黄河下游地区河水主要离子和锶同位素的地球化学特征

对黄河下游地区河水主要阴阳离子、锶元素及其同位素组成进行了分析.结果发现其水化学组成主要以Ca~(2+),Na~+,HCO_3~-和SO_4~(2-)离子为主,分别占阴阳离子组成的75%以上.干流与支流间在化学组成上存在显著差异,黄河干流的SO_4~(2-),NO_3~-和Cl~-具有共同的来源,而支流河水中的SO_4~(2-),NO_3~-和Cl~-来源不同.黄河下游具有较高的锶含量及较低的锶同位素组成,锶含量变化范围在0.0429 mg·l~(-1)-0.936mg·l~(-1)之间,平均含量为0.394 mg·l~(-1),锶同位素组成变化范围在0.70986-0.71139之间,平均值为0.71118,其中黄河人海口的锶同位素组成(~(87)Sr/~(86)Sr=0.70986)与现代海水锶同位素比值(0.70916)相近,表明其锶同位素组成受海水作用影响较大.对主要元素、微量元素锶及其同位素组成分析研究发现,黄河下游地区河水锶同位素组成主要源于蒸发盐岩和碳酸盐岩的风化溶解作用,而人类活动的影响相对较小.由锶同位素平衡方程计算得出,黄河下游地区河水锶同位素组成由大气降水和岩石风化作用混合而成,其中大气降水对黄河下游地区~(87)Sr/~(86)Sr的贡献率约为30%,而岩石风化对其贡献率约为70%.

GEOCHEMISTRY OF THE MAIN IONS AND Sr ISOTOPIC COMPOSITION IN THE LOWER REACH OF THE YELLOW RIVER, NORTH CHINA

The Yellow River is one of the largest rivers in China, and plays significant role in the development of the society and economy, as well as the ecosystem health in northern China. Major ions and the strontium isotopic composition are important geochemical characters of the water body, and provide insight into the regional hydrogeochemistry, rock weathering rates in drainage basins, and anthropogenic influences on the river. This study determined ~(87)Sr/~(86)Sr ratios and concentration of Sr and major anions and cations in 16 water samples from the lower reach of the Yellow River. Ca~(2+) , Na~+ , HCO_3~- and SO_4~(2-) are the dominant ions. The concentration of the ions accounts for more than 75% in the respective categories, and differ significantly between the tributary and the mainstream. Sources of SO_4~(2-), NO_3~- and Cl~- are homogenized in the mainstream, while clearly different in the tributaries. The lower section of the reach is higher in Sr concentration while lower in the Srisotope composition, which range from 0.0429mg ·l~(-1) to 0.936mg ·l~(-1) and from 0.70986 to 0.71139, respectively. The isotopic composition in the estuary is similar to that of the sea water, suggesting that the isotopic geochemistry has been under the control of the sea. The research of major elements, the Sr concentration and ~(87)Sr/~(86)Sr ratios show that the weathering of carbonates and evaporates in the drainage basins are responsible for the high water Sr concentrations. According to the balance equation of Sr, the Sr in river water is derived from two end members, that is, the ratio of ~(87)Sr/~(86)Sr from atmosphere precipitation is about 30% and from rock weathering is about 70%.