Quantifying the Role of Mixing Interfaces in Biogeochemical Cycling in a Contaminated Aquifer-Wetland System: Linking Hydrogeological, Microbiological and Geochemical Processes

量化控制氧化还原电位的水文地质、微生物和地球化学过程是了解营养物质和污染物在地下系统中的去向和传输，从而保护饮用水和生态系统健康的一个基本问题。在地下系统中，氧化还原状态的变化通常由微生物末端电子接受过程(TEAP)的变化控制，起始于限制性末端电子受体的传递，如氧、硝酸盐或硫酸盐。因此，还原的水体系和更多的含氧“再充水”水之间的混合界面是TEAP动态增强的区域。尽管混合界面的重要性已得到公认，但由于难以在相关的空间和时间尺度上获得水文、地球化学和微生物测量，很少有实地调查针对这些小规模的过渡地带。这项跨学科的研究试图量化受污染的含水层-湿地系统中混合界面上的溶质迁移、地球化学、动力学和微生物对TEAP的控制。将开发高分辨率数值模式，以综合观测，测试关于界面对系统总体还原能力的作用的假设，了解过程和指导野外/实验室实验，并评估水文条件变化对营养物质和有机污染物的去向和传输的潜在影响。为了实现这一点并检验中心假设，由于有限的电子受体或供体的输送，在界面观察到最大的TEAP动态，包括微生物的活动和转化率，我们将执行以下任务：1)绘制和量化不同水文条件下TEAP在重要混合界面上的分布；2)对诱导混合界面上的电子受体利用率进行原位动力学研究；3)确定与水化学变化直接相关的微生物群落的原位变化；以及4)使用数值模型和测试假设整合测量的控制，以了解在不同的水文条件下混合界面带对生物地球化学循环的影响。我们对现有和最近开发的工具的新应用将使量化微生物群落结构和活动的小范围变化与相应的地球化学之间的复杂联系成为可能。对混合界面TEAP控制的新的基础知识有望提高我们对包括营养物质和人为污染物在内的氧化还原敏感物种的去向和运输的理解，从而提高我们评估风险和保护饮用水和生态系统功能的能力。这项研究的结果不仅对寻求改进方法来测量和解释复杂的、耦合的地球系统过程的科学家具有重要价值，而且对工业、监管机构和普通公众也有重要价值。为了确保这项研究的更广泛影响被广泛传播，我们制定了战略，1)通过直接就业、课程开发和教育工作者培训让学生(K-12、本科生和研究生)参与进来；2)通过研讨会、会议和同行评议的出版物吸引来自其他领域的研究人员；3)通过广泛分发的情况说明书、研究网站参观和网页设计来教育公众；以及4)通过鼓励代表性不足的群体的参与来增加多样性。

0418488McGuireQuantifying the coupled hydrogeological, microbiological, and geochemical processes that control redox potential is a fundamental issue in understanding the fate and transport of nutrients and contaminants in subsurface systems and thus in protecting drinking water and ecosystem health. In subsurface systems, changes in redox state are often controlled by shifts in the terminal electron accepting processes (TEAPs) of microorganisms, initi-ated by the delivery of limiting terminal electron acceptors such as oxygen, nitrate, or sul-fate. Thus, mixing interfaces between reduced aqueous systems and more oxic "re-charge" water, are zones of increased TEAP dynamics. Despite the well-recognized im-portance of mixing interfaces, few field investigations have targeted these small-scale, transient zones due to difficulties in obtaining hydrologic, geochemical and microbial measurements at relevant spatial and temporal scales. This interdisciplinary study seeks to quantify the solute transport, geochemical, kinetic, and microbiological controls on TEAPs at mixing interfaces within a contami-nated aquifer-wetland system. High-resolution numerical models will be developed to integrate observations, test hypotheses regarding the role of interfaces on the overall re-ducing capabilities of the system, understand processes and guide field/laboratory ex-periments, and evaluate the potential effects of changing hydrologic conditions on the fate and transport of nutrients and organic contaminants. To accomplish this and test the central hypothesis that maximum TEAP dynamics, including microbial activity and transformation rates, are observed at interfaces due to the delivery of limiting electron acceptors or donors we will perform the following tasks: 1) map and quantify the distri-bution of TEAPs across significant mixing interfaces during various hydrologic condi-tions; 2) conduct in-situ kinetic studies of electron acceptor utilization rates at induced mixing interfaces; 3) identify in-situ changes in microbial community directly related to changes in water chemistry; and 4) integrate measured controls using numerical models and test hypotheses regarding the impact of mixing-interface zones on biogeochemical cycling during variable hydrologic conditions. Our novel application of existing and re-cently developed tools will make it possible to quantify the complex linkages between small-scale changes in microbial community structure and activity and the corresponding geochemistry. New and fundamental knowledge of the controls on TEAPs at mixing in-terfaces is expected to improve our understanding of the fate and transport of redox-sensitive species including nutrients and anthropogenic contaminants and thereby im-prove our ability to assess risk and protect drinking water and ecosystem function. The findings of this research are expected to be of great value not only to scien-tists searching for improved ways to measure and interpret complex, coupled earth sys-tem processes but also to industry, regulatory agencies, and the general public. To ensure the broader impacts of this research are widely disseminated we have developed strate-gies to 1) involve students (K-12, undergraduate and graduate) through direct employ-ment, course development, and educator training; 2) attract researchers from other fields through workshops, meetings, and peer reviewed publications; 3) educate the public through widely distributed fact sheets, research site tours and web page design; and 4) increase diversity by encouraging the participation of underrepresented groups.