Karst Aquifer Research Articles

On-manifold probabilistic Iterative Closest Point: Application to underwater karst exploration

This paper proposes MpIC, an on-manifold derivation of the probabilistic Iterative Correspondence (pIC) algorithm, which is a stochastic version of the original Iterative Closest Point. It is developed in the context of autonomous underwater karst exploration based on acoustic sonars. First, a derivation of pIC based on the Lie group structure of is developed. The closed-form expression of the covariance modeling the estimated rigid transformation is also provided. In a second part, its application to 3D scan matching between acoustic sonar measurements is proposed. It is a prolongation of previous work on elevation angle estimation from wide-beam acoustic sonar. While the pIC approach proposed is intended to be a key component in a Simultaneous Localization and Mapping framework, this paper focuses on assessing its viability on a unitary basis. As ground truth data in karst aquifer are difficult to obtain, quantitative experiments are carried out on a simulated karst environment and show improvement compared to previous state-of-the-art approach. The algorithm is also evaluated on a real underwater cave dataset demonstrating its practical applicability.

Characterizing the hierarchical groundwater flow systems in Karstic Xiangxi River Basin, West Hubei, Central China

Karstification degree is a key factor in controlling the characteristics of karst GFP. In this study, hydrogeology, karst development, hydrograph, artificial and natural tracers and hydrochemistry were integrated to characterize the groundwater flow patterns (GFP) in the Cambrian-Ordovician karst aquifer in Xiangxi River Basin. Groundwater samples were collected from three karst groundwater points: Wulongdong spring (WLD), Shuimoxi spring (SMX), and groundwater exposed by Borehole ZK03 (ZK03), which have different discharge variations. The hydrogeological analysis and the artificial tracer tests showed that groundwater runoff channel for WLD, SMX and ZK03 are dominated by conduits, fracture networks and micro fissures-matrix, respectively. The natural responses (discharge, electrical conductivity and temperature) of WLD to rainfall indicated that flow in this system is discharged by conduit, fracture and matrix, respectively. Stable isotopes (2H, 18O) of precipitation and groundwater suggested that the WLD and SMX recharge at the adjacent zone with mean elevations of 878 m and 676 m, respectively; while ZK03 recharge at mean elevations of 1338 m from thousands of meters away. Mean residence times calculated by artificial and natural tracers (18O, CFC) of conduit flow in WLD (7–19 h), fracture flow in WLD and SMX (243 and 600 days), and matrix flow in ZK03 (41 years) were obviously increased gradually. Hydro-chemical analysis shows that ZK03 has higher concentrations of ions that related to carbonate dissolution, indicating groundwater in ZK03 has longer time to interact with rocks. The results show that GFP in study aquifer are characterized by local fast conduit flow, local intermediate fracture networks flow and regional slow matrix flow with progressively slower groundwater refresh rate. The conceptual model was also proposed to enable a better understanding of groundwater circulation, water resources and vulnerability of the karst system in Central China.

The Interplay of Environment and Biota in Assessing the Freshwater Quality in Karst

Karst aquifers are both a valuable resource for humankind and a habitat for unique biota. The quality of freshwater sources may be easily affected by natural (e.g., geology, climate, and vegetation) and anthropogenic (e.g., agriculture, livestock, and tourism) changes, particularly in karst landscapes with highly vulnerable groundwater reservoirs. We seasonally monitored nine representative freshwater sources (i.e., six springs, a well, a surface stream, and a cave stream resurgence) in the karst system of the Runcuri Plateau (KSRP) (Western Romanian Carpathians) during seven sampling campaigns in 2019–2021. We assessed how these natural and anthropogenic factors influenced the water quality based on the European and national standards for drinking water. The geological structure (i.e., tectonics and lithology) of the KSRP was reassessed, and the environmental variables of the freshwater sites were investigated in order to evaluate their impact on the physicochemical profile, the microbial contamination, and on the meiofauna presence. Multivariate statistics were performed to gain insights into the interplay among all these factors and to evaluate the self-purification capacity of the KSRP for chemical and microbial pollutants. The most relevant drivers shaping the microbial content of the freshwater sources were the altitude of the sampling sites, the normalized difference vegetation index (NDVI), and air temperature, followed by the physicochemical profile of the waters (i.e., calcium hardness, magnesium hardness, nitrites, nitrates, conductivity, phosphates, total dissolved solids, and iron concentrations). The meiofauna presence was influenced mostly by precipitation, air temperature, and NDVI. Our results reflected the effect of the geological structure and environment on water chemistry and biota assemblages. A pollutant attenuation trend was observed in discharging waters, even though the self-purification capacity of the studied karst system was not statistically supported. More investigations are needed to comprehend the processes developed in the black box of the KSRP.

