Karst Aquifer System Research Articles

Using Hydrogeophysical Techniques to Characterise and Map Sea Water Intrusion and Preferential Flow Paths in Howards East Aquifer, Darwin Rural Area, Northern Territory

In the Howards East Aquifer (HEA) in Darwin’s Rural District, groundwater resources in a dolomitic and karstic aquifer system provide important water security for Darwin and a large horticultural i...

Contribution of isotopic research techniques to characterize high-mountain-Mediterranean karst aquifers: The Port del Comte (Eastern Pyrenees) aquifer

Water resources in high mountain karst aquifers are usually characterized by high rainfall, recharge and discharge that lead to the sustainability of the downstream ecosystems. Nevertheless, these hydrological systems are vulnerable to the global change impact. The mean transit time (MTT) is a key parameter to describe the behavior of these hydrologic systems and also to assess their vulnerability. This work is focused on estimating MTT by using environmental tracers in the framework of high-mountain karst systems with a very thick unsaturated zone (USZ). To this end, it is adapted to alpine zones a methodology that combines a semi-distributed rainfall-runoff model to estimate recharge time series, and a lumped-parameter model to obtain ΜΤΤ. The methodology has been applied to the Port del Comte Massif (PCM) hydrological system (Southeastern Pyrenees, NE Spain), a karst aquifer system with an overlying 1000 m thick USZ. Six catchment areas corresponding to most important springs of the system are considered. The obtained results show that hydrologically the behavior of the system can be described by an exponential flow model (EM), with MTT ranging between 1.9 and 2.9 years. These ΜΤΤ values are shorter than those obtained by considering a constant recharge rate along time, which is the easiest and most applied aquifer recharge hypothesis when estimating ΜΤΤ through lumped-parameter models.

FDOM Conversion in Karst Watersheds Expressed by Three-Dimensional Fluorescence Spectroscopy

A karst system, formed by the dissolution of carbonate rocks, is usually susceptible to contamination. Little is known about the composition of natural dissolved organic matter (DOM) in groundwater systems, especially in karstic groundwater. To reveal the characteristics of DOM in a karst aquifer, the Yufuhe River Basin, a typical karst watershed in northern China, was selected. DOM fluorescence (FDOM) was measured with the excitation-emission matrices (EEMs) spectroscopy technique. Parallel factor analysis (PARAFAC) was used to analyze the karst hydrogeological factors that affect FDOM biogeochemical behavior. Three fluorescent components, i.e., tyrosine-like, tryptophan-like, and ultraviolet fulvic acid were found. Their fluorescence properties were closely related to human activity and subterranean hydrology. Fluorescence properties suggested that FDOM in the Yufuhe River karst aquifer was predominant from anthropogenic activity. In addition, due to the effect of karstic heterogeneous hydrological conditions, FDOM showed obvious differentiation in the recharge, flow path, and discharge systems. The FDOM fluorescence intensity (FI) was weak in surface water and groundwater at the upper reaches (recharge area). In the middle of the flow path area, the percentage of tyrosine-like and tryptophan-like substances degraded and fulvic acid rose gradually. However, after infiltrating into the lower reaches (discharge area) of the deep karst aquifer system, the fulvic acid matter was consumed and protein-like matter accumulated.

A New Perspective to Explore the Hydraulic Connectivity of Karst Aquifer System in Jinan Spring Catchment, China

Investigating the hydraulic connectivity of a complex karst aquifer system is an important research topic for sustainable operation and optimization layout of karst groundwater exploitation and recharge. However, the identification of preferential sites of recharge and exploitation is usually subject to regional hydrogeology conditions and the mechanisms of recharge and exploitation. The conventional research methods of hydraulic connectivity often have some limitations. In this study, we developed an improved grey amplitude relation model to explore the hydraulic connectivity in Jinan spring catchment and presented a quantized evaluation index water table fluctuation relation degree (WTFRD) using karst groundwater table data in Western Jinan and Jinan spring groups from 2014 to 2017. Results showed that the total WTFRD was 0.854 between Western Jinan and Jinan spring groups when the external distraction for karst groundwater table was the smallest, which was in high relation degree grade. Meanwhile, the change rules of karst groundwater table in the two sites were basically the same. Accordingly, a high connectivity occurred between the two karst aquifers from a statistical perspective, and further illustrated that Western Jinan could be selected as preferential experiment sites. A comprehensive case in Jinan spring catchment indicated that the WTFRD provided a preliminary idea to investigate hydraulic connectivity quantitatively. This method could be considered as a pre-study of the conventional experiments to form a high-efficiency and low-cost combined method, which has great potential and merits further study.

