中国岩溶

2024, 43(2): 219-227. doi: 10.11932/karst2024y019

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410 ka weak monsoon event recorded by stalagmites in Jinfo Cave of Chongqing

XU Yibin, YANG Xunlin, YUAN Daoxian, HU Mingguang, GE Xiaoyan, GONG Meng

2024, 43(2): 228-238. doi: 10.11932/karst20240201

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The freshwater discharge from melting ice sheets in the deglaciation or glaciation is prone to anomalies in ocean−atmosphere transport between different latitudes, which can lead to a series of abrupt millennial-scale climate events, either obvious or not, such as the Younger Dryas (YD) events and YD-like events. Marine Isotope Stage 11c (MIS 11c) serves as one of the best references for the current Holocene, and the studies of possible YD-like events and their triggering mechanisms during Holocene are conducive to the understanding of the occurrence pattern of extreme climate events. In this paper, the results of the study on the J33 δ¹⁸O sequence records of stalagmites in Jinfo Cave, Chongqing, are shown: (1) Stalagmites in the Asian monsoon climate zone reveal a millennial-scale weak monsoon event that occurred around 410 ka BP prior to the Glacial Maximum of MIS 11 interglacial period. (2) Both the 410 ka weak monsoon event and the YD event occurred during the gradual strengthening of the monsoon and ascending branch of summer insolation in the Northern Hemisphere prior to the Glacial Maximum of interglacial period. This was also a time when Atlantic Meridional Overturning Circulation (AMOC) disturbance occurred. The duration, internal structure, and pattern of the events were similar, with differences in the change magnitude and ice volume conditions. (3) The weak monsoon event that occurred in 410 ka BP was primarily influenced by the combined effects of insolation and AMOC. This event was characterized by a sustained warming process that accelerated the melting of the Greenland ice sheet, leading to the destabilization of this ice sheet. The continuous flowing of freshwater into the North Atlantic resulted in a short-lived AMOC oscillation. The weakening of the AMOC resulted in a cold anomaly over the North Atlantic. As a result of atmospheric telecorrelation, the weaker AMOC led to a weaker Asian Summer Monsoon (ASM)

2024, 43(2): 239-252. doi: 10.11932/karst2023y030

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Indicative function of karst spring temperatures on rainfall-flow response

HE Qing, CHEN Xi, ZHANG Zhicai, CHENG Qinbo

2024, 43(2): 272-278, 335. doi: 10.11932/karst2024y003

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Karst in Southwest China is located in hot and humid climate region. Strong dissolution produces various combinations of soil, rock fractures and conduits. Therefore, the hydrogeological heterogeneity in this area contributes the difficulty to the identification of various precipitation recharge formations and multiple flow components. Tracers, such as stable isotopes, electrical conductivity, and chemical ions, have been widely used to aid our understanding of hydrological processes. Compared to these tracers, the temperature is a much cheaper alternative for high spatial-temporal resolution monitoring. In this study, the dynamics of hydrograph and temperatures in atmosphere, soils and spring water were used to trace hydrological processes of precipitation infiltration, recharge into conduits and flow exchange between conduits and fractures. Taking a hillslope spring of Chenqi basin in the karst area of Southwest China as the study area, we compared variations in atmospheric temperatures, soil temperatures, spring water temperatures before and after 21 rainfall events from the middle May to the middle September in the years of 2016 and 2017. In addition, on the basis of heat-water transfer mechanism of soil, surface karst zones, and karst conduits in spring areas, we identified the infiltration and recharge modes of different types of rainfall and the effects of fast and slow flows on the decline of spring discharge, in order to reveal the formation mechanism of runoff and infiltration recharge in karst areas. Results show that soil temperatures were much higher than spring discharge temperatures, and rainfall infiltration could sufficiently lowered soil temperatures and spring discharge temperatures in the study period. However, for the 21 rainfall events, the discharge temperatures varied in the rising phase of hydrograph because of different extents of heat mixture between the cool infiltration water and warm soils/rocks at ground surface. These differences were proven to be related with three types of precipitation infiltration and recharge, i.e. recharge by dispersed infiltration, recharge by concentrated infiltration of shallow runoff and direct recharge by concentrated rainfall. The study indicates that the recharge by dispersed infiltration occurred in the rainfall that was not heavy but lasted for a long time. In such type of rainfall, the spring discharge temperatures showed a slow rise with the increase of discharge. This phenomenon was attributed to the fact that the long-term thermal conduction in soils or small fractures heated infiltration water. However, as rainfall became more intensive but lasted for shorter time, the recharge by concentrated infiltration of shallow runoff and the direct recharge by concentrated rainfall dominated the rise of hydrograph. When the shallow runoff was developed, the spring discharge temperatures showed a decline after a rapid increase in the rising phase of hydrograph. This research finding indicates that both thermal conduction and convection affected discharge temperatures. The thermal conduction of infiltration in soils or small fractures played a role in heating infiltration water, and thus in raising discharge temperatures. In contrast, the thermal convection via large fractures and sinkholes made the cool water (e.g., the rainfall and runoff in the flow peak) into conduits, which lowered discharge temperatures. The direct recharge by concentrated rainfall only occurred in extremely heavy but short rainfall. For such type of rainfall, the spring discharge temperatures showed a short and rapid increase in the rising phase of hydrograph, which can be inferred that the thermal convection may control discharge temperatures. Furthermore, in the recession period of hydrograph, variations in the spring discharge and temperatures can be used to distinguish mixture of the cool water in small fractures (slow flow) with conduit flow (fast flow). In the early recession period, the hydrograph maintained a high discharge and receded at a slow rate but discharge temperatures declined at a great rate, which indicated that there was a large amount of cool water in small fractures releasing to conduits. In the late recession period, the spring discharge receded to a stable state and its temperature remained steady and lowest, which can be inferred that water release from small fractures to conduits significantly reduced. The study results demonstrate that the temperature information is useful in tracing the complicated hydrological processes while more observations particularly those in epikarst and conduits are needed to increase the tracing reliability.

