Objective Karstic spring water is an important source of water supply for the karst areas of northern China. To rationally evaluate and scientifically exploit karstic water resources, it is important ...to identify the recharge, runoff and discharge conditions of spring water and to clearly depict the boundary of the spring area. Methods Targeting the issues of ambiguous border and unknown replenishment situations of the Gudui-Nanliang spring groups, this paper investigated and analysed the karst hydrogeological conditions of the spring area and the distribution characteristics of δD, δ18O and 87Sr/86Sr isotopes in the karstic water. The water-rock interactions and the hydraulic connection along the recharge-runoff path of karstic water were systematically examined by using isotope technique. Results The results show relatively large range of δ18O values in the karstic water. This is mainly attributed to the impacts of altitude effect, isotopic shift of oxygen in hot water, evaporation-induced enrichment and mix
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•Confined Quaternary groundwater reverse recharge contaminates buried karst water.•Upper coal mining activities pose a threat to the buried karst aquifers.•The vertical seepage of ...contaminated river water worsens karst water quality.•Hydrologic connectivity and source availability determine the contamination process.
Karst groundwater contamination has emerged as a worldwide environmental and health hazard. Karst aquifers, even for the buried karst systems, have strong contamination sensitivity and great pollution risk due to the good pipe fracture connectivity. The large burial depth and invisible hydrologic connectivity pose a challenge for the diagnosis of the contamination sources and identification of the contamination pathways of buried karst aquifers. To address it, a comprehensive application of hydrogeological and hydrogeochemical investigation combined with multiple isotopes (δ2H, δ18O, δ34S, δ13C and 87Sr/86Sr) were performed to elucidate the multiple contamination sources and migration pathways of contaminants in Jinci Spring, a complex buried karst water system. The results obtained highlight that the hydrological connectivity and source availability determine the specific contamination process in buried karst aquifer. Karst aquifer under the river channel is observed to be influenced by the vertical infiltration of polluted river water as indicated by elevated chloride levels (mean 79.4 mg/L) and higher δ2H (mean −8.8 ‰) and δ18O (mean −64.5 ‰) values. Evidenced by the excess of sulfate (mean: 1454 mg/L) and depleted δ34S (mean: −1.6 ‰), the lower karst aquifer may receive the leaking recharge of the mining waste water in the overlying coal seams. The occurrence of nitrate in karst water may be induced by reverse recharge from neighboring confined quaternary aquifers, indicated by the elevated nitrate concentration (15.0–50.8 mg/L) with high 87Sr/86Sr ratios (mean 0.7124). Our findings suggest that over-pumping of deep karst waters may produce additional pollution sources by altering the natural recharge relationship between montanic karst waters and the neighboring pore waters within the basin. Research in this paper improves our understanding of groundwater pollution and hydrological connectivity in buried carbonate aquifers and the protection of karst water resources.
Karst water are important for water supply and ecological protection. However, climate changes and human activities have caused severe water supply crisis. The Jinci spring, one of the famous karst ...springs in China, is located at the basin‐mountain coupling belt and dried up since 1994. This study integrated hydrogeological conditions, water table logs, hydrogeochemistry, multiple isotopes, and numerical modeling to understand dynamic changes of interaction pattern between karst water‐Quaternary groundwater response to human activity in the basin‐mountain coupling belt over the past 60 years. Our investigation indicated that under natural conditions (1960s), karst water discharges as springs and laterally recharges into Quaternary groundwater at the fault area. In the 1980s, overexploitation caused a significant reduction in spring discharge and a decline in karst water levels, especially in coal mining areas. Further declines in water levels and mixing recharge by karst water‐Quaternary groundwater were observed in the 2000s, which were eased in 2018. Calculations both by oxygen isotope and models indicated that contribution of Quaternary groundwater to Jinci spring ranged from 11.8% to 42.1%, with the highest in the 2000s. Evidenced by multiple isotopes, the recharging of karst water‐Quaternary groundwater varied spatially along the belt in 2018, with delayed water level elevation in coal mining and heavy groundwater exploration areas. This study demonstrated that artificial disturbance fundamentally affected the karst water‐Quaternary groundwater flow and water exchange between them. Precautions should be taken when evaluating global water resources changes, in view of the dynamic interaction between the karst water‐Quaternary groundwater spatially and temporally.
