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Over the past decades, fractured and karst groundwater systems have been studied intensively due to their high vulnerability to nitrate (NO3−) contamination, yet nitrogen (N) turnover processes within the recharge area are still poorly understood. This study investigated the role of the karstified recharge area in NO3− transfer and turnover by combining isotopic analysis of NO3− and nitrite (NO2−) with time series data of hydraulic heads and specific electrical conductivity from groundwater monitoring wells and a karstic spring in Germany. A large spatial variability of groundwater NO3− concentrations (0.1–0.8 mM) was observed, which cannot be explained solely by agricultural land use. Natural-abundance N and O isotope measurements of NO3− (δ15N and δ18O) confirm that NO3− derives mainly from manure or fertilizer applications. Fractional N elimination by denitrification is indicated by relatively high δ15N- and δ18O-NO3− values, elevated NO2− concentrations (0.05–0.14 mM), and δ15N-NO2− values that were systematically lower than the corresponding values of δ15N-NO3−. Hydraulic and chemical response patterns of groundwater wells suggest that rain events result in the displacement of water from transient storage compartments such as the epikarst or the fissure network of the phreatic zone. Although O2 levels of the investigated groundwaters were close to saturation, local denitrification might be promoted in microoxic or anoxic niches formed in the ferrous iron-bearing carbonate rock formations. The results revealed that (temporarily) saturated fissure networks in the phreatic zone and the epikarst may play an important role in N turnover during the recharge of fractured aquifers.

The Classical Karst (sensu stricto) represents a complex hydro-geomorphological unit as well as one of the best-known karstic systems in the world. For this reason, it was selected as a model area both for applied research and for the conservation of its highly diverse subterranean fauna. With this paper, we aim to provide an overview of groundwater fauna in the phreatic zone of the Classical Karst aquifer, based on all published material along with new surveys, and search for patterns of species distribution within hydrogeological subunits, with a focus on the potential use of species as tracers of hydrological connections and groundwater flowpaths. The Classical Karst, with an area of approximately 750 km2, and adjacent to alluvial and flysch areas provides habitats for 83 stygobionts (accompanied by 16 stygophiles) and is one of the richest hotspots for groundwater fauna across the globe. The rate of endemism within the area is very high (around 50%). Multivariate statistical analyses revealed the faunal turnover between hydrogeological subunits, as well as the effect of water flow regime. Our approach, using species turnover and the species indicator value, allowed us to recognise groups of indicator species, which can be considered as descriptors of aquifer type and habitat structure, as well as water flow regime and groundwater flowpaths.

Aquifers with time variant catchment boundaries, regional flows, and inflows from surface streams and accumulations are common in karst areas. Due to the lack of reliable methods for determination of water balance in the phreatic zone of such aquifers, groundwater recharge estimation is a challenge task. This paper introduces a new method for estimation of groundwater recharge in karst – the so-called partial correlation method (PCM). The basic hypothesis is that the groundwater recharge rates can be determined from the time series of precipitation, air temperature, relative humidity, and spring discharge, by using a partial cross-correlation function as objective function. Following this hypothesis, a simple conceptual model of water balance in the soil cover, epikarst and vadose zone is developed, and an objective function for estimation of the optimal value of parameter of this model is proposed. PCM is applied on the catchment of Žrnovnica Spring located in the Dinaric karst area of Croatia. The results of application are compared with the results of previous studies, as well as with the results obtained by five empirical models that have been used for estimation of groundwater recharge in the Mediterranean karst. The effective infiltration coefficients obtained by PCM for the Žrnovnica Spring are generally in accordance with the previously published ones.

We report preliminary results of a field study of the natural discharge styles of a Pleistocene karst aquifer in uplifted Cenozoic coral-algal reef and lagoonal limestone. Discharge in deeply enscalloped embayments appears to be characterized by closely distributed springs and seeps that occur along the entire length of the bays. Along the rocky, cliff-dominated coastlines, discharge appears to be dominated by flow from cavernous openings and solution-widened fractures at the waterline, with occasional submarine springs. Documentation of the discharge styles and relative contributions of observed discharge points to total discharge, along with separate data on aquifer lithology and hydrology, provide bases for inferences regarding the degree and style of karst development. Observations from this study are consistent with separate evidence for a mixed karst in which flow may be relatively diffuse in the current phreatic zone, even though flow in the vadose zone has been observed to be strongly conduit-controlled in some areas. The following conclusions appear defensible on the basis of observations to date: (1) Discharge on embayed beaches is more evenly distributed than along the cliff-dominated coast. (2) The aquifer can best be described as mixed karst, and significant local variation can be expected in aquifer characteristics.

Shaft development can be documented on the basis of comparative studies of specific shaft lengths and shaft patterns. We calculated the specific length of shafts and the average specific shaft length of the shafts in some karst areas and we investigated the relation between the altitude of shaft floors and the specific shaft length. Taking the registered specific shaft lengths and the shaft patterns into consideration, it can be stated that some parts of the shafts developed paragenetically in the studied karst areas. In the Bakony Region, this was caused by surface water influx, rise of karst water level, and their simultaneous effect. As a result, shaft systems, bifurcating shafts and storeyed shafts developed. On glaciokarst areas, shafts may constitute a system with phreatic passages: either because a phreatic envi ronment developed in the vadose zone due to the permanent impoundment of karst water or because a phreatic passage got into the vadose zone since the karst became elevated. On the studied karst areas, the following shaft development types are distinguished: glacial-high mountain surface flood development type (1), glacial-high mountain karst water and surface flood development type (2), glacial karst water and surface flood later phreatic development type (3), shaft with a passage that got into the vadose zone (4).

The Lower Paleozoic gas reservoirs in central Sulige gas field are mainly accumulated in Ordovician ancient weathering crust karst carbonate reservoirs, and they are especially rich in the upper assemblage of Ordovician Majiagou formation (Ma51–Ma54 sub-members). However, the spatial distribution of gas is unclear yet because of the different denudation degree and uneven development of paleokarstification. This paper mainly focuses on the characteristics of paleogeomorphology and paleokarstification and their impact on natural gas accumulation. Geological stratifying has been done based on the observation of cores and thin sections, and the analysis of drilling, logging and seismic data. The paleogeologic map of pre-carboniferous was depicted according to the ancient weathering crust outcropped strata. Paleogeomorphology reconstruction is based on a comprehensive method combining the moulage method with the residual thickness method. Result indicates that the paleogeomorphology can be divided into western karst highland and eastern karst slope in the area investigated, and the denudation degree of ancient weathering crust in the west is more serious than that in the east. The karst highland can be divided into remnant hill and depression while the karst slope can be divided into gentle hill and shallow depression in detail. Paleokarst section can be vertically divided into epikarstic zone, vertical vadose zone, horizontal phreatic zone and deep slow flow zone based on the analysis of paleokarst identification mark and vertical dissection of single well. By analyzing the relationship between paleokarst characteristics and production data, the study shows that paleogeomorphology and paleokarstification have a significant control on nature gas accumulation and distribution. Gentle hills on karst slope are expected to be the most favorable areas for reservoirs horizontally, horizontal phreatic zone is more advantageous vertically, and second the vertical vadose zone.

The meteoric diagenetic environment has multiphase characteristic, but the scales of the reservoirs in different meteoric diagenetic environments have been rarely considered. On the basis of geological and well-logging analyses, three distinct phases of the meteoric diagenetic process were observed in the Ordovician of the Jingxi area in Ordos Basin, China. The phreatic zone formed in the first phase is partially preserved, whereas those formed in the second and third phases are completely retained. Strata in the western (close to the Central Uplift Belt) and eastern parts underwent bedding-parallel meteoric dissolution and cross-layer meteoric dissolution, respectively. The distributions of the dissolution formation thicknesses in two successive phases of the meteoric diagenetic process exhibit complementarity at the same positions in the plane. The favorable reservoirs at the top of the Ordovician are mainly distributed in the western parts. The second phase of the meteoric diagenetic process is most conducive to the formation of carbonate reservoirs. By dividing and comparing the multiphases of the meteoric diagenetic environment of carbonates, the favorable karst reservoirs can be predicted in each phase.