Hydrochemical characteristics and formation mechanism of karst water in Baotu Spring watershed

WANG Nan, XU Qin, SUN Xiaoyan, WU Xiancang, LI Changsuo, GAO Shuai

2024, 43(2): 279-290. doi: 10.11932/karst20240203

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Karst groundwater is an important water source for human production and livelihood, but it faces the risk of pollution. The study of the hydrochemical formation mechanism of karst groundwater is an important research topic. However, due to the evident control of factors such as local hydrogeological conditions and the intensity and manner of human activities on karst groundwater, it is challenging for us to explore the hydrochemical formation mechanism of karst groundwater. The Baotu Spring watershed is a typical distribution area of karst in Northern China, which has faced water quality deterioration in recent years. However, there is a lack of comprehensive case studies that combine multiple mathematical and statistical methods with hydrochemical analysis in the study of spatial differences in the hydrochemical formation mechanism of groundwater in Baotu Spring watershed. This study collected three surface water samples, six pore water samples, 47 karst groundwater samples, and four fracture water samples from the Baotu Spring watershed. Hydrochemical and multivariate statistical methods, such as Piper diagram, ion ratio, correlation analysis, factor analysis, and cluster analysis, were used. Additionally, ArcGIS geostatistical functionality was applied to investigate the hydrochemical formation mechanism and spatial differences of karst groundwater in the Baotu Spring watershed. The results indicate that the contents of Total Dissolved Solid (TDSs) in surface water samples ranged from 268.65 to 317.86 mg·L⁻¹, with small spatial variations in different chemical parameters. The hydrochemical type was primarily HCO₃·SO₄-Ca, indicating good connectivity of surface water. The TDS contents in groundwater samples ranged from 191.65 to 948.69 mg·L⁻¹, with large variations in all chemical parameters except for K⁺, indicating significant influences from local hydrogeological conditions or human activities on karst groundwater. The hydrochemical types of karst groundwater were mainly HCO₃-Ca, HCO₃·SO₄-Ca and HCO₃-Ca·Mg, with an increasing proportion of ${\rm{SO}}_4^{2-}$. The dominant cations in karst groundwater were Ca²⁺ and Mg²⁺. For anion, in the indirect recharge zone and discharge zone, karst groundwater was mainly dominated by ${\rm{HCO}}_3^{-}$ and ${\rm{SO}}_4^{2-}$, while in the direct recharge zone, the proportions of ${\rm{SO}}_4^{2-}$ and Cl⁻ in karst groundwater significantly increased. Correlation analysis and ion ratio analysis reveal that the hydrochemical composition of karst groundwater in the study area is mainly influenced by the dissolution/precipitation of minerals such as carbonate, sulfate, and halite. With an increase in the flow path, the interaction between water and rock became more thorough, leading to an increase in ion content in groundwater. Pollution caused by human activities increased the concentration of ${\rm{NO}}_3^{-}$ in groundwater, and the nitration process reduced the release of carbonates resulting from carbonate mineral dissolution. Therefore, human activities can directly pollute groundwate and affect the natural water–rock interaction mechanisms in groundwater. Overall, the degree of pollution in groundwater in the study area is not significant, with the hydrochemical composition being mainly influenced by water–rock interactions. However, human activities have also led to the contamination of Cl⁻ and ${\rm{NO}}_3^{-}$ in groundwater, with the polluted groundwater primarily distributed in the central karst zone with strong leakage in the study area. The karst groundwater in the northwest area was polluted in a lower degree, mainly because the thickness of the Quaternary system may reduce the direct pollution of karst groundwater by human activities. This study explores the hydrochemical formation mechanisms of the Baotu Spring watershed and provides preliminary analysis of the spatial differences in the hydrochemical formation mechanism, which can support the protection of local groundwater environment.

