Si and NO3- rose as mean elevation decreased. Variations of nss-K, nss-Mg, and nss-Ca in stream waters seem to reflect the elemental content in bedrocks. An Al variation seems to reflect the variation of Ca acting as a competitive cation for ion exchange and/or complexation. Variations of Si and NO3- appear to reflect variations of temperature, soil thickness and water residence time with the mean elevation of watersheds. Under the influence of rain events, concentrations of Si decreased whereas nss-K, Al, NO3- increased. It was presumed that Si in stream waters was supplied mainly from the deep soil layer and weathered bedrock, while nss-K, Al, NO3- were supplied mainly from the surface soil layer, under the influence of rain events.View full abstractDownload PDF (893K)
Limnological record
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Hiroki HAGA, Kanako ISHIKAWA2011 Volume 72 Issue 1 Pages 81-88
Published: 2011
Released on J-STAGE: April 28, 2012
JOURNAL FREE ACCESSSpatial distributions in terms of biomass and species composition of submerged macrophytes were surveyed in the southern basin of Lake Biwa in September, 2007. Macrophyte samples were collected from 52 sites by SCUBA. The vegetated area and total biomass (dry weight) of submerged macrophytes in the southern basin during the study period were estimated to be 48.6 km2 and 9623±2665 t, respectively. The vegetated area increased by 6 km2 between 2002 and 2007, but the total biomass did not increase significantly during the same period. Although total biomass of submerged macrophytes increased along the west coast and in the central part of the southern basin, it decreased in the southern and northern parts of this basin. Twelve species of submerged macrophytes were recorded in this survey. Potamogeton maackianus was highly dominant; its biomass was 5370±2217 t and accounted for 56% of the total biomass. Egeria densa (1211±531 t) and Ceratophyllum demersum (1194±709 t) were of the second rank. A third group of moderately abundant species (200 - 555 t) consisted of Elodea nuttallii, Hydrilla verticillata, Myriophyllum spicatum, Potamogeton malaianus, and Vallisneria denseserrulata. Other species were rare, having a biomass about 1 t or less. Filamentous algae found with submerged macrophytes had considerable biomass (726±419 t). Biomass of P. maackianus, E. densa, and C. demersum did not change significantly from 2002 to 2007. Although the biomass of H. verticillata and M. spicatum decreased significantly in that period, that of E. nuttallii increased significantly.View full abstractDownload PDF (566K)
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