The complete mitochondrial genome of the Mexican blind brotula Typhlias pearsei (Ophidiiformes: Dinematichthydae): an endemic and troglomorphic cavefish from the Yucatán Peninsula karst aquifer

In this study we report the first complete and annotated mitochondrial genome of the Mexican blind brotula, Typhlias pearsei, a troglobitic cavefish endemic to the Yucatán peninsula karst aquifer in southeastern Mexico. Genomic sequencing was accomplished via next generation sequencing (NGS). The resulting mitogenome is 16,813 bp long and, as in most vertebrates, consists of a total of 37 genes (13 PCGs, 2 rRNAs, 22 tRNAs) and two non-coding regions (control region and origin of the light strand replication). Other than a rearrangement in the position of two tRNAs (shuffling between tRNA-Ile and tRNA-Gln), the mitogenome of T. pearsei exhibits a genomic composition and organization similar to that of most teleost mitogenomes. Besides offering this valuable genomic resource for future studies, the resulting mitogenome was used in a comparative context to test the current higher-level taxonomy of ophidiiform fishes and to examine the phylogenetic position of T. pearsei among viviparous brotulas. Our phylogenetic results confirm those from the most comprehensive molecular phylogenetic study of the group.

Water Quality Monitoring of Five Karst Springs within a Pastureland in Southwest Polk County, Missouri

ABSTRACT The fractured nature of karst terrain makes these areas highly susceptible to contamination. Besides aquifer contamination, impaired karst springs can negatively impact the aquatic habitat of their receiving streams. Five springs of a shallow karst aquifer in southwest Polk County, Missouri, and their receiving stream were selected to construct a baseline of water quality data, using nitrate (NO3) as indicator. The main land use in the study area is cattle farming. Water samples were collected during a 12-month period and analyzed for pH, turbidity, Ca, Mg, HCO3, Cl, SO4, and NO3. Results show that each spring had its own range of values. NO3 and Cl values were below contamination levels and only in a few instances exceeded threshold levels reported for karst areas (NO3-N <3 mg/L; Cl <13 mg/L), implying that the number of cattle per acre is maintained at a sustainable level and leaking from the Springfield Plateau aquifer to the underlying Ozark aquifer poses a minor threat. Interestingly, NO3 and Cl did not correlate despite their common source, suggesting that they undergo different chemical and microbiological processes along their path. The yearly nitrate export from the Little Sac River was estimated as 286.8 Mg, and the maximum N load was observed in March. Monitoring of springs and streams is recommended for this environmentally fragile area.