Runoff simulation of modified SWAT model in karst watershed: A case study of Yangjichong sub-watershed

YANG Li, YANG Guangbin, LI Yiqiu, LI Man

2024, 43(2): 291-301. doi: 10.11932/karst2024y011

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In the karst area of Guizhou, many factors can limit the formation of surface runoff, such as developed karst structures, strong rainfall leakage, rapidly changing hydrological processes, low water storage capacities, and lost surface runoff through soil fissures, karst pipes and other pathways. Therefore, for the protection of the ecological environment and the control of soil erosion in this area, it is of great significance for us to investigate the variation of surface runoff in karst areas and the law of flow production. The model of Soil and Water Assessment Tool (SWAT) is a distributed hydrological model developed by the Agricultural Research Center, United States Department of Agriculture (USDA-ARS), and it is widely used in the simulation and prediction of watershed runoff, sediment, water quality and so on in different environments. However, due to the dissolution and erosion in karst areas, the development of water systems and hydrological dynamics show great differences from non-karst areas. In general, scholars' modification of the SWAT model mainly focuses on the modeling of karst features, but the SWAT model has seldom been used in the study of the effect of soil fissures on runoff under wet conditions. Guizhou is located in the subtropical monsoon climate zone, with concentrated precipitation, alternating wet and dry conditions. The soil in Guizhou is characterized by strong expansion and contraction. Consequently, the fissure flow is developed from soil fissures during rainfall. Even after rewetting, the soil fissures will not close, leading to significant water infiltration, which in turn will affect surface-produced flows. However, in the original SWAT model, volume of fissures (volcr) under wet conditions will close by default, and hence water cannot infiltrate. In order to make the conditions of SWAT model closer to the real situation in the karst watershed, the calculation of the fissure volume in the SWAT model was modified in this study to balance the wet and dry soil conditions to prevent fissure closure and to ensure that soil fissures can be formed in wet soils as well. The modification process is as follows: the crack flow module was firstly activated; then the maximum crack volume of the soil layer was calculated; finally, the crack volume on the simulation day was modified in crackvol.f. Taking Yangjichong sub-watershed in Longli county as the study area, this study modified the fissure flow module of the SWAT model and the representation of fissure infiltration, based on the measured data from 2013 to 2019. Subsequently, a comparative analysis of daily runoff simulation before and after the modification was carried out so as to make the results of surface runoff simulation closer to the actual situation of the humid karst region. The study results show as follows: (1) The Nash coefficient increased from 0.32 to 0.60 and the coefficient of determination from 0.37 to 0.58 in the period of determining rate. In the validation period, the Nash coefficient increased from 0.52 to 0.55 and the coefficient of determination from 0.56 to 0.60. These data indicate that the runoff time series of the modified model is more consistent with the measured data, which can show a better applicability of the modified model than the original one. (2) There are some differences in the parameter sensitivity of the model before and after the modification, and the parameters SOL_BD, SOL_CRK, and CANMX are important to affect the soil fissure volume. (3) The modified model improved the water infiltration capacity of the soil. The soil moisture content was positively correlated with infiltration, and the surface runoff was negatively correlated with infiltration. The average daily infiltration increased from 0.23 mm to 0.84 mm, an increase of 3.65 times; the average daily surface runoff decreased from 3.98 mm to 3.14 mm, with a significant increase in infiltration and a decrease in surface runoff. At the same time, the soil water content increased from 139.53 mm to 158.30 mm, an increase of 18.77 mm. (4) The modified model showed a significant increase in infiltration and obvious seasonal differences, which was basically similar to the variation of rainfall, that is, the larger the rainfall is, the more infiltration recharge becomes, and the more significant infiltration is. The results of the study provide reference for water resource management in the karst sub-watershed.

