亚热带小流域河水水化学、锶同位素特征及其对风化的指示意义

【作者】 刘静；

【导师】 季宏兵；

【作者基本信息】 首都师范大学 ， 自然地理学， 2008， 硕士

【摘要】 本文选取了赣江上游小流域和黔中红枫湖小流域做为研究对象，利用河流水化学组成，溶解态锶特征去示踪河水中溶解质的来源，计算各种岩石风化对河水中溶解态元素的相对贡献率；探讨河流水化学特征与人为活动、岩性，大气降水之间的关系。利用锶同位素端元方程定量的计算各个端元的贡献率，流域盆地的化学风化速率。经过以上研究，得出如下主要结论和几点认识：1、赣江上游小流域的雨水表现出硅酸盐岩的风化特征，而黔中红枫湖小流域的雨水和地下水表现出碳酸盐岩的风化特征。2、通过河水的主元素分析得到：赣江上游小流域河水中主离子组成相对富集Na⁺+K⁺，Ca²⁺、Mg²⁺含量低，而黔中红枫湖小流域河水中主离子组成明显富集Ca²⁺，Mg²⁺，Na⁺+K⁺含量很低；将主离子标准化后，赣江上游小流域主离子组成靠近碳酸风化花岗岩，碳酸风化玄武岩和硫酸风化花岗岩端元，黔中红枫湖小流域河水中主离子的化学组成靠近碳酸风化碳酸盐岩和硫酸风化碳酸盐岩端元。3、利用主元素物质平衡方程模型计算得出：赣江上游小流域在硅酸盐岩和碳酸盐岩系统中，X_sil平均值为0．69（赣江上游流域硅酸盐岩风化对流域系统主离子的相对贡献率为0．69），反映了硅酸盐岩的风化对赣江上游流域河水水化学组成的控制作用。黔中红枫湖小流域X_sil（硅酸盐岩风化对河水的贡献率）数值为0．015-0．256,平均值为0．066，从而得出碳酸盐岩风化的贡献率平均值为0．834。其结果也与主元素分析得出的结论相一致。通过TDS，SO₄^2-／Na⁺，NO₃^-／Na⁺与Na⁺／Cl^-之间的关系图表明：赣江上游小流域受人为活动影响较小，黔中红枫湖小流域受人为活动影响较大。4、根据溶解态锶的平衡方程计算得出：赣江上游小流域来源于硅酸盐岩风化的锶占流域河水中锶含量的48．3％，来源于碳酸盐岩风化的锶占27．4％，来源于蒸发盐岩的风化的锶占4．3％。黔中红枫湖小流域来源于硅酸盐岩风化的锶为6．4％，来源于碳酸盐岩风化的锶占锶含量的75．5％，来源于蒸发盐岩风化的锶占0．5％，可见：赣江上游小流域溶解态锶主要来源于硅酸盐岩的风化，碳酸盐岩次之，蒸发盐岩最小；而黔中红枫湖小流域溶解态锶主要来源于碳酸盐岩的风化，硅酸盐岩次之，蒸发盐岩最小。5、赣江上游小流域和黔中红枫湖小流域⁸⁷Sr／⁸⁶Sr与1／Sr成显著的正相关关系，并且在Mg/Na^*，Ca／Na^*，Mg/Ca，HCO₃^2-／HCO₃^-+SO₄²-和⁸⁷Sr／⁸⁶Sr的关系图上发现：赣江上游小流域硅酸盐岩的风化对河流水化学组成起主要控制作用；黔中红枫湖小流域碳酸盐岩的风化对该流域水体的水化学组成起到主要的控制作用。6、利用锶同位素的端元模拟方程得出：赣江上游小流域大气沉降对赣江上游⁸⁷Sr／⁸⁶Sr的贡献率约为9．7％，岩石风化对其贡献率约为90．3％。黔中红枫湖小流域大气沉降对流域河水中⁸⁷Sr／⁸⁶Sr的贡献率约为8．3％，岩石风化对其贡献率约为91．7％。说明了赣江上游小流域河水中的可溶态元素来源是大气降水和岩石风化的混和型，而黔中红枫湖小流域主要是岩石风化型。并且对黔中流域的王家寨的土壤剖面进行研究发现：粒度频率分布曲线以及土壤的矿物组成指示了风化壳与下伏基岩具有良好的继承关系。7、通过将锶同位素组成与流域参数相结合计算得到：赣江上游小流域的化学风化速率为0．28（keq／hm²·a），而黔中红枫湖小流域的化学风化速率为0．35（keq／hm²·a），比赣江上游小流域风化速率稍大，但是与段雷计算的结果相比，还是偏小的，这可能是由于采样点是丰水期，所采的样品中元素的含量偏低所致。更多还原