Effects of an abandoned Pb-Zn mine on a karstic groundwater reservoir

The release and transport of metals in active mines pose a threat to water quality when mine sites become abandoned. Karst aquifer systems are especially vulnerable due to their ability to quick transport polluted water over large distances through surface and subsurface routes. Surface and groundwater samples collected from the Guilin-Yangshuo Basin in southwestern China were analyzed for δ18O and δ2H of water, major and trace elements, including Sr, pH, temperature, and electrical conductivity to gain an understanding of how an abandoned Pb-Zn mine and its tailing deposits influence the groundwater quality of a downgradient karst carbonate aquifer. The δ18O and δ2H values of the water samples indicate that the karst aquifer is dominantly recharged by local precipitation during the wet season and additionally by water from upstream mountainous areas during the dry period. Severe heavy metal contamination (9154, 1081, 37 and 55 μg/L of Zn, Mn, Ni and Cd, respectively) was detected in the mine drainage water. Ninety-one percent of the downstream surface samples and 67% of the groundwater samples collected during the dry season exceeded the limit value for As (10 μg/L) according to the China Standards for Drinking Water Quality. Factor analysis was applied, and showed the river and groundwater were affected by the Pb-Zn mine and its tailing deposits and by carbonate dissolution. The Sidi River plays an important role in trace element transport, which supported by a strong correlation between sulfate and strontium (with r2 = 0.85 in the dry season; r2 = 0.94 in the wet season). The strong acid generated during sulfide oxidation of the mine tailings is neutralized by carbonate rock dissolution, resulting in neutral to alkaline water which hinders the mobility of trace elements. However, the increasing sulfate contents and the elevated total trace element concentrations (from undetectable to 1503 μg/L except for the mine drainage with 10,350 μg/L) confirm the release of toxic metals into the water system. In addition, adsorbed arsenate anions may exchange with dissolved carbonate anions and be released into the groundwater.

Water circulation in karst systems: comparing physicochemical and environmental isotopic data interpretation

Many studies have used physicochemical response observed at karst springs during storm events to investigate the concept of diffuse flow in karst systems, but the complete description of the karst systems including the interactions of all components is not fully understood. Studies have shown that physicochemical response measured at karst springs can decrease or increase in response to storm events. It is clear from these studies that the use of only physicochemical response in interpreting water circulation in karst systems can be ambiguous. In this study, both physicochemical and isotope (stable and radiogenic) responses at City Spring, Cookeville, Tennessee, during snowmelt were used to interpret the hydrological cycle of a karst system. At the beginning of snow melting, all physicochemical parameters dropped, and thereafter, temperature, Ca, Mg, and HCO3 increased steadily with increased discharge and total dissolved solids. In contrast, generally Na, Cl, and SO4 remained constant after dropping; however, very high values were observed in the spring water mixed with stormwater runoff. δ2H, δ18O, and 87Sr/86Sr of spring water were stable and contrastingly different from the snow, rain, and spring water mixed with stormwater runoff samples. CO2 pressure was higher than atmospheric and appeared to be degassing. The data suggest that spring discharge is a mix of pre-event water stored in the soil, epikarst zone, and underlying bedrock. The circulation depth is unknown, but is likely controlled by the amount of storm event recharge that occurs through the piston effect. There is little evidence to support dilution by snowmelt. This study shows that combining the techniques and data can provide greater insight into water circulation and monitoring of karst aquifer systems than applying the techniques and data individually.

