Karst Spring Water Research Articles

Using multivariate statistics to link major ion chemistry changes at karst springs to agriculture

Agricultural contamination is a pervasive problem in karst landscapes that negatively impacts groundwater quality, and subsequently harms hydraulically connected springs and associated ecosystems. While most research on agricultural contamination in karst aquifers has focused on nitrate, agricultural operations also alter major ion chemistry in groundwater, which can have significant implications on water rock interactions, geochemical interpretability, and enrichment of harmful contamination. Additionally, recent evidence has questioned the singular role of nutrient enrichment on aquatic ecosystem degradation, thus prompting further investigation into the broader extent of agricultural contamination for improved water quality restoration. In karst aquifers, quantifying the disruption of groundwater quality from agricultural contamination at springs can be challenging as major ions associated with agricultural contamination may be conflated with natural processes and interpretation further compounded by complex flow dynamics. These factors can render traditional statistical methods inadequate for identifying more comprehensive groundwater quality disruptions. To overcome these challenges, we use principal component analysis to classify the major ion covariance signature of agriculturally impaired and unimpaired groundwater and develop a new impairment metric to characterize the relative major ion impairment from agriculture to karst spring water quality. We apply our method to a primarily rural region in northern Florida whereby major ion chemistry has been changing over the last several decades. Our results identify a significant difference in major ion covariance structure between agriculturally impaired and unimpaired groundwater which is exploited to directly link major ion changes at karst springs to agriculture via relating a derived impairment metric to measured nitrate. Our newly developed method is easy to apply and can be used to identify more comprehensive contamination from pollutant sources and prioritize relative water quality restoration.

Evaluation of karst spring water quality in northeast Tennessee using water quality indices

AbstractEnsuring access to safe drinking water to protect public health in communities underserved or unserved by centralized water systems requires regular water quality testing and reporting. However, households depending on unregulated water systems like wells and springs, which are less routinely tested, may be unaware of their water quality. Access to easy‐to‐comprehend water quality information may be challenging. Therefore, this study utilized multiple water quality parameters to determine karst spring water quality using two water quality index (WQI) methods. This approach aggregates and summarizes water quality data into a single value or index characterizing the general health status of water at a given location in an easy‐to‐understand way. In situ measurements of physicochemical parameters (pH, dissolved oxygen, temperature, turbidity, conductivity, specific conductance, total dissolved solids, and oxidation–reduction potential) were taken at 50 karst springs in east Tennessee during summer 2021. Water samples were analyzed for microbial (fecal coliform and Escherichia coli), nutrients (nitrate and nitrite), and radiological (radon) constituents using standard analytical methods. WQI method 1 (Brown et al. Water Quality Index) rated 12% of springs as “very poor” water quality and 88% as “unfit for drinking.” WQI method 2 (National Sanitation Foundation Water Quality Index) rated 4% of the sampled springs as “good,” 92% as “moderate,” and 4% as “bad.” Given the prevalence of fecal contamination in the sampled springs, even springs rated good should be properly treated before consumption. Overall, these findings demonstrate the importance of selecting appropriate WQI for the end water use, and for water quality information that is easily understandable by water users.

Influence of Anthropogenic Sulfuric Acid on Different Lithological Carbonate Weathering and the Related Carbon Sink Budget: Examples from Southwest China

Accurate estimate of carbonate weathering and the related carbon sink flux induced by anthropogenic H2SO4 is of great significance for improving understanding of the hydrogeochemical evolution and the global carbon cycle. Here, to quantitatively evaluate the influence of anthropogenic H2SO4 on different lithological carbonate weathering and the related carbon sink budget, karst spring water in the typical limestone and mixed limestone–dolomite catchments in Yaji and Beidiping affected by acid precipitation in southwest China were sampled monthly for the analysis of hydrochemical and δ13CDIC characteristics. Results show for the period of sampling (August 2013 to December 2014) that the average contribution rates of atmospheric inputs and carbonate weathering to total dissolved cations are 2.24% and 97.8%, and 3.09% and 96.9% in Yaji and Beidiping, respectively. The δ13CDIC values (−17.0% to −14.7‰) and the [Ca2+ + Mg2+]/[HCO3−] (0.98 to 1.25) and [Ca2+ + Mg2+]/[HCO3− + SO42−] (approximately 1) equivalent ratios of samples prove that H2CO3 and H2SO4 simultaneously participate in carbonate weathering. The contribution rates of H2SO4 to [Ca2+ + Mg2+] and [HCO3−] produced by carbonate weathering in Yaji and Beidiping are 0–30% and 0–18%, and 0–37% and 0–23%, with average values of 14% and 7%, and 19% and 11%, respectively, suggesting that the influence of H2SO4 on different lithological carbonate weathering is different. H2SO4 precipitation participating in carbonate weathering increases the weathering rate by 14–19%, whereas it decreases the flux of karst carbon sink by 7–11% in Southwest China. Therefore, anthropogenic acids have influenced the global carbon cycle and climate change by carbonate weathering due to the large karst areas in the world, and their influences on different lithological carbonate weathering should not be ignored in the regional and global carbon cycles in future studies.

