Any human intervention or action in karst terrains can unexpectedly, suddenly, strongly and, generally, dangerously change a local and/or a regional hydrological regime. A characteristic example of ...the Dinaric karst is given in this paper. The operation of two reservoirs in Livanjsko Polje at an altitude of about 702 m above sea level (m a.s.l.) and hydro-electric development of the Cetina River system started in 1973. This year marked a drastic and instantaneous change in the regional hydrological regime. A significant drop in the minimum, mean and maximum annual discharges of two neighbouring karst springs, Rumin Mali and Rumin Veliki, was caused by this anthropogenic construction. The exits of the two analysed karst springs, Rumin Mali and Veliki, are located at altitudes of about 326.8 m a.s.l. and 307.6 m a.s.l. respectively. The areal distance between them is 640 m. Their hydrological regimes have been altered in different ways. The drop in discharges is stronger for the Rumin Veliki than for the Rumin Mali. The analysis shows that the system development influenced the redistribution of the regional karst aquifer and, in this manner, contributed to the reduction of both karst springs' recharge areas.
Editor D. Koutsoyiannis Associate editor E. Rozos
Integration of the abundant information derived from different sources, characterizing techniques and modeling methodologies, is crucial for extending our knowledge of karst aquifers and their ...available water resources. In this work, a numerically based approach derived from an improved version of the lumped VarKarst model is proposed, which jointly considers spring discharge and dye test results in calibration routine, to assess independently the contribution of the allogenic and autogenic components to the total recharge of a complex karst system with proved duality in its recharge mechanisms. A newly developed parameter estimation procedure based on rather soft performance rules is employed to confine the uncertainty of the water budget previously obtained with two other independent methods (Soil Water Balance and APLIS). Unlike other methodologies that lead to semiquantitative estimations of input sources, results from our approach display reliable ranges of calibrated values for recharge rate, recharge area, and, to a lesser extent, for water runoff infiltration coming from the streamflow. The integration of all these quantitative results with data (qualitative) previously derived from other experimental methodologies has meant a significant advance in understanding the behavior of the pilot system, allowing a more realistic and robust conceptual model to be developed. We conclude by emphasizing that a continuous transfer of improvements from conceptual to numerical modeling approaches, and vice versa, is necessary to enhance knowledge of carbonate aquifer functioning and ultimately achieve better evaluation and management of water resources. During this process, frequent mutual evaluation between the modeling approaches must be performed.
Key Points
The lumped VarKarst model is used to assess allogenic and autogenic contributions to the recharge of karst systems
Coupling field data by a new estimation parameter procedure serves to confine ambiguity of the water budget estimated with two other methods
Mutual evaluation between conceptual and numerical modeling approaches must be constantly conducted to enhance knowledge of karst systems
► Water sources of tree growing on continuous and isolated outcrops were different. ► Water sources of shrub growing on continuous and isolated outcrops were the same. ► Trees on continuous outcrops ...and nearly thin soils had different water use patterns. ► Shrubs on outcrops and nearby thin soils both relied on shallow water sources.
In the seasonally dry karst region of Southwest China, woodland vegetation is frequently associated with rocky outcrops. We used stable isotope techniques to determine the water sources of two woody plant species (the semideciduous tree
Rademachera sinica and the deciduous shrub
Alchornea trewioides) across three surface types: continuous and isolated dolomite outcrops, as well as adjacent surfaces with soils. Main water sources for
R. sinica growing on the continuous outcrops shifted from deep water sources (e.g., water in the saturated zone) on March 23, 2009 (the late dry season of 2008–2009) to rainwater stored in rock fissures of the unsaturated zone on November 8, 2009 (the early dry season of 2009–2010).
R. sinica growing on nearby thin soils exhibited a similar shift of main water sources, from deep water sources in the late dry season to shallow soil water (0–30
cm) in the early dry season. However, they extracted deep water sources from the bottom of nearby outcrops rather than from deeper layers below the soil surface. Main water sources for
R. sinica growing on the isolated outcrops shifted from previous (one to two months ago) rainwater in the late dry season to the mixture of recent (within the last one month) and previous rainwater in the early dry season, while using little or no deep water sources. In contrast,
A. trewioides growing on these two kinds of outcrops always relied on recent rainwater, while those growing on soils always relied on shallow soil water. The shift of water sources for tree species (especially those growing on continuous rock outcrops and nearby soils) may allow them to maintain normal transpiration throughout the year, which increases the amount of evapotranspiration in the watershed and further enhances the water storage capacity of the study area.
