In the Mediterranean area, the high water demand frequently leads to an excessive exploitation of the water resource, which involves a qualitative degradation of the freshwaters stored in coastal ...karst aquifers, as a result of phenomena such as sea saltwater intrusion. In this study, the NARX network was used to predict the daily groundwater level fluctuation for 76 monitored wells located on the Apulian territory. A preliminary analysis on reference wells was performed in order to assess the impact on the groundwater level prediction of two input parameters, rainfall and evapotranspiration, and the sensitivity to changes of training algorithm and input time delay. Based on the findings of the preliminary analysis, a comprehensive regional analysis and extensive sub-regional analyses were performed, proving the reliability of the NARX-BR network for the groundwater level prediction in wells located on different hydrogeological structures. The accurate results obtained for the Apulia region suggest the NARX network application for groundwater level prediction in other areas affected by groundwater resource management issues.
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•NARX neural networks were applied for groundwater level predictions.•NARX-BR produced accurate groundwater level predictions in four reference wells.•Modeling of a network consisting of 76 wells located in the Apulia region.•Sub-regional analyses, based on hydrogeological features, were performed.•Results suggest the application for other karst and Mediterranean climate areas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A block-centered finite difference method is proposed for solving an unsteady asymptotic coupled model, in which the flow is governed by Darcy’s law both in the one-dimensional fracture and ...two-dimensional porous media. The second-order error estimates in discrete norms are derived on nonuniform rectangular grids for both pressure and velocity. The numerical scheme can be extended to nonmatching spatial and temporal grids without loss of accuracy. Numerical experiments are performed to verify the efficiency and accuracy of the proposed method. It is shown that the pressure and velocity are discontinuous across the fracture-interface and the fracture indeed acts as the fast pathway or geological barrier in the aquifer system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Karstic environments are characterized as areas of intense rock dissolution, which allows the generation of several typical features, such as sinkholes, resurgences, caves, and dolines. The spatial ...distribution of these features is of great importance to identify the contamination vulnerability of karst aquifers and serve as a basis for the application of assessment methods. This study aimed to identify and classify the areas vulnerable to underground contamination in the karstic region of the Terra Ronca State Park (PETeR) and its surroundings. The method chosen was the COP, which assesses the physical conditions of the environment (relief, lithology, soils, precipitation, karst features, and vegetation) to determine the areas naturally vulnerable to contamination. The analyses were performed in a GIS environment. The results indicated five categories of areas vulnerable to groundwater contamination: Very High to High (3.14%), Moderate (16.21%), and Low to Very Low (80.62%). The Terra Ronca State Park was the analysis unit with the highest vulnerability in the region (9.91%), due to the concentration of karstic features in the area. The acquired results aim to help in the underground water resources conservation as well as the speleological patrimony.
•Use of the COP method to assess the vulnerability to contamination of the karst aquifer in Terra Ronca State Park, Brazil.•Areas of greater vulnerability are located inside conservation units.•The highly vulnerable areas are concentrated in places with the presence of karst features such as caves, sinkholes and swallow hole.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Estudo hidrogeoquímico foi realizado envolvendo a região da Área de Proteção Ambiental Carste de Lagoa Santa, 504km2, a norte do município de Belo Horizonte. As litologias aquíferas envolvidas foram ...a sequência pelito-carbonática da Formação Sete Lagoas, metapelitos da Formação Serra de Santa Helena e granito-gnaisses do Complexo Belo Horizonte. A primeira divide-se em Membro Pedro Leopoldo, inferior, encerrando calcários impuros, com intercalações pelíticas, e Membro Lagoa Santa, superior, contendo calcários puros. As águas são bicarbonatadas cálcicas, secundariamente bicarbonatadas mistas a sódicas, quando associadas ao embasamento e coberturas. As concentrações de Ca2+ e Si4+ foram fundamentais para a distinção entre as unidades aquíferas carbonáticas e não carbonáticas, permitindo também identificar águas mistas, elucidar sobre o meio de recarga e compartimentar horizontal e verticalmente o sistema aquífero. A heterogeneidade litológica conferida ao membro inferior levou a sua subdivisão em 4 tipos hídricos, enquanto as águas do Mb. Lagoa Santa são homogêneas, refletindo a sua homogeneidade litológica. A alta produtividade dos poços profundos deve-se à dissolução de porções rochosas mais puras e à localização próxima a falhamentos e de contato litológico entre os membros, enquanto nas nascentes é controlada pela intensidade dos processos de carstificação dos calcários mais puros do Membro Lagoa Santa.
