Study on Flow, Sediment and Nutrients, Primary Production in Gravel rivers for Restoration of Ecosystem

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1.Laboratory experiments were performed to know the characteristics of growth, detachment and interspecific competition of filamentous and non-filamentous periphyton, in which the primary production rates, the respiration rates and the detachment rates of each kind of periphyton were measured by using various methods. The results of the experiments show that there are no significant differences of the primary production rates and the respiration rates between filamentous and non-filamentous periphyton. The detachment rate of periphyton is found to increase with friction velocity, and the detachment rate of filamentous periphyton takes smaller value than that of non-filamentous periphyton.2.The field observations were performed to understand the characteristics of growth and nutrient uptake of Phragmites japonica on flood plain in a gravel river, in which the temporal variation of plant biomass, the content of nutrients of vegetation and the concentrations of nutrients in the groundwater were measured. The result of the field observations show that the growth of the vegetation was restricted by the groundwater level in the present observation site. The hydroponics experiment of the riparian vegetation was conducted to understand the nutrition uptake due to photosynthesis. The results of the experiment show that the nitrogen uptake of the vegetation was closely associated with the amount of respiration of the roots of the vegetation.3.Field observation on the supply of sediment and nutrients from Nagura river basin, Ishigaki Island, was studied. They were estimated by measuring water velocity, depth, turbidity, concentrations of carbon, nitrogen and phosphrous. It was found that heavy rains yield nutrients mainly in particulate type. However, sugar cane field yields dissolved nutrients gradually after the rain. The timing of flood and tide is an important factor to control the discharge of sediment and nutrients to the tidal area such as lagoon and river mouth.