抄録
The water quality of six rivers in Hadano basin was investigated and its relationship with nonpoint sources of pollution was analyzed. This study was undertaken to spatially examine the present status of the river water quality of Hadano basin. Ground water circulation influenced both the water quality and quantity. In the downstream basins of Muro and Kuzuha Rivers, COD and TP were diluted by the ground water inflow. In Mizunashi River and the upstream of Kuzuha River, water infiltrated to the subsurface due to the higher permeability of the river bed. Chemical oxygen demand (COD), total phosphorus (TP) and total dissolved solids (TDS) showed good correlation with unsewered population and agriculture area. While total nitrogen (TN) had good correlation with atmospheric nitrogen (N) deposition loads. Multiple regression analysis between water quality pollution loads and influencing factors revealed that unsewered population had higher impact on the river water quality; nonetheless, agriculture also had some effects. For TN, atmospheric N deposition load was taking effect, implying that it plays a significant role on the water quality and cannot be denied for proper water quality management. Development of sewerage system could be considered as the decisive factor to maintain the river water quality in the Hadano basin.
