Technical Note: Uncovering the influence of methodological variations on the extractability of iron bound organic carbon
Technical Note: Uncovering the influence of methodological variations on the extractability of iron bound organic carbon
复制标题
DOI：
10.5194/bg-2020-399
复制
发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Ben J. Fisher;J. Faust;O. Moore;C. Peacock;C. März
中科院分区：
文献类型：
--
作者：
Ben J. Fisher;J. Faust;O. Moore;C. Peacock;C. März
有机碳（OC）与活性铁（FeR）的结合是保护土壤和海洋沉积物中OC免受重金属化的重要机制。最近的研究表明，有机化合物的分子结构和/或相关的FeR相的身份施加控制的能力的OC-FeR络合物被提取的柠檬酸盐-碳酸氢盐-连二亚硫酸盐（CBD）的方法。然而，使用CBD提取的许多变化，并且这些变化通常彼此未校准，使得通过不同方法提取的OC-FeR值的比较是不可能的。在这里，我们创建了合成的水铁矿样品与简单的有机结构共沉淀，并对这些样品进行了最常见的CBD方法的修改。我们改变了一些方法参数（试剂浓度、提取时间和样品制备方法），并测量了FeR回收率，以确定哪些（如有）修改影响了合成样品中FeR的释放。我们提供了一个评估的还原能力的钠连二亚硫酸盐的CBD方法（铁的量减少了固定量的连二亚硫酸盐），并发现部署的连二亚硫酸盐的浓度可以限制OC-FeR的可提取性与高FeR含量的沉积物。此外，我们表明，延长任何CBD提取的长度对去除FeR没有任何好处。此外，我们表明，人工合成的OC-FeR样品为主的水铁矿，冷冻干燥样品可以显着降低OC-FeR的可提取性，这似乎是一个问题，天然海洋沉积物的自然老化机制可能会模仿更稳定的铁相的冷冻干燥过程。虽然我们的研究不是一个包罗万象的方法比较，并不是为了提供“完美”的提取设置，我们的研究结果提供了一个收集的总结的关键因素，影响CBD提取OC-FeR的效率。因此，我们提供了一个平台，从不同的方法下获得的OC-FeR值可以解释和沉积物碳循环的未来研究可以建立在。
Association of organic carbon (OC) with reactive iron (FeR) represents an important mechanism by which OC is protected against remineralisation in soils and marine sediments. Recent studies indicate that the molecular structure of organic compounds and/or the identity of associated FeR phases exert a control on the ability of an OC–FeR complex to be extracted by the citrate–bicarbonate–dithionite (CBD) method. However, many variations of the CBD extraction are used, and these are often uncalibrated to each other, rendering comparisons of OC–FeR values extracted via the different methods impossible. Here, we created synthetic ferrihydrite samples coprecipitated with simple organic structures and subjected these to modifications of the most common CBD method. We altered some of the method parameters (reagent concentration, time of the extraction and sample preparation methods) and measured FeR recovery to determine which (if any) modifications affected the release of FeR from the synthetic sample. We provide an assessment of the reducing capacity of Na dithionite in the CBD method (the amount of Fe reduced by a fixed amount of dithionite) and find that the concentration of dithionite deployed can limit OC–FeR extractability for sediments with a high FeR content. Additionally, we show that extending the length of any CBD extraction offers no benefit in removing FeR. Moreover, we demonstrate that for synthetic OC–FeR samples dominated by ferrihydrite, freeze-drying samples can significantly reduce OC–FeR extractability; this appears to be less of an issue for natural marine sediments where natural ageing mechanisms may mimic the freeze-drying process for more stable Fe phases. While our study is not an all-inclusive method comparison and is not aimed at delivering the “perfect” extraction setup, our findings provide a collected summary of critical factors which influence the efficiency of the CBD extraction for OC–FeR. As such, we provide a platform from which OC–FeR values obtained under different methods can be interpreted and future studies of sediment carbon cycling can build upon.