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Highlights: [•] Water chemistry and isotopes (δ34S, δ18O, δ13C) reveal the weathering process. [•] 72% of sulphate derived from sulphide oxidation in the Yalong River. [•] Dynamics of DIC affected by carbonate weathering and equilibration processes. [•] Sulphuric acid dominate carbonate weathering in the cold and dry zone with high elevation. [ABSTRACT FROM AUTHOR]

• Carbonate weathering dominates the water chemistry of river water which accounts for about 80.5 % of solutes. • The sensitivity of chemical weathering to climate change and topographic factors were found. • Forward model is combined with the mass balance to calculate the weathering rates. • Weathering rate is 6.0 t km−2 a−1 for silicate and 70.1 t km−2 a−1 for carbonate. Chemical weathering acts as a linkage between the solid earth and atmospheric CO 2 and thus affects the global climate throughout the geologic time. However, these processes have not been well-documented in the Himalayan Rivers due to the lack of information on the sources of solutes and pyrite oxidation. Here we present chemical compositions of surface water in the upper Indus River basin (UIRB), Western Himalayas, aiming to explore the sources of major ions, chemical weathering rates, associated CO 2 consumption rates, and their controlling factors. The total cation charge (1611 µEq) and average total dissolved solids (133 mg/L) of the UIRB waters were higher than those of the world's major rivers. HCO 3 − and Ca2+ dominated the ionic compositions of river water. The total major ions of analyzed rivers were mainly sourced from reservoirs including carbonates, evaporites, silicates, and atmospheric inputs. Quantitative investigation of solute sources indicated that carbonate weathering dominates the dissolved loads in river water, which accounts for approximately 80.5 %. The chemical weathering rates of silicate and carbonate were estimated to be 6.0 and 70.1 t km−2 a−1, with atmospheric CO 2 consumption rates of 91 × 103 and 503 × 103 mol km−2 a−1, respectively. The highest carbonate weathering rate (128.2 t km−2 a−1) in the UIRB was observed in the Suru River basin, which has the steepest catchment average slope. After considering pyrite oxidation, the actual CO 2 consumption rates by the silicates and carbonate in the basin were only approximately 80 % of the amount estimated under the presumption that carbonic acid donates all protons included in the chemical weathering. This study highlights the importance of pyrite oxidation for riverine carbon budget in the mountain rivers, Western Himalayas. [ABSTRACT FROM AUTHOR]

This study focuses on the chemical and Sr isotopic compositions of the dissolved load of the rivers in the Liao River basin, which is one of the principal river systems in northeast China. Water samples were collected from both the tributaries and the main channel of the Liao River, Daling River and Hun-Tai River. Chemical and isotopic analyses indicated that four major reservoirs (carbonates (+gypsum), silicates, evaporites and anthropogenic inputs) contribute to the total dissolved solutes. Other than carbonate (+gypsum) weathering, anthropogenic inputs provide the majority of the solutes in the river water. The estimated chemical weathering rates (as TDS) of silicate, carbonate (+gypsum) and evaporites are 0.28, 3.12 and 0.75 t/km 2 /yr for the main stream of the Liao River and 7.01, 25.0 and 2.80 t/km 2 /yr for the Daliao River, respectively. The associated CO 2 consumption rates by silicate weathering and carbonate (+gypsum) weathering are 10.1 and 9.94 × 10 3 mol/km 2 /yr in the main stream of the Liao River and 69.0 and 80.4 × 10 3 mol/km 2 /yr in the Hun-Tai River, respectively. The Daling River basin has the highest silicate weathering rate (TDS sil , 3.84 t/km 2 /yr), and the Hun-Tai River has the highest carbonate weathering rate (TDS carb , 25.0 t/km 2 /yr). The Raoyang River, with an anthropogenic cation input fraction of up to 49%, has the lowest chemical weathering rates, which indicates that human impact is not a negligible parameter when studying the chemical weathering of these rivers. Both short-term and long-term study of riverine dissolved loads are needed to a better understanding of the chemical weathering and controlling factors. [ABSTRACT FROM AUTHOR]