Migration and Transformation of Dissolved Organic Matter in Karst Water Systems and an Analysis of Their Influencing Factors

Fluorescent substances are used as good tracers in dissolved organic matter (DOM) to identify the source of DOM and its geochemical behavior in a hydrological system. However, there are few studies on the karst aquifer system. Many parameters in karst systems affect the DOM spectral information. A typical karst watershed in Northern China was selected in this research. Excitation-emission matrices (EEMs), parallel factor analysis (PARAFAC), and hydrochemical data were applied to reveal the relationship between the composition and transformation of DOM fluorescent substances in different karst water-bearing spaces. The source of DOM and the effect of water chemistry on DOM transfer were also discussed. The results showed that DOM in exogenous surface water and karst surface water in the Yufu River watershed were mainly composed of tryptophan-like substances, while the DOM in shallow karst water and deep karst water consisted of tryptophan-like and tyrosine-like substances. A comprehensive analysis by fluorescence index (FI), biological index (BIX), and humification index (HIX) displayed that the DOM in shallow and deep karst water resulted from microbial decomposition. In contrast, the DOM in karst surface water and exogenous surface water resulted from land-based input and endogenous microbial decomposition, in which endogenous contributions occupy a large proportion. Due to the chemical parameters of karst water, these three kinds of fluorescent substances extracted by PARAFAC had obviously different characteristics, i.e., ① the tyrosine-like substances had a strong adaptability to Ca2+ and HCO3-, and the proportion of the tyrosine in karst water was relatively large; ② the tryptophan substance followed an opposite trend; and ③ there was a significant positive correlation between fulvic acid and TDS, turbidity, Cl-, and SO42-. Observations of the watershed runoff revealed that the DOM in shallow karst water in the upper reaches came mainly from the soil and microbial degradation. The organic matter underwent a large amount of microbial decomposition and exogenous input when the water was rejuvenated with springs. After infiltration to the deep karst water in the lower reaches, the DOM gradually were converted to low aromatic hydrocarbon organic compounds and decreased macromolecules of DOM. Subsequently, the fluorescence intensity was weakened. The principal component analysis (PCA) extracted three principal components. They were the water mineralization index, soil leaching index, and hydrochemical/biochemical process index. The water mineralization index consists of hydrochemical parameters reflecting the water infiltration, transformation, and flow conditions in the karst system. The soil leaching index contains TOC, NO3-, and protein-like indicators relating to the relationship between protein-like substances and soil and natural leaching. The hydrochemical/biochemical process index is composed of Ca2+, HCO3-, FI, and fulvic acid indicators that illustrate the water chemistry and biochemical processes in the karst water system. In addition, the study also showed that total fluorescence intensity, fulvate-like substances, and protein-like substances can be used as a tracer for rapid seepage, transformation, and aquifer fragility for karst water, respectively. The results of the study are important in understanding the biogeochemical cycle of DOM in the karst water system and also helpful for controlling organic pollution. It also provides a new tool for characterizing the geochemical processes of organic matter in karst system.

ERT, GPR, InSAR, and tracer tests to characterize karst aquifer systems under urban areas: The case of Quebec City

Urban infrastructures built over karst settings may be at risk of collapse due to hydro-chemical erosion of underlying rock structures. In such settings, mapping cave networks and monitoring ground stability is important to assure civil safety and guide future infrastructure development decisions. However, no technique can directly and comprehensively map these hydrogeological features and monitor their stability. The most reliable method to map a cave network is through speleological exploration, which is not always possible due to restrictions, narrow corridors/passages, or high water levels. Borehole drilling is expensive and is often only performed where the presence of karsts is suggested by other techniques. Numerous indirect and cost-effective methods exist to map a karst flow system, such as geophysics, geodesy, and tracer tests. This paper presents the outcomes from a challenging application in Quebec City, Canada, where a multidisciplinary approach was designed to better understand the groundwater dynamics and cave paths.Two tracer tests in groundwater flowing through the cave system indicated that water flows along an approximately straight path from the sinking stream to the spring. It also suggests the presence of a parallel flow path close to the one already partially mapped. This observation was confirmed by combining Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) techniques, and ultimately by observing voids in several boreholes drilled close to the main cave path. Lowering the water levels at the suspected infiltration zone and inside the karst, the infiltration cracks were identified and the hydraulic link between them was confirmed. In fact, almost no infiltration occurs into the karst system when the water level at the sinking stream drops below a threshold level. Finally, SAR interferometry (InSAR) using RADARSAT-2 images detected movements on few buildings located over a backfilled sinkhole intercepted by the karst system and confirmed the stability of the rest of the karst area. The knowledge of the flow system described in this paper is used by policy makers to assure civil security of this densely populated area.

