Nitrogen migration analysis in the Yamato river using nitrogen stable isotope

大和河的BOD值是日本所有一级河流中最高的。为了改善水质，对大和河沿岸的水化学进行了深入研究。结果表明，生活污水中BOD和NH_4 +-N的季节浓度冬季高，夏季低。浓度随水温升高而降低。总的发现是，河水中含有有机化合物和来自生活污水的Cl^-，而Cl^-在河流中相当稳定。由于BOD/Cl^-的比率在河流下游下降并随季节变化，有机化合物被认为在流动过程中被分解。有机化合物最终分解成的NO_3^-在下游也逐渐减少，冬季高，夏季低。由于大和河的pH、DO、δ^<15>N值和叶绿素浓度随温度升高和NO_3^—N浓度降低而升高，因此认为NO_3^—N被用于光合作用。因此，夏季有机物大量分解为NO_3^-，大和河沿岸植物吸收NO_3^-，夏季BOD值变低。因此，大和河的自然修复在夏季降低了BOD值。污水中的有机化合物在私人污水系统中分解，在大和河流域的河流中自然分解。由于这两种分解系统都依赖于温度，因此冬季的BOD值被认为很高。由于污水处理厂规模较大，该系统可以保持较高的温度，并且可以控制最终出水的质量。因此，虽然大和河的BOD值是日本一级河流中最高的，但随着大和河支流新建一些污水处理厂，大和河的BOD值逐年下降。将私人污水处理系统改造为大型污水处理厂，对改善水质具有重要意义。

The BOD value of the Yamato River is the highest of all the Japanese first class rivers. Water chemistries along the Yamato River were investigated intensively to improve water quality. As a result, seasonal concentrations of BOD and NH_4^+-N derived from domestic sewage were high in winter and low in summer. The concentrations decreased with an increase in water temperature.The general finding was that river water contains organic compounds and Cl^- derived from domestic sewage, and Cl^- was quite stable in rivers. As the ratios of BOD/Cl^- decreased down the river and changed seasonally, organic compounds were thought to be decomposed during flow. NO_3^- which organic compounds were finally decomposed into, also decreased further down the river, and were high in winter and low in summer. NO_3^--N is thought to be used for photosynthesis because pH, DO, δ^<15>N values and chlorophyll concentration of the Yamato River increased with temperature and decrease of NO_3^--N concentration. Therefore, organic compounds are decomposed into NO_3^- intensively in summer and plants along the Yamato River absorb NO_3^- and then the BOD value in summer becomes low. Hence, natural remediation for the Yamato River reduces BOD value in summer. Organic compounds in sewage are decomposed in private sewage systems and naturally in rivers in the Yamato River catchment.As both decomposition systems depend on temperature, the BOD value in winter is thought to be high. As sewage disposal plants are large scale, the system can keep high temperature and the quality of the final effluent can be controlled. Therefore, the BOD value of Yamato River decreases annually as some new sewage disposal plants are built in the branches of the Yamato River, although the BOD value of Yamato River is the highest of any Japanese first class river. It is important to change private sewage systems into large scale disposal plants, to improving water quality.