Coastal fresh groundwater is threatened by salinization due to both sea-level rise and storm-surge overwash. Most studies of subsurface saltwater intrusion focus on sea-level rise, but storms that are becoming more frequent and intense with climate change could have more imminent and permanent effects on aquifer salinity. Few studies directly compare saltwater intrusion due to sea-level rise with saltwater intrusion due to storm-surge overwash, and no studies address this issue on barrier islands. In this study, a hydrological model simulating coupled, variable-density, surface and subsurface flow and salt transport was developed and calibrated to water level and specific conductance data at Assateague Island, MD. The calibrated model was used to calculate the mass of salt and the total volume of aquifer salinized in 2080 due to both sea-level rise and more frequent storm surges. The results suggest that the total mass of salt that intrudes into the aquifer due to changes in the 2-year storm surge height is approximately equal to that of sea-level rise (∼300 kg), and the surges salinize nearly the entire aquifer, exceeding the volume salinized by sea-level rise (∼80 %). The influence of aquifer properties and unsaturated zone thickness was investigated by reducing aquifer hydraulic conductivity, resulting in greater salinization from storm-surge overwash (100 % of aquifer volume) than from sea-level rise (∼20 %). Higher storm surges are expected to overtop the dunes on Assateague by 2080 causing a 75 % decline in areas above the 2-year storm event while sea-level rise will only inundate ∼ 40 % of the land area on Assateague. This analysis suggests that groundwater is likely more vulnerable to storm-surge overwash than to sea-level rise induced salinization, even in systems where sea-level rise is expected to be most severe.

中文翻译：

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海平面上升和风暴潮过度冲刷对障壁岛地下水盐度影响的比较


由于海平面上升和风暴潮过度冲刷，沿海淡水地下水受到盐化的威胁。大多数关于地下盐水入侵的研究都集中在海平面上升上，但随着气候变化而变得更加频繁和强烈的风暴可能会对含水层盐度产生更迫在眉睫和永久性的影响。很少有研究直接比较海平面上升导致的咸水入侵与风暴潮过度冲刷造成的咸水入侵，也没有研究解决障壁岛上的这个问题。在这项研究中，开发了一个模拟耦合、可变密度、地表和地下流动以及盐输送的水文模型，并根据马里兰州阿萨蒂格岛的水位和比电导数据进行了校准。校准模型用于计算 2080 年由于海平面上升和更频繁的风暴潮而盐化的盐质量和含水层盐化总体积。结果表明，由于两年风暴潮高度变化而侵入含水层的盐分总质量大约等于海平面上升的量（约300千克），并且风暴潮几乎使整个含水层盐化，超过因海平面上升而盐化的体积（∼80%）。通过降低含水层水力传导率来研究含水层性质和非饱和区厚度的影响，风暴潮过度冲刷（含水层体积的 100%）导致的盐化程度高于海平面上升（约 20%）造成的盐化程度。预计到 2080 年，更高的风暴潮将漫过阿萨蒂格的沙丘，导致两年风暴事件以上的地区面积减少 75%，而海平面上升只会淹没阿萨蒂格约 40% 的陆地面积。 这项分析表明，即使在海平面上升预计最严重的系统中，地下水也可能更容易受到风暴潮过度冲刷的影响，而不是海平面上升引起的盐碱化。