Characterizing Hydrological Functioning of Three Large Karst Springs in the Salem Plateau, Missouri, USA

Spring discharge hydrographs can provide information on karst aquifer connectivity and responses to precipitation. However, few studies have conducted time-series analyses of spring hydrographs over multi-decadal time scales. We examine daily discharge for three large karst springs and daily precipitation for adjoining weather stations during 1928–2019 in the Salem Plateau of southern Missouri, one of the major karst regions in the USA. For different time periods, we conducted baseflow index calculations and time-series (autocorrelation, spectral density, and cross-correlation with precipitation) analyses for discharge data, and Mann–Kendall (MK) trend analyses for discharge and precipitation data. Hydrograph separation indicates discharge is baseflow-dominated (86–94%) at all three springs. The memory effect is lower for Bennett Spring (with an auto-correlation lag time 29–41 days) than for Big Spring (60–92 days) and Greer Spring (77–112 days). Spectral density analysis indicates that annual signals dominate all three springs. Cross-correlation analysis shows a quicker response to precipitation at Bennett Spring (0–1 days) than at Big and Greer springs (1–2 days). MK trend analysis shows significant increases in discharge for all three springs over multiple decades, but not for the period 2007–2019. Increased discharge accompanies regional increases in precipitation, but may also reflect increased recharge associated with reversion of farmland to forest.

An Integrated Approach for Investigating the Salinity Evolution in a Mediterranean Coastal Karst Aquifer

Coastal areas are characterized by considerable demographic pressure that generally leads to groundwater overexploitation. In the Mediterranean region, this situation is exacerbated by a recharge reduction enhanced by climate change. The consequence is water table drawdown that alters the freshwater/seawater interface facilitating seawater intrusion. However, the groundwater salinity may also be affected by other natural/anthropogenic sources. In this paper, water quality data gathered at 47 private and public wells in a coastal karst aquifer in Apulia (southern Italy), were interpreted by applying disparate methods to reveal the different sources of groundwater salinity. Chemical characterization, multivariate statistical analysis, and mixing calculations supplied the groundwater salinization degree. Characteristic ion ratios, strontium isotope (87Sr/86Sr), and pure mixing modelling identified the current seawater intrusion as a main salinity source, also highlighting the contribution of water–rock interaction to groundwater composition and excluding influence from Cretaceous paleo-seawater. Only the combined approach of all the methodologies allowed a clear identification of the main sources of salinization, excluding other less probable ones (e.g., paleo-seawater). The proposed approach enables effective investigation of processes governing salinity changes in coastal aquifers, to support more informed management.

Statistical evidence of recharge and supply controlling nitrate variability at springs discharging from the upper Floridan Aquifer

Over the last several decades, rising nitrate concentrations in springs discharging from north Florida's karstic Upper Floridan Aquifer have coincided with proliferation of algae in Florida spring runs and subsequent ecosystem degradation. As agriculture and development are primary contributors to groundwater nitrate and are predicted to continue expanding, understanding unique contributions and transmission pathways of nitrate pollution is vital to restoring impaired spring ecosystems. In this study, we use statistics and signal processing to analyze continuous nitrate timeseries data collected over five years at four north Florida springs. We quantified a significant, low-frequency annual signal in nitrate concentrations superimposed on increasing nitrate trends. We show nitrate concentrations at springs increase during the rainy season, potentially in response to recharge and seasonal fertilizer application. Thus, we suggest seasonal fluctuations observed in nitrate concentrations are caused by increased recharge of nutrient-rich soil waters through fractures that deliver water on relatively short timescales to conduits during the rainy season. We further speculate the steady, monotonically increasing concentration is maintained by accumulation of Nitrogen as slow flow through matrix porosity through the remainder of the year. Seasonal nitrate concentrations resulting from flow through karst aquifers may thus be poorly simulated using equivalent porous media models that are increasingly being used for nutrient management, because they do not capture heterogenous flow and transport dynamics.

Identifying and predicting karst water inrush in a deep tunnel, South China

Identifying the source of tunnel inrush is essential for its prediction and mitigation. In this work, hydrological, hydrochemical, and isotopic methods were used to identify the source of water inrush into the deep Xiakou tunnel of south China. In addition, a rainfall-runoff model was calibrated to predict its anticipated runoff volume and temporal characteristics. These methods reveal that water inrush in the northern tunnel originates in the Permian-Triassic karst aquifer to the north, and that a groundwater divide exists between two major springs (Xianglong Spring and Xiakou Spring). The southern tunnel also discharges karst water during heavy rainfall conditions, but mainly drains Jurassic fissure water in the dry season. The peak flows, peak times, and recession processes of five inrush events were effectively simulated with our calibrated, rainfall-runoff model. A catchment area of 16.3 km2 was delineated based on the water inrush point identified by optimal model parameters. The catchment analysis shows that about 53% of rainfall recharges into the water inrush point. These methods presented in this study facilitate the estimation of recharge areas in mountainous karst areas and provide a basis for the design of hydraulic structures for the control and mitigation of tunnel inrush.