Most bauxite in China is located upon the karst surface, yet the relation between karstification process and bauxite formation is barely known. Here we discuss how the relation affects the karst and bauxite evolution through analyzing distributions of orebody parameters from 9,007 exploration wells (434 orebodies) in western Guangxi, South China block. In high-elevation karst terrain dominated by peaks, orebodies have greater average thickness, lower Al2O3 and higher Fe2O3T than those in low-elevation region dominated by depressions. Principal component and multifractal analyses show that the Al2O3, Fe2O3T and LOI and the orebody thickness, determined by depression geometry, have more even distributions in high-elevation terrain. This explains that the interaction between the oxidized, alkaline water in karst surface and the ferrous clay minerals that released H+ during bauxite secondary weathering was more intensive in high-elevation terrain than in low-elevation one. The interaction with self-organized nature is considered responsible for the even development of karstic depressions and bauxite orebody thicknesses in high-elevation terrain. In comparison, SiO2 distribution is more even in low-elevation terrain, where connected depressions near the phreatic zone facilitated SiO2 mobilization and even distribution.

This study focuses on the impact of surface reservoirs (fish ponds) on a multi aquifer coastal system, and the relation between the aquifer and the sea. The study was conducted in an Israeli Mediterranean coastal aquifer, which includes a sandy phreatic unit and two confined calcareous sandstone units. The geological description is based on 52 wells, from which 33 samples were collected for stable isotope analysis and 25 samples for organic and inorganic parameters. Hydraulic head and chemical measurements suggest that there is an hydraulic connection between the fish ponds above the aquifer and the phreatic unit, whereas the connection with the confined units is very limited. The phreatic unit is characterized by a low concentration of oxygen and high concentrations of ammonium and phosphate, while the confined units are characterized by higher oxygen and much lower ammonium and phosphate concentrations. Organic matter fluorescence was found to be a tool to distinguish the contribution of the pond waters, whereby a pond water signature (characterized by proteinaceous (tryptophan-like) and typical humic-matter fluorescence) was found in the phreatic aquifer. The phreatic unit is also isotopically enriched, similar to pond waters, with δ18O of −1‰ and δD of −4.6‰, indicating enhanced evaporation of the pond water before infiltration, whereas there is a depleted isotopic composition in the confined units (δ18O = −4.3‰, δD = −20.4‰), which are also OM-poor. The Phreeqc model was used for quantitative calculation of the effect of pond losses on the different units. The Dissolved Inorganic Nitrogen (DIN) in the upper unit increases downstream from the ponds toward the sea, probably due to organic matter degradation, suggesting contribution of DIN from shallow groundwater flow to the sea. 87Sr/86Sr and Mg/Ca in the brackish and saline groundwater of the lower confined units increase toward seawater value, suggesting that the salinization process in the region is connected to seawater intrusion and not to old brine from the underlying Cretaceous aquitard.

One of the greatest challenges in critical zone studies is to document the moisture dynamics, water flux, and solute chemistry of the unsaturated, fractured and weathered bedrock that lies between the soil and groundwater table. The central impediment to quantifying this component of the subsurface is the difficulty associated with direct observations. Here, we report solute chemistry as a function of depth collected over a full year across the shale-derived vadose zone of the Eel River Critical Zone Observatory using a set of novel sub-horizontal wellbores, referred to as the vadose zone monitoring system. The results of this first geochemical glimpse into the deep vadose zone indicate a dynamic temporal and depth-resolved structure. Major cation concentrations reflect seasonal changes in precipitation and water saturation, and normalized ratios span the full range of values reported for the world’s largest rivers.

The new railway line between Divača and Koper/Capodistria in south-western Slovenia is being built, a part of which crosses the southern outskirts of the Classical Karst plateaux. It will run through two tunnels, the northern tunnel T1 (6.7 km long) and the southern T2 (6 km long), which partially cross karst aquifer system. A multi-tracer test with injections of fluorescent dyes uranine and naphthionate, bypassing the karst vadose zone, was carried out to define the directions and dynamics of the underground water flow. The main goals were better understanding of the complex hydrogeological conditions in the area and assessment of possible environmental impacts on the nearby water sources. With tracing of uranine injected into a nearby cave stream, the direction of flow from the northern T1 tunnel mainly towards the Reka-Timavo aquifer system and further towards the Timava/Timavo springs was proved. The peak velocities, as determined from the peaks of the tracer breakthrough curves, range from 29 m/h to 36 m/h. Through the wider and well-connected conduits of the Reka-Timavo system, the peak velocities can reach up to 88 m/h. The recovery of uranine in an intermediate cave, i.e., Jama 1 v Kanjaducah, amounted to approximately 74 %. The northern section of the southern T2 tunnel is a part of a wider bifurcation zone between the Osapska Reka and the Boljunec/Bagnoli springs, where peak flow velocities between 10 and 13 m/h have been determined by tracing of naphthionate injected into a borehole located in the line of the planned tunnel. It has been estimated that about 25 % of the injected naphthionate flew out through the Osapska Reka spring and about 5 % through the Boljunec/ Bagnoli springs. Based on this research, proper monitoring of any potential negative impacts of the new railway line will be made possible. The study presents an approach to better planning of hazard control of traffic routes in complex and highly karstified rock settings.

Karst aquifers are hydraulic structures where dissolution conduits dictate complex spatial and temporal flow patterns. These aquifers are vertically divided into phreatic, epiphreatic and vadose zones. While the phreatic zone is permanently saturated, providing the major contribution to base flow, most of the flood event water is transferred through the epiphreatic zone. The spatial distribution of conduits within karst aquifers is largely unknown. The only technique giving accurate results is direct human exploration, although some limited information can be obtained from hydrograph analyses in springs and wells, through hydraulic tomography and by geophysical surveys.

Caves reaching the (epi)phreatic zone may provide the only access to groundwater in the internal parts of karst aquifers. Modern instruments enable unattended high frequency measurements of groundwater parameters in such caves. A network of distributed observation points may give new information on temporal and spatial pattern of groundwater flow. Such network, recording water level, temperature and specific electrical conductivity was established in all major ponors and active water caves of the karst aquifer between Planinsko Polje and springs of the Ljubljanica River, Slovenia. Up to three and a half years long records were analysed in view of available and relevant geological, speleological, meteorological and hydrological information, and basic hydraulic principles of the epiphreatic flow. The result of the interpretation were models of possible conduit networks of the three main flow subsystems draining Planinsko Polje. For each subsystem a hydraulic model comprising the main features of the inferred conduit network and inputs was made. The models were adjusted until their response to the typical flood situations gave a good qualitative fit to the response of the observation network. The results provide new insights into the mechanism of flood propagation through the system and its relation to the known conduit geometry. The hydraulic role of known cave passages is assessed and new flow pathways are proposed. Back-flooding within the aquifer causes an increase of head in the polje, followed by the activation of higher located ponor zones and flow pathways related to them. Hydrographs recorded in two caves located northwest from Planinsko Polje revealed pos sible high transmissivity zone of the Idrija Fault Zone and the mechanism of estavelles located at the polje’s north-western border. The approach taken in this work offers new insights into the relation between the conduit network geometry and flood mechanism. It can be used elsewhere in conduit-dominated systems with multiple accesses to groundwater flow and well constrained recharge.Key words: karst aquifer, epiphreatic zone, groundwater monitoring, hydraulic models, Planinsko Polje, Ljubljanica River.Dinamika podzemne vode med Planinskim poljem in izviri Ljubljanice, Slovenija Jame v epifraticni coni obicajno predstavljajo edini dostop do podzemne vode znotraj kraskega vodonosnika. Sodobni merilniki omogocajo kakovostne zvezne meritve razlicnih parametrov tudi v taksnih jamah. Merilna mreža z vec lokacijami znotraj izbranega vodonosnika lahko ponudi nove podatke o casovni in prostorski dinamiki toka podzemne vode. Taksna merilna mreža, z meritvami visine, temperature in elektroprevodnosti vode, je bila vzpostavljena v vseh pomembnejsih ponorih in vodnih jamah na obmocju med Planinskim poljem in izviri Ljubljanice. Do tri in pol leta dolgi nizi podatkov so bili analizirani z vidika razpoložljivih geoloskih, speleoloskih, meteoroloskih in hidroloskih podatkov ter osnovnih hidravlicnih nacel o epifreaticnem toku vode. Rezultat interpretacij so poenostavljeni modeli z domnevno razporeditvijo podzemnih kanalov v treh glavnih podsistemih, ki odvajajo Planisko polje. Za vsak podsistem je bil napravljen hidravlicen model z dotokom in mrežo kanalov, ki najbolje ponazarja resnicno stanje. Tekom raziskave so se hidravlicni modeli nadgrajevali do taksne mere, da je simulacija vodnega toka zadovoljivo ponazarjala dogajanje, izmerjeno v resnicnem okolju. Rezultati so prinesli nove ugotovitve o sirjenju in dinamiki poplavljanja skozi sistem ter njihovo povezavo s poznano geometrijo proucevanega vodonosnika. Ocenjena je bila hidravlicna vloga poznanih jamskih rovov, na podlagi njih pa interpretirane nove smeri pretakanja vode. Ugotovljeno je bilo tudi zajezitveno poplavljanje znotraj vodonosnika, ki vpliva tudi na vodostaj na polju in nadalje na aktivacijo visje ležecih požiralnikov ter njim sledecih kanalov. V dveh jamah severozahodno od Planinskega polja so visinski hidrogrami nakazali na obstoj bolj prepustnega obmocja Idrijske prelomne cone ter delovanje estavel na severozahodnem obrobju polja. Postopek, ki je bil uporabljen v pricujocem delu, omogoca nova dognanja o razporeditvi podzemnih kanalov in s tem povezano dinamiko poplavljanja v kraskem vodonosniku. Predstavljeno metodo je mogoce uporabiti tudi v drugih kraskih sistemih z dobro razvitimi kanali, z vec dostopi do toka podzemne toka vode in dobro poznanem dotoku v sistem.Kljucne besede: kraski vodonosnik, epifreaticna cona, spremljanje podzemne vode, hidravlicni modeli, Planinsko polje, Ljubljanica.

