青弋江流域河流水化学与岩石风化过程

Riverine Water Chemistry and Rock Weathering Processes of Qingyi River Basin

为研究中国东部亚热带流域的岩石风化特征,以长江下游青弋江流域为研究区,通过测定青弋江干支流河水及雨水的主要离子浓度,结合水化学和正演模型识别流域岩石风化特征并估算其岩石风化速率和对大气CO_(2)消耗速率.结果表明:流域岩石风化受人为活动影响小,岩石风化以碳酸参与风化为主,硫酸与硝酸的作用可忽略.流域河水阳离子主要来源为碳酸盐岩风化(占59.2%),其次为硅酸盐岩(17.9%).大气降水和蒸发岩的贡献较低,分别占9.6%和5.6%.碳酸盐岩和硅酸盐岩风化速率均为上游山区支流‒徽水(32.04 t·km^(-2)·a^(-1)和20.97 t·km^(-2)·a^(-1))>青弋江干流(24.12 t·km^(-2)·a^(-1)和8.91 t·km^(-2)·a^(-1))>下游平原支流‒漳河(13.68 t·km^(-2)·a^(-1)和2.85 t·km^(-2)·a^(-1));CO_(2)消耗速率为徽水(5.86×10^(5) mol·km^(-2)·a^(-1)和3.29×10^(5) mol·km^(-2)·a^(-1))>青弋江(2.45×10^(5) mol·km^(-2)·a^(-1)和2.43×10^(5) mol·km^(-2)·a^(-1))>漳河(0.77×10^(5) mol·km^(-2)·a^(-1)和1.39×10^(5) mol·km^(-2)·a^(-1)).青弋江流域的岩石风化以碳酸风化碳酸盐岩为主,其风化速率略低于我国东部的其他亚热带硅酸盐岩分布区.青弋江流域的化学风化速率在空间上有所差异,上游山区的硅酸盐岩风化为全流域贡献了更多碳汇,对区域碳循环过程具有重要意义.

To investigate the rock weathering processes in subtropical basin in east China,we analyzed major ion compositions of rivers and precipitation samples in the Qingyi River Basin in the lower reach of the Yangtze River.In this study,the characteristics of weathering processes in the Qingyi River Basin were identified,and the rock weathering rates and consumption rates of atmospheric CO_(2) were estimated based on water chemistry and the forward model.The results show that the anthropogenic influences on rock weathering were not significant,which means the rock weathering in the study area was mainly induced by carbonic acid while the influence of sulfuric acid and nitric acid could be neglected.The cations of rivers were mainly contributed by weathering of carbonates(59.2%),followed by weathering of silicates(17.9%).Atmospheric precipitation and evaporites contributed 9.6%and 5.6%,respectively.Spatially,the carbonate weathering rates and silicate weathering rates decreased in the order of tributary Huishui River in the upstream mountainous areas(32.04 t·km^(-2)·a^(-1) and 20.97 t·km^(-2)·a^(-1))>main stream of Qingyi River(24.12 t·km^(-2)·a^(-1) and 8.91 t·km^(-2)·a^(-1))>tributary Zhanghe River in the downstream areas(13.68 t·km^(-2)·a^(-1) and 2.85 t·km^(-2)·a^(-1)).Similarly,the CO_(2) consumption rates from carbonates weathering and silicate weathering were in the order of tributary Huishui River(5.86×10^(5) mol·km^(-2)·a^(-1) and 3.29×10^(5) mol·km^(-2)·a^(-1))>main stream of Qingyi River(2.45×10^(5) mol·km^(-2)·a^(-1) and 2.43×10^(5) mol·km^(-2)·a^(-1))>tributary Zhanghe River(0.77×10^(5) mol·km^(-2)·a^(-1) and 1.39×10^(5) mol·km^(-2)·a^(-1)).In conclusion,carbonate weathering induced by carbonic acid was dominant in the Qingyi River Basin,with chemical weathering rates slightly lower than those of similar silicate-dominated subtropical areas in east China.The rock weathering rates in the study area differed spatially.In particular,silicate weathering in upstream mountainous areas accounted for more carbon sink of the whole Qingyi River Basin,which is of great importance for the regional carbon cycle.