Karst Groundwater Quality Research Articles

Tracing pesticide dynamics: High resolution offers new insights to karst groundwater quality

Generally, karst aquifers and springs are highly susceptible to contamination due to the high permeability and, therefore, groundwater flow velocities. The often thin soil cover, accompanied by dolines, can lead to fast infiltration of precipitation water loaded with mobilized contaminants such as pesticides and their transformation products. To date, continuous, temporally highly resolved in-situ monitoring to decipher concentration dynamics for a broad range of pesticides is missing. Therefore, a transportable HPLC-HRMS/MS system (MS2field) was positioned at two karst study sites in the Swiss Jura. Water samples were collected and analyzed for pesticides and their transformation products in-situ every 20 min for 6 weeks in 2021 and 8 weeks in 2022. During the spraying season in 2021, six rain events at site 1 and three at site 2 in 2022 were captured. Concurrently, the water quality parameters electrical conductivity, pH, nitrate, turbidity, and water level, were monitored continuously at high temporal resolution. Further, bacterial cell counts were monitored via online flow cytometry.In 2021, several pesticides and pesticide transformation products were detected in peak concentrations after rain events, of which metamitron showed the highest concentration of up to 1000 ng/L. In one rain event, the Swiss federal and EU drinking water limit of 100 ng/L was exceeded for up to 38 h. Compared with highly frequent MS2field samples collected every 20 min, 42-hours composite samples severely underestimated peak concentrations for all compounds, especially for labile ones. Therefore, it was demonstrated that exceedences of the regulatory limit would have been missed if just composite sampling would have been conducted. Peak concentrations of pesticides coincided with peaks in nitrate concentration and bacterial cell counts following rain events. The correlation analysis showed strong correlations between the three analyzed contaminants (pesticides, nitrate and bacteria), and the proxy parameters electrical conductivity, and pH. The investigation of a second spring revealed similar dynamics indicating that these can be expected in other karst aquifers as well.

Hydrogeochemical characteristics, driving factors, and health risk assessment of karst groundwater in Southwest Hubei Province, China.

In South China, karst groundwater is an important water resource for industrial, agricultural, and drinking purposes. However, karst aquifers are highly vulnerable to pollution, leading to deteriorating karst groundwater quality and posing potential health risks to local residents. In this study, 22 groundwater samples were collected from a karst aquifer in the southwestern part of Hubei Province. The hydrogeochemical characteristics and their controlling factors were examined, and the potential health risks associated with groundwater pollutant concentrations in karst groundwater were assessed. The results showed that the groundwater is slightly alkaline with low chemical oxygen demand values, indicating good water quality. The groundwater facies type was identified as HCO3-Ca at most sample spots, showing low total dissolved solids concentrations. Substantial spatial variations in Na+, CO3 2-, and NO2 - concentrations were found, whereas spatial variations in the K+, Ca2+, Cl-, HCO3 -, and F- concentrations were small. In addition, the dissolution of gypsum deposits and magnesium carbonate sedimentary rocks at sampling sites resulted in groundwater facies types of HCO3•SO4-Ca and HCO3-Ca•Mg, with low total dissolved solids concentrations. The karst groundwater chemistry in the study area was mainly controlled by water-rock interactions, as well as by the dissolution of gypsum deposits and magnesium carbonate sedimentary rocks at specific groundwater sampling sites. The groundwater Cl- concentrations were mainly affected by atmospheric precipitation. NO3 - was mainly derived from atmospheric precipitation, domestic sewage, septic tanks, and industrial activities, whereas SO4 2- was derived from atmospheric precipitation, sulfate rock dissolution, and sulfide mineral oxidation. These results highlight the absence of potential human health risks of NO3 - and F- to infants, children, and adults, as their concentrations are below the corresponding regional background values. In contrast, the potential health risks of Cl- cannot be ignored, particularly for infants. This study offers scientific guidelines for protecting and allocating local groundwater resources.

