Collaborative Research: How does groundwater inundation of carbonate island interiors from sea level rise impact surface water-aquifer interactions and evaporative losses?

众所周知，海平面上升和沿海洪水会减少淡水资源。然而，人们较少认识到，海平面上升会将地下水位推到陆地表面之上，淹没低洼的洼地。由地下水泛滥形成的湖泊和湿地使相连的含水层直接、持续地蒸发，这可能导致水资源的大量损失。地下水泛滥和蒸发的影响将在低洼的碳酸盐岛屿上最为强烈，在那里，蒸发的淡水被穿过基岩的海水所取代。这些模型纳入了气候的影响，并预测在潮湿地区的岛屿下，湖泊应该保持新鲜，地下水资源应该是连续的。在干旱地区，湖泊将是高盐度的，许多新鲜的地下水将被海水取代。与预期相反，在干旱的巴哈马群岛南部，由地下水泛滥形成的现代湖泊的盐度从新鲜到高盐度不等。模拟和观察到的湖泊盐度之间的矛盾强调了我们缺乏了解地下水泛滥如何影响岛屿水资源。在该项目期间，将收集新的现场数据，并将开发新的瞬态建模工具，以测试地下水泛滥将如何影响岛屿水资源的总体假设。我们将测试湖泊面积相对于其地下水贡献面积的影响，湖泊和海洋之间的连通程度，以及与气候和海平面变化的动态相互作用。这项研究的结果应改善预测的淡水资源损失的小岛屿发展中国家（SIDS）的地下水泛滥，也许是主要的环境因素触发其丧失的可居住性。作为该项目一部分开发的建模工具将免费分发给水文界。将制定一项实地水文地质学课程练习，并提供定量沿海水文学的学习成果，供每年访问杰雷斯研究中心（本项目的运作基地）的100多个学生团体使用。项目成果将作为巴哈马大学和国际会议客座讲师系列的一部分介绍。该项目将通过向密歇根理工大学的两名地质学博士生和一名土木工程博士后研究员介绍沿海水文学来加强人力资源。每个PI都将与其机构的多样性办公室合作，以确保这些职位有效地向代表性不足的群体宣传。由于地下水泛滥，岛屿上形成的湖泊和湿地的蒸发重新组织了地下水流动路径，降低了地下水位。地下水淹没和蒸发对低洼碳酸盐岛屿的影响将最为严重，在这些岛屿，Ghyben-Herzberg关系导致淡水透镜体（主要淡水资源）的损失是地下水位下降的40倍。对地下水淹没的主要控制因素是海平面上升和岛屿地形，但对淡水资源的影响可能会受到气候（降水和蒸发）、含水层渗透性、地下水贡献面积与湖面面积的比率以及湖泊与海岸之间的距离的影响。在该项目期间，将收集新的现场数据，并将开发新的瞬态建模工具，以检验以下总体假设：地下水淹没将通过湖泊面积相对于其地下水贡献区的相互作用、湖泊与海洋之间的连通程度以及与气候和海平面变化的动态相互作用来减少淡水透镜体积。假设检验将采取三管齐下的方法。首先，数字高程模型的圣萨尔瓦多岛，巴哈马，将表征湖泊水文地质环境（集水区/湖泊面积比）。水文地质参数和天气数据的实地观测将用于估计地下水通量和湖泊蒸发;地下水、湖水和降水的化学和同位素组成将用于估计补给阈值和湖泊水源（海洋、地下水、补给降水）。第二，将开发一个模拟湖泊和地下水之间动态水流和溶质运移的软件包，并将其与美国地质调查局的SEAWAT/MODFLOW模式集成。将利用在圣萨尔瓦多岛收集的观测数据对该模型进行参数化。第三，岛屿淡水透镜体对多个海平面上升、气候变化和湖泊形成情景的瞬态响应将用新开发的数值模拟工具进行测试。模拟将确定淡水透镜体积与海平面、气候变量和岛屿湖泊水文地质环境之间关系的性质。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Sea-level rise and coastal flooding are well-known to reduce freshwater resources. It is however less recognized that sea level rise can push water tables above the land surface to flood low-lying depressions. Lakes and wetlands that form by groundwater flooding expose connected aquifers to direct, continuous evaporation, which can result in substantial losses of water resources. Impacts from groundwater flooding and evaporation will be most intense on low-lying carbonate islands, where evaporated freshwater is replaced by seawater that percolates through the bedrock. These models incorporate impact of climate and predicted that lakes should remain fresh, and groundwater resources continuous, beneath islands in humid regions. In arid regions, lakes would be hypersaline, and much fresh groundwater would be replaced by seawater. In contrast to expectations, modern lakes that are formed by groundwater flooding in the arid southern Bahamas islands have salinities that range from fresh to hypersaline. This paradox between modeled and observed lake salinity underscores our lack of understanding of how groundwater flooding impacts island water resources. During this project, new field data will be collected, and new transient modeling tools will be developed, to test the overarching hypothesis that how groundwater flooding will impact island water resources. We will test the impact of lake area relative to its groundwater contributing area, the degree of connectivity between lakes and the ocean, and dynamic interactions with climate and sea level change on this process. The results of this study should improve predictions of freshwater resource loss of Small Island Developing States (SIDS) from groundwater flooding, perhaps the primary environmental factor triggering their loss of habitability. The modeling tools to be developed as part of this project will be freely distributed to the hydrological community. A field hydrogeology curricular exercise, with learning outcomes of quantitative coastal hydrology, will be developed to be used by the more than 100 student groups that visit the Gerace Research Centre (base of operation for this project) each year. Project results will be presented as part of a guest lecturer series at the University of the Bahamas and at international conferences. The project will enhance human resources by introducing coastal hydrology to 2 geology PhD students, and one civil engineering postdoctoral researcher at Michigan Tech. Each PI will work with their institution's diversity office to ensure that these positions are effectively advertised to under-represented groups.Evaporation of lakes and wetlands that form on islands by groundwater inundation reorganizes groundwater flow paths and lowers water tables. Impacts from groundwater inundation and evaporation will be most intense on low-lying carbonate islands, where the Ghyben-Herzberg relationship results in losses from freshwater lenses (the primary freshwater resource) being 40x the lowering of the water table. Primary controls on groundwater inundation will be sea-level rise and island topography, but impacts to freshwater resources could be moderated by climate (precipitation, and evaporation), aquifer permeability, ratio of groundwater contributing area to lake surface area, and distance between the lake and coast. During this project, new field data will be collected, and new transient modeling tools will be developed, to test the overarching hypothesis that groundwater inundation will reduce freshwater lens volumes through interactions of lake area relative to its groundwater contributing area, degree of connectivity between lakes and ocean, and dynamic interactions with climate and sea level change. Hypothesis testing will take a three-pronged approach. First, DEMs of San Salvador Island, Bahamas, will characterize lake hydrogeological setting (catchment/lake area ratios). Field observations of hydrogeological parameters and weather data will be used to estimate groundwater fluxes and lake evaporation; chemical and isotopic compositions of groundwater, lake water, and precipitation will be used to estimate recharge thresholds and lake water sources (ocean, groundwater, recharged precipitation). Second, a package for simulating dynamic flow and solute transport between lakes and groundwater will be developed and integrated into the SEAWAT/MODFLOW model in cllaboration with USGS. The model will be parameterized with observational data collected on San Salvador Island. Third, transient responses of island freshwater lenses to multiple sea level rise, climate change, and lake formation scenarios will be tested with the newly developed numerical modeling tool. Simulations will determine the nature of relationships between freshwater lens volumes and sea level, climatic variables, and island-lake hydrogeological settings.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.