中国岩溶

Evaluation results, issues, and prospects of investigations into groundwater, mineral water, and geothermal (water) resources in Yunnan Province

ZHANG Hua, GAO Yu, WU Hongmei, WANG Yu, CHAI Jinlong, WANG Bo, LIU Fang, ZHOU Junrong

2025, 44(5): 897-911, 927. doi: 10.11932/karst20250501

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At present, China is deploying the basic survey of water resources. Provinces have initiated surveys of surface reserves and investigations into the quantity and quality of groundwater resources based on their specific circumstances. The goal is to accurately assess the surface water reserves as well as the quantity and quality of groundwater resources within each province. Over the years, Yunnan Province has carried out small-scale evaluation work, including regional hydrogeological surveys at scales of 1:200,000 and 1:250,000, county-level hydrogeological surveys at 1:100,000, and hydrogeological environment geological surveys at key river basins at 1:50,000. Since the 1980s, specialized groundwater dynamic monitoring has been initiated, and the construction of the national groundwater monitoring project has been launched in 2017. Based on extensive investigations, explorations, and thematic research findings, this paper comprehensively discusses and evaluates the current status of exploitation and utilization of groundwater, mineral water, and geothermal water in Yunnan Province through summary, statistical analysis, and comprehensive evaluation. The evaluation results show that Yunnan's distinctive plateau landforms, stratigraphic structures, neotectonic movements, and hydrogeological conditions have contributed to abundant groundwater, mineral water, and geothermal resources. On the basis of regional hydrogeological investigations and evaluations, the natural groundwater resources in Yunnan were estimated using the multi-year average underground runoff modulus method, yielding a total of 75.244 billion m³·a⁻¹. The recoverable resources amount to 19.035 billion m³·a⁻¹. Mineral water resources are generally underexplored, making accurate resource quantification challenging. The evaluation uses summaries of spring flow during the dry season and calculations of water inflow from drilling and pumping tests. The total mineral water resources is estimated at 154.37×10⁴ m³·d⁻¹, with a recoverable volume of 123.50×10⁴ m³·d⁻¹. Yunnan mainly utilizes natural hot springs and geothermal fluids extracted by artificial drilling. The province is rich in geothermal resources, with numerous hot springs distributed across almost all counties and cities. There are 851 naturally exposed hot springs with temperatures of 25°C or higher. Calculation results of geothermal resources through the heat storage method indicate that the heat flow is 9,216.3 L·s⁻¹, and the natural heat release is 1,056,443.27 kJ·s⁻¹. The reserves of geothermal resources amount to 197.77×10¹⁵ kJ. This is equivalent to 6,748.50×10⁶ t of standard coal. The mining heat is 435,116.5×10⁸ kJ·a⁻¹, with an additional 120,377×10⁸kJ·a⁻¹ extracted. The development and utilization rate is about 27.66%. According to the monitoring results of groundwater, the overall water quality is high. Compared to other regions across Yunnan Province, the proportion of water classified as Class I–III is slightly higher. The quality of geothermal water is superior to that of pore water, which in turn is better than that of bedrock water. Groundwater quality in the red bed area of bedrock water is more complex and variable. The water quality of the weathered fissure water in the red bed area is generally higher in the mountainous and hilly areas. In low-lying areas such as the intermountain basins and valley bottoms, water quality is highly variable and often poor due to the slow water circulation. For example, the third member of the Jiangdihe Formation (K₂j³) of the Upper Cretaceous in Middle Yunnan contains gypsum and rock salt, and well-developed dissolution fissures facilitate groundwater accumulation. When recharge conditions are favorable, groundwater circulation is rapid, and drainage is efficient, resulting in generally high water quality. However, in areas with slow groundwater runoff, chloride and sulfate concentrations often exceed the permitted levels significantly, leading to poor water quality. Mineral water is classified into five categories: metasilicic mineral water, carbonated mineral water, trace element mineral water, salt mineral water, and compound mineral water. There are 24 hydrochemical types of geothermal fluids, including HCO₃-Ca, HCO₃-Na, HCO₃-Ca·Na, HCO₃-Ca·Mg, HCO₃·SO₄-Ca, HCO₃·SO₄-Na, and HCO₃·SO₄- Ca·Na, etc.This paper also summarizes and analyzes the existing issues and deficiencies in current investigations and evaluations of water resources, such as low overall investigation accuracy, insufficient systematic consideration of water system delineation, limited parameters for groundwater resources, and a lack of integrated systems for the investigation, evaluation, development, utilization, and management of geothermal resources. For the future investigations of groundwater, mineral water, and geothermal water, it is suggested that a comprehensive application of field investigations, drilling, geophysical exploration, tracing, and other technical methods, combined with advanced techniques such as hydrodynamics, hydrochemistry, environmental isotope analysis, and modeling, should be used to scientifically delineate the boundaries of water systems in karst areas. Pilot work and scientific research should be conducted in small river basins to address critical parameters in groundwater evaluation. Research should focus on water balance in small watersheds and the processes and mechanisms of water transformation among precipitation, surface water, and ground water. The groundwater monitoring network in Yunnan Province should be improved by leveraging the National Groundwater Monitoring Project (Phase II) to complete monitoring of major basins. Monitoring stations should be strategically established in areas with significant geological issues in karst environments, ecologically sensitive and fragile zones, nature reserves, important wetlands, geothermal water-rich areas, and mineral water sources, thereby strengthening multi-dimensional systematic monitoring. Establishing a comprehensive water resources monitoring system will enhance the accuracy of groundwater resource evaluations and support the rational development and sustainable utilization of groundwater resources.

Key technical points for integrated surface water-groundwater surveys and assessment in karst basins of South China

ZHOU Changsong, ZOU Shengzhang, LU Haiping, XIA Riyuan, LU Li, WANG Jia, JIQIN Kebuzi, LIN Yongsheng, FAN Lianjie, ZHAO Yi, LI Jun, YANG Yeyu, DENG Rixin, WEI Xianyu, WU Shucheng

2025, 44(5): 912-927. doi: 10.11932/karst2025y019

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This study focuses on the karst region of South China, centered in Guizhou Province and encompassing Yunnan, Guangxi, Hunan, Hubei, Sichuan, Chongqing, and Guangdong. The study area covers 780,000 km² with survey data indicating 520,000 km² of exposed karst and 260,000 km² of covered or buried karst. Karst water resources in the region amount to 169.536 billion m³·a⁻¹, representing 83.12% of China's total karst water resources. Characterized by a tropical-subtropical monsoon climate-with annual rainfall ranging from 1,000 to 2,200 mm, 60% to 80% of which occurs between May and September-the region exhibits complex hydrogeological structures. These include highly heterogeneous aquifers, frequent surface water–groundwater (SW–GW) transformations (with more than 13 types), rapid flow dynamics (conduit flow velocities exceeding 80 m·h⁻¹ during wet seasons), and marked ecological vulnerability.Since the 1970s, with collaborative efforts, the China Geological Survey (CGS) and provincial departments have completed 1:250,000-scale hydrogeological surveys covering 780,000 km² and 1:50,000-scale hydrogeological surveys covering 350,000 km². Despite the accumulation of extensive data, no integrated technical standards have been established. The 2023 Notice on Carrying out Water Resource Baseline Surveys, issued by the Ministry of Natural Resources, mandates unified investigations of all water bodies. Against this backdrop, this study aims to: (1) systematically define the unique characteristics of water resources and hydrological cycles of the karst areas in Southern China; (2) construct an integrated SW–GW investigation and evaluation framework; (3) identify key technical challenges and propose solutions.Based on four decades of survey data and relevant literature, we systematically synthesized the characteristics of water resources and hydrological cycle. By integrating current standards (e.g., DD 2019-01, DZ/T 0469-2024) with karst-specific practices, we developed a comprehensive technical workflow. The key results are as follows: (1) Characteristics and Patterns: Seven water resource traits were identified: systemic structural complexity, spatiotemporal heterogeneity of resources, frequent SW–GW exchange, occurrence heterogeneity, hydrochemical erosivity, geomorphological control, and ecological vulnerability. Six hydrological patterns were observed: diverse circulation pathways; close interconnection among atmospheric precipitation, surface water, and groundwater; the high-frequency exchange; rapid flow velocity; multi-layer aquifer connectivity; and coexistence of fast and slow flows. (2) Technical Framework: A six-phase workflow was established: pre-survey planning → field investigation → monitoring → evaluation → database development → reporting. This approach replaces traditional map-based surveys with karst watershed units. (3) Critical Technical Solutions: Unit delineation-Level V karst water systems were designated as core assessment units. Boundary identification-discriminant boundaries were determined based on hydrodynamic fields and geological structures. SW–GW flux quantification-13 transformation subtypes were defined, each with corresponding monitoring strategies. Hydrological process characterization-differentiation was based on the intensity of karst development. Monitoring network optimization-stratified deployment was implemented according to aquifer structure; at least one surface water or groundwater monitoring site per system, with denser coverage at critical exchange nodes (e.g., sinkholes, spring clusters). Evaluation methods-scale-adapted models, such as Modflow-CFP, were applied for small basins. The integrated framework addresses technical gaps in holistic SW–GW assessment for karst regions in South China, effectively resolving challenges of spatial heterogeneity and dynamic transformations. The six technical pillars-unit delineation, boundary identification, transformation quantification, process characterization, monitoring optimization, and scale-adapted evaluation-provide standardized support for water resource surveys and sustainable management.