Research and application of groundwater level as a water replenishment control signal in the restoration of Lijiang Heilongtan spring group

HAN Xiao, WANG Senlin, HE Rui, ZHENG Kexun

2024, 43(2): 302-313. doi: 10.11932/karst2024y007

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The paper takes Heilongtan in Lijiang as an example to study the recharge control process of spring water restoration in the karst area. Despite much work on Heilongtan in the previous period, there still exist problems in terms of the spring water restoration of Heilongtan, such as difficulties of detecting recharge sources and of controlling the recharge time, and the high cost of constructing recharge channels. On the basis of the groundwater system theory, and the spatial geographic information and geologic information of Heilongtan spring system, this paper aims to study the restoration of Heilongtan spring group, which may provide a scientific basis for the restoration of karst springs and environmental protection.The Lijiang area, where the study area is located, belongs to the low-latitude plateau monsoon climate zone, with unique mountain monsoon climate characteristics, distinct dry and wet seasons, and significant vertical climate changes, but slight seasonal variations in temperature. Because the Lijiang area is surrounded by the Jinsha River in the west, north and east, deep-cut canyons and a peninsula-like mountainous area protruding northward have been developed. With an elevation of about 2,400 m, a width of 4-5 km from east to west and a length of 32 km from north to south, the Lijiang Basin—a long and narrow mountainous basin—is located in the southern part of the Lijiang Peninsula.The study area is located in the northeast side of the mountainous area of Lijiang Basin, and the Heilongtan spring group is located in the southwest corner of the study area at the foot of Xiangshan hill in the north of the Lijiang ancient city at the east of Lijiang Basin. The study area generally belongs to the alpine mountainous terrain in the dissolution fault block, and the karst in this area is developed. Based on three-dimensional data on basic geological conditions, karst hydrogeological conditions, and characteristics of water balance, seepage field, temperature field, chemical field, etc., connection tests have been conducted to verify that there are two karst groundwater flow systems in the north and south of the study area: Jiuzihai-Lijiangba karst groundwater flow system (Ⅰ) and Hongshuitang-Bailanghua karst groundwater flow system (II). There is no hydraulic connection between these two systems. The Jiuzhihai-Lijiangba karst water flow system (Ⅰ) can be laterally divided into the karst water flow subsystem of Heilongtan spring basin (Ⅰ-1), the karst water flow subsystem of Qingxi spring basin (Ⅰ-2) , and the decentralized groundwater flow system of eastern spring group (Ⅰ-3). These three karst water flow subsystems are self-contained in terms of recharge-runoff-discharge conditions, with weak hydraulic connection, and there is no hydraulic connection between the Jiuzihai recharge area and the Qingxi spring basin and the eastern spring group.Many discharge points in the Heilongtan spring group result to the difficulty in flow observation. At present, only monthly average flow values with low accuracy have been obtained but not in real time; consequently, it is difficult for us to realize the real-time and accurate control of the spring recharge process. Moreover, when the Heilongtan spring group dry up, it is even impossible for us to control the recharge process through the flow data. The observation values of water level per minute in a hydrological observation well near the Heilongtan spring group and the qualitative analysis of geological structure indicate that the hydrological observation well and the spring group are located in the same karst groundwater system. In addition, the high correlation coefficient of 0.8813 between the water level of the hydrological observation well and the flow of the Heilongtan spring group , indicating that it is possible to control the water level of the Heilongtan spring group through the regulation of water level of the hydrological observation well.The Heilongtan spring group consists of four main springs, namely, Lieshimu spring, Wufenglou spring, Zhenzhu spring and Wanshousi spring, and the elevation of each spring is slightly different. The landscape of Heilongtan Park can meet the requirement only if the flow of these four springs is maintained. According to the monitoring data of the Heilongtan spring group, when all of these four springs flow, the overall flow of the Heilongtan spring group is 1.00 m³·s⁻¹, which is also the target flow rate for spring restoration. Based on the actual flow and its change trend of springs, two conditions can be determined: water maintenance and recharge when water is in shortage. Under the condition of water maintenance, the signal of replenishing water should be firstly determined, during which predictors needs to be set given the time of water replenishment. Then, an inversion can be conducted to obtain the water level of hydrological observation well and the flow of the Heilongtan spring group, based on the time when groundwater flows from Jiuzihai to the Heilongtan spring group. When the water level of hydrological observation well drops to 2,409.41 m or the spring flow reduces to 1.27 m³·s⁻¹, the spring water in Jiuzhihai recharge area should be recharged, with water flow of 2.08-2.35 m³·s⁻¹, and the recharge can be lasted to the next flood season in which the rainfall and water discharge achieve an equilibrium again and Jiuzihai is restored. Under the state condition of replenishment when water is in shortage, the spring water in Jiuzhihai recharge area needs to be recharged with the maximum flow rate (greater than the minimum flow rate of recharge), so that the spring flow rate can reach 1.00 m³·s⁻¹ as soon as possible. Then, the spring water can be recharged with a flow rate of 2.08 m³·s⁻¹, so that the groundwater recharge and discharge keep balanced and the spring flow rate maintains 1.00 m³·s⁻¹. The replenishment can be lasted to the next flood season, in which the rainfall and discharge achieve an equilibrium again and the Jiuzhihai is restored for the next recharge.In summary, in order to determine the signal of control well given the time of water recharge and finally carry out the accurate and real-time water recharge based on the water level of observation well as the control signal, the following steps should be completed: formulating the target state of the spring group, corresponding to the water level of replenishment control well, considering the time predictor in the recharge process, and correcting the water level of control well.