•Detailed monitoring of different types of dripwater in a karst cave was conducted.•Dripwater δ13CDIC is mainly controlled by local rainfall coupled with soil CO2 dynamics.•Variations of dripwater ...δ13CDIC from East Asia reflect monsoonal rainfall change.
Stable carbon isotopic composition (δ13C) of speleothems has often been recognized as a proxy of vegetation and soil processes in many climatic regimes. In monsoonal regions, the speleothem δ13C records are thought to be able to document changes in local and/or regional precipitation as well. Due to the complexity of carbon isotopic evolution within heterogeneous karst aquifers, accurate interpretations of this proxy are challenging. It is essential to carry out detailed monitoring of cave dripwater δ13CDIC to disentangle various processes governing carbon isotopic evolution and decipher the hydroclimatic constraints. Here, we reported the results of a five-year monitoring of the δ13CDIC as well as hydrochemical compositions of dripwaters in the Maomaotou Big Cave, Guilin, South China. Great spatiotemporal variations in the dripwater δ13CDIC values were observed: (i) seepage flow-fed drips commonly had lower δ13CDIC values, with smaller temporal variation; (ii) the lowest δ13CDIC values were found at fracture-fed drips that had a large supply of soil CO2, whereas the fracture-fed drips with less, episodic CO2 recharge had much more positive δ13CDIC; (iii) the δ13CDIC exhibits remarkable season changes, particularly at fracture-fed drips where higher δ13CDIC values were observed in winter seasons; and (iv) an increasing trend in mean value of δ13CDIC at individual sites during 2015–2019 was found. Both hydrochemical and isotopic analyses revealed that the dripwater δ13CDIC is mainly controlled by spatiotemporal variations in water-CO2-rock interactions in association with hydrological processes, coupled with soil CO2 dynamics, which are closely linked to changes in local rainfall at monthly to annual timescales. Prior calcite precipitation (PCP) along the flow path above the cave could also affect the δ13CDIC of fracture-fed dripwaters in dry periods. Comparisons of the dripwater δ13CDIC records with local climate showed that the change of summer monsoonal rainfall, particularly the August-September-October precipitation, significantly influences the annual mean δ13CDIC value of dripwaters in caves of South China. Further comparison analyses of dripwater δ13CDIC records from both southern and northern China suggested that variations of dripwater δ13CDIC could reflect changes of regional monsoonal precipitation over inter-annual (and maybe decadal) timescale. This demonstrates that the δ13C of speleothems, if precipitated at isotopic equilibrium and not greatly influenced by the CO2 degassing, is likely to be a valuable proxy of monsoon rainfall variability across East Asia.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Karst aquifers are globally prized freshwater sources, posing a significant preservation challenge. These aquifers typically exhibit dual or even triple porosities, encompassing matrix, ...fractures-fissures and conduits, rendering them highly responsive to variations in chemical characteristics and hydraulic head. In coastal regions, these aquifers often possess extensive subsurface conduit networks intricately linked to the rock matrix, facilitating groundwater discharge into the sea. Therefore, they display acute sensitivity to seawater intrusion, swiftly reacting to changes in precipitation and pumping regimes. This makes them exceptionally vulnerable to short-term meteorological fluctuations and long-term climate change. Their high heterogeneity leads to uneven penetration of the freshwater-seawater interface, causing rapid seawater intrusion inland over significant distances. The Mediterranean region, characterized by water deficit and water stress, faces strong impacts from climate change, featuring a warming atmospheric trend exceeding the global average, along with diminished rainfall exacerbating water scarcity. Increasing water demands for agriculture, urban development, and the growing tourism industry, because of global change, are worsening water stress. Our primary research objectives were analyzing the environmental consequences of global and climate change on seawater intrusion in Mediterranean coastal karst aquifers, with a focus on the role of the double-flow model, thus contributing to the understanding of the processes involved. To achieve this, we selected a study region on Mallorca Island in the western Mediterranean, where a karst aquifer system discharges into the sea. We employed various study methods, notably hydrochemical techniques and multi-isotopic analysis, encompassing the examination of 2H and 18O isotopes in water, 87Sr/86Sr ratio, Sr and B concentrations, and δ11B in water. A key finding is the rebound effect, wherein aquifers recontaminate due to solute molecular back-diffusion following cessation of extractions and the retreat of marine intrusion, providing insight into the impact of climate and global change on Mediterranean karst aquifers.
