The interactions between the atmosphere, ocean, and beach in the swash zone are dynamic, influencing water flux and solute exchange across the land-sea interface. This study employs groundwater simulations to examine the combined effects of waves and evaporation on subsurface flow and salinity dynamics in a shallow beach environment. Our simulations reveal that wave motion generates a saline plume beneath the swash zone, where evaporation induces hypersalinity near the sand surface. This leads to the formation of a hypersaline plume beneath the swash zone during periods of wave recession, which extends vertically downward to a maximum depth of 30 cm, driven by the resulting vertical density gradients. This hypersaline plume moves approximately 2 m landward to the top of the swash zone and down the beachface due to wave-induced seawater infiltration and is subsequently diluted by the surrounding saline groundwater. Furthermore, swash motion increases near-surface moisture, leading to an elevated evaporation rate, with dynamic fluctuations in both moisture and evaporation rate due to high-frequency surface inundation caused by individual waves. Notably, the highest evaporation rates on the swash zone surface do not always correspond to the greatest elevations of salt concentration within the swash zone. This is because optimal moisture is also required—neither too low to impede evaporation nor too high to dilute accumulated salt near the surface. These insights are crucial for enhancing our understanding of coastal groundwater flow, biogeochemical conditions, and the subsequent nutrient cycling and contaminant transport in coastal zones.

中文翻译：

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蒸发和高频海水淹没对斜体带盐度动态的影响


斜面带中的大气、海洋和海滩之间的相互作用是动态的，影响着陆地-海洋界面上的水通量和溶质交换。本研究采用地下水模拟来检查波浪和蒸发对浅滩环境中地下水流和盐度动态的综合影响。我们的模拟表明，波浪运动在斜面带下方产生盐水羽流，蒸发在沙子表面附近引起高盐度。这导致在波浪退缩期间在斜区下方形成高盐羽流，在由此产生的垂直密度梯度的驱动下，该羽流垂直向下延伸至最大深度 30 厘米。由于波浪引起的海水渗透，这种高盐羽流向陆地移动约 2 m 到斜面顶部并沿着海滩向下移动，随后被周围的含盐地下水稀释。此外，斜摆运动会增加近地表水分，导致蒸发速率升高，由于单个波引起的高频表面淹没，水分和蒸发速率都会发生动态波动。值得注意的是，斜面带表面的最高蒸发速率并不总是对应于斜面带内盐浓度的最大升高。这是因为还需要最佳的水分 — 既不能太低而阻碍蒸发，也不能太高而无法稀释表面附近积累的盐分。这些见解对于增强我们对沿海地下水流、生物地球化学条件以及随后的沿海地区营养循环和污染物运输的理解至关重要。