A new ecosystem assessment method based on exergy efficiency is employed to evaluate the health of fluvial ecosystems. The exergy takes into account both energy quantity and energy quality. In this method, the ecological exergy efficiency, which is calculated as the ratio of organism exergy produced in a system to exergy supplied from outside the system (photosynthetically active radiation exergy and organic exergy supplied by flood) , is defined as an indicator of the health of a fluvial ecosystem. This ecosystem assessment method is applied to three small rivers on the main island of Okinawa, Japan. The results show that the exergy efficiency of the fluvial ecosystems takes different values among the three rivers and can clarify the difference in the health between the natural zone and the artificial zone with bank protection of the Genga River, which is difficult to identify by means of the evaluation using water quality and biological environment.

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A Ceriodaphnia dubia reproductive inhibition test method was proposed for whole effluent toxicity (WET) management by the National Institute for Environment Studies. However, in this method, the complex influence of residual chlorine in wastewater and countermeasures are not described. In this study, the popular, convenient and economical Daphnia magna acute toxicity test, which was recommended by Nishida et al. and authors, was conducted for wastewater before and after chlorine disinfection at six factories, as well as wastewater from which residual chlorine was eliminated by adding sodium thiosulfate after chlorine disinfection, and for aqueous solutions of hypochlorite. As a result, it was verified that toxicity was exhibited to Daphnia with the residual chlorine of 0.15 mg L^-1 or more in wastewater, but 0.01 - 0.02 mg L^-1 or more in hypochlorite solutions. The toxicity of the wastewater after the elimination of the residual chlorine was less than that of the wastewater after chlorine disinfection. It is appropriate, for WET management, that the toxicity test be conducted on wastewater after the elimination of residual chlorine by adding an adequate amount of sodium thiosulfate.

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To investigate the sources of suspended solids in lined water pipes and polyvinyl chloride pipes, the interior of the water pipes was observed, and the composition of surface-attached materials and corrosion as candidate matter and suspended solids were analyzed. As a result of the observation of the interior of lined water pipes using an underwater camera, brown surface-attached materials were noticed and corrosion was often observed in the seam joints of pipes. As a result of the analysis, the surface-attached materials and corrosion surfaces were found to have a wide variety of elements besides O, Al, Si, Mn and Fe. However, the component in the interior portion of corrosion was chiefly iron oxide. The concentration and composition of three particle sizes (≤25 μm, 25–97 μm, ≥97 μm) shows that the particles smaller than 25 μm had the highest total element concentration. This indicates that the suspended solids were concentrated on this particle size range both in number and in weight. The common feature was seen between the surface-attached material and corrosion surfaces and suspended solids was the high content rate of Al and Fe although they were of different origins.

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In October 2014, a high concentration of 2-methylisoborneol (MIB) was confirmed in the Serikawa dam reservoir because the concentration of musty-odor-producing cyanobacteria had increased. Therefore, serious off-flavor problems with the drinking water occurred in Oita city located downstream of the reservoir. We investigated the species that had the potential to produce musty/earthly odor compounds by genetic analysis, and determined them to be Pseudanabaena limnetica and Pseudanabaena galeata. After the autumn thermal destratification in the reservoir, the MIB concentration in the reservoir rapidly decreased. We considered that it was caused by biodegradation and analyzed the water in the reservoir by next-generation sequencing (NGS) . The results showed changes in the bacterial community composition around the time of the autumn thermal destratification in the reservoir. The cyanobacteria survived in the low-temperature environment of a water temperature less than 10 ℃ and then showed an increase and high MIB-producing ability when the temperature reached 15 ℃. We hypothesize that the onset of biodegradation has an optimal temperature.

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