Abstract We analysed precipitation and river water samples from the Lijiang River basin with the aim of understanding the important role of acid rain components, especially NH4, in chemical weathering of karst areas. First, analysis of the hydrochemical characteristics revealed the following: In the precipitation samples, the volume-weighted mean pH was 4.91, and the acid rain rate was 65%. The major ion composition was characterized by a dominance of NH4, Ca, SO4 and NO3, accounting for 40.0%, 35.3%, 46.3% and 30.5%, respectively, of the total cation and anion concentrations. In the river water samples, the pH ranged from 6.75 to 9.16, with an average of 7.55. The major hydrogeochemical species in the river water samples were Ca–HCO3 and Mg–HCO3. Second, by employing chloride-normalized ratios of the other major ions in precipitation, we estimated that the contributions of SO4 and NO3 from the atmosphere to the river were53.6% and 35.0%, respectively. Third, combining the hydrochemical index with the value of δ13CDIC and using the hydrochemical composition method showed that the proportion of carbonate weathered (R) by NH4, H2SO4 and HNO3 from acid rain accounted for 9.3%, 9.4% and 3.1% of the total weathering rate, respectively, and the proportions in the upper reaches were significantly higher than those in the lower reaches of the river. The average values of the carbonate weathering proportion (R) and the carbonate weathering rate (CWR) due to acid rain were approximately 22.0% and 2.1 t/km2/yr, respectively. Taken together, our results revealed that carbonate weathering by acid rain can significantly increase the carbonate weathering rate, which is essential information for accurate estimation of the carbon cycle (namely, inorganic carbon sources and sinks).

中文翻译：

---

主要酸雨成分尤其是NH4的大气沉降对漓江流域典型喀斯特地区补给过程中碳酸盐风化的影响

摘要 我们分析了漓江流域的降水和河水样品，旨在了解酸雨成分，尤其是 NH4 在岩溶地区化学风化中的重要作用。首先，水化学特征分析表明：在降水样本中，体积加权平均pH值为4.91，酸雨率为65%。主要离子组成以NH4、Ca、SO4和NO3为主，分别占阳离子和阴离子总浓度的40.0%、35.3%、46.3%和30.5%。河水样品pH值在6.75～9.16之间，平均值为7.55。河水样品中的主要水文地球化学物质是 Ca-HCO3 和 Mg-HCO3。其次，通过使用沉淀中其他主要离子的氯化物归一化比率，我们估计大气中 SO4 和 NO3 对河流的贡献分别为 53.6% 和 35.0%。第三，结合水化学指数和δ13CDIC值，采用水化学成分法表明酸雨中NH4、H2SO4和HNO3风化的碳酸盐（R）占总风化的9.3%、9.4%和3.1%分别是，上游的比例明显高于下游的比例。酸雨导致的碳酸盐风化比例（R）和碳酸盐风化率（CWR）的平均值分别约为22.0%和2.1 t/km2/yr。综上所述，我们的结果表明酸雨导致的碳酸盐风化可以显着增加碳酸盐风化率，