CAREER: Multiphysics research and education for understanding coupled mechanical-biogeochemical surface-subsurface processes

职业：多物理场研究和教育，以理解机械-生物地球化学耦合的地表-地下过程河流与含水层、河岸带和洪泛平原相连，这种耦合是水生系统的一个组成部分。这种连接是由通道与河床和河岸之间的流体流动所介导的；这种交换也被称为次循环流。发生在河流-沉积物界面或潜流带（HZ）的过程显著影响着营养物和金属化学、生态和热能收支。该研究将研究与教育相结合，以推进机械-生物地球化学耦合建模和新兴观测技术的应用。科学假设包括：1)河床地形通过影响河道中诱发次流的湍流，对沉积物内养分循环起一级控制作用；(2)河道向沉积物的热传递导致河床温度变化，进而引起生物地球化学反应速率的变化；3)河床的时间热变异性导致金属吸附的逆转，从而引起瞬态地表水化学反应；4)沉积物水力性质的非均质性导致流体停留时间分布更广，生物地球化学梯度更陡、更斑，有利于反应热点。虽然科学假设适用于各种营养物质和金属，但本研究将重点放在反硝化作用上，作为营养循环的一个例子，以及锌和铜的流动性，作为温度依赖性金属运输的例子。这些假设正在通过串联水槽和柱实验进行验证，并得到数值模型的支持，这些模型考虑了水槽通道中的湍流和水槽下潜区的非等温流动和反应性输运。温度和溶解氧被绘制成二维地图，在赫兹范围内精确到毫米尺度。教育方面的努力是将基于探究的多物理场建模练习整合到教学中，以增强学习和学生的动机。正在定性和定量地评估开发和传播生物地球化学耦合模型对互动式探究性学习练习的影响。

CAREER: Multiphysics research and education for understandingcoupled mechanical-biogeochemical surface-subsurface processesRivers are connected to aquifers, to riparian zones, and to floodplains, and this coupling is an integral component of aquatic systems. The connection is mediated by fluid flow between the channel and its bed and bank; this exchange is also referred to as hyporheic flow. Processes occurring along the river-sediment interface or the hyporheic zone (HZ) significantly impact nutrient and metal chemistry, ecology, and thermal energy budgets. The study is integrating research and education to advance the application of coupled mechanical-biogeochemical modeling and emerging observational technology. The scientific hypotheses include: 1) riverbed topography exerts first order control on nutrient cycling within the sediment by affecting hyporheic-flow-inducing turbulent flow in a river; 2) heat transfer from the channel to the sediment due to hyporheic flow leads to variable riverbed temperatures which in turn leads to changes in biogeochemical reaction rates; 3) temporal thermal variability in the riverbed causes reversal in sorption of metals which causes transient surface water chemistry; and 4) heterogeneity in sediment hydraulic properties leads to broader fluid residence time distributions resulting in sharper and patchier biogeochemical gradients which may favor reaction hotspots. While the scientific hypotheses apply to a variety of nutrients and metals, this study will focus on denitrification, as an example of nutrient cycling, and zinc and copper mobility, as examples for temperature-dependent metal transport. The hypotheses are being tested using tandem flume and column experiments supported by numerical models that consider turbulent flow in the flume channel and non-isothermal flow and reactive transport in the flume hyporheic zone. Temperature and dissolved oxygen are being mapped in 2D within the HZ down to the millimeter scale. The educational effort is integrating inquiry-based multiphysics modeling exercises into teaching to enhance learning and student motivation. The impact of developing and disseminating biogeochemical coupled models for interactive inquiry-based learning exercises is being qualitatively and quantitatively assessed.