The hydrological cycle in karst subterranean river basins is complex and concealed, posing challenges to conventional monitoring and sustainable water management. This study investigates the hydrogen and oxygen isotopic characteristics in a typical subterranean river basin within the karst region of Southwest China, to elucidate seasonal water sources and hydrological processes. Results reveal distinct seasonal isotopic patterns in karst water, with the degree of isotopic enrichment decreasing in the following order: Transitional seasons (characterized by moderate precipitation and stable hydrological conditions), the wet season and then the dry season. Natural isotopic fractionation is limited, with dry-season samples showing a slightly stronger influence of evaporation. Spatially, spring water δ18O exhibits an elevation effect, and subterranean river water shows progressive isotopic depletion downstream. The karst vadose zone significantly buffers and mixes precipitation signals, leading to more stable isotopic compositions in karst water. Bayesian mixing analysis indicates that baseflow (from epikarst springs, descending springs, and surface streams) is the dominant recharge source for the subterranean river, with direct precipitation contribution being limited (<10

The Sichuan Basin, having undergone multi-stage tectonic evolution, provides an ideal site to study structure-fluid interactions. Based on the collection of more than 200 hydrochemical datasets of various Middle-Lower Triassic karst groundwater, ion ratios, stable isotopes and Principal component analysis (PCA) were combined to quantify hydrogeochemical processes and to reveal structural controls on groundwater circulation and regional hydrochemical differentiation. Results show that the Huayingshan Fault (HYF) and Mingyueshan Anticline (MYAc) act as key first and secondary boundaries that divide the groundwater systems into different environments. Tectonics drove the groundwater to evolve through at most four stages, namely the residual paleo-seawater, chloride-dominated dissolution, sulfate-dominated dissolution and carbonate-dominated dissolution. Two groundwater circulation conceptual models were established for the Eastern Sichuan Fold Belt (ESFB). High-steep elongated anticlines with intense river incision have high structural permeability and active groundwater circulation, while short-axis anticlines under strong compression and lack large-scale river dissection, leading to shallower circulating depth. This study demonstrates that tectonic deformation intensity regulates groundwater circulation pattern, thereby governing hydrochemistry evolution.

Tunnel construction in karst aquifers can substantially alter groundwater flow systems. In this study, a three-dimensional groundwater flow model based on MODFLOW-CFP was developed to simulate the Pingyanggai synclinal karst system in Chongqing, China, incorporating dynamic tunnel excavation and lining processes. Under natural conditions, groundwater recharge is approximately 4.8 & times; 104 m3/d and is primarily balanced by discharge to the Yanmenkou and Miaolongtang underground rivers. Tunnel excavation introduced a new drainage outlet, generating an inflow of about 5.6 & times; 104 m3/d. The two underground rivers exhibited contrasting responses to excavation. Discharge from the Yanmenkou underground river decreased by approximately 6 & times; 103 m3/d (about 30%), indicating strong hydraulic connectivity with the tunnel, whereas the Miaolongtang underground river showed only minor changes. The simulated responses were qualitatively consistent with field observations during key excavation stages. These results demonstrate that tunnel excavation modifies not only the overall groundwater balance but also the internal redistribution of discharge pathways within the karst system, providing a quantitative basis for evaluating tunnel-induced hydrogeological impacts in complex karst environments.