Spatial Distribution, Source Analysis, and Health Risk Assessment of Metal Elements in Karst Water in Southeastern Chongqing

Dispersed karst water is an important water supply source, or even the only water supply source, for some districts and counties in Chongqing City. It is particularly necessary to understand the distribution characteristics of metal elements in karst water and the health risks exposed. In this study, the scattered karst water in the southeastern part of Chongqing was taken as the main research object, and the concentrations of Al, Cu, Pb, Zn, Cr, Cd, Ni, Mn, As, and Hg in 42 groups of karst spring water samples were determined. The spatial distribution of metal elements with a high detection rate was revealed using the ordinary kriging interpolation method, and the spatial distribution characteristics, sources, and health risks of metal elements were analyzed using multivariate statistical methods and health risk models. The results showed that the quality of dispersed karst water in southeastern Chongqing was generally good, and the spatial scale variability in the occurrence of metal elements in karst water was strong, especially for Ni and As. The sources of Cu, Pb, As, Zn, and Cr were mainly affected by the regional geological background; Al and Mn were mainly affected by human industrial, agricultural, and mining activities; and Ni was affected by both the natural background and human activities. The total health risk of exposure through the drinking route was higher than that of the skin infiltration route, which was the main exposure route of the human body. The total health risk of children exposed through the drinking route was higher than that of adults, and the total health risk of adults exposed through the skin infiltration route was higher than that of children. It is worth noting that Cr was the determinant of total health risk. From the perspective of drinking water safety, local residents need to pay certain attention to water quality when drinking distributed karst groundwater, in order to reduce the health risk of the population.

Predicting and explaining karst spring dissolved oxygen using interpretable deep learning approach

AbstractDissolved oxygen (DO) is one of the most important indicators of water quality and an essential measure for the aquatic organisms and the local ecosystem. DO concentrations in karst spring flow involves complex hydrological processes because of the heterogeneous nature of the karst system. In this study, an interpretable and explainable model that integrates the shapley additive explanations (SHAP) algorithm with the long short‐term memory network model (LSTM) is proposed to evaluate the contributions of karst spring discharge, precipitation, water temperature, and specific conductance to DO concentrations in karst spring flow. The hybrid model can predict the temporal fluctuations of DO levels and provide a robust characterization of DO behaviours. To demonstrate the applicability of the proposed model, we adopted the hydrological and meteorological data from Barton Springs, situated within a highly karstified segment of the Edwards aquifer characterized by extensive fractures and openings. The optimal prediction performance is achieved with a 14‐day time step, which is considered as the effective response time between various hydrological processes and DO concentrations at Barton Springs. It reveals that the influence of karst spring discharge, precipitation, water temperature, and specific conductance in previous 14 days collectively contribute to the current DO concentration in karst spring flow. The SHAP values of input features provide both local and global explanations, demonstrating the magnitude and the direction of each feature's impact on DO levels in karst spring flow. In descending order, the contributions of various hydrological processes to DO are ranked as follows: precipitation, karst spring discharge, temperature, and specific conductance. Precipitation and discharge exhibit positive SHAP values, indicating that increases in these hydrological processes contribute to higher DO levels in the karst flow. Water temperature and specific conductance have negative SHAP values, suggesting that higher water temperature and specific conductance will lead to decreased DO levels in the karst flow.

Adherence of polystyrene microspheres on cave sediment: implications for organic contaminants and microplastics in karst systems.

