It has been reported about aquatic insects in Lake Suwa since the late 1910s. However, few reports of adult caddisflies in this lake have been published to date. The objective of this study was to describe the fundamental information and characteristic about adult caddisflies in Lake Suwa. We tried to clarify the abundance and distribution of adults caddisflies caught by light traps. The abundance of adult caddisflies was monitored every day at the Research and Education Center for Inlandwater Environment, Shinshu University from April to November in 2003 and 2004. Moreover, we also carried out the multipoint sampling surveys at 8 sampling stations on the bank of the lake in June, July and October in 2003 and 2004. The total number of adult caddisflies caught more than 1,000 individual numbers per year. There were large numbers of adult caddisflies in the summer. At 8 sampling stations, we recorded a total of 32 species (16 family, 23 genus). The dominant species was Cheumatopsyche brevilineata (92.0% of the total number of trichopteran communities) and followed by Psychomyia acutipennis (2.9%). At the lake outlet sampling station, the maximum number of C. brevilineata was caught over 26,000 individuals on 28 July 2004.

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Seasonal variation in the species composition and abundance of epilithic algal community on a rock located at the upper littoral area in the north basin of Lake Biwa was investigated. Schizothrix sp., Calothrix parietina and one species of Pleurocapsaceae were always found at the splash zone of a rock. It seemed to indicate that those Cyanophyceaen algae were tolerant to desiccation and/or high energy of solar radiation including high UV-radiation. The dominated taxa and algal biomass in the epilithic algal community underwater zone changed seasonally and vertically during the investigation period. Spirogyra sp. (Chlorophyceae) increased from February and occupied a greater part of total algal biomass until July. In August and October, algal biomass was extremely low, in which Calothrix parietina and Homoeothrix janthina were dominated. Diatom such as Cymbella turgidula dominated through low temperature season. Numbers of diatom taxa actually increased during the occurrence of marked growth of Spirogyra. It seemed to be related to the geo-morphological complexity caused by the presence of the large filamentous algal biomass.

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Dissolved humic substances (HS) are refractory organic compounds in water systems. HS make up ~50% or more of dissolved organic carbon (DOC) in freshwater ecosystems, yet their origins remain unresolved. Recent analytical techniques have revealed that aquatic HS are mainly composed of fulvic acids having molecular weights less than 10,000. High-performance size exclusion chromatography (HPSEC) with fluorescence detection can separate HS in Lake Biwa basin system into three molecular size classes, i.e., high(MW:5400)-, middle(4000)- and low(2000-1000)-molecular-weight classes.HS in Lake Biwa and outflow river waters contains much amounts of the low-molecular-weight class as compared to those in inflow river waters. This indicates a possibility of in situ generation of low-molecular-weight HS in Lake Biwa. To certify this possibility, we made biodegradation experiments of phytoplanktons (Cryptomonas tetrapyrenoidosa and Chlamydomonas reinhardi) at 20C in the dark. Degradation rapidly proceeded, producing a new organic fraction. This fraction coincided in HPSEC retention time with the low-molecular-weight class of HS in Lake Biwa and remained stably during the long experimental period (100days). It is thus certain that biodegradation of phytoplanktons makes an important contribution to the generation of organic compounds having low-molecular-weights in Lake Biwa.

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Lake Fukami-ike is a small eutrophic lake located in central Japan, which stratifies from March to October. This lake has a maximum depth of 7.75 m and an anoxic condition prevails below 4-5 m depths. Vertical distributions of inorganic nitrogen and nitrous oxide and their seasonal and diel changes were studied.
Nitrate supply through precipitation remarkably increased nitrous oxide concentration which accompanied decreases in nitrate and nitrite concentrations in the range between the surface water and the immediately upper layer of oxic and anoxic zones from 21 to 22 June 2003. This phenomenon may have resulted from the denitrification process. Nitrate and nitrous oxide decreased by 15.6 mg at N m ^-2 (6 h) ^-1 and 1.09 mg at N m ^-2 (6 h) ^-1, respectively. The denitrification seems to have occurred within a very short term (diel change).
Nitrate concentrations throughout the year ranged from 0.571 to 39 mg at N l ^-3 in the surface water. Increases in nitrite concentration in correspondence with decreasing nitrate concentration were often observed when denitrification in the oxic and anoxic layers took place. Ammonium amounts during the stratification periods were high in the hypolimnion, the maximum value being 696 mg at N m ^-3 on 10 May 2003.

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C:N:P ratios of epilithic periphyton were measured in littoral zones (25 stations), inflow rivers (30 stations), and lagoons (23 stations) of Lake Biwa to evaluate the nutrient status of freshwater epilithic periphyton. Dissolved inorganic nitrogen (DIN) and phosphorus (DIP) in surface waters at respective station were also determined. The results of DIN:DIP ratios in surface water suggested that the growth of periphyton was limited by phosphorus at most stations (71 stations of all stations). The results of C:N:P ratios of periphyton suggested that the growth of periphyton was not limited by each nutrient concentration at most stations (69 stations of all stations). The present study seems that C:N:P ratios of periphyton were influenced not only by DIN:DIP ratios in water, but also by water temperature, light intensity, water current, algal species, and so on.

