EAR-PF: Source or Sink? Hyporheic zone controls on the biogeochemical processing of arsenic in rivers impacted by acid mine drainage

砷从沉积物、固体到进入饮用水的过程和条件可能影响公共安全和环境健康。Nell Hoagland博士获得了科罗拉多矿业学院的博士后奖学金，以确定受酸性矿山排水影响的河流中砷（As）从潜流区吸收或释放的驱动条件。利用微生物和水文方法的结合，研究人员将研究潜流带的空间和时间尺度，在潜流带中，地下水和地表水的相互作用调节溶质的时间、大小和形态。这项工作将建立在美国地质调查局（USGS）之前对科罗拉多州阿尼玛斯河（Animas River）暗流带的调查基础上。2015年8月，阿尼玛斯河的矿池废水意外泄漏，导致1100万升尾矿直接流入河中。通过限制流入河道的总As和As（III）通量的位置和时间，本研究将提供开发受矿山影响的流域河流恢复工程解决方案所需的地球化学和水文背景。与向阿尼玛斯河排放砷的时间有关的新见解将在一份可公开获取的技术报告中与受影响地区的公共卫生官员和市政供水当局分享。该项目将吸引科罗拉多矿业学院和当地社区学院的本科生和研究生，通过提供夏季短期课程，学生将学习环境水文学领域和酸性矿山排水的影响。在氧化还原过渡带，砷等类金属的生物地球化学过程是不可预测的。低氧带的氧化还原条件将在季节和风暴事件尺度上发生变化，影响净As释放或储存。本研究的工作假设包括：(a)在风暴事件过程中，酸性矿山排水流中潜流带的总As输出和As(III)/As(V)的比率随着沉积物条件的日益减少而增加；(b)潜流带在夏季（如潮湿、高流量）充当河道的As源，在冬季充当As汇。本研究将在高时空分辨率下对亚隐带进行评估，从而为控制氧化还原梯度上砷物种形成的微生物和矿物学机制提供新的信息。交付成果将包括一个概念模型，该模型将潜流带面积和交换率的气候控制与河段范围内潜流沉积物中污染物的动员联系起来。结合反应输运模型的概念框架将指导对流域尺度上污染物输运的解释。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The process and conditions by which arsenic (As) goes from being in sediment loads, in solids, and into the drinking water may effect public safety and environmental health. Dr. Nell Hoagland has been awarded a postdoctoral fellowship to work at the Colorado School of Mines to determine the conditions driving the sequestration or release of arsenic (As) from the hyporheic zone in rivers impacted by acid mine drainage. Using a combination of microbial and hydrological methods, the researcher will investigate the spatial and temporal scaling of the hyporheic zone, where groundwater-surface water interactions modulate the timing, magnitude, and speciation of solutes. This work will build upon previous U.S. Geological Survey (USGS) investigations of the hyporheic zone in the Animas River of Colorado, where an accidental breach of mine pond wastewaters in August 2015 led to the release of 11 million liters of tailings directly into the river. By constraining the location and timing of total As and As(III) fluxes to the stream channel, this study will provide the geochemical and hydrological context needed to develop engineering solutions for river recovery in mine-impacted catchments. New insights related to the timing of As release to the Animas River will be shared in a publically accessible technical report with public health officials and municipal water authorities in the affected region. This project will engage undergraduate and graduate students at Colorado School of Mines and local community colleges by offering a summer short-course, where students will learn about the field of environmental hydrology and the impacts of acid mine drainage. The biogeochemical processing of metalloids such as arsenic is unpredictable in redox transition zones. Redox conditions in the hyporheic zone will change on seasonal and storm-event scales, impacting net As release or storage. The working hypotheses for this study include: (a) the export of total As and the ratio of As(III)/As(V) from the hyporheic zone in an acid mine drainage stream increases over the course of a storm event in response to increasingly reduced sediment conditions, and (b) the hyporheic zone acts as a source of As to the stream channel during the summer (e.g. wet, high discharge) and a sink of As in the winter. The proposed work will evaluate the hyporheic zone at high temporal and spatial resolution in order to provide new information on microbial and mineralogical mechanisms controlling As speciation across redox gradients. Deliverables will include a conceptual model that relates climatic controls on hyporheic zone area and exchange rates to the mobilization of contaminants from hyporheic sediments at the reach-scale. The conceptual framework in combination with reactive-transport modeling will guide interpretations of contaminant transport at the watershed-scale.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.