Mixed Recharge and Epikarst Role in a Complex Metamorphic Karst Aquifer: The Pollaccia System, Apuan Alps (Tuscany, Italy)

The Apuan Alps (Italy) are an internationally renowned karst region where several karst springs have a mean discharge exceeding 100 L/s, thus representing important water resources. One of the major springs, the Pollaccia, was monitored for approximately one year. This spring drains a structurally complex metamorphic karst aquifer that is characterized by multiple hydrologic sectors with variable recharge and infiltration styles. Spring discharge, water temperature, and electrical conductivity were compared to precipitation data, and time lag analysis was performed on 27 storm hydro/thermo/chemographs (HTC-graphs) that occurred in different hydrological phases. A marked seasonality was observed for all the monitored parameters and for the measured lags. The comparison of the storm HTC-graphs with no precipitation phases permitted recognition of the differential contribution of the various sectors. The Pollaccia’s hydrodynamic behavior was related to three different scenarios in the recharge area: (1) allogenic runoff recharge in the noncarbonate sectors; (2) autogenic recharge and runoff over the steeply dipping marble outcrops, characterized by fast epiphreatic flow through master conduits and low epikarst storage; (3) autogenic recharge through highly fractured, gently dipping marble outcrops, characterized by quick hydraulic pressure transfer to the phreatic zone and relevant epikarst storage.

Surface water and groundwater hydraulics of lowland karst aquifers of Estonia

In Estonia, karst aquifers supply roughly a third of annually abstracted domestic groundwater. Karst systems recharged by allogenic humic-rich streams originating from mire-dominated watersheds are common in Lower Estonia (lowlands). This study aimed to characterize the hydrology and hydraulics of two binary lowland karst systems: Salajõe (SKS) and Tuhala karst system (TKS), and their interaction with the hosting karst aquifer. High-resolution water level, discharge, specific conductance time series data combined with tracer test results were analyzed to assess the two systems. The temporal effect of evapotranspiration, snow deposition and snowmelt floods contributed to the variability in recharge event sensitivity of studied watersheds and aquifers, resulting in time-varying CCF strength between precipitation and discharge. The greatest event sensitivity was observed during the autumn and snowless winter seasons. The celerity and solute transport were the greatest in the preferential flow paths of both karst systems, however, solute transport characteristics varied significantly because of differences in structure and maturity of karst porosity. While the dilute allogenic recharge flushed the karst systems occasionally, the contribution of high-SEC groundwater baseflow was significant. During flood events, the matrix-conduit hydraulic gradient could be inverted, resulting in dilute floodwater being pushed into the hosting aquifer from the karst system.

First application of the Integrated Karst Aquifer Vulnerability (IKAV) method – potential and actual vulnerability in Yucatán, Mexico