Karst regions represent 7–12% of the Earth's continental area, and about one quarter of the global population is completely or partially dependent on drinking water from karst aquifers. Climate ...simulations project a strong increase in temperature and a decrease of precipitation in many karst regions in the world over the next decades. Despite this potentially bleak future, few studies specifically quantify the impact of climate change on karst water resources. This review provides an introduction to karst, its evolution, and its particular hydrological processes. We explore different conceptual models of karst systems and how they can be translated into numerical models of varying complexity and therefore varying data requirements and depths of process representation. We discuss limitations of current karst models and show that at the present state, we face a challenge in terms of data availability and information content of the available data. We conclude by providing new research directions to develop and evaluate better prediction models to address the most challenging problems of karst water resources management, including opportunities for data collection and for karst model applications at so far unprecedented scales.
Key Points
We elaborate the importance of karst water resourcesWe provide a detailed overview of karst modeling approachWe present new methods and directions for their improvement
Karst water are important for water supply and ecological protection. However, climate changes and human activities have caused severe water supply crisis. The Jinci spring, one of the famous karst ...springs in China, is located at the basin‐mountain coupling belt and dried up since 1994. This study integrated hydrogeological conditions, water table logs, hydrogeochemistry, multiple isotopes, and numerical modeling to understand dynamic changes of interaction pattern between karst water‐Quaternary groundwater response to human activity in the basin‐mountain coupling belt over the past 60 years. Our investigation indicated that under natural conditions (1960s), karst water discharges as springs and laterally recharges into Quaternary groundwater at the fault area. In the 1980s, overexploitation caused a significant reduction in spring discharge and a decline in karst water levels, especially in coal mining areas. Further declines in water levels and mixing recharge by karst water‐Quaternary groundwater were observed in the 2000s, which were eased in 2018. Calculations both by oxygen isotope and models indicated that contribution of Quaternary groundwater to Jinci spring ranged from 11.8% to 42.1%, with the highest in the 2000s. Evidenced by multiple isotopes, the recharging of karst water‐Quaternary groundwater varied spatially along the belt in 2018, with delayed water level elevation in coal mining and heavy groundwater exploration areas. This study demonstrated that artificial disturbance fundamentally affected the karst water‐Quaternary groundwater flow and water exchange between them. Precautions should be taken when evaluating global water resources changes, in view of the dynamic interaction between the karst water‐Quaternary groundwater spatially and temporally.
Plain Language Summary
Global changes and human activities have changed groundwater flow and cycle, which is more pronounced in basin‐mountain coupling belt. However, how human activity influences the groundwater dynamics is unknown. The Jinci spring, one of the famous karst springs located at basin‐mountain coupling belt, was selected as a study area to address this knowledge gap. Based on the hydrogeological investigation, multiple isotopes and numerical modeling, we demonstrated the dynamic interaction of the karst water‐Quaternary groundwater and the potential impact of human activity along basin‐mountain coupling belt over the past decades. The interaction between the karst water‐Quaternary groundwater has changed in time and space. Under natural conditions in 1960s, karst water laterally flows into the Quaternary water. However, in 1980s, water level declines, and thus a part of Quaternary groundwater recharge into the karst water, which was even worse in 2000s. In 2018, water level rises, with a delay elevation in coal mining and heavy groundwater exploration areas. Over the past decades, Quaternary groundwater contributes to Jinci spring with varying ratios (11.8%–42.1%, with the highest in 2000s). Our findings emphasize that precautions should be taken when evaluating global water resources changes, considering the dynamic interaction between the karst‐Quaternary groundwater spatially and temporally.
