2013年长江丰水期河水化学特征及控制因素

为掌握长江河水化学组成特征及其控制因素,笔者运用Gibbs图、多种离子比例系数法和主成分分析法综合分析了长江流域丰水期河水化学及氢氧同位素特征。结果表明,长江丰水期河水主要来源为大气降水,河水化学类型主要为HCO₃·SO₄-Ca型,化学成分主要受流域内广泛分布的碳酸盐岩等岩石风化作用控制;河水pH值、HCO₃^-浓度沿长江径流方向降低,SO₄^2-、Ca²⁺浓度沿长江径流方向升高。2013年丰水期,长江河水化学组成特征变化的主要影响因子,是易溶盐岩溶解和人类活动(贡献率40%),其次为川贵及长江三角洲地区的酸雨沉降以及人为酸性废水排放促进了流域内石灰岩和富含碳酸盐的三叠系砂页岩溶解(贡献率20%),最后为硅酸盐矿物及其风化产物的溶解(贡献率19%)。为了解长江河水水质状况及其演变趋势,合理评价长江流域水资源提供很好的科学依据。

WATER CHEMICAL CHARACTERISTICS AND CONTROLLING FACTORS OF THE YANGTZE RIVER IN THE WET SEASON, 2013

The Yangtze River, one of the longest rivers in China, plays an important role in the development of national economy. To understand chemical characteristics and its controlling factors of the Yangtze River, 42 samples were collected from the Yangtze River and its main tributaries during the period of high-discharge in July and August, 2013. The major ions of the water samples such as K⁺, Na⁺, Ca²⁺, Mg²⁺, HCO₃^-,SO₄^2- and Cl^- were analyzed, as well as hydrogen and oxygen isotopic compositions (δD and δ¹⁸O). The δD and δ¹⁸O values of the Yangtze River ranged from -106‰ to -31‰ and from -14.6‰ to -4.1‰, respectively, located around the local meteoric water line (LMWL), indicating that atmospheric precipitation is the main source of the river in the wet season. The chemical type of the Yangtze River was mainly represented as HCO₃·SO₄-Ca, associated with chemical weathering of carbonates distributing widely in the drainage basin. The median of the total dissolved solid was about 242 mg/L, three times of the world average level. The pH values and concentrations decreased from the upper reaches down to the lower reaches along the Yangtze River, whereas both SO₄^2- and Ca²⁺ concentrations increased. The most significant factor controlling variation of the chemical composition of the Yangtze River, in wet season of 2013, was the dissolution of soluble salts contained in the surrounding rocks and the influence of human activities. The second potential affecting factor was chemical weathering dissolution of carbonate accelerated by acid rainwater in the upper Sichuan and Guizhou areas and the lower Yangtze River Delta and acid waste drainage by human activities. The dissolution of silicate minerals and associated weathering products was another possible affecting factor for chemical composition of the Yangtze River. The research can help better understand water quality and its evolution trend of the Yangtze River, and provide a scientific basis for assessment and management of water resources in the Yangtze River Basin.