Genetic mechanisms and effective control of karst waterlogging

HUANG Qibo, KANG Zhiqiang, DENG Zhong, TANG Yongchen, WU Huaying, ZOU Changpei, LI Tengfang, LIAO Hongwei, MA Junfei, LIANG Jian

2025, 44(5): 928-936. doi: 10.11932/karst2025y020

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The global karst area covers about 22 million km², accounting for 15% of the Earth's land surface. Populations living in karst areas face varying degrees of threat from droughts and floods. Waterlogging is a geological hazard resulting from the interaction of karst geological and geomorphological conditions with human activities. The enclosed karst terrain, combined with intensive human engineering, has led to severe soil erosion. Soil leaks into the lower karst pipeline through the sinkholes, causing underground pipeline blockages, drainage obstructions, and frequent waterlogging events. With the increase in extreme weather, intensified human activities, soil erosion in low-lying areas, and blockage of karst pipelines, untreated conditions will lead to more frequent and severe waterlogging in these areas.Karst waterlogging disasters have caused significant losses to people in karst areas, seriously threatening their production and life. Comprehensive management of these disasters is a critical national priority. Waterlogging disasters are characterized by periodicity, clustered occurrences, and sudden onset. The enclosed karst landforms and their distinctive "binary" structure of the karst aquifer are the internal factors contributing to karst waterlogging. The subtropical monsoon climate, with its concentrated rainfall, provides the external condition necessary for the occurrence of karst waterlogging. Unreasonable engineering activities have caused a large amount of soil and water loss, blocking underground karst channels; this human impact has increasingly exacerbated karst waterlogging. Severe karst waterlogging mainly occurs in karst valleys and depressions where underground rivers and pipelines are developed. The recharge, runoff, and discharge areas of an underground river each has distinct mechanisms that contribute to internal waterlogging.At present, there is a lack of systematic research and characterization of the "binary" structure of karst aquifers. Soil erosion reduces the rainfall threshold required to cause waterlogging, yet no relevant studies examined the impact of soil erosion on the degeneration of the water conveyance capacity of underground pipeline. Furthermore, in-depth research on the formation mechanisms of karst waterlogging disasters is insufficient, making it difficult to predict the extent of such disasters and the associated losses caused under extreme climate events. This significantly undermines the effectiveness of karst waterlogging control measures. Moving forward, systematic observations of the hydrological dynamics and soil erosion dynamics that contribute to urban waterlogging should be carried out. Detailed characterization of the karst aquifer's fracture-cave "binary" structure is necessary, along with clarification of the rainfall threshold and its variability that trigger urban waterlogging. Additionally, the hydrological and soil erosion processes, as well as their controlling factors leading to karst waterlogging disasters, should be elucidated. The relationship between the reduction coefficient of outlet flow and the amount of soil erosion in low-lying areas should be analyzed. Ultimately, the mechanisms, evolutionary patterns, and principles underlying karst waterlogging formation should be systematically revealed to inform the development of scientifically sound and effective countermeasures for karst waterlogging management.

Comparative study of deep learning models for daily karst spring discharge forecasting: LSTM Versus Hybrid VMD–LSTM

YANG Yang, ZHAO Liangjie

2025, 44(5): 937-948. doi: 10.11932/karst20250502

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The discharge process of karst spring is controlled by complex hydrogeological structure and multi-scale dynamic mechanisms,exhibits characteristics of non-stationary and strongly nonlinearity, posing significant challenges for high-precision predictive modelings. Conventional physics-based models rely heavily on extensive hydrogeological parameters and often struggle to accurately capture non-stationary processes during extreme events. Consequently,integrating signal decomposition techniques with deep learning has emerged as a promising approach to enhance both prediction accuracy and physical interpretability. This study develops a hybrid model that combines Variational Mode Decomposition (VMD) with a Long-Short-Term Memory (LSTM) networks, referred to as VMD-LSTM, aiming to address non-stationarity and multi-scale coupling issues in daily karst spring discharge forecasting. Through a system comparison of the performance of the VMD-LSTM model and standard LSTM model during training, validation, and testing phases, the study evaluates improvements in prediction accuracy, extreme events characterization, and model stability, while elucidating the mechanisms by which VMD enhances the modeling performance of LSTM.This study utilized daily spring discharge and corresponding precipitation data from the Zhaidi karst system in Guilin, Guangxi, spanning from 2013 to 2023. The original spring discharge series was decomposed using VMD into ten Intrinsic Mode Functions (IMFs). Among them,six modes(Mode 5 to Mode10), which collectively represent the dominant karst hydrodynamic processes, were selected as inputs to a two-layer LSTM network for modeling. The model was trained using the Adam optimizer and the mean squared error loss function. The dataset was chronologically partitioned into a training set (80%), a validation set (10%), and a testing set (10%). Model performance was comprehensively evaluated using metrics including RMSE, MAE, NSE, KGE, and peak RMSE (caculated for the top 5% of high-flow events).Results demonstrated that the VMD-LSTM model consistently outperformed the standard LSTM across all three phases of the training,validation and testing. During the testing phase, the VMD-LSTM achieved an NSE of 0.951 and an RMSE of 0.524, representing improvements of 57.0% and 64.6%, respectively, compared to the LSTM model. Notably, the hybrid model exhibited substantially enhanced capability in predicting extreme discharges, reducing the peak RMSE from 6.208 to 1.542(a decrease of 75.2%). The VMD decomposition effectively mitigated non-stationarity and mode mixing present in the original series, enabling the LSTM network to more reliably identify and simulate the "rapid response–slow recession" characteristcs inherent in karst hydrological processes. This approach significantly syppressed the systematic underestimation and error dispersion during high-flow events. The VMD-LSTM hybrid model not only markedly enhanced the forecasting accuracy and extreme event modeling for karst spring discharge but also exhibited strong cross-phase consistency and physical interpretability, demonstrating high generalizability and robustness in practical forecasting scenarios. Future research could focus on incorporating hydrological physical constraints, conducting uncertainty quantification analysis, and extending the framework to higher spatiotemporal resolutions and multivariable coupling to further enhance model applicability and forcasting reliability across diverse karst systems.

Application of radon dynamics in analyzing karst spring flood processes: A case study of the Yaji Experimental Site, Guilin