Influence of hydrogeological conditions on the pollution of karst underground rivers

LIU Hao, TIAN Maozhong, CHEN Zaiqian

2024, 43(2): 314-325. doi: 10.11932/karst2023y040

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With an area of about 5×10⁵ km², the largest contiguous karst area in the world is distributed in Southwest China. Karst underground rivers are the most important karst landscapes in karst areas, and also important water sources for human production and life in karst areas of Southwest China. However, with the development of industry and agriculture, the intensification of human activities, and the openness and vulnerability of the karst aquifer system, karst groundwater is facing many threats such as water pollution, depletion of water resources and so on. The water body of a karst underground river in southwestern Guizhou Province was seriously polluted, which resulted in the pollution of the water body of Qingping river downstream. Muer cave, one section of the Qingping river, is a first-class protection area of drinking water source. There are about 30,000 people living in the surrounding towns, in which water for drinking and irrigation is taken from the Muerdong underground river; therefore, the pollution of this river will greatly influence the people's life. This paper studies the influence of hydrogeological conditions of pollution in the karst underground river by means of basic data collection, analysis of karst hydrogeological conditions, microbial indicators and water pollution indexes.The results show as follows: (1) Muer cave is located near the phase transition zone between karst and non-karst rocks, with highly permeable carbonate rocks in the west and weakly permeable clastic rocks in the east. Groundwater in this area is discharged to the surface in the form of karst underground river in Muer cave near the lowest discharge datum. (2) Because of the strong uplift of neotectonic movement and the rapid cut-off of rivers, the underground karst water system and karst cave system have been developed in this area, and there exist multiple complex hydrogeological units formed by surface flows and underground flows, which may create conditions for the pollution of underground river caused by surface pollutants penetrating into underground karst water system. (3) Six spring points and two karst caves are concentrated at the outlet of the Muerdong underground river, but their water quality is different, which indicates that they belong to different underground karst water systems. This also indicates that the range of recharge source of Muerdong underground river is wide, the regional karst groundwater system is very complex, and the ecological environment of the underground river is vulnerable. (4) The characteristics that pollutants are discharged in a concentrated way and in a large amount indicate that the discharge channel is relatively unblocked after the infiltration of pollutants into the underground. It is likely that pollutants are discharged through channels with large cross-sections such as karst pipelines developed in the soluble rock, instead of small channels like bedrock fractures in non-soluble rocks. Therefore, sources of pollution may be distributed in the area west of the Muludong river. Few households are scattered in the upper reaches of the Muerdong underground river, and the sewage such as residents' excreta is mainly stored in septic tanks and used for irrigation. Besides, given that no large industrial and mining enterprises or schools, etc. have been established, there exist no conditions that sewage such as human excrement is discharged in a concentrated way and in a large amount. Therefore, we can exclude the possible pollution caused by the discharge of human excrement and other sewage into the underground river. According to the field investigation, water quality monitoring and microbial index analysis, the pollutants may be the excrement of livestock. By tracer connectivity test and investigation of the surface, we can exclude the pollution sources from the areas of Dajiang (Ronglai) trough and Tanping trough. The Yangjiaba karst depression is characterized by high elevation and thick water-rich rock mass. Under the control of topographic height difference and fault structure, groundwater flows from west to east along the karst cave and karst pipeline system to the outlet of the Muerdong underground river. The geophysical prospecting results also show that there is a deep karst pipeline system in the lower part of Yangjiaba karst depression. At the same time, combined with microbial indicators of water samples from this depression and from Muerdong spring, the source of discharge of livestock was from a piggery in Yangjiaba karst depression. Several sinkholes located in this piggery become the channels of discharging sewage and pig excrement which are likely the source of pollutants in the Muerdong underground river.In this study, some suggestions have been put forward. In the economically underdeveloped karst areas, the protection and treatment of karst spring water is relatively difficult under the background of economic and social development. In accordance with the principles of controlling, recycling, and reducing pollutant discharge, strengthening the protection of water sources and improving the environment, the development of large-scale aquaculture and the construction of large and medium-sized towns in the recharge area of the Muludong underground river should be controlled, sewage of livestock and domestic sewage should be recycled to reduce the discharge of pollutants. At the same time, it is suggested to strengthen the local construction and protection of water sources and increase new stable and reliable drinking water sources.