Interactions of karst aquifer sediments with organic contaminants or microplastics (MPs) have received relatively little attention even though the susceptibility of karst aquifers to contamination and their ability to store and transport sediment is well documented. Studies using polystyrene microspheres as surrogate tracers for bacteria transport in karst systems have generally observed low recovery of microspheres and attributed this to microsphere adsorption onto aquifer sediments. In addition to being used as surrogate tracer for bacteria, microspheres have the potential to be used as surrogate material for organic contaminants and MPs. Using cave sediments as a proxy for karst aquifer sediments, the adherence of two types of microspheres (carboxylated and nonfunctionalized) was measured in three different types of solutions: deionized water, a calcium carbonate solution, and a karst spring water. Both types of microspheres adhered to the sediments; the most influential factor in adherence was solution type not microsphere type. Average adherence ranged from 51%-94% with average adsorption coefficients (KD) ranging from 11.8-442. Average estimated organic-carbon water partition coefficients (KOC) and retardation factors (RF) ranged from 1.64×103 - 6.13×104 and 6.20×101 - 2.29 × 103, respectively. KD, KOC, and RF were an order of magnitude higher in the karst water than in DI or CaCO3 solution. The results illustrate the importance of sediment interactions with potential organic or MP contaminants in karst systems.

Subterranean transport of microplastics as evidenced in karst springs and their characterization using Raman spectroscopy

The increasing use of plastic materials has led to accumulation of large amounts of plastic waste in environment and a global challenge to be tackled with. The natural process of macro-plastics aging generates a multitude of secondary microplastic fragments accumulating in all areas of the planet. The pollution with microplastics of large water bodies, such as rivers, seas and oceans was already proven, but the presence of microplastics even in karst spring water was not reported yet. In this study, Raman micro-spectroscopy was used to confirm the presence of microplastics in the spring water samples collected from two rural karst springs in the Apuseni Mountains (Țarina and Josani), North-Western Romania. Two sets of water samples of 1000 L collected in spring time 2021 and one in autumn 2021 were filtered and analyzed. Using the Python programming language and combining two separate Raman databases, one for plastics and the other for pigments, we established a customized database to unambiguously identify the type of plastic and pigment present in the discovered micro-fragments. The generated reference pigment-plastic spectra were compared to those of potential microplastics found on filters and Pearson's coefficient was used to measure the level of similarity. The presence of microplastics in karst spring waters was confirmed and a quantitative estimation expressed as number of fragments or fibers per liter was 0.034 in Josani and 0.06 in Țarina karst spring. Five months later sampling (autumn 2021) revealed 0.05 microplastics per liter. The spectral results revealed that most microplastics found were dominated by polyethylene terephthalate (PET), followed by polypropylene and interestingly, abundant blue micro-fragments were identified according to their copper phthalocyanine pigments (pigment Blue 15) or indigo carmine (pigment Blue 63) characteristic spectral fingerprints, which surpassed the inherent spectral background level characteristic for the Raman spectra of naturally contaminated waste micro-samples. Their origin in mountain karst spring waters and potential decrease in time is discussed.

Integration of multiple hydrogeological survey technologies for exploring the groundwater distribution in karst areas: A case study in Xingfu Spring, Chaohu City, China

Exploring the developing characteristics and spatial distribution of fractures and conduits in the karst system is of great significance for utilizing groundwater resources and preventing geological disasters. This study took the field of Xingfu Spring, Chaohu City, China as a target zone, three geophysical methods including MALM, TEM, and ERT were used to disclose the distribution regulation of the karst system. Based on the geophysical methods results, a hydrogeological borehole with a depth of 24.4 m was constructed to observe the structure of stratum. Then, the point velocity probe (PVP) technique was used to reveal the structure characteristics of stratum in borehole and measure the flow velocity and direction of the karst system. Finally, the tracer test was carried out in the borehole to explore the connection between borehole area and spring system. The main results show: (1) the extension direction of the karst cave in borehole is about 20° west by south and the direction of spring water flow path is about 30° north by east; (2) the groundwater in this karst cave and spring water flow path system has a similar flow direction, roughly from northeast to west; (3) there is no direct hydraulic connection between the borehole area and the spring water flow path based on the result of the tracer test. In this paper, the spatial distribution of groundwater in the study area has been successfully revealed based on the ensemble hydrogeological survey technologies. The good application of the integrated geophysical method and PVP technique can provide the reliable technology means for researching the spatial distribution and development regulation of groundwater in karst system.