Identifying sources and transformations of nitrate in different occurrence environments of carbonate rocks using a coupled isotopic approach (δ15N, δ18O, 87Sr/86Sr) in karst groundwater system, North China

Karst water as the vital water supply source is an increasingly serious problem suffering from NO3− pollution. Identifying sources and transformations is the key to effectively controlling diffuse NO3− pollution. In this study, 25 karst groundwater samples were collected from the Xujiagou karst groundwater system in June 2023, and chemical variables and stable isotopes (δ15N, δ18O, 87Sr/86Sr) were determined in different occurrence environments of carbonate rocks (exposed, covered, and buried carbonate rock areas). The results showed that the karst groundwater is dominated by nitrification. Human activities have affected the water quality of karst groundwater. The nitrate concentration ranged from 5.69 to 124.22 mg/L, and 4 % exceeds the quality indexes of class III water in China's standard for groundwater quality (20 mg/L as NO3−-N). NH4+ in fertilizer, manure and septic waste, and soil N were the main sources of nitrate pollution in the karst groundwater system. The distribution of NO3− sources is closely related to land-use types. Soil N (72.2 %) became the dominant nitrate source in the exposed area due to the small amount of urban land and the large distribution of forest and grassland. There were more cultivated land and large agricultural activities in the covered area, NH4+ in fertilizer (59.1 %) contributes the most to NO3− sources. The buried area dominated by urban land, the influence of human activities (densely population and agricultural production activities) caused the highest concentration and coefficient of variation of nitrate in this area, and manure and septic waste (64.2 %) were the most to NO3− sources. This study can provide an important scientific basis for the protection of karst groundwater, and provide theoretical support for the treatment of karst groundwater pollution sources in the “monoclinic paraclinal” strata in northern China.

Antimicrobial resistance and karst groundwater systems: A policy gap analysis for addressing water quality and contaminants of emerging concern

Aquifers are a significant drinking water source for the United States. Although vital to human well-being, development, and economies, these systems, specifically karst, either have minimal protections or are entirely overlooked in federal and state-level water quality policies and regulations. A lack of policies and regulations for the protection of karst groundwater resources is problematic, especially because these systems are characterized by distinctive landforms such as interconnected networks of underground rivers, sinkholes, springs and caves, and are extremely susceptible to contamination from polluted overland flows. This study considers policy approaches to improve water quality in groundwater, specifically karst systems, especially with regard to emerging contaminants of concern (CECs) and health threats, such as antimicrobial resistance (AMR). The study reviews and evaluates groundwater and karst groundwater quality and AMR policy gaps in federal water legislation (including the U.S. Clean Water Act and the Safe Drinking Water Act), and state-level programs in 44 states to provide recommendations for future policy development. Presently, there is limited federal and state-level protection for groundwater systems and minimal state-level for karst throughout the U.S. Also, there are neither federal nor state regulations for AMR mitigation in water resources. There is a need for policies and monitoring and regulatory programs that support water quality protection and management strategies for water resources with distinctive hydrology. Addressing water quality policy gaps for groundwater resources – especially karst aquifers – and prioritizing emerging contaminants in research, monitoring, and policymaking, are critical to safeguard the public against nascent public and environmental health threats.

Study on the Influence of Mining Activities on the Quality of Deep Karst Groundwater Based on Multivariate Statistical Analysis and Hydrochemical Analysis.

Long-term mining activities have changed the hydrogeochemical evolution process of groundwater and threatened the safe use of groundwater. By using the methods of hydrochemistry and multivariate statistical analysis, this study determined the hydrogeochemical evolution mechanism affecting the quality of karst groundwater by analyzing the conventional hydrochemistry data of the karst groundwater of the Carboniferous Taiyuan Formation in Hengyuan Coal Mine in the recent 12 years. The results show that, under the disturbance of mining, the quality of karst groundwater in Taiyuan Formation is poor, mainly because the contents of Na++K+ and SO42- are too high to allow usage as drinking water. The reason for the high content of SO42- in karst groundwater lies in the dissolution of gypsum and the oxidation of pyrite, and the high content of Na++K+ lies in the cation exchange. Influenced by the stratum grouting, the circulation of karst groundwater is improved, the cation exchange is weakened, and the desulfurization is enhanced. In the future, it is predicted that the hydrochemical type of karst groundwater in Taiyuan Formation in the study area will evolve from SO4-Ca·Mg type to HCO3-Ca Mg type.

Hydrochemical characteristics and formation mechanisms of groundwater in west Zoucheng City, Shandong Province, China.

