『Abstract
　Three large rivers - the Chang Jiang (Yangtze), Mekong (Lancang Jiang) and Salween (Nu Jiang) - originate in eastern Tibet and run in close parallel over 300 km near the eastern Himalayan syntaxis. Seventy-four river water samples were collected mostly during the summer season from 1999 to 2004. Their major element compositions vary widely, with total dissolved solids (TDS) ranging from 31 to 3037 mg/l, reflecting the complex geologic makeup of the vast drainage basins. The major ion distribution of the main channel samples primarily reflects the weathering of carbonates. Evaporite dissolution prevails in the headwater samples of the Chang Jiang in the Tibetan Plateau interior, as evidenced by the high TDS (928 and 3037 mg/l) and the Na-Cl dominant major element composition. Local tributary samples of the Mekong and Salween, draining the Lincang Batholith and the Tengchong Volcano, show distinctive silicate weathering signatures. We used five reservoirs - rain, halite, sulfate, carbonate, and silicate - in a forward model to calculate the contribution from silicate weathering to the total dissolved load and to estimate the consumption rate of atmospheric CO2 by silicate weathering. Carbonate weathering accounts for about 50％ of the total cationic charge (TZ⁺) in the samples of the Mekong and the Salween exiting the Tibetan Plateau. In the “exit” sample of the Chang Jiang, 45％ of TZ⁺ is from halite dissolution inherited from the extreme headwater tributaries in the interior of the plateau, and carbonates contribute only 26％ to the TZ⁺. The net rate of CO2 consumption by silicate weathering is (103-121)×10³ mol km^-2 year^-1, lower than the rivers draining the Himalayan front. GIS-based analyses indicate that runoff and relief can explain 52％ of the spread in the rate of atmospheric CO2 drawdown by silicate weathering, but other climatic (temperature, precipitation, potential evapotranspiration) and geomorphic (elevation, slope) factors also show collinearity. Only qualitative conclusions can be drawn for the significance of lithology due to lack of digitized lithologic information. The effect of the peculiar drainage pattern due to tectonic forcing is not readily apparent in the major element composition or in increased chemical weathering rates. The ⁸⁷Sr/⁸⁶Sr ratios and the silicate weathering rates are in general lower in the Three Rivers than in the rivers draining the Himalayan front.』

1. Introduction
2. Study area
　2.1. Geological setting
　2.2. Climate, vegetation, and population
3. Sampling and analytical methods
4. Results and discussion
　4.1. Major ion distribution
　4.2. Strontium and its isotopic composition in the TRR
　4.3. Sources and dissolved load
　　4.3.1. Atmospheric input
　　4.3.2. Evaporite contribution
　　4.3.3. Silicate contribution
　　4.3.4. Carbonate contribution
　4.4. Rates of CO2 consumption by silicate weathering
　4.5. What controls chemical weathering in the TRR?
　　4.5.1. Physical erosion
　　4.5.2. Climatic and geomorphic factors
5. Conclusions
Acknowledgments
References