Integrated Physical and Chemical Observations of Water-rock Interactions and Coupled Matrix-conduit Flow in the Karstic Floridan Aquifer

0510054 martinintellectual优点。最近人们已经认识到，岩溶含水层的流场包括管道、裂缝和基质的粒间孔隙度，对流动的全面描述需要了解每个组成部分的流动、组成部分之间的耦合以及水如何从地表重新进入含水层。大多数研究充分的岩溶含水层具有较低的粒间孔隙度，其中弥散流动仅限于管道周围的细裂缝网络。相比之下，该工作中心位于佛罗里达含水层，该含水层保留了高（高达~20%）的粒间基质孔隙度。以前在物理水文地质学方面的工作（流量测量、流速的温度追踪、水头观察）表明，佛罗里达含水层管道和基质之间的水交换是由基质和导管之间水头梯度的逆转控制的，这是由于管道系统的高异体输入造成的。以前的工作没有量化地表弥漫性补给的贡献，管道和基质之间交换的大小，交换的水的停留时间，或通过溶解反应对含水层的化学修饰。因此，这个提议的项目将通过整合新的化学测量和以前使用的物理观测技术来确定含水层成分和水源之间的耦合。该油田将位于佛罗里达州中北部的Santa Fe Sink/Rise系统。要做的观察将包括来自嵌套的新井和现有井和溶水计（土壤水采样器）的水的主要元素和同位素组成，用于地下水特征，来自河流汇、上升和喀斯特窗口的水用于表征管道水，以及来自降水的水用于表征输入源。化学测量将提供流速与管道和基质之间的水头梯度以及碳酸盐和硅酸盐矿物的饱和状态进行比较。嵌套井和降水化学成分的数据将允许表征水化学的垂直差异，以确定来自地表的弥漫性补给的大小。这些数据将与其他具有低粒间孔隙度的岩溶含水层进行比较，使用现有的确定性模型，如化学分离。还将与以前和正在进行的对佛罗里达含水层其他地区的研究结果进行比较。由于高孔隙率的佛罗里达含水层具有较高的透过率，预计粒间孔隙度成分将在含水层的整体流场中发挥重要作用。更广泛的影响。这项工作将提高对在基质孔隙中有很大一部分流动的喀斯特含水层的认识和管理。这些含水层通常代表着主要的水资源，但以前一直使用概念模型进行管理，这些模型认为水要么主要通过管道流动，要么将系统视为等效的多孔介质。特别是，这些结果将直接适用于佛罗里达含水层的管理，并将通过马丁参与佛罗里达泉工作组将结果传播给关键的水资源管理人员。人力资源将受到研究生和本科教育的影响，无论是作为当前授课课程的正式资源，还是通过研究生的论文。一名二年级博士生目前正在研究这个课题，作为他的论文的一部分，两名硕士生和几名本科生将参与现场、实验室和分析工作。

0510054MartinIntellectual Merit. It has been recognized recently that the flow field of karstaquifers includes conduits, fractures, and intergranular porosity of the matrix and that fullcharacterization of flow requires understanding flow in each component, couplingbetween the components, and how water recharges to the aquifer from the surface. Mostwell-studied karst aquifers have low intergranular porosity where diffuse flow is confinedto a network of fine fractures surrounding conduits. In contrast, this proposed workcenters on the Floridan aquifer, which retains high (up to ~20%) intergranular matrixporosity. Previous work on physical hydrogeology (discharge measurements,temperature tracing of flow rates, observations of hydraulic head), suggests that waterexchanged between conduits and the matrix of the Floridan aquifer is controlled byreversals in head gradients between the matrix and conduits as a result of high allogenicinput into the conduit system. The previous work has not quantified contributions fromdiffuse recharge from the surface, the magnitude of exchange between the conduits andmatrix, the residence time of water that exchanges, or chemical modifications of theaquifer through dissolution reactions. Consequently, this proposed project will determinecoupling between aquifer components and water sources by integrating new chemicalmeasurements with previously used physical observational techniques.The field area will be the Santa Fe Sink/Rise system in north-central Florida.Observations to be made will include major element and isotope compositions of waterfrom nested new and existing wells and lysimeters (soil water samplers) for ground watercharacterization, from the River Sink, Rise, and karst windows for characterization ofconduit water, and from precipitation for characterization of the input sources. Thechemical measurements will provide flow velocities to be compared with head gradientsbetween the conduits and the matrix and saturation states with respect to carbonate andsilicate minerals. The nested wells and data on chemical composition of precipitationwill allow characterization of vertical differences in water chemistry to determinemagnitudes of diffuse recharge from the surface. These data will be compared to otherkarst aquifers with low intergranular porosity using available deterministic models suchas chemograph separation. Comparisons will also be made to results of previous and ongoingstudies of other regions of the Floridan aquifer. Because of the highertransmissivity of the highly porous Floridan aquifer, it is anticipated that the intergranularporosity component will play a large role in the overall flow field of the aquifer.Broader Impacts. This work should improve the understanding andmanagement of karst aquifers that have significant portions of their flow within matrixporosity. These aquifers commonly represent major water resources, but have previouslybeen managed using conceptual models that consider either flow primarily throughconduits or treat the system as an equivalent porous medium. In particular, these resultswill be directly applicable to management of the Floridan aquifer and results will bedisseminated to critical water managers through Martin's participation in the FloridaSprings Task Force. Human resources will be impacted through graduate andundergraduate education, both formally as a resource for currently taught courses andthrough graduate student theses. One second-year PhD student is currently working onthis topic as part of his dissertation, and two masters students and several undergraduateswill participate in the field, laboratory, and analytical work.