Study on the Ecosystem and its Physical Structure of the Creek

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The field studies have been made on the ecosystem and water temperature change of the creek in the Nagara-River. The site of the creek is located at 15.6km upstream from the river-mouth. Because of operation of the Nagara-River Wier, this area have been changed to the fresh water from estuary. The size of creek is 800m in length along the river. The average depth was 1.0m at the entrance, 1.8m at the middle portion, and 0.8m in the end of the creek. The conclutions have been obtained from the research as follows ;(1) Bird-Watching : 30 kind of birds have been observed along the downstream of the Nagara-River in 2km distance, according to the previous research. Almost one third of them were found in the creek. It has been understood that the creek plays an important role of birds habitat.(2) Benthos and Sediments Analysis : The density of crabs in the creek were investigated. It was found out that the density was increased in comparison with the results in 1992. This may be explained that the land area of the creek was decreased due to a rise of the water level by the Wier. It was recommended to monitor the change of crabs density for a few years to evaluate the effect of environmental change.The pH and microorganism activity analysis in the sediments were checked. The pH were observed within the range of 6.1 to 7.7. The activity of microorganism was found to be higher at the vicinity of plants root and a habitat area of crabs.(3) Thermal conditions : Water temperature was measured for two weeks in autumn and four weeks in winter seasons. It was found out that the characteristics of the water temperature in the creek is similar to the one in the lake and reservoir rather than river.