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Effect of time-varying wave conditions on the fate of nitrogen in a freshwater unconfined nearshore aquifer
Advances in Water Resources ( IF 4.7 ) Pub Date : 2022-07-13 , DOI: 10.1016/j.advwatres.2022.104273
Sabina Rakhimbekova, Ming Zhi Wu, Vincent Post, Clare E. Robinson

Coastal forcing including waves lead to complex and dynamic mixing between discharging groundwater and recirculating coastal water in permeable unconfined nearshore aquifers. This mixing can drive biogeochemical transformations that affect the fate of pollutants in nearshore aquifers and their ultimate discharge to coastal waters. The objective of this study was to examine the effect of time-varying wave conditions on the fate of nitrogen in a freshwater unconfined nearshore aquifer. This was achieved by conducting numerical groundwater flow and reactive transport simulations using MODFLOW-NWT 2005 with a new modified wave-PBC package together with PHT3D v2.10. The simulations demonstrate that time-varying wave conditions enhance mixing in the nearshore aquifer compared to simulations that only consider constant wave conditions, and in doing so impact nitrogen transformations. For the conditions and reaction network simulated, time-varying wave conditions resulted in up to 99% of nitrogen removal in the nearshore aquifer due to the intensified mixing and increased delivery of organic matter into the mixing zone. Sensitivity analysis shows that the abundance and reactivity of coastal-derived organic matter plays a key role in nitrogen removal in aquifers along wave-influenced shorelines. The simulations highlight the importance of considering time-varying wave conditions when designing field investigations and analysing field data. The findings have implications for prediction and estimation of chemical fluxes to the coastal waters and also suggest that increasingly frequent storm events and higher wave conditions as the climate changes may modify pollutant fluxes from nearshore aquifers to coastal waters.



中文翻译:

时变波浪条件对淡水非承压近岸含水层中氮去向的影响

包括波浪在内的海岸强迫导致在可渗透的无承压近岸含水层中排放地下水和再循环沿海水之间的复杂和动态混合。这种混合可以推动生物地球化学转变,从而影响近岸含水层中污染物的命运及其最终排放到沿海水域。本研究的目的是检查随时间变化的波浪条件对淡水无承压近岸含水层中氮的去向的影响。这是通过使用 MODFLOW-NWT 2005 和新的修改后的 wave-PBC 包以及 PHT3D v2.10 进行数值地下水流和反应传输模拟来实现的。模拟表明,与仅考虑恒定波浪条件的模拟相比,随时间变化的波浪条件增强了近岸含水层的混合,这样做会影响氮的转化。对于模拟的条件和反应网络,随时间变化的波浪条件导致近岸含水层中高达 99% 的氮去除,这是由于强化混合和有机物质进入混合区的增加。敏感性分析表明,沿海有机质的丰度和反应性在受波浪影响的海岸线含水层中的氮去除中起着关键作用。模拟强调了在设计现场调查和分析现场数据时考虑随时间变化的波浪条件的重要性。

更新日期:2022-07-18
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