环境地球化学国家重点实验室知识库

The chemical composition of the Qiantangjiang River, the largest river in Zhejiang province in eastern China, was measured to understand the chemical weathering of rocks and the associated CO₂ consumption and anthropogenic influences within a silicate-dominated river basin. The average total dissolved solids (TDS, 113 mg l⁻¹) and total cation concentration (TZ+, 1357 μeq l⁻¹) of the river waters are comparable with those of global major rivers. Ca²⁺ and HCO₃⁻ followed by Na²⁺ and SO₄²⁻, dominate the ionic composition of the river water. There are four major reservoirs (carbonates, silicates, atmospheric and anthropogenic inputs) contributing to the total dissolved load of the investigated rivers. The dissolved loads of the rivers are dominated by both carbonate and silicate weathering, which together account for about 76.3% of the total cationic load origin. The cationic chemical weathering rates of silicate and carbonate for the Qiantangjiang basin are estimated to be approximately 4.9 ton km⁻² a⁻¹ and 13.9 ton km⁻² a⁻¹, respectively. The calculated CO₂ consumption rates with the assumption that all the protons involved in the weathering reaction are provided by carbonic acid are 369 × 10³ mol km⁻² a⁻¹ and 273 × 10³ mol km⁻² a⁻¹ by carbonate and silicate weathering, respectively. As one of the most severe impacted area by acid rain in China, H₂SO₄ from acid precipitation is also an important proton donor in weathering reactions. When H₂SO₄ is considered, the CO₂ consumption rates for the river basin are estimated at 286 × 10³ mol km⁻² a⁻¹ for carbonate weathering and 211 × 10³ mol km⁻² a⁻¹ for silicate weathering, respectively. The results highlight that the drawdown effect of CO₂ consumption by carbonate and silicate weathering can be largely overestimated if the role of sulfuric acid is ignored, especially in the area heavily impacted by acid deposition like Qiantangjiang basin. The actual CO₂ consumption rates (after sulfuric acid weathering effect deduction) is only about 77% of the value calculated with the assumption that carbonic acid donates all the protons involved in the weathering reaction.