LI Zhijie, JIANG Guanghui, GUO Fang, LIU Fan, WEI Liqiong, WANG Qigang

2025, 44(5): 949-958. doi: 10.11932/karst20250503

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This study utilized the naturally occurring tracer radon (²²²Rn) to analyze the hydrological responses of a karst spring system, aiming to elucidate variations in flow composition and recharge pathways within the karst aquifer. Three typical flood events were investigated at the Yaji Experimental Site in Guilin to understand the response mechanisms of this karst aquifer, which exhibits high heterogeneity due to its conduit-fracture system. This heterogeneity leads to rapid responses to rainfall, frequently resulting in flash floods. High-resolution monitoring of spring discharge, electrical conductivity, stable hydrogen isotope (δ²H), and ²²²Rn activity during these events captured the dynamic response of the system to rainfall-induced recharge, allowing for an assessment of contributions from different water sources to spring discharge. These sensitive hydrological indicators, including ²²²Rn and other hydrochemical parameters, revealed the complexities of aquifer recharge processes, thereby enriching our understanding of karst system responses to intense precipitation.The response time and tracer variations in the karst spring exhibited significant dependence on rainfall intensity and duration, showing a notable lag effect. Peak spring discharge lagged behind rainfall peaks by 5 to 12 hours, depending on specific rainfall characteristics. A decrease in electrical conductivity after peak discharge suggested a rapid influx of surface runoff; conversely, the peak in ²²²Rn activity was delayed by approximately 10 hours relative to the conductivity peak, indicating multi-pathway recharge into the aquifer. While conductivity primarily reflected the rapid influx of surface runoff, the delayed ²²²Rn peak indicated slower percolation through the soil and epikarst zone. Variations in hydrogen isotopes further illustrated the mixing between event water and pre-event water, highlighting complex recharge dynamics under varying rainfall conditions.Under the influence of rainfall intensity and recharge pathways, the responses of various tracers to rainfall events showed significant differences. During high-intensity rainfall, rapid surface runoff infiltrated the system, significantly altering spring hydrochemistry. In contrast, recharge from the soil and epikarst zone, characterized by slow infiltration, gradually increased ²²²Rn activity. End-member analysis, based on tracer concentrations, differentiated pre-event water (stored water prior to rainfall) from newly introduced event water. Modeling indicated that changes in conductivity and ²²²Rn activity corresponded to rapid surface input and slower subsurface recharge, capturing the effects of diverse recharge sources and pathways.Post-rainfall increases in ²²²Rn activity suggested prolonged recharge from the soil and epikarst zone, a feature not fully captured by conductivity and δ²H data. The delayed ²²²Rn response highlighted the sustained recharge from the epikarst zone, thereby enhancing the understanding of recharge timing and pathways in karst systems. ²²²Rn has been validated as an effective tracer in groundwater recharge processes, providing valuable insights for water resource management in karst regions. By distinguishing the contributions of surface runoff and groundwater flow, this method offers significant implications for flood risk prediction and groundwater recharge management, providing essential support for water resource planning and risk management in karst landscapes.

Multi-scale response characteristics of extreme hydrological events and reservoir regulation effects in the Pearl River Delta

ZHANG Ling, BAO Weijia, LUAN Song, WU Shucheng

2025, 44(5): 959-970. doi: 10.11932/karst20250504

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The Pearl River Delta (PRD) is experiencing increased hydroclimatic variability alongside intensive human regulation, resulting concurrent risks of floods, droughts, and saltwater intrusion. This study examines multi-scale changes in extreme flow events and quantifies reservoir regulation, with attention to the combined effects of upstream karst–surface water interactions and downstream tidal dynamics. We compiled daily discharge and precipitation records from seven representative stations across upstream, midstream, and downstream reaches, along with operational data from one key reservoir, covering the period from 2006 to 2017. Methods include the Mann-Kendall test with linear slope estimation for trend detection, seasonal indices for flood−drought allocations, extreme value models (Gumbel distribution for flood peaks and Gamma distribution for low flows), and a physically interpretable reservoir regulation ratio R. This ratio isolates the operational contribution of the reservoir under varying hydrological regimes. Trend diagnostics indicate significant increases in annual flow at Makou (the Xijiang River) and Sanshui (the Beijiang River), while Boluo (the Dongjiang River) shows no monotonic trend. Estimated slopes are approximately 171.4 and 50.3 m³·s⁻¹ at Makou and Sanshui, respectively. Seasonal indices reveal that upstream stations retain a pronounced flood-season amplification consistent with natural precipitation variability; midstream stations exhibit stabilization due to regulation; and downstream stations, influenced by tidal backwater and diversions, display more balanced flood-drought allocations. Frequency analysis reveals spatially contrasting hazards. At Makou, the 10-year flood is about 5.9×10⁴ m³·s⁻¹, reflecting strong basin-scale concentration and operational constraints during heavy rainfall. For drought risk, the 20-year low flow at Sanshui is 53 m³·s⁻¹, indicating elevated supply risk during prolonged deficits. The Gamma model for low flows avoids nonphysical negative values and preserves the lower-tail behavior needed for drought design. Overall, flood hazard scales with contributing area (Boluo<Sanshui<Makou), whereas drought vulnerability is station-specific, shaped by both regulation and tidal backwater. Downstream, days with flow reversal (upstream-directed velocity), which diagnose tidal dominance and salt-intrusion propensity, have increased over the study period. Reversal-day counts rise by 12% on average and cluster in the dry season (December-March), when upstream inflows are minimal. This trend is consistent with sea-level rise and dredging-altered hydraulics that enhance tidal penetration. The regulation ratio R captures operational fingerprints across regimes. During flood seasons, R<1 dominates, indicating peak shaving; typical events yield between 0.3 and 0.9. In dry seasons, R>1 occurs frequently, with support ratios above 0.8 in most years, showing active augmentation of downstream flows for ecological and municipal needs. The R series exhibits spikes during basin-wide droughts (emergency releases) and troughs during intercepted flood peaks, directly evidencing dual mitigation by storage.Synthesizing the results, climate change and human activities jointly polarize the PRD hydrologic regime, resulting higher flood peaks and lower low flows upstream, and more frequent tidal reversals downstream. Large reservoirs serve as effective tools for managing the flood-drought trade-off by reducing peak discharges while maintaining environmental flows, but they also alter natural hydrographs and sediment-morphodynamic processes. The proposed R metric provides a concise, physically grounded indicator for diagnosing and comparing regulatory efficacy across events and years, as well as for communicating operational targets under multi-hazard constraints. Although the analysis is limited by the 2006 to 2017 record and idealizations in tributary corrections, the framework is transferable to other mixed karst/non-karst river systems facing compound hazards.

Isotope-based identification of karst water system in Xin’an Spring Region

ZHAI Huwei, HU Xiaobing, ZHANG Kai, MA Yongming, GAO Xubo, JIN Jianhong

2025, 44(5): 971-980. doi: 10.11932/karst2023y004

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Xin’an Spring Region is located in the southeast of Shanxi Province, on the western side of the middle-southern section of the Taihang Mountains. The main area lies within Changzhi City, covering an area of 10,950 km². The overall structure of the spring area is monoclonal, with a strike direction of NNE and a dip toward the NW; the strata are generally flat. Karst groundwater generally flows from west to east, which is opposite to the dip direction of the strata. The flow field is a fan-shaped spring group originating from the north, west, and south, characteristic of a "monoclinic inverted" karst water system.Karst groundwater in Xin'an Spring Region serves as the primary source of urban domestic water for Changzhi City. In recent years, the continuous increase in karst groundwater extraction has led to geological and environmental issues, such as the decline of karst water levels and the decrease of spring flow, which have severely constrained the sustainable development of the local economy and society. To provide technical support for the scientific protection and utilization of karst water resources, this project adopts isotope tracing method to conduct a comprehensive analysis and diagnosis of the spring field. This approach utilizes variations in natural isotopes in water to accurately interpret and identify the recharging runoff pathways within the groundwater system. In the relatively active hydrological cycle area in the central-eastern part of the spring domain, a total of 85 groups of isotope water samples were collected, including 14 groups of surface water samples and 71 groups of karst groundwater samples.The analyzed isotopes include stable isotopes D (²H), ¹⁸O, ⁸⁷Sr/⁸⁶Sr, ³⁴S and ¹³C. The isotope composition is expressed as the per mil(‰) difference (δ) between the sample's stable isotope ratio and that of a standard reference, reflecting the direction and magnitude of isotopic variation relative to the standard. Based on the natural principles of isotope fractionation and the distribution of isotope test values, this study interprets characteristics such as boundaries of karst water subsystems, surface water leakage, and mine water contamination. Based on a consensus on the basic framework of the spring region, the isotopic data from water samples were divided into 14 system units. These include the Zhuozhang River, reservoir, Changzhi recharge area, Changzhi runoff area, Xiangyuan recharge area, Xiangyuan runoff area, Pingshun–Huguan recharge area, Pingshun–Huguan runoff area, Licheng recharge area, Licheng runoff area, Lucheng runoff area, Anchang–Zhonghua fault runoff zone, discharge area, and slow flow area.Isotopes in the spring region generally follow these rules: D (²H) and ¹⁸O isotopes are the inherent components of water, exhibiting similar distribution rules and characteristics, and originate from atmospheric precipitation, resulting in low δD (²H) and δ¹⁸O values. Sr in underground karst water mainly derives from celestite (SrSO₄) and strontium rhodochrosite (SrCO₃) present in soluble rocks. The ⁸⁷Sr/⁸⁶Sr in the same water body does not change due to SR fractionation. In its original state, the ⁸⁷Sr/⁸⁶Sr ratio in karst water is low. The ³⁴S isotope in karst groundwater mainly originates from the dissolution of sulfate minerals, so the δ³⁴S value is similar to that of sulfate minerals, and is relatively high. Dissolved inorganic carbon from carbonate dissolution typically exhibits a high δ¹³C value. Surface water, influenced by evaporation, shows elevated δD (²H) and δ¹⁸O values. It is also affected by the high ⁸⁷Sr/⁸⁶Sr ratio of non-carbonate rocks and the mixing of multiple water sources. The δ³⁴S value in surface water due to microbial degradation, and the δ¹³C value is also low. Due to recharge from surface water leakage and mine water pollution, the isotopic values generally fall between these two end-members.Based on the isotopic indication rules outlined above and combined with isotopic test data, the hydraulic connections between various system units are analyzed. A collaborative analysis is conducted incorporating with geological water control structures, water levels, water quality, hydrochemistry, and other relevant factors. Finally, the karst water system in the Xin’an Spring Region is further divided into six zones: western stagnant slow-flow area, Changzhi subsystem, Xiangyuan subsystem, Pingshun–Huguan subsystem, Licheng subsystem, and discharge area.In addition, surface water leakage and mine water pollution are clearly reflected in the data. The δD(²H) and δ¹⁸O values of spring water in the discharge area are lower than those of karst well water in the discharge area, indicating that as the karst well water level declines, the karst well water is recharged by surface water from the Zhuozhang River. The Lucheng runoff area is a section of the river with abundant water leakage and is strongly affected by leakage;its δ¹³C value is -7.8 ‰, which is close to that of surface water. The ⁸⁷Sr/⁸⁶Sr value in the Pingshun–Huguan recharge area is higher than in the runoff area, likely because the southern recharge area is contaminated by pit water. Sampling points near the Taoqing River exhibit very low δ³⁴S value, showing that the karst water is heavily affected by pit water pollution.

