Abstract Karst science is beginning to recognize and understand better the interaction between conduits and the fractures and/or pore spaces within the aquifer. The relationship has important significance in relation to the understanding of contaminant transport, resource management and dewatering practices. This study presents the results of a dye trace carried out to investigate the link between the aquifer and conduits near a large dewatered quarry in the Mendip Hills in Somerset, England. At the point of undertaking the study, there were no records of the quarry directly intercepting any conduits but water from the conduit(s) is known to be drawn into the quarry. During the study, water from the conduits was observed to be lost to and gained from the fractures in different places in the aquifer. This complexity highlights the dependence of conduit flow on water levels in the aquifer and the sensitivity of groundwater in karstified aquifers to contamination.

ABSTRACT The Mitchell Plateau of south-central Indiana is one of the iconic karst landscapes of the United States. The sinkhole-dimpled forests, fields, and farms; the extensive cave systems; and the deep windows into the groundwater system have fostered curiosity, exploration, and publication since the mid-1800s. This paper is designed to complement a field excursion to the classic features of this landscape. Included are literature reviews focused on three karst basins of the Mitchell Plateau: Mill Creek–Mosquito Creek, Bluespring Caverns, and Lost River. Geomorphic, hydrologic, and geochemical data are synthesized in the modern context of our understanding of epigenetic karst. Revealed are three styles of karst basin: (1) small, shallow karst aquifers strongly controlled by meteoric recharge and epikarst percolation; (2) intermediate-size karst aquifers with significant base flow and surface-water–groundwater interaction; and (3) regional aquifer systems with outcrop belt recharge, downdip transport into confinement with long water-rock interaction times, and artesian flow or entrainment of mineralized waters through fractures into springs or surface waters. Quaternary glaciation has greatly influenced the vertical position of base level through river incision and sediment aggradation; conduit development is controlled by proximity to the major rivers and the stratigraphic position of conduits.

ABSTRACT The geology of Great Smoky Mountains National Park (GRSM) in Tennessee and North Carolina is dominated by siliciclastics and metamorphic strata. However, in the western portion of GRSM, a series of carbonate fensters (windows) expose the Lower Ordovician–age section of the Knox Group, a series of dolomite and limestone units that are partially marbleized as a result of contact metamorphism from the Great Smoky fault. The fensters create opportunities for allogenic recharge to occur at points along the contact of the surrounding insoluble strata with the underlying soluble carbonates. The combination of chemically aggressive surface recharge and vertical relief has resulted in the formation of deep caves, many of which have active streams and water resources. Though the karst is limited in extent and the number of caves is fairly small, the significance of the resources is substantial, with several of the caves in the area over 150 m in depth and at least two being major bat hibernacula. In 2017, the U.S. Geological Survey (USGS) began a study to better understand the hydrologic behavior of these karst systems through hydrologic and geochemical monitoring, groundwater tracing using fluorescent dyes, and seepage runs. Stage and water-quality instrumentation was installed in two caves in GRSM, the main stream of Bull Cave, and in a sump pool in Whiteoak Blowhole, at 173 m and 70 m below land surface, respectively. Following setup of the cave sites, dye injections were conducted to determine discharge points for four of the deep cave systems on Rich Mountain and Turkeypen ridge. Results show water in these systems has an extremely rapid travel time, with tracers detected from caves to springs in less than 24 h for each of the systems. This field guide describes the complex geology, regional hydrogeology, and unique landscape characterized by high-gradient subterranean streams, carbonate fensters, and deep caves of the GRSM karst.

ABSTRACT This guide explores relationships among macroscale folds, mesoscale structures, the Nashville dome, and an inferred Precambrian or Cambrian rift in the basement beneath the dome. The Nashville dome, central Tennessee, is an ~12,000 km 2 north-northeast–trending, elliptical cratonic uplift. A published crustal density model shows that a previously undescribed Precambrian or Cambrian rift, herein named the Nashville rift, probably runs from northwestern Alabama through the Nashville dome to southern Kentucky. Within the Nashville dome, macroscale folds and mesoscale structures of the Stones River and Harpeth River fault zones have been interpreted previously as the surface manifestation of subsurface normal faults. This road guide describes two previously undescribed inferred subsurface fault zones: the Marshall Knobs fault zone and the Northern Highland Rim fault zone. The Marshall Knobs fault zone, which is ~16.3 km long, is associated with ~35 m of structural relief, trends east-southeast, is down on the north side, and is inside the geophysically defined rift. The Northern Highland Rim fault zone consists of east-northeast–­striking minor normal and reverse faults and a minor strike-slip fault exposed above the western margin of the geophysically defined rift. The authors hypothesize that the Northern Highland Rim fault zone may be the surface manifestation of the subsurface continuation of a macroscale fault previously mapped at the surface 25 km to the southwest. All of the inferred faults fit into a tectonic model in which they originally formed within a rift and later reactivated, accommodating extension of the uppermost crust during uplift of the Nashville dome.