Groundwater is an important water source for domestic, industrial, and agricultural use in the western part of Zoucheng, China. Understanding its hydrochemical characteristics and formation mechanisms is important for the sustainable development and utilization of groundwater. In this study, 36 water samples were collected during the wet and dry seasons, respectively, and the hydrochemical components such as K+, Na+, Ca2+, Mg2+, Cl-, SO42-, HCO3-, NO3-, F-, TH, and TDS were analyzed. A graphical method, correlation analysis, and principal component analysis were applied to explore the hydrochemical characteristics and evolution mechanisms of groundwater in the study area. The results show that the orders of the anion and cation concentrations of karst groundwater and pore groundwater are Ca2+ > Na+ > Mg2+ > K+ and HCO3- > SO42- > Cl- > NO3- > F-, respectively. On the whole, the karst groundwater quality is better than the pore groundwater quality, which in turn is better than the surface water quality. In addition, water quality in the dry season is better than water quality in the wet season for all the three water sources. The hydrochemical types of groundwater are complex and changeable. Compared with dry seasons, HCO3 and SO4 type water increase during the wet seasons, while the Cl type and Mg type water decrease. Na type is significantly more prevalent in pore groundwater than in karst groundwater. The chemical formations of karst groundwater and pore groundwater in the dry and wet seasons are mainly affected by water-rock interactions and human activities.

Hydrogeochemistry of karst groundwater for the environmental and health risk assessment: The case of the suburban area of Chongqing (Southwest China)

Karst groundwater is a vital resource for drinking, living and irrigation purposes in karst agricultural areas of the world. Due to the vulnerability of karst aquifers, surface pollutants are easily transferred to the subsurface and make karst groundwater be deteriorated, thereby restricting the rational exploitation of karst groundwater resource. In view of this, 49 karst groundwater samples were collected from spring (SW) and underground river (URW) sites in the suburban area of Chongqing City and analyzed for various hydrochemical components. Particularly, the karst groundwater quality was comprehensively uncovered by combining characteristics of hydrogeochemical evolution and health risks caused by nitrate and fluoride. The results revealed that the karst groundwater was slightly alkaline in nature and the water types were mainly characterized by Ca-HCO3 accounting for 93.88% of the total samples due to the heavy dissolution of carbonate rock. The relatively high concentrations of Na+, SO42− and NO3− up to 271.88 mg/L, 277.94 mg/L and 56.94 mg/L were over the corresponding maximum acceptable limits for drinking water, which can be predominately attributed to the emissions of industrial park, dissolution of gypsum and pyrite and excessive application of chemical fertilizers. Although agricultural activities were stopped and chemical fertilizers were no longer applied during the sampling period, long-term application of fertilizers have a persistent adverse effect on the karst groundwater NO3−. The pollution index of the karst groundwater (PIG) revealed that the low pollution and potential pollution zones were noticed in the northwestern parts of the study area. With respect of the SW, all the total hazard index (HI) values were below 1 suggesting no significant health risk. On the contrary, HI values of 0.11–1.16 for adults, 0.15–1.61 for children and 0.17–1.83 for infants in the URW indicated significant noncarcinogenic health risks. Particularly, infants and children were more vulnerable to karst groundwater NO3− than adults. Furthermore, the noncarcinogenic health risks of karst groundwater can be mainly attributed to NO3−, confirmed by the higher contribution ratio (66.55%) to the HI values. Therefore, special and targeted measures need to be taken to decrease the NO3− concentration in agricultural area.

Application of improved fuzzy comprehensive evaluation method in karst groundwater quality evaluation: a case study of Cengong county

Groundwater quality is affected by various indexes, and the influence of each index on groundwater quality is fuzzy. Therefore, adopting a reasonable evaluation method can make the groundwater quality evaluation more accurate. Although fuzzy comprehensive evaluation method has great advantages in analyzing fuzzy problems, it has shortcomings in solving problems like weight calculation. The fuzzy comprehensive evaluation method was improved by combining with the entropy weight method in this study. On basis of this, a groundwater quality evaluation model was established. At the same time, by taking the groundwater aquifer of Cambrian Gaotai formation in Cengong County, Guizhou Province as a research object and based on the water quality monitoring data of 14 boreholes there, the model was adopted to evaluate the water quality of the aquifer by combining with GIS technology. The results demonstrated the feasibility and superiority of the improved fuzzy comprehensive theory in groundwater quality evaluation.