Microbial water quality and health risk assessment in karst springs from Apuseni Mountains, Romania

In Apuseni Mountains (North-Western Romania), many of the inhabitants live in rural communities with limited or no access to the centralized and controlled water supply. This study assesses the microbiological quality of six karst spring waters from Bihor County used by rural communities as drinking water sources. Twenty-four water samples collected in January, April, June, and November 2021 were analyzed for E. coli, total coliforms, intestinal enterococci, Pseudomonas aeruginosa, and heterotrophic plate count at 37 and 22°C. Standard microbiological methods based on the membrane filter technique or pour plate method were used for the microbiological characterization of the spring waters. The study revealed that the karst springs from the studied area present microbiological contamination. The microbiological parameters for five out of the six studied spring waters exceeded the maximum limits allowed by the 98/83/EC Directive. Quantitative Microbial Risk Assessment estimated the risk of gastrointestinal illness for both adults and children due to the enteropathogenic E. coli contamination. According to the health risk evaluation model, the risk of infection/day and the risk of infection/year were high, with the maximum values of 0.24 and 1.00, respectively. The probability of illness caused by E. coli contamination of water ranged between 0.09 and 0.35 for five out of six groundwater sources. The local communities using the contaminated springs are exposed to daily and accumulated health threats. Therefore, preventive measures accompanied by continuous monitoring are necessary mainly for those water sources that are critical drinking water sources for the rural communities.

Relief and climate influence on isotopic composition of Atlantic‐Mediterranean karst spring waters (Andalusia, southern Spain)

AbstractThe geographic location of Andalusia, bordered by the Atlantic Ocean and the Mediterranean Sea, and its great topographic and climate diversity enable the analysis of different factors that condition the isotopic composition of precipitation and groundwater. A total of 42 karst springs representative of the main carbonate aquifers were selected in order to sample the base flow waters during the summer of 2020. Isotopic analyses revealed that groundwater δ18O was between −5.04 and −9.85‰ while that of δ2H was between −26.39 and −62.69‰. Weighted mean isotopic data for precipitation, from six IAEA stations in the study area, was between −4.67 and −9.06‰ for δ18O, and between −24.93 and −58.99 ‰ for δ2H. The results showed that diffuse flow groundwaters are lighter and have higher d‐excess than meteoric waters, which may be due to preferential recharge during winter months and the sub‐cloud evaporation effect. The spatial variation of d‐excess, with average values around 14 ‰ in the Atlantic watershed and 17 ‰ in the Mediterranean watershed, has showed for the first time the effect of the Atlantic‐Mediterranean divide on the isotopic composition of spring waters. Furthermore, a progressive decrease in δ18O towards the east of the study area seems to be related to the effects of continentality and altitude. This also allowed us to conclude that, in the areas with highest rainfall, springs drain waters with a relatively higher content of heavy isotopes than expected from the regional altitudinal gradient, while springs in drier areas discharge lighter waters. These differences can be attributed to a longer recharge period in the former, which extends in the warmer months or autumn and spring.

Geospatial Assessment of Karst Spring Water Quality in Northeast Tennessee, USA

Karst springs are an essential source of private water supply for about 10% of households in Tennessee. However, the water quality of these springs is unmonitored and unregulated even though many springs are highly productive yet vulnerable to contamination. This study assesses spatial patterns in the water quality of roadside springs in northeast Tennessee. Karst spring water samples collected from 50 springs were assessed using EPA Standard methods for pathogens, nutrients, radon, and physicochemical parameters. From statistical and spatial analyses, all but five samples contained E. coli, while all samples contained fecal coliform. High E. coli was spatially clustered (Local Moran’s I = 0.177, pseudo p-value = 0.012) in regions of high agricultural land use, resulting in a fecal contamination hot spot on the border of Washington and Sullivan Counties, Tennessee. Radon concentrations exceeded the 300 pCi/L proposed MCL in 29 (58%) of springs, with one spring in Unicoi County exceeding 1000 pCi/L. A radon hot spot was identified in northern Washington County (Local Moran’s I = 0.160, pseudo p-value = 0.014). Cokriging of E. coli with land use and radon with distance to mapped fault did not improve interpolation models for either parameter. Other parameters, including nitrate, pH, and total dissolved solids, were within recommended ranges for drinking water. This snapshot of spring water quality status identifies areas of poor spring water quality of which spring water users in the region should be aware, and establishes the need for longitudinal sampling of spring water quality in contamination hot spots.

