祁连山中段排露沟流域水化学特征及成因

Hydrochemical characteristics and controlling factors at Pailugou catchment in the central Qilian Mountains

2012年11月-2013年10月,在祁连山中段排露沟流域持续采集1 a的大气降水和出口断面径流样品,对主要可溶离子、pH、电导率EC和总溶解固体TDS进行了分析。结果表明:流域径流与大气降水相比,各项对应离子浓度显著增加,径流TDS均值(255.50 mg·L^(-1))远大于降水(46.77 mg·L^(-1))。径流离子类型为Ca2+-M g2+-HCO_3^-,呈弱碱性。大气降水离子类型为Ca2+-HCO_3^-,接近中性。所有径流样品都落在Gibbs分布图的左中端,表明径流离子组成主要受流域岩石风化作用控制。根据Piper图和主要离子的摩尔比值,综合分析得出控制径流离子过程主要是流域碳酸盐岩风化,其次伴随部分硫酸盐和硅酸盐岩石风化。并通过海盐校正分析方法,得出大气降水对出口断面径流主要离子贡献率仅为4.58%。

The aim of this study was to investigate the hydrochemical characteristics and controlling factors of Pailugou catchment in the Central Qilian Mountains.One-year continuous precipitation and runoff samples were analyzed for major cations（Mg2＋,Ca2＋,Na~＋,and K~＋） and anions（SO2-4,NO_3^-,Cl-and HCO_3^-）,pH,electrical conductivity（EC） and total dissolved solids（TDS）.The results revealed that Ca2＋ and Mg2＋ were the dominant cations,and HCO_3^- was the dominant anion in runoff.While the anions and cations in precipitation were dominated by Ca2＋ and HCO_3^-,respectively.The wide water-rock interaction and chemical denudation of mineral solutes resulted in higher solute concentration in stream.The average TDS of runoff was 255.50 mg·L^（-1）,which was much higher than that of precipitation（46.77 mg·L^（-1））.The average pH value in runoff was alkaline,while in precipitation was close to neutral.All of the runoff samples fall within the mid-left side of Gibbs distribution graph,indicating that the major origin of ions in runoff was the weathering of rocks.Based on the piper trilinear nomograph and the major ion molar concentration ratios,this paper further explored that the main processes controlling the water chemistry were mainly by chemical weathering of carbonate rock,partially by sulfate weathering and silicate weathering in rocks.Based on seawater correction approach,the contribution proportion of local precipitation to the solute of runoff at the Pailugou catchment was 4.58%.