Abstract. Groundwater vulnerability maps are important decision support tools for water resource protection against pollution and helpful in minimizing environmental damage. However, these tools carry a high subjectivity along the multiple steps taken for the development of such maps. Additionally, the theoretical model on which they are based does not consider other important parameters, such as pollutant concentration or pollutant residence time in a given section of the aquifer, solely focusing on the theoretical travel time of a pollutant particle from a release point towards a target. In this work, an integrated methodology for the evaluation of potential (intrinsic) and actual vulnerability is presented. This integrated method, named Integrated Karst Aquifer Vulnerability (IKAV), was developed after the analysis of several study cases around the world and the application of multiple intrinsic groundwater vulnerability methods in a selected study area. Also, a solute transport model served as the basis to define additional parameters for vulnerability analysis for areas severely affected by anthropogenic practices. However, the focus of the transport model must not be mistaken to be hazards and risk mapping. A defined workflow and several criteria for parameters and attributes selection, rating and weighting, and vulnerability classification are presented here. The first application of the IKAV method was carried out in the Yucatán karst, demonstrating to be a reliable method for vulnerability estimation. Results demonstrated the scope of the IKAV method in highlighting important regional conditions, minimizing the subjectivity, and expanding the analysis of vulnerability.

Risk Assessment of Water Inrush from Coal Floor Based on Karst Fractal-Vulnerability Index Method

Hidden karst structures are developed irregularly in the Middle Permian Maokou Formation aquifer from the northern part of the Guizhou coalfield, China. Mining operations associated with the exploitation of coal seams from the lower part of the Upper Permian Longtan Formation are threatened by karst waters from the underlying strata. To improve the accuracy of water inrush risk assessment of the karst aquifer floor in the northern Guizhou coalfield, the karst fractal quantification technique is implemented. In this study, the karst aquifer of the Maokou Formation located under the floor of the No. 15 coal seam from the Honglin Coal Mine is considered as the research object. Based on the karst results predicted by geophysical exploration methods, the fractal theory is used to quantify the degree of karst development, while the risk of water inrush from the floor of the coal seam is evaluated by applying ArcGIS information processing technology combined with the vulnerability index method. The results indicate the following observations: the mean fractal dimension of karst in the study area is 1.53, the karst structures are highly developed, and the overall distribution of karst is characterized by an irregular NW-SE direction; the main controlling factors affecting water inrush from the floor of the No. 15 coal seam are expressed by the water pressure of the aquifer, the abundance of water in the aquifer, the degree of karst development, the thickness of the effective impermeable layer, the mining depth, the coal seam dip angle, and the degree of fault complexity; the areas with the highest risk of floor water inrush are predominantly concentrated in the northwestern and central parts, but there is also a risk of floor water inrush in the first mining area of the No. 15 coal seam. This study takes into consideration complex factors such as the typical karst aquifer and the hydrogeological conditions in the northern part of the Guizhou coalfield, which results in a more realistic interpretation and can provide further guidance for water control activities in the mining area.

Hydrodynamic model for independent cold and thermo-mineral twin springs in a stratified continental karst aquifer, Camou, Arbailles Massif, Pyrénées, France

The Camou springs (Arbailles Massif, French Western Pyrenees) display an unusual close association of a typically cold karstic spring that drains the Urgonian western limb of the Arbailles, and a thermo-mineral spring (33.5°C; salinity 17.7 g/L). The latter gains its mineralization at the contact of Triassic evaporites mainly through a deep loop in the Apanicé syncline. The fast upflow of this deep water occurs at the cross of large active lines (the North-Pyrenean thrust located at depth, and the Saison transverse fault). Cave diving in the nearby Maddalen Cave allowed reaching the phreatic passage at the origin of the cold spring, which however also crosses the thermal body in the third sump (S3). Both water bodies are separated by a sharp thermocline. 6 pressure-temperature dataloggers were placed in both water bodies along the thermocline for 6 months. The dataloggers located downstream on either side of the thermocline show at the beginning of flood first a rise of the thermal body, then an invasion of the whole phreatic passage by the cold floodwater, controlled by head pressure changes in the karst aquifer. From observation of these mechanisms, we deduce a hydrodynamic model with a warm plume rising into the cold aquifer, without significant mixing. Such independence of water bodies is explained by the decrease of turbulent rate at the interface, due to the sharp density gradient. The relative absence of mixing does not actually require independent “watertight” routes, both water bodies can thus coexist even in the same conduit. This model locally implies the existence of unknown secondary passages close to the spring, which allow an independent draining of each water body toward separate outlets during low stage. Such type of stratified aquifer linked to density differences is common in coastal karst (Florida, French Calanques…), in the continental evaporite karst (Schlotten of the Harz in Germany, Kungur karst in Ural…), but remains poorly identified in continental carbonate karst areas, mainly because of the difficulty of access. Together with the Mescla spring in French Alpes-Maritimes, the Camou twin springs discharging in the same porch are an outstanding example, allowing a direct study of the stratification and the dynamic of highly contrasted water bodies.