WATER RESOURCE MANAGEMENT UNDER CLIMATE CHANGE: IMPLICATIONS FOR SUSTAINABLE USE ON KARST TERRAIN

The scarcity of freshwater is a critical issue that continuously is considered to be important around the world. The availability of freshwater steadily decreases because of growing population, high water demand and global climate change. Underground streams water and aquifers within karst terrain is assessed as an substantial factor of water supply systems in karst areas, and in the case that is assessed in this paper as well. Therefore, water management on karst area is essential to solve water deficiency problems, particularly during dry season. In this paper, management of karst spring water is discussed based on some cases from Citatah karst. Management of spring water is the main object of this paper that use mix method design, incorporating a qualitative and a quantitative approach. Result showed that inadequate human resource, infrastructure, database system; lack assertiveness, supervision and instrument of rules implementation; and low level of awareness and participation are found as the main factor of poor management of karst spring water at Citatah karst. However, better management could be attained by improving capacity building, strengthening monitoring capabilities, formulation of groundwater policy, implementing economic and financial instruments, improving participatory management and applying sustainable technology for agricultural and domestic water use.

Transport-based source tracking of contaminants in a karst aquifer: Model implementation, proof of concept, and application to event-based field data

Identification and location of contamination sources is crucial for water resource protection — especially in karst aquifers which provide 25% of the world´s population with water but are highly vulnerable to contamination. Transport-based source tracking is proposed and verified here as a complementary approach to microbial and chemical source tracking in karst aquifers for identifying and locating such sources of contamination and for avoiding ambiguities that might arise from using one method alone. The transport distance is inversely modelled from contaminant breakthrough curves (BTC), based on analytical solutions of the 1D two-region non-equilibrium advection dispersion equation using GNU Octave. Besides the BTC, the model requires reliable estimates of transport velocity and input time. The model is shown to be robust, allows scripted based, automated 2D sensitivity analyses (interplay of two parameters), and can be favourable when distributed numerical models are inappropriate due to insufficient data. Sensitivity analyses illustrate that the model is highly sensitive to the input time, the flow velocity, and the fraction of the mobile fluid region. A conclusive verification approach was performed by applying the method to synthetic data, tracer tests, and event-based field data. Transport distances were correctly modelled for a set of artificial tracer tests using a discharge-velocity relationship that could be established for the respective karst catchment. For the first time such an approach was shown to be applicable to estimate the maximum distance to the contamination source for coliform bacteria in karst spring water combined with microbial source tracking. However, prediction intervals for the transport distance can be large even in well-studied karst catchments mainly related to uncertainties in the flow velocity and the input time. Using a maximum transport distance is proposed to account for less permeable, “slower” pathways. In general, transport-based source tracking might be used wherever transport can be described by the 1D two-region non-equilibrium model, e.g. rivers and fractured or porous aquifers.

Water abstraction management under climate change: Jadro spring Croatia

This study aims to assess the vulnerability of drinking water abstraction in a karst spring in an uncertain future. Karst spring water is an important source of drinking water for the Croatian coastal area and is characterised by a high fluctuation of discharge and turbidity. Various climate models have predicted drier summers, wet winters, and a significant increase in the frequency of extreme events in the future. Therefore, it is necessary to determine the possible consequences on the water-supply system and increase its reliability and resilience. In this study, this assessment was conducted using a bottom-up approach that threatens vulnerability as an internal property of the system. To reduce the uncertainty in drawing conclusions, hazard-relevant indicators and tools based on the physical reality of the hydrological system and stochastic characteristics of the discharge time series were introduced. The study results indicate that, for meeting the drinking water standard, turbidity will be larger and more frequent, and thus, will be a growing problem, while discharge will not significantly reduce the water-supply capacity in the near future. Although a karst aquifer is sensitive to climate change, it will continue to be a reliable resource for drinking water supply. The applied assessment approach and tools prove to be pragmatic and effective for assessing the vulnerability of water abstraction.