Analysis of characteristics and controlling factors of underground river pipeline based on tracer tests and fracture measurement: Take the Luohandu underground river as an example

LI Tengfang, HUANG Qibo, SHEN Lina, WU Qingpeng, MA Junfei, LIAO Hongwei, WU Huaying, ZOU Changpei, PU Zhenggong, LENG Rubing

2025, 44(5): 981-991. doi: 10.11932/karst20250505

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The karst development in Southwest China is very remarkable. At present, 3,066 karst underground rivers have been identified. As the main reservoir of groundwater resources, studying the distribution characteristics and controlling factors of karst pipelines is of great importance. In this study, the Luohandu underground river in Gongcheng county was selected as the research object, and a 1: 50,000-scale hydrogeological survey was carried out. It was found that an upper karst cave exists at the outlet of the Luohandu Underground River, which is supposed to be the original discharge outlet. The karst cave measures 567.9 m in length, and investigations revealed that the pipeline of the lower underground river extends about 1.6 km. Based on regional geological data, the Luohandu underground river is located near the structural belt formed by Limu–Heping fault and the Jiahui translational fault. The Limu–Heping fault trends north–south, while the Jiahui translational fault trends east-west direction. The Limu–Heping fault intersects the study area, and its structure controls the development of underground river pipelines.To identify the controlling factors of pipeline development, groundwater tracer tests and fracture measurement were conducted. The tracer was introduced into the skylight of the underground river in its upper reaches, and the tracer was detected after only 1.5 hours. The tracer concentration peaked at 1.7 hours and then began to decline. It was calculated that the maximum velocity of groundwater between the skylight and the outlet of the underground river was 550.4 m·h⁻¹, with an average velocity of 447.7 m·h⁻¹. These results showed that the groundwater flow between the skylight and the outlet of the underground river is closely connected, the migration path is relatively smooth, and the karst has been developed in the form of a single pipe. At the same time, four groups of fractures were measured by statistical window method, including three groups of structural fractures and one group of bedding fractures. To investigate the influence of fractures on the development of karst pipelines, the statistical analysis of fractures measurements revealed that the direction of the first and fourth fracture groups are generally consistent with the development direction of the underground river. Further analysis showed that high-angle structural fractures provide important channels for groundwater recharge into underground rivers. By calculating the principal values of permeability tensor for the structural fractures, it was found that the dip directions of the third principal permeability tensor (K3) at five measurement points ranged from 254° to 292°, with dip angles mostly less than 25°. The direction of maximum permeability governs the seepage direction of karst groundwater, and long-term erosion and dissolution along this direction ultimately control the development of the underground river pipilines.Based on a 1:50,000-scale hydrogeological survey and regional geological data, this study examines the structural patterns and provides a detailed description of the distribution and spatial characteristics of underground river pipelines using high-precision tracer tests. It also analyzes the influence of structural fractures on these underground river pipelines by combining fracture measurements with permeability tensor calculations. Through various technical approaches, this study not only systematically characterizes the distribution characteristics of underground river pipelines but also reveals the controlling factors in their formation, thereby providing an important scientific foundation for subsequent investigations of underground rivers and water resource evaluation.

Causes of groundwater hydrochemical characteristics and assessment of health risk to humans in the karst area of southeastern Chongqing

ZHANG Guiquan, ZHU Aiping, REN Kun, ZENG Jie, PENG Cong, PAN Xiaodong, LIANG Jiapeng, SONG Chen, ZHANG Wenping, TANG Weiwei, JIANG Dansi

2025, 44(5): 992-1005. doi: 10.11932/karst20250506

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This study conducted comprehensive water sampling and testing at 71 groundwater sites in a typical karst area of southeastern Chongqing during the summer. The research utilized methods including Gibbs diagrams, ion ratios analysis, multivariate statistical technique, the entropy-weighted water quality index (EWQI), and assessment models of human health risk to investigate the hydrochemical composition, water quality status, and health risks of groundwater in the region.The results indicate that the hydrochemical type of groundwater in the karst area of southeastern Chongqing is predominantly HCO₃-Ca (61.97%), followed by mixed types of HCO₃-Ca·Mg (30.98%) and a small proportion of HCO₃·SO₄-Ca(7.04%). The dominant cations is Ca²⁺, while the primary anions is HCO$_3^{-}$. The average cation concentrations follow the order: Ca²⁺ > Mg²⁺ > Na⁺ > K⁺(60.67 mg·L⁻¹, 10.09 mg·L⁻¹, 2.45 mg·L⁻¹, and 1.23 mg·L⁻¹, respectively), while the average anion concentrations are ranked as HCO$_3^{-}$ > SO$_4^{2}$⁻ > NO$_3^{-}$ > Cl⁻(195.04 mg·L⁻¹, 26.95 mg·L⁻¹, 9.04 mg·L⁻¹, and 3.69 mg·L⁻¹, respectively). The pH values range from 6.98 to 8.17, with a mean of 7.58, indicating weakly alkaline conditions. The total dissolved solids (TDS) range from 101.48 to 578.44 mg·L⁻¹, with an average value of 300.13 mg·L⁻¹. The coefficients of variation (CV) of the major ions Cl⁻, SO$_4^{2}$⁻, and Na⁺ in the groundwater exceed 100%, suggesting complex sources.The hydrochemistry of groundwater in the karst area of southeastern Chongqing is predominantly controlled by rock weathering. The ions of K⁺ and Na⁺ primarily originate from dissolution of and halite, with a limited role played by cation exchange. In some localized areas, elevated Na⁺ levels are influenced by domestic sewage inputs. Ca²⁺, Mg²⁺, and HCO$_3^{-}$ are mainly derived from the weathering and dissolution of carbonate rocks such as calcite and dolomite. Cl⁻ is partly sourced from halite dissolution but predominantly reflects anthropogenic contamination from domestic wastewater. NO$_3^{-}$ is primarily attributed to the application of agricultural fertilizer. SO$_4^{2}$⁻ originates from the dissolution of sulfur-bearing minerals, industrial and mining activities, and gypsum dissolution, with the gypsum dissolution contributing minimally.The water quality evaluation of the karst area in the southeastern Chongqing was conducted using the EWQI method. The EWQI values range from 7.29 to 182.68, with an average value of 21.83, indicating overall high water quality. Specifically, the proportions of high-quality, good, and poor are 92.96%, 5.63%, and 1.41%, respectively. Correlation analysis revealed a strong relationship between TDS, TFe, Mn, Al, and the EWQI. Multivariate linear regression further confirmed that groundwater is mainly affected by TFe, TDS, Al, Mn, and NO$_3^{-}$. Some sampling points exhibited poor water quality (Class IV), greatly affected by elevated levels of TFe, Mn, and Al. According to the Groundwater Quality Standard (GB/T 14848-2017), the single-factor evaluation classified water quality as Class I to V in proportions of 7.04%, 47.89%, 32.39%, 9.86%, and 2.82% respectively. Overall, groundwater quality is mainly affected by industrial and mining activities associated with local mining operations.The assessment of health risk of groundwater in southeastern Chongqing show that most of the risks are within safe levels,with an exceedance rate of 4.23%.However, in some areas, TFe and ${\rm{NO}}_3^{-}$ surpass the comprehensive health risk threshold for children(HI=1),indicating elevated hazard risks,with the highest risk value of ${\rm{NO}}_3^{-}$ reaching HI_nitate=2.17277. Therefore, these areas require increased attention.

