Influences of nitrate and phosphate concentrations on Microcystis species composition and microcystin concentration were confirmed by the results of Lake Suwa investigation between June and October from 1992 to 2003. Phosphate concentration decreased gradually but nitrate concentration remained constant for 12 years. Nitrate : phosphate concentration ratio varied below 10 between 1992 and 1998, but was more than 10 after 1999. The changes in this ratio indicated that the Microcystis bloom limited factor shifted from nitrate to phosphate since 1999. From 1992 to 1998 under a nitrates-limited condition, toxic species (M. aeruginosa and M. viridis) dominated and a high microcystin concentration was detected. A nontoxic species, M. ichthyoblabe, dominated under a phosphate-limited condition and a low microcystin concentration was detected since 1999. These results suggested that the low phosphate concentration (blow 10μg L^-1) shifted from toxic M. aeruginosa and M. viridis to nontoxic M. ichthyoblabe in the Microcystis blooms. Nitrate concentration affected the competition between M. aeruginosa and M. viridis.

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An alga-lytic bacterium, Pseudomonas KA6, was isolated from Lake Kasumigaura by a double-layer method. the filtrate of Pseudomonas KA6 culture lysed Phormidium tenue promptly. It was found that the growth of P. tenue is controlled by the addition of the filtrate 5 % and more. The lysis of P. tenue occurred efficiently at 25-35°C and pH 7-9. the cell of P. tenue in the stationary and endogenous phases was lysed promptly compared with that of P. tenue in the logarithmic phase. The filtrate lysed Oscillatoria sp. and Anabaena planktonica immediately as well as P. tenue; however, the filtrate lysed Microcystis aeruginosa slowly, and did not lyse green algae and diatoms. It was suggested that lytic compounds in the filtrate of KA6 culture affect only cyanobacteria in a water environment.

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The trophic structures of benthic faunal communities in a river are expected to respond to the relative amounts of autochthonous and allochthonous energy sources in the environment. Using isotopic analysis of δ¹³C, we investigated the percentage of autochthonous energy of benthic fauna at 3 sites longitudinally sited along the Hirose River, and at a site at the outlet of the Okura reservoir in a tributary. The relative trophic level of each taxon was also estimated from δ¹⁵N, and a biomass pyramid for each community was produced. As a result, the percentage of autochthonous energy of benthic faunal community formed a longitudinal distribution along the river, showing a high peak midstream with lower values both upperstream and downstream. This profile was similar to a longitudinal pattern of that of Fine Particulate Organic Matters (FPOM) in flowing water, a main resource for filtering-collectors that dominate these communities. At the Okura reservoir outlet, the percentage of autochthonous energy of the community was the lowest among the four sites, reflecting a low percentage of autochthonous energy in FROM due to the decomposition of allochthonous organic matter in standing water. The biomass pyramid for each community showed an energy peak in the middle trophic level.

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The turbidity maximum (TM) is a special region where the maximum concentrations of suspended particulate material (SPM) occur relative to SPM concentrations both upstream and downstream of an estuary. Therefore, SPM concentrations show a specific distribution in an estuary. Published observations of SPM concentrations within a short, weakly tidal, and microtidal estuary are not sufficient. We investigated longitudinal and vertical distributions of SPM and salinity at spring and neap tides in the weakly mixed, microtidal MIYAKO river estuary. The maximum concentration of SPM in the water column of the tidal area occurred at a constant distance from the mouth of the MIYAKO river estuary at ebb tide. The phenomena of the maximum concentration of SPM in the water column of a tidal area do not correspond to the definition of TM. The distance of the maximum concentration of SPM from the river mouth is not affected by tidal range. The maximum concentration of SPM in the water column of a tidal area increases with tidal range. The order of the maximum concentration of SPM in the MIYAKO river estuary is comparable to that in other microtidal estuaries. We presumed the export of SPM in the MIYAKO river estuary is comparable to that in other microtidal estuaries We presumed the export of SPM in the MIYAKO river from our own investigated data.

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The study area was located in the Makinohara collective tea fields in Shizuoka, Japan. There are flourishing tea industries in this area. The quality and level of the groundwater were observed from Jun. 2002 to Sept. 2003 and examined on the basis of hydrogeology. The Makinohara plateau comprises of clay layers between gravel beds. It yielded discontinuous water qualities caused by perched water in a geological structure. The average concentrations of T-N and NO₃-N in the surface water were 26.4 mg·l^-1, 23.8mg·l^-1, respectively. In contrast, for the groundwater, these concentrations were 17.2 mg·l^-1 and 12.6 mg·l^-1, respectively. The average concentrations of T-P were 0.012 mg·l^-1 in the surface water and 0.022 mg·l^-1 in the groundwater. This difference is caused by the dilution effect and release of phosphorus from on aquifer. The annual groundwater effluent loads of nitrogen and phosphorus from the catchments of the Makinohara plateau were 406 t·y^-1 and 0.7 t·y^-1, respectively.

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The carbon isotopic compositions (δ¹³C) of suspended particulate and sedimentary organic matters (POM and SOM, respectively) collected in August and September 2000 at Hakata Bay and its surrounding watershed were measured to clarify the dynamics of organic carbon. The δ¹³C values of POM at the watershed were typical values of C3 plants with an average of -26.6±1.6‰ (n=17). There was little difference between the δ¹³C values of POM and SOM from the watershed. On the other hand, the δ¹³C values of POM in the central area of the Bay ranged from -17.4‰ to -16.3‰ ad were considerably higher than those of general phytoplankton (-20‰). This might be attributed to the limitation of the rate of CO₂ diffusion into the cells because of the abrupt growth of phytoplankton in summer. The δ¹³C values of SOM at the Bay ranged from -21.0‰ to -20.1‰ and did not reflect those of POM. The fraction of terrestrial organic carbon in the SOM of the Bay were estimated using the δ¹³C values of two end members of terrestrial and marine organic matters.

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