Figure 3 a & b. Mean (+ 1stdv) of Pb and Cu concentrations in bed sediments collected above and below the confluences of Flint Creek and Rock Creek, respectively, in 1989 plotted with the regression line (solid) and the 95& confidence intervals (dashed lines) for the regression of metal concentrations on river km for the combined data for 1986 and 1987. The metal concentrations in sediments collected from each tributary are indicated by an arrow.