Key Points
Hydrodynamic field and interaction between karst water‐Quaternary water have changed in spatial and temporal scales
Human activity have fundamentally affected the natural groundwater evolution
Precautions are required for the evaluation of global water resources changes
The characterization of the karst conduit network is an essential task to understand the complex flow system within karst aquifers. However, this task is challenging and often associated with ...uncertainty. Equivalent porous media approaches for modeling flow in karst aquifers fall short of capturing the hydraulic effect of individual karst features, while process‐oriented karst evolution models imply major computational efforts. In this study, we apply the Stochastic Karst Simulator (SKS) developed by Borghi et al. (2012) to generate karst conduit networks at a regional scale of a highly karstified carbonate aquifer located in the Eastern Mediterranean region and extensively used for water supply. The SKS generates conduit network geometries reasonably quick, using a mathematical proxy that mimics conduit evolution. The conduit simulation is based on a conceptual model of the genesis of the aquifer, consisting of different karstification phases. The stochastic approach of the algorithm enables us to generate an ensemble of conduit network realizations and to represent the uncertainties of these simulations in a Karst Probability Map. With only soft input information to constrain conduit evolution, multiple equivalent realizations yield similar resulting network geometries, indicating a robust approach. The presented methodology is numerically efficient, and its input can be easily adjusted. Subsequently, the resulting stochastic spatial distribution of conductivities can be employed for the parametrization of regional karst groundwater models.
Key Points
We statistically generate multiple sets of karst conduit network geometries using input data based on soft information
The resulting Karst Probability Map accounts for uncertainty in the spatial distribution of the karst conduit network
Our approach can assist in the integration of soft information into the parametrization of karst groundwater models
Groundwater pollution is a critical concern in karst areas. This study used the PLEIK (P: protective cover; L: land use; E: epikarst development; I: infiltration conditions; K: karst development) ...method to assess the vulnerability of groundwater pollution in Guangxi Province, which is the largest karst area in China. The pollution sources and attenuation consist of groundwater pollution hazards. The attributions for the vulnerability and hazard were measured using the geodetector method from geographical information system in Luzhai County in Guangxi. The results confirmed that the vulnerability of groundwater pollution was higher in karst areas than in non-karst areas. In Guangxi, 36.35% of the groundwater samples were polluted. A total of 49.73% of the areas in Luzhai County contained hazardous levels of pollution. The risk assessment map, which interacted with the vulnerability and hazards, was 58.2% similar to the groundwater pollution distribution. The influence of the hazard on groundwater pollution was 2.6 times that of the vulnerability. It is crucial to control pollution sources to prevent groundwater pollution.
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•CCME WQI was used to evaluate the integrated groundwater pollutant classes.•Geodetector method was used to detect the effect degree of V and H quantitatively.•Hazard influence on the groundwater pollution was 2.6 times that of vulnerability.
The influence of the hazard on groundwater pollution was 2.6 times that of the vulnerability in the karst areas of Guangxi Province, China.
•We coupled a conduit model with a reservoir model.•We simulated a geologically complex alpine karst aquifer system at catchment scale.•Hydrographs from three karst springs were used to calibrate the ...transient model.•The global optimization approach was implemented to achieve efficient calibration.•The model reproduced correctly the observed hydrographs of all three springs.
Karst aquifers are important for freshwater supply, but difficult to manage, due to highly variable water levels and spring discharge rates. Conduits are crucial for groundwater flow in karst aquifers, but their location is often unknown, thus limiting the applicability and validity of numerical models. We have applied a conduit model (SWMM) to simulate highly variable flow in a folded alpine karst aquifer system, where the underground drainage pattern is comparatively well-known from previous tracer studies. The conduit model was coupled with a reservoir model representing recharge, storage and transfer of water in the epikarst and unsaturated zone. The global optimization approach (GA) was applied to achieve an efficient model calibration. It was possible to simultaneously simulate the highly variable discharge characteristics of an estavelle, and overflow spring and a permanent spring draining the conduit system. The model allowed for the collection of spatially differentiated information on recharge, rapid flow and slow flow in four individual sub-catchments. The formation of backwater upgradient from conduit restrictions turned out to be a key process in activating overflow springs. The proposed modeling approach appears to be transferrable to other karst systems with predominant conduit drainage, but requires previous knowledge of the configuration of the conduit system.