Due to overlying loads or groundwater extraction, the boundary stresses of in-situ aquitards are complex and variable. Consequently, the consolidation deformation caused thereby makes it challenging to accurately determine hydrogeological parameters and predict deformation using traditional methods. Complex stress boundaries impose a significant computational burden on the estimation of hydrogeological parameters. To simplify the computational complexity, this study proposes two generalization methods for complex stress boundaries: multistage constant and multistage linear loads. Based on these two methods, analytical solutions for the nonlinear consolidation deformation rate and magnitude of aquitards are derived. Through dimensionless analysis of the deformation rate, a new type-curve fitting method is proposed for estimating hydrogeological parameters; parameter inversion results are obtained by fitting the analytical model with laboratory measured data. Finally, by comparing the measured data with the predicted curve of subsequent deformation based on the inversion results, the results exhibit a good degree of fitting. The results show that the hydrogeological parameters estimated by the two generalization methods and corresponding analytical solutions proposed in this study exhibit good accuracy in predicting deformations under subsequent loading stages, directly verifying the rationality of the two generalizations and the accuracy of the analytical solutions. The proposed analytical approach enhances our understanding of the nonlinear consolidation behavior of aquitards, contributes to the development of consolidation theory, and provides practical guidance for engineering applications.

The complex geological environments and frequent landslide hazards in the mountainous regions of Southwest China, particularly those characterized by high velocity and extended runout distances, pose severe threats to post-disaster rescue operations. Secondary deformation and failure hazards often jeopardize emergency response efforts, yet existing early warning systems frequently suffer from temporal lags, omissions, and false alarms. To address these challenges, this research introduces an innovative early warning method for critical sliding in secondary landslide disasters utilizing the Triangular Area Ratio (TAR, Φ) of displacement curves. Grounded in the characteristic triphasic evolutionary patterns of landslide displacement-time curves, this approach establishes warning criteria through geometric analysis. The results demonstrate that: (1) quantitative calculation formulas for the Φ index were established through the triphasic evolutionary laws, rendering it applicable to secondary landslide disasters with diverse failure mechanisms; (2) the Φ index effectively circumvents the dependency of traditional indicators, such as the improved tangent angle, on a constant-velocity phase baseline, exhibiting higher accuracy when processing displacement curves with complex deformation patterns; (3) retrospective validation utilizing the Baishuihe, Xinmo, and Baishulin landslide cases confirms the effectiveness of the hierarchical Φ thresholds for the three critical sub-stages of the accelerating deformation phase: slow intensification (1<Φ<1.2), moderate intensification (1.2≤Φ<1.4), and rapid intensification (Φ≥1.4). This warning indicator provides a robust, baseline-independent, and precise approach for the real-time monitoring and early warning of secondary landslide disasters in high-risk geological environments.

