Arsenic, iron and sulfur co-diagenesis in lake sediments
Arsenic, iron and sulfur co-diagenesis in lake sediments
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DOI：
10.1016/j.gca.2009.11.028
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发表时间：
2010-02-15
影响因子：
5
通讯作者：
Tessier, Andre
中科院分区：
文献类型：
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作者：
Couture, Raoul-Marie;Gobeil, Charles;Tessier, Andre
孔隙水pH值和溶解的As、Fe、Mn、硫酸盐、总硫化物（Sigma S-11）、总零价硫（Sigma S-0）、有机碳和主要离子浓度以及固体As、酸挥发性硫化物（AVS）、总S。测定了不同氧化还原和地球化学条件下四湖沉积物中Fe、Mn、Al、有机C、Pb-210和Cs-137的含量。一个逆模型的方法，假设稳态的一维传输反应方程的基础上，应用到孔隙水作为配置文件，并用于约束涉及作为（R-净（As））的反应的净速率。该模型定义了深度间隔，其中As被释放到（正R-net（As））或从（负R-net（As））孔隙水。在两个采样点，其底层水在采样时被氧化，生产区域（R-net（As）= 12 × 10（-18）mol cm（-3）s（-1）-71 × 10（-18）mol cm（-3）s（-1））推断在沉积物-水界面以下几厘米处，与尖锐的孔隙水As和Fe峰一致，表明As和Fe的强烈耦合再循环。这一过程证实了固体砷和铁的最大值就在沉积物表面以下。在这两个湖泊中，As消耗区（R-net（As）= -5 x 10（-18）mol cm（-3）s（-1）至-53 x 10（-18）mol cm（-3）s（-1）），归因于As对自生Fe羟基氧化物的缓慢吸附，位于生产区上方。该吸附反应的二级速率常数k（ads）（As）为0.12 +/- 0.03 cm（3）mol（-1）s（-1），而在另外两个季节性缺氧的低层湖泊中，孔隙水和固体剖面中不存在这种特征。热力学计算表明，四湖的孔隙水，当硫化物（即，Sigma S-11 >= 0.1 μ M），相对于所有已知的固体砷硫化物不饱和;计算还预测了硫化沃茨中存在As-V氧硫代阴离子，正如最近的一项研究所表明的那样。在含硫沃茨中，As的去除（R-net（As）= -1 × 10（-18）mol cm（-3）s（-1）至-23 × 10（-18）mol cm（-3）s（-1））始终发生在相对于FeS（，）达到饱和时，并且Asv硫代氧阴离子被预测为总溶解As的重要组分时。这一发现具有潜在的影响，作为运输在其他缺氧沃茨，并应在更广泛的自然环境中进行测试。版权所有（C）2009由爱思唯尔有限公司出版。保留所有权利。
Profiles of porewater pH and dissolved As, Fe, Mn, sulfate, total sulfide (Sigma S-11), total zero-valent sulfur (Sigma S-0), organic carbon and major ion concentrations, as well as those of solid As, acid-volatile sulfide (AVS), total S. Fe, Mn, Al, organic C, Pb-210 and Cs-137 were determined in the sediment of four lakes spanning a range of redox and geochemical conditions. An inverse modeling approach, based on a one-dimensional transport-reaction equation assuming steady-state, was applied to the porewater As profiles and used to constrain the net rates of reactions involving As (R-net(As)). The model defines depth intervals where As is either released to (positive R-net(As)) or removed from (negative R-net(As)) the porewaters.At two of the sites, whose bottom water were oxygenated at sampling time, a production zone (R-net(As) = 12 x 10(-18) mol cm(-3) s(-1)-71 X 10(-18) mol cm(-3) s(-1)) is inferred a few cm below the sediment-water interface, coincident with sharp porewater As and Fe peaks that indicate an intense coupled recycling of As and Fe. This process is confirmed by solid As and Fe maxima just below the sediment surface. In these two lakes a zone of As consumption (R-net(As) = -5 x 10(-18) mol cm(-3) s(-1) to -53 x 10(-18) mol cm(-3) s(-1)), attributed to the slow adsorption of As to authigenic Fe oxyhydroxides, occurs just above the production zone. A second-order rate constant k(ads)(As) of 0.12 +/- 0.03 cm(3) mol(-1) s(-1) is estimated for this adsorption reaction.Such features in the porewater and solid profiles were absent from the two other lakes that develop a seasonally anoxic hypolimnion. Thermodynamic calculations indicate that the porewaters of the four lakes, when sulfidic (i.e., Sigma S-11 >= 0.1 mu M), were undersaturated with respect to all known solid As sulfides; the calculation also predicts the presence of As-V oxythioanions in the sulfidic waters, as suggested by a recent study. In the sulfidic waters, the removal of As (R-net(As) = -1 X 10(-18) mol cm(-3) s(-1) to -23 x 10(-18) mol cm(-3) s(-1)) consistently occurred when saturation, with respect to FeS(,), was reached and when Asv oxythioanionswere predicted to be significant components of total dissolved As. This finding has potential implications for As transport in other anoxic waters and should be tested in a wider variety of natural environments. Crown copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.