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

为了阐明与水生态系统相协调的山洪沉积控制方法，我们对川上筑波大学森林的仓本溪的水流量、包括有机物在内的悬浮泥沙径流量和水质进行了监测，并对河床形态进行了调查。首先阐明了阶距随河床坡度增大而减小的阶池序列特征。其次，我们认为，由于沿溪流的斜坡沿着破坏而引起的沉积物供应对溪流的扰动通过溪流中形成和减少的台阶和/或池来吸收。三是在洪水期间，由于悬沙浓度和有机质浓度的峰值出现在洪峰之前或几乎同时出现，因此认为监测径流中悬沙和有机质的来源是河床和河岸中的细颗粒物和有机质。第四，NO_3离子在洪水径流中的响应与其它离子不同，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，利用悬沙和有机质定量曲线，估算出长江流域洪水年输沙量为22.4t（59.3t/km^2/y），洪水年有机质输沙量为8.4t（22.23t/km^2/y）。洪水年悬移质产沙量约为推移质年径流量的12倍。最后，我们认为沉积波是一个非常重要的因素，变形的台阶-池序列。

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.