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This article presents an introduction to the fundamentals of tracing techniques and their application in cave and karst environments, illustrated by case studies from the Mammoth Cave, USA, and a small experimental site in Switzerland. The properties and limitations of the most important artificial tracers are discussed, and the available methods o...
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... of Buffalo Creek at the Green River. The spring is stratigraphically situated in the middle of the Girkin Formation, a 25 m thick cavernous limestone forming the uppermost of the >100 m, nearly horizontally bedded limestone sequence comprising the Mammoth Cave Aquifer. The primary tributaries to Buffalo Creek, the Wet Prong and the Dry Prong (Fig. 6), are oriented roughly NE-SW, along the regional strike. Surface flow in the tributaries typically sinks into the Girkin Formation, which is exposed only along the floors of the Wet and Dry Prongs, just downstream from the contact of the overlying Big Clifty Sandstone. Point-to point tracing using charcoal detectors indicated that the ...
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... tracer dye Rhodamine WT (classified as "genotoxic" by Behrens et al. 2001 but still widely used in the US) was injected at the Wet Prong sinkpoint at the same time fluorescein (uranine) was injected into the cave stream of Fort's Funnel Cave (Fig. 6). The dye cloud from the Wet Prong arrived at the sampling site at Buffalo Spring ahead of the dye from the much closer Fort's Funnel. These results seemed to conflict with qualitative tracer tests, which had shown that water sinking in the Wet Prong passes through Fort's Funnel on its way to Buffalo Spring. From quantitative traces it ...
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... the Wet Prong conduit implies a smaller system volume relative to the discharge allowing the tracer through faster. Whether this indicates a steeper hydraulic gradient and lower flow resistance would require flood impulse tests to be investigated. The cross-link between the two conduits is shown as the "Piracy Route" in the pipe-diagram of Fig. 6. Further tests would be required to show whether it was an abandoned route functioning only during high flows, or a newly developing piracy of limited capacity carrying small flows at all ...
Citations
... Artificial tracing techniques involve the "intentional" injection of substances such as salt and uranine into the flow system, which help determine the actual flow paths and rates mainly associated with conduits (or fast flow). For a more detailed analysis of flow systems, however, discharge and natural tracer data should complement the use of artificial tracers (Goldscheider et al., 2008). Natural tracers do not involve "intentional" injection of substances for experimental purposes (Perrin, 2003) but are derived from the inherent physicochemical properties of groundwater affected by flow and interaction processes with the soil and rock. ...
Effectively managing water resources in karst systems requires a thorough understanding of their general conduit network along with their seasonal dynamics. Their investigation has involved well construction or several advanced natural tracer data, most of which are not always available. Hence, this work showcases a pragmatic approach that makes use of basic hydrochemical variables of springs with coarse temporal resolution in characterising a karst system. In this study’s example, physicochemical variables like major ion concentrations/ratios, Electrical Conductivity (EC), pH and water temperature (Tw) were measured on 20-day basis for a hydrological year at the Louros Catchment, Greece. We further performed the frequency distribution and variation analysis of EC and Tw, principal component analysis (PCA), scatter plots of carbonate ions vs sulphate and hydrochemographs to determine relevant hydrochemical processes and hydrogeological features. PCA and the scatter plots showed that the simple-type upper karst level is entirely dominated by carbonate dissolution, whereas the complex-type middle and lower levels also involve gypsum and dolomite dissolution. Presence of mixing between karst units was also detected. EC and Tw analyses revealed the degree of karstification of different units and relative depths of flow systems. Hydrochemographs reflected the seasonality of limestone and gypsum dissolution’s contributions linked to the dominant flow type (conduit vs diffuse). This study thus was able to demonstrate the usefulness of such holistic hydrochemical analyses to better understand karst systems. Given their cost-effectiveness, they can be easily applied to any understudied karst system worldwide.
... Em seguida, as substâncias extraídas são analisadas por instrumentos fluorimétricos, como espectrofotômetros, que medem a intensidade da energia eletromagnética em diferentes comprimentos de onda de luz em uma região específica, incluindo a ultravioleta, visível e infravermelho próximo. Esse método apresenta como vantagem a capacidade de monitorar vários pontos a baixo custo, sendo em alguns casos a única opção em locais de difícil acesso (Goldscheider et al., 2008). ...