The problem of water inrush and mud gushing is a major hazard encountered during the construction of karst tunnels.During the excavation of the inclined shaft of the Siding tunnel on the Guilin-Liucheng expressway in Guangxi,karst caves were discovered at XK0+410 m and XK0+365 m,respectively.The karst pipelines exposed by the inclined shaft excavation caused groundwater to gush from the karst cave at XK0+365 m after rainfall,flowing back into the tunnel along the inclined shaft and disrupting construction.In May to June of 2020,the tunnel site experienced a rainstorm that significantly increased water inrush at XK0+365 m due to the karst cave,with a maximum flow rate of approximately 300 m3·h-1.Meanwhile,large-scale water accumulation occurred in the Xiaguling Depression,located south of the inclined shaft entrance,with water depths ranging from 1.50 to 4.67 m and a flood level of 444.874 m.The massive inflow of accumulated water into the tunnel made construction impossible,severely impeding project progress. This study takes the water inrush from the inclined shaft of the Siding tunnel on the Guilin-Liucheng expressway as the research object.Through karst hydrogeological surveys,high-density electrical resistivity prospecting,and connectivity experiments conducted in the tunnel site area,the study identified the water inrush channels and sources associated with the inclined shaft.It elucidated the genetic mechanism of water inrush,predicted the volume of water inflow,validated the accuracy of prediction in conjunction with the water inrush mechanism,and comprehensively compared three treatment measures.The results indicate the following:(1)During the construction of the Siding tunnel inclined shaft,a karst conduit was exposed,through which rainfall surged into the working area,resulting in a water inrush disaster.The primary sources of the water inrush are identified as:water from gullies on the hillslope,groundwater discharged via underground river conduits from the Duzhangtun depression from the north,and groundwater discharged from underground river tributary near Malong village from the northeast.All of these sources originate from atmospheric precipitation collected in karst negative terrains.(2)The formation process of the water inrush disaster at the Siding tunnel was as follows:during the construction of the inclined shaft,the upper conduit of the Duzhang underground river was exposed,resulting in immediate water inflow upon the occurrence of rainfall.Under heavy rain conditions,in addition to the drainage of rainwater from high-elevation depressions,the water level in the Xiaguling depression rose to 443.7 m,causing backflow into the tunnel's inclined shaft.The synergistic effect of these two factors led to a major water inrush.The water inrush mechanism at the inclined shaft of the Siding tunnel is classified as karst conduit-type water inrush,which can be divided into two processes:① Rainwater drainage from high-elevation karst depressions.When the elevation of a karst depression is higher than that of the tunnel,after rainfall,water accumulates within the depression and flows along the karst conduit,discharging into the inclined shaft through the karst cave opening exposed during excavation.② Backflow from low-elevation karst depressions.When the elevation of a karst depression is lower than that of the tunnel,during heavy rainfall,a large volume of rainwater accumulates instantaneously in the depression.Due to poor drainage,the water level rises continuously.When the water level exceeds the elevation of the karst conduit exposed by excavation,a hydraulic head difference drives the accumulated water to backflow into the inclined shaft via the karst conduit,resulting in a major inrush.(3)Based on the principle that groundwater in karst areas should be drained rather than blocked,and considering the sources of water inrush,channels,topography,and karst development characteristics of the inclined shaft of the Siding tunnel,a measure of intercepting and externally diverting water was adopted.This involved intercepting part of the floodwater in the Duzhangtun depression and using the natural drainage channel developed at the northwestern foot of the mountain in Duzhangtun to divert some of floodwater to Matang'ao village by raising the water level.Simultaneously,the accumulated water in the depression was directly diverted into the Tianchuang karst cave through tunnels or open ditches to achieve rapid drainage,reduce the flood level in the depression,and thereby decrease recharge sources and the water pressure in karst conduits.This approach effectively solves the water inrush problem in the inclined shaft and provides a basis for the treatment of water inrush in shallow-buried tunnels in similar karst areas.This study not only ensures the construction safety of the Siding tunnel,but also holds significant importance for ecological protection in the tunnel site area.

The western region of the Qinghai-Tibet Plateau is characterized by an arid climate with minimal rainfall, making groundwater the primary water source for local towns. In recent years, levated concentrations of arsenic(As), fluoride(F-) and nitrate(NO3-) in groundwater have raised concerns about drinking water safety. This study, collected 52 groundwater samples from wells in seven towns across six basins in the Ali region. By employing methods such as mathematical statistics, major ion ratio analysis, the Entropy-Weighted Water Quality Index (EWQI), and Monte Carlo simulation, the characteristics of hydrogeochemical components, controlling factors, and potential risks of groundwater in this region were clarified. The groundwater chemistry type is dominated by HCO3-Ca, and its ion concentration from high to low is Ca2+ > Na+ > Mg2+ > K+ and HCO3- > SO42- > Cl- > NO3- >F-. The most severe As pollution (0-0.09 mg/L) occurred in Gaer(GR)and Geji(GJ) towns within the Shiquan River Basin in the western part of the study area, This is primarily attributed to high As hot spring discharge, ion exchange, and the weathering and dissolution of As-containing minerals in silicate rocks Elevated F- concentrations (0.01-1.41 mg/L) were observed in Gaize(GZ) of the Luoren River Basin and Ritu(RT) of the Maka River Basin, driven by evaporation and the dissolution of F--containing minerals in evaporitic salt rocks and silicate rocks. NO3- concentrations ranged from 1.44-30.2 mg/L, and were mainly influenced by human activities. Groundwater quality was evaluated using the EWQI method. Groundwater samples from Gaer(GR)and Geji(GJ) in the Shiquan River Basin exhibited poor to very poor quality, while samples from the other five towns ranged from excellent to good. Health risks were simulated using the Monte Carlo method, revealing that both carcinogenic and non-carcinogenic risks require attention, particularly in the Shiquan River Basin, where As pollution is significant. The effective exposure factor (EF) was the most critical parameter influencing health risks, followed by As concentration and body weight (BW), with BW showing a negative correlation and other parameters showing positive correlations with risk. This study offers new insights into groundwater pollution control mechanisms and associated health risks in the western urban area of the Qinghai-Tibet Plateau. It also provides valuable references for groundwater resource management and pollution prevention in the region and downstream South Asian countries.