Effects of Fe-rich acid mine drainage on percolation features and pore structure in carbonate rocks

Acid mine drainage (AMD) poses significant ecological, environmental and geological challenges worldwide, especially in more vulnerable karst areas. However, the impact of AMD on percolation features and pore structure of carbonate strata is poorly understood, despite its importance for the evolution of carbonate aquifer as well as karst groundwater quality. To fill this knowledge gap, field investigations, core-flooding experiments, reactive transport modeling and pore structure studies [mercury intrusion porosimetry (MIP) and nitrogen physisorption analysis] were conducted to understand the geochemical processes and associated pore development in carbonate strata exposed to Fe-rich AMD. Our field investigation shows that the AMD is characterized by low pH values (2.4–3.8), high contents of sulfate (1457–4217 mg/L), Fe (100–830 mg/L, Fe3+/Fe2+) and heavy metals, that can potentially leak into carbonate strata. The major findings of this study include: (1) core-flooding experiments reveal that the interaction of carbonate rock with AMD causes a rapid elevation of solution pH and simultaneous precipitation of Fe3+/Fe2+ as iron (oxy)hydroxides or (oxy)hydroxy sulfates within the rock; (2) the results of reactive transport modeling suggest that ferrous iron has a longer transport distance than ferric iron in the carbonate core plug, and then it precipitates to fill the pore space; and (3) despite the precipitation, the flooding of AMD increases the overall permeability of cores by creating large numbers of pores with throat diameter between 0.001 and 10 μm. We also found that the interaction of AMD with the carbonate rock might stimulate the formation of preferential flow channel(s). Our results have been incorporated into a conceptual model, built to illustrate the geochemical processes and mechanisms involved. Our research has important applications in AMD treatment for coal-mining industries, and for local governments devising strategies for karst water resource protection and management.

Natural attenuation of lead by microbial manganese oxides in a karst aquifer

Lead is a toxic environmental contaminant associated with current and historic mine sites. Here we studied the natural attenuation of Pb in a limestone cave system that receives drainage from the ancient Priddy Mineries, UK. Extensive deposits of manganese oxides were observed to be forming on the cave walls and as coatings in the stream beds. Analysis of these deposits identified them as birnessite (δ-MnO2), with some extremely high concentrations of sorbed Pb (up to 56 wt%) also present. We hypothesised that these cave crusts were actively being formed by microbial Mn(II)-oxidation, and to investigate this the microbial communities were characterised by DNA sequencing, enrichment and isolation experiments. The birnessite deposits contained abundant and diverse prokaryotes and fungi, with ~5% of prokaryotes and ~ 10% of fungi closely related to known heterotrophic Mn(II)-oxidisers. A substantial proportion (up to 17%) of prokaryote sequences were assigned to groups known as autotrophic ammonia and nitrite oxidisers, suggesting that nitrogen cycling may play an important role in contributing energy and carbon to the cave crust microbial communities and consequently the formation of Mn(IV) oxides and Pb attenuation. Enrichment and isolation experiments showed that the birnessite deposits contained Mn(II)-oxidising microorganisms, and two isolates (Streptomyces sp. and Phyllobacterium sp.) could oxidise Mn(II) in the presence of 0.1 mM Pb. Supplying the enrichment cultures with acetate as a source of energy and carbon stimulated Mn(II)-oxidation, but excess organics in the form of glucose generated aqueous Mn(II), likely via microbial Mn(IV)-reduction. In this karst cave, microbial Mn(II)-oxidation contributes to the active sequestration and natural attenuation of Pb from contaminated waters, and therefore may be considered a natural analogue for the design of wastewater remediation systems and for understanding the geochemical controls on karst groundwater quality, a resource relied upon by billions of people across the globe.