... A amostragem contínua ou quantitativa consiste em medir a concentração do traçador corante fluorescente utilizando instrumentos fluorimétricos de campo, o que proporciona dados com alta resolução temporal (de segundos a minutos) e em concentrações em partes por milhão, bilhão e trilhão (Smart, 2005;Goldscheider et al., 2008). Esse método é o mais econômico, pois substitui os amostradores automáticos e não requer intervenção de um operador por dias ou semanas (Barckzewski et al., 1996). ...
The transport of pollutants through karst conduits is of growing concern, as irreversible environmental damage can be caused, such as the loss of aquatic biodiversity and the contamination of groundwater resources. For the identification and assessment of, for example, the origin and fate of contaminants and the interactions between surface and subsurface flows (subsurface connections, flow direction), fluorescent dye tracers are widely used. Therefore, this work aimed to present a review on the methodological evolution of the use of dye tracers in karstic systems and the main advances of these studies in Brazil. To this end, a bibliographical survey was carried out using the quantitative exploratory analysis method, which included an analysis of books, journals, theses and national and international dissertations published recently in the last 10 years, available on the CAPES Journals Portal, Web of Science and Google Scholar. As a result, it was possible to identify the advances of new field and laboratory instruments, specific modeling software, and new dye tracers. For the studies in Brazil, an increase in the number of research in the explored historical series was observed, which enabled a better understanding of the hydrodynamic behavior of karst systems, such as the identification of karst springshed limits and the identification and quantification of the flow and transport parameters.
... Em seguida, as substâncias extraídas são analisadas por instrumentos fluorimétricos, como espectrofotômetros, que medem a intensidade da energia eletromagnética em diferentes comprimentos de onda de luz em uma região específica, incluindo a ultravioleta, visível e infravermelho próximo. Esse método apresenta como vantagem a capacidade de monitorar vários pontos a baixo custo, sendo em alguns casos a única opção em locais de difícil acesso (Goldscheider et al., 2008). ...
... A amostragem contínua ou quantitativa consiste em medir a concentração do traçador corante fluorescente utilizando instrumentos fluorimétricos de campo, o que proporciona dados com alta resolução temporal (de segundos a minutos) e em concentrações em partes por milhão, bilhão e trilhão (Smart, 2005;Goldscheider et al., 2008). Esse método é o mais econômico, pois substitui os amostradores automáticos e não requer intervenção de um operador por dias ou semanas (Barckzewski et al., 1996). ...
O transporte de poluentes por condutos subterrâneos em aquíferos cársticos é uma preocupação crescente, visto que danos ambientais irreversíveis podem ser ocasionados, como a perda da biodiversidade aquática e a contaminação dos recursos hídricos subterrâneos. Para a identificação e avaliação, por exemplo, da origem e destino dos contaminantes e as interações entre fluxos superficiais e subterrâneos (conexões subterrâneas, direção de fluxo), os traçadores corantes fluorescentes, são amplamente usados. Logo, este trabalho teve como objetivo apresentar uma revisão sobre a evolução metodológica do uso de traçadores corantes nos sistemas cársticos e os principais avanços desses estudos no Brasil. Para atingir esse objetivo, foi realizado uma pesquisa bibliográfica sobre a temática contemplando diversos livros, periódicos, teses e dissertações nacionais e internacionais. Para os estudos no Brasil, foram selecionados os periódicos publicados nos últimos 10 anos, disponíveis no Portal Periódicos CAPES, base Web of Science e Google Scholar. Como resultado, foi possível identificar os avanços de novos instrumentos de campo e laboratoriais, softwares de modelagem específicos, e novos traçadores corantes. Para os estudos no Brasil, observou-se um crescimento no número de pesquisas na série histórica explorada, aos quais, possibilitaram uma melhor compreensão do comportamento hidrodinâmico dos sistemas cársticos, como a identificação dos limites cársticos e na identificação e quantificação de contaminantes.Palavras-chave: fluxo subterrâneo, traçadores fluorescentes, contaminação.
