Merokarst aquifers — relatively thin (<1–2 m) karstified carbonate units interbedded between mudstone, shale, or sandstone — constitute a significant proportion of carbonate terrain and underlie a large portion of the west‐ and south‐central USA, yet few advances have been made in our understanding of porosity development and flow‐path generation in these complex systems in decades. Toward this end, we used a multi‐geophysical approach at the well‐studied Konza Prairie Biological Station (KPBS), a part of the larger Flint Hills (25,734 km²), underlain by thin limestone units (1–2 m thick) interbedded with mudstone/shale units (2–4 m thick), to elucidate hydrologic connectivity and potential controls on known groundwater flow directions. We combined electrical resistivity tomography (ERT), surface and borehole nuclear magnetic resonance (NMR), and ground penetrating radar (GPR) measurements across a low order catchment where over 25 boreholes and groundwater wells sampling perched aquifers could be used to constrain interpretation of lithology, potential flow paths, and permeability. Data revealed that groundwater export may be an unappreciated component of lateral‐flow‐dominated models used to represent merokarst in that: (a) potentiometric surfaces from two limestone units showed groundwater flows toward a hydrologic depression, opposite the direction of stream flow, in the upstream portion of the catchment, (b) long term measures of groundwater levels revealed a greater variance and overall water storage in this same upstream area compared to wells near the outlet, and (c) ERT and NMR results indicate pronounced lateral heterogeneity within a given unit, suggestive of a greater degree of vertical hydrological connectivity than usually considered for horizontally‐layered merokarst. Our data suggest vertical connectivity can shunt water to depth in these “sandwiched” merokarst aquifers, yielding atypical groundwater flow directions and unrealized deep export of weathering solutes and carbon.

中文翻译：

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拟定喀斯特喀斯特系统地下水流动的新概念模型：多种地球物理方法的见解

Merokarst含水层（夹在泥岩，页岩或砂岩之间的相对较薄（小于1-2 m）的岩溶碳酸盐岩单元）构成了碳酸盐岩地带的很大一部分，并且位于美国中南部的大部分地区，但进展甚微几十年来，我们对这些复杂系统中的孔隙度发展和流路生成的理解已成为现实。为此，我们在经过仔细研究的Konza草原生物学站（KPBS）（较大的弗林特山（25,734 km ²）的一部分）中采用了多种地球物理方法。），然后在薄的石灰岩单元（厚度为1-2 m）和泥岩/页岩单元（厚度为2-4 m）之间穿插，以阐明已知的地下水流向的水文连通性和潜在控制。我们结合了低层流域的电阻率层析成像（ERT），地表和井孔核磁共振（NMR）和探地雷达（GPR）测量，其中超过25个井眼和地下水井取样的蓄水层可用于限制岩性解释，潜在的流动路径和渗透率。数据显示，地下水出口可能是用来表示喀斯特喀斯特地貌的横向流主导模型的一个未被认识的组成部分，因为：（a）来自两个石灰岩单元的电位表面显示地下水流向水文低压，与水流方向相反，在集水区上游，（b）与出口附近的井相比，长期测量的地下水水位与该上游区域相比，具有更大的方差和总储水量；（c）ERT和NMR结果表明，该区域的横向非均质性给定单位，表明垂直水文连通度比通常考虑的水平层状喀斯特喀斯特要高。我们的数据表明，垂直连通性可以将这些“夹层”梅尔喀斯特含水层中的水分流到更深处，产生非典型的地下水流向以及未实现的风化溶质和碳的深层出口。（c）ERT和NMR结果表明，给定单元内存在明显的横向非均质性，这表明垂直水文连通性程度要比通常考虑的水平层状喀斯特喀斯特地层要大。我们的数据表明，垂直连通性可以将这些“夹层”梅尔喀斯特含水层中的水分流到更深处，产生非典型的地下水流向以及未实现的风化溶质和碳的深层出口。（c）ERT和NMR结果表明，给定单元内存在明显的横向非均质性，这表明垂直水文连通性程度要比通常考虑的水平层状喀斯特喀斯特地层要大。我们的数据表明，垂直连通性可以将这些“夹层”湿地喀斯特含水层中的水分流至更深处，产生非典型的地下水流向以及未实现的风化溶质和碳的深层出口。