Study on the Ecosystem and its Physical Structure of the Creek

本文对长垣河河溪的生态系统和水温变化进行了野外研究。溪址位于河口上游15.6公里处。由于长原河水库的运行，该地区已由河口改为淡水。这条小河沿河长800米。平均水深为入口1.0m，中部1.8m，尾端0.8m。研究得出以下结论：(1)观鸟：根据以往的研究，在长原河下游2公里的范围内观察到30种鸟类。其中近三分之一是在小溪里发现的。据了解，小溪对鸟类的栖息地起着重要的作用。(2)底栖生物及沉积物分析：调查了河川蟹类密度。结果发现，与1992年的结果相比，密度有所增加。这可以解释为，由于维尔河的水位上升，小溪的土地面积减少了。建议监测数年的蟹密度变化，以评价环境变化的影响。检查了沉积物的pH值和微生物活性分析。pH值在6.1 ~ 7.7范围内。在植物根系附近和蟹类生活区，微生物活性较高。(3)热条件：秋季测水温2周，冬季测水温4周。研究发现，小溪的水温特征与湖泊和水库的水温特征相似，而与河流的水温特征不同。

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.