Turbulent and Laminar Flow in Karst Conduits Under Unsteady Flow Conditions: Interpretation of Pumping Tests by Discrete Conduit‐Continuum Modeling

AbstractDue to the duality in terms of (1) the groundwater flow field and (2) the discharge conditions, flow patterns of karst aquifer systems are complex. Estimated aquifer parameters may differ by several orders of magnitude from local (borehole) to regional (catchment) scale because of the large contrast in hydraulic parameters between matrix and conduit, their heterogeneity and anisotropy. One approach to deal with the scale effect problem in the estimation of hydraulic parameters of karst aquifers is the application of large‐scale experiments such as long‐term high‐abstraction conduit pumping tests, stimulating measurable groundwater drawdown in both, the karst conduit system as well as the fractured matrix. The numerical discrete conduit‐continuum modeling approach MODFLOW‐2005 Conduit Flow Process Mode 1 (CFPM1) is employed to simulate laminar and nonlaminar conduit flow, induced by large‐scale experiments, in combination with Darcian matrix flow. Effects of large‐scale experiments were simulated for idealized settings. Subsequently, diagnostic plots and analyses of different fluxes are applied to interpret differences in the simulated conduit drawdown and general flow patterns. The main focus is set on the question to which extent different conduit flow regimes will affect the drawdown in conduit and matrix depending on the hydraulic properties of the conduit system, i.e., conduit diameter and relative roughness. In this context, CFPM1 is applied to investigate the importance of considering turbulent conditions for the simulation of karst conduit flow. This work quantifies the relative error that results from assuming laminar conduit flow for the interpretation of a synthetic large‐scale pumping test in karst.

Relevance Between Hydrochemical and Hydrodynamic Data in a Deep Karstified Limestone Aquifer: a Mining Area Case Study

Safe coal mining in a karst region requires that mining operations assess any disturbances in the hydrogeological functioning of local aquifers and flow systems, and determine if disruptions are likely in the mine. We studied the geologic, hydraulic, and geochemical characteristics of the deep Ordovician karstified aquifer in the Xinglongzhuang and Dongtan mines of the Yanzhou coal mining district (China). The presence of a 100 m deep research borehole in the Ordovician limestone aquifer nearby facilitated hydrochemical and hydrodynamic data collection. The buried depth affected karst rock porosity, and the reduced porosity increased karst development. This, in turn, affected the abundance of water in the karst fissure. In addition to calcite and dolomite, the Ordovician limestone contains gypsum, which dissolves to form sulfate ions. Hydraulic data revealed that the water abundance in the research area is comparatively low, except for the C8 syncline zone. The Ordovician strata in this area is located in the deep, slow-flow zone of a vertical karst aquifer system, and the drilling unit water inflow is very low, which could represent the water abundance of the aquifer. Understanding this complex flow system is critical to appropriately assess the area’s deep groundwater resources and guide decision making regarding coal extraction.

Hydrogeological Investigation of a Karst Aquifer System

This study aims to present the hydrogeological and hydrochemical characteristics of Paradisos Karst aquifer system (PAS), Northeast Greece. The average area of the PAS is estimated according to Thornthwaite and Mather (1957) (T-M) procedure at 74.2 km2. The karst system, which is largely fault-controlled, discharges through three permanent karst springs: KS15, KS20 and KS21. The average discharge rate was calculated for two of them at 0.726 m3/s. The time series analysis shows that: (a) the memory effect for the PAS is extremely high; and (b) the karst system is a poorly developed with high storage capacity and absence of a quick flow component. The chemical type for the majority of the groundwater samples is of Ca-HCO3 type. The chemical properties of the groundwaters are strongly influenced by alkaline earth metals and weak acids. The presence (sporadically) of high NH4 + content and slightly increased nitrate, ammonium and phosphate values in springs KS20 and KS21 is attributed to the presence of anthropogenic sources, especially septic tanks and agriculture. All studied groundwaters are oversaturated in calcite and aragonite, which suggests a mechanism of diffuse flow. The morphology and geology of the PAS catchment area, and data from hydrographs and chemographs, show that the hydrologic system is dominantly of diffuse flow. The use of time series analysis combined with classic hydrogeological techniques (i.e., degree of karstification, T-M procedure, chemographs and saturation indices) can be used in order to successfully characterize a karst system and achieve a sustainable integrated water management in it.

