西南不同岩性混合小流域化学风化特征

岩石化学风化影响着全球碳循环和气候变化,化学风化速率的估算及控制因素一直是研究的热点。为探究不同岩性混合小流域内化学风化速率及影响因素,于2018年9月对印江河流域、石阡河流域及余庆河流域采集河水样品并分析水化学特征。结果表明:河水的总溶解性固体(TDS)平均值为244 mg·L^-1,高于世界河流平均值(100 mg·L^-1);TDS值的空间差异显示,岩性分布不同导致离子浓度的明显变化。流域中的优势阴阳离子分别为HCO3^-和Ca^2+,表明流域碳酸盐岩风化对河水水化学组成起主导作用;通过正演模型解析不同端元(大气、人为、硅酸盐岩和碳酸盐岩)对河流中总溶解阳离子贡献发现,支流中碳酸盐岩贡献变化明显(55.0%~93.9%),空间差异主要受岩性影响;印江河、石阡河和余庆河的硅酸盐岩风化速率分别为4.4、2.8和2.5 t·km^-2·a^-1,相应的CO2消耗速率为45×10^3、18×10^3和16×10^3mol·km^-2·a^-1;碳酸盐岩风化速率显著高于硅酸盐岩风化速率,3条河流的碳酸盐岩风化速率分别为43.7、24.7和29.8 t·km^-2·a^-1;CO2消耗速率为498×10^3、284×10^3和354×10^3mol·km^-2·a^-1。研究表明,同一区域相同气候条件下流域风化的空间差异显示了岩性对河流风化的控制作用,其结果可用于区域水环境质量和碳循环评估。

The chemical weathering characteristics of different lithologic mixed small watersheds in Southwest China

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 45×10^3,18×10^3 and 16×10^3 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 498×10^3,284×10^3 and 354×10^3 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.