ObjectiveThe lower reaches of the Yarlung Tsangpo River, characterized by a significant topographical gradient, play a crucial role in transporting moisture from the Indian Ocean through the Indian monsoon to the Tibetan Plateau. This study investigates isotopic altitudinal effects on atmospheric precipitation and the distribution characteristics of d-excess in this region. It compares the isotopic altitudinal gradients of atmospheric precipitation in the midstream and downstream regions of the Yarlung Tsangpo River to clarify the factors contributing to discernible differences. The study explores the complex dynamics of the Indian Ocean monsoon airflow as it traverses and circulates within this geographical expanse by carefully examining these disparities. This expanded investigation proves pivotal for advancing comprehension of the nuanced interactions between topography and meteorological phenomena, shedding light on the complex mechanisms influencing isotopic variations in precipitation and refining insights into broader climatic processes in the studied area.MethodsThe data source for this study included atmospheric precipitation and surface water samples collected through field surveys. The Karst Geological Resources and Environment Supervision and Testing Center of the Ministry of Land and Resources conducted sample testing using a liquid water isotope analyzer (L2130-i). Isotope results were expressed as the relative thousandth deviation value of the same isotope ratio Rsample and the international standard Rstandard (V‒SMOW, Vienna standard average ocean water): δ = (Rsample/Rstandard‒1) × 1 000. The primary research methodology employed in this study involved the simulation of isotopic altitudinal gradients using the Rayleigh distillation model. This model operated under the assumption of an idealized open system in which condensed rainwater promptly exited the atmospheric system, leading to variations in the stable isotopic content of hydrogen and oxygen in precipitation at different altitudes. The study aimed to capture the complex processes that contributed to observed isotopic differences in precipitation at various elevations utilizing the Rayleigh distillation model. This approach provided a theoretical framework for understanding the dynamics of isotopic fractionation in rainfall within the context of altitude, facilitating a comprehensive analysis of atmospheric conditions in the studied region. Building upon this theoretical framework, the study involved inputting actual isotopic initial values within the research area and simulating the altitudinal effects of precipitation isotopes under ideal conditions. The simulation assumed that for every 1 000 meters of elevation gain, 10% of the precipitation condensed, allowing for the verification of actual altitudinal gradient values within the study area. In addition, the backward trajectory model employed the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. This Lagrangian trajectory model analyzed atmospheric transport, providing insights into the composition of water vapor sources within the research area. The model served as a complementary tool to support the understanding of the transport processes of the Indian Ocean monsoon within the study area, enriching the interpretation of the complex dynamics that influenced isotopic variations in precipitation at different altitudes.Results and DiscussionsThe stable hydrogen and oxygen isotope analysis enabled the establishment of a local atmospheric precipitation line and isotopic altitudinal gradient. The equation representing the atmospheric precipitation line in the research area is δ(D) = 8.02δ(18O) + 13.21. The elevated d-excess in this region is attributed to the abrupt ascent of moist air encountering the topography upon entering the Tibetan Plateau, leading to a sudden decrease in temperature and relative humidity. Another contributing factor is the local vapor recycling within the large canyon, which contributes to the observed high d-excess. These findings provide valuable insights into the factors that influence isotopic variations in precipitation in the study area, highlighting the complex interplay between atmospheric dynamics and geographical features. Interpolation analysis was employed to discern the distribution pattern of d-excess in atmospheric precipitation within the study area. The findings revealed a distinctive low-high-low pattern of d-excess across the research region, with elevated d-excess observed in the Himalayan eastern tectonic zone. This geographical area exhibited a high d-excess, indicating unique atmospheric processes and moisture sources that contributed to the isotopic composition in this specific locale. Identifying such spatial variations in d-excess enhanced the understanding of regional atmospheric dynamics and the complex factors influencing isotopic characteristics in precipitation. Through regression analysis and validation using an ideal model, the altitudinal gradient in the Yarlung Tsangpo River Grand Canyon region was determined to be ‒1.43‰/km, while in the midstream, the altitudinal gradient was found to be 3.30‰/km. The primary drivers for this disparity were attributed to variations in topographical slopes and the influence of monsoons. The distinct altitudinal gradients were validated by the composition of airflow sources across different locations in the backward trajectory model. This analysis highlighted the significance of both topography and monsoonal patterns in shaping the isotopic characteristics of precipitation, providing valuable insights into the regional atmospheric dynamics within the Yarlung Tsangpo River basin.ConclusionsThrough an examination of atmospheric precipitation isotopes in the Yarlung Tsangpo River Grand Canyon region, this study,establishes the atmospheric precipitation line and the isotopic altitudinal gradient within the area. Compared to the midstream, the altitudinal gradient in this region is relatively modest and closely linked to variations in topography and water vapor composition. In addition, the research highlights the retention of Indian Ocean moisture within the Yarlung Tsangpo Grand Canyon region following its ingress into the Tibetan Plateau.