Plain Language Summary
Global changes and human activities have changed groundwater flow and cycle, which is more pronounced in basin‐mountain coupling belt. However, how human activity influences the groundwater dynamics is unknown. The Jinci spring, one of the famous karst springs located at basin‐mountain coupling belt, was selected as a study area to address this knowledge gap. Based on the hydrogeological investigation, multiple isotopes and numerical modeling, we demonstrated the dynamic interaction of the karst water‐Quaternary groundwater and the potential impact of human activity along basin‐mountain coupling belt over the past decades. The interaction between the karst water‐Quaternary groundwater has changed in time and space. Under natural conditions in 1960s, karst water laterally flows into the Quaternary water. However, in 1980s, water level declines, and thus a part of Quaternary groundwater recharge into the karst water, which was even worse in 2000s. In 2018, water level rises, with a delay elevation in coal mining and heavy groundwater exploration areas. Over the past decades, Quaternary groundwater contributes to Jinci spring with varying ratios (11.8%–42.1%, with the highest in 2000s). Our findings emphasize that precautions should be taken when evaluating global water resources changes, considering the dynamic interaction between the karst‐Quaternary groundwater spatially and temporally.
Key Points
Hydrodynamic field and interaction between karst water‐Quaternary water have changed in spatial and temporal scales
Human activity have fundamentally affected the natural groundwater evolution
Precautions are required for the evaluation of global water resources changes
Abstract
Various methods have been developed in recent decades to predict hazards associated with karst voids in underground construction. Common to all these methods is that the predicted range of ...water inflow is often insufficient for the purpose of implementing the planned construction works. This is usually due to an incomplete knowledge of the karst conduit system within a project area, making it difficult to predict the position and characteristics of karst voids. The method presented in this paper permits a robust prediction of karst water inflow. It is based on a combination of stochastically generated, pseudo‐genetic karst conduit systems and hydraulic modelling of the hydrogeological conditions using a Monte Carlo approach. This approach facilitates a plausible estimation of the expected range of karst‐induced water inflows and also enables the probability of encountering a karst voids. to be determined. The predictions allow for differentiated treatment of the hazards associated with karst water during the construction and operation phase of underground structures. In concrete terms, this relates to the planning and implementation of exploratory measures and ground‐improvement measures, the design of the dewatering system and its monitoring during the construction and operation phase.
Abstract
In den letzten Jahrzehnten wurden verschiedene Methoden zur Prognose von Karstgefährdungen für den Untertagebau entwickelt. Diesen Methoden ist gemein, dass die prognostizierte Bandbreite von Wasserzutritten für die planerische Umsetzung des Bauwerks häufig ungenügend ist. Das liegt unter anderem an den oft lückenhaften Kenntnissen über das in einem Projektgebiet vorkommende Karströhrensystem resp. der unzureichenden Vorhersagbarkeit der Lage von Karsthohlräumen und ihren Eigenschaften. Die vorgestellte Methode erlaubt eine robuste Prognose von Karstwasserzuritten. Die Methode basiert auf einer Kombination aus stochastisch generierten, pseudogenetischen Karströhrensystemen und einer hydraulischen Modellierung der hydrogeologischen Bedingungen unter Verwendung eines Monte‐Carlo Ansatzes. Der Ansatz erlaubt eine plausible Abschätzung der zu erwartenden Bandbreite karstbedingter Wassereintritte und ermöglicht darüber hinaus, die Ereigniswahrscheinlichkeit des Anfahrens eines Karsthohlraums zu bestimmen. Die Prognosen ermöglichen einen differenzierten Umgang mit der Karstwassergefährdung während Bau‐ und Betriebsphase eines Untertagebauwerks. Konkret betrifft dies die Planung und Durchführung von Erkundungsmaßnahmen, Maßnahmen zur Baugrundverbesserung sowie die Planung der Wasserhaltung und des Monitorings während der Bau‐ und Betriebsphase.
Nitrate (NO3−) pollution in karst water is an important environmental issue in intensive agricultural regions worldwide. The integrated understanding of the spatiotemporal variability and control ...factors of NO3− pollution in karst water is imperative for controlling the diffuse pollution caused by agricultural activities. In this study, 49 water samples were collected from surface water (SW) and groundwater (GW) in the Huixian karst wetland (HKW) and analyzed using hydrogeochemical and isotopic data (δ18O–NO3–, δ15N–NO3– and δ13CDIC) in combination with a Bayesian mixing model to investigate the spatiotemporal distribution and control factors in NO3−-polluted karst water. The results showed that approximately 40.82% of the karst water samples exceeded the natural threshold value of 3 mg/L for NO3−-N, and 32.14% of the GW samples exceeded the permissible limit for drinking water established by WHO (10 mg/L as NO3−-N), indicating that high levels of NO3− were mainly found in GW samples from the agricultural core area, especially in the dry season. The NH4+-synthetic fertilizer (NHF) and soil organic nitrogen (SON) were the dominant factors controlling pollution sources in the HKW, accounting for 36.13% ± 4.66% and 28.68% ± 4.75% of the karst GW NO3− concentration, respectively. However, the seasonal differences in NO3− pollution sources were not significant in GW. Microbial nitrification was the main process affecting the NO3− levels in GW, whereas the occurrence of denitrification did not significantly affect NO3− concentration in the HKW due to the relatively low rate. Moreover, the HNO3 produced from NH4+ via microbial nitrification facilitated carbonate weathering, thereby controlling NO3− enrichment in karst GW. Our results suggest that NHF should be controlled to prevent further GW pollution in the HKW. Our study also provides a scientific basis for understanding the factors controlling the NO3− concentrations in karst water systems.
