Abstract Intertidal sediments host many biogeochemical processes which drastically affect coastal ecosystems. Dissolved Oxygen (DO) plays a major role in many of these biogeochemical reactions, and is of primary importance for intertidal groundwater quality. Groundwater level of intertidal zone fluctuates regularly corresponding to the tidal cycle. During the fluctuation of water table, the oxygen-rich air could be entrapped in the pore space of sediments, and hence serve as an important oxygen source to replenish oxygen-depleted groundwater. Although oxygenation enhanced by fluctuated water table has been studied in river banks, no study has been conducted in ocean intertidal sediments under tide-induced groundwater table fluctuations, and quantification of interphase oxygen mass transfer is lacking. In this study, combined laboratory experimental and numerical modeling approach is developed to study the mechanism of oxygenation of aquifers with regularly fluctuated water table. Two column experiments are conducted with regular multiple drainage-imbibition periods to mimic the Oman sea tidal cycles controlled by 3.5 and 5.75 mL/min of pumping rate respectively. The numerical model is developed and calibrated by the column experiment data, and used to simulate two additional columns by increasing the entrapped air saturation to 0.25 from 0.15 and using 30 ppt of saline water respectively. The results suggest that the larger water table fluctuation leads to 35% more dissolved oxygen, and higher entrapped air saturation enables 22% more oxygen transferred to the anoxic aqueous phase and significantly enhanced the oxygenation of the aquifer, especially the deep zone below the water table. Dissolved oxygen is 4.81% less in the column with 30 ppt of saline water than with fresh water.

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地下水位波动的含水层的氧化：实验室和模型研究

摘要 潮间带沉积物承载着许多严重影响沿海生态系统的生物地球化学过程。溶解氧 (DO) 在许多这些生物地球化学反应中起着重要作用，并且对潮间带地下水质量至关重要。潮间带地下水位随潮汐周期有规律地波动。在地下水位波动过程中，富氧空气会滞留在沉积物的孔隙空间中，成为补充缺氧地下水的重要氧源。尽管已经研究了河岸水位波动增强的氧化作用，但尚未对潮汐引起的地下水位波动下的海洋潮间带沉积物进行研究，并且缺乏对相间氧传质的量化。在这项研究中，开发了结合实验室实验和数值建模的方法来研究具有规律性波动地下水位的含水层的氧化机制。两个柱实验进行了规律的多次排水-渗吸周期，以模拟分别由 3.5 和 5.75 毫升/分钟的泵送速率控制的阿曼海潮循环。该数值模型是根据柱实验数据开发和校准的，并用于通过将截留空气饱和度从 0.15 增加到 0.25 并分别使用 30 ppt 盐水来模拟两个额外的柱。结果表明，较大的地下水位波动导致溶解氧增加 35%，更高的截留空气饱和度使转移到缺氧水相的氧气增加 22%，显着增强了含水层的氧化作用，尤其是地下水位以下的深层区域。使用 30 ppt 盐水的色谱柱中的溶解氧比使用淡水少 4.81%。