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生物需氧量的行为，探索通过生物群落法创造生态河流环境的方法，阐明河流结构与水净化功能的关系，以及河流净化系统中河沟和水塘的作用。结果表明：1)当污水处理厂出水流入河流时，河流中氮生物需氧量（N- bod）的检测频率较高，特别是当C/N比较低、NH4-N浓度和水温较高时。这一结果表明，由于河流中特别是池中DO的缺陷，污水系统流出物的流动可能对河流生态系统产生负面影响。2)基于室内实验结果，通过简单的模拟模型预测，当氮化合物浓度较高时，河流池中DO浓度可能降至4 mg/l。为了使池内DO浓度保持在7.5mg/l以上，有必要将NH4-N浓度降低到0.5mg/l以下。3)为保持良好的河流生态环境，应采取生态河流整治和自然多样性河流修复等措施，如生物群落和生态工程等。在海峡两岸设置河堤和水池，提高河水净化功能是有效的。水塘在河流生态系统中起着重要的净水作用，同时也是微生物的栖息地。4)利用净化块和净化网在河道中形成沟槽和水池，可以有效去除有机物和氮。

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.