Abstract
Hot-spring water and mine effluent flow into the Toyohira River, which runs through the center of Sapporo, Japan. In the river, the concentrations of components from hot-spring water and mine effluent change according to the flow regime. This phenomenon must be addressed in water quality management. The authors focused on arsenic supplied to the Toyohira River. Arsenic washout load was quantitatively assessed, and the flow-regime-dependent characteristics of the washout load were studied. We found that the washout load of dissolved arsenic increases during snowmelt and fall flood, phenomena that increase the inflow of hot-spring water. The highest washout load of suspended arsenic occurs during flood. The estimated annual arsenic washout load is 10,763 kg·year-1 (2002), 43% of which is washout during flood (snowmelt or rainfall). According to the arsenic washout load balance of the river basin as a whole, approximately 20% of arsenic supplied to the Toyohira River is suspended and sediment there. Also, approximately 40% of suspended arsenic washed into the Toyohira River by flood comes directly from hot-spring water.
