Beach recovery is a natural dynamic process of beach evolution in which beaches are eroded by storms and post-storm rebuilding due to the action of tides. However, the salinity and nitrate (NO) dynamics during beach recovery remain unclear. We reconstructed the beach recovery model used a complete profile evolution measured at Narrabeen-Collaroy Beach, Australia, and verified the reliability of the model based on previous field and incubation experiments and on a lab experiment. Numerical analysis results indicated the impact of beach evolution on NO transport and transformation in heterogeneous unconfined aquifers under spring-neap tide. Heterogeneity can increase the denitrification area and a decrease in NO influx, and the removal of NO can be increased by 5.2 % compared with homogeneous sediment. Deeper NO-sources lead to greater denitrification and NO removal rates. However, this effect can be weakened during beach recovery owing to an increasing amount of O entering the aquifer, leading to a decrease in NO removal. To some extent, the effect of beach evolution on biogeochemical reactions is thus more important than geological heterogeneity in beach aquifers. This study provides a physical and biogeochemistry explanation for the dynamic process in beach aquifers, demonstrating the importance of protecting coastal ecosystems.

中文翻译：

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海滩恢复对异质沿海含水层中硝酸盐去向的影响

海滩恢复是海滩演变的自然动态过程，其中海滩受到风暴侵蚀以及风暴后潮汐作用下的重建。然而，海滩恢复期间的盐度和硝酸盐（NO）动态仍不清楚。我们使用在澳大利亚纳拉宾-科拉罗伊海滩测量的完整剖面演化重建了海滩恢复模型，并根据之前的现场和孵化实验以及实验室实验验证了模型的可靠性。数值分析结果表明了小潮下海滩演化对非均质无承压含水层NO输运和转化的影响。异质性可以增加反硝化面积，减少NO流入量，与均质沉积物相比，NO的去除率可提高5.2%。更深的 NO 源导致更高的反硝化和 NO 去除率。然而，在海滩恢复过程中，由于进入含水层的 O 量增加，这种效应可能会减弱，导致 NO 去除量减少。在某种程度上，海滩演化对生物地球化学反应的影响比海滩含水层的地质异质性更重要。这项研究为海滩含水层的动态过程提供了物理和生物地球化学解释，证明了保护沿海生态系统的重要性。