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We examined food selectivity on microalgae by aquatic insects in Hiji Steram, Ehime, whose main water source is a eutrophic reservoir, from July to August 2004. Abundance and composition of planktonic and epilithic algae, those of aquatic insects and their gut content were determined, followed by estimation of food selectivity using Chesson's alpha index. One of the dominant species in aquatic insects was the filter feeder Cheumatopsyche spp. (Hydropsychidae) during the study period. For phytoplankton, Coelastrum (Chlorophyceae) and Microcystis spp. (Cyanophyceae) were dominant throughout the study period and in August, respectively. Food selectivity of the insect on Coelastrum was negative, suggesting inedibility of Coelastrum for the insect. Positive food selectivity was detected for Microcystis in July, but, in August, the insect showed negative selectivity on Microcystis . In August, there were positive food selectivities on Pediastrum (Chlorophyceae) and Synedra (Bacillariophyceae), both of which were less dominant at the upper station. Thus, Microcystis is edible but not preferable prey for the insect. These results suggest that Cheumatopsyche spp. graze on Microcystis when there is no other edible prey available, and that the insect show selective grazing on some eukaryotic microalgae such as Pediastrum and Synedra .

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Pseudomonas fluorescens HYK0210-SK09 (SK09) has the algicidal activity against Stephanodiscus hantzschii that frequently forms bloom in winter season. In this study, the growth possibility of SK09 was investigated in two microcosm experiments using Stephanodiscus hantzschii culture. We monitored the abundance of SK09 using the Pseudomonas specific probe in tyramide signal amplification ? fluorescence in situ hybridization. In the first experiment, we inoculated SK09 into Stephanodiscus culture. Stephanodiscus cell density decreased to the half within two days. Simultaneously, both SK09 and other bacterial cell densities increased to about 3 times higher densities. In the second experiment, we inoculated Stephanodiscus to enriched-filtered river water and monitored cell densities of Stephanodiscus, SK09, other bacteria and flagellates. Inoculation of SK09 cells on 8 days caused rapid decrease in Stephanodiscus cell density to the half within 2 days. SK09 and other bacterial cell densities increased in 1.5 times on 1 day after the inoculation, and then their cell densities rapidly decreased probably due to grazing by flagellates. Flagellates cell density increased in 5 times after the inoculation. These results demonstrate that SK09 can grow using their algicidal activity on Stephanodiscus and that the algicidal activity of SK09 affect abundance of other bacteria and flagellates.

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The compatibility of E. coli indicator measured by Colilert system and other indicator microorganisms for the environmental water was examined. The Colilert system indicated a good correlation with fecal indicators. The Colilert system detected higher values of coliforms especially in the upper reaches of a river. A newer Colilert18 system was compared with Colilert system. Risk assessment of river water was performed to determine the water quality suitable for bathing. The water quality suitable for bathing was expressed in terms of coliforms. This was compared with ongoing river water quality standard in Japan.

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To see dynamics of organic matter supplied from a dam reservoir to a stream, we studied changes in phytoplankton abundance, composition and physiological activity in Kanogawa Dam Reservoir and Hiji Stream between July 2004 and June 2005. For physical variables, water temperatures from the upper to the lower stream were less variable, whereas current velocities at upper stream stations were higher than those at lower stream stations. This suggests higher mixing turbulence in stream water at the upper stream stations. Chl.a concentration remained almost constant or slightly increased from the reservoir to the nearest station in the stream, and showed no marked differences at five stations within the stream. Algal physiological activity was also almost constant from the upper to the lower streams. By contrast, remarkable changes in phytoplankton composition were detected from the upper to lower stream. Cell densities of the cyanobacterium Microcystis and the diatom Fragilaria decreased from the upper to lower streams. By contrast, those of the diatoms Cymbella and Cyclotella increased, and the attached diatom Cocconeis showed almost constant cell densities from the upper to lower streams. The results suggested that water velocity and mixing turbulence are important for changes in phytoplankton composition in the stream.

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Stable isotopes of sedimentary nitrogen, carbon and the C to N ratio have been used as the available proxies for origins of organic matter and other biogeochemical parameters. In this research, organic nitrogen and labile organic carbon was separated from total nitrogen and total organic carbon by KOBr-KOH treatment. Organic nitrogen concentration of sediment was calculated by difference between total nitrogen and inorganic nitrogen (Ntot-Nbnd=Norg) in two artificial lakes (Lake Shi-hwa and Hwa-ong). The average organic nitrogen fractions of total nitrogen contents in surface sediment were 42% in Lake Shi-hwa and 62% in Lake Hwa-ong, respectively. As a result, Corg / Ntot ratios(mean=12) are much higher than Corg / Norg ratios(mean=24), showing the significant presences of inorganic nitrogen in surface sediments of both lakes. In addition, stable isotope compositions of each fractionated carbon and nitrogen indicate different tendency, suggesting their different origin. The stable isotope compositions of organic nitrogen are heavier than those of inorganic nitrogen (approximately 0.18 in Hwa-ong and 2.15 in Shi-hwa) except a few stations in Lake Hwa-ong. Stable isotope of organic labile carbon, which is removed by KOBr-KOH solution, is heavier (approximately 0.1 to 2.4 per-mil, average: 1.4) than residual organic carbon.

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Concentrations of nutrients in the sediment in the estuary of the Chikugo River, Japan were surveyed before and after the flood period in 2003. The Chikugo River discharged 1900 ton of particulate nitrogen (PN) and 600 ton of particulate phosphorous (PP) in the period of 6 months (from May 1 to Oct. 31, 2003). As for the fluvial suspended sediment (SS), 70% of the total particulate phosphorous was soluble in the anaerobic conditions in the seawater. Nutrients and organic carbon content of fluvial SS was higher than those of the estuarine sediment. After the flood period, Fe-P, Al-P and Ads-P concentration in the sediment of the tidal flat at the front of the rivers increased. On the other hand, at the points those were far from the river mouths, the concentration of these components in the sediment of the tidal flat did not increase. It was clarified that the discharged sediment from the river basin affected the nutrient concentration and environment of the surface sediment in the estuary. Moreover, concentrations of nitrogen and organic carbon in the sediment decreased in the tidal flat. It means that organic compounds in the surface sediment were degraded in the tidal flat.

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