Application of hydrochemical and isotopic data to determine the origin and circulation conditions of karst groundwater in an alpine and gorge region in the Qinghai–Xizang Plateau: a case study of Genie Mountain

Complex structural systems, lithological differences, and extreme heterogeneity of aquifers combine to create a complex karst aquifer structure in alpine and gorge areas; however, because of the topography, direct investigation of aquifer structure is difficult. In this study, field survey, hydrochemical, and isotopic data are analyzed to reveal the development of karst groundwater and to describe the karst water cycle in Genie Mountain, Qinghai–Xizang Plateau. The results show that groundwater circulation is mainly controlled by active fracture. Atmospheric precipitation and melting ice and snow are the groundwater recharge sources, and recharge areas are mostly located in high mountains above 4500 m a.s.l. The direction of groundwater flow is mostly controlled by the Jinshajiang active Fault, with drainage areas at the intersection of multiple faults. There are two regional karst water runoff conduits. One is along the Edexi-Hongjunshan Fault, where groundwater runs from south to north; the other is along Gangtonglong Fault, where groundwater runs from north to south, and is discharged at Gangtonglong gully. The groundwater cycle can be divided into three levels: epikarst water circulation; mid to deep karst water circulation; and deep geothermal water circulation. The karst springs located in the outlet of the Huolong gully contain markedly higher levels of Na+ and SO42− than other karst springs because of the leaching effect of groundwater on mirabilite. The presence of evaporites in Huolong gully indicates that the plateau planation formed by the structural uplift will change the local climatic conditions, and then affect the groundwater circulation process and the water–rock reaction in the process.

Flow Cytometry and Fecal Indicator Bacteria Analyses for Fingerprinting Microbial Pollution in Karst Aquifer Systems.

Microbial pollution of aquifers is a persistent water quality problem globally which poses significant risks to public health. Karst aquifer systems are exceptionally vulnerable to pollution from fecal contamination sources as a result of rapid recharge of water from the surface via discrete pathways linked to highly conductive, solutionally enlarged conduits alongside strong aquifer heterogeneity. Consequently, rapid changes in microbial water quality, which are difficult to monitor with expensive and time‐consuming conventional microbiological methods, are a major concern in karst environments. This study examined flow cytometric (FCM) fingerprinting of bacterial cells in groundwater together with fecal indicator bacteria (FIB) at nine separate karst springs of varying catchment size over a 14 month period in order to assess whether such a technique can provide faster and more descriptive information about microbial pollution through such karst aquifer systems. Moreover, the data have also been evaluated with respect to the potential of using turbidity as an easy‐to‐measure proxy indicator of microbial pollution in a novel way. We argue that FCM provides additional data from which enhanced insights into fecal pollution sources and its fate and transport in such karst catchments can be gained. We also present valuable new information on the potential and limitations of turbidity as an indicator of fecal groundwater contamination in karst. FCM has the potential to become a more widely used tool in the field of contaminant hydrogeology.

