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 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.

Abstract A strong and potentially dangerous decreasing trend in the level of water in Vrana Lake over the last three decades was analysed. This freshwater lake is a unique karst hydrology feature located on the small Adriatic island of Cres (405.71 km 2 ), which is entirely composed of carbonate rocks. The lake is situated in a large cryptodepression and its base reaches a depth of 61.3 m below mean sea-level. The lake is a complex hydrological–hydrogeological system with an average water volume of c. 220 × 10 6 m 3 . The larger geographical region has been affected by an increase in air temperature over the last c. 40 years. This exceptionally clean freshwater lake is the only source of potable water for the whole Cres archipelago. A dangerous drop in the water level of the lake started in 1983. This decreasing trend is driven by both global climate change and anthropogenic (the overexploitation of water) factors.

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.