Vadose zone hydraulic properties impact the performance of surface-spreading MAR systems by controlling the rate of flow of water from land surface to the water table. Single- or double-ring or basin (pilot) infiltration tests are typically performed to estimate infiltration rates. Vadose zone hydraulic properties obtained from infiltration tests at land surface may differ greatly from those at depth, especially where the vadose zone is very thick. Evaluation of vadose zone properties is complicated by the zone being two phase (air and water), as opposed to the single-phase system of the phreatic zone. Vadose zone testing programs needs to consider the spatial variability in properties and the volume and area of investigation of tests relative to aquifer heterogeneity. Where project budgets and time are limited, the use of safety factors in design can compensate for uncertainty.

The present paper deals with a field experiments on evaporite rock samples and groundwater investigations in the Quinis test site, a hamlet of the Enemonzo municipality in NE Italy, were sinkholes occurred in the past and are still occurring causing severe damage to the existing infrastructures. The area is characterised by a Carnian evaporitic bedrock made of gypsum and anhydrite mantled by alluvial and colluvial deposits. In order to evaluate the loss of weight and volume of the subcropping evaporites as responsible for sinkholes, a field-experiment was carried out. Inside seven piezometers, at different depths, evaporitic rock samples were exposed to the naturally occurring variable climatic conditions such as degree of humidity, different air flow and hydrodynamic. The rock samples were installed at the beginning of April 2017 in the dry sections of piezometric tubes, in the vadose zone and in the phreatic zone. Data related to water level fluctuations were recorded by using data-logger devices and highlight significant changes in the water table. After 13 months of data recording (May 2018), rock samples were removed, reweighted and the volume loss measured. In addition, water from piezometer-experiment, representative of the groundwater circulation, were collected at different depths. The obtained results indicate that rock sample reduction is dependent on the hydrological regime and water chemistry and not on the number of days during which the samples remained submersed. In particular, the water geochemistry highlights the possible role in gypsum/anhydrite dissolution due to NaCl water admixing in a complex scenario. In additional, the geochemical data highlight the occurrence of some potentially toxic elements (As, Fe, Mn) at concentrations of concern in some water. This approach represents a novel contribution in the study of karst hazard in evaporites adding a tile to the knowledge of the fast evolutionary processes which cause sinkhole formation.

The concept model of ancient buried hill karst reservoirs was built taking the NWKK carbonate rock oilfield in the South Turgay Basin in Kazakhstan as an example, and the characteristics of karst reservoirs and their controls on productivity were analyzed in vertical and horizontal directions. Vertically, the karst reservoirs can be subdivided into, from top to bottom, weathering crust zone, epikarst zone, caves zone, vadose zone and phreatic zone, in which the development of fractures is strengthened gradually; Six reservoir types, breccia pore, cave, vug, fracture-vug, fracture-pore and pore, were developed; Each karst zone has high oil production and low water cut in the initial stage because of the developed fractures and karst caves, but the production declines rapidly and the water cut rises fast. Horizontally, the karst reservoir characteristics are controlled by structure altitude and ancient lithofacies: the ancient buried hill with high structure altitude and loose lithology suffers from stronger weathering and leaching, has much more solution caves and holes, the main reservoir types are breccia pore, cave, and vug, while the ancient buried hill with low structure altitude and compacted lithology has highly developed fractures and stronger communication with bottom water, the main reservoir types are fracture-vug and fracture-pore, and the reservoirs have better productivity effect but rapid production declines and water cut rising. Different areas in plane should adopt different development techniques and policies. Key words: ancient buried hill, karst reservoir, reservoir characteristics, reservoir concept model, productivity characteristics, South Turgay Basin

Summary Even though karstic aquifers are important freshwater resources and frequently occur in mountainous areas, recharge processes related to snowmelt have received little attention thus far. Given the context of climate change, where alterations to seasonal snow patterns are anticipated, and the often-strong coupling between recharge and discharge in karst aquifers, this research area is of great importance. Therefore, we investigated how snowmelt water transits through the vadose and phreatic zone of a karst aquifer. This was accomplished by evaluating the relationships between meteorological data, soil–water content, vadose zone flow in a cave 53 m below ground and aquifer discharge. Time series data indicate that the quantity and duration of meltwater input at the soil surface influences flow and storage within the soil and epikarst. Prolonged periods of snowmelt promote perched storage in surficial soils and encourage surficial, lateral flow to preferential flow paths. Thus, in karstic watersheds overlain by crystalline loess, a typical pedologic and lithologic pairing in central Europe and parts of North America, soils can serve as the dominant mechanism impeding infiltration and promoting shallow lateral flow. Further, hydrograph analysis of vadose zone flow and aquifer discharge, suggests that storage associated with shallow soils is the dominant source of discharge at time scales of up to several weeks after melt events, while phreatic storage becomes import during prolonged periods without input. Soils can moderate karst aquifer dynamics and play a more governing role on karst aquifer storage and discharge than previously credited. Overall, this signifies that a fundamental understanding of soil structure and distribution is critical when assessing recharge to karstic aquifers, particularly in cold regions.

Summary Above a shallow unconfined aquifer, a considerable amount of water is stored in the vadose zone. Through water exchange with the underlying unconfined aquifer, the vadose zone affects the groundwater table dynamics and overall behavior of the aquifer. In this paper, we examine tide-induced groundwater table fluctuations in unconfined aquifers influenced by vadose zone of finite thickness. Under the condition of small aquifer thickness ( D ) compared with the groundwater wavelength ( L ) (i.e., μ 2 = D / L 2 ≪ 1 ) and small boundary oscillation amplitude ( a ) (i.e., e = a / D ≪ 1 ) (where μ 2 and e are two parameters), an approximate analytical solution was derived to quantify systematically the vadose zone effects, with a particular consideration of capping by the ground surface, i.e., the upper boundary of the vadose zone. Depending on the extent to which the capillary rise is truncated by the ground surface, the vadose zone enhances the groundwater table fluctuations in an unconfined aquifer. However, the mean groundwater table height and exchange between surface water and groundwater are reduced due to the presence of the vadose zone. These effects are intensified with increased capillary rise, but weakened as the vadose zone thickens. This study provides a criterion for assessing the importance of vadose zone in modulating the response of unconfined aquifers to low-frequency forcing oscillations such as tides.

We characterize the fracture pattern, including both meso-scale joints and macro-scale faults, within the central sector of Sierra de las Nieves (Betic Cordillera, S Spain), which contains one of the largest karstification systems in Europe. Structural data were compared with the direction pattern of the karstic conduit network of the largest caves. Carbonate rocks were deformed in a collisional setting and exposed at the surface since the early Miocene. Normal and normal–oblique faults trending NW–SE to WNW–ESE are the most prominent brittle structures, having formed coevally with shorter NE–SW normal to normal–dextral after the main thrusting phase. In addition, two main open joint sets striking NW–SE and NE–SW developed on a broad scale. Orthogonal normal faults and open joints suggest an extensional setting characterized by horizontal minimum (S3) and intermediate (S2) stress axes of similar magnitudes that intermittently shifted their positions during the middle-to-late Miocene. Vertical water flow coming from direct recharge sectors tends to infiltrate across these high-dipping faults, mainly concentrating at fault intersections, thus favoring sub-vertical conduit formation within the vadose zone. Horizontal paleo-phreatic levels are perched linked to the recent uplift undergone by the sector, giving us the opportunity to analyze the incidence of fractures at the phreatic zone. Joint sets determine the hydraulic anisotropy within the former phreatic levels. Because our study illustrates the primary role of diverse tectonic structures during massive multiphase cave development above and below the water table, it could contribute to better constraining of the models of karstic conduit formation.