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•Nitrate pollution is severe in karst groundwater in agricultural areas.•NH4+-synthetic fertilizer and soil organic nitrogen increase NO3− pollution.•Nitrification and carbonate weathering control NO3− enrichment in karst groundwater.
Improper exploitation and massive coal mines closures without proper solutions bring about the extensive occurrence of goaf water in China where over 3500 coal mines have been shut down in the last ...30 years. Discharge of goaf water poses severe environmental impact, especially in fragile karst areas. Based on the extensively literatures reading, field investigation combined with hydrogeochemical and isotopic (δ34S) analysis, this paper reviewed the distribution, characteristics and formation of coal mine goaf water in karst areas in China. The occurrence of goaf water is reported in over 50% of the coal fields, with more than 30 water discharges. Distinct major ion chemistry in goaf water (low pH, high total dissolved solids, SO42− and negative δ34S values) are closely related to a combination of comprehensive physical, chemical and biological interactions. Recharge water, water filling channels and storage space constitute hydrogeological conditions necessarily for the produce of goaf water. Oxidation of sulfides minerals with air and water, acidic dissolution of minerals (e.g., gypsum, calcite and dolomite) and cation exchange, under the action of bacteria, are major processes in the genesis of goaf water. A case study on the environmental impact of goaf water is also done at Jinci, northern China. Our research suggests that goaf water in Jinci (TDS: 3595 mg/L - 9841 mg/L, SO42−: 2463 mg/L - 3256 mg/L; negative δ34S values < −5‰) may pollute the surface and karst water via fractures or faults evidenced by the high SO42− and low δ34S values in these waters. Finally, a conceptual model is established to demonstrate the influences of goaf water on karst water-surface water environment in karst areas.
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•Goaf water occurs in over 50% of the coal fields, with more than 30 water discharges.•Goaf water is acidic with high salinity and sulfate contents and depleted δ34S values.•A case study on the environmental impact of goaf water at Jinci, northern China.•Goaf water contaminates karst aquifers directly/indirectly.
In this study, disinfection by-products (DBP) formation from dissolved organic matter (DOM) and its fractions, including both hydrophilic and hydrophobic components, were investigated at a typical ...karst surface water. The subsequent DBP formation potential was evaluated by deducing chemical characteristics of DOM fractions and representative algal organic matter (Chlorella sp. AOM) under the influence of divalent ions (Ca2+ and Mg2+) via spectra analysis. Both terrigenous and autochthonous DOM performed as critical DBP precursors, and DBP formation patterns were tightly correlated to organic matter chemical variations. DBP formation was significantly higher in drought period compared to that in wet period (P < 0.05). Particularly, trichloromethane (TCM) and dichloroacetonitrile (DCAN) showed distinct formation patterns compared to the scenarios in non-karst water. For DOM fractions, hydrophobic components showed higher DBP formation compared to hydrophilic counterparts, hydrophilic neutral enriched more reactive organic nitrogen for N-DBPs production. It was preferable to enrich humic-like substances after Ca2+ and Mg2+complexation in Chlorella sp. AOM, TCM formation increased whereas DCAN production remained unchanged in the presence of divalent ions. This study innovatively provided a linkage between chemical characteristics of DOM and understanding of DBP formation in karst surface water.
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•DBP formation from DOM and its fractions were investigated at karst surface water.•DOM characteristics responded to spatiotemporal DBPs formation.•TCM and DCAN formation was significantly higher in drought period than post-wet period.•Both flushed terrestrial and endogenous organic matter were important DBP precursors.•Ca2+ and Mg2+ complexation in AOM affects DBP formation.
As a type of corrosive mixed solution, karst water contains not only chloride and sulfate ions, but also a significant amount of bicarbonate ions. The early mechanical properties and microstructure ...of a metakaolin-based geopolymer and metakaolin/slag geopolymers (with 20 and 40 wt% slag replacing the metakaolin) immersed in karst water were investigated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Barrett-Joyner-Halenda (BJH) analysis, and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). The results showed that a reduction in mechanical strengths associated with variations in the pore size, excess of alkalis (Na2O), decalcification of C-S-H, and calcium carbonate precipitation occurred after immersion in karst water. Furthermore, the geopolymers with the addition of less slag had a greater ability to resist corrosion by karst water. This is related to the formation of calcium carbonate in the calcium-rich geopolymer, along with the excess of alkali (Na+) for activated slag led to dissolve to the karst water.
