Biogeochemical Cycling of Redox-Sensitive Metals During Surface-Subsurface Water Exchange in a Shallow Alluvial Aquifer

小行星9630285 了解溶解的氧化还原敏感的物种和含水层基质中的固体反应相之间的联系是至关重要的营养物质的途径，碳的地球化学循环和地下水系统中的污染物传输的预测。 在许多冲积含水层中，氧化还原敏感金属在终端电子接受过程中起着重要作用。 由于这些金属是至关重要的含水层能量学和地球化学，本研究的重点是时间和空间的控制和氧化还原敏感的金属流动性在浅冲积含水层的影响，地表-地下水交换。 该研究包括两个研究内容。 研究要素I将研究对氧化还原敏感的金属流动性的时间/季节控制。 通过系统的地表-地下水和沉积物取样和分析，将确定Rio Calaveras（新墨西哥州Jemez山脉一个仪器密集、未受干扰的地点）的含水层特征、含水地球化学和生物功能。 浅层冲积充填物的特征将体现在细尺度含水层结构（地层元素）、沉积物地球化学（例如，可提取的金属、有机物含量和可提取的碳）和水生态地球化学（溶解的气体、有机和无机溶质）。 每两个月对一个广泛的井网进行一次采样，以便测量动态地球化学和生物学对季节和降水事件的扰动。 确保在研究期间观察几个完整周期。 多层次水取样仪器将提供必要的高垂直分辨率，以量化沉积物特性（生物可利用的碳和金属）、水的地球化学和微生物功能之间的联系。 研究要素2侧重于冲积含水层内的空间异质性，并提出了一系列假设和测试，以评估（a）沿着地下水流路径的位置，（B）溶解有机碳物种的螯合作用，（c）微生物介导的铁还原反应对金属流动性的控制。 水文控制将通过沿（现有特定地点水文模型定义的）流动路径沿着采样地球化学参数和应用地球化学模型（用于水形态和反应路径建模）进行评估。 将使用沉积物孵育进行受控实验室实验，以区分铁动员的非生物（螯合）和生物（微生物还原）机制。 含水层的异质性将是实验设计中的主要组织因素。 该提案是应环境地球化学和生物地球化学的要求提交的，该项目得到了地球科学司和海洋科学司（地球科学）的联合支持。

9630285 Crossey Understanding the linkage between dissolved redox-sensitive species and solid reactive phases in an aquifer matrix is crucial to the prediction of nutrient pathways, biogeochemical cycling of carbon, and contaminant transport in ground water systems. In many alluvial aquifers redox-sensitive metals play an important role in terminal electron-accepting processes. Because these metals are critical to aquifer energetics and biogeochemistry, this research focuses on the temporal and spatial controls and redox-sensitive metal mobility in a shallow alluvial aquifer influenced by surface-subsurface water exchange. The study comprises two Research Elements. Research Element I will examine temporal/seasonal controls on redox-sensitive metal mobility. Through systematic surface-subsurface water and sediment sampling and analysis; aquifer characteristics, aqueous geochemistry, and biological functioning will be identified at Rio Calaveras (a heavily-instrumented, unperturbed site in the Jemez Mountains of New Mexico). The shallow alluvial fill will be characterized with respect to fine-scale aquifer structure (stratigraphic elements), sediment geochemistry (e.g., extractable metals, organic matter content, and extractable carbon), and aqueous biogeochemistry (dissolved gases, organic and inorganic solutes). Bi-monthly sampling of an extensive well network will permit measurement of dynamic geochemically, and biologically to seasonal and precipitation event perturbations. Observation of several complete cycles are assured over the time period of the study. Multi-level water sampling instrumentation will allow the high vertical resolution necessary to quantify links among sediment characteristics (bioavailable carbon and metals), aqueous geochemistry, and microbial functioning. Research Element 2 focuses on spatial heterogeneity within the alluvial aquifer, and poses a series of hypotheses and tests to assess the control on metal mobility exerted by (a) position along gro undwater flow paths, (b) chelation by dissolved organic carbon species, and (c) microbially-mediated iron reduction reactions. Hydrologic controls will be assessed through sampling geochemical parameters along flow paths (defined by an existing site-specific hydrologic model) and through application of geochemical models (for aqueous speciation and reaction path modeling). Controlled laboratory experiments will be conducted using sediment incubations to distinguish abiotic (chelation) and biotic (microbial reduction) mechanisms of iron mobilization. Aquifer heterogeneity will be a primary organizing factor in the experimental design. This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry solicitation, and the project is being jointly supported by the Divisions of Earth Sciences and Divisions of Ocean Sciences (Geosciences).