Tectonic research and morphological observations were carried out in six caves (Kalacka, Goryczkowa, Kasprowa Nizna, Kasprowa Średnia, Kasprowa Wyznia and Magurska) in the Bystra Valley, in the Tatra Mountains. There are three cave levels, with the youngest active and the other two inactive, reflecting development partly under epiphreatic and partly under phreatic conditions. These studies demonstrate strong control of the cave pattern by tectonic features, including faults and related fractures that originated or were rejuvenated during uplift, lasting from the Late Miocene. In a few local cases, the cave passages are guided by the combined influence of bedding, joints and fractures in the hinge zone of a chevron anticline. That these cave passages are guided by tectonic structures, irrespective of lithological differences, indicates that these proto-conduits were formed by “tectonic inception”. Differences in the cave pattern between the phreatic and epiphreatic zones at a given cave level may be a result of massif relaxation. Below the bottom of the valley, the effect of stress on the rock mass is related to the regional stress field and only individual faults extend below the bottom of the valley. Thus in the phreatic zone, the flow is focused and a single conduit becomes enlarged. The local extension is more intense in the epiphreatic zone above the valley floor and more fractures have been sufficiently extended to allow water to flow. The water migrates along a network of fissures and a maze could be forming. Neotectonic displacements (of up to 15 cm), which are more recent than the passages, were also identified in the caves. Neotectonic activity is no longer believed to have as great an impact on cave morphology as previously was thought. Those faults with displacements of several metres, described as younger than the cave by other authors, should be reclassified as older faults, the surfaces of which have been exposed by speleogenesis. The possible presence of neotectonic faults with greater displacements is not excluded, but they would have had a much greater morphological impact than the observed features suggest.

The Ogallala-High Plains aquifer is an important resource for irrigated agriculture in a semi-arid region of the United States. Steep declines in groundwater levels are putting increasing strain on the viability of the aquifer for irrigation, necessitating improved estimates of recharge rates and sources to the aquifer. This study uses a combined approach to obtain high resolution geochemical and isotopic composition of the vadose zone and aquifer pore fluids to better understand recharge dynamics to the aquifer. Significant differences between the shallow, intermediate and deep vadose zone and shallow and deep aquifer indicate modern precipitation is not providing a significant source of recharge to the aquifer across a large area (diffuse recharge). Rather, recharge to the aquifer is a result of either focused recharge or long-term, delayed drainage from the portion of the vadose zone which was saturated before irrigation development.

Hydrochemical solute concentrations in the shallow subsurface can be spatially highly variable within small scales, particularly at interfaces. However, most monitoring systems fail to capture these small scale variations. Within this study, we developed a high resolution multilevel well (HR-MLW) with which we monitored water across the interface of the unsaturated and saturated zone with a vertical resolution of 0.05-0.5 m. We installed three of these 4 m deep HR-MLWs in the riparian zone of a third-order river and analyzed for hydrochemical parameters and stable water isotopes. The results showed three distinct vertical zones (unsaturated zone, upper saturated zone, lower saturated zone) within the alluvial aquifer. A 2 m thick layer influenced by river water (upper saturated zone) was not captured by existing monitoring wells with higher screen length. Hydrochemical data (isotopes, total ions) were consistent in all HR-MLWs and showed similar variation over time emphasizing the reliability of the installed monitoring system. Further, the depths zones were also reflected in the NO

Little is known about how trace metals accumulate and cycle in conduits within the phreatic zone. These water-filled conduits can receive floodwater that allows metals to accumulate, similar to air-filled caves, but are more susceptible to reducing conditions following floods because oxygen is limited to dissolved concentrations. If sufficient reactive organic carbon is transported into the aquifer, oxygen consumption will lower Eh and mobilize manganese and iron. To evaluate this accumulation and mobilization of metals, we analyzed the geochemical and isotopic composition of water, solid metal oxide, and limestone samples from two phreatic systems in north-central Florida where river water displaces aquifer water following storms. River water was a net source of trace metals to the aquifer; however, manganese depletion in the interior of the metal oxides relative to concentrations in intruding river water indicates not all metals are retained in the aquifer as redox conditions changed. The metal oxides are actively incorporating metals from floods, with anthropogenically sourced lead from surface water on the outer portion of the metal oxide.

International audience; The concept of superficial structure relates to surficial deformations that are determined neither by tectonic deformation nor by surface geomorphic processes sensu stricto. This work addresses two mechanisms leading to structural surface disturbances in the Lutetian strata of the Eocene plateaux of the eastern Paris Basin. Firstly, mechanical release which is associated with stress-relief during Quaternary valley downcutting. It results in lateral spreading of the middle Lutetian limestone, and subsequent sub-erosion of underlying sands may cause valley-side cambering. Secondly, ghost-rock karstification in the phreatic zone which is leading to surficial collapse of the upper Lutetian cover. Geological structure (thickness and porosity of the middle Lutetian limestone) and valley-side slopes stratigraphy (position of the upper Ypresian sand) control the spatial distribution of these processes. Ghost-rock karstification, conditioned by tectonic joints is confined to the west; to the east, cambering processes occur where upper Ypresian sand aquifer and alluvial aquifer are connected. During the Quaternary, periglacial conditions account for cambering processes and also for a second phase of karstification within an aquifer perched in the active layer, and from mechanical release joints. Resultant morphological features are then inherited and cambering is even a fossil process where upper Ypresian sand crops out above the valley floor. Consequently, large-scale landforms, derived from the superficial structure, are essentially inactive.

Groundwater is the main need of society in everyday life. Groundwater is one of renewable resources but it doesn’t mean that it can be exploitated without limit. Several factors that affect the availability of groundwater derived from nature such as geological conditions, rainfall, and green areas should be considered. Water in the soil is stored in a porous layer and has a good permeability is called an aquifer. Cisarua area is located in West Bandung regency, West Java which is a hilly area that has a topography with a slope ranging from normal to steep. The land use in this area is still dominated with plantation and forest as green area. Groundwater aquifer characteristics in that area needs to be examined and analysed for the needs of the community and agricultural business. In this research, the writer used inversion modeling technique of geoelectric data to visualize the condition of subsurface. Resistivity inversion modelling of apparent resistivity data as a result of resistivity method with Wenner-Schlumberger configuration is then carried out with least-square method. The initial model is modified in an iterative manner such that the sum of square error of the difference between the model response and the observed data values is minimized. The result of resistivity modelling is used for analysis of aquifer characteristic such as lithology, depth and structure along with considering geological reference. As the result of modelling, the area of measurement is divided into three zones which are Zone of aeration, Zone of Saturation, and endapan formasi. Zone of aeration is located at depth 0-25 m with resistivity 20-100 Ohm.m and the predicted lithology is gravel or weathered soil. Zone of Saturation (akuifer) is located at depth 25-60 m with resistivity 4-30 Ohm.m and the predicted lithology is sandstone or clay. Endapan Formasi Cibereum is located at more than 60 m from ground with resistivity more than 100 Ohm.m and the predicted lithology is sandy tuff or dry breccia.

Multi-directional fluid flow and transport dynamics as intrinsic characteristics of hillslope flow regimes can strongly contribute to the quality evolution of groundwater resources and compartmentalization of subsurface ecosystems. However, their extent and importance in topographic highs (groundwater recharge areas) is typically less investigated, because productive groundwater bodies and thus monitoring activities are frequently lacking. In the Hainich Critical Zone Exploratory, we explored the hydrogeological functioning of the widely distributed setting of thin-bedded, alternating mixed carbonate-/siliciclastic bedrock, by using basic environmental timeseries. Up to 8-year records of weather parameters, ground temperatures, multi-depth hydraulic heads, and non-conservative tracers, were exploited applying a scheme for the exploratory analysis of dis-/continuous groundwater quality data. We identified transient, multi-directional flow dynamics, comprising fluctuating perched groundwater, localized recharge and groundwater mounding in the aeration zone that modify and partly reverse flow patterns in the phreatic zone. This interplay of flow dynamics within the hillslope aeration and phreatic zone causes significant re-distribution (e.g. oxygen, nitrate) that even overcome the “protective cover” of thick argillaceous strata by supplying surface-sourced substances to deep groundwater resources. As a factor for ecosystem compartmentalization, our results further suggest to carefully consider the hillslope multi-directional flow and matter exchange in biogeochemical models, as well as in resource protection and groundwater management practices.