Prediction of water inflow and evaluation of curtain water-blocking effect in the Panlong lead-zinc mining area

PENG Sanxi, LI Guifu, SHAN Huimei, LIU Yunquan, LU Danmei

2025, 44(5): 1006-1024. doi: 10.11932/karst20250507

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The importance of metal mineral resources as a vital component of China's social and economic development is self-evident. With the acceleration of industrialization, the demand for mineral resources has increased sharply, and mining activities have extended progressively deeper underground. However, the resulting water-inflow disasters are becoming increasingly frequent, seriously threatening both the safety of mine operations and balance of the ecological environment. Therefore, it is of great significance to scientifically and reasonably calculate and predict changes in water inflow and groundwater levels in mining areas, and to develop effective water prevention and control strategies to ensure safe production in these areas.Since the exploitation of the Panlong lead-zinc mine in Guangxi began, mine production has been affected by the erosion of surface water and groundwater. The Panlong lead-zinc mine is adjacent to the Datengxia Water Conservancy Project. When the Datengxia Water Conservancy Project commenced impoundment, the water level of the Qianjiang River rose significantly, enhancing the resistance to recharge of the Qianjiang River and greatly increased the risk of water inflow in the mining area. Focusing on the Panlong lead-zinc mine in Guangxi as the research subject, this study addresses the water inflow problems encountered during deep mining operations. By integrating with the hydrogeological conditions, karst development characteristics, and the current mining status, a three-dimensional numerical model of groundwater flow in the mining area was developed by GMS software. This model predicts water inflow and changes in underground flow field at different mining depths and evaluates the water-blocking effectiveness of grouting curtain project. The main research contents and conclusions are as follows: (1) Prior to the construction of the Datengxia Water Conservancy Project, the water level of the Qianjiang River reached 42 m, with the average total daily water inflow of the mine being 20,610 m³∙d⁻¹ and 21,263 m³∙d⁻¹, respectively, when mining extended to the middle of −380 m and −440 m.(2) Following reservoir impoundment with the water level of the Qianjiang River at 61.5 m, the total water inflow at the −440 m level increased to 26,639 m³∙d⁻¹, representing an increase of 5,376 m³∙d⁻¹ relative to pre-impoundment conditions. Meanwhile, a significant drawdown funnel developed, with recharge from the Qianjiang River on the eastern side and lateral groundwater inflow on the western side becoming the dominant water sources. This suggests that the elevated water level of the Qianjiang River, caused by the Datengxia Water Conservancy Project, may pose potential risks to the safety of mining operations.(3) Prior to the implementation of the eastern curtain, mining at the −440 m level under reservoir impoundment conditions resulted in a total water inflow rise of increase of 5,376 m³∙d⁻¹. Following the implementation of the eastern curtain grouting project, with reservoir impoundment (the water level of the Qianjiang River: 61.5 m) and mining at the −440 m level, the total average daily water inflow was 23,548 m³∙d⁻¹, representing a reduction of approximately 3,091 m³∙d⁻¹ compared to pre-curtain conditions (26,639 m³∙d⁻¹). The results show that the eastern curtain project blocked only 3,091 m³∙d⁻¹ of water inflow, failing to completely eliminate the inflow problem.(4) Following the east–west curtain grouting project, under conditions of reservoir impoundment and mining at the –440 m level, the total average daily water inflow was 19,744 m³∙d⁻¹-an approximate reduction of 6,895 m³∙d⁻¹ compared to pre-curtain conditions. This effectively eliminates the increased water inflow caused by the impoundment-induced water-level rise, indicating the effective water prevention and control achieved by the east–west curtain project in the mining area.(5) Numerical simulation predicts that the total water inflow of the mine will reach 23,285 m³∙d⁻¹ when mining attains −740 m level, with the rate of water inflow increase slows down as the mining depth increases. In addition, flow field simulations indicate that, as mining depth increases, the range of the drawdown funnel gradually expands, hydraulic gradients intensify, and groundwater recharge pathways shift toward the bed of the Qianjiang River.This study can provide a scientific basis for the prevention and control of water inflow during the deep mining of the Panlong lead-zinc mine, while also offer theoretical support and practical guidance for safe mining and prevention and control of groundwater disasters in karst mining areas characterized by complex hydrogeological conditions.

Study on an in-situ dissolution experiment of gypsum boreholes

ZHOU Jianwei, HE Xiao, GAO Xiaofeng, PENG Tao, XU Ke, ZHAO Yong

2025, 44(5): 1025-1035, 1048. doi: 10.11932/karst20250508

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Gypsum is characterized by high solubility and a rapid dissolution rate, which can trigger geological disasters such as subsidence and collapse, especially under the influence of inappropriate human engineering activities like groundwater extraction and drainage. However, most research on gypsum has focused on itsn occurance in the marine sedimentary environments, with relatively few studies addressing gypsum in the lacustrine sedimentary settings. The latter is generally considered to exhibit rare karst phenomena and to occur on a smaller scale. The gypsum in the Cretaceous Guankou Formation (K₂g) is a typical example of lacustrine sedimentary gypsum. Its dissolution has caused abnormal settlement of buildings constructed on it. However, most research on the dissolution of the gypsum has been limited to laboratory experiments, such as the static water and flowing water dissolution tests, which do not fully capture the actual dissolution conditions of gypsum. Some in-situ dissolution tests on gypsum have been carried out in Russia, Ukraine, Spain and Italy with the use of tablet or the MEM method in boreholes and cavities. But no in-situ dissolution research on gypsum has been conducted in China.In this study, three groups of standard gypsum (K₂g) tablet specimen, packed in nylon bags, were suspended at depth of 15 m, 25 m and 35 m within the borehole. Steel pipe were used to prevent the upper sandy and gravel aquifer from directly entering to the borehole. This setup simulated the dynamic dissolution process of gypsum under the in-situ hydrodynamic, hydrochemical and temperature conditions representative of the real stratigraphy environment. After 3 days, 7 days, 15 days and 30 days, the specimens were retrieved from the borehole for measurement and observation, and the chemistry of groundwater was analyzed simultaneously.The tests showed that the specimens at the depths of 15 m and 25 m exhibited intense dissolution phenomena, while the specimens at the depth of 35 m showed only slight dissolution. After 30 days of in-site testing, the average mass loss rates of the specimens at 15 m and 25 m reached 73.9% and 73.7% respectively, with average dissolution rates of 1.16×10⁻² g·cm⁻²·d⁻¹ and 1.13×10⁻² g·cm⁻²·d⁻¹, respectively. The recession rates at 15 m and 25 m were 0.246 mm·d⁻¹ and 0.245 mm·d⁻¹, respectively. The average mass loss rate of the specimens at 35 m was only 18.4%, and the average dissolution rate was 0.39×10⁻² g·cm⁻²·d⁻¹, which was only a quarter of that of the specimens at 15 m and 25 m, and was comparable to the dissolution rate of the gypsum reported by other researchers in static water environments. This dissolution rate was much greater than that of gypsum specimens in boreholes measured by Calligaris C. The dissolution rates of the specimens at 15 m and 25 m initially increased and then decreased over time,while the dissolution rate of the specimens at 35m did not change significantly with time.Groundwater samples were collected from the borehole for chemical analysis both before and during the test. It was observed that the concentrations of SO$_4^{2-}$ and Ca²⁺ in the groundwater at 15 m and 35 m were lower than those at 25 m. Nevertheless, neither the concentration of SO$_4^{2-}$ nor that of Ca²⁺ reached saturation at any point during the experiment. The dissolution rate constants (K) at the site were approximately 0.030×10⁻⁵ to 0.114×10⁻⁵ m·s⁻¹.Influenced by hydrogeological conditions at various depths, the rapid dissolution rate of gypsum was primarily controlled by mass transport driven by the hydraulic gradient, with surface reactions driven by ion concentration playing a secondary role. The dissolution processes of the specimens at 15 m and 25 m were affected by both mechanical erosion and chemical dissolution, progressing through four stages: adsorption and saturation, shallow pit formation, lateral pit merging, and deep disintegration. In contrast, the dissolution of the specimens at 35 m was mainly controlled by chemical dissolution and only underwent the first two stages: adsorption and saturation, and shallow pit formation.This in-situ dissolution experiment and evaluation method for gypsum supplements the existing dissolution data of gypsum in China, providing an important reference for karst risk assessment in gypsum-rich areas.

