Supplementary Data - Table S5 Modeled Ganga Chemical composition and associated uncertainties (0.68 confidence interval) Elements marked with a star could not be modeled as their abundance was not found to be grain size dependend. Element Ganga modeled Ganga Ganga Ganga Ganga Suspended load Bed load Total sediments Surface sediments /UCC wt% ± wt% ± wt% ± wt% SiO2 65.173 0.653 76.770 3.543 65.291 0.808 55.386 0.991 Al2O3 12.390 0.361 8.698 0.724 12.353 0.404 17.011 0.813 Fe2O3 4.788 0.165 3.378 1.076 4.774 0.190 6.822 1.061 MnO 0.070 0.002 0.085 0.049 0.070 0.003 0.090 1.007 MgO 1.936 0.072 1.166 0.309 1.928 0.083 2.670 0.874 CaO * 3.376 1.126 3.061 0.893 3.373 1.127 3.278 0.805 Na2O 1.202 0.023 1.397 0.145 1.204 0.026 0.907 0.310 K2O 2.648 0.080 1.898 0.323 2.640 0.091 3.401 0.777 TiO2 0.640 0.013 0.591 0.239 0.639 0.016 0.769 1.278 P2O5 * 0.137 0.038 0.144 0.067 0.137 0.038 0.141 0.687 LOI 5.867 0.316 2.614 1.133 5.834 0.360 8.960 mol:mol ± mol:mol ± mol:mol ± mol:mol mol:mol Al/Si 0.233 0.009 0.136 0.018 0.232 0.010 0.375 0.842 Fe/Si 0.057 0.003 0.034 0.012 0.056 0.003 0.095 1.082 ppm ± ppm ± ppm ± ppm ppm As 7.3 0.4 3.0 1.0 7.3 0.5 12.0 4.9 Ba 428.8 13.1 296.4 44.3 427.5 14.8 561.5 0.8 Be 2.8 0.1 2.4 0.1 2.7 0.1 3.4 0.9 Bi 0.8 0.1 0.4 0.3 0.8 0.1 1.2 6.4 Cd * 0.4 1.4 0.4 0.2 0.4 1.4 0.2 4.4 Ce 84.5 1.1 155.8 84.8 85.2 2.7 85.0 1.3 Co 11.4 0.5 6.1 1.4 11.3 0.5 17.1 1.1 Cr 71.9 3.2 44.3 12.6 71.6 3.6 98.5 2.0 Cs 8.1 0.5 4.2 1.0 8.1 0.5 12.3 2.2 Cu 20.5 1.6 3.7 4.9 20.3 1.8 40.2 0.8 Dy 5.3 0.1 8.7 4.8 5.3 0.2 5.6 1.5 Er 2.9 0.0 4.8 2.8 2.9 0.1 3.1 1.3 Eu 1.2 0.0 1.5 0.6 1.2 0.0 1.4 1.4 Ga 17.0 0.6 11.3 1.4 17.0 0.7 24.1 1.0 Gd 5.9 0.1 10.0 5.4 5.9 0.2 6.2 1.6 Ge 1.8 0.0 1.8 0.3 1.8 0.0 2.1 1.1 Hf 6.9 0.2 15.6 11.7 7.0 0.5 4.8 1.2 Ho 1.0 0.0 1.7 0.9 1.0 0.0 1.1 1.3 In * 0.2 0.1 0.1 0.2 0.2 0.1 0.2 3.1 La 41.7 0.6 77.3 41.8 42.0 1.4 41.9 1.4 Lu 0.4 0.0 0.8 0.5 0.5 0.0 0.5 1.4 Mo * 0.4 0.7 0.0 0.0 0.4 0.7 0.5 0.3 Nb 12.1 0.2 11.7 4.8 12.1 0.3 14.4 0.5 Nd 35.4 0.5 63.7 34.7 35.7 1.1 36.0 1.4 Ni 38.0 1.8 15.6 6.2 37.8 2.1 48.7 1.9 Pb 22.9 0.6 17.6 1.7 22.8 0.7 29.5 1.1 Pr 9.5 0.1 17.4 9.5 9.6 0.3 9.7 1.4 Rb 139.2 5.7 87.6 17.9 138.7 6.4 191.6 1.2 Sb * 1.2 0.4 0.8 0.3 1.2 0.4 1.5 5.9 Sm 7.0 0.1 12.2 6.7 7.0 0.2 7.1 1.6 Sn 6.4 0.7 10.4 10.0 6.5 0.8 6.9 2.6 Sr * 97.3 8.4 94.8 7.1 97.3 8.5 92.5 0.3 Ta 1.4 0.0 1.7 0.9 1.4 0.0 1.6 0.6 Tb 0.9 0.0 1.5 0.8 0.9 0.0 1.0 1.4 Th 18.2 0.2 34.7 19.4 18.4 0.6 19.6 1.7 Tm 0.4 0.0 0.7 0.4 0.4 0.0 0.5 1.3 U 3.7 0.1 6.3 3.5 3.8 0.2 4.1 1.4 V 71.2 2.7 44.3 10.6 70.9 3.1 108.6 1.2 W * 3.4 0.8 3.5 1.4 3.4 0.8 3.9 1.7 Y 29.8 0.4 48.7 28.4 29.9 0.9 31.5 1.4 Yb 2.9 0.0 5.0 3.0 3.0 0.1 3.1 1.3 Zn 67.3 3.9 34.5 8.9 66.9 4.3 105.4 0.9 Zr 253.4 9.1 608.6 445.7 257.0 17.4 173.8 1.4