The enrichment of As in the western Qinghai-Tibet Plateau and its surrounding basins has been widely reported. However, the spatial distribution of arsenic content in the Surface's Critical Zone (SCZ) of the Shiquan River Basin in the western Qinghai-Tibet Plateau is poorly understood, as is the mechanisms through which water-rock interactions and surface water-groundwater interactions influence arsenic enrichment and migration. In this study, the contents of arsenic and other chemical components in surface water, groundwater, sediment, soil, and rock in the Shiquan River Basin were analyzed to investigate the hydrogeochemical process of arsenic migration. The results indicate that the concentration ratios of HCO3-/(Na++K+), Ca2+/(Na++K+), Na+/ (Na++Ca2+) and delta 18O in the surface water of the Shiquan River Basin vary along the runoff path. Carbonate and silicate weathering dominate the middle and upper reaches, while evaporite dissolution gradually increases in the lower reaches. Arsenic is enriched in rocks, soil, surface water, and groundwater in the SCZ, with slightly higher concentrations found in the surface water, sediment, and soil in the middle reaches than in the upper and lower reaches. This spatial distribution suggested that the hydrogeochemical processes along the runoff path controlled the distribution of As in the basin. Water-rock interactions and hot spring discharge of arsenic-bearing minerals contributed to its enrichment in the basin, while adsorption by riverbed sediment led to the gradual decay of dissolved arsenic. The underlying aquifer (alluvial-diluvial layer) recharged by surface water is the main source of high arsenic concentration in groundwater. The findings of this study can serve as a reference for studying arsenic in similar high-arsenic basins worldwide.

