赣南小流域的水文地球化学特征和主要风化过程

HYDRO-GEOCHEMISTRY AND CHEMICAL WEATHERING PROCESSES OF SMALL WATERSHEDS IN THE SOUTHERN JIANGXI PROVINCE

对赣南花岗岩小流域进行采样、测试及分析,发现其河水含有较低的矿化度,水化学组成以Na+,Ca2+,C l-和HCO3-为主,溶解性S i的含量明显较高,代表了典型硅酸盐地区河流的相应化学组成.通过G ibbs图分析,赣南流域大部分地区受大气降水的影响比较显著,“蒸发-浓缩”类型的小流域也较多.根据主成分分析和因子分析的结果,定量地估算了大气中CO2和三类岩石对河水中各种离子的贡献比例.与黄河相比,赣南流域受硅酸盐岩风化作用强烈,但主要影响因素仍是碳酸盐和蒸发盐岩,二者对赣南流域溶解质的贡献率分别为42.8%和29.2%,大气中CO2对河水溶解质的贡献率为21.4%,低于世界平均水平.主要风化反应以岩盐和方解石的溶解为主,S i/(Na*+K)比值较低,说明风化反应在表生环境中进行,其产物是富含阳离子的次生矿物.

Base on tests and analysis of the samples collected from the small granite watersheds in the southern Jiangxi province, it is found the Ganjiang river and its tributaries have low total dissolved solids and the chemical compositions of river waters on dominated by Na^＋ , Ca^2＋ , Cl^- , HCO3^- and Si （the water has higher Si concentration）, which represents that of the river water from the typical silicate rock areas. According to the Gibbs graph analysis, most watersheds of the southern Jiangxi province are evidently influenced by precipitation, and many watersheds are the type of ＂evaporation-condensation＂. On the basis of the principal composition analysis and factor analysis, the contributions of atmospheric CO2 and three types of rock to the total dissolved solids are estimated quantificationally. Being compared with the Yellow River, the watersheds in the southern Jiangxi province are influenced strongly by silicate weathering, but the dominant factors still are carbonates and evaporates, which are responsible for 42.8% and 29.2% of total ion equivalent concentration, and that of atmosphere CO2 is 21.4% which is lower than the average value of the world. The evaporate and calcite dissolution are the primary weathering processes. The low Si/（ Na＊ ＋ K）ratio indicates the weathering reactions take place in superficial environment and its products are cation-rich secondary minerals.