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•In double-flow karst aquifers, flow in conduits may supply solutes to the rock-matrix.•Irrigation returns, re-evaporated and saline waters, increase aquifer salinization.•Aquifer salinization sodifies agricultural soil.•Soil sodification is an adverse effect of climate change-driven drought.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Hydrotectonic analysis of karst aquifers requires an interdisciplinary approach.•There are severe water imbalances in tectonically complex karst catchments (TCKCs).•In TCKCs, ...fault-controlled hydraulic connections cause heterogeneous recharge patterns.•TCKCs have mostly conduit-type recharge zones shaped by regional faults.•In TCKCs, there are large volumes of external water flowing into downstream aquifers.
For many countries, karst aquifers are a significant source of potable water; thus, understanding their hydrogeological behavior is of great importance. However, in tectonically complex karst areas, knowledge of their hydrogeological behaviors has remained largely limited due to the high heterogeneity, often necessitating the use of costly and time-consuming techniques. In this study, spring discharge hydrographs, water balance estimates, hydrochemical and stable isotopic analyses, geomorphological surveys, and a consideration of the geological and structural setting of the study area were used to investigate the hydrogeological function of karst aquifers drained by two large permanent springs: the Bibitalkhone (Bt) and Sabzab (Sa) springs, located in a highly faulted catchment in the Zagros Mountains (southwest Iran). The results obtained from these different approaches suggested that fault-controlled, external waters from neighboring karst aquifers are responsible for more than two-thirds of the total discharge recorded at both springs. In this study, this predominantly conduit-type recharge is referred to as “regional (or external) autogenic recharge”. A smaller portion of the springs’ discharge (∼25% and ∼5% of the Bt and Sa springs’ discharge, respectively) originates from internal waters associated with the springs’ host aquifer, which is supplied by rainfall and infiltrates into the subsurface via joints and fractures. This type of recharge is largely diffuse and is referred to here as “local (or internal) autogenic recharge”. A relatively large portion of the Sa Spring’s discharge (∼35%) originates from a nearby dam reservoir, which can leak into the host spring aquifer through joints and fractures. This type of recharge is described as “local (or internal) allogenic recharge” and is primarily diffuse. The results of this study demonstrate that the karst aquifers in the downstream catchments can supply a stable and continuous source of potable groundwater that can meet the region’s annual consumption, agricultural, and industrial demands. This study will provide insights into the hydrogeological regimes of fault-influenced aquifers, contributing to the sustainable development and proper management of water resources in tectonically complex karst catchments.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Assessment of groundwater discharge to the sea in a coastal karst aquifer.•Combining 224Ra, 222Rn, salinity, seepage meters, and flowmeters measurements.•Nitrate fluxes to coastal waters of an ...ecologically protected coastal area.•Groundwater discharge to the sea occurs in four different forms.•Assessment only possible with a multi-method approach specific to discharge forms.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•A modular conceptual model showed multi-dynamics exchange flows in a karst system.•Internal dynamics of the model were consistent with spring natural tracer variations.•Multiresolution analysis ...brings out the same multi-dynamics processes.•Spring Fourier spectra cut-off frequencies matched internal fluxes of the model.•This combined approach gives insights on the internal behavior of the system.