Distribution Characteristics and Health Risk Assessment of Metal Elements in Groundwater of Longzici Spring Area

Longzici Spring is an important water source for industry, agriculture, and urban life in Linfen City. With the improvements in public environmental health awareness, it is particularly necessary to study the health risk of posed by metal elements in groundwater. In this study, 43 groundwater samples from Longzici Spring area were analyzed for ten metal elements (As, Cd, Hg, Al, Pb, Co, Mn, Fe, Cu, and Ni). The distribution and health risk of these metal elements in the groundwater were studied using multivariate statistical analysis and a health risk assessment model. The results show that metal elements can be ranked, from high to low, by their average concentrations in groundwater in the following order: Fe, Al, Mn, Ni, As, Cu, Co, Pb, Hg, and Cd. The concentration of Al, Mn, Fe, and As exceed the limit for class Ⅲ water, as defined in the quality standard for groundwater (GB/T 14848-2017). Different types of groundwater in the spring area showed different metal contents. The quality of karst spring water was good, reaching the standard for drinking water, while mine drainage water exceeded the standard for drinking water, with the highest metal concentration (60%) and the worst water quality. Multivariate statistical results show that Pb, Ni, Co, Cd, Mn, and Cu concentrations were mainly affected by the geochemical background, while Al, Fe, Hg, and As concentrations were closely related to human mining activities under the unique geological background of Shanxi Province. The health risk assessment showed that the different types of groundwater could be ranked by the annual total health risks, posed by metal elements to adults and children through drinking water and skin infiltration, as follows: karst well > non-karst spring > non-karst well > karst spring. The health risks mainly came from drinking water, while health risks through skin infiltration would not cause obvious harm to the human body. The metal element causing the greatest health risk in spring groundwater was As, which should therefore be controlled in the utilization of water resources, especially in children's drinking water.

Hydrogeology, hydrogeochemistry, and isotope method application to investigate the hydraulic connection between Emam-Gheis karst spring and adjacent water wells (Iran)

The Emam-Gheis Karst Aquifer is located in the southeast of Borujen city in Iran. The Emam-Gheis Spring with the average flow rate of about 90 L s−1 has emerged in the south of the aquifer. Seven deep drinking water wells have been drilled in the east of the aquifer (15 years ago). The spring flow rate has decreased significantly after water harvesting from the water wells began. In this study, the presence or lack of a hydraulic connection between the Emam-Gheis karst spring and its adjacent water supply wells has been investigated. The hydrogeology, water chemistry, and isotopic investigations were done in the catchment area of the spring and the wells from December 2016 to December 2017. The obtained results revealed that there were significant differences between the spring and the wells regarding the electrical conductivity, major ions concentrations, ion ratios, saturation indices (of calcite, dolomite, gypsum, and halite), and water stable isotopes. In addition, the hydrogeological investigations implied that the existence of a hydraulic connection between the spring and the wells seems unlikely. It seems that due to the excessive groundwater extraction in recent years, the groundwater level has declined in the adjacent alluvial plains. This seems to have intensified the water discharge from the karst aquifer toward the alluvial deposits and resulted in a decrease in water discharge rate at Emam-Gheis spring.

Key drivers of microbial abundance, activity, and diversity in karst spring waters across an altitudinal gradient in Slovenia

In aquatic ecosystems, the biomass, activity and composition of microorganisms are determined to a large extent by local and regional environmental conditions. While karst aquifers are an important source for drinking water, the ecology of microbial communities in karst waters has hardly been studied. This study examined the regional variations and seasonal dynamics of microbial communities in pristine karst spring waters of Slovenia (Central Europe). Fifteen springs distributed across 5 eco-regions exhibiting a strong altitudinal gradient were sampled 4 times a year. Evaluation of the microbial communities included quantification of prokaryotic biomass via total cell counts and microbial activity estimated via measurements of electron transport system activity. The taxonomic structure of the bacterial communities was analysed by terminal restriction fragment length polymorphism fingerprinting. Biological measures were complemented by a set of physico-chemical parameters, including dissolved organic carbon, nutrients, major ions, temperature, electrical conductivity, pH, and dissolved oxygen. Bacterial community structure differed significantly with seasons and eco-regions, with the latter causing greater variation. While the overall power of the environmental variable tested was a moderate factor (15%) in explaining the variability in microbial community structure, catchment altitude was a key determinant. Prokaryotic cell density and microbial activity in spring water decreased with an increase in catchment altitude and were significantly positively correlated. For a better understanding of karst ecosystems and the ecosystem service of water purification, future investigation should address karst microbial communities at a higher phylogenetic and functional resolution.

