Field study on suspended sediment, organic matter and water quality in streams and relationships with riffle or step-pool sequences of riverbed

通过对川上筑波大学森林库拉本溪的水量、含有机质的悬浮泥沙径流和水质的监测，以及对河床形态的观测，以明确与水生态系统相协调的洪流泥沙控制方法。因此，我们首先阐明了阶梯塘层序的特征，即阶跃间隔随着河床坡度的增加而减小。其次，我们认为，河流坡面崩塌引起的泥沙供给对河流的扰动是通过河流中阶梯和/或水池的形成和减少来吸收的。第三，认为监测径流中悬浮泥沙和有机质的来源是河床和岸边的细粒物质和有机质，因为悬浮泥沙和有机质浓度的峰值出现在洪水流量高峰之前或几乎同时出现。第四，我们发现在洪水径流中，NO_3离子与其他离子的响应不同，表明NO_3离子与有机质径流有关，因为硝酸条件下的氮不是地圈来源，而是大气来源。第五，根据监测资料，利用悬沙和有机质分级曲线估算了洪水年悬浮泥沙产生量为22.4t(59.3t/km2/年)，洪水有机产沙量为8.4t(22.23t/km2/年)。洪水的年悬移量大约是泥沙年径流量的12倍。最后，我们认为沉积波是形成阶梯塘层序的一个非常重要的因素。

We monitoerd water discharge, suspended sediment runoff including organic matter and water quality in the Kurabone stream of Tsukuba University forest at Kawakami and surveyed riverbed morphology in order to clarify the method of sedinment control in torrents harmonaizing with aquatic ecosystem. As a result, first we clarified characteristics of step-pool sequenses which step intervals decreased with increasing slope of riverbed. Secondly we suggested that disturbance to the stream caused by sediment supply owing to a slope failure along the stream was absorbed through forming and diminishing step and/or pool in the stream. Thirdly we suggested that the source of suspended sediment and organic matter in monitored runoff was fine materials and organic matter in the riverbed and bank becuase the peak of suspended sediment and organic matter concentration appeared before the peak of water discharge in floods or it almost appeared simultaneously. Forth we found that a NO_3 ion was different response from the other ions in runoff of floods, it suggested that the NO_3 ion had a relationship with organic matter runoff because nitrogen in condition of nitric acid is not geosphere origin but is atmosphere origin. Fifth we estimated that the annual suspended sediment yield in floods was 22.4t (59.3t/km^2/y) and the annual organic yield in floods was 8.4t (22.23t/km^2/y) using suspended sediment and organic mater rating curves based on monitoring data. The annual suspended yield in floods was roughly 12 times as large as the annual runoff of bed load. Lastly we suggested that a sediment wave is an very important factor for deforming step-pool sequences.