A sophisticated dual-permeability flow model of the T-tunnel complex, Rainier Mesa, Nevada National Security Site, was developed and calibrated to facilitate predictions of radionuclide transport from underground nuclear tests within a perched zone of saturation downward through a series of variably saturated, sparsely fractured and faulted Tertiary tuff units to a regional flow system. The hydrogeologic complexity of the site necessitated a multistage calibration effort to capture the dominant flow characteristics of the site including: laterally and vertically extensive saturation in the Tertiary volcanics, pressure heads consistent with water level measurements, variably saturated flow conditions involving a thin unsaturated zone situated between two saturated zones, unsaturated Paleozoic carbonates located immediately adjacent to saturated Tertiary volcanic units, and fracture saturations congruent with field observations that range from fully saturated to dry. The incorporation of discontinuous fault networks into the dual-permeability model played a key role in reproducing the salient hydrologic features of the site. Successful model reproduction of observed cumulative tunnel discharge volume and tunnel discharge rates before tunnel sealing served as a novel transient test of the ability of the discontinuous fault networks to realistically honor field-scale fault network connectivity and permeability. The excellent reproduction of field observations by the numerical model, and the uniqueness of the primary parameters used to calibrate the model, demonstrate the advantage of incorporating discontinuous fault networks over equivalent fracture properties in sparsely fractured, dual-permeability media.

This research was financially supported by Observatoire Hommes/Milieux Vallee du Rhone, The Royal Society (RG100590), The Carnegie Trust for the Universities of Scotland, and the Rhone-Alpes region via the ARC Environment program 2013. We also acknowledge NERC PhD studentship support to Sargeant and Evans. Seasonal and annual partitioning of water within river floodplains has important implications for ecohydrologic links between the water cycle and tree growth. Climatic and hydrologic shifts alter water distribution between floodplain storage reservoirs (e.g., vadose, phreatic), affecting water availability to tree roots. Water partitioning is also dependent on the physical conditions that control tree rooting depth (e.g., gravel layers that impede root growth), the sources of contributing water, the rate of water drainage, and water residence times within particular storage reservoirs. We employ instrumental climate records alongside oxygen isotopes within tree rings and regional source waters, as well as topographic data and soil depth measurements, to infer the water sources used over several decades by two co-occurring tree species within a riparian floodplain along the Rhône River in France. We find that water partitioning to riparian trees is influenced by annual (wet versus dry years) and seasonal (spring snowmelt versus spring rainfall) fluctuations in climate. This influence depends strongly on local (tree level) conditions including floodplain surface elevation and subsurface gravel layer elevation. The latter represents the upper limit of the phreatic zone and therefore controls access to shallow groundwater. The difference between them, the thickness of the vadose zone, controls total soil moisture retention capacity. These factors thus modulate the climatic influence on tree ring isotopes. Additionally, we identified growth signatures and tree ring isotope changes associated with recent restoration of minimum streamflows in the Rhône, which made new phreatic water sources available to some trees in otherwise dry years. Publisher PDF

Managed aquifer recharge (MAR) will play an increasingly important role in solving water scarcity. The performance of MAR systems depends primarily upon local hydrogeology. Greatest opportunities for improvement in the implementation of MAR systems lie in the targeted application of conventional and advanced technologies to improve aquifer characterization. Surface geophysics (e.g., VES, TDEM, and seismic reflection and refraction) generally provide low resolution, but areal extensive data on subsurface hydrogeology. Times series of relative microgravity measurements have been used to map changes in both vadose and phreatic zone storage and to augment monitoring well systems. Surface nuclear magnetic resonance (NMR) has the potential to provide quantitative data on water-filled porosity and pore size distribution and, in turn, an estimate of hydraulic conductivity. Standard borehole geophysical logging techniques can provide coarse-scale data on aquifer heterogeneity. Advanced borehole logging techniques, such as NMR, microresistivity imaging, and gamma ray spectroscopy, have been used in MAR projects in the USA and UAE to provide fine-scale petrophysical data (e.g., porosity, porosity-types, and pore-size distribution). Groundwater modeling is used in MAR investigations to evaluate system feasibility and to optimize system design and operation. Opportunities to improve groundwater modeling exist through the application of advanced reservoir simulation platforms that allow for the processing and integration of available lithological, geophysical, and aquifer testing data and their subsequent incorporation into groundwater flow models. Advanced groundwater modeling programs are available that allow for the simulation of complex aquifers such as dual-porosity systems and variable density.

In this study, depth of phreatic zone of Malayer plain, which is the third largest plain of the province, has been investigated. The drainage basin of Malayer water, covering an area of 2965 km 2 , is located 80 km south of Hamadan. For this study, performance records of 43 existing wells were monitored over a period of 17 years (1994-2011). Data obtained were subjected to statistical analysis. The aquifer level hydrograph and equipotential maps were drawn in AutoCAD environment. The results of this study are indicative of the estimation of a 20.20 meter total dip and a 415.96 million-cubic-meter reservoir volume shortage in the 17 year period, caused by uncontrolled exploitations. In the water year of 1998-1999 the dip amount has reached 3.72 meters which is equivalent to more than one sixth of the total dip. The largest dip between years 1999-2010 with 39 meters was in Aznav village and the smallest dip in the same period of time with 1.08 meters was in Farvaz village. From the elements of dropping the phreatic surface, precipitation decrease and waiving the maximum exploitation limits through under-exploitation wells could be mentioned.

The problem of groundwater flow in an unconfined aquifer, formulated as a free-surface problem, is solved numerically through a new approach by employing the arbitrary Lagrangian-Eulerian (ALE) method. The domain of interest is three dimensional or a two dimensional vertical cross-section of a phreatic zone of an aquifer, where the groundwater table is the upper boundary that is allowed to move. The ALE method allows capturing the location of the free-surface by transforming the moving domain to a fixed reference domain through arbitrary forced boundary conditions. The results of the verification runs of this new approach agree well with the known analytical solutions for aquifer characterization tests. Beside the comprehensive and accurate evaluation of the groundwater flow in the tested cases, the approach is also suitable for modeling complex situations. The implementation of our method for selected cases is illustrated by means of practically relevant examples. Steady state unconfined groundwater flow simulation.Tracking free-surface using arbitrary Lagrangian-Eulerian (ALE) method.Good agreement with classic analytical solutions.Flexible application for single borehole pumping and injection model set-ups.

A VDEAL (V is the lithology of the vadose zone, D is the groundwater depth, E is the degree of groundwater exploitation, A is the aquifer characteristics and L is the land use pattern.) model, which is suitable for a vulnerability evaluation of the groundwater in arid inland areas, and that is based on the GOD (G is the groundwater status, O is overburden feature and D is groundwater depth) method and DRASTIC (D is the depth of water-table, R is the net recharge, A is the aquifer media, S is the soil media, T is the topography, I is the impact of the vadose and C is the conductivity of the aquifer.) model is proposed in this paper. Five indicators were selected by reference to the DRAV (D is the depth of water-table, R is the net recharge, A is the aquifer media and V is the impact of the vadose.) and VLDA (V is the lithology of the vadose zone , L is the land use pattern, D is the groundwater depth and A is the aquifer characteristics and.) models, namely, the lithology of the vadose zone (V), the groundwater depth (D), the degree of groundwater exploitation (E), the aquifer characteristics (A) and the land use pattern (L). According to monitoring data from 2003 and 2011, the variations of phreatic water quality in the plain area of the Junggar Basin were divided into three types: the water quality may have deteriorated, be unchanged or improved. Four groups of indicator weights were configured to calculate the vulnerability index using the VDEAL model. The changes of phreatic water quality were then compared against the vulnerability index. The normalized weights of V, D, E, A, and L were respectively 0.15, 0.25, 0.10, 0.10, and 0.40, this is according to the principle that the sampling sites of deteriorated water quality are generally distributed in a high-vulnerability region, and the sites of unchanged and improved water quality are distributed in middle vulnerability, low vulnerability and invulnerable regions. The evaluation results of phreatic water vulnerability in the plain area of the Junggar Basin based on the VDEAL model are as follows. The regions with vulnerability indexes of 2.0–4.0, 4.0–6.0, 6.0–8.0, and &gt, 8.0, respectively account for 2.2%, 61.0%, 35.9%, and 0.9% of the region. The regions with a higher vulnerability are mainly distributed in the farmlands and the sand and gravel regions with a phreatic water depth of &lt, 3 m. Moreover, the regions with a lower vulnerability are generally located in the non-irrigation regions with a sandy loam or silty fine sand and a phreatic water depth of &gt, 6 m. The phreatic water in these regions is deficient with regard to the infiltration of irrigation water and the recharge from precipitation.