Relationship between topsoil pollen and modern vegetation at the Huanjiang Karst Observation Station of Guangxi

HAO Xiudong, LU Yaxian, OUYANG Xuhong, LI Lixue, QIN Linjuan, WEI Jiasheng, WANG Ailan, HUANG Linqian, LIN Chunyu

2025, 44(5): 1036-1048. doi: 10.11932/karst2025y017

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This study takes topsoil pollen samples from different land use methods/vegetation types at the Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences (hereinafter referred to as the Huanjiang Station) as its research object. The Huanjiang Station is located in the southern part of Huanjiang Maonan Autonomous county, Hechi City, Guangxi and represents typical karst peak-cluster depression ecosystem in China. It is situated in the subtropical monsoon climate zone, with a mild climate and abundant rainfall throughout the county. The forest communities are primarily composed of evergreen broadleaf forests, followed by some deciduous broadleaf and mixed evergreen coniferous and broadleaf forests.This study aims to explore the characteristics of topsoil pollen assemblages under different land use methods/vegetation types at the Huanjiang Station. It seeks to establish a correlation between topsoil pollen and modern vegetation to provide theoretical references for ecological restoration, Quaternary paleoenvironmental and paleoclimate reconstruction, and historical research on human interference activities in the study area and comparable karst regions. All 24 topsoil and moss samples were prepared at the Key Laboratory of Environment Change and Resources Use in Beibu Gulf (Nanning Normal University), Ministry of Education. Standard conventional acid-base methods were then used to extract the pollen. About 30 g of dry topsoil samples and about 3 g of dry moss samples were weighted. HCL was added to dissolve calcareous minerals, and HF was used to digest silica, followed by several rinses with distilled water. Finally, a 7-μm nylon sieve was employed to remove unwanted small particles, and the pollen was collected to a 5-ml centrifuge tube. A tablet containing Lycopodium spores (10,315 grains per tablet) was added to each sample to calculate pollen concentration. The percentage of each pollen taxon is based solely on the total terrestrial pollen sum, whereas the percentage of spores is calculated from the combined sum of both pollen and spores. Pollen and spores were identified with the use of a Leica DM4000 B microscope at 200/400x magnification. More than 300 pollen grains of per sample were counted. The program Tilia (Version 1.7.16) was used to construct the pollen diagrams. Principal Component Analysis (PCA) was applied to the data pollen percentage with the use of Canoco (Versions 5.0) software.The results show: (1) A total of 49 pollen taxa (genera or family) were identified from 24 topsoil (or moss) samples collected at Huanjiang Station. Among these, 25 taxa belonged to trees and shrubs, mainly including Pinus, Cupressaceae/Taxodiaceae, Fabaceae, Euphorbiaceae, Magnoliaceae, and Moraceae. Pinus had the highest content, averaging 56.8% and reaching a maximum of 87.62%. Additionally, 20 taxa were Herbaceous, mainly Poaceae, Asteraceae, and Araceae. Fern spores were mainly from Nephrolepis, Dicranopteris, and Pteris. Freshwater algae (Concentricystis) spores were also present in the samples. (2) There was a large variation in the concentration of topsoil pollen among different land use methods/vegetation types in the depression of Huanjiang Station. The lowest pollen concentration was 4,131 grains·g⁻¹ in topsoil samples from secondary growth forest, while the highest was 416,781 grains·g⁻¹ in planted restoration forest. The average pollen concentration was relatively low, at 54,432 grains·g⁻¹.A significant difference was observed between the average concentrations of topsoil samples (27,371 grains·g⁻¹) and moss samples (189,738 grains·g⁻¹). Among all samples, Pinus pollen had the highest concentration, reaching 19,232 grains·g⁻¹, followed by Asteraceae (2,280 grains·g⁻¹), Poaceae (1,535 grains·g⁻¹), and Euphorbiaceae (1,461 grains·g⁻¹). In addition, fren spore concentration was relatively high, with an average of 6,353 spores·g⁻¹.(3) PCA results showed that the pollen assemblage was well separated and heterogeneous, allowing for rough classification. Among different land use methods/vegetation types, corn fields corresponded clearly with Zea, and coniferous woodland corresponded clearly with Moraceae, enabling effective differentiation. Secondary growth forest and planted restoration forest were relatively well grouped. The conclusion are as follows: (1) The topsoil pollen composition corresponds well with the vegetation types of each land use method/vegetation type, and the combined topsoil pollen assemblage can basically reflect the overall characteristics of vegetation surrounding the depression. (2) PCA analysis can effectively distinguish grassland, planted restoration forest, coniferous woodland, secondary growth forest, and cornfields, indicating that topsoil pollen from different land use methods/vegetation types exhibits clear differentiation. However, mulberry forests cannot be well distinguished, which may be related to the timing of Morus sampling and pollen preservation conditions. (3) Pollen concentrations of different land use methods/vegetation types follow the order: planted restoration forest > mulberry forest > cornfield > secondary growth forest > grassland > coniferous woodland. This pattern may be closely related to vegetation composition, soil disturbance, and pollen preservation conditions.

CO₂ emission fluxes and bacterial community structures characteristics in the water bodies of the Lingqu and the Darongjiang Rivers

LUO Ting, JIN Zhenjiang, YUAN Wu, YANG Chengxi, LI Jia, WANG Shixuan, FAN Chen, CHEN Guilun, ZHANG Xiaowen

2025, 44(5): 1049-1062, 1073. doi: 10.11932/karst20250509

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Rivers connect two major carbon pools-terrestrial ecosystems and marine ecosystems-and play a crucial role in the global carbon cycle. Microorganisms are the main agents driving the carbon cycling processes within river ecosystems. To some extent, microorganisms and the physicochemical characteristics of rivers can affect the production of CO₂ in rivers and are the key factors in the riverine carbon cycle. Therefore, studying the interrelationships among CO₂ emission fluxes, microorganisms and physicochemical properties at the water-air interface of rivers is essential for understanding the underlying mechanisms of riverine carbon emissions. In South China, carbonates are widely distributed, and karst processes are highly active, serving as significant drivers of the river carbon cycle. However, the differences in CO₂ emission characteristics between rivers in Karst Areas (KA) and Non-Karst Areas (NKA) as well as their driving mechanisms, remain unclear. To investigate CO₂ emission fluxes and their driving factors in river sections in KA, the Lingqu section (KA) and the Darongjiang River section (NKA) in the upper reaches of the Lijiang River were selected as the sampling points. During the wet season (August 2023), dry season (January 2024), and normal season (March 2024), CO₂ emission fluxes were measured over 48-hour periods at both the Lingqu River section and the Darongjiang River section by the static chamber method. The bacterial community structures of the rivers were characterized by high-throughput sequencing technology. Correlations between CO₂ emission fluxes, river physicochemical properties, and the microbial communities were analyzed. The main results are as follows.(1) Within 48 hours during the three hydrological periods, the CO₂ emission fluxes at the Lingqu River section were 14.54 to 352.88 mg·(m²·h)⁻¹, 0.85 to 10.47 mg·(m²·h)⁻¹, and 1.05 to 13.83 mg·(m²·h)⁻¹, respectively. The total emissions were 25.82 kg·hm⁻², 1.38 kg·hm⁻², and 2.29 kg·hm⁻², respectively. At the Darongjiang River section, CO₂ emission fluxes were 3.70 to 399.90 mg·(m²·h)⁻¹, 1.25 to 8.24 mg·(m²·h)⁻¹, and 4.14 to 36.09 mg·(m²·h)⁻¹, respectively, with total emissions of 40.46 kg·hm⁻², 1.88 kg·hm⁻², and 4.36 kg·hm⁻², respectively. The CO₂ emission fluxes at the water-air interface in both KA and NKA were positive, indicating that the study area is a source of CO₂. The CO₂ emission followed the pattern: flood season > normal season > dry season. (2) The CO₂ emission flux at the Lingqu River section was significantly negatively correlated with pH (P<0.01) and Total Nitrogen (TN) (P<0.05), while the CO₂ emission flux at the Darongjiang River was significantly positively correlated with Dissolved Organic Carbon (DOC) (P<0.05) and TN (P<0.01). When the CO₂ emission flux and physicochemical properties of both the Lingqu River and Darongjiang River sections were analyzed, the CO₂ emission flux showed a significant positive correlation with DOC (P<0.05) and a significant negative correlation with pH (P<0.01). (3) At the bacterial genus level, twelve dominant bacterial genera were identified in the Lingqujiang River section, including Limnohabitans (1.20% to 26.58%), Pseudomonas (0.24% to 22.00%), and unclassified Micrococcaceae (0.45% to 21.07%). In contrast, nine dominant bacterial genera were found in the Darongjiang River section, including Acinetobacter (0.23% to 23.79%), unclassified Sporichthyaceae (1.64% to 13.54%), and the CL500-29 marine group (3.74% to 12.02%). Heat map analysis showed that the CO₂ emission fluxes at both the Lingqu and Darongjiang River sections were significantly positively correlated with the relative abundances of the CL500-29 marine group (P<0.01) and the hgcI clade (P<0.01). Conversely, emissions were significantly negatively correlated with the relative abundance of Pseudomonas (P<0.01). (4) Ecological network analysis shows that the number of nodes, the total number of edges, and the modularity index of the Lingqu River section network are all lower than those of the Darongjiang River section. This indicates that the interactions among bacteria in the KA are weaker, the community structure is unstable, and the ecosystem is more fragile. Therefore, both biological factors (such as the CL500-29 marine group, hgcI clade, and Pseudomonas) and abiotic factors (such as pH, DOC, and TN) jointly regulate the CO₂ emission process of the Lijiang River. To maintain a low CO₂ emission at the water-air interface, interference to the river ecosystem in the KA should be minimized as much as possible. This study analyzes the CO₂ emissions and microbial communities at the water-air interface of the river in the KA (the Lingqu River section) and the NKA (the Darongjiang River section) of the upper reaches of the Lijiang River. The research shows that the CO₂ emission flux in the KA basin is relatively low and reveals differences in the community structure and stability of microorganisms between these two areas.

