Fig. 7. Sulfur isotopic composition plotted versus 1/SO₄ for surface waters W1–W9. Dissolved sulfate increases with distance downstream. Tic marks on the apparent mixing line connecting mixing endmembers W1 and W9 indicate the calculated percentage of W9 in the mixture, based on sulfate concentrations. Estimated precision of ³⁴S values (±0.2) is approximated by the diameter of the dots.