Microcrustacean (Copepoda, Ostracoda) assemblages were investigated at the interface of the vadose and phreatic zones in the alpine karstic aquifer from the Julian Alps in Slovenia (SE Europe). Two temporary and one perennial karstic outlets were sampled by filtering the water several times over 2 years. Concurrently, benthos from the mouth of a perennial spring and from an adjacent spring brook were collected. Altogether 24 microcrustacean species were recorded. The spatial and temporal variation in drift densities and species composition was high indicating complex groundwater hydrological pathways being dependent on precipitation regime. Non-metric Multidimensional Scaling (NMDS) clearly separated drift samples from temporary springs and other sample groups (drift in perennial spring, spring mouth and spring brook benthos). ANOSIM revealed statistically significant differences between all sample groups (Diacyclops zschokkei, Elaphoidella phreatica and Mixtacandona sp. B contributed over 50 % to the observed differences among sample groups. Three species (Nitocrella sp., Speocyclops infernus, Lessinocamptus pivai), known to be typical epikarst species, were collected only in the drift from one temporary spring (T2). Mao Tau species accumulation curves did not reach asymptote for the drift from temporary springs, but did for the drift from perennial spring, and for the spring mouth and the spring brook benthos. The results on drift composition indicated the variation in the origin of the water discharging at the interface of vadoze and phreatic zones depending greatly on water level conditions, while the drift densities were higher in the water presumably discharging from phreatic zone (perennial spring and temporary springs during low water levels). Julian Alps; alpine karst; groundwater; drift; Copepoda; Ostracoda

In this paper, numerical simulations of regional-scale groundwater flow of North Bengal Plain have been carried out with special emphasis on the arsenic (As)-rich alluvium filled gap between the Rajmahal hills on the west and the Garo hills on the east. The proposed concern of this modelling arose from development that has led to large water table declines in the urban area of English Bazar block, Malda district, West Bengal and possible transport of As in the near future from the adjacent As-polluted aquifer. Groundwater occurs under unconfined condition in a thick zone of saturation within the Quaternary alluvial sediments. Modelling indicates that current pumping has significantly changed the groundwater flowpaths from pre-development condition. At the present pumping rate, the pumping wells of the urban area may remain uncontaminated till the next 25 yrs, considering only pure advection of water but some water from the As-polluted zone may enter wells by 50 yrs. But geochemical and other processes such as adsorption, precipitation, redox reaction and microbial activity may significantly retard the predicted rate by advective transport. In the rural areas, majority of the water pumped from the aquifer is for irrigation, which is continuously re-applied on the surface. The near-vertical nature of the flowpaths indicates that, where As is present or released at shallow depths, it will continue to occur in pumping wells. Modelling also indicates that placing all the pumping wells at depths below 100 m may not provide As-free water permanently.

The Frasassi caves present a unique opportunity to study sulfuric acid speleogenesis in a large karst system that contains active sulfidic processes as well as relict features produced by past speleogenetic episodes. The caves consist of a network of ramifying, mainly subhorizontal passages that reach more than 30 km in total length, and are organized in superimposed and interconnected levels. Sulfidic groundwaters are accessible in the lowermost levels. The water chemistry in the shallow phreatic zone is influenced by mixing phenomena between the sulfidic groundwaters and descending oxygenated water and, to some extent, gas exchange with the cave atmosphere. The sulfidic waters are corrosive with respect to limestone, with average limestone dissolution rates around 100 mm 10−3 year−1 for submerged tablets. The release of gases to the air also causes wall corrosion (linear corrosion rate up to 85 mm 10−3 year−1), which produces gypsum replacement crusts above the water table. Morphological and isotopic analyses show that large relict gypsum deposits in the upper dry levels were created by the same mechanism. Sulfide-oxidizing chemosynthetic bacteria living in the cave produce organic matter and support a rich and diverse ecosystem in the sulfidic branches, and these microorganisms contribute to sulfur cycling and cave formation processes. The evolution of the older cave levels during the Pleistocene was a complex result of changing regional geomorphological and hydrogeological regimes as well as local factors that affect water movement and gas exchange in the shallow phreatic zone within the cave.

The paper presents the varied presence of nitrates and phosphates in water from caves located in Częstochowa and Kraków, in urban, strongly anthropogenic conditions, representing the vadose zone of the fissure-karstic-porous massif of Upper Jurassic limestones. Hydrochemical research was carried out by the authors in the Cave on the Stone in Częstochowa in 2012–2015, in caves of the Zakrzówek horst from 1996 to 2002, and in the Dragon’s Cave by the research team of J. Motyka in 1995–1998. A number of NO3 and PO4 measurements were performed in waters sampled at these research sites: 20 measurements each ofNO3 and PO4 at the Cave on the Stone, 228 of NO3 and 422 of PO4 at Zakrzówek, and 19 each of NO3 and PO4 at the Dragon’s Cave. To assess the quality aspect of N and P compounds in waters from the Cave on the Stone, the results of geochemical modelling were processed using PHREEQC software. In cave waters, the oxidised form of nitrogen NO3 − predominates; in surface waters in the vicinity, unoxidised forms prevail: NH4+, NH3, and NH4SO4 −. Among phosphorus speciations, dissolved forms are dominant: HPO4 2−, H2PO4 −, and the insoluble form CaHPO4; in surface waters, these forms are practically absent. Transformations of water chemistry in ‘urban’ caves, often centuries old, manifest themselves in, inter alia, the occurrence of multi-ionic waters, including seasonal variations and extremely diversified concentrations, with very high concentrations in subpopulations of NO3 (0.2–485 mg dm−3) and P (0.02–6.87 mg dm−3). The common presence of NO3 in waters of the phreatic zone of the Częstochowa Upland, an area developed in an agricultural direction, is documented by, inter alia, the exploitation of intakes supplying the city of Częstochowa (10–57 mg dm−3, 2011) and crenological studies from 2008 to 2015 (NO3, 2–58 mg dm−3), at simultaneously low phosphate concentrations (PO4, 0.02–0.24 mg dm−3).

Hypogene speleogenesis is important for karstification in the Apennines because of widespread, aggressive groundwaters containing endogenic H2S and CO2. Evidence for karst processes can be found throughout the region, from solutional limestone caves to deposition of carbonate travertine. The caves are up to few tens of kilometers long and show different patterns, ranging from phreatic to almost ideal water table caves. The caves often have a maze pattern and contain large rooms, cupola roofs, blind pits, and anastomotic zones. Solutional processes prevailed in the phreatic zone, also in deep-seated conditions, but subaerial corrosion is developed as well and can play an important morphogenetic role. The main cave-forming processes are related to the H2S oxidation to sulfuric acid, a process that involves chemotrophic microbial activity, and are responsible for the diffuse deposition of replacement gypsum in subaerial conditions. The great variety of geological settings makes the Apennines a good place to study hypogene karst, and the existence of active branches in several caves also permits a direct study of the cave-forming processes and the comparison with the resultant morphologies.

The karst area of Acquasanta Terme is located in the eastern side of central Apennine. The thermal sulfidic springs reach the surface in the core of the anticline where the river valley reaches the top of a Meso-Cenozoic limestone succession, capped by less permeable rocks. An important terraced travertine deposit was produced by the thermal water throughout the Pleistocene. The most interesting caves are in the valley of the Rio Garrafo, a tributary of the Tronto River. These caves developed mainly below the valley bottom, and a part of the stream water sinks through preexisting karst passages mixing with the thermal groundwater ~50 m below. Water temperature in the caves reaches 42 °C, and the water has high salinity (up to > 6 g L−1) with elevated levels of chloride, sulfates and carbonates. Sinking water from the caves and the travertine plate is responsible for the significant dilution of thermal water at the main spring, located 2 km downstream, in the Tronto Valley. The speleogenetic process is mainly related to H2S oxidation, which is enhanced by the recharge of oxygenated fresh water from the surface. Cave development occurred in different phases. Early passages formed mainly in the phreatic zone, due to the rising thermal water. Deepening of the main surface stream (Tronto River) caused lowering of the water table. As a result, the Rio Garrafo caves were partly dried and invaded by sinking water, while rising gases activated condensation corrosion and the growth of replacement gypsum crusts.

