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Anthropogenic activities and climate change exert significant pressures on the quality and availability of water resources in karst environments, which supply drinking water to about 9.2% of the world's population. Increasing temperatures and changes in precipitation regimes will strongly impact water recharge processes. Understanding the karst hydrodynamic behaviour in the present context of climate change constitutes a major challenge for a sustainable management of karst groundwater. This study focuses on the Mediterranean area, where up to 90% of the drinking water supply depends on carbonate aquifers. The spring discharge and/or water level of six karst systems in the Mediterranean area (France, Italy, Lebanon, Slovenia, Spain and Tunisia) are simulated using precipitation-discharge reservoir modelling tools. The studied karst systems are well known and have different characteristics in terms of climatic conditions, hydrogeological properties and available data. Using different model structures, the hydrological models are first calibrated and validated over a historical period and then used to simulate spring discharge time series under various climate projections (up to 2100). To account for uncertainties in climate projection, 12 coupled GCM/RCM climate models are considered with two emission scenarios (RCP 4.5 and RCP 8.5) proposed in the framework of the CMIP5 initiative. The analysis of the forecasted spring discharge and water level time series focuses on (i) the long-term trends in the hydrological functioning of karst systems, (ii) the effects of climate change on spring discharges (intensity and duration of extreme events), and (iii) the study of uncertainties related to the exceedance of the known functioning ranges of the systems. Further discussion is also dedicated to model uncertainties in relation to model parameters and structure, climate models, and the estimation of potential evapotranspiration in future climate. This research has been conducted within the KARMA (Karst Aquifer Resources availability and quality in the Mediterranean Area) project into the PRIMA (Partnership for Research and Innovation in the Mediterranean Area) EU program.

This paper presents a quantitative study of the relationship between the cave system and the tectonic and karst evolution of the Dong Van Karst Plateau based on analysis and statistics of geometric parameters and orientation of cave passages. The region is located in northern Vietnam and belongs to the extended part of the South China karst belt (Yunnan karst plateau), which is composed mainly of carbonate rocks. Cave classification based on cave conduits geometric parameters shows that caves developed mainly in the vadose zone (27 vadose branchwork caves, 10 mixed caves developed under the control of fault systems, and 12 water-table caves). The degree of correlation between cave levels and planation surfaces suggests that the development of horizontal cave passages is related to two levels of planation surfaces, including one at 1250–1450 masl (equivalent to cave level at 1350–1450 masl), and at 1000–1250 masl (corresponding to cave level at 1200–1250 masl). Additionally, cave passage orientation shows that the cave system formed and developed under the influence of tectonic activities in the Cenozoic. The dominant orientation trend is roughly in the East–West direction and occurred in the early phase (Eocene–Miocene). Next is a trend roughly North–South that occurred in the late phase (Pliocene–Quaternary). The last orientation trend follows the NW–SE direction due to the reactivation of paleo-fault systems in the same direction. Although there are limitations due to accessibility and the level of cave exploration, this research suggests that analysis and statistics of the geometric parameters and orientation of cave passages based on cave survey data can be one of the effective approaches used to identify the development and structure of karstification in the karst region.

Groundwater monitoring wells or boreholes often show complex flow behaviors that are essential to understand for the characterization of aquifer systems. In karst or fractured aquifers, where complex conduit and/or fracture networks with differing hydraulic heads can be intersected by a well or borehole, vertical flow is highly probable. Single-borehole dilution tests (SBDT) with uniform injections are, in general, a good method to gain knowledge about a specific well or borehole, but tend to deliver ambiguous results regarding vertical flow, while SBDTs with point injections are an effective method to identify vertical flow. This technical note introduces a newly developed probe for point injections in groundwater without disturbing the natural flow field. In order to evaluate this probe, several tests were conducted in the laboratory and in groundwater monitoring wells that show vertical flow. During repeated tests in the laboratory, the new point injection probe showed a good reproducibility regarding the shape and extent of the tracer cloud after an injection. The opening mechanism was found to be well-functioning and reliable. Field tests lead to significant results for all tested wells and showed that the probe can easily be operated by a single person. Due to the flexibility regarding tracer, aquifer and injection depth, combined with the easy handling, it is a useful device, suitable for the investigation of boreholes and groundwater monitoring wells, and a good alternative to existing methods.

Hydrological models are widely used to characterize, understand and manage hydrosystems. Lumped parameter models are of particular interest in karst environments given the complexity and heterogeneity of these systems. There is a multitude of lumped parameter modelling approaches, which can make it difficult for a manager or researcher to choose. We therefore conducted a comparison of two lumped parameter modelling approaches: artificial neural networks (ANNs) and reservoir models. We investigate five karst systems in the Mediterranean and Alpine regions with different characteristics in terms of climatic conditions, hydrogeological properties and data availability. We compare the results of ANN and reservoir modelling approaches using several performance criteria over different hydrological periods. The results show that both ANNs and reservoir models can accurately simulate karst spring discharge but also that they have different advantages and drawbacks: (i) ANN models are very flexible regarding the format and amount of input data, (ii) reservoir models can provide good results even with a few years of relevant discharge in the calibration period and (iii) ANN models seem robust for reproducing high-flow conditions, while reservoir models are superior in reproducing low-flow conditions. However, both modelling approaches struggle to reproduce extreme events (droughts, floods), which is a known problem in hydrological modelling. For research purposes, ANN models have been shown to be useful for identifying recharge areas and delineating catchments, based on insights into the input data. Reservoir models are adapted to understand the hydrological functioning of a system by studying model structure and parameters.