Assessing submarine groundwater discharge (SGD) and nitrate fluxes in highly heterogeneous coastal karst aquifers: Challenges and solutions

Groundwater discharge in coastal karst aquifers worldwide represents a substantial part of the water budget and is a main pathway for nutrient transport to the sea. Groundwater discharge to the sea manifests under different forms, making its assessment very challenging particularly in highly heterogeneous coastal systems karst systems. In this study, we present a methodology approach to identify and quantify four forms of groundwater discharge in a mixed lithology system in southern Spain (Maro-Cerro Gordo) that includes an ecologically protected coastal area comprised of karstic marble. We found that groundwater discharge to the sea occurs via: (1) groundwater-fed creeks, (2) coastal springs, (3) diffuse groundwater seepage through seabed sediments, and (4) submarine springs. We used a multi-method approach combining tracer techniques (salinity, 224Ra, and 222Rn) and direct measurements (seepage meters and flowmeters) to evaluate the discharge. Groundwater discharge via submarine springs was the most difficult to assess due to their depth (up to 15 m) and extensive development of the springs conduits. We determined that the total groundwater discharge over the 16 km of shoreline of the study area was at least 11 ± 3 × 103 m3 d−1 for the four types of discharge assessed. Groundwater-derived nitrate (NO3−) fluxes to coastal waters over ∼3 km (or 20%) in a highly populated and farmed section of Maro-Cerro Gordo was 641 ± 166 mol d−1, or ∼75% of the total NO3− loading in the study area. We demonstrate in this study that a multi-method approach must be applied to assess all forms of SGD and derived nutrient fluxes to the sea in highly heterogeneous karst aquifer systems.

Differentiated spring behavior under changing hydrological conditions in an alpine karst aquifer

Limestone massifs with a high density of dolines form important karst aquifers in most of the Alps, often with groundwater circulating through deep karst conduits and water coming out of closely spaced springs with flow rates of over some cubic meters per second. Although several hydrogeological studies and tracing experiments were carried out in many of these carbonate mountains in the past, the hydrogeology of most of these karst aquifers is still poorly known.Geological, hydrodynamic and hydrochemical investigations have been carried out in one of the most representative of these areas (Cansiglio-Monte Cavallo, NE Italy) since spring 2015, in order to enhance the knowledge on this important type of aquifer system. Additionally, a cave-to-spring multitracer test was carried out in late spring 2016 by using three different fluorescent tracers. This hydrogeological study allowed: 1) gathering new detailed information on the geological and tectonic structure of such alpine karst plateau; 2) defining discharge rates of the three main springs (Gorgazzo, Santissima, and Molinetto) by constructing rating curves; 3) understanding the discharging behavior of the system with respect to different recharge conditions; 4) better defining the recharge areas of the three springs.The three nearby springs (the spring front stretches over 5 km), that drain the investigated karst aquifer system, show different behaviors with respect to changing discharge conditions, demonstrating this aquifer to be divided in partially independent drainage systems under low-flow conditions, when their chemistry is clearly differentiated. Under high-flow conditions, waters discharging at all springs show more similar geochemical characteristics. The combination of geochemistry, hydrodynamic monitoring and dye tracing tests has shown that the three springs have different recharge areas. The study points out that even closely spaced karst springs, that apparently drain the same karst mountain, can have different behaviors, and thus distinctive reactions toward polluting events, a characteristic to be taken into account for their management.