... These tests, initially developed for the investigation of karst aquifer systems (and still most widely used in karst), have been conducted using a variety of artificial and natural tracers (e.g. inorganic ions, radionuclides, fluorescent dyes, fluorescent microspheres, various microorganisms and viruses, natural sediments, etc.) to trace groundwater flow in different hydrological and hydrogeological environments and are of great value across many applications (Wood and Ehrlich, 1978;Auckenthaler et al., 2002;Goldscheider et al., 2003Goldscheider et al., , 2008Goldscheider, 2008, 2019;Maurice et al., 2010;Schiperski et al., 2016;Ward et al., 2016;Bandy et al., 2018Bandy et al., , 2019Richter et al., 2021). For example, artificial tracer tests are used to establish hydraulic connections between a defined injection site (e.g. ...
... Pore and size exclusion processes, which affect only particles, are a commonly accepted explanation for higher peak and mean flow velocities (Bradford et al., 2003) since microorganisms and particles cannot enter smaller pores or the pore space closer to walls where lower flow velocities occur (Goeppert and Goldscheider, 2019). Hence, the results of solute tracer tests are considered to be of limited value in predicting the movement of microorganisms in the subsurface (Kaess, 1998;Goldscheider et al., 2008;Ward et al., 2016). Nevertheless, tracer tests using various particle types and/or microorganisms (as surrogates for pathogens, colloidal and other natural particles, etc.) are still not a standard method used in karst hydrogeology (Schiperski et al., 2016;Goeppert and Goldscheider, 2019) even though the processes influencing the fate and transport of particulate contaminants in karst aquifer systems are only poorly understood (Flynn and Sinreich, 2010). ...
... Nevertheless, tracer tests using various particle types and/or microorganisms (as surrogates for pathogens, colloidal and other natural particles, etc.) are still not a standard method used in karst hydrogeology (Schiperski et al., 2016;Goeppert and Goldscheider, 2019) even though the processes influencing the fate and transport of particulate contaminants in karst aquifer systems are only poorly understood (Flynn and Sinreich, 2010). It remains a challenge to find widely applicable, inexpensive, and readily available tracers that will accurately mimic microbial properties and behavior during transport in the subsurface (Kaess, 1998;Ward et al., 2016;Bandy et al., 2018Bandy et al., , 2019Goeppert and Goldscheider, 2019) but which also pose no potential threats to public health and/or the wider environment (Cronin and Pedley, 2002;Goldscheider et al., 2008). For example, Serratia marcescens bacteria were used as a tracer in the past but are now classified as pathogens and not in use anymore (Goeppert and Goldscheider, 2008). ...
Bacterial contamination of karst groundwater is a major concern for public health. Artificial tracing studies are crucial for establishing links between locations where pollutants can rapidly reach the aquifer systems and subsequent receptors, as well as for enhanced understanding of pollutant transport. However, widely used solute artificial tracers do not always move through the subsurface in the same manner as particles and microorganisms, hence may not be ideal proxies for predicting movement of bacterial contaminants. This study evaluates whether a historically used microbial tracer (yeast) which is readily available, inexpensive, and environmentally friendly, but usually overlooked in modern karst hydrogeological studies due to challenges associated with its detection and quantification in the past, can reemerge as a valuable tracer using the latest technology for its detection. Two field-based studies on separate karst systems were carried out during low-flow conditions using a portable particle counter along with flow cytometry measurements to monitor the recovery of the yeast at the springs. Soluble fluorescent dyes were also injected simultaneously with the yeast for comparison of transport dynamics. On one tracer test, through a karst conduit of much higher velocities, the injected yeast and fluorescent dye arrived at the same time at the spring, in comparison to the tracer test on a conduit system with lower groundwater velocities in which the yeast particles were detected before the dye at the sampling site. Both a portable particle counter and flow cytometry successfully detected yeast during both tests, thereby demonstrating the applicability of this tracer with contemporary instrumentation. Even though no significant advantages of flow cytometry over the portable counter system can be reported on the basis of the presented results, this study has shown that flow cytometry can be successfully used to detect and quantify introduced microbial tracers in karst environments with extremely high precision.
