Reactivation of the Yamato River Water Quality Survey Project Y:Water Research Teams Report

Abstract

The Yamato River, flowing from Nara Prefecture to Osaka Prefecture, was once considered the most polluted river in Japan. From 2002 to 2005, the Osaka Museum of Natural History led Project Y: Yamato River Edition, a river system survey project that investigated the river's biology and water quality. In 2023, Project Y: Yamato River Edition was relaunched. In addition to reporting on the long-term changes in major ionic components first reported in the early 2000s, the project now includes new survey items such as trace heavy metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) and humic substances (humic and fulvic acids) supplied from soil to the river. This study reports on the changes and current status of the Yamato River's water quality.Comparing concentrations between the early 2000s and 2023-2024, nitrate and phosphate ions showed increased concentrations at almost all sampling points in 2023-2024. The increase in nitrate ions is likely due to changes in wastewater treatment methods since 1995, where effluent previously discharged as NH₄ is now released as NO₃. Sulfate ion concentrations decreased at most sampling points.