The pollution of karst aquifers by acid mine drainage (AMD) waters is increasing. Major and minor ions (Ca2+, Mg2+, HCO3−, SO42−, F−, and Fe), stable sulfur and oxygen isotopes of dissolved sulfates ...(δ34SSO4 and δ18OSO4) and oxygen isotope of water (δ18OH2O), were analyzed in rainwater, surface water, groundwater, and AMD water sampled from the Babu subterranean stream watershed, in Southwest China. The principal aim of this study was to explore the impact of AMD waters on the evolution of karst aquifers. Based on hydrogeochemistry and stable isotopes (δ18OH2O, δ18OSO4 and δ34SSO4): (1) the chemistry of AMD waters was primarily controlled by pyrite oxidation, karst conduit water by AMD waters and mixing with calcite and dolomite dissolution, and spring water by atmospheric precipitation and carbonate dissolution; (2) contamination of the karst conduit water was mainly attributed to the input of AMD waters, resulting in a shift of δ34SSO4 towards more negative values (from 3.4‰ to −13.2‰); (3) the quality of karst conduit water changed from suitable to unsuitable for irrigation and drinking, particularly due to the increase in total Fe, SO42−, and F− concentrations, reflecting the cumulative effect of AMD waters derived from tailings dumps; this influence was enhanced during rainstorm/drought and anthropogenic activities; and (4) the flow of contaminated groundwater through the conduit promoted the dissolution of carbonates, especially during the dry season due to the greater proportion of AMD in the groundwater. This released more CO2 to the atmosphere. We believe that analysis of stable isotopes (δ18OH2O, δ18OSO4, and δ34SSO4), combined with hydrogeochemistry, is effective for exploring the impact of AMD on karst aquifers. Therefore, reasonable treatment methods should be taken to reduce the negative impacts of tailings dumps on karst aquifers.
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•Hydrogeochemistry and stable isotopes were employed to assess the impact of AMD on karst aquifers.•Total Fe, SO42− and F− were identified as the predominant pollutants in groundwater.•Groundwater contamination occurred because of the Houlongshan AMD waters.•The contaminated groundwater promoted the dissolution of carbonates, especially during the dry season.
The Karst aquifers are usually characterized by high spatial heterogeneity in the humid tropics and subtropics, evidenced by specific landforms features (e.g., heavily fractured outcrops, sinkholes, ...etc.) and complex subterranean conduit networks. The marked high heterogeneity leads to the temporal–spatial variability of hydrological and hydro-chemical processes, making its environments extremely vulnerable to natural and anthropogenic hazards. The complicated temporal–spatial variability of hydrochemistry in karst systems depends on several underlying factors which influence the hydro-chemical processes. Investigating the factors of the karst water hydrochemistry variability is necessary to understand the hydro-chemical processes and mitigate natural and anthropogenic hazards for ensuring the sustainability of karst water resources. In this paper, an attempt is made to couple geostatistical and geochemical analysis to extract the underlying controlling factors and effective information about the geochemical evolution behave of karst water in Houzhai karst area, southwestern China. Factor analysis was performed to obtain significant statistical relationship of the hydrochemistry variation in the Houzhai karst basin. The ordinary kriging method was applied to the factor scores to investigate the contributions of factors on different regions. The results of the factor analysis indicated four principal factors which explained > 81.678% of the total sample variance: (1) the dilution effect by rainfall; (2) the dissolution effect dominated by calcite; (3) the human agricultural activities effect; (4) the migration of dissolved components under the control of alkaline environments in karst water. It revealed that the dilution effect was more significant (36.579%) than the dissolution effect (22.036%) and human agricultural activities effect (14.596%). These factors made more significant difference of contributions on the karst area in the dry periods than in the rainy periods. The dilution process by rainfall and the dissolution process of carbonate rock had a great influence on the upstream area whereas the human agricultural activities played important roles in the middle-stream area, especially in the dry periods. This integrated approach which combine factor analysis with kriging method is effective in the identification and interpretation of factors related to the variability of hydrochemistry, as well as the contributions of these factors on space and time.
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