Collaborative Research: Geophysical characterization of a karst aquifer using dynamic recharge events

岩溶含水层是重要的水资源，为世界上多达四分之一的S人口提供水源。这些含水层是复杂的水文地质系统，水流和运输主要通过优先流动的路径或管道进行，这些路径或管道的大小从厘米级的开口到远大于人类通道(洞穴)所需的通道。尽管它们在水文上很重要，但岩溶管道的位置和较大含水层的特征通常很少受到约束。为了解决这些问题，我们将使用地球物理仪器监测佛罗里达州岩溶含水层中水流入地下时产生的补给反应，以表征管道、地下水流和更大的岩溶系统。非侵入性遥感调查将产生直接社会效益方面的知识，包括改进岩溶灾害地图的创建，以突出容易形成天坑的地区，查明与污染物运输有关的优先流动路径，以及制定用于供水考虑的确定地下水流的方法。我们将与国家洞穴和喀斯特研究所合作开发一个临时的互动巡回展览，该展览将经常访问佛罗里达州和新墨西哥州现场附近的游客中心，以提高公众对喀斯特水文地质学和环境地震学的参与和科学素养。该项目还将通过新墨西哥理工学院的两名研究生、佛罗里达大学的一名本科生、通过IRIS本科生实习生计划的两名本科生实习生以及EPSCoR州的两名早期职业科学家和一名职业中期女科学家的参与，为下一代科学工作者的教育做出贡献。最后，收集的数据集将被纳入新墨西哥理工学院本科生和研究生课程的授课材料和作业集，这是一所为拉美裔服务的学院。之前的一项试点研究展示了在岩溶含水层中人工补给实验和自然补给事件中地震信号的产生。这些和其他地球物理信号是在岩溶含水层流动过程中产生的，包括补给以全管道流动进入管道时产生的压力脉冲、裂缝和岩石基质中的孔压变化、由于水团变化而导致的质量负荷引起的下沉，以及水流与围岩的湍流相互作用。为了充分利用这些信号提供的信息内容，我们将利用对两个共同定位的地球物理传感器网络的补给事件进行同时、大规模的观测，以确定管道网络、该网络内的流动过程以及更大的岩溶系统的材料特性。地震仪、倾斜仪和其他仪器将部署在佛罗里达州的圣菲河下沉上升系统，以观察两年内的岩溶补给事件。这个现场有一个很好的管道网络，因此它可以核实水文过程中产生的解释的地球物理信号。这一变革性的项目不仅将能够划定岩溶管道网络，而且还将这样做，同时根据几秒至几个月之间的时间尺度上的变形观测，对岩溶含水层水流系统进行区域综合分析。由于补给激活了新的流动路径，地球物理监测能够对补给引起的含水层变化过程中流动的动态和演变进行广泛的三维描述。此外，这些信号将有助于确定管道和地表之间的地下结构，促进对临界区环境的了解，例如，通过具体确定土壤和风化层厚度以及土壤-岩石界面的深度。环境地震学的年轻领域包括对一系列地球表面过程的研究，该项目将使用和扩展各自的方法，以改变对整个变形频率范围内的岩溶含水层的理解，并开发技术，为未来的岩溶临界区观测站做准备。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Karst aquifers are important water resources, providing water for up to a quarter of the world?s population. These aquifers are complex hydrogeologic systems, where flow and transport predominantly occur through preferential flow paths or conduits that range in size from cm-scale openings to passages much larger than required for human access (caves). Despite their hydrologic importance, the location of karst conduits and characteristics of the larger aquifer are typically poorly constrained. To address these problems, we will monitor recharge-induced responses that arise as water flows into the subsurface in a karst aquifer in Florida using geophysical instrumentation to characterize the conduits, subsurface flow, and the larger karst system. The noninvasive remote sensing investigation will generate knowledge for direct societal benefit, including tools to improve the creation of karst hazards maps that highlight areas susceptible to sinkhole formation, the identification of preferential flow paths relevant to contaminant transport, and the development of a methodology to determine subsurface flow for water supply considerations. We will develop a temporary, interactive traveling exhibit in collaboration with the National Cave and Karst Research Institute that will frequent visitor centers near the field site in Florida and in New Mexico to increase public engagement and scientific literacy about karst hydrogeology and environmental seismology. The project will also contribute to the education of the next generation of the scientific workforce through the involvement of two graduate students at New Mexico Tech, an undergraduate student at the University of Florida, two undergraduate student interns through the IRIS undergraduate student intern program, and two early career scientists and a mid-career female scientist in an EPSCoR state. Finally, collected datasets will be incorporated into lecture material and homework sets of undergraduate and graduate courses at New Mexico Tech, which is a Hispanic-serving institution.A previous pilot study demonstrated the generation of seismic signals during artificial recharge experiments and a natural recharge event in a karst aquifer. These and other geophysical signals are caused by processes during flow through karst aquifers and includes pressure pulses generated as recharge enters conduits with full pipe flow, pore pressure changes in fractures and the rock matrix, mass loading induced subsidence due to changes in water mass, and turbulent interaction of flow with the wall rocks. To capitalize on the information content provided by these signals, we will use simultaneous, large-scale observations of recharge events at two co-located geophysical sensor networks to characterize the conduit network, flow processes within this network, and material properties of the larger karst system. Seismometers, tiltmeters, and other instruments will be deployed at the Santa Fe River Sink-Rise system in Florida to observe karst recharge events over a two-year period. This field site has a well-constrained conduit network, and thus it permits verification of the interpreted geophysical signals that arise from hydrologic processes. This transformative project will not only enable delineation of the karst conduit network, but will do so while providing a regionally integrated analysis of the karst aquifer flow system based on deformation observations on the timescales between fractions of a second to months. As recharge activates new flow paths, geophysical monitoring enables extensive 3D characterization of the dynamics and evolution of flow during recharge-induced changes in the aquifer. Furthermore, the signals will help to determine the architecture in the subsurface between the conduits and the surface, advancing knowledge of critical zone environments, for example, by specifically determining soil and regolith thicknesses and depths to the soil-rock interface. The young field of environmental seismology encompasses studies of a range of Earth surface processes, and this project will use and expand the respective methods to transform the understanding of karst aquifers across the full frequency range of deformation and develop techniques in preparation for a future karst critical zone observatory.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.