Performance criteria play a key role in the calibration and evaluation of hydrological models and have been extensively developed and studied, but some of the most used criteria still have unknown pitfalls. This study set out to examine counterbalancing errors, which are inherent to the Kling–Gupta efficiency (KGE) and its variants. A total of nine performance criteria – including the KGE and its variants, as well as the Nash–Sutcliffe efficiency (NSE) and the modified index of agreement (d1) – were analysed using synthetic time series and a real case study. Results showed that, when assessing a simulation, the score of the KGE and some of its variants can be increased by concurrent overestimation and underestimation of discharge. These counterbalancing errors may favour bias and variability parameters, therefore preserving an overall high score of the performance criteria. As bias and variability parameters generally account for two-thirds of the weight in the equation of performance criteria such as the KGE, this can lead to an overall higher criterion score without being associated with an increase in model relevance. We recommend using (i) performance criteria that are not or less prone to counterbalancing errors (d1, modified KGE, non-parametric KGE, diagnostic efficiency) and/or (ii) scaling factors in the equation to reduce the influence of relative parameters.

Reconstructing the geologic history of a karst area can advance understanding of the system’s present-day hydrogeologic functioning, and help predict the location of unexplored conduits. This study tests competing hypotheses describing past conditions controlling cave formation in an alpine karst catchment, by comparing an ensemble of modelled networks to the observed network map. The catchment, the Gottesacker karst system (Germany/Austria), is drained by three major springs and a paleo-spring, and includes the partially explored Hölloch cave, which consists of an active section whose formation is well-understood, and an inactive section whose formation is the subject of debate. Two hypotheses for the formation of the inactive section are: 1) glaciation obscured the three present-day springs, leaving only the paleo-spring, or 2) the lowest of the three major springs (Sägebach) is comparatively young, so its subcatchment previously drained to the paleo-spring. These hypotheses were tested using the pyKasso Python library (built on anisotropic fast marching methods) to generate two ensembles of networks, one representing each scenario. Each ensemble was then compared to the known cave map. The simulated networks generated under Hypothesis 2 match the observed cave map more closely than those generated under Hypothesis 1. This supports the conclusion that the Sägebach spring is young, and suggests that the cave likely continues southwards. Finally, this study extends the applicability of model ensemble methods from situations where the geologic setting is known but the network is unknown, to situations where the network is known but the geologic evolution is not.

Karst aquifers in subtropical regions are characterized by high variability of water availability and quality due to changes associated with rainy and dry seasons. An additional challenge for water management is the combination of surface-water and karst groundwater systems since high spatiotemporal dynamics cause high variability of water quality. In these cases, adapted protection strategies are required. In this study, a protection approach for the catchment of a river-water diversion point in a rural area in northern Vietnam is developed. The variability of water quality was evaluated by rainy and dry season synoptic surveys of suspended particles and microbial contamination at 49 sites and time series at three sets of paired sites under constant hydraulic conditions. The anthropogenic land-use activities in the catchment were mapped to identify potential contamination sources and to highlight the challenging combination of surface-water and karst groundwater management. The analyzed data indicate differences in water quality between the dry and rainy seasons and a higher influence on water quality from land use than from hydrologic conditions. Furthermore, the results suggest a high risk of contamination resulting from residential areas, agriculture, and livestock farming, and reveal the necessity of implementation of appropriate measures such as restricted farming and the hook-up of buildings to municipal sewage disposal. Finally, the data show that water quality can be improved by adjusting water withdrawals by the time of day. The applied methods can be transferred to other surface-water and karst groundwater systems in similar subtropical environments.

Karst springs are the natural outflow of karst water to the surface. These springs occur where the water table can reach the surface unimpeded. This study examines the effect of alluvial deposits with varying thickness and permeability, covering the main outlet (karst spring) of a karst network on karst drainage (e.g., development of the karst water, drainage patterns, conduit-matrix interaction) as a result of a positive base level shift. This was realized with a numerical conceptual model (FEFLOW) of a hypothetical karst aquifer with 6 model configurations (inactive vs. active conduit flow, free vs. confined spring conditions with 20 m and 50 m sediment cover, respectively, with low and high hydraulic conductivity). Conduit flow and coupled conduit-matrix interactions were incorporated into the model with one-dimensional discrete feature elements. The results show that the permeability of the sediments has a more distinctive effect on conduit discharge than their thickness. The conduit network significantly contributes to the drainage even with a fully confined spring outlet. The conduit system acts as a water collector from the matrix in the recharge zone. The buried outlet increases the hydrostatic pressure farther along the conduit, and water is pushed upwards back into the matrix in the vicinity of the stratigraphic contact. Depending on the depositional setting, this results in the evolution of one to multiple new flow systems towards new potential spring sites. The results obtained here provide insight into the likely responses of natural karst systems.