Spatiotemporal variation characteristics and water flow path of soil moisture of the critical zones fissures in karst area

YANG Jixiang, ZHANG Zhicai, CHEN Xi, LIU Xiuqiang, XIE Yongyu, PENG Tao, CHEN Bo

2025, 44(5): 1063-1073. doi: 10.11932/karst20250510

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The dynamics of soil moisture in the critical karst zone fissures and their controlling factors form the foundation for studying ecological hydrological processes in this region. Analyzing the spatiotemporal dynamics of soil moisture within soil-rock fill structures and elucidating the controlling effects of changes in water flow pathways will provide scientific basis for research on ecological hydrological processes in karst regions and the efficient utilization of water resources. The study area is located at the Puding Karst Ecosystem Research Station in Guizhou Province, southwest China, situated on the watershed between the Yangtze River and Pearl River systems of the Guizhou Plateau. It is the core region of the southern Chinese karst landscape, which is one of the three major contiguous karst landform regions globally.In the study, representative critical karst zone soil-rock filling structure profiles were selected within the station, and a soil-rock fissure moisture observation system was established. Using moisture monitoring probes installed at different depths, high-resolution spatiotemporal observations of fissure soil moisture were conducted. By observing Soil Water Content (SWC) at different depth levels, soil-rock interface water content (S-R), and fine rock soil water content (RWC), the study investigated the spatiotemporal variation patterns of soil moisture in different types of fissures within the critical karst zone. By combining rainfall characteristics with the response patterns of fissure soil water content, the study revealed the control mechanisms of rainfall infiltration processes on fissure soil moisture. The results indicate that the dynamic changes in soil moisture in fine fissures are significantly higher than those in large fissures far from the soil-rock interface, with higher moisture content and better water-holding capacity, providing a reserve water source for vegetation growth. Due to the rapid infiltration influenced by the fissure network or soil-rock interface, fissure soils connected to rapid pathways in the critical karst zone can be rapidly replenished with moisture, exhibiting more intense moisture change dynamics. In contrast, soil in fissures controlled by slow infiltration exhibits slow water replenishment and relatively mild moisture dynamics. Additionally, rainfall infiltration pathways vary with dry-wet conditions and fissure development, further complicating the spatiotemporal variability of soil moisture in fissures. Rainfall characteristics significantly influence moisture changes in fissure soils during rainfall events. In single-peak rainfall events, moisture content in all types of fissure soils is significantly higher than in continuous rainfall events. Influenced by rapid flow channels at the soil-rock interface, the soil moisture content in the middle and lower layers of large fissures, as well as the soil moisture content in small fissures in the middle layer, respond rapidly to rainfall. The developed rock fissure network increases the connectivity between fissures and the surface, accelerating rainfall infiltration recharge to fissures. Rainfall intensity regulates water flow pathways. As rainfall intensity increases, the hydrological connectivity of the soil-rock interface rises, and its role in water transport process during rainfall infiltration gradually strengthens. Especially under heavy rainfall conditions, lateral hydrological connectivity within the soil-rock fissure system increases, and lateral water flow processes become a key controlling factor in the moisture dynamics of fissures soils.

Grading of germanium contents and establishment of standard for germanium-enrichment in cultivated soils in Guizhou Province

MA Hua, CAI Dawei, REN Mingqiang, LI Longbo

2025, 44(5): 1074-1083. doi: 10.11932/karst20250511

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Germanium is a rare and dispersed element in nature. Positioned between metals and non-metals on the periodic table, germanium possesses properties of both groups. In soils, germanium mainly originates from rock weathering and mineral formation. Monitoring and statistical data show that the background content of germanium in soil in China is 1.7 mg·kg⁻¹, while the latest research suggests that the background or benchmark value for germanium in cultivated soils in China ranges from 1.3 mg·kg⁻¹to 1.4 mg·kg⁻¹. At present, studies on grading germanium contents in soils mostly adopt the cumulative frequency analysis method. This approach tests whether the data follow a normal distribution or log-normal distribution. Once the data conform to one of these distributions, a critical percentile value is established to determine the grading standard, which is typically divided into five levels. This germanium content in soils is then classified according to these levels. In recent years, Chinese government’s emphasis on functional agriculture has led to a surge in research and exploitation of germanium-enriched soil and crops. However, no unified national or industry standards currently exist; only Heilongjiang Province has issued the local standard for evaluating germanium-enriched soil. Therefore, the timely establishment of such standard is of great significance for the industrialization of germanium-enriched products and for the sustainable and healthy development of the relevant market.The geochemical survey and evaluation of cultivated land quality in Guizhou Province is a high-precision study encompassing all cultivated land in the province at a scale of 1:50,000. The sampling areas mainly include cultivated lands, such as paddy fields, dry land, irrigated land, and a small proportion of tea gardens, orchards, etc. A total of 454,453 surface soil samples from cultivated lands were collected. Based on the analysis and testing results of these samples, this study adopted three grading methods to classify soil germanium contents and calculated the critical values for grading soil germanium contents according to different influencing factors. The threshold values for five grades of all samples were calculated as 2.00 mg·kg⁻¹, 1.70 mg·kg⁻¹, 1.35 mg·kg⁻¹ and 1.07 mg·kg⁻¹, respectively. These values were divided into five levels to represent the abundance or deficiency of germanium contents in soils. The critical value of the first level is generally used as the standard for germanium enrichment. Considering the current germanium contents in cultivated soils of Guizhou Province, the proportion of germanium-enriched soils, and the development needs of the germanium enrichment industry, it is advisable to use the second-level critical value of 1.70 mg·kg⁻¹-corrected by the arithmetic mean method across all samples-as the reference standard for germanium enrichment in cultivated soils in the province. Additionally, reference values for germanium enrichment in soils can also be established based on variations in soil pH ranges, parent rocks, or land use types. This study uses 1.70 mg·kg⁻¹ as the reference value. The number of samples meeting the standard for germanium enrichment in soils is 126,395, accounting for 27.8%. The cultivated area characterized by soils enriched with germanium in the province is about 16.08 million mu, representing 22.3% of the total surveyed area. The sample scope of this study covers agricultural soils throughout Guizhou Province, ensuring broad representativeness and diversity. Analysis and testing were carried out in accordance with the established standard, employing quality control measures such as inclusion of the substances meeting the national first-class standard, monitoring samples, repeated checks, and spot checks for anomalies. Therefore, the results are authentic, scientific, and valuable for reference. In addition, the contents of organic matter, aluminum/iron oxides, clay minerals, and redox potential in soils have a certain impact on the available contents of germanium in soils. Future research should focus on a more detailed classification of standards for germanium enrichment in soils.