Assessing the Karst Groundwater Quality and Hydrogeochemical Characteristics of a Prominent Dolomite Aquifer in Guizhou, China

Karst groundwater is one of the primary water resources in most provinces of Southwestern China where karst topography is strongly featured. In Guizhou Province, a prominent geologic sedimentary formation is the dolomite stratum which exists as the restricted platform facies and potentially provides a large reservoir for drinking water. A proper understanding and evaluation of its hydrogeochemical characteristics and water quality is the key to ensuring the drinking water safety. In the present study, groundwater samples were collected from 25 locations of the dolomite aquifer across Guizhou to determine their major chemical compounds, including the cations (K+, Na+, Ca2+, Mg2+) and the anions (HCO3−, F−, Cl−, NO3−, SO42−), as well as the pH, total hardness, and total dissolved solids. HCO3− and Ca2+ were found to be the dominant anion and cation, respectively, which is characteristic of typical karst groundwater and supports the overall observation of a slightly weak acid to weak alkaline environment in the studied groundwater, as the pH measurements ranged from 6.80 to 8.37. Fuzzy comprehensive evaluation method is used to evaluate the groundwater quality based on typical drinking water safety standard. The results show that the groundwater in most of the studied aquifers is of reasonably good quality. However, in some aquifers, concentrations of NO3− and/or SO42− were found to be excessively high. Overall, the studied dolomite aquifer in its natural environment as investigated in the present study can be considered as a potential geological stratum for water resources exploitation in Guizhou.

Identification and quantification of contributions to karst groundwater using a triple stable isotope labeling and mass balance model

Although karst groundwater systems provide critical ecosystem services in many regions worldwide, anthropogenic contamination has seriously degraded groundwater quality. Properly elucidating geochemical processes, quantifying contributions of natural and anthropogenic end members, and then protecting karst aquifer systems remain challenging from scientific and engineering aspects. To identify the hydrochemical processes and quantifying contributions of end members (especially, contamination end members), 49 samples were collected from cave waters (CW), artesian springs (AS), and gravity springs (GS) in a karst watershed in Guiyang, China. With increased anthropogenic contamination, the CW, AS, and GS characterized by a Ca–Mg–SO42--HCO3- composition often had pH and SO42− concentrations exceeding USEPA secondary drinking water standards. That is attributed to the influence of water-rock interaction, rainfall, and anthropogenic sources (mainly, sewage and fertilizers), in agreement with the compositions of δ34SSO4, δ18OSO4, and 87Sr/86Sr as well as the results of principal component analysis and correlation coefficients. Based on an end-member mixing model, contributions of rainfall and anthropogenic sources were 47% and 33% of GS, 52% and 41% of CW, and 58% and 35% of AS, respectively. It suggests that the karst groundwater quality is predominantly controlled by rainfall and anthropogenic sources (especially, land use). Results may be applied to properly evaluate the impacts of natural and anthropogenic sources on karst aquifers, coupled with actions to efficiently control potential contamination end members.

Hydrochemical characteristics and evolution processes of karst groundwater in Carboniferous Taiyuan formation in the Pingdingshan coalfield

Coal mining may affect the hydrochemical characteristics and evolution processes of groundwater, leading to a deterioration in groundwater quality. This study was conducted to understand the hydrochemical characteristics and determine the hydrochemical processes controlling the karst groundwater hydrogeochemistry in Carboniferous Taiyuan formation in the Pingdingshan coalfield, Henan Province, China. Statistical techniques and conventional methods were utilized to gain a comprehensive understanding of the hydrogeochemical processes of karst groundwater. Results showed that the groundwater was fresh water, and was slightly acidic-to-slightly alkaline. The main cations were Ca2+ and Na+, and the predominant anions were HCO3− and SO42−. Most of the groundwater was predominantly of the Ca–HCO3 type. Principal Component Analysis (PCA), ion correlation analysis, and conventional graphic methods (Piper and Gibbs diagrams) indicated that the dissolution of silicate, gypsum, and carbonate minerals controlled the formation of Na+, Mg2+, Ca2+, SO42−, and HCO3−. Meanwhile, cation exchange was another important process regulating karst groundwater quality. Moreover, the concentrations of SO42− and NO3− were high, suggesting that the karst groundwater in this study area had been affected by anthropogenic activities, such as agriculture and mining. To avoid water inrush and keep mines east of the study area safely operational, the Guodishan faults within the mining area should be grouted to cut off the connection between limestone aquifers in the east and west study areas. In addition, it is necessary to strengthen the scientific research on fertilizers that allow plants to absorb nitrogen rapidly and control the amount of fertilizer used to protect the groundwater from pollution. The results of this study are helpful for the prevention and control of water disasters, and are beneficial for groundwater resource protection in the Pingdingshan mining areas. They will also provide a reference for similar studies by other mining hydrogeologists across the world.