【Abstract】 In this paper, we take the upstream basin of Ganjiang River in the southern Jiangxi Province and Hongfeng Lake in the middle Guizhou Province as the research objects. The dissolved elements of watersheds were traced and a clear contrast for rock weathering contribution of different lithologies to river was observed through calculating water chemical constitutes and dissolved Sr of two small basins. The relationships between water chemical characteristic of river and human activity, the lithologies and atmosphere precipitation were also discussed, and the contribution of every end is calculated by using the end member equation of ⁸⁷Sr/⁸⁶Sr.The main conclusions are showed as follows:1.The rainwater of the upstream basin of Ganjiang River represent the characteristics ofthe silicate weathering , while the rainwater and groundwater in Hongfeng Lake watershed represent the characteristics of the carbonate rock weathering.2.On the basis of the principal composition analysis, several conclusions could be drawn: The upstream basin of Ganjiang River has enrichment in Na⁺+K⁺, poor in Ca²⁺+Mg²⁺ and the concentration of Si is high.While that of Hongfeng lake watershed is poor in Na⁺+K⁺, rich in Ca²⁺+Mg²⁺and the concentration of Si is low. The source of the major ions of river in the upstream basin of Ganjiang River is close to the end members of granite weathering by HCO₃^-, basalt weathering by HCO₃^-granite weathering by H₂SO₄, and that of Hongfeng Lake watershed is close to the end members of carbonate weathering by HCO₃^- and carbonate weathering by H₂SO₄ after making the standardization of major elements .3.Basing on the model of major element balance equation, conclusions are showed as follows: the proportion of source from the weathering of silicate rock is 69% in the upstream basin of Ganjiang River, which reflects the dominant inputs of its water chemical component coming from the weathering of silicate rock. The proportion of source from the weathering of carbonate rock is 83.4% in the Hongfeng Lake watershed, which reflects the dominant inputs of its water chemical component coming from the weathering of carbonate rock. In addition, according to the relationship among SO₄^2-/Na⁺ , NO₃^-/Na⁺ , Cl^- /Na⁺ ,we find that the influence of human activity is low in the upstream basin of Ganjiang River ,and that is relatively high in the Hongfeng Lake watershed .4.Deduced from the balance equation of dissolved Sr, the source of Sr in both river basins most are from the rock weathering excluding the atmosphere precipitation, the proportion of source from the weathering of silicate rock, the carbonate rock ,evaporated rock for dissolved Sr in the upstream basin of Ganjiang River is 48.3%,27.4%,4.3%. and relative value of that in the Hongfeng Lake watershed is 6.4%,75.5%,0.5%.5.The relationship between ⁸⁷Sr/⁸⁶Sr and 1/Sr in two small watersheds shows prominent positive correlation, and the plots between Mg/Na^*,Ca/Na^*, Mg/Ca, HCO₃^2-/HCO₃^-+SO₄^2-and⁸⁷Sr/⁸⁶Sr indicate that the weathering of silicate rock mainly controls the water chemistry components in the upstream basin of Ganjiang River, the weathering of carbonate rock mainly controls the water chemical components in the Hongfeng Lake watershed.6.According to end member simulated equation of Sr isotope, the contribution of the atmospheric deposition in the upstream basin of Ganjiang River to the ⁸⁷Sr/ ⁸⁶Sr is about 9.7 % and the rock weathering’s contribution of ⁸⁷Sr/⁸⁶Sr is 90.3 % ,and those of which are 8.3% and 91.7% in Hongfeng lake watershed. The data above indicates that the elements in the upstream basin are from atmospheric precipitation and rock weathering, which is called the mixed type, while the elements in the Hongfeng Lake are from rock weathering. Moreover, studying on soil section in Wang Jiazhai in the Hongfeng Lake in the middle Guizhou Province shows that: the grain size frequency distribution curves and mineral components indicate that the weathering crust and the lower bedrock have well inheritance relations.7.Through calculating of the parameters of Sr isotope and the basin, the results are showed as follows: the weathering rate of the upper reaches of Ganjiang River is 0.28 （keq/hm²·a）,and that is 0.35 （keq/hm²·a） in the Hongfeng Lake watershed. The weathering rate of the Hongfeng Lake watershed is slightly higher than that of the upstream basin of Ganjiang River. But compared with the result of Duanlei（Duan lei,2002）, the numerical value is still small. The possible reason is that the time of sampling is in the monsoon and the contributions of elements in the river are in a low status.更多还原