A model for oxygen and sulfur isotope fractionation in sulfate during bacterial sulfate reduction processes
A model for oxygen and sulfur isotope fractionation in sulfate during bacterial sulfate reduction processes
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DOI：
10.1016/j.gca.2005.04.017
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发表时间：
2005-10-15
影响因子：
5
通讯作者：
Schroth, MH
中科院分区：
文献类型：
--
作者：
Brunner, B;Bernasconi, SM;Schroth, MH
本文提出了一个硫酸盐细菌还原模型，该模型包括描述残余硫酸盐的硫、氧同位素组成（δ S-34（SO_4）_（residual），δ O-18（SO_4）_（residual））与残余硫酸盐量之间分馏关系的方程。该模型是完全基于氧同位素交换细胞内部的硫化合物和环境水作为控制氧同位素分馏过程的主导机制。我们的模型解释了自然环境和实验室实验中观测到的δ S-34（SO 4）_（residual）和δ O-18（SO 4）_（residual）模式，而其他模型，倾向于动力学同位素分馏过程为主导过程，未能解释许多（但不是全部）观测到的δ S-34（SO 4）_（residual）和δ O-18（SO 4）_（residual）模式。此外，我们还指出，不存在一个典型的δ S-34（SO 4）_（residual）与δ O-18（SO 4）_（residual）的斜率。我们假设δ S-34（SO 4）_（residual）和δ O-18（SO 4）_（residual）的测量可以用作确定细胞特异性硫酸盐还原速率、氧同位素交换速率和平衡氧同位素交换因子的工具。培养实验的数据被用来确定硫同位素分馏因子的范围，其中可以使用一组简化的方程。数值例子说明了方程的应用。我们推测，在反硝化过程中，残留硝酸盐中的氧同位素效应也是与环境水进行氧同位素交换的结果。因此，可以对δ S-34（SO 4）_（residual）、δ O-18（SO 4）_（residual）与残余硫酸盐量之间的关系式进行修正，进而计算反硝化过程中δ N-15（NO3）_（residual）、δ O-18（NO3）_（residual）与残余硝酸盐量之间的分馏关系。版权所有（c）2005 Elsevier Ltd.
We present a model of bacterial sulfate reduction that includes equations describing the fractionation relationship between the sulfur and the oxygen isotope composition of residual sulfate (delta S-34(SO4)_(residual), delta O-18(S04)_(residual)) and the amount of residual sulfate. The model is based exclusively on oxygen isotope exchange between cell-internal sulfur compounds and ambient water as the dominating mechanism controlling oxygen isotope fractionation processes. We show that our model explains delta S-34(SO4)_(residual) vs. delta O-18(SO4)_(residual) patterns observed from natural environments and from laboratory experiments, whereas other models, favoring kinetic isotope fractionation processes as dominant process, fail to explain many (but not all) observed delta S-34(SO4)_(residual) vs. delta O-18(S04)_(residual) patterns. Moreover, we show that a "typical, delta S-34(SO4)_(residual) VS. delta O-18(SO4)_(residual) slope does not exist. We postulate that measurements of delta S-34(SO4)_(residual) and delta O-18(SO4)_(residual) can be used as a tool to determine cell-specific sulfate reduction rates, oxygen isotope exchange rates, and equilibrium oxygen isotope exchange factors. Data from culture experiments are used to determine the range of sulfur isotope fractionation factors in which a simplified set of equations can be used. Numerical examples demonstrate the application of the equations. We postulate that, during denitrification, the oxygen isotope effects in residual nitrate are also the result of oxygen isotope exchange with ambient water. Consequently, the equations for the relationship between delta S-34(SO4)_(residual), delta O-18(SO4)_(residual), and the amount of residual sulfate could be modified and used to calculate the fractionation-relationship between delta N-15(NO3)_(residual), delta O-18(NO3)_(residual), and the amount of residual nitrate during denitrification. Copyright (c) 2005 Elsevier Ltd.