Spatial-temporal pattern of land use evolution in mountain–basin systems based on three typical villages

HE Xianxian, YANG Zhimou, ZHAO Yuluan, ZHANG Meng

2024, 43(2): 326-335. doi: 10.11932/karst2024y006

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As a typical eco-vulnerable area of rocky desertification in karst mountains of Southwest China, Guizhou Province is characterized by a large number of mountains and hills, and a scarcity of basin land and high-quality cultivated land. Consequently, the contradiction between large human need and small farmland acreage is increasingly prominent. In this study, we selected three typical villages—Shuiyuan village, Manyu village and Haohuahong village in Haohuahong town, Huishui county, Guizhou Province as the study areas. Shuiyuan village is located in a remote mountainous area with a large number of barren sloping farmlands. This village is mainly developing the agricultural economy. Manyu village is a typical of low hills and gentle slopes, distributed with both sloping farmlands and basin land. This village is mainly developing the breeding industry. Haohuahong village is characterized by the flat terrain, with rich farmland resources and high degree of agricultural mechanization, and it is a typical model village of modern agricultural development in Huishui county. These three villages have jointly formed a mountain–basin system.On the basis of the regional characteristics of mountain–basin system, we explored the spatial-temporal differentiation characteristics of the coupling evolution of rural population, farmland and homestead in these three villages from 1990 to 2018.We acquired the data of depopulation, farmland and rural homestead in these three villages by participatory rural appraisal, analyzed the spatial-temporal evolution of population, farmland and homestead from the village gradient perspective, and further divided the functions of farmland and rural homestead. The results show as follows: (1) The degree of rural depopulation is different. Population outflows are severe in mountainous areas with marked depopulation. There are less population outflows in basin areas, with depopulation. Population outflows are very common with prominent depopulation in the intersected areas between mountains and basins. (2) Regional differences of farmland abandonment are obvious. Farmland abandonment is the most severe in mountain areas, followed by the areas intersected between mountains and basins, and farmland abandonment in basin areas was less severe. Abandonment or transformation of farmland has caused the changes of utilization types and functions of the farmland. (3) From the perspective of homestead use, the number of homesteads increased and the space of homestead expanded to outside but was deserted inside. Structures and functions of homestead changed noticeably. (4) Rural depopulation drove the change of land use, which was mainly driven by socio-economic change and regional population migration from rural to urban areas. Various factors affecting the changes of land use and the processes of these changes are interdependent and restrict each other, which has constituted a dynamic coupling phenomenon.To sum up, the spatial-temporal variation characteristics of land use evolution in mountain areas, intersected areas between mountains and basins and basin areas are different in different periods. The research results are helpful to guide the rural farmland utilization and protection, homestead activation and utilization in mountain–basin systems with different geographical conditions, socio-economic development levels, traffic conditions and geological backgrounds in Guizhou Province. It is of reference value for us to realize the sustainable development of society and economy in terms of mountain–basin system.

Evolution and attribution of net primary productivity of vegetation in the peak-cluster depression basin of Southwest Guangxi from 2000 to 2021

WANG Donghua, TIAN Yichao, ZHANG Qiang, ZHANG Yali, LIN Junliang, TAO Jin, HUANG Liangliang