Performance criteria such as the mean squared error (MSE), the Nash-Sutcliffe efficiency (NSE) and the Kling-Glupta efficiency (KGE) are extensively used to calibrate hydrological models. In recent years, numerous authors have stressed the inherent limitations of squared-error based criteria such as MSE and NSE. As a result, KGE criterion is gaining in popularity and is being widely used for calibration and for assessment. KGE has been initially proposed to address the poor consideration of discharge variability by NSE, but it also helps to lower the impact of squared errors in highly variable time series. KGE is a combination of (i) the Pearson correlation coefficient (r), (ii) the ratio between simulated and observed means (β), and (iii) the ratio between simulated and observed variances (α). In this study, we used KGE to compare the performance of two karst hydrological models (ANN and LP) over different flow regimes (dry, intermediate, wet) of two karst springs. The considered karst systems exhibit high contrasts in geometrical and hydrodynamic properties, inducing a high variability of the discharge at the springs. The discharge time series were divided into three sub-time series (dry, intermediate, and wet flows) according to fixed thresholds of discharge values. KGE values were higher for LP model for each sub-time series of both karst systems, thus indicating a better performance of LP over ANN at dry, intermediate and wet flows. However, KGE of the whole discharge time series were higher for ANN model, thus indicating a better overall performance of ANN over LP. The analysis of the decomposition of KGE (r, β, α) alongside a visual assessment of the simulated discharges of both models revealed that a compensation bias may be induced by β and α parameters. Simultaneous and equal overestimations and underestimations of multiple parts of the discharge time series seem to favour β and α values, leading to an overall better KGE coefficient without being associated to an increased model relevance.

This study compares and analyzes high-frequency hydrochemical data from three karst catchments in the mountainous Gadenalpe (GAC, Austrian Alps), Tsanfleuron-Sanetsch (TSC, Swiss Alps), and Banzhai (BZC, SW China) regions, to differentiate the effects of temperature, runoff, and land-cover on carbonate weathering. The results show that when bare rock dominates in the recharge area, as in the GAC and TSC, the seasonal discharge variations account for the most significant change in HCO3− concentration. In these two alpine catchments, maximum HCO3− concentrations occurred in the cold season when the areas were covered by snow and discharge was low, whereas minimum HCO3− concentrations occurred in the warm season, when snowmelt and/or glacier melt caused higher discharge and dilution. In contrast, control by the strong seasonal variation in soil respiration in the subtropical catchment (BZC), caused by the well-developed forest cover, exceeded the negative impact of temperature on carbonate weathering. This led to higher HCO3− concentrations during the summer growing season than in the winter dormant season. This study demonstrates that the occurrence of different soils/vegetation has a profound impact on the behavior of carbonate weathering on land, from negative temperature- and discharge-driven correlations in alpine catchments to positive soil CO2-driven correlation in subtropical catchments. Based on the equilibrium modeling of HCO3− concentration for a global temperature range, it is predicted that under future global warming, karst regions in cold climates with vegetation cover will have increasing CO2 consumption potential, whereas karst regions in warm climates will have decreasing CO2 consumption potential.

Colloidal particles are an important vector for the transport of contaminants in karst aquifers, characterized by a high degree of hydrologic variability. Understanding this heterogeneity and hydrogeological functioning is of particular importance for water management strategies. Until now, transport parameters for particles were mostly determined by injection of solutes or surrogates for natural sediments. But suspended particles are easier to analyse, less expensive and better represent natural conditions. Therefore, tracer tests with sediments represent natural transport and a conservative solute dye were conducted simultaneously in an active and partly accessible cave system in Vietnam during constant high‐flow and low‐flow conditions. Breakthrough curves (BTCs) for 10 different particle sizes classes ranging from 1 to 15 μm and the solute were recorded in situ at the two main resurgences of the cave stream at high temporal resolution. This study gives new insights into the transport processes of suspended particles and the highly dynamic exchange between mobile and immobile regions. Major findings include: (1) at low‐flow conditions, inflow from the surrounding aquifer matrix and the velocity distribution inside the karst conduits themselves lead to hydrodynamic focusing, mainly affecting particles; (2) this highly advective, preferential transport of particles in the centre of the karst conduits results in narrow BTC. The more dispersive transport of solutes results in a longer tailing; (3) at high‐flow conditions a more homogeneous distribution of the particles indicates a reversal of the conduit‐matrix interaction; (4) by comparing the results at different hydraulic conditions, the activation of additional flow paths with increasing discharge could be identified. This study also presents the first tracer test in the field resulting in pronounced double peaks for the particulate tracer but only a single, right‐skewed BTC for the simultaneously injected solute, including a conceptual model for particle transport., New insights into the transport processes of suspended particles and the highly dynamic exchanges between karst conduits and the surrounding matrix. Inflow and velocity distribution in karst conduits lead to hydrodynamic focusing mainly affecting particles. Highly advective, preferential transport of particles in the centre of the karst conduit results in narrow BTCs. By comparing the results at different hydraulic conditions, the activation of additional flow paths with increasing discharge could be identified by double‐peaks., Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

