Relationship between water discharge and sulfate sources of the Yangtze River inferred from seasonal variations of sulfur and oxygen isotopic compositions
Relationship between water discharge and sulfate sources of the Yangtze River inferred from seasonal variations of sulfur and oxygen isotopic compositions
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从硫氧同位素季节变化推断长江流量与硫酸盐来源的关系
DOI：
10.1016/j.gexplo.2015.02.009
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发表时间：
2015-06-01
影响因子：
3.9
通讯作者：
Liu, Yunde
中科院分区：
文献类型：
--
作者：
Li, Xiaoqian;Gan, Yiqun;Liu, Yunde
解析河流水系中的硫酸盐来源，进而解析到全球海洋中，对于理解硫的生物地球化学循环具有重要意义。长江是我国最重要的陆海大河之一，呈现出以SO42-浓度持续升高为特征的酸化趋势。2011年，在武汉长江中游进行了为期1年的每周采样活动，系统地研究了季节性和相关水排放对长江硫酸盐源平衡的影响。SO42-浓度变化范围为8.6 ~ 55.4 mg/L，排放加权平均值为30.0 mg/L； SO42-通量变化范围为1032 ~ 1257.6 kg/s，年平均值为532.5 kg/s。δ O-34（SO4）值在6.7 ~ 16.2‰之间，排放加权平均值为10.4%。而O-18(SO4) δ值在1.6 - 10.5 ppm之间，排放加权平均值为5.1 ppm。与低放水量期相比，长江武汉段高放水量期表现为：高放水量增加一倍，高放水量增加5 ~ 10 m；2)在SO42-浓度没有实质性变化的情况下，SO42-通量增加了一倍；3) δ S-34（SO4）和δ O-18（SO4）值系统增加；4)蒸发岩溶解对硫酸盐的贡献显著增加。根据观测到的硫酸盐硫氧同位素组成的季节变化，推断了长江动态水量与主要硫酸盐源的关系。在1 - 5月中旬低水量期，S-34三角洲（SO4）和S-18三角洲（SO4）的硫氧同位素组成平均值分别为8.3 +/- 0.4和4.9 +/- 0.7，表明长江河道SO42-主要由硫化物氧化、大气沉降和蒸发岩溶解作用形成；而在12月低水量期间，人为硫酸盐的贡献可能是重要的，表现为δ S-34(SO4)（10.5 +/- 1.5）和δ O-18(SO4)（9.6 +/- 1.0）值相对较高。在6 ~ 9月高放水量期，S-34（SO4）和O-18（SO4）的双同位素组成分别为14.7 +/- 0.7和8.1 +/- 0.7，表明蒸发岩溶解的硫酸盐可能是主要来源。当半年干旱突然转为汛期时，双同位素组成出现了低流量和高流量的跃变事件。由于三峡大坝的蓄水调度，在10 - 11月高、低放水量转换期间，汉江对长江放水量变化的影响较大，从而对长江的硫酸盐源产生影响。但是，长江水量与硫酸盐源之间的关系还需要通过多年的观测来证实。迫切需要进一步研究长江水排放控制硫酸盐源的机理，并建立混合模型来计算不同硫酸盐源的贡献。(C) 2015 Elsevier B.V.版权所有
Resolving sulfate sources in river systems and thus to the global ocean is important for understanding the sulfur biogeochemical cycle. The Yangtze River is one of most important large rivers connecting land and sea, showing a trend of acidification characterized by persistently increasing SO42- concentration. A weekly sampling campaign from the middle Yangtze River in Wuhan was conducted, over a 1-year period in 2011, to systematically examine the effects of seasonality and associated water discharge on the balance of sulfate sources of the Yangtze River. The SO42- concentrations varied from 8.6 to 55.4 mg/L with a discharge-weighted average of 30.0 mg/L, while the SO42- fluxes varied from 1032 to 1257.6 kg/s with an annual average of 532.5 kg/s. The delta O-34(SO4) values ranged between 6.7 parts per thousand and 16.2 parts per thousand with a discharge-weighted average of 10.4%., while the delta O-18(SO4) values ranged between 1.6 parts per thousand and 10.5 parts per thousand with a discharge-weighted average of 5.1 parts per thousand. In comparison to the low water discharge period, the period of high water discharge of the Yangtze River in Wuhan is characterized by 1) a doubling in water discharge with higher water level by 5-10 m; 2) a concomitant doubling in SO42- flux without substantial change in SO42- concentration; 3) a systematic increase of delta S-34(SO4) and delta O-18(SO4) values; 4) a significant increase of sulfate contribution from evaporites dissolution. From the observed seasonal variation of sulfur and oxygen isotopic composition of sulfate, a relationship between the dynamic water discharge and dominant sulfate sources of the Yangtze River was inferred. During the period of low water discharge in January-mid May, the sulfur and oxygen isotopic compositions of sulfate had averaged values of 8.3 +/- 0.4 parts per thousand for delta S-34(SO4) and 4.9 +/- 0.7 parts per thousand for delta S-18(SO4), suggesting the riverine SO42- of the Yangtze Riveris derived from sulfide oxidation, atmospheric deposition and evaporite dissolution; whereas during the period of low water discharge in December, the contribution of anthropogenic sulfate could be important, indicated by relatively higher delta S-34(SO4) (10.5 +/- 1.5 parts per thousand) and delta O-18(SO4) (9.6 +/- 1.0 parts per thousand) values. In contrast, during the period of high water discharge in June-September, the dual-isotope compositions were characterized by 14.7 +/- 0.7 parts per thousand for delta S-34(SO4) and 8.1 +/- 0.7 parts per thousand for delta O-18(SO4), indicating sulfate from dissolution of evaporites would be a dominant source. The jump event of dual-isotopic composition between low and high water discharge occurred when a half-year drought suddenly turned into the flood season. Due to the water storage dispatch of the Three Gorge Dam, the Hanjiang River could make a greater impact on the variation of water discharge and thus sulfate sources of the Yangtze River during the transition from high to low water discharge in October-November. However, the relationship between water discharge and sulfate sources of the Yangtze River need s to be confirmed by additional years of observation.Further studies on the mechanisms of water discharge controlling sulfate sources of the Yangtze River is urgently required, as well as a mixing model to calculate the contribution of different sulfate sources. (C) 2015 Elsevier B.V. All rights reserved.