2024, 43(2): 336-348. doi: 10.11932/karst20240204

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China has about 3.44×10⁶ km² of karst area, and the most typical karst landscape—one of the largest in the world—is distributed in Southwest China, covering an area of 4.26×10⁵ km². The karst area in Southwest China has a total population of more than 100 million in 48 ethnic minorities. Meanwhile, it is the major poverty-stricken area in China, with nearly half of the country's poor population. The peak-cluster depression basin in Guangxi is located in the southwest of Guangxi Zhuang Autonomous Region, including most parts of 3 prefecture-level cities—Baise, Wenshan and Chongzuo, as well as some areas of Nanning City and Fangchenggang City. The peak-cluster depression basin in southwest Guangxi is an old revolutionary base area and autonomous region for ethnic minorities along China's land boundary. It is not only an essential ecological barrier of the Pearl river basin, but also an important area for water conservation and biodiversity protection in China. However, this peak-cluster depression basin is subject to severe rock desertification and the scarcity of vegetation, because this basin is extensively developed with karst landscape, characterized by unique double-layer hydrogeological structures and shallow soil layer with severe soil erosion. This basin falls under the zone of southern subtropical climate, which is subdivided into the central subtropical climate zone (southern Guangxi climate zone), including Fangchenggang and Nanning, and the western subtropical climate zone (southwestern Guangxi climate zone), mainly including Baise, Pingxiang and Chongzuo. Due to the unique geography and fragile ecological environment of this basin, monitoring and analyzing the evolution and driving mechanism of the net primary productivity (NPP) of vegetation plays an important role in insight into the terrestrial carbon cycle mechanism and in sustainable development of the ecological environment.This study assessed the spatial and temporal evolution of NPP in the typical karst peak-cluster depression basin in southwestern Guangxi from 2000 to 2021, based on the MOD17A3 dataset NPP products, and investigated the spatial distribution, future trends, sustainability and driving mechanisms of NPP in this region with Theil-Sen Median trend analysis, Mann-Kendall test method, Hurst index and geodetector. The results show: (1) From 2000 to 2021, the average value of NPP in the study area was 945.23 gC∙m⁻²∙a⁻¹, with an increase rate of 3.5596 gC∙m⁻²∙a⁻¹. The increase rate can be ranked as: 4.5148 gC∙m⁻²∙a⁻¹ in the karst area >3.5596 gC∙m⁻²∙a⁻¹ in the study area >2.7219 gC∙m⁻²∙a⁻¹ in the non-karst area. (2) The areas with high NPP values (all greater than 1,200 gC∙m⁻²∙a⁻¹) were situated around Fangchenggang City; the areas with low values were scattered along the hydrological line. (3) The trend of Sen showed that the area with an increase of vegetation NPP (77.98%) was significantly larger than the area with a decrease of NPP (22.02%) during 22 years in the study area. Hurst index showed that the regional vegetation NPP values ranged from 0 to 1, averaging 0.65, with a negative skew distribution. (4) The quantitative attribution results of geodetector showed that land use/cover, vegetation coverage and elevation factors were the significant control factors of NPP in the study area, followed by slope and soil type.

Identification of key areas for the ecological restoration of karst mountainous territorial space based on the construction of ecological security pattern: A case study of Guanling, Guizhou Province

LU Hongxing, ZHAO Yuluan

2024, 43(2): 349-363. doi: 10.11932/karst2024y017

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As one of the most ecologically fragile regions in the world, the ecosystem in the karst area is characterized by low environmental bearing capacity, high vulnerability and acute conflicts between human and land use, and thus the karst area requires strict ecological protection and effective ecological restoration. Guanling Buyi Miao Autonomous County (hereinafter referred to as Guanling county) is located in Anshun City, Guizhou Province. The karst landform accounts for 83.83% of the total land area of this county. Guanling county is a desertification area of Yunnan, Guangxi and Guizhou, with the ecological protection red line area amounting to 25.10% of the land area of this county; therefore, Chinese government listed it as a key county receiving assistance for rural revitalization. The karst mountainous area of Guanling county is distributed with a wide area of severe rocky desertification, with prominent conflicts between human and land use, and at the same time a number of national ecological zones are located there. In recent years, ecological degradation problems have caused habitat fragmentation and poor capacity for ecosystem supply in this county. Therefore, the identification of key areas for ecological restoration of national territorial space is of great significance to the ecological security of the Beipan river basin and even the Pearl river basin.The objectives of this study are: (1) to determine the importance level of ecological source areas, and to identify these areas by combining multiple factors such as MSPA, ecological protection red line, landscape connectivity analysis, etc.; (2) to construct the ecological resistance surface by synthesizing the impacts of human beings and nature, and to construct the regional ecological security pattern by using the circuit theory to extract the ecological elements such as ecological corridors, ecological pinch points, ecological barriers, etc.; (3) to classify the ecological control area based on the regional ecological background, and to propose targeted ecological restoration measures for territorial space.The results of the study show that: (1) Thirty-seven ecological source areas (449.78 km²), affected by different degrees of rocky desertification, in Guanling county have been identified. These areas are contiguously concentrated in the east and west, and scattered in the central part of the county. (2) Seventy-four ecological corridors (140.775 km) have been extracted, with important ecological corridors concentrated in the areas in a lower degree of rock desertification. At the same time, 36 ecological pinch-points and 14 ecological barriers have been identified as key areas for ecological restoration of territorial space, and the ecological restoration effectiveness have been improved by the construction of an ecological restoration pattern of "three zones, two axes and multiple points". (3) The ecological restoration area of the identified ecological pinch-points covers 757.84 hm², which is mainly distributed in the low-resistance area in the central part of the study area. The ecological restoration area of the identified ecological barriers covers 364.48 hm², which is mainly concentrated in the central part of the study area with intensive human activities, and its distribution is subjected to the double interference of human activities and extensive and severe rocky desertification. (4) Ecological restoration measures need to be promoted scientifically in combination with the actual effectiveness of rock desertification management and the restoration cost. Besides, the planning conducive to ecological restoration and environmental protection of karst areas in Guanling county should be proposed according to the variability of stress factors.