Groundwater flow mechanism in the well-developed karst aquifer system in the western Croatia: Insights from spring discharge and water isotopes

Karst aquifers have a fundamental importance to water supply in many countries. Due to their specific hydrogeologic properties, these aquifers are sometimes difficult to use because of the high discharge variations of the karst springs and are almost always sensitive to pollution. With an aim to better understand karst aquifers, different research methods are used to study the karst groundwater system in Croatia.The spring hydrograph and the stable isotope (δ18O, δ2H) compositions in the water samples collected from the Rječina and Zvir springs and precipitation were analysed and used to characterize the karst aquifer. The recession coefficient obtained from the hydrograph analysis indicates only a fast-flow spring component at the Rječina spring. The lack of the base-flow spring component is the primary reason for the spring drying out during the dry periods. The low recession coefficient of the Zvir spring indicates a base-flow and discharge from well-drained fissures and fractures in the spring catchment area during the low water stage. A mean residence time (MRT) of groundwater was calculated for stable isotope δ18O using lumped parameter approach by applying the exponential model, combined exponential-piston and dispersion models to isotopic input (rainfall) and output (spring) data sets during 2011–2013. The MRT of 3.24 and 3.6months for the Rječina spring and 7.2months for the Zvir spring suggests recent groundwater recharge from precipitation.

Hydrogeochemistry of Shallow Groundwater in a Karst Aquifer System of Bijie City, Guizhou Province

In this study, the major chemical compositions of 159 shallow groundwater samples incorporated saturation index (SI) and Principal Component Analysis (PCA) were employed to evaluate the mainly geochemical processes that control the hydrogeochemical evolution of groundwater in a typical karst area, Bijie city, Guizhou Province. The groundwater samples in this study area were dominated of HCO3-Ca, HCO3-Ca-Mg, and HCO3-SO4-Ca types. The PCA suggested that four principal components could explain 88.85% of the total variance of 10 parameters, indicating that the hydrogeochemical evolution of groundwater was mainly controlled by the dissolution/precipitation of carbonates, gypsum, and halite minerals, cation exchange, and anthropogenic activities. To be specific, the enrichment of Ca2+, Mg2+, HCO3− and SO42− in groundwater were primarily affected by the dissolution of dolomite and gypsum minerals, and the role of calcite dissolution was relatively weaker because most groundwater samples were saturated with respect to calcite. Besides, cation exchange was another factor that may affect the concentration of Ca2+ and Mg2+ in groundwater, and the concentration of SO42− can also be influenced by coal mining activity. In addition, the concentrations of Na+ and Cl− in groundwater were likely influenced by the dissolution of halite, cation exchange, and human activities.

A block-centered finite difference method for reduced fracture model in Karst aquifer system

A block-centered finite difference scheme is given for the approximation of reduced coupled model in the fractured media aquifer system. The fluid flow of aquifer system is governed by Darcy’s law in both fracture and surrounding porous media. The degrees of freedom are given separately on both sides of fracture to capture the discontinuity of pressure and velocity. Optimal error estimates in discrete L2 norms are obtained. Numerical experiments are provided to verify the second-order accuracy of presented method. It is demonstrated whether the fracture acts as a fast pathway or geological barrier is totally determined by the value of its permeability tensor.

Analysis of the Hydrogeological and Hydrochemical Characteristics of an Immature Karst Aquifer System

This study intends, using classic and new techniques (e.g., Time Series Analysis, TSA), and hydrogeological data for the period February 2008 - May 2011, to improve the existing knowledge on the hydrogeology of the immature karst Philippi aquifer system (PHAS), Northeast Greece, in order to introduce the sustainable integrated water management of this system. The PHAS catchment consists of Mesozoic fissured and slightly karstified marbles, and covers an area of 121.7 km2. It discharges through the perennial, fault-controlled, overflow Voirani spring, which serves the needs of 85,000 inhabitants. Source of recharge is direct diffuse infiltration of precipitation. The Voirani spring mean discharge rate is 1.48 m3/s and ranges from 1 to 2.1 m3/s. Its variability index ranges from 1.73 to 2.07 m3/s. Auto- and cross-correlation and spectral analyses were used in combination with PHAS hydrogeological characteristics to study the interrelationship of daily spring discharge and rainfall, and provided useful information about the PHAS memory effect. PHAS baseflow prevailed greatly and had a behavior similar to a porous aquifer. The catchment area recharges and stores deep circulating water, while its karstification is poorly developed with high storages. The Voirani spring water is of Ca-HCO3 chemical type, of high quality, and oversaturated with respect to calcite. Examination of hydrograph and chemograph data revealed that PHAS is dominated by diffuse flow of stable hydrochemical composition. The application of TSA combined with classic hydrogeological techniques can be used in order to achieve a sustainable integrated water management of this system.

