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

0001049希勒了解是什么控制着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运输有关的基本科学问题的研究人员以及从事污染控制、评价和监测水质以促进人类健康和生物毒性目的的科学家具有重大意义。随着超净采样和分析方法的采用，越来越多的工作者正在获得可靠的河流溶解微量元素数据，并在概述河流溶解微量元素的一些控制方面取得了进展。然而，我们还没有达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含量的程度的地步。了解溶解态和颗粒态之间影响铁和锰的过程尤为重要：1)在溶解态和颗粒态之间存在铁和锰的快速循环。2)这种循环可能强烈依赖于温度，因此是季节性的。3)快速循环的变化影响了Fe和Mn的溶解颗粒分配以及Zn和Pb等颗粒反应性微量元素。4)循环涉及Mn和Fe的氧化还原过程，尽管有机络合作用可能是Fe的更重要因素。我们提出的工作目标包括了解河流中铁和锰微生物氧化的程度、相关性和模式，阐明河流中铁和锰的还原过程，了解在什么条件下光化学过程对河流中铁和锰的循环是重要的，以及了解DOC在河流铁和锰循环中的作用。我们的方法包括研究将铁和锰从一相转化为另一相的各种关键过程（例如微生物氧化，DOC还原，光化学）的可变性，控制和速率。我们的工作将包括实地研究和实验室研究。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，以确定河流有机质的特征，并将有机组成（例如，与络合或还原有关的官能团）与铁和锰循环联系起来。利用速率和过程信息，可以建立模型来预测河流中铁和锰的浓度作为时间的函数。增加对河流溶解微量元素控制的了解的好处是多方面的。首先，它使我们能够更好地预测溶解的微量元素浓度，既可以在没有从给定系统中采集样本的时间上预测，也可以在没有数据存在的系统中预测。其次，关于各种过程如何导致季节性溶解微量元素变化的信息与采样和监测程序的设计有关。最后，了解在调节溶解的微量元素浓度中哪些过程是重要的，使我们能够更好地了解人类活动如何以直接金属污染以外的方式影响河流中的微量元素。例如，微生物之间的联系表明，毒素可以间接影响溶解的微量元素。这项工作还将提供关于河流过氧化氢水平及其产生的基本信息，以及与光氧化和显色性溶解有机物的命运问题有关的结果。除了两位PI之外，还有一位微生物学家将参与这项工作。

0001049ShillerUnderstanding 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.