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

本文通过对川上筑波大学森林库拉本河的径流量、悬浮物径流（含有机质）和水质进行监测，并对河床形态进行调查，以阐明与水生生态系统相协调的河流控制泥沙的方法。结果表明：首先明确了台阶-池层序的特征，台阶间距随河床坡度的增加而减小；其次，我们认为由于沿河流的斜坡破坏而引起的泥沙供应对河流的干扰是通过形成和减少河流中的台阶和/或池来吸收的。③汛期悬沙和有机质浓度峰值出现在汛期排水量峰值之前或几乎同时出现，表明监测径流中悬沙和有机质的来源为河床和河岸的细粒物质和有机质。四是NO_3离子对洪水径流的响应不同于其他离子，表明NO_3离子与有机质径流有一定的关系，因为硝酸条件下的氮不是地圈来源，而是大气来源。第五，基于监测数据，利用悬沙和有机质等级曲线估算洪涝年悬沙产量为22.4t (59.3t/km^2/y)，洪涝年有机产量为8.4t （22.23t/km^2/y）。洪水的年悬浮量大约是河床年径流量的12倍。最后提出沉积波是使台阶-池层序变形的重要因素。

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.