Water suppliers face major challenges such as climate change and population growth. To prepare for the future, detailed knowledge of water resources is needed. In southern Germany, the state water supplier Zweckverband Landeswasserversorgung provides 3 million people with drinking water obtained from a complex karst and alluvial aquifer system and the river Danube. In this study, a combination of different tracing techniques was used with the goal of a multi-scale characterization of the aquifer system and to gain additional knowledge about groundwater flow toward the extraction wells in the Danube Valley. For the small-scale characterization, selected groundwater monitoring wells were examined using single-borehole dilution tests. With these tests, a wide range of flow behavior could be documented, including fast outflow within just a few hours in wells with good connection to the aquifer, but also durations of many weeks in low-permeability formations. Vertical flow, caused by multiple flow horizons or uprising groundwater, was detected in 40% of the tested wells. A regional multi-tracer test with three injections was used to investigate the aquifer on a large scale. For the highly karstified connection between a swallow hole and a spring group, high flow velocities of around 80 m/h could be documented. Exceptionally delayed arrivals, 250 and 307 days after the injection, respectively showing maximum velocities of 0.44 and 0.39 m/h, were observed in an area where low-permeability sediments overlay the karst conduits. With the chosen methods, a distinct heterogeneity caused by the geological setting could be documented on both scales.

International audience; Despite many existing approaches, modeling karst water resources remains challenging as conventional approaches usually heavily rely on distinct system knowledge. Artificial neural networks (ANNs), however, require only little prior knowledge to automatically establish an input-output relationship. For ANN modeling in karst, the temporal and spatial data availability is often an important constraint, as usually no or few climate stations are located within or near karst spring catchments. Hence, spatial coverage is often not satisfactory and can result in substantial uncertainties about the true conditions in the catchment, leading to lower model performance. To overcome these problems, we apply convolutional neural networks (CNNs) to simulate karst spring discharge and to directly learn from spatially distributed climate input data (combined 2D-1D CNNs). We investigate three karst spring catchments in the Alpine and Mediterranean region with different meteorological-hydrological characteristics and hydrodynamic system properties. We compare the proposed approach both to existing modeling studies in these regions and to our own 1D CNN models that are conventionally trained with climate station input data. Our results show that all the models are excellently suited to modeling karst spring discharge (NSE: 0.73-0.87, KGE: 0.63-0.86) and can compete with the simulation results of existing approaches in the respective areas. The 2D models show a better fit than the 1D models in two of three cases and automatically learn to focus on the relevant areas of the input domain. By performing a spatial input sensitivity analysis, we can further show their usefulness in localizing the position of karst catchments.

Anisotropic fast-marching algorithms are computationally efficient tools for generating realistic maps of karst conduit networks, constrained by both the spatial extent and the orientation of karstifiable geologic units. Existing models to generate conduit network maps are limited either by high computational requirements (for chemistry-based models) or by their inability to incorporate the effects of elevation and orientation gradients (for isotropic fast-marching models). The new anisotropic fast-marching approach described here provides a significant improvement, though it imitates rather than reproduces actual speleogenetic processes. It can rapidly generate a stochastic ensemble of plausible networks from basic geologic information, which can also be used as input to karst-appropriate flow models. This paper introduces an open-source, easy-to-use implementation through the Python package pyKasso, then describes its application to a well-mapped geologically complex long-term study site: the Gottesacker alpine karst system (Germany/Austria). Groundwater flow in this system is exceptionally well understood from speleological investigations and tracer tests. Conduit formation primarily occurs at the base of the karst aquifer, following plunging synclines. Although previous attempts to reproduce the conduit network at this site yielded implausible network maps, pyKasso quickly generated networks faithful to the known conduit system. However, the model was only able to generate these realistic networks when the inlet-outlet connections of the system were correctly assigned, highlighting the importance of pairing modeling efforts with field tracer tests. Therefore, a model ensemble method is also presented, to optimize field efforts by identifying the most informative tracer tests to perform.

Karst aquifers are important resources for drinking water supply and are very vulnerable to contamination. Microbial concentrations at karst springs, in particular, often vary quickly over a short period of time. In this study, the response of microbial water quality and particle-size distribution of two alpine karst springs to rainfall events was investigated to test and validate parameters that can be used as early-warning systems for fecal contamination. At both investigated karst springs, total organic carbon, particle-size distribution (especially small particle fractions), and particle load show a good correlation to the fecal indicator bacteria E. coli and can therefore be used as a real-time indicator of fecal contamination at the investigated springs. In addition to conventional bacterial determination methods, the β-D-glucuronidase activity, which can be measured in near real-time, was used as a novel indicator parameter for fecal contamination. At the event scale, the β-D-glucuronidase (GLUC) activity shows a good correlation to E. coli and can be used as an additional real-time indicator of fecal contamination. For the studied springs, when they show two peaks in turbidity and small particles, these two parameters are suitable for an early warning system because the bacterial contamination occurs during the secondary peak of these parameters. These results highlight the vulnerability of karst aquifers and demonstrate the applicability of advanced measurement techniques in detecting fecal contamination in real-time, which is especially important given the time-consuming nature of conventional bacterial detection methods.