Evolution of rocky desertification and its response to land use changes in the karst areas of Guangxi

ZHU Degen, YANG Hui, ZHAO Hu, SHI Shaoliang, WU Xiuqin, Mitja Prelovšek, Nataša Ravbar

2025, 44(5): 1084-1100. doi: 10.11932/karst2024y042

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This study focuses on the karst areas of Guangxi, Southwest China, which cover an area of 9.87×10⁴km² (accounting for 41% of Guangxi's total land area) and feature a subtropical monsoon climate, complete karst landforms (dominated by peak cluster depressions, peak forests, and peak cluster valleys), and a fragile ecological environment with thin soil layers (mostly less than 30 cm) and severe rocky desertification.The study aims to quantitatively analyze the impact of land use change on rocky desertification in the Guangxi karst area, resolve the lack of quantitative assessment of such impacts in previous studies, and provide a scientific basis for rocky desertification control and ecological restoration.Based on Landsat data and land use data of Guangxi from 2001, 2006, 2011, 2016, and 2020, GIS methods were used to construct a rocky desertification transfer matrix, a land use transfer matrix, and their interaction matrix. Additionally, the Habitat Quality Change Index (CI) and Habitat Quality Contribution Index (HQCI) were introduced to evaluate the effect of land use conversion on rocky desertification. Rocky desertification was classified into five grades using the NDVI-based vegetation coverage method, and the accuracy verification was conducted with 92 field survey points.The results showed that: (1) Both rocky desertification and land use in the study area showed a dynamic improvement trend. Spatially, rocky desertification presented the characteristics of "severe in the west and mild in the east, severe in the south and mild in the north", which was correlated with the spatial distribution of cropland ("increase in the east-west and decrease in the north-south") and forestland ("decrease in the east-west and increase in the north-south"). (2) Different land use conversions had distinct effects on different rocky desertification grades: grassland conversion to forestland had the most significant improvement effect on severe rocky desertification, cropland conversion to forestland was effective for moderate and mild rocky desertification, and shrubland conversion to forestland worked best for potential rocky desertification. (3) Vegetation restoration was the main driving force for rocky desertification control. According to HQCI, cropland conversion to forestland contributed the most (HQCI = 1.196), followed by shrubland to forestland (HQCI = 0.328) and forestland to shrubland (HQCI = 0.095); conversions of other land use types to grassland had negative contributions.In conclusion, land use change has a significant impact on rocky desertification evolution in the Guangxi karst area. Targeted land use adjustment (e.g., converting cropland, grassland, and shrubland to forestland based on rocky desertification grades) can effectively promote rocky desertification improvement. Future study should further explore the application effects of different ecological restoration technologies to optimize rocky desertification control strategies.

Cause analysis of travertine blackening：A case study of travertine at Huanglong Ravine, Sichuan Province, China

JIANG Ruiyang, DAI Qunwei, ZHANG Ting, DENG Zhiqing, WANG Lihui, SHAN Jing, RAN Yue, GAO Jun, CAI Jiangrong, WANG Guoyue

2025, 44(5): 1101-1108, 1120. doi: 10.11932/karst20250512

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Abstract:
Travertine is one of the most precious resources provided to human beings by nature, and its formation mechanism is highly complex. The formation process involves intricate interactions among multiple factors, including geomorphological features, hydrochemical conditions, hydrodynamic forces, climate variations, environmental changes, and biological activities, all of which collectively preserve critical environmental records. As one of the five world travertine heritage sites, Sichuan Huanglong is famous for its colorful and large-scale travertine landscapes. These unique geological features hold exceptional value for scientific research, tourism, and ecological aesthetics. Every year, Huanglong attracts a large number of tourists from home and abroad, which promotes the rapid development of the local economy. However, in recent years, some of the travertine bodies in the core scenic area of Huanglong have shown obvious blackening phenomena, which not only significantly diminish the aesthetic value of the travertine landscape, but may also indicate the potential changes in the regional ecological environment. At the same time, the blackening of travertine bodies will reduce the quality of the tourists' experience, which will have a certain negative impact on the development of the local tourism industry. As a unique environmental and geological formation developed over tens of thousands of years, travertine landscapes are fragile and non-renewable. Therefore, protecting travertine resources is an urgent matter, and it is important for all of us to work together to preserve them.In order to clarify the causes of travertine blackening, this study focuses on both blackened and unblackened travertine samples from Huanglong, Sichuan Province, China. Representative samples were collected through on-site surveys and analyzed with laboratory testing. A comparative analysis was then conducted between the two types of travertine samples. X-ray diffraction analysis revealed that both the blackened and unblackened travertine corresponded to the PDF#86-2334 standard card, indicating they are calcite-type travertine. X-ray fluorescence spectroscopy results showed that the main chemical composition of both blackened and unblackened travertine were CaO, suggesting no significant changes in the mineral phase composition and chemical components occurred during the blackening process. Further elemental analyses showed that the contents of Total Carbon (TC) and Total Organic Carbon (TOC) of the blackened travertine were significantly higher than those of the unblackened travertine, suggesting that organic matter may play an important role in the blackening process. Meanwhile, Scanning Electron Microscope (SEM) revealed that the biological traces on the surface of the blackened travertine were more pronounced compared to those on the unblackened travertine. Notably, the experiment also detected the presence of substances insoluble in hydrochloric acid on the surface of the blackened travertine. Thermogravimetric analysis of the substance showed that the main mass loss occurred between 200°C and 500°C, a range that closely corresponds to the thermal decomposition of organic matter. Therefore, it is inferred that the substance is an acid-insoluble organic matter. These results show that the mineral phase and chemical composition of the blackened travertine remain largely unchanged compared to those of the unblackened travertine, suggesting that the biological effect is the main cause of the travertine blackening.This study provides direct evidence of the biological factors contributing to travertine blackening, offering a new scientific perspective for a deeper understanding of the degradation mechanism of travertine landscapes. It also supplies essential data to support the conservation and management of the Huanglong World Heritage Site. These findings hold great theoretical and practical implications for the conservation and sustainable development of the World Natural Heritage site.

Experimental study on water-gas pressure balance technology for the prevention and control of karst collapses

MA Xiao, ZHOU Zhihua, ZHENG Zhiwen, LI Xiujuan, JIANG Xiaozhen, WEI Pingxin, LIAO Zhongzhen, PAN Zongyuan

2025, 44(5): 1109-1120. doi: 10.11932/karst20250513

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With the expansion and increasing scale of underground engineering projects in China, geological hazards in karst areas, particularly the frequent occurrence of karst collapses, have become a major concern. To effectively prevent and control karst collapses, scholars have conducted in-depth research on the treatment methods over many years, yielding significant results. However, research on the method of balancing the water-gas pressure within karst pipeline systems remains insufficient, lacking both theoretical support and practical application to actual karst areas.To further explore this theoretical model, this study focuses on water-gas pressure balance technology for the prevention and control of karst collapses. A generalized geological model was developed, and two different specifications of indoor physical test models were designed and established. High-precision, high-frequency fiber optic pressure sensors were utilized to monitor pressure variations inside simulated karst cavities under varying conditions of vent diameter, initial water level, and flow velocity. This study specifically examined pressure fluctuations within the simulated cavities during changes in water level and the pressure pulsations occurring during water level drawdown. The aim was to identify a vent diameter capable of eliminating these pressure pulsations and balancing the internal pressure of the cavity, thereby establishing a general method for determining the vent diameter. The results of experiments show that the vent diameter required to balance water-gas pressure within the cavity can be categorized into three levels: the primary balance vent diameter that can eliminate pressure pulsations caused by water level drop; the effective balance vent diameter that can significantly reduce negative pressure within the cavity; and the optimal balance vent diameter that can effectively balance the water-gas pressure within the cavity. By analyzing the relationship between the vent diameter at each level and the cavity section diameter, the correlation between these diameters was determined, and the ratio of the vent diameter at each level to the cavity section diameter was established. It was found that the ratio of the balance vent diameter to the diameter of cavity section for eliminating water and gas pressure pulsations should exceed 0.5%. If the water vapor pressure within the cavity is to significantly reduce, this ratio should exceed 1.25%. Besides, this ratio should exceed 4.16% to fully balance the water-gas pressure inside the cavity.Finally, the determination of the vent diameter for pressure regulation, layout methods, depth design, and drilling process requirements should be considered when the application of water-gas pressure balance technology in practical prevention and control of karst collapses are discussed. This aims to refine the water-gas pressure balance technology for karst collapses and provide a theoretical basis for prevention and control measures.

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2025, Volume 44, Issue 5

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Current Issue 2025, Volume 44, Issue 5

Archive

Submission Guide

Current Issue
2025, Volume 44, Issue 5