Relative Roles of Stream-Subsurface Hydrologic Exchange and Microbial and Chemical Transformations in Controlling Heavy Metal Transport

这个项目的具体目的是确定在一个具有低溶解氧的浅层地下水含水层中重金属运输的限制条件，该含水层拦截了多年生河流中的含氧地表水。由于与含氧水流的混合以及与地球化学和生物活性沉积物涂层的接触增加，在从河流（暗沉区）补给的浅层地下水流动路径中，非均质化学和生物反应增强。我们的中心假设是，次水文停留时间和河流与沉积物接触的增加足以使重金属的微生物/化学转化成为耦合河流-含水层系统的主要去除机制。我们计划确定最重要的水文，生物和化学因素，加强氧化的溶解金属在潜流带。建议的工作涵盖点测量（批量实验）到公里尺度的现场测量。我们将在亚利桑那州的一个受污染的冲积盆地（Pinal Creek）研究的现场情况是典型的重金属污染的河流-浅层地下水系统。先前在野外进行的物质平衡工作表明，Pinal Creek深沉带的水文和微生物/化学过程之间的相互作用显著减少了溶解锰（本研究地点的主要金属污染物）向下游地区的全流域出口。在这项研究中，我们将使用实验室测量（批，柱和沙盒）的组合，以及现场实验数据和建模分析，以确定物理和化学过程的相对重要性。具体来说，我们将确定Mn（II）在低渗区氧化的主要机制，并确定生物和化学因素以及水文传质限制的相对作用。我们将调整和扩展暂态储存模型，使其作为河流-浅层地下水系统的反应输运模型。我们的多尺度研究将使我们能够确定在整个受污染的冲积流域中，潜沉带过程对锰质量平衡的作用。该系统提供了一个独特的机会，将潜流带过程与盆地范围的过程分开；本研究确定的参数将用于约束河流-浅层地下水耦合运输模型，并应用于其他流域。

9523881 Conklin The specific aims of this project are to determine the constraints on heavy-metal transport in a shallow groundwater aquifer with low dissolved oxygen that intercepts oxic surface water in a perennial stream. Heterogeneous chemical and biological reactions are enhanced in shallow groundwater flow paths that are recharged from the stream (hyporheic zone), due to mixing with oxic streamwater and increased contact with geochemically and biologically active sediment coatings. Our central hypothesis is that the secondary hydrologic residence time in the hyporheic zone and the increased contact of the streamwater with the sediment are adequate to permit microbial/chemical transformations of heavy metals to be the dominant removal mechanism for a coupled stream-aquifer system. We plan to identify the most important hydrologic, biological and chemical factors that enhance oxidation of dissolved metals in the hyporheic zone. The proposed work spans point measurements (batch experiments) to field measurement at the kilometer-scale. The field situation that we will study in a contaminated alluvial basin in Arizona (Pinal Creek) is typical of heavy-metal contaminated stream-shallow groundwater systems. Previous mass balance work at the field site indicated that interplay between hydrologic and microbial/chemical processes in the hyporheic zone at Pinal Creek significantly reduced basin-wide exports of dissolved manganese (the principal metal contaminant at this study site) to downstream areas. In this study we will use a combination of measurements in the laboratory (batch, column, and sandbox), along with field experimental data and modeling analysis to determine the relative importance of physical and chemical processes. Specifically, we will identify the dominant mechanism of Mn(II) oxidation in the hyporheic zone and determine the relative roles of biological and chemical factors, and hydrologic mass transfer limitations. We will adapt and extend the Transient Storage Mod el for application as a reactive transport model for stream-shallow groundwater systems. Our multi-scale study will allow us to determine the role the hyporheic-zone processes have on the mass balance of manganese in the entire contaminated alluvial drainage basin. This system provides a unique opportunity to separate hyporheic zone processes from basin-wide processes; the parameters determined from this study will be used to constrain a coupled stream-shallow groundwater transport model with applications in other drainage basins.