3-4. Al concentration
Figure 3-16 shows the relationship between nitrate concentrations and aluminum concentrations. Over the past 24 years, aluminum concentrations increased as nitrate concentrations increased. The low pH caused by the high nitrate concentration in the high flow rate brought high concentrations of aluminum. Since fish mortality is reported with an aluminum concentration of 11 μeq/L (Baker & Schofield, 1982), the aluminum concentration of the Hyakumakidani stream sometimes exceeded the fish mortality threshold level.