Collaborative Research: Redox Controls on and Seasonal Variability of Dissolved Iron and Manganese in Rivers

0001286 Bianchi了解是什么控制了河流中溶解的微量元素浓度，对于研究与地球化学风化和元素迁移相关的基础科学问题的研究人员以及参与污染控制评估和监测水质以促进人类健康和生物毒性的科学家来说，具有重大意义。 随着超净取样和分析方法的采用，越来越多的工作人员正在制作可靠的河流溶解微量元素数据，在概述对河流溶解微量元素的一些控制方面也取得了进展。 然而，我们还没有到可以利用河流的水文和化学特征来合理预测溶解的微量元素浓度如何随季节变化，甚至预测溶解的金属水平的地步。 特别重要的是要了解溶解态和颗粒态假设之间影响Fe和Mn的过程：1）河流中Fe和Mn在溶解态和颗粒态之间存在快速循环。 2)这种循环可以是强烈的温度依赖性，因此季节性变化。 3)在快速循环的变化影响溶解颗粒的铁和锰以及颗粒反应性的微量元素，如锌和铅的分区。 4)循环涉及锰和可能的铁的氧化还原过程，虽然有机络合可能是一个更重要的因素铁。 我们的工作目标包括了解河流中Fe和Mn的微生物氧化的程度、程度和方式，阐明河流中Fe和Mn的还原过程，了解在什么条件下光化学过程对河流中Fe和Mn的循环很重要，以及了解DOC在河流Fe和Mn循环中的作用。 我们的方法涉及研究的可变性，控制，和各种关键过程（如微生物氧化，减少DOC，光化学），从一个阶段到另一个转换铁和锰的速率。 我们的工作将包括实地和实验室研究。 实地工作包括每月对河流系统进行采样，以及对两个或两个以上具有不同水文地球化学特征的系统（密西西比河和珠江）进行详细的过程导向研究。 实验室研究将用于确定工作中最重要的过程以及确定速率常数。 还将进行实地和实验室工作，以确定河流有机物质和相关有机成分的特征（例如，与络合或还原有关的官能团）与Fe和Mn循环的反应。 利用速率和过程信息，可以构建模型来预测河流中Fe和Mn浓度随时间的变化。 这种增加对河流溶解微量元素控制的理解的好处是几倍的。 首先，它给了我们一个更好的能力来预测溶解的微量元素的浓度，无论是在时间上的样品时，从一个给定的系统没有采取，可以在空间上的系统，没有数据存在。 其次，各种过程如何导致季节性溶解微量元素变化的信息是相关的采样和监测方案的设计。 最后，了解溶解的微量元素浓度的调节过程是重要的，使我们更好地了解人类活动如何影响河流中的微量元素的方式超越直接的金属污染。 例如，微生物的联系表明毒素可以间接影响溶解的微量元素。 这项工作还将提供有关河流过氧化氢水平及其生成的基本信息，以及与发色溶解有机物的光氧化和归宿问题有关的结果。 除了两名PI外，一名微生物学家将参与这项工作。

0001286BianchiUnderstanding what controls dissolved trace element concentrations in rivers is of substantial interest to researchers examining basic scientific questions related to geochemical weathering and transport of elements and to scientists involved in pollution control evaluation and monitoring of water quality for human health and biotoxicity purposes. With the adoption of ultraclean sampling and analysis methods more workers are now producing relaible fluvial dissolved trace element data and progress has been made in outlining some of the controls on fluvial dissolved trace elements. However, we are not yet to the point where one can use the hydrological and chemical characteristics of a river to make a reasonable prediction of how dissolved trace element concentrations will vary seasonally or even what levels of dissolved metals to expect. It is especially important to understand the processes affecting Fe and Mn between dissolved and particulate hypotheses of this project: 1) There is rapid cycling of Fe and Mn between dissolved and particulate form is rivers. 2) This cycling can be strongly temperature-dependant and hence seasonally variable. 3) Changes in the rapid cycling affect the dissolved-particulate partitioning of Fe and Mn as well as particle-reactive trace elements such as Zn and Pb. 4) The cycling involves redox processes for Mn and possibly Fe, though organic complexation may be a more important factor for Fe. Objectives of our proposed work include understanding the extent, relevence and mode of microbial oxidation of Fe and Mn in rivers, elucidating the process(es) of reduction of Fe and Mn in rivers, understand under what conditions photochemical processes are important for Fe and Mn cycling in rivers, and understanding the role of DOC in fluvial Fe and Mn cycling. Our approach involves studying the variability, controls, and rates of the various key processes (e.g. microbial oxidation, reduction by DOC, photochemistry) that transform Fe and Mn from one phase to another. OUr work will involve both field and laboratory studies. The field work includes monthly sampling of river systems as well as detailed process-oriented studies of two or more of the systems having different hydrogeochemistries (Mississippi and Pearl Rivers). Laboratory studies will be used to identify the most important processes at work as well as determine rate constants. Field and laboratory work will also be done to characterize the fluvial organic matter and relate organic composition (e.g., functional groups related to complexation or reduction) to Fe and Mn cycling. With rate and process information, models can be constructed to predict Fe and Mn concentrations in rivers as a function of time. The benefits of this increased understanding of the controls on fluvial dissolved trace elements are several-fold. First, it gives us a better capability to predict dissolved trace element concentrations, both temporally at times when samples from a given system are not taken and can spacially in systems for which no data exist. Second, information on how various processes can cause seasonal dissolved trace element variability is pertinent to the design of sampling and monitoring programs. Finally, an understanding of what processes are important in the regulation of dissolved trace element concentrations gives us better insight into how human activities can affect fluvial trace elements in ways beyond direct metal contamination. For example, the microbial connection suggests a means by which toxins could indirectly affect dissolved trace elements. The work will also provide basic information on fluvial hydrogen peroxide levels and its generation as well as results pertinent to the issue of the photooxidation and fate of chromophoric dissolved organic matter. Besides the two PI's, a microbiologist will be involved in this work.