... The mean residence of the tracer is: Noraee -Nejad et al. (2021) combined the consideration of the velocity determined from the arrival time (maximum velocity) and the peak time (average velocity) at piezometers to identify the primary flow direction of the preferential flow path at the Shahghasem Dam (Iran). Similarly, various t-concepts were used to assess the water volume in karst caves using the tracer method: Atkinson et al. (1973) proposed to use the peak time; Birk et al. (2004) used the arrival time; Smart (1988), Goldscheider et al. (2008) used the mean residence time; Käss (1998) concluded that when the tracer curve is severely affected by the dispersion process, using the peak time yielded better results. ...
The local pore water velocity along the preferential flow path signifies the hydraulic parameter responsible for erosion within an earthen dam. This study introduces an empirical approach to ascertain the local pore water velocity within the earth dam's leakage zones by monitoring the travel time of the salt tracer through the corresponding electric potential anomalies in the ground. The alignment of electric potential anomalies with the movement of the salt tracer plume over time was confirmed through experiments on a physical model coupled with numerical simulations. The pore water velocity, calculated based on the location of the maximum electric potential anomaly, demonstrated excellent agreement with the experimental value, with an error of under 6%. For illustrative purposes, a field-scale salt tracer test was conducted at a leaking earthen dam in Vietnam. The tracer breakthrough curve originating from the leakage point revealed that the seepage water's travel time is approximately 40 days. The results of electric potential anomalies over time indicate that the pathway of seepage flow from upstream to the leakage point forms a horizontal V-shape, with the local pore water velocity ranging from 1.7 to 9.9x10-5 m/s. These local pore water velocities are subsequently compared with the critical seepage velocity to assess in-situ information regarding the internal erosion status of the target dam.
... Water within karst aquifers can be stored and transmitted in distinct pore spaces, including micropores originating from deposition, small fissures because of tectonic activities, and large fractures and conduits resulting from karstification. Thus, karst aquifers often exhibit high heterogeneity and indicate intricate hydrological patterns (Bakalowicz, 2005;Goldscheider et al., 2008). Karst spring discharge is crucial for understanding karst systems and managing groundwater resource in karst aquifers and has garnered significant attention Song et al., 2022;Zhou and Zhang, 2022a). ...
Karst spring discharge plays a vital role in understanding karst systems and managing karst groundwater resources. Due to its inherent heterogeneity and complexity, hydrological factors in the karst system often exhibit highly nonlinear and nonstationary characteristics. To overcome this challenge, a novel self-adaptive deep learning architecture is proposed to forecast daily karst spring runoff with precipitation in this study. The newly proposed model effectively integrates discrete wavelet transform (DWT), WaveNet, and long short-term memory (LSTM), enhanced by the attention mechanism and residual connections to learn underlying patterns, mitigate the overfitting risk, focus on the most relevant time steps, and improve the prediction accuracy. The framework is structured into two parts: one part is dedicated to predicting the karst spring discharge, whereas another part primarily predicts the residuals arising from the main predictions. By intergrading the two-part approach, the innovative model can adaptively correct the systematic errors and refine its understanding of some aspects that it might initially struggle with. The newly proposed model and three existing deep learning models including LSTM, GRU and simple RNN models are applied to predict karst spring discharge at Barton Springs, Texas, USA. The results imply that the newly developed DWT-WaveNet-LSTM model can leverage the advantages of various models, adapt to various aspects of the hydrometeorological data, and better capture intrinsic patterns from nonlinear and nonstationary input features. It outperforms other models at all time steps, evidenced by lower RMSE and higher NSE values. The residual analysis is conducted by comparing the predicted and observed spring discharge values. The self-adaptive DWT-WaveNet-LSTM model exhibits residuals that are closely centered around zero with a symmetrical, bell-shaped distribution, indicating superior performance and robust predictions in the karst system due to its effective capture of complex and nonlinear patterns.
... At the end of the nineteenth century, fluorescent dyes were applied to assess surface water flow to support growing demand for clean water for drinking and for use in industrial activities [2,5]. They have also been used to delineate catchment areas [6] and study groundwater trajectories and active conduit networks in karst aquifers and caves [7,8]. Furthermore, they have been used to evaluate pipe flow [9], investigate leaks from reservoirs [10], and examine the behavior of contaminants (e.g., pesticides) in surface water [11,12]. ...
