Evaluation for the creation of reed fields with seedlings on dredged sediments was discussed in this study. Results indicated that germination rates of seedlings of reed increased with the increment of temperature, and was independent of locations, but decreased with the increase of salinity. The pre-treatment of seedlings under low-temperature 5°C before germination played an important role in overcoming the adverse effect of high salinity. The growth of seedlings on dredged sediments was good and stable during two-year experiments. It suggested that the creation of reed fields with seedlings on dredged sediments may be applicable to large areas including brackish-water area.

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In the Hinuma River, the runoff characteristics of Chl-a as an indicator for algae were evaluated based on detailed observations during three and a half years. The higher the water temperature and the longer the days lasted after the last storm event were, the greater the Chl-a concentration during a low flow period. When the flow was increased by storm events, the Chl-a concentration became higher as the days lasted after the last storm event was extended. The algal biomass accounted for 13%, 23% and 7.8% of the particulate matter as carbon, nitrogen and phosphorus, respectively. Moreover, it was suggested that algae absorb and utilize 3.6% and 31% of dissolved nitrogen and phosphorus in terms of the annual runoff loading, respectively.

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The construction of a high level radioactive waste repository is commenced, by the steps of site characterization survey, design, construction, operation and sealing after the disposal site is selected. The required technologies of sealing are backfill, plugging and grouting. Upon composing of the sealing concept, it is important to rationally combine these technologies. This report made an evaluation on the performance of the element technologies for sealing from the view point of radioactive nuclide migration. As the result, we indicated that the plugging and grouting are effective for sealing against the disturbed zone, cracks, etc., of rockbed which increase the migration speed of the radioactive nuclide, and we proposed the main points of the sealing concept.

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The soil vapor extraction system is an effective technique to remediate the soil contaminated by volatile organic compounds. In order to remediate all over the contaminated soil evenly, extraction wells must be located properly and the extraction equipment should be designed appropriately to meet the required capacity. Dominant factors of soil properties which influence the remediation efficiency are clarified quantitatively through the case studies of various site records. As a result, radiuses of influence spread by negative pressure can beclassified depending on the nature of the soil, and air permeability correlates with gas porosity. The developed remediation efficiency analysis can predict the trend of vapor concentration diminution, and fairly agree with site records by applying the concept of effective air volume ratio.

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In order to manipulate the preservation and management of reed communities, from the aspect of water purification, the characteristics of reeds life span are indispensable. In this study, field observation of the reed community was carried out. The growth and aging process, regeneration after harvest, and nutrient contents of reed tissue were examined. Reed shoots grow significantly until summer and nutrient contents were maximum in spring. Height distribution and growth rate were precisely investigated. On the basis of these results, nutrient removal efficiency by harvesting was estimated and its cost was analyzed.

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High concentrations of NO₃^-, SO₄^2-, phosphate, and Al³⁺ and low pH values were found in spring water which originated from a tea plantation. Although acidic spring water flowed into a local pond, the pH value of the pond water remained above 7 because of photosynthesis, denitrification and sulfate reduction. Photosynthesis caused by an increase of phosphate and NO₃^- concentrations was concluded to have given rise to increases in pH values. Denitrification was thought to have caused the pond to eliminate NO₃^- annually. Sulfate reduction was thought to have caused a disappearance of SO₄^2-. Phosphate was stored within a pond in the form of organic compounds. Al³⁺ was precipitated within the pond because of increases in pH values.

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Antimutagenic effect of humic substances has been reported by various investigators. In this research, the diminishing effect of DNA damaging toxicity by humic acid was evaluated for the influent and effluent of activated sludge tank receiving municipal wastewater and several DNA damaging chemicals {e. g., pyrene, 1-aminopyrene and benzo(a)pyrene} using Bacillus subtilis rec-assay. The diminishing effect was not apparent for influent but observed in the effluent. Among the DNA damaging chemicals, the DNA toxicity was effectively suppressed by humic acid for pyrene and benzo(a)pyrene. However, the effect was relatively smaller for 1-aminopyrene.

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In order to clarify the effects of forest vegetation on the characteristics of river water quality and on the management of water resources, we investigated clean sources upstream for water supply in Japan and analyzed hydrological, geographical and water quality data of first class rivers in contrastive wet 1993 and dry 1994. Significant co-relation between broadleaf forest area and the concentration of COD and TOC was found and vice versa with coniferous forest area. The positive co-relation between broadleaf forest area and the mean runoff ratio was obtained and vice versa with coniferous forest area. Comparing the relation between the low runoff or the maximum runoff ratio in wet year of 1993 and broadleaf or coniferous forest area also, then we concluded that the broad leaf forest could play a better role for water resource management than coniferous forest.

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Wastewater reuse systems have been increasing in some urban areas in Japan recently. In this study, the present status of wastewater reuse systems was investigated with a questionnaire and a hearing survey of operators of wastewater reuse systems. Furthermore, the consciousness of users was investigated with a user questionnaire. The results obtained were summarized as follows: (1) In case of using the toilet flush water as a part of source, number of troubles on the water quality was increased compared with other sources; (2) Users of reuse water who had known that they had used it showed a better acceptance of reuse water than users who had used it but not known.

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