Abstract
The concentration variations of dissolved metal ions and their buffering effect in an acidified river were investigated by analyzing the data collected through a long-term field investigation and an intensive field investigation. The field investigations targeted Matsukawa River in Japan, which is acidified by the inflow of acid mine drainage. In periods of rainfall and snowmelt, Al, Mn, Fe, Cu, and Zn ions exhibited different decreasing trends than did alkali and alkaline earth metal ions and sulfate. These findings suggested that the decreases in Al, Mn, Fe, Cu, and Zn ion concentration were attributable not only to dilution by the inflow of rainwater and snowmelt but also to the hydrolysis of Al. Additionally, the mineral phases of Al in this acidified river were analyzed by using the geochemical modeling software (PHREEQC). From the results, dissolved Al ions acted as a buffer from pH 4 to 6, and the basaluminite (Al4(SO4)(OH)10) as the dominant chemical species, mainly controlled the solubility of Al from pH 4 to 6.