Large karst springs are important surface water resources and play a particularly significant role in the vast karst mountainous regions. In China, research on large karst springs has a long history with remarkable achievements, but it is predominantly concentrated in northern regions. However, studies on large karst springs in southern regions still remain insufficient and require deeper and broader investigation. In recent years, due to the frequent occurrence of extreme weather events and the intensified human engineering activities in southern karst areas, large karst springs have been faced with ecological and environmental challenges. Therefore, it is urgent to conduct scientific and targeted analyses of the hydrological processes of karst springs in south China under multifactorial disturbances.The eastern part of Yunnan is widely recognized as one of the most prominent and typical regions for environmental issues related to large karst springs in south China’s karst area. This study focuses on the Xiaolunan large karst spring in southeastern Yunnan. Persistent drought in the region, combined with tunnel dewatering within the spring area, has disrupted the discharge dynamics of the Xiaolunan karst spring, causing abnormal fluctuations. Based on hydrogeological investigations and regional hydrochemical and isotopic tests, this study identified the genetic characteristics of the spring, its recharge sources, and hydraulic connections with the tunnel project. Using synchronous monitoring data of precipitation, spring discharge, and tunnel borehole water levels, we analyzed their variation trends and correlations. Finally, a hierarchical groundwater flow system for the spring area was constructed to enhance understanding of the hydrological processes in large karst springs.The primary findings of this study are as follows: (1) The recharge area of the Xiaolunan large karst spring is located within the Honghe River Basin. During groundwater runoff, the water transitions from phreatic to confined conditions and eventually rises and discharges as a spring due to fault obstruction. After surfacing, the spring water flows downhill into the Pearl River Basin’s water system. Therefore, the Xiaolunan large karst spring is a fault-controlled uplifted spring with cross-basin recharge. The hydrogen and oxygen isotopes of the spring closely align with the atmospheric precipitation line, indicating that its recharge originates from atmospheric precipitation. Hydrochemical ion signatures show that tunnel construction drainage has impacted the hydrological processes of the large karst spring.(2) Precipitation in the spring area exhibits marked seasonality under the influence of the plateau monsoon climate. The borehole water level generally shows a downward trend, primarily caused by continuous dewatering from tunnel construction. Over a two-year period, under the combined influence of precipitation changes and tunnel disturbances, the discharge of the large karst spring remained stable. The time-series curves were categorized into two types: asymmetric sharp peaks characterized by steep rises and falls, and relatively gentle, wave-like undulations. The exhibited a weak correlation with precipitation, with a lag time of 1 to 2 months during certain periods.(3) Multiple crustal uplifts since the Neotectonic Movement have caused spatial shifts in the erosional datum within the spring area, which have sequentially evolved into the present-day local and regional flow systems. The impacts of tunnel construction have created an intermediate flow system within a specific part of the spring area. The combined synergistic effects of the intrinsic properties of the regional flow system and the local flow system maintain the dynamic balance of large karst spring discharge across different hydrological periods, while also reducing the spring’s sensitivity to precipitation events. The intermediate flow system induces groundwater capture and pressure relief in the karst aquifer, directly leading to a reduction in discharge from the large karst spring.Continuous drainage of static groundwater reserves from the aquifer by the tunnel will cause the drawdown cone to expand progressively, increasingly threatening spring discharge. To protect the water resources of the large karst spring, it is recommended that the tunnel construction strictly implement water sealing and discharge limitations. Grouting and sealing of excavated sections should be promptly carried out, with particular focus on outer lining gaps and sections containing concentrated runoff channels, to minimize groundwater extraction. During the tunnel’s operational period, borehole water levels and spring discharge should be continuously monitored, and their recovery dynamics should be consistently tracked.

Thallium (Tl) is a rare and toxic metal present in the Earth’s crust. Its geochemical behavior and mobility closely resemble those of potassium (K). The concentration of Tl in uncontaminated soil typically does not surpass 1 mg/kg. The development and utilization of Tl-containing resources, such as ore mining and cement production, contribute significantly to the contamination of the soil through the release of substantial amounts of Tl. The soil Tl content in severely polluted mining areas can exceed 100 mg/kg, leading to regional Tl pollution and posing a serious threat to the environment and health. Thallium can be readily absorbed by plants, particularly crops, and subsequently enter the human body through the food chain, leading to potential health risks. Currently, comprehensive overview of the entire environmental process of Tl in soil-plant systems remains limited, particularly regarding its migration, accumulation, uptake, detoxification, and remediation mechanisms. Herein, the underlying mechanisms of Tl migration and accumulation within the soil-plant system and the Tl detoxification mechanisms in plants and ecological remediation of contaminated sites were fully elucidated. The review could provide theoretical foundations for future ecological restoration technologies targeting Tl-contaminated soils.