Abstract Small-size karst landforms may potentially provide very useful information to fully understand the behaviour of karst systems and their dynamics. In this chapter we demonstrate the need to pay attention to such features. ‘Inghiottitoio della Masseria Rotolo’, located in a remarkable karst area of southern Italy, has in recent years become the most controversial and discussed speleological site in Apulia. Even though it has been known for several decades, recently excavation work has allowed cavers to enter a huge karst system, eventually reaching the water table. The total depth of the cave is now 324 m, making it the deepest in the region. This chapter summarizes the history of discoveries at the site, starting from the description of the polje, also including information about the link between toponymy and karst. The works carried out at the swallet site are then described to emphasize the importance of the often neglected small-size karst features. In fact, when carefully observed and studied, these might be able to shed new light and greatly increase our knowledge about karst. The final part of the chapter deals with the cave system and provides an outline of the ongoing research.

Abstract The Puerto Princesa Underground River, amongst the largest caves of the Philippine Islands, is the most visited show cave in the country, even though it has undergone no tourism adaptation at all. Its scientific importance primarily relies on the fact that it is one of the largest known underground estuaries in the world, and the effect of tides is visible along more than 7 km of the cave length. The complex relationships between sea and freshwater influence not only the hydrodynamics of the system and the speleogenetic processes presently active, but also its climate and its ecosystem. The systematic exploration and research of this coastal karst system started some 40 years ago and have shown that the Puerto Princesa Underground River is one of the most important caves in the world with regard to many different scientific fields. Speleogenesis concerns the initial phreatic solution followed by vadose erosion with periodical marine invasion, and subsequent saline/freshwater-mixing processes during sea-level highstands. The hydrodynamic behaviour of the water flowing inside the cave is rather complex, being simultaneously controlled by allogenic recharge and tides. Speleothems abundantly occur with several forms, some of which have never been described before. Several minerals, some of which are very rare, are present, together with palaeontological remains exposed by differential corrosion on rock walls. Last but not least, two large populations of bats and swiftlets sustain a complex subterranean ecosystem.

Abstract Ashalim maze cave, and neighbouring caves in the NW Negev Desert, Israel demonstrate hypogene karst features. These features are shown to have developed as a result of the mixing of two types of groundwater flowing in opposite directions within two tiers of Cretaceous rock aquifers. The stable isotope composition indicates that the lower Kurnub sandstone aquifer was recharged over far-field Nubian Sandstone outcrops in the vicinity of the Precambrian basement outcrops of the Sinai Desert, which belongs to the Afro-Arabian dome. The water flows northward and rises into the Judea carbonate aquifer through deep faults. A similar hydrogeological system is inferred for the speleogenetic period of Ashalim Cave. Dewatering of the cave occurred in the Pliocene due to regional uplift. This is indicated by the first vadose speleothems, dated to the late Pliocene (3.1 Ma). This was followed by surface denudation, which breached the cave and formed the present entrance.

Abstract Karst aquifers are some of the most important and well-used sources of water worldwide. The tapping of karst waters for use as drinking water has been important in the historical and economic development of many karst regions. Recent studies have found that karstified rocks and aquifer systems cover c. 15% of the Earth’s ice-free land. The greatest area of karst outcrops (>1 × 10 6 km 2 ) is in Russia, the USA, China and Canada. In the Mediterranean basin, groundwater is generally more abundant in karst than in other aquifers and has been extensively exploited. Karst groundwater is also widely used in the Middle East, China, North America, and northern and eastern Africa and is of crucial importance for the sustainable development of tourism and the economy. Karst aquifers currently supply c. 10% of the global population with drinking water and, in some zones, they are the only water resource available. However, the share of karst aquifers in the global supply of water will decrease with the predicted increase in population, concentrated in urban areas, and improvements in treatment technologies for water from other sources.