Determination of Heavy Metal Concentration and Correlation Analysis of Turbidity: a Case Study of the Zlot Source (Bor, Serbia)

Karst aquifers are significant sources of water of the highest quality. Inaccessible and uninhabited karst areas are mostly away from urban centers and human activities. That is of crucial significance for karst groundwater quality. The discharge regime and karst water quality show the considerable rapid changeability of and dependence on the rainfall distribution and quantity in the catchment area. The purpose of this study is to show that there is no influence of anthropogenic factors on karst water by determining the heavy metal concentration in the water, the significance of monitoring karst water quality parameters, and to show how autocorrelation and cross-correlation analysis could be useful in defining the dependence rainfall–turbidity. The results presented in this paper refer to a case study of the Zlot Source (Bor, Serbia).

Groundwater hydrogeochemical formation and evolution in a karst aquifer system affected by anthropogenic impacts.

Karst groundwater, an important water source, is often highly influenced by human impacts, causing environmental damage and threats to human health. However, studies on the anthropogenic influences on the hydrogeochemical evolution of karst groundwater are relatively rare. To assess hydrogeochemical formation and evolution, we focused on a typical karst groundwater system (Jinan, China) which is composed of cold groundwater (av. temperature 13-17°C), springs and geothermal water (av. temperature > 30°C) and is significantly affected by human activities. The study was performed by means of water samples collecting and analyzing and isotope analysis (2H, 18O and 14C). The statistical analysis and inverse models were also applied to further understand geochemical processes and anthropogenic influences. The 2H, 18O and 14C results indicate that the cold karst groundwater is easily influenced and contaminated by the local environment, while geothermal water is relatively old with a slow rate of recharge. The hydrochemical types of cold karst groundwater are mainly HCO3-Ca and HCO3·SO4-Ca, while geothermal water hydrochemical types are SO4-Ca·Na and SO4-Ca. Groundwater Ca2+, Mg2+, HCO3- and SO42- are mainly controlled by carbonate equilibrium, gypsum dissolution and dedolomitization. Groundwater Na+, K+ and Cl- are mainly derived from halite dissolution, and in geothermal water, they are also affected by incongruent dissolution of albite and K-feldspar. Anthropogenic nitrogen produces ammonium resulting in nitrification and reduction in CO2(g) consumption and HCO3- release from carbonate dissolution. Principal component analysis and inverse models also indicate that nitrification and denitrification have significantly affected water-rock interactions. Our study suggests that karst groundwater quality is dominated by water-rock interactions and elucidates the influence of anthropogenic nitrogen. We believe that this paper will be a good reference point to study anthropogenic influences on the groundwater environment and to protect karst groundwater globally.

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.

Karst Spring Protection for the Sustainable and Healthy Living: The Examples of Niangziguan Spring and Shuishentang Spring in Shanxi, China

The karst springs, among which the Niangziguan spring and the Shuishentang spring are two typical ones, account for 24% of the total water resources in Shanxi, China and play an important role in the economic and social development of Shanxi Province. However, the spring discharge has sharply declined due to climate change and increasing anthropogenic activities. In this study, the Mann–Kendall trend test was used to analyze the trend of precipitation and spring discharge in Niangziguan spring and Shuishentang spring. Physicochemical data were also collected to delineate the karst groundwater quality variations in the two karst springs. The results show that both the precipitation and the spring discharge show a declining trend in Niangziguan spring and Shuishentang spring. Climate change is one of the critical factors that cause spring discharge attenuation. The impacts of human activities on the springs are becoming increasingly prominent, resulting in various water eco-environmental problems. TDS, TH, SO42−, Cl−, NH4+ all show increasing trend in Niangziguan spring, and the increasing concentrations of TDS and SO42− are posing a serious threat to the safety of drinking water. In Shuishentang spring, CODMn, NO3−, and NO2− present increasing trend caused by domestic sewage and agricultural fertilizers and pesticides. Anthropogenic activities such as coal mining and quarrying, urbanization, and groundwater over exploitation should be regulated to protect the karst spring and to ensure the safety of water supply for residents.