Road salt retention and transport through vadose zone soils to shallow groundwater

Increasing background salinity in watersheds has largely been attributed to road salt retention in groundwaters due to their long residence times. However, laboratory studies demonstrate that soils temporarily store salts, either in porewater or adsorbed onto particles. Field studies of road salt retention in soils are nevertheless rare, and mechanisms of salt transport across multiple hydrological reservoirs (e.g., from soil to groundwater) are unknown. Thus, we collected roadside soil porewater and karst spring water weekly for ~1.5 yr to determine salt transport through the vadose zone into the phreatic zone. We observed dual retention mechanisms of sodium (Na+) and chloride (Cl−) in soils due to slow porewater movement, causing ion movement through the soil as slow as 1.3 cm/day, and cation exchange processes, leading to initial Na+ retention followed by later release months after application. Cation exchange processes also caused base cation loss from exchange sites into mobile porewater. Rapid Na+ and Cl− delivery to groundwater occurred through karst conduits during the winter. However, elevated background levels of salt ions in groundwater during the non-salting months indicated accumulation in the catchment due to slower porewater flow in the soil and rock matrix and delayed Na+ release from soil exchange sites.

Assessment of spring waters from Lourdes (France) by contact angle method

The geochemical investigations on karst spring waters in the area of Lourdes showed differences between the waters for numerous components, including main solutes and trace elements. In this study, a multidisciplinary approach was proposed, based on the surface free energy of solids and the surface tension of liquids using the contact angle method, by raising the hypothesis that different spring waters diverge in surface tension characteristics, which allow to discriminate waters origin in a natural system. Surface energy characteristics of spring waters from Batsurguère Valley were investigated here using the contact angle measured over time and the tangent method in relation to the variations of the droplet volume. Wettability of various test solids was analyzed using static and kinetic contact angle methods which led to the individuation of the spring waters on the base of the different adhesion processes occurring at the interface between water and solid, particularly on the silica glass solid. The analyses demonstrated that the surface tensiometry technique can discriminate one of such spring waters (i.e. the Massabielle spring) from other studied spring waters, regardless of their natural hydrological conditions. Contact angle hysteresis in kinetic modality, based on several repeated and extemporary set of experiment determinations, suggested a link between the water chemistry and the wettability over time of the test solids, confirming that chemical composition has an influence on the surface tension of spring waters. This investigation demonstrates that the surface tensiometry approach may represent a useful tool for monitoring quality of natural waters.

Contaminant sources and processes affecting spring water quality in a typical karst basin (Hongjiadu Basin, SW China): insights provided by hydrochemical and isotopic data.

Springs are an important source of drinking water supply in mountainous karst areas of SW China. However, the quality of many spring waters has deteriorated greatly in recent years, which leads to a significant problem of drinking water scarcity. In this study, hydrochemistry and stable sulfur and oxygen isotopic compositions of SO42- (δ34S and δ18OSO4) of 38 representative samples of waters (incl. spring water, surface water, rainwater, and sewage) from the Hongjiadu Basin, Guizhou province, SW China, were investigated in order to identify the sources of contaminates in spring waters and trace the processes affecting the karst groundwater quality. Approximately 28% of the total investigated springs has been suffered from serious contamination and the concentrations of NO3-, SO42-, and total iron (TFe) in many spring waters have exceeded the standards for drinking water. The springs that have NO3- concentrations of > 30 mg/L are concentrated in residential and agricultural areas, suggesting that NO3- in spring water are mainly derived from chemical fertilizers, manure, and sewage. δ34S and δ18OSO4 data indicate that SO42- in spring water mainly originates from sulfide oxidation, acid rain, and sewage. Furthermore, the high δ34S and δ18OSO4 values of SO42- in some spring waters may be related to the occurrence of bacterial sulfate reduction. Some springs that are discharged from abandoned coal mines have SO42- concentrations of > 250 mg/L, demonstrating that mining activities have accelerated the deterioration of spring water quality. Also, springs with TFe concentrations of > 0.3 mg/L are discharged from coal-bearing strata, revealing that iron in spring waters is mainly derived from the oxidation of pyrite. Our results show that the karst spring waters are highly vulnerable to anthropogenic contaminations and human activities, such as agricultural fertilizing and sewage and waste disposal as well as mining activities, which exert a great impact on the quality of groundwater in karst areas.