The objective of our research was to analyze the environmental factors determining short-term fluctuation in the concentration of suspended and/or dissolved matters in rivers. We conducted the analysis by using the 10 year water quality and precipitation monitoring data of short-term variation in four fixed rivers. All water-quality parameters were extracted by time-series analysis. We found that the particulate matter concentrations were affected by 2 days of rain, while the major ion concentrations were affected by 3 days of rain. However, the nutrient concentrations were affected by only 1 day of rain. After a rain event, suspended matter concentrations increased as a result of turbid water inflow. On the other hand, the major ion concentrations were diluted by rainwater after flooding. The dynamics in the nutrient concentration after rain differed among nutrient species and rivers. Meanwhile, in larger rivers, nutrient concentrations were affected by instream processes such as nutrient uptake by algae. Most of the above findings were confirmed by the direct observation data of two runoff events. Our results showed that the short-term variation in river water quality could be determined and evaluated by the time-series analysis of monitoring data without the need for direct frequent runoff sampling.

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A full-scale UASB (Up-flow Anaerobic Sludge Blanket) -DHS (Down-flow Hanging Sponge) system, which is a sewage treatment technology for developing countries, was applied in India, and its performance was evaluated. In the initial phase of start-up (up to the 3rd month) , the DHS system showed a 60% COD_Cr removal efficiency. Up to the 9th month, the operation of the DHS reactor was affected by various unforeseeable situations, e.g. inappropriate volume of DHS influent. However, from the 9th month onwards, a stable flow was received by the DHS reactor. From the 9th to the 12th month, the average COD_Cr in the DHS effluent was 92 (±20) mg L^-1. During this period, organic load fluctuated from 2.59 to 12.59 kg-COD_Cr m^-3 day^-1, and was high. However, the organic load and removal of the DHS reactor were directly proportional to each other. As a result, it was clarified that this system can maintain its organic matter treatment performance even under high organic load. Also start-up of the DHS reactor was achieved without maintenance, despite some common problem that can be seen in developing countries. It was shown that the DHS reactor is an appropriate sewage treatment technology for developing countries.

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In this study, we developed a new measurement method of sediment oxygen demand (SOD) . SOD in the bottom layer of lakes is closely related to the change in dissolved oxygen (DO) which is to be a new environmental standard for aquatic environments. Our method makes use of undisturbed sediment cores and measures SOD more easily and faster than the existing methods. Since the instruments are portable, our method can be widely applied to many lakes. SOD measurements in Lake Kasumigaura and Lake Biwa (the northern and southern basins) revealed that the SOD values were different among the locations and showed a seasonal variation. In Lake Biwa (the southern basin) samples, rapid DO consumption was observed from the beginning of the incubation, implying that DO was consumed by the reduced forms of iron and/or manganese diffused from the sediments. There were significant correlations between the amount of iron and phosphorus eluted to the overlying water and the SOD values, but no correlation was observed between the iron and manganese contents in the sediments and the SOD values. These findings indicate that the amounts of iron eluted from sediment should be evaluated to assess its contribution to SOD.

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The Water Environmental Soundness Index (WESI) has been applied to environmental education at the elementary-school level. Although the effectiveness of WESI has been reported, there has been no specific study to verify this. In this study, to verify the effectiveness of WESI in environmental education, we examined the same student group over two years (2013–2014) , when they were in the 4th and 5th grades. Furthermore, last year (2015) , a new group of 5th-grade students was examined for comparison. This investigation included a river survey using WESI, an awareness survey and a survey of students’ impressions. We considered that by comparing the differences between the two groups of students regarding their answers to questions on WESI and their environmental awareness, the effectiveness of WESI could be verified. In conclusion, the experience of carrying out a survey using WESI contributes not only to the acquisition of water environmental knowledge, but also to environmental awareness of other factors such as waste. The learning effect was thus confirmed.

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