Formation of extensive phreatic caves in eogenetic karst aquifers is widely believed to require mixing of fresh and saltwater. Extensive phreatic caves also occur, however, in eogenetic karst aquifers where fresh and saltwater do not mix, for example in the upper Floridan aquifer. These caves are thought to have formed in their modern settings by dissolution from sinking streams or by convergence of groundwater flow paths on springs. Alternatively, these caves have been hypothesized to have formed at lower water tables during sea level low-stands. These hypotheses have not previously been tested against one another. Analyzing morphological data and water chemistry from caves in the Suwannee River Basin in north-central Florida and water chemistry from wells in the central Florida carbonate platform indicates that phreatic caves within the Suwannee River Basin most likely formed at lower water tables during lower sea levels. Consideration of the hydrological and geochemical constraints posed by the upper Floridan aquifer leads to the conclusion that cave formation was most likely driven by dissolution of vadose CO2 gas into the groundwater. Sea level rise and a wetter climate during the mid-Holocene lifted the water table above the elevation of the caves and placed the caves tens of meters below the modern water table. When rising water tables reached the land surface, surface streams formed. Incision of surface streams breached the pre-existing caves to form modern springs, which provide access to the phreatic caves. Phreatic caves in the Suwannee River Basin are thus relict and have no causal relationship with modern surficial drainage systems. Neither mixing dissolution nor sinking streams are necessary to form laterally extensive phreatic caves in eogenetic karst aquifers. Dissolution at water tables, potentially driven by vadose CO2 gas, offers an underappreciated mechanism to form cavernous porosity in eogenetic carbonate rocks. Copyright © 2012 John Wiley & Sons, Ltd.

O,δ 2 H). The input signal (rainwater) was compared with the isotopic content of a 35-meter groundwater vertical prof ile, over a 1-year period. Within the studied aquifer, recharge and flow are diffuse in a well-connected fissure network. At the test site, the comparison between input and groundwater isotopic signals illustrates that no efficient mixing takes place in the whole unsaturated zone, between the fresh infiltration water and the stored water. When analysing the stable isotope composition of groundwater, significant variations were observed above the threshold elevation of 1062 m asl, while a nearly constant composition was observed below the same threshold. Thus, temporal variations in stable isotope composition of rainwater are completely attenuated just in the deeper phreatic zone. On the whole, taking into consideration also the results of previous studies in the same area, the investigations showed that physical characteristics of the carbonate bedrock, as well as aquifer heterogeneity, are factors of utmost importance in influencing the complete mixing of water. These findings suggest a more complex scenario at catchment scale.

Cave development is related to the geomorphic evolution. Their morphology, preserved far longer than correlative surface features allows reconstructing the regional history of the surrounding landscape. Modeling shows that initial cave development occurs along the water table with loops in the phreatic zone along fractures. Consequently, cave profiles and levels reflect the local base level and its changes. Cave profile is controlled by timing, geological structure, and recharge. In first exposed rocks, juvenile pattern displays steep vadose passages. In perched aquifers, vadose erosion produces large passage along aquiclude. In dammed aquifers, the main drain is established at the water table when recharge is fairly regular. But when irregular recharge causes backflooding, looping profiles develop throughout the epiphreatic zone. Interconnected cave levels correspond to some of the largest cave systems in the world. The oldest abandoned highest levels have been dated beyond 3.5 Ma (Mammoth Cave). However, when base level rises, the deepest parts of the karst are flooded; the flow rises along phreatic lifts, and discharges at vauclusian springs. In the epiphreatic zone, floodwater produces looping tubes above the low-flow water table. In such a case of baselevel rise, per ascensum speleogenesis can produce higher-elevation passages that are younger than passages at lower elevations. Base-level rises occur after tectonic subsidence, filling of valleys, or sea-level rise, as for instance around the Mediterranean in response to the Messinian Crisis. Deep-phreatic karst, if not hypogenic, can generally be attributed to flooding by a base-level rise. L’évolution des cavités dépend de l’évolution géomorphologique. Leurs morphologies, beaucoup mieux conservées que les témoins de surface correspondants, permettent de reconstituer l’évolution régionaledes paysages. Les modélisations montrent que le développement initial se produit à proximité de la surface piézométrique, avec des boucles le long des fractures plongeant dans la zone noyée. Par conséquent, le profil des cavités reflète la position du niveau de base et ses changements. Ce profil est contrôlé par le temps, la structure géologique et le mode de recharge. Lors d’une première karstification un réseau juvénile se développe, constitué de conduits vadoses inclinés. Dans les aquifères perchés, l’érosion torrentielle produit de vastes conduits ébouleux au contact du soubassement imperméable. Dans les aquifères barrés, lorsque l’alimentation est régularisée, le collecteur s’établit à proximité de la surface piézométrique. Quand l’alimentation est irrégulière, les mises en charge sont fréquentes et favorisent le développement d’un profil en montagnes russes dans la zone épinoyée. Les niveaux de cavités interconnectés ont produit certains des plus longs réseaux au monde. Dans Mammoth Cave (USA), les niveaux les plus hauts ont plus de 3,5 Ma. Cependant, en cas de remontée du niveau de base, les parties du karst les plus profondes sont ennoyées ; les écoulements remontent le long de puits-cheminées et émergent à des sources vauclusiennes. Dans la zone épinoyée, les mises en charge produisent des conduits en montagnes russes au-dessus de la surface piézométrique d’étiage. Dans ce cas de remontée du niveau de base, la spéléogenèse per ascensum produit des niveaux plus élevés qui sont finalement plus récents que les niveaux inférieurs. De telles remontées du niveau de base proviennent de subsidence tectonique, de remplissage de vallées, ou de remontées du niveau marin, ce qui fut le cas autour de la Méditerranée à la fin de la Crise messinienne. Par conséquent, les karsts noyés profonds, s’ils ne sont pas d’origine hypogène, peuvent être généralement attribués à des remontées du niveau de base.

Collapse dolines are among the most striking surface features in karst areas. Although they can be the result of different formation mechanisms, evidence suggests that large collapse dolines form due to chemical and mechanical removal of material at and below the level of groundwater. We have applied a genetic model of a two-dimensional fracture network to calculate the rate of dissolutional bedrock removal in the heavily fractured (crushed) zone intersecting a karst conduit in the phreatic zone. To account for infilling and breakdown processes in the crushed zone two simple rules were added to the basic model: 1) continuous infilling of dissolutionally created voids prevents fractures from growing beyond some limited aperture, although the dissolution proceeds, 2) discontinuous collapsing causes sudden closure of a fracture once some critical aperture has been reached. Both rules limit the transmissivity of the network and the related flow rates. Therefore, the constant head difference between the input and the output points is sustained and the flow remains distributed over the entire crushed zone. Provided that restrictions posed by the two rules permit turbulent flow, dissolution rates also remain high in the entire region. High surface area of water–rock contact and high dissolution rates result in high overall removal rates of rock from the crushed zone, one of the necessary conditions for the formation of large closed depressions. Despite the fact that the model neglects some processes and dynamics that would increase the removal rate, the results suggest that large closed depressions could form in the order of 1 million years.

We consider the case of pumping a semiconfined aquifer overlain by a phreatic aquifer hydraulically connected to an infinitely long and straight stream. The hydraulics of the system are described by a linearized model in which it is assumed that flow in the aquifers is essentially horizontal, and that drawdown in the phreatic aquifer is small enough to allow the water table to be sufficiently well described by the Theis equation. Fourier-Laplace transforms of drawdown are obtained and numerically inverted. Comparisons are made with another well-known analytic model of Hunt, who considered a single aquifer/aquitard system. It is observed that while both models may have excellent agreement during the initial phase of pumping, the longer-term consequences of sustained pumping are quite distinct.

