Abstract: Chishui River, the only tributary without the dam in the upper reaches of YangtzeRiver, is of importance for better understanding solute transportation in rivers and the chemical weathering processes. In this study, we investigated the hydrochemical characteristics of the mainstream and major tributaries and its major driving factors in Chishui River Basin. Mass balance and forward model approach were applied to calculate the contribution of different endmembers, the chemical weathering rates, and the atmospheric CO₂ consumption rates in the river. Theresults showed that cations of the rivers were dominated by Ca²⁺ and Mg²⁺. The contributions of cations derived from atmospheric input, human activities, silicate weathering, and carbonate weathering were 12%, 3%, 9% and 77%, respectively. The anions of the rivers were dominated by HCO₃^- and SO₄^2-. The Chishui River water had higher SO₄^2- and lower HCO₃^- concentrations compared with Yangtze River and Wujiang River. The weathering rates and CO₂ consumption rates of silicate were estimated to be 7 t·km^-2·a^-1 and 1.7×10⁵ mol·km^-2·a^-1, respectively, which were similar to those in other rivers located in karstic areas of southwest China. The weathering rates and CO₂ consumption rates of carbonate were estimated to be 57.6 t·km^-2·a^-1 and 4.52×10⁵ mol·km^-2·a^-1 after excluding the impacts of sulfuric acid in weathering reactions, respectively. The weathering rates increased to 74.6 t·km^-2·a^-1 and CO₂ consumption ratesdecreased to 1.74×10⁵ mol·km^-2·a^-1 when considering the sulfuric acid as a carbonate weathering agent. The results suggested that the carbonate weathering rates increased by 30% due to the involvement of sulfuric acid. Due to higher concentration of SO₄^2- and lower concentration of HCO₃^- in water, CO₂ consumption rates were lower in the Chishui River compared to other rivers in karstic areas of southwest China.

Key words: plastic litter, physical effect, forest regeneration, plantation, biomass allocation