Monitoring Groundwater Storage Changes in a Karst Aquifer using Superconducting Gravimeter OSG-066 at the Lijiang Station in China

Monitoring Groundwater Storage Changes in a Karst Aquifer using Superconducting Gravimeter OSG-066 at the Lijiang Station in China

Impact of Withdrawals on Karst Watershed Water Supply

Karst systems consist of heterogeneous aquifers characterized by non-linear hydrogeological behavior. This is intrinsically linked to the coexistence of saturated versus unsaturated, open-channel versus closed-conduit flow and laminar versus turbulent flows within these aquifers. These multiple dualities together with a lack of knowledge of their internal structure lead to increasing difficulties in the management of groundwater resources related to karst aquifers. However, karst aquifers constitute strategic fresh water resources and many stakeholders carry out withdrawals sometimes continuously or centered on the period of low water level as for the irrigation. These withdrawals generate discharge decreases that can constitute sources of conflicts between upstream and downstream users of the resource. In this study, we propose a methodology to assess the impact of withdrawals on the spring discharge of a karst aquifer based on a conceptual non-linear reservoirs model. This methodology is applied to the second largest karst system in France: The Touvre karst system (La Rochefoucauld). The simulated influence of the total withdrawals on runoff deficit is larger than the total withdrawals in relationship with the non-linearity of the conceptual models. Globally, this impact is about one and a half of the total withdrawal depending of the year under consideration. Moreover, we show that it also implies a decrease from 10% to 20% of the low-flow annual discharge. The next step will be to also address the issues raised by the climate change projections.

Delineation of discrete conduit networks in karst aquifers via combined analysis of tracer tests and geophysical data

Abstract. Assessment of the karst network geometry based on field data is an important challenge in the accurate modeling of karst aquifers. In this study, we propose an integrated approach for the identification of effective three-dimensional (3D) discrete karst conduit networks conditioned on tracer tests and geophysical data. The procedure is threefold: (i) tracer breakthrough curves (BTCs) are processed via a regularized inversion procedure to determine the minimum number of distinct tracer flow paths between injection and monitoring points, (ii) available surface-based geophysical data and borehole-logging measurements are aggregated into a 3D proxy model of aquifer hydraulic properties, and (iii) single or multiple tracer flow paths are identified through the application of an alternative shortest path (SP) algorithm to the 3D proxy model. The capability of the proposed approach to adequately capture the geometrical structure of actual karst conduit systems mainly depends on the sensitivity of geophysical signals to karst features, whereas the relative completeness of the identified conduit network depends on the number and spatial configuration of tracer tests. The applicability of the proposed approach is illustrated through a case study at the Hydrogeological Experimental Site (HES) in Poitiers, France.

Multidisciplinary investigations of a karst reservoir for managed aquifer recharge applications on the island of Vis (Croatia)

Managed aquifer recharge (MAR) refers to a suite of methods by which excess surface water or non-conventional water is stored underground for subsequent recovery or environmental purposes. MAR solutions have been largely used in unconsolidated aquifers, while their application in karst aquifers is rare. This research presents the first results of a MAR viability study on the island of Vis, a small karstic island in the Adriatic Sea. Favorable geological and hydrogeological conditions enable the formation of karst aquifers, making the island autonomous in terms of water supply. The island’s main aquifer, exploited in the Korita well field, is protected from seawater intrusion by several hydrogeological barriers. However, climate change and high seasonal pressures related to tourism pose a threat to the future availability of freshwater. Multidisciplinary field and laboratory investigations were carried out to detail the geological and hydrogeological setting of the island and its groundwater resource. Field analyses consisted of groundwater monitoring and sampling, geophysical investigations (i.e., electrical resistivity tomography), and structural measurements. Laboratory analyses included measurements of principal cations and anions and tritium activity. Despite low precipitation during the observation period (September 2019 - December 2020), the groundwater resource at the Korita site showed stable trends of physico-chemical parameters with a good storage potential and a long-term reserve. Geophysical investigations evidenced a relatively homogeneous sequence of the rock mass at a larger scale, while structural analyses indicated the occurrence of E-W karstified and open fractures that could represent a preferential flow path in the carbonate aquifer. A MAR solution for the Vis island was proposed combining an infiltration pond scheme with the direct injection of the accumulated waters into the aquifer using available wells. The potential water source could be represented by the runoff collected in an old artificial channel and the associated pond system in Korita.