Occurrence of Pepper Mild Mottle Virus (PMMoV) in Groundwater from a Karst Aquifer System in the Yucatan Peninsula, Mexico.

The Yucatan Peninsula of Mexico hosts a karst aquifer system that is the only source of freshwater for the area; however, it is vulnerable to human-mediated contamination. Pepper mild mottle virus (PMMoV) is one of the most abundant RNA viruses associated with human feces, making it a viable indicator for tracking fecal pollution in aquatic environments, including groundwater. In this study, groundwater samples collected from a karst aquifer from fresh and brackish water locations were analyzed for fecal indicator bacteria, somatic and male F+ specific coliphages, and PMMoV during the rainy and dry seasons. Total coliform bacteria were detected at all sites, whereas Escherichia coli were found at relatively low levels <40 MPN/100ml. The highest average concentrations of somatic and male F+ specific coliphages were 920 and 330 plaque forming units per 100ml, respectively, detected in freshwater during the rainy season. PMMoV RNA was detected in 85% of the samples with gene sequences sharing 99-100% of nucleotide identity with PMMoV sequences available in GenBank. Quantification of PMMoV genome copies (GC) by quantitative real-time PCR indicated concentrations ranging from 1.7×101 to 1.0×104 GC/L, with the highest number of GC detected during the rainy season. No significant correlation was observed between PMMoV occurrence by season or water type (p>0.05). Physicochemical and indicator bacteria were not correlated with PMMoV concentrations. The abundance and prevalence of PMMoV in the karst aquifer may reflect its environmental persistence and its potential as a fecal indicator in this karst aquifer system.

A Grey Water Footprint Assessment of Groundwater Chemical Pollution: Case Study in Salento (Southern Italy)

The worsening of groundwater quality is a huge problem for some regions, especially where a karst aquifer system is the most important water resource because of the deficiency of a well-developed superficial water supply. In this study the chemical quality of a deep aquifer of the Salento peninsula (Southern Italy), where a shallow aquifer and an extensive deep aquifer are exploited as a source of drinking water and irrigation water, was monitored. The indicator used to assess the sustainability of pollution produce by human activities is the “grey water footprint” (GWF) which measures the amount of water required to assimilate a polluting load produced from anthropic activity. The GWF, calculated for each chemical parameter, shows a widespread contamination by Mercury (Hg), Vanadium (V) and Ammonium (NH4+) with concentrations above the limits (Lgs. D. 31/2001). The high Mercury and Vanadium concentrations may thus be associated with anthropic pressures on the aquifer, while Ammonium derives mainly from fertilizers used in agriculture. The situation that emerged involves reflections on the continuous human pressure on natural resources. Therefore, the management of groundwater quality requires a multidisciplinary approach focused on identifying the measures necessary to protect our water resources.

Application of the flow dimension concept for numerical drawdown data analyses in mixed-flow karst systems

A numerical discrete conduit-continuum model is employed to investigate large-scale groundwater abstraction in karst aquifers. The application of large-scale experiments is one approach to deal with the scale problem in hydraulic parameter assessment, caused by significant contrasts of hydraulic parameters in a karst aquifer. Here, conduit drawdown is evaluated by diagnostic plots and by considering the apparent flow dimension. These tools are frequently used for the interpretation of hydraulic borehole tests by analytical solutions. In contrast to existing analytical solutions, a numerical groundwater model allows the incorporation of the effect of complex parameter distributions. The objective is to demonstrate the application of diagnostic plots and flow dimension analysis for a systematic analysis of the effect of different boundary conditions as well as sink/source terms for idealized two-dimensional mixed karst aquifer systems, which ultimately extends existing analytical solutions and, therefore, contributes to the interpretation of measured field data. The analysis is focused on the apparent flow dimension and shows the extension of the cross-sectional flow area for selected models. The results are used to evaluate the large-scale pumping test of the karstified Cent Fonts catchment (Languedoc, France). The inverse calibration of two realistic, but still simplified, catchment models reveals that the apparent flow dimension supplies useful information about the general flow pattern during the Cent Fonts pumping test. The flow dimension after the end of the storage period can be explained by a large contribution of exchange flow resulting in a strong influence of radial flow on regional, i.e., kilometer scale.