The fold-thrust belt in eastern Sichuan exhibits a unique Jura-type Mountain landscape, characterized by the development of the Middle and Lower Triassic karst aquifers within anticlines (T2l and T1j formations, respectively), where both cold and warm springs are present. However, previous studies have focused primarily on warm spring genesis, neglecting a comprehensive understanding from the perspective of groundwater flow system. This study integrates regional tectonic settings, karst hydrogeology and diverse groundwater sample data (karst cold springs, warm springs, boreholes, tunnel drainage, and deep wells). Hydrochemistry, stable isotopes (δ²H, δ¹⁸O), and radiocarbon (¹⁴C) and tritium (³H) age analyses reveal a three-level nested karst groundwater flow system. Enrichment of Mg2+ in the groundwater is one effective indicator of a longer residence time in karst aquifers, which can be used to identify and divide the hierarchically flow system. Additionally, age analysis indicates a regional groundwater system over 10,000 years old, an intermediate system spanning a century, and a local flow system comprising modern water. Finally, we proposed a conceptual model of a hierarchically nested karst groundwater flow pattern: regional thermal water primarily originates from high-altitude rainfall, emerging as medium-low temperature warm springs in the gorges or drained by boreholes. Local flow systems, recharged by near source, manifest as karst cold springs in the shallow-cut valleys, with intermediate flow systems developing in between. This study deepens the understanding of the karst groundwater circulation laws in high-steep anticline areas, and enriches the application of the Tóth multi-level nested flow system theory, and provides an important scientific basis for the evaluation, management, and protection of regional groundwater resources.

Geothermal resources, as a renewable and clean source of energy, are attracting widespread attention globally. In China, most medium to high enthalpy geothermal resources are developed in the Tibetan Plateau, especially in the rift zone of Southern Tibet. To further investigate the genesis mechanisms of geothermal resources, this study collected geothermal spring samples from the Cuona-Woka rift zone in Southern Tibet. Hydrochemical and isotopic characteristics were analyzed to reveal the origin, evolution, reservoir temperature, and circulation mechanisms of the geothermal waters. The exposed temperature of the geothermal spring ranges from 34 to 67 °C. Compared with HCO3-Ca·Na and HCO3-Na type samples, HCO3·Cl-Na and HCO3·SO4-Na type samples have higher concentrations of Cl− and trace elements. The geothermal springs are recharged by a mixture of meteoric water, snow-melt water, and magmatic water. The recharge areas had an elevation range from 5091 to 6087 m, with temperatures from −5 to −10 °C. The hydrochemical processes are dominated by silicate and carbonate dissolution, and positive cation exchange, with local gypsum dissolution. Solute geothermometers, silica-enthalpy mixing models, and geothermal conceptual model indicate that there exist shallow geothermal reservoirs (temperature = 137–162 °C) mixed by surficial cold groundwater and initial deep geothermal reservoirs (temperature = 196–212 °C), respectively. Finally, two genesis models of geothermal waters are proposed: the deep melt mixing and heating model (Type A) and the high-temperature steam heating model (Type B). The achievements of this study would provide valuable insight into geothermal research and exploitation in the Tibetan Plateau.