More than 25% of the world’s population either lives on or obtains its water from karst aquifers, which makes the understanding of these systems essential for water resources management. However it is often difficult to observe and assess their internal dynamics precisely. In this study we investigated (1) the ability of both conceptual model approach and signal decomposition methods to extract meaningful components from karst spring hydrographs and (2) how a modelled spring discharge acquires its spectral signature through a conceptual reservoirs model.
We used the conceptual modeling software KARSTMOD to model the discharge of a small karst spring in Normandy (France). We compared the model internal discharges with natural tracers of the system (conductivity, turbidity) and piezometry. The results suggested that the conceptual model was able to reproduce part of the internal hydrological behavior of the karst system, especially the exchange dynamics between conduits and the surrounding aquifer.
We compared the internal flows of the model with wavelet details obtained from multiresolution analysis of the spring discharge. These internal flows appeared strongly correlated to specific consecutive sums of wavelet details. Finally we studied how the modeled discharge at the spring was acquiring its spectral characteristics across the model, using Fourier spectra analysis. Cut-off frequencies visible on the Fourier spectrum of the spring were matching the frequencies obtained with the multiresolution analysis. These results combined illustrate the ability of decomposition methods to reproduce the spectral variations of the different discharges within the model, and likely within the observed karst system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•The role of the soil mantle on groundwater recharge of karst aquifers was investigated.•A characterization of soil and land cover was performed by field and laboratory analysis.•Soil ...Water Balance code was applied to evaluate the variability of the recharge.•Groundwater recharge rates depend on land cover types and soil thickness.
Karst aquifers represent the fundamental groundwater resources in Italy and in many other countries because supplying urban areas of drinking water and sustaining industrial and agricultural activities. Accordingly, advancing the assessment of groundwater recharge of these aquifers is a major scientific challenge, specifically if considering the hydrological role exerted by soil covering and the related land cover types. In such a framework, the soil water balance model is an effective tool for providing accurate estimates of groundwater recharge depending on precise field and laboratory characterizations of the soil covering.
Considering the features of karst aquifers of southern Italy and the ubiquitous occurrence of a soil mantle, mainly of ash-fall pyroclastic origin, a methodology based on field and laboratory characterizations, as well as modeling approaches, is proposed in this work to advance the knowledge on groundwater recharge processes. The experimental approach was applied to the Soprano-Vesole-Chianello Mts. karst aquifer (Campania region, southern Italy) which is considered representative of karst aquifers of southern Italy and Mediterranean areas as well.
A comprehensive characterization of the soil mantle was developed, considering different land cover classes, measurements and stochastic spatial modeling of soil thickness. The unsaturated hydraulic properties of undisturbed soil samples were analyzed by laboratory tests resulting in the determination of Soil Water Retention Curves (SWRCs). Moreover, a field monitoring of soil water content was carried out by multi-profile soil moisture sensors, allowing the assessment of the hydrological response of the soil covering and of the regime of groundwater recharge process as well.
Among the principal outcomes is the recognition, for each land cover class, of different values of the depth to which the evapotranspiration effect is extended. Based on a consistent spatial modeling of soil thickness and soil hydrologic properties, the Soil Water Balance code (SWB 1.2) was applied to evaluate the spatial and temporal variability of the groundwater recharge of the karst aquifer.
As a principal outcome, groundwater recharge rates were found to be dependent on land cover class and soil thickness as well, showing lower values for wooded areas and higher for denudated ones, respectively due to the higher and lower evapotranspiration rates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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