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

小行星9523881 该项目的具体目标是确定在一个浅层地下水含水层中的重金属运输的限制与低溶解氧，拦截在常年流的氧化地表水。 非均质化学和生物反应增强浅地下水流的路径，从流（潜流区），由于与含氧溪流混合，并增加与地球化学和生物活性沉积物涂层的接触。 我们的中心假设是，二次水文停留时间在潜流区和增加接触的溪流与沉积物是足够的允许微生物/化学转化的重金属是一个耦合的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，提高溶解金属的氧化在潜流带。 拟议的工作跨越点测量（批量实验），以现场测量的大规模。 我们将在亚利桑那州（皮纳尔溪）的污染冲积盆地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。 以前的现场质量平衡工作表明，在皮纳尔河的潜流区的水文和微生物/化学过程之间的相互作用显着减少了流域范围内的出口溶解锰（主要金属污染物在本研究现场）到下游地区。 在这项研究中，我们将使用一个组合的测量在实验室（批次，列，沙箱），沿着与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。 具体而言，我们将确定的主导机制，锰（II）氧化在潜流区，并确定生物和化学因素的相对作用，水文传质的限制。 我们将调整和扩展瞬态存储模型的应用程序作为一个反应传输模型河流浅层地下水系统。 我们的多尺度研究将使我们能够确定的作用，在整个污染的冲积流域流域的锰的质量平衡的潜流带过程。 该系统提供了一个独特的机会，从全流域的过程中分离的潜流带过程，从这项研究中确定的参数将被用来约束耦合流-浅层地下水输运模型在其他流域的应用。

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.