Hydrogeological characterization and environmental effects of the deteriorating urban karst groundwater in a karst trough valley: Nanshan, SW China

The unique hydrogeology of karst makes the associated groundwater respond quickly to rainfall events and vulnerable to anthropogenic pollutions. In this study, high-frequency monitoring of spring discharge, temperature, electrical conductivity (EC) and pH, along with monthly hydrochemical and microbial analyses, was undertaken at the outlet of Laolondong karst underground river in Nanshan, southwestern China. The aim was to explore the environmental effects of the catchment’s urban area on the karst groundwater resources. The monitoring data of a tracer test and the response of discharge to rainfall events demonstrate that conduits and narrow fissures coexist in the Laolongdong karst aquifer. The EC, Na+, Cl− and SO42− values (840 μS/cm, 33.7, 38.6 and 137.2 μg/L, respectively), along with high concentrations of fecal coliform bacteria, at the outlet indicate considerable urban pollution in this area. The contaminants sulfate and nitrate showed different relationships with discharge and EC in different stages of a rainfall event. This behavior provided information about aquifer structure and the influence of transport properties. Meanwhile, the hydrological processes of groundwater flow could be modified by urbanization and result in increasing magnitude of urban floods in the underground river. In addition, sulfuric and nitric acids introduced by urbanization not only impact the karst groundwater quality, but also result in a significant perturbation to the carbon cycling system in the karst area.

Geoecological Monitoring of Karst Water in Georgia, Caucasus (Case Study of Racha Limestone Massif)

Karst groundwater is the major natural resource of drinking water for many countries in the world. Especially in karstic regions, karst water requirements for settlements are provided from karst aquifers. Also, we should consider, that karst groundwater is becoming more and more valuable for drinking water supply. Thus, karst groundwater quality and permanent ecological monitoring are very important for populations. Moreover, if we consider that the karst landscape is the extremely sensitive system towards anthropogenic activities, since exaclty the anthropogenic activities largely identify the karst water pollution-turbidity causing factors. This paper presents a new study regarding the quality of the karst groundwater of the study area, which contains important resource of drinking water. In the mentioned study, 12 water samples were collected from different locations of the 4 main karst springs (Krikhula, Dolabistavi, Kidobana and Sakishore) during the spring and summer of 2014 and 2015 years. The main aim was to identify chemical compositions (Ni, Ag, Co, Cd, Zn, Pb, Al, Mg, Fe, F, Cu), and also, it was important to detect Escherichia coli (E. coli). Our research regarding all these chemical compositions shows that all the values are low and under the environmental limit according to the Georgian standards. We measured chemical parameters of all these samples by Atomic Absorption Spectroscopy (AAS) in the chemical laboratory of Ivane Javakhishvili Tbilisi State University, country of Georgia.

Groundwater Baseline Water Quality in a Shale Gas Exploration Site and Fracturing Fluid - Shale Rock Interaction

Hydraulic fracturing for shale gas exploration is not free from environmental risk. The environmental concerns related to hydraulic fracturing has been greatly attracted. One of most important environmental concerns is regional water quality which may be contaminated by produced waters through induced and natural fractures and wastewater discharge. At present, the baseline water quality must be firstly obtained to identify potential pollution of the activity and monitoring indicators should be studied for better environmental monitoring. We sampled shallow groundwater, produced waters, shale rock and soil in the Jiaoshiba shale-gas region, SW China and measurements have included water chemistry and isotopes. Preliminary results show that the present shallow karst groundwater quality is pretty good with the total dissolved solids (TDS) ranging from 129 to 343mg/L and with water chemistry type of HCO3-Ca, However, some groundwaters have been polluted by agricultural activities. Produced waters have relatively high salinity with TDS ranging from 2 to 14g/L. Laboratory experiment of fracturing liquid and shale rock interaction at simulated reservoir conditions shows that TDS in the flowback fluid increases 10 times and Ca2+, Na+, Cl− and SO42− make dominant contributions. The main geochemical reactions are inferred to be pyrite oxidation and the dissolution of calcite, dolomite and plagioclase, resulting in increases of major ions in the flowback fluid. The inorganic geochemical monitoring indicators for shale gas exploration of the Silurian Longmaxi formation has been determined.