This study employs groundwater simulations to examine the combined effects of waves, evaporation, and geologic heterogeneity on the flow and salinity dynamics in a shallow beach environment. The modeling results reveal that wave motion generates a saline plume beneath the swash zone, with hypersalinity near the surface triggered by evaporation. Geologic heterogeneity critically controls the temporal and spatial patterns of evaporation, moisture content, and salinity in the swash zone. Heterogeneous capillarity creates localized moisture hotspots within the unsaturated zone, which support enhanced evaporation and therefore facilitate salt accumulation at the surface, even when the overall moisture conditions along the swash zone are not conducive to high rates of evaporation. The formation of capillary barriers allows these moisture hotspots to persist over tidal cycles, leading to the retention of saltwater pockets within heterogeneous unsaturated finer sediments. As the swash zone recedes and evaporation intensifies, salt begins to accumulate near the beach surface. The moisture hotspots create preferential pathways that facilitate the penetration of hypersaline water into deeper, saturated sediments. In contrast, within the saturated zone, groundwater flow and salt transport are predominantly driven by preferential flow within high-permeability coarse sediments where capillarity is relatively low. Such transport and capillary mechanisms are crucial for a better understanding of coastal groundwater flow, interstitial habitats, biogeochemical conditions, and consequent nutrient cycling and contaminant transport in coastal zones. This highlights the necessity of considering integrated coastal physical drivers when investigating flow and transport processes in coastal swash zones.

中文翻译：

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斜面带的地下水流和盐度动态：蒸发、波浪和地质非均质性的综合影响


本研究采用地下水模拟来检查波浪、蒸发和地质非均质性对浅滩环境中流动和盐度动态的综合影响。建模结果表明，波浪运动在斜面带下方产生盐水羽流，蒸发触发了地表附近的高盐度。地质非均质性关键控制着斜纹带蒸发、含水率和盐度的时空模式。非均质毛细作用会在非饱和区内产生局部水分热点，这有助于增强蒸发，从而促进盐分在表面的积累，即使斜面带的整体水分条件不利于高蒸发速率。毛细管屏障的形成使这些水分热点在潮汐循环中持续存在，导致盐水袋保留在非均质不饱和较细的沉积物中。随着斜面区的消退和蒸发的加剧，盐分开始在海滩表面附近积累。水分热点创造了优先途径，促进了高盐水渗透到更深的饱和沉积物中。相比之下，在饱和带内，地下水流和盐分输送主要由毛细作用相对较低的高渗透性粗沉积物中的优先流驱动。这种运输和毛细管机制对于更好地了解沿海地下水流、间隙栖息地、生物地球化学条件以及随之而来的沿海地区营养物质循环和污染物运输至关重要。 这突出了在研究沿海斜面带的流动和运输过程时考虑综合沿海物理驱动因素的必要性。