Isotopic study of the source and cycle of sulfur in the Yamdrok Tso basin, Southern Tibet, China
Isotopic study of the source and cycle of sulfur in the Yamdrok Tso basin, Southern Tibet, China
复制标题
藏南羊卓雍错盆地硫的来源与循环同位素研究
DOI：
10.1016/j.apgeochem.2017.09.005
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发表时间：
2017-10-01
影响因子：
3.4
通讯作者：
Hu, Hai-Ping
中科院分区：
文献类型：
--
作者：
Feng, Jin-Liang;Chen, Feng;Hu, Hai-Ping
本研究以西藏南部海拔4394-4989米的Yamdrok Tso(藏语中Tso的意思是湖)内陆流域为研究对象。该盆地位于特提斯喜马拉雅带，由7个不同水文特征的湖泊组成。研究的主要目的是研究地下水-河流-湖泊系统中溶解SO42-的来源和硫循环。测定了河流、泉水和湖水中硫酸盐的三角洲(OH2O-O-18)、S-34三角洲(SO4)和O-18三角洲(SO4)的水文地球化学组成，湖泊沉积岩芯中总硫的全硫含量(S-全硫)和S-34三角洲(全硫)，以及基岩中黄铁矿的S-34三角洲(黄铁矿)。结果表明，研究区大部分河流硫酸盐含量高达270 mg/L，基岩中黄铁矿S-34(黄铁矿)含量介于-4.31%~-5.77%之间，河流和泉水中硫酸盐主要为负值的S 34(SO4)(-7.14%~-2.02%)和O-18(SO4)(-13.2%~-4.04%)。相比之下，研究盆地闭合湖泊水体中的S-34(SO4)三角洲(3.44%-8.58%)和O-18三角洲(SO4)(7.26%-10.3%)值较高。硫酸盐的负S 34(SO4)和O18(SO4)双同位素组成表明，黄铁矿风化控制着河流和泉水中溶解的硫酸盐和其他溶质，而人为污染物硫的通量可以忽略不计。水是黄铁矿氧化生成硫酸盐的主要氧源，而Fe3+是黄铁矿S氧化的主要直接助剂。研究盆地的湖水和沉积物是硫磺的重要汇/库。闭合全混交湖沉积岩心的S-34(全硫)值在-8.5%~-44.9%之间。湖水中残留SO_4~(2-)中的S-34和O-18的强烈富集性以及沉积物中S-34的显著亏损表明，湖泊沉积物中的异化微生物硫酸盐还原作用一般会导致S-32中富硫的优先固硫。此外，湖水中硫酸盐与沉积物总硫之间的S-34/S-32分馏幅度可达48.3%。这种异常高的分馏值主要是由湖泊水位波动引起的沉积物中还原的无机硫化合物的再氧化以及沉积物中的歧化途径造成的。STOTOTAL和DETA S-34(总)值随沉积岩心深度的变化也可以用同样的机制解释。(C)2017爱思唯尔有限公司。保留所有权利。
This study focuses on the inland drainage basin of Yamdrok Tso (Tso means 'lake' in the Tibetan language), which lies at altitudes between 4394 and 4989 m, in southern Tibet. The basin is located in the Tethys Himalayan zone, and consists of seven lakes with different hydrological characteristics. The main purpose of the study was to investigate the source of dissolved SO42- and the sulfur cycle in the groundwater-river-lake system. We measured the hydrogeochemical composition, delta(OH2O)-O-18, delta S-34(SO4) and delta O-18(SO4) of sulfate in river, spring and lake water; the total sulfur content (S-Total) and delta S-34(Total) of total sulfur in a lake sediment core; and the delta S-34(pyrite) of pyrite in the bedrock. The results indicate that most of the rivers in the study area are characterized by a high sulfate content with values of up to 270 mg/L. In addition, the delta S-34(pyrite) of pyrite in the bedrock ranges between -4.31% and -5.77%, while the sulfate in river and spring waters has mainly negative values of delta S-34(SO4) (-7.14% to -2.02%) and delta O-18(SO4) (-13.2% to -4.04%). In contrast, the waters of closed lakes in the study basin have high values of delta S-34(SO4) (3.44% -8.58%) and delta O-18(SO4) (7.26%-10.3%). The negative delta S-34(SO4) and delta O-18(SO4) dual-isotopic composition of sulfate indicates that pyrite weathering controls the dissolved sulfate and other solutes in rivers and spring water, while the anthropogenic pollutant sulfur flux is negligible. Water is the main oxygen source for sulfate derived from the oxidation of pyrite, while Fe3+ is the main direct agent of pyrite S oxidation. The lake water and sediments in the study basin are important sinks/stores of sulfur. The delta S-34(Total) values of total sulfur in a sediment core from a closed and holomictic lake ranges between -8.5% and -44.9%. As evidenced by the strong S-34 and O-18 enrichment in the residual pool of SO42- in the lake waters, and the marked depletion of S-34 in the sediment core, the dissimilatory microbial sulfate reduction (MSR) in the lake sediments generally results in the preferential sequestration of sulfur enriched in S-32. In addition, the magnitude of S-34/S-32 fractionation between sulfate in the lake water and sedimentary total sulfur can reach up to 48.3%. This abnormally high fractionation value can be explained mainly by the reoxidation of reduced inorganic sulfur compounds, together with the dispropotionation pathway in the sediments, caused by lake level fluctuations. The changes in STotal and delta S-34(Total) values with depth in the sediment core can also be explained by the same mechanism. (C) 2017 Elsevier Ltd. All rights reserved.