Study on Distribution of Nitrate Ion in the Asakawa River Basin, Tamagawa River System

<p>Nitrate ion in river water is an indicator of the effects of anthropogenic activities. There are various factors that contribute to the presence of nitrate ion in river water, and clarifying the distribution of nitrate ion concentration and considering the reasons for it is useful in understanding the characteristics of the river basin. In the Asakawa River in the Tama River system, water pollution caused by domestic wastewater after the period of rapid economic growth has been considered a problem, and various studies have been conducted. Although the inflow of domestic wastewater has been greatly reduced due to the construction of a sewerage system, a large amount of nitrate ions still exist in the river water, and it is necessary to clarify the cause of this problem. The purpose of this study is to clarify the distribution of nitrate ions in the entire Asakawa River basin and to elucidate the causes of nitrate ions. It was suggested that sewage treatment plant effluent, septic tank effluent, agricultural land, and nitrogen saturation of forest ecosystems affect the spatial distribution of nitrate ions in the watershed. In the future, it will be necessary to examine seasonal changes and other factors in order to elucidate more detailed factors.</p>