Regional tectonic uplift information is recorded by knickpoints distributed in multiple rivers. The changing base level (mainstream) caused by tectonic uplift also controls karst development. Groundwater should drain as springs near the base level due to karstification usually occurring near the base level, but some drains were higher than the present river in the canyon. The assumption is proposed that the spring is more elevated than the current river formed at the older intermittent stage in uplift processes and that knickpoints at the elevation can correspond to the springs. A typical basin south of Daba Mountain is selected to identify the assumption. Three knickpoints with 11 karst landforms suggest that knickpoints can indicate the karst development elevation in the basin. This method is promoted to 29 basins around Daba Mountain which are separated into DTB (North Daba Mountain Pre-Land Thrust Fault Belt) representing north part and DFB (South Daba Mountain Pre-Land Fold Belt) representing south part to verify the effectiveness of the assumption. The result discovers that the knickpoints and karst landforms have a similar high-frequency elevation interval in DFB and little variance in DTB. The reason may be that DFB has better karstification conditions, including precipitation and carbonate rock cover area, than DTB. Knickpoints is an effective indicator for karst development in area that has sufficient karstification condition like DFB. This study may provide a new perspective on the relationship between karst development and tectonic uplift and a method to find the karst groundwater drain elevation.

As an important part of the ecological civilization construction, the protection of the groundwater environment should take prevention as the main and remediation as the secondary. To prevent the groundwater pollution crisis in advance, short-term prediction models are established to grasp the groundwater quality changes. The purpose of this study is to investigate the suitability of linear and non-linear prediction models for groundwater quality indexes in Pinggu Plain, Beijing. The water quality indexes in monitoring wells W1 and W2 are selected as research objects, autoregressive integrated moving average (ARIMA) model and backpropagation neural network (BP) model are constructed to predict Cl−, SO42− and TDS concentrations in these two wells, respectively. Furthermore, the ARIMA and BP models of monitoring well W2 are combined with equal weighting method and optimal weighting method. The results show that the linear and nonlinear prediction effects of W1 are unsatisfactory, while both ARIMA and BP models extract effective water quality change information to a certain extent in W2. The prediction accuracy of the ARIMA-BP model based on the combination of different methods is higher than that of the single model, which verified the superiority of the combined model prediction effect. The relevant conclusions can provide important theoretical and methodological support for groundwater pollution prevention and control in Pinggu District and have important practical significance for promoting sustainable utilization of groundwater resources.

As a common geological hazard in karst areas, the water inrush has been a great threat to tunnel construction. Therefore, a reasonable risk evaluation of sudden water inrush is the key to tunnel construction. Based on the combination of the entropy method and catastrophe theory, a risk evaluation system of water inrush for tunnel excavation has been established in this study. Taking the ventilation incline of Dengloushan tunnel from Yunnan as an example, the entropy method is applied to rank the importance of seven target segments with different geological condition. After that, the corresponding catastrophe models are selected for each group of evaluation indicators, and the catastrophe affiliations are calculated layer by layer to evaluate the system. The results show that the accuracy of model calculation is in good agreement with practical engineering situation: the three main locations, where concentrated water inrush occurred during the excavation of the ventilation incline, are next to the evaluation segment X6, and the total catastrophe affiliation calculated by the entropy- catastrophe theory model belongs to the extremely high risk. This study provides an effective scientific basis for identifying the water inrush location in Dengloushan tunnel construction, and the relevant conclusions can be used as a reference for other tunnels with similar geological conditions.

As a special rock dissolution phenomenon, dolomite’s karst-sandification is widely distributed in the Triassic strata of the Yuxi area of Yunnan Province, China. In order to investigate the influence of karst-sandification on dolomite’s geotechnical geological properties, various methods were applied on Triassic dolomite in the study area from macroscope to microscope. Firstly, field investigation, microscopic identification, geochemical analysis and X-ray diffraction tests were used to inquire into the karst-sandification characteristics of dolomites. Furthermore, borehole sonic testing and a series of rock physical and mechanical tests were carried out to quantifying the effect of the karst-sandification on the Triassic dolomite. The results show that the Ca and Mg elements in dolomite were lost during karst-sandification by way of dissolution, whereas SiO2 was significantly enriched. After the karst-sandification, the integrity of the dolomite was reduced, and the elastic modulus, dry compressive strength, saturated compressive strength and tensile strength of the dolomite were reduced by 64.8