Abstract The Kaibab Plateau and Grand Canyon National Park in the USA contain both shallow and deep karst systems, which interact in ways that are not well known, although recent studies have allowed better interpretations of this unique system. Detailed characterization of sinkholes and their distribution on the surface using geographical information system and LiDAR data can be used to relate the infiltration points to the overall hydrogeological system. Flow paths through the deep regional geological structure were delineated using non-toxic fluorescent dyes. The flow characteristics of the coupled aquifer system were evaluated using hydrograph recession curve analysis via discharge data from Roaring Springs, the sole source of the water supply for the Grand Canyon National Park. The interactions between these coupled surface and deep karst systems are complex and challenging to understand. Although the surface karst behaves in much the same way as karst in other similar regions, the deep karst has a base flow recession coefficient an order of magnitude lower than many other karst aquifers throughout the world. Dye trace analysis reveals rapid, conduit-dominated flow that demonstrates fracture connectivity along faults between the surface and deep karst. An understanding of this coupled karst system will better inform aquifer management and research in other complex karst systems.

Abstract Reliability is the greatest concern in recent karst vulnerability assessments. Checking the validity of results and understanding the operation of karst systems are therefore the most promising areas for improvement. We report an application of the Slovene Approach to a test site in the Gömör-Torna Karst of Hungary and Slovakia. The resource vulnerability map provided an appropriate result and showed that the overlying sediments and thicker soil may effectively decrease the vulnerability of this unconfined area. The source vulnerability of the Kis-Tohonya Spring was evaluated for the purposes of protection zoning. The results of long-term hydrograph and recession curve analyses were helpful in understanding the functioning of the Kis-Tohonya Spring and the karst system. The importance of the different regimes contributing to the slow and fast flow of the spring under different hydrological conditions was shown. Ongoing research aims to feed these results back into the source vulnerability assessment of the spring.

Abstract We used hydrogeochemical techniques and environmental isotopes (δ 18 O and δ 2 H) to characterize karst aquifers without a well-known hydrogeological conceptual model. The selected study area corresponds to carbonate outcrops located in the Sierra Grazalema Natural Park (SGNP) in southern Spain. The combination of high rainfall, large areas of carbonate outcrops and the high permeability of the outcropping rocks means that the SGNP is a strategic water reserve in a region that periodically suffers from a scarcity of water. There are still many uncertainties regarding the hydrogeological functioning of these aquifers, such as the groundwater flow paths, the identification of recharge areas and a possible hydrogeological connection with adjacent systems. The objectives of this work were: (1) to gain an insight into the hydrogeochemistry of groundwater in the SGNP aquifers; (2) to identify the recharge areas of the main springs of the karst system; and (3) to contribute to our understanding and conceptualization of the SGNP aquifers. Our results show marked differences in the chemical composition of the groundwater, which can be classified into three main groups: CaHCO 3 waters (southern sector); Ca–MgHCO 3 waters (northern sector); and those with higher SO 4 2− , Na + and/or Cl − concentrations. These hydrochemical differences are principally dependent on the mineral composition of the rocks the groundwater flows through and comes into contact with. These results also shed light on the recharge areas associated with the main springs and seem to corroborate a possible net groundwater flow from the eastern part of the SGNP (Sierra del Endrinal) towards carbonate outcrops situated several kilometres to the SE.

Abstract The behaviour of aquifers with karst porosity is dependent on hydrological conditions. This is due to the peculiar characteristics of the groundwater flow and dynamics of hydrological processes in karst. As a result, karst aquifers are especially vulnerable to the effects of environmental change. We assessed the long-term climatological and hydrological trends and the short-term effects of increasingly frequent extreme hydrological events (droughts) for the Mediterranean karst spring Rižana in SW Slovenia. The findings predict higher mean annual air temperatures of 0.34°C decade −1 , lower annual precipitation of c. 60 mm decade −1 and higher annual actual evapotranspiration (especially during spring and summer) of 32–49 mm decade −1 . As a consequence, we can expect a decrease in the mean annual discharge of the spring of c. 480 l s −1 decade −1 with prolonged dry summer periods. Detailed monitoring of the physical, chemical and microbiological parameters showed that the flood pulses caused by precipitation events after a long dry period cause a significant deterioration in water quality. In such situations, contaminants stored in the unsaturated zone are flushed out and counts of coliform bacteria can reach >1400 cfu (100 ml) −1 , with total Al and Fe concentrations up to 206 and 474 μg l −1 , respectively. These results suggest that there should be urgent adherence to water quality standards to protect karst water sources in view of the anticipated climatological stresses. Management strategies should promote monitoring and the rational use of karst water supplies.