Abstract: Chemical weathering affects global carbon cycle and climate change, and thus the rates and controlling factors of which are research hotspots. To explore the chemical weathering rates and their influencing factors in basins with different rock lithology, we collected river water samples and analyzed hydrochemical characteristics in the Yinjiang River basin, Shiqian River basin and Yuqing River basin in September 2018. The results showed that the average total dissolved solids (TDS) in river water was 244 mg·L^-1, which was much higher than global mean value (100 mg·L^-1). The spatial difference in TDS values showed that the lithologic distribution caused a large variation in ion concentration. The most abundant anion and cation in basins were HCO₃^- and Ca²⁺, respectively, indicating that the weathering of carbonate rock in these basins played a leading role in river water chemistry. The forward model was used to estimate the contribution of different endmembers (atmosphere, anthropogenic activities, silicate rock, and carbonate rock) to the total dissolved cations in the river. We found that the contributions of carbonate rocks in the tributaries showed significant variations (55.0%-93.9%), which was mainly affected by lithology distribution. The silicate weathering rates in Yinjiang River, Shiqian River and Yuqing River were 4.4, 2.8 and 2.5 t·km^-2·a^-1, and the corresponding CO₂ consumption rate was 45×10³, 18×10³ and 16×10³ mol·km^-2·a^-1, respectively. The carbonate weathering rates were much higher, being 43.7, 24.7 and 29.8 t·km^-2·a^-1 for the Yinjiang River, Shiqian River and Yuqing River respectively. The corresponding CO₂ consumption rates for the threerivers were 498×10³, 284×10³ and 354×10³ mol·km^-2·a^-1, respectively. The spatial variations of weathering under the same climatic conditions highlighted the importance of lithology on chemical weathering. Our results suggest high spatial variations of chemical weathering under various lithologic conditions, which can be used for assessing regional water environmental quality and its effect on global carbon cycle.

Key words: atmospheric visibility, PM_2.5 and PM₁₀., relative humidity (RH), PROVSV curve analysis