Sedimentary interfaces between contrasting hydrogeological facies in alluvial aquifers drive the development of biogeochemical interfaces that influence subsurface and surface water quality. Here, we calibrate a reactive transport model on a series of dual-domain column experiments, where centimeter-scale, low-permeability, organic-rich anoxic lenses are embedded in coarser-grained aquifer material. Simulations explicitly account for C, Fe, and S cycling at the interface between the lenses and the aquifer in water-saturated conditions. Our results highlight the role of fine-grained, organic-rich inclusions not only as sources or sinks for redox-sensitive species, but also as exporters of nutrients that stimulate downgradient biogeochemical cycling. By releasing large amounts of organic carbon into the surrounding aquifer, such lenses drive the development of proximal secondary reduction zones (“halos”), characterized by high microbial activity (e.g., sulfate reduction) and accumulation of reduced reaction products (e.g., iron sulfide). If similar secondary reduction zones develop within the hydraulically conductive domain of an aquifer, they would be highly susceptible to changes in hydrologic conditions, for instance oxygen pulses associated with seasonal snowmelt. Our results also emphasize the limitations of relying solely on aqueous species measurements to inform reactivity in systems where fast redox cycling and/or sizeable particulate transport may limit the signature of reactivity in the dissolved phase.

冲积含水层中对比水文地质相之间的沉积界面推动了影响地下和地表水质量的生物地球化学界面的发展。在这里，我们在一系列双域柱实验中校准反应传输模型，其中厘米级、低渗透性、富含有机物的缺氧透镜嵌入粗粒含水层材料中。模拟明确说明了水饱和条件下透镜与含水层之间界面处的 C、Fe 和 S 循环。我们的研究结果突出了细粒、富含有机物的包裹体的作用，不仅作为氧化还原敏感物种的来源或汇，而且作为刺激降梯度生物地球化学循环的营养物质的输出者。通过将大量有机碳释放到周围的含水层中，例如硫酸盐还原）和还原反应产物（例如硫化铁）的积累。如果在含水层的水力传导区域内形成类似的二次还原带，它们将非常容易受到水文条件变化的影响，例如与季节性融雪相关的氧气脉冲。我们的结果还强调了仅依靠水性物质测量来告知系统中反应性的局限性，在这些系统中，快速氧化还原循环和/或大量颗粒传输可能会限制溶解相中反应性的特征。