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.