... Because such errors could seriously affect the results of experiments, the reactions and processes that change fluorescent dye concentrations need to be understood. The properties and limitations of fluorescent dyes and their use in groundwater studies have been reviewed [1,5,8,21], including their detection sensitivities, effects on water quality, photodegradation by sunlight, adsorption losses, environmental contamination risks, and toxicity. Nakata et al. [4] found that the pH, temperature, co-existence of natural organic matter, and filtration of fluorescent dye solutions greatly affected quantitative determination, and they proposed treatment methods to address each of these factors. ...
... These results are a strong indication that microbes contribute to the decreases in the UR concentration. Goldscheider et al. [8] mentioned that UR degrades in organic-rich environments. The input of organic matter may trigger the degradation of previously unreactive organic matter [41], and this has already been shown with contaminants [42]. ...
Fluorescent dyes are commonly used as conservative groundwater tracers to track the migration of water. Over- or underestimation of important parameters such as the water flow rate can occur if the concentration of a dye is changed by unexpected reactions. Because such errors may seriously affect the results of experiments, the reactions and processes that change fluorescent dye concentrations need to be understood. In this study, we focused on the widely used fluorescent dye uranine (UR) and aimed to identify microbes contributing to decreases in UR concentrations in groundwater. First, we identified the conditions (water temperature, pH, and salinity) under which significant decreases in UR concentrations occurred to show that the decrease in UR concentrations were caused by the effects of microbes in the groundwater. Next, we obtained information about the metabolism of organic matter by potential contributing microbes. These results were used to narrow down possible microbes that could decrease the UR concentration. Analysis of the microbial community in groundwater using 16S rRNA gene sequencing was then used to further identify contributing microbes. Finally, a verification experiment was conducted using a strain of one of the identified microbes (Parapontixanthobacter aurantiacus). Our results showed that conservation of the concentration of fluorescent dye solutions prepared with on-site groundwater was affected by several microbes with different metabolic characteristics, including P. aurantiacus. When fluorescent dye solutions prepared with on-site groundwater are used in field investigations or tracer tests, the pros and cons of using fluorescent dyes should be carefully evaluated because of the potential effects of microbes in the groundwater.
... Several types of investigations can be performed at the surface in order to assess the spatial flow behavior of a karst underground hydrosystem: artificial tracers tests (Bailly-Comte and Pistre, 2021; Goeppert et al., 2020;Goldscheider et al., 2008) highlighting large-scale connectivity, geophysical methods (Bechtel et al., 2007) to investigate the unsaturated vertical flows, or more local monitoring of physicochemical data and assessments of hydrodynamic properties in the saturated zone, in wells or at the spring (Olarinoye et al., 2020). Largescale interpretations of these investigations often require numerical modeling tools. ...
This article presents a multiphysics-based approach for a large-scale spatial reconstitution of head and tracer
tests responses measured in a regional scale karst aquifer in Southern France. The main dataset consists in hydraulic
heads measured in 11 wells during 6 weeks and 4 tracer tests. A pump station withdraws groundwater
from this aquifer at varying flow rates during days and nights to supply water to Montpellier agglomeration,
generating a periodic signal which propagates in the whole aquifer. Some of the measurements show a periodic
response, some others not. As a first step, this specificity is exploited to localize spatially the preferential flow
paths network with a structural deterministic inversion approach. Then, inversions of the weekly averaged head
variations are performed on the first and the last weeks of the dataset (showing different drawdown trends) to
assess the hydraulic diffusivity field. Finally, the tracer restitutions at the spring are inverted in order to optimize
the conduits diameters associated to the fastest flow paths.
The proposed approach permits a satisfying reproduction of the hydraulic heads and tracer measurements.
Simulations with the optimized model on a week of the dataset not used in the inversion allows to validate the
inversion result. The inverted model suggests that daily periodic responses represent efficient constraints for the
localization of the preferential flows, while the integration of weekly head variations provides a characterization
of the hydraulic properties between each well and the closest preferential flow paths, and tracer restitutions
permit to characterize the velocities in the preferential paths.