Improving water availability and distribution is key to combatting water stress in semi-arid regions. This study presents an approach that integrates hydrogeological surveys and economic analysis at a pilot site in the eastern Lower Jordan Valley to assess the potential for managed aquifer recharge (MAR). Based on exploratory drillings, hydraulic tests, water-quality analyses and previous studies, an appropriate storage space in the alluvial fans along the eastern margin of the valley was found. Average measured infiltration rates of 9.8 × 10−5 m/s in a gravel pit and average hydraulic conductivity values of 6.8 × 10−5 m/s in the aquifer indicate that up to 1 Mm3/year can be infiltrated and stored underground. It is assumed that water is trapped towards the center of the valley where the alluvial sediments inter-finger with fine-grained layers. An increase in electrical conductivity values in the same direction probably indicates irrigation return flow and the presence of evaporitic layers and suggests a water recovery before reaching these saline zones. Depending on whether the water provided by MAR is used for irrigation or domestic water purpose, an average incremental profit of 0.81 and 2.44 US$/m3 can be achieved, respectively. These calculations result in a net present value of the MAR plant of 10.6 or 31.9 million US$, respectively, over a lifetime of 30 years. The presented study serves as a basis for further investigations and planning of a MAR plant, and can be transferred and upscaled to other sites in the Jordan Valley.

International audience; Groundwater pollution threatens human and ecosystem health in many regions around the globe. Fast flow to the groundwater through focused recharge is known to transmit short-lived pollutants into carbonate aquifers, endangering the quality of groundwaters where one quarter of the world’s population lives. However, the large-scale impact of such focused recharge on groundwater quality remains poorly understood. Here, we apply a continental-scale model to quantify the risk of groundwater contamination by degradable pollutants through focused recharge in the carbonate rock regions of Europe, North Africa, and the Middle East. We show that focused recharge is the primary reason for widespread rapid transport of contaminants to the groundwater. Where it occurs, the concentration of pollutants in groundwater recharge that have not yet degraded increases from

A holistic conceptual approach to groundwater and natural resources protection, surface and subsurface biodiversity conservation and ecosystem services in karst terrains is presented. Karst landscapes and aquifers consist of carbonate rock in which a part of the fractures has been enlarged by chemical dissolution. They are characterized by unique geomorphological and hydrogeological characteristics, such as rapid infiltration of rainwater, lack of surface waters, and turbulent flow in a network of fractures, conduits and caves. Karst terrains contain valuable but vulnerable resources, such as water, soil and vegetation, and they provide a great variety of habitats to many species, both at the surface and underground, including many rare and endemic species. Karst terrains deliver valuable ecosystem services and act as natural sinks for carbon dioxide (CO2) thus helping to mitigate climate change. It is demonstrated that all these resources and ecosystem services cannot be considered in an isolated way, but are intensely interconnected. Because of these complex feedback mechanisms, impacts on isolated elements of the karst ecosystem can have unexpected impacts on other elements or even on the entire ecosystem. Therefore, the protection of natural resources, biodiversity and ecosystem services in karst requires a holistic approach.

Large areas of Europe, especially in the Alps, are covered by carbonate rocks and in many alpine regions, karst springs are important sources for drinking water supply. Because of their high variability and heterogeneity, the understanding of the hydrogeological functioning of karst aquifers is of particular importance for their protection and utilisation. Climate change and heavy rainfall events are major challenges in managing alpine karst aquifers which possess an enormous potential for future drinking water supply. In this study, we present research from a high‐alpine karst system in the UNESCO Biosphere Reserve Großes Walsertal in Austria, which has a clearly defined catchment and is drained by only one spring system. Results show that (a) the investigated system is a highly dynamic karst aquifer with distinct reactions to rainfall events in discharge and electrical conductivity; (b) the estimated transient atmospheric CO2 sink is about 270 t/a; (c) the calculated carbonate rock denudation rate is between 23 and 47 mm/1000a and (d) the rainfall‐discharge behaviour and the internal flow dynamics can be successfully simulated using the modelling package KarstMod. The modelling results indicate the relevance of matrix storage in determining the discharge behaviour of the spring, particularly during low‐flow periods. This research and the consequent results can contribute and initiate a better understanding and management of alpine karst aquifers considering climate change with more heavy rainfall events and also longer dry periods., The investigated karst system contributes to the transient atmospheric CO2 sink with about 270 t/a. Carbonate denudation rates vary between 23 and 47 mm/1000a. Rainfall‐discharge modelling results indicate the importance of matrix storage particularly during low‐flow periods. image, Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347, FP7 People: Marie‐Curie Actions http://dx.doi.org/10.13039/100011264

Karst systems are challenging to model due to their heterogeneous hydraulic properties resulting in highly variable discharge behavior. Distributed models can be applied to karst aquifers but require detailed system knowledge and extensive hydraulic parameter datasets; lumped-parameter models are less complex, but still require parametrization. In this work, we demonstrate the application of a data-driven approach to model the discharge behavior of the Aubach spring in the Gottesacker karst system in the northern Alps, a well-investigated study site for which previous models are available for comparison (Chen et al. 2018; Fandel et al. 2020). Our approach is based on convolutional neural networks (CNN), which have proved to be well suited for time series forecasting in water-related contexts like runoff modelling or groundwater level prediction (Wunsch et al.). The approach is comparably simple in terms of data requirements as we rely mainly on widely available and easy-to-measure parameters such as precipitation and temperature. By implementing Bayesian techniques (Monte-Carlo dropout) we are able to report the predictive uncertainty of the CNN based forecasts. Our results challenge existing modelling results based on lumped-parameter models in terms of common error measures such as Nash-Sutcliffe efficiency. Furthermore, we explore the important role of snow accumulation and melting by coupling our model with a snow-routine to better represent their influence on spring discharge and further improve model performance. Our results demonstrate that the presented machine-learning approach can be applied to simulate karst spring discharge and has certain advantages in comparison with conventional karst modelling approaches, which require hydraulic parameters that are often not available.Chen, Z.; Hartmann, A.; Wagener, T.; Goldscheider, N. (2018) Dynamics of water fluxes and storages in an Alpine karst catchment under current and potential future climate conditions. Hydrology and earth system sciences, 22 (7), 3807–3823.Fandel, C.; Ferré, T.; Chen, Z.; Renard, P.; Goldscheider, N. (2020) A model ensemble generator to explore structural uncertainty in karst systems with unmapped conduits. Hydrogeology journal, published online.Wunsch, A.; Liesch, T.; Broda, S. (2020) Groundwater Level Forecasting with Artificial Neural Networks: A Comparison of LSTM, CNN and NARX. Hydrology and Earth System Sciences Discussions 2020:1–23. https://doi.org/10/ghtcz3

The monitoring of water quality, especially of karst springs, requires methods for rapidly estimating and quantifying parameters that indicate contamination. In the last few years, fluorescence-based measurements of tryptophan and humic acid have become a promising tool to assess water quality in near real-time. In this study, we conducted comparative tracer tests in a karst experimental site to investigate the transport properties and behavior of tryptophan and humic acid in a natural karst aquifer. These two tracers were compared with the conservative tracer uranine. Fluorescence measurements were conducted with an online field fluorometer and in the laboratory. The obtained breakthrough curves (BTCs) and the modeling results demonstrate that (1) the online field fluorometer is suitable for real-time fluorescence measurements of all three tracers; (2) the transport parameters obtained for uranine, tryptophan, and humic acid are comparable in the fast flow areas of the karst system; (3) the transport velocities of humic acid are slower and the resulting residence times are accordingly higher, compared to uranine and tryptophan, in the slower and longer flow paths; (4) the obtained BTCs reveal additional information about the investigated karst system. As a conclusion, the experiments show that the transport properties of tryptophan are similar to those of uranine while humic acid is partly transported slower and with retardation. These findings allow a better and quantitative interpretation of the results when these substances are used as natural fecal and contamination indicators.

We use the magnitude and centroid period of Rayleigh wave along with the amplitude of fluctuations of water level in a well to calculate effective porosity of a karst aquifer at the site scale. The radial and vertical displacements of Rayleigh wave are first related to the confining pressure of rock, which is then related to fluid pressure via the Gassmann equation. Three seismograms recorded at station 633A of the USARRAY and the induced responses of Well J-17 in the Edwards Aquifer (Texas) allow the calculation of an effective porosity between 17.0 and 24.4 percent, the average of which is close to the total porosity of core samples determined by geophysical well logs. This paper provides an innovative method to measure effective porosity in aquifers. Because of the long wavelengths of Rayleigh wave, the interdisciplinary approach is advantageous in that the resulting effective porosity is at the site scale which includes large conduits or voids.Za izračun efektivne poroznosti kraškega vodonosnika na lokalni ravni smo uporabili velikost in centroidno časovno vrednost Rayleighjevega valovanja, skupaj z amplitudo nihanja vodne gladine v vrtini. Radialni in vertikalni premiki Rayleighjevega valovanja so najprej povezani s tlakom neprepustne kamnine, ki je nato z Gassmannovo enačbo povezan s tlakom tekočine. Trije seizmogrami, evidentirani na postaji 633A USARRAY, in inducirani odzivi vrtine J-17 v vodonosniku Edwards (v Teksasu) omogočajo izračun efektivne poroznosti med 17,0 in 24,4 odstotka, povprečje teh vrednosti pa je blizu poroznosti jedra v vzorcih, ki so bili določeni z geofizikalnimi meritvami v vrtinah. V prispevku je predstavljena inovativna metoda za merjenje efektivne poroznosti v vodonosnikih. Zaradi dolgih valovnih dolžin Rayleighjevega valovanja je interdisciplinarni pristop ugoden, saj efektivna poroznost obravnavanega območja vključuje velike kanale ali praznine.

(IF 6.44; Q1); International audience; Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset’s coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations.

Groundwater depletion through drinking water abstraction, irrigation or climate change generally has a negative impact on terrestrial groundwater-dependent ecosystems. Towards the concept of ecologically sustainable groundwater abstraction management, a method is needed to uniformly evaluate different areas on the basis of biotic value. Biotic value represents the natural value of a habitat for protected species conservation (nature value). Established and currently indispensable methods of landscape planning generally evaluate habitat function via the habitats, whereby the inventory of animal species is largely ignored. Thus, there is a crucial need for additional species-based animal and ecology data to be methodologically standardised, quantified and incorporated into planning practice. Initial faunistic assessment methods already have been developed and applied in practice, but are generally limited to single groups of species, such as birds and bird breeding areas. In this paper, we present a new method that, in addition to the established habitat type module, incorporates a species module to enable multiple plant or animal species besides birds to be included in biotic area assessment. The use of this approach allows for standardized comparison of changing biotic area values over time, or among, for example, European Natura 2000 areas. By considering groundwater dependency and groundwater impact, special attention can be paid to derivation of the hydroecological vulnerability. This method makes it possible to calculate further vulnerabilities by considering other environmental threat factors. We test this method in the case study of the drinking water catchment area of the city of Karlsruhe.

Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset’s coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a wide range of applications: comparative studies, trend analysis and model evaluation. This database will largely contribute to research advancement in karst hydrology, supports karst groundwater management, and promotes international and interdisciplinary collaborations., Measurement(s)hydrographic feature • fluid flow rateTechnology Type(s)digital curationFactor Type(s)geographic location • yearSample Characteristic - Environmentkarst • spring • groundwater Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.11336507

Availability of long-term and high-resolution measurements of soil moisture is crucial when it comes to understanding all sorts of changes to past soil moisture variations and the prediction of future dynamics. This is particularly true in a world struggling against climate change and its impacts on ecology and economy. Feedback mechanisms between soil moisture dynamics and meteorological influences are key factors when it comes to understanding the occurrence of drought events. We used long-term high-resolution measurements of soil moisture on a large inclined lysimeter at a test site near Karlsruhe, Germany. The measurements indicate (i) a seasonal evaporation depth of over two meters. Statistical analysis and linear regressions indicate (ii) a significant decrease in soil moisture levels over the past two decades. This decrease is most pronounced at the start and the end of the vegetation period. Furthermore, Bayesian change point detection revealed (iii), that this decrease is not uniformly distributed over the complete observation period. Largest changes occur at tipping points during years of extreme drought, with significant changes to the subsequent soil moisture levels. This change affects not only the overall trend in soil moisture, but also the seasonal dynamics. A comparison to modeled data showed (iv) that the occurrence of deep desiccation is not merely dependent on the properties of the soil but is spatially heterogeneous. The study highlights the importance of soil moisture measurements for the understanding of soil moisture fluxes in the vadose zone.

This essay discusses the need for, advantages and challenges of integrating the scientific disciplines of ecology and hydrogeology in the study of groundwater-dependent ecosystems (GDEs). We provide a definition for ecohydrogeology as “a unifying, synthetic field of study integrating the approaches from the ecological and hydrogeological sciences in the study of groundwater (GW)-related ecosystems, habitats, and organisms to advance science, stewardship, and policy”. We selected specific case studies to illustrate first how hydrogeological approaches can favour in-depth understanding and modelling of springs and crenobiontic (spring-dependent) species distribution, assemblage composition and organization. Second, this essay also examines how taxa and assemblages serve as bioassays and ecosystem indicators to infer hydrogeological aspects of GW flow and discharge, as well as quantitative and qualitative human impacts. We consider both types of features and parameters as ecohydrogeological indicators. The examples presented include topics related to springs and other GDE geomorphological types and classification, GW quality influences on crenobiont distribution, phreatophyte (= plant species the roots of which reach to and into the water table) ecophysiology in relation to water table depth, and flow variability in karstic systems, to nutrient dynamics in relation to dinoflagellate blooms in GDE montane lakes. Conceptual approaches that integrate ecology with hydrogeology include the investigation of GDE distribution and ecology, groundwater-surface water (GW-SW) interactions, and the development of the discipline of ecohydrology. Despite widespread applications, the scientific community still lacks a complete or effective integration of the principles described in the fields of groundwater hydrogeology with ecology, ecophysiology, and environmental biology. Springs are aquatic-wetland-riparian habitats that link shallow subsurface-surface processes and assemblages, often functioning as biodiversity hotspots, ecotones, keystone, and refugial ecosystems, for which coordination between studies of hydrogeology and ecology are both obvious and essential. Over the past century, springs ecosystem ecology has been largely ignored by hydrologists, and, conversely, hydrogeology has been under-emphasized by ecologists. Recent global recognition of the extraordinary biodiversity and socio-cultural significance of springs, coupled with their globally highly threatened conservation status, stimulated this inquiry into how to better integrate hydrogeology with springs ecosystem ecology. Acknowledging the highly threatened status of springs ecosystems around the world, there is an urgent need to integrate and invigorate the union of these disciplines into ecohydrogeology, the study of groundwater-dependent organisms, habitats, ecosystems, and management policy.

