Studies on the Effect of River structure on River Ecosystem

本研究的目的是研究河流生态系统中氮素生物需氧量的行为，寻求一种通过生物群落方法创造生态河流环境的方法，阐明河流结构与净水功能的关系，以及冲洗池在河流净水系统中的作用。主要研究结果如下：1)污水处理厂出水进入河流后，特别是当C/N比低、NH4-N浓度和水温较高时，河流中氮的生物需氧量(N-BOD)检测频率较高。这一结果表明，由于河流中DO的缺陷，排水系统出水的流量可能会对河流生态系统产生负面影响，特别是在池塘中。2)根据实验室实验结果，通过一个简单的模拟模型预测，如果氮化合物含量较高，河流池塘中的DO浓度可能会下降到4 mg/L。为了使池水中的DO浓度保持在7.5 mg/L以上，必须将NH_4-N浓度降低到0.5 mg/L以下。3)为了保持良好的河流生态环境，必须采用生态河流整治和生物栖息法、生态工程等自然多样的河流修复方法。在海峡两岸设置冲沟和水池是改善河流水质净化功能的有效措施。冲沟和水池在河流生态系统中发挥着重要的作用，不仅是为了净化水质，也是为了微生物的栖息地。4)事实证明，使用净化块和网在河道中形成冲沟和水池，可以预期有机物和氮的有效去除。

The objective of this is study was to investigate the behavior of nitrogenous biological oxygen demand in river ecosystem, to search a method to create an ecological river environment through the biotope method, to clarify the relationship between river structure and the water purification function, and the role of riffles and pools in river water purification systems. The results obtained can be summarized as follows :1) Nitrogenous biological oxygen demand (N-BOD) was detected in high frequency in rivers if the effluent from the wastewater treatment plant flows into the rivers, especially, when C/N ratio is low, NH4-N concentration and water temperature are high. This result suggested that the flow of the effluent from sewer system might have negative impact on the river ecosystem due to the defect of DO in the river especially in the pools.2) It was predicted from a simple simulation model based on the laboratory experimental results that the DO concentration in the pools of the river may decrease to 4 mg/l if the nitrogen compound is high. In order to keep the DO concentration more than 7.5mg/l in pools, it is necessary to decrease the NH4-N concentration less than 0.5mg/l.3) To maintain a sound river ecosystem environment, it is important to use the ecological river improvement and natural diverse river restoration methods such as biotope and ecological engineering. It is effective to create riffles and pools in strait river banks to improve river water purification function. Riffles and pools play an important role in river ecosystem not only for water purification but also for the habitat of microorganisms.4) It was proved that to use the purification blocks and nets to create riffles and pools in the river channels, effective removals of organic matter and nitrogen can be expected.