Composition and diversity of microbial communities in high-altitude karst soil

XIAREKEYAMU·Yitiniyazi, DONG Faqin, LI Qiongfang, AN Dejun, DAI Qunwei, ZHANG Qiang, RAO Hanyun, REN Yazhen, LIU Fengqi, LIU Mingxue

2024, 43(2): 364-378. doi: 10.11932/karst2024y015

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As a World Natural Heritage Site, Huanglong Scenic Area, is located in the eastern part of the Qinghai–Tibet Plateau in Songpan county, Aba Tibetan and Qiang Autonomous Prefecture, Sichuan Province. Huanglong valley is 3.50 km long, with an altitude of 3,145–3,578 m. In the Huanglong Scenic Area, there is a six-month freezing period, with a minimum temperature of 3 ℃. The main vegetation types are coniferous and broad-leaved mixed forests and coniferous forests, belonging to a typical plateau temperate to subfrigid monsoon climate. This scenic area is renowned at home and abroad for its rare and colorful karst landscape. At present, there is still a research gap in the structure and function of soil microorganisms of high-altitude karst habitats. Therefore, in order to explore the characteristics of soil microbial communities in Huanglong Scenic Area—a high-altitude karst area, we compared the differences in soil microbial community structure and diversity between high-altitude karst and non-high-altitude karst areas, with typical primary karst in Guilin—a non-high-altitude karst area. By analyzing the structural characteristics of soil microbial communities and their correlation with environmental impact factors, we laid a theoretical foundation for the relationship between soil microbial communities and ecological environment in high-altitude karst areas. In this study, we collected and analyzed soil samples from Huanglong valley, the main scenic area of the Huanglong Scenic Area. A total of 27 (three replicates) samples were collected and compared with the samples from the typical primary karst area in Guilin. We collected data on environmental factor, such as Total Organic Carbon (TOC), Soil Organic Matter (SOM), Total Nitrogen (TN), Total Product (TP), Temperature (T), Soil Water Content (SWC), and pH. Meanwhile, we employed high-throughput sequencing techniques such as ¹⁶SrRNA and ITS gene sequencing to perform bioinformatics analysis on sequencing data, including species diversity and β diversity. Then, we identified the main driving factors affecting soil in the Huanglong Scenic Area through principal component analysis (PCA), and explored the relationship between environmental factors and soil microbial communities by Spearman correlation analysis and redundancy analysis (RDA).The results show that the soil pH at each sampling point in Huanglong valley indicates a neutral to alkaline property, with no significant difference. But there are significant temperature differences at various sampling points. Compared to the soil from slopes of the Yaji test site in the non-high-altitude karst area of Guilin, the SOC, SOM, and TN contents in soil at various points in the Huanglong Scenic Area are relatively higher. There are differences in the bacterial chao1 index and observed OTUs index between Guilin's primary karst area and Huanglong valley. Similarly, the ACE index of bacteria and fungi also shows differences. These results may be attributed to the influence of vegetation types, soil types, and topographical factors on the distribution of soil microorganisms. The diversity indices of Shannon and Chao1 at HJ.4 sampling point in Huanglong valley are higher than those of other sampling points, indicating the richest biodiversity in this sampling point. At a phylum level, the bacterial community is mainly composed of Proteobacteria and Acidobacteria. Ascomycota and Basidiomycota are the dominant microbial groups in the high-altitude karst habitat of the Huanglong area. At a subordinate level, the main dominant bacteria in Huanglong valley are Pseudomonas, RB41, and Candidatus_Udaeobacter, with an average abundance of 14.57%, 3.11%, and 2.29%, respectively. The most dominant group in the primary karst area of Guilin is Candidatus_Udaeobacter, with an abundance of 6%. At a genus level, the dominant fungi in Huanglong valley are Humicola (22%) and Mortierella (22%). The dominant groups of the primary karst area in Guilin are Staphylococcum (5%), Absidia (5%), and Fusarium (4%). The differences in fungi at the phylum and genus levels are greater than those in bacteria. In summary, the proportion of dominant microorganisms in the primary karst area is relatively low, and the community types differ significantly compared to those in Huanglong valley. Samples collected from nine sampling points (three replicates) in Huanglong valley and in the primary karst area of Guilin show varying degrees of dispersion. UPGMA clustering analysis shows a high degree of similarity in various eukaryotic communities in Huanglong valley, while there are certain differences in the composition of prokaryotes among them. Redundancy analysis indicates that in bacteria, TP is the most correlated factor with community distribution, while T is the second most important environmental factor. In fungi, TP is also the most correlated factor, while T and pH are the second most important environmental factors. Both soil TP and T have a significant impact on the distribution of fungal and bacterial communities.

Correlation mechanism between rocky desertification degrees and slope position factors in karst mountainous area of southeast Yunnan

CHEN Yanjun, ZