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Concentrations of dissolved silicon in river waters reflect a complex interplay among chemical weathering of primary silicate minerals, formation and weathering of secondary clay minerals, hydrothermal input and biological cycling (formation and dissolution of opal phytoliths and growth of diatoms). We applied the Ge/Si ratio to assess the different sources of dissolved Si in rivers hailing from the eastern Tibetan Plateau - the Salween, Mekong, Chang Jiang (Yangtze), Hong (Red) and Huang He (Yellow) and from Mt. Baekdu - the Duman. Elevated riverine Ge/Si ratios were observed in arid regions with high geothermal activity in the Salween, Chang Jiang and Mt. Baekdu streams. In the Huang He and Hong River basins geothermal influence was not as pronounced, but weathering of sulfide- and coal-bearing minerals may be responsible for the high Ge/Si ratios. In rivers where inputs from hydrothermal and sulfide weathering are minimal, our data mostly fall in the weathering-limited regime of high riverine Si concentrations and low Ge/Si ratios. (C) 2015 Elsevier B.V. All rights reserved.