... Hydrologic tracing is a vital method of identifying and characterising pollutant sourcepathway-receptor linkages in karst aquifers [8,9]. In densely populated catchments, the effectiveness of fluorescent dye tracers is limited as the visible colouration of the water supplies is generally deemed unacceptable by water providers and regulatory bodies. ...
... The term 'breakthrough curve' (BTC) is used to describe tracer concentration-time data. Non-reactive tracer BTC data are evaluated and interpreted to gain information about aquifer transport properties, such as transit time, dilution and dispersivity [9,17]. However, the reactive nature of microbial tracers complicates the interpretation of BTC data beyond the establishment of a hydrologic connection and tracer-specific transit times. ...
Groundwater flow and contaminant migration tracing is a vital method of identifying and characterising pollutant source-pathway-receptor linkages in karst aquifers. Bacteriophages are an attractive alternative tracer to non-reactive fluorescent dye tracers, as high titres (>1012 pfu mL−1) can be safely released into the aquifer, offering improved tracer detectability. However, the interpretation of bacteriophage tracer breakthrough curves is complicated as their fate and transport are impacted by aquifer physicochemical conditions. A comparative tracer migration experiment was conducted in a peri-urban catchment in southeast England to characterise the behaviour of MS2 bacteriophage relative to sodium fluorescein dye in a karstic chalk aquifer. Tracers were released into a stream sink and detected at two abstraction boreholes located 3 km and 10 km away. At both sites, the loss of MS2 phage greatly exceeded that of the solute tracer. In contrast, the qualitative shape of the dye and phage breakthrough curves were visually very similar, suggesting that the bacteriophage arriving at each site was governed by comparable transport parameters to the non-reactive dye tracer. The colloid filtration theory was applied to explain the apparent contradiction of comparable tracer breakthrough patterns despite massive phage losses in the subsurface. One-dimensional transport models were also fitted to each breakthrough curve to facilitate a quantitative comparison of the transport parameter values. The model results suggest that the bacteriophage migrates through the conduit system slightly faster than the fluorescent dye, but that the former is significantly less dispersed. These results suggest that whilst the bacteriophage tracer cannot be used to predict receptor concentrations from transport via karstic flow paths, it can provide estimates for groundwater flow and solute contaminant transit times. This study also provides insight into the attenuation and transport of pathogenic viruses in karstic chalk aquifers.
... If the same cave-adapted species are found in multiple caves, then these caves were likely recently connected via pathways that the cave-adapted species can travel [13,14]. This concept may address the limitations of existing methodologies as defined by Goldscheider et al. [15] by providing a measure of ephemeral connectivity that may not be captured by artificial tracers. Ecosystem-level data, however, are limited by our understanding of the organisms as a community. ...
Karst aquifers are unique among groundwater systems because of variable permeability and flow-path organization changes resulting from dissolution processes. Over time, changes in flow-path connectivity complicate interpretations of conduit network evolution in karst hydrogeology. Natural and artificial tracer techniques have long provided critical information for protecting karst aquifers and understanding the potential impacts on ecosystems and human populations. Conventional tracer methods are useful in karst hydrogeologic studies for delineating flow paths and defining recharge, storage, and discharge properties. However, these methods only provide snapshots of the current conditions and do not provide sufficient information to understand the changes in interconnection or larger-scale evolution of flow paths in the aquifer over time. With advances in population genetics, it is possible to assess population connectivity, which may provide greater insights into complex groundwater flow paths. To assess this potential, we combined the more traditional approaches collected in this and associated studies, including artificial (dye) and natural (geochemistry, isotopes, and discharge) tracers, with the population genetic data of a groundwater crustacean to determine whether these data can provide insights into seasonal or longer changes in connections between conduits. The data collected included dye trace, hydrographs, geochemistry, and asellid isopod (Caecidotea bicrenenta) population genetics in Fern Cave, AL, USA, a 25 km-long cave system. Combined, these data show the connections between two separate flow paths during flood events as the downstream populations of isopods belonging to the same subpopulation were measured in both systems. Additionally, the sub-populations found in higher elevations of the cave suggest a highly interconnected unsaturated zone that allows for genetic movement in the vadose zone. Although upstream populations show some similarities in genetics, hydrologic barriers, in the form of large waterfalls, likely separate populations within the same stream.