A robust classification scheme for partitioning groundwater chemistry into homogeneous groups was an important tool for the characterization of Eocene limestone aquifer. The aquifer locally is composed of chalky limestone with thin clay intercalated (Samalut Fm.), the fissures, the joints, and the fractures are represented the conduits of the aquifer system. The flow patterns are conditioned by karstification processes which develop a conduit network and preserve low permeability microfractured blocks. The aquifer is mainly recharged by surrounding aquifers and agricultural wastewaters. The groundwater flows in the eastern part (due the Bahr Yossef and River Nile), which is a discharge area rather than a recharge. Twenty-eight groundwater samples was collected from the Eocene limestone aquifer and analyzed for isotopes, major, and trace elements. δD and δ18O concentrations ranged widely due to geology, infiltration of different surface waters, evaporation, and hydrogeology. The concentration of δD and δ18O isotopes is depleted in the northern zone of the northern part and western zone of the central and southern part of the study area. They are enriched due the eastern area of the central and southern part of the study area. δD vs. δ18O delineate the Pleistocene aquifer and has a strong influence than other waters on aquifer hydrogeochemistry. It is confirmed by the AquaChem outputs of the mixing proportions of different water types included in the aquifer system. Cl-δD and Cl-δ18O relationships indicate the role of evaporation especially due the eastern area of the central and southern part of the study area. This research tests the performance of the many available graphical and statistical methodologies used to classify water samples. R-mode clustering, correlation analysis, and principal component analysis were investigated. All the methods were discussed and compared as to their ability to cluster, ease of use, and ease of interpretation. Nearly most low-salinity waters are in equilibrium to supersaturate with respect to both carbonate minerals, while it is shifted to undersaturate with salinity. The inverse modeling findings clarify that the calcite, gypsum, and anhydrite dissolution increased due the northeastern area, middle zone, and southern corner of the northern, central, and southern part of the study area, respectively. The latter areas also were characterized by the lowest precipitation of the dolomite. Such areas are distinguished by much more enhancement for aquifer permeability and therefore transmissivity. The latter areas can be use as injection zone by fresh water. It can be a triple function; firstly, it recharges the saline Eocene limestone aquifer through the enhancement hydraulic conductivity and dilutes it. Secondly, it enhances much more the aquifer permeability and therefore the transmissivity. The Eocene limestone aquifer can be improved in quality and quantity by using such a model and exploits it as an alternative water resource with Quaternary aquifer and Nile water. Thirdly, it irrigates more areas to increase the income/capita. The dedolomitization represents the main hydrogeochemical process in the aquifer system. The geomedia (limestone, clay, marl, shale, and sand deposits) are in contact with water, therefore, the rock/water interaction, mixing, and ion exchange were estimated by the geochemical evolution of the groundwater systems.

Little is known about the hypogean fauna of Algeria, with studies mostly dating to the beginning of the twentieth century (Gurney 1908; Racovitza 1912; Monod 1924; Pesce and Tetè 1978); moreover, the knowledge varies markedly among regions. In this study, we examined the composition and distribution of the invertebrate communities in the phreatic zone of the Tafna aquifer (N-W Algeria). Twelve wells close to the Tafna wadi, ranging between 120 and 1100 m a.s.l., were studied from May 2005 to March 2006. Many specimens belonging to 37 taxa were collected, the most frequent taxa being Typhlocirolana sp., a stygobitic Gammaridae species, Cyclopidae and Ostracoda. Other crustacean species were relatively scarce, with discontinuous distribution, being present only in a few wells. The taxonomic richness and abundance of stygobitic crustacean communities were relatively constant over time. The spatial distribution of stygobionts was mainly related to the exchanges with surface water.

Summary From analysis of the hydrodynamic and hydrochemical responses of karst springs, it is possible to know the behaviour of the aquifers they drain. This manuscript aims to contribute to the characterization of infiltration process, and to determine the relative importance of the saturated zone and of the unsaturated zone in the hydrogeological functioning of carbonate aquifers, using natural hydrochemical tracers. Thus, chemical components together with temperature and electrical conductivity (both punctual and continuous records) have been monitored in three springs which drain Alta Cadena carbonate aquifer, Southern Spain. An evaluation of the percentage of the electrical conductivity frequency peaks determined for each of the three springs is linked to the chemical parameters that comprise the conductivity signal. One of these springs responds rapidly to precipitation (conduit flow system), due to the existence of a high degree of karstification in the unsaturated zone and in the saturated zone, both of which play a similar role in the functioning of the spring. Another spring responds to precipitation with small increases in water flow, somewhat lagged, because the aquifer has a low degree of karstification, even in the unsaturated zone, which seems to influence its functioning more strongly than does the saturated zone. The third spring drains a sector of the aquifer with a moderately developed degree of karstification, one that is intermediate between the other two, in which both the unsaturated zone and the saturated zone participate in the functioning of the spring, but with the latter zone having a stronger influence. These three springs show different hydrogeological functioning although they are in similar geological and climatic contexts, which show the heterogeneity of karst media and the importance of an adequate investigation for groundwater management and protection in karst areas.

The vadose zone is the main region controlling water movement from the land surface to the aquifer and has a very complex structure. The use of non-invasive or minimally invasive geophysical methods especially electrical resistivity imaging is a cost-effective approach adapted for long-term monitoring of the vadose zone. The main aim of this work is to know the fractures in the vadose zone, of granitic terrene, through which the recharge or preferred path recharge to the aquifer takes place and thus to relate moisture and electrical resistivity. Time lapse electrical resistivity tomography (TLERT) experiment was carried out in the vadose zone of granitic terrene at the Indian Geophysical Research Institute, Hyderabad along two profiles to a depth of 18 m and 13 m each. The profiles are 300 m apart. Piezometric, rainfall and soil moisture data were recorded to correlate with changes in the rainfall recharge. These TLERT difference images showed that the conductivity distribution was consistent with the recharge occurring along the minor fractures. We mapped the fractures in hard rock or granites to see the effect of the recharge on resistivity variation and estimation of moisture content. These fractures act as the preferred pathways for the recharge to take place. A good correlation between the soil moisture and resistivity is established in the vadose zone of granitic aquifer. Since the vadose zone exhibits extremely high variability, both in space and time, the surface geophysical investigations such as TLERT have been a simple and useful method to characterize the vadose zone, which would not have been possible with the point measurements alone. The analyses of the pseudosection with time indicate clearly that the assumption of the piston flow of the moisture front is not valid in hard rocks. The outcome of this study may provide some indirect parameters to the well known Richard's equation in studying the unsaturated zone.

Most conceptual models of epigenic conduit development assume that conduits sourcing karst springs form as water that is undersaturated with respect to carbonate minerals flows from recharge to discharge points. This process is not possible in springs fed by distributed recharge that is transmitted through aquifer matrix porosity, such as unconfined aquifers in eogenetic carbonate rocks. Diffusely recharged water has a long residence time within the aquifer, and thus would have equilibrated with the aquifer rocks prior to discharge to the conduits. The upper Floridan aquifer has high matrix permeability (∼10 −13 m 2 ), and many springs lack discrete inputs of undersaturated allogenic water in their recharge areas. Consequently, another explanation for their development is necessary. During flooding of the Suwannee River in north-central Florida, water highly undersaturated with respect to carbonate minerals commonly recharges the upper Floridan aquifer through spring vents, and solution scallops oriented away from the vents suggest most dissolution along conduit walls occurs during these flow reversals. During a single flow reversal at the Peacock Spring cave system, flood water was capable of dissolving up to 3.4 mm of the conduit wall rock. Dissolution occurs as flow reversals follow preexisting features that include joints and paleo–water-table caves. Lack of speleothems in conduits in the upper Floridan aquifer has been used as evidence that the caves formed in the phreatic zone; however, flooding would dissolve any speleothems that may have formed during previous subaerial exposure. Conduit enlargement during flow reversals suggests that dissolution can progress in the normal upstream directions, and this process may be an important driver of dissolution in any karst aquifer with outflows to surface water that are subject to flooding. Flow reversals would also introduce dissolved organic carbon and oxygen into the groundwater and provide important energy sources for cave ecosystems as well as altering redox chemistry of the aquifer water.

Water table dynamics, dissolved oxygen (DO) content, electrical resistivity (ER) in monitoring wells and air pressure in the vadose zone are monitored in air sparging (AS) accompanied by soil vapor extraction (SVE) at a hydrocarbon-contaminated groundwater site in Oman, where a diesel spillover affected a heterogeneous unconfined aquifer. The formation of a groundwater mound at the early stage of air injection and potential lateral migration of contaminants from the mound apex called for an additional hydrodynamic barrier constructed as a pair of pump-and-treat (P&T) wells whose recirculation zone encompassed the AS and SVE wells. In all monitored piezometers the phreatic surface showed a rapid and distinct peak, which is attributed to the time of air breakthrough from the injection point to the vadose zone and a relatively mild recession limb interpreted as a decay of the mound. Tracer tests showed a layer of a relatively low hydraulic conductivity at an intermediate depth of the screened interval of the wells. Increased levels of DO and borehole air pressure that have been observed (as far as 50 m away) are likely mitigated by SVE and P&T. Radius of influence can be indirectly inferred from ER and DO changes in the AS operation zone. Salt tracer tests have shown that groundwater velocity within the AS zone decreases with the increase of air injection rate.