Karstregionen beinhalten eine Vielzahl natürlicher Ressourcen, wie Süßwasser und Biodiversität, sowie zahlreiche kulturelle und historische Ressourcen. Die Welt-Karstaquifer-Karte (WOKAM) ist die erste detaillierte und vollständige globale Datenbasis über die Verbreitung von verkarstungsfähigen Gesteinen (Carbonate und Evaporite), welche potentielle Karstaquifere darstellen. Diese Studie präsentiert eine statistische Auswertung von WOKAM, mit dem Fokus auf Karst in Carbonatgesteinen, und adressiert vier wesentliche Aspekte: (i) globales Vorkommen und geografische Verteilung von Karst; (ii) Karst in verschiedenen topografischen Settings und in Küstengebieten; (iii) Karst in verschiedenen Klimazonen; und (iv) Bevölkerung in Karstgebieten. Die Analyse ergibt, dass 15,2 % der globalen, eisfreien Kontinentalfläche durch Carbonatgesteine charakterisiert sind. Der höchste prozentuale Anteil tritt in Europa auf (21,8 %); die größte absolute Fläche in Asien (8,35 Mio. km²). Weltweit treten 31,1 % aller anstehenden Carbonatgesteine in Ebenen auf, 28,1 % im Hügelland und 40,8 % in Gebirgen; 151,400 km oder 15,7 % der globalen marinen Küstenlinie wird von Carbonatgesteinen geprägt. Etwa 34,2 % aller Carbonatgesteine kommen im ariden Klima vor, gefolgt von 28,2 % in kalten und 15,9 % in gemäßigten Klimaten, während nur 13,1 % bzw. 8,6 % im tropischen bzw. polaren Klima anzutreffen sind. Global leben etwa 1,18 Milliarden Menschen (16,5 % der Weltbevölkerung) in Karstgebieten. Die höchste absolute Anzahl wurde in Asien ermittelt (661,7 Mio.), während die höchsten prozentualen Anteile in Europa (25,3 %) und Nordamerika (23,5 %) auftreten. Diese Ergebnisse zeigen die globale Bedeutung von Karst und dienen als Basis für weitere Forschung und internationale Wassermanagement-Strategien.

Dense non-aqueous phase liquids (DNAPLs) can easily penetrate into karst aquifers, may accumulate in the sediment-filled depressions of conduits, and constitute a long-term source of groundwater contamination. In contrast to porous media, DNAPL dissolution in karst settings has not received much attention. This study investigated the dissolution of sediment-entrapped DNAPLs using a laboratory analogue model corresponding to a syphon structure partly filled by sediments and using numerical simulations. The mass transfer rate increased with an increasing conduit Reynolds number (Re) and increasing conduit angle, as both of these factors led to a more intense hyporheic flow in the sediments. In addition, the mass transfer rate increased linearly with the average flow velocity in the sediment and was higher than expected for an infinite porous medium considered as a reference case. The enhanced mass transfer rate can be explained by the curved streamlines associated with hyporheic flow, which transport solutes away from the DNAPL interface. This study demonstrates that hyporheic flow through karst sediment is a possible mechanism for the mobilization of DNAPL components and might explain the persistent occurrence of such contaminants in karst springs.

Spring water chemistry is influenced by many factors, including geology, climate, vegetation and land use, which determine groundwater residence times and water–rock interaction. Changes in water chemistry can have a profound impact on their associated ecosystems. To protect these ecosystems and to evaluate possible changes, knowledge of the underlying processes and dynamics is important. We collected water samples at 20 locations during 5 campaigns within the water catchment area of the upper Schonmunz river in the Black Forest National Park, Southwest Germany and analyzed them hydro-chemically for their contents of inorganic constituents, organic carbon content, fluorescence properties as well as several physico chemical field parameters and spring discharge. Results show that water chemistry is strongly dependent on geology and that the response of dissolved organic carbon to changes in hydraulic conditions is highly dynamic. Due to increased flow through the upper soil layer during and after rain events, more organic carbon is extracted from the soil and transported with the water. Fluorescence EEM measurements indicate an allochthonous source of this organic carbon. This study can be used as baseline to assess future changes and serve as a supplement to ongoing studies of the spring ecosystems.

Die okologisch nachhaltige Bewirtschaftung von Grundwasservorkommen zum Schutz grundwasserabhangiger Okosysteme ist gesetzlich vorgeschrieben. In der aktuellen Genehmigungspraxis werden Grundwasserentnahmen hinsichtlich ihrer Umweltwirkungen bislang isoliert bewertet, auch wenn bei groseren Wasserversorgern durch den von ausen vorgegebenen Wasserbedarf die Entnahmemengen der einzelnen Wassergewinnungsanlagen voneinander abhangig sind. Im Rahmen der Konzeption eines okologischen Entnahmemanagements fur die Wasserwerke der Stadt Karlsruhe wurden mehrere Arbeitsschritte durchgefuhrt: (1) Aufbau eines regionalen numerischen instationaren Grundwasserstromungsmodells, das die einzelnen, sich hydraulisch beeinflussenden Wasserwerke mit ihren Einzugsgebieten beinhaltet; (2) Ermittlung wasserrechtlich, technisch und hygienisch abgesicherter Minimalentnahmen, die in der Praxis realisierbar sind; (3) Ermittlung des raum-zeitlichen Steuerungspotenzials mittels Simulationsstudien des Wirkraums eines okologischen Entnahmemanagements. Da das Wasserdefizit, das aus Forderreduzierungen eines Wasserwerks resultiert, auf andere Wasserwerke verteilt werden muss, konnen okologische Verbesserungen an einem Ort mit okologischen Verschlechterungen anderenorts einhergehen. In auf den Ergebnissen aufbauenden Arbeiten wird die hydrookologische Vulnerabilitat des Bewirtschaftungsgebiets beschrieben und ein Verfahren zur okologischen Bewertung unterschiedlicher Entnahmeszenarien entwickelt.