Groundwater (GW) contaminants upwelling toward surface water (SW) can attenuate in the hyporheic zone, with dissolved oxygen (DO) frequently controlling the attenuation. In a laboratory mesocosm, we induced downwelling of SW into the sediments to create a hyporheic flow cell (HFC). We added DO to downwelling SW and sodium sulfite (Na₂SO₃) to anoxic upwelling GW to induce an abiotic mixing‐dependent reaction along the mixing zone between the HFC and upwelling GW. Using planar optodes and SO₄ measurements, we observed movement of the DO mixing zone (oxic front position), extent of DO mixing (mixing zone thickness), and location of MD reaction (SO₄ peak concentration). Oxic front position and mixing zone thickness were stable during nonreactive control experiments, indicating that dispersion of DO across the mixing zone had come into equilibrium with supply of DO to the mixing zone. By contrast, mixing zone thickness shrank over time during the reaction experiments, as MD reaction consumed DO in the mixing zone. The decrease in mixing zone thickness for the reaction experiments indicates steeper DO gradients and greater dispersion (transport) limitation, quantified by Damköhler numbers farther above unity. Maximum SO₄ concentrations always occurred further from the center of the HFC (i.e., more toward surrounding upwelling GW) than did the oxic front. In most riverbeds, transport and mixing dynamics are thus superimposed upon existing hydraulic dynamics, with implications for monitoring and attenuation of contaminants.

中文翻译：

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实验室模拟的亲水区中的非生物混合依赖反应

向上流至地表水（SW）的地下水（GW）污染物可以在流变带中衰减，而溶解氧（DO）经常控制该衰减。在实验室中观宇宙中，我们诱导SW向下沉入沉积物中，从而形成了流变流动池（HFC）。我们在下行流SW中添加了DO，在缺氧上行流GW中添加了亚硫酸钠（Na ₂ SO ₃），以沿HFC和上行流GW之间的混合区引发非生物混合依赖性反应。使用平面光电二极管和SO ₄测量，我们观察到DO混合区的运动（有氧的前位置），DO混合的程度（混合区的厚度）和MD反应的位置（SO ₄峰值浓度）。在非反应性对照实验中，氧的前沿位置和混合区的厚度是稳定的，这表明溶解氧在整个混合区的分散与向混合区提供的溶解氧达到平衡。相反，随着MD反应消耗混合区中的DO，混合区的厚度在反应实验过程中会随着时间而收缩。反应实验中混合区厚度的减小表明DO梯度更陡，分散（传输）极限更大，这由Damköhler数远大于1量化。最大SO ₄总是比HFC中心离HFC中心更远（即，更多地向周围上升的GW）。因此，在大多数河床中，运输和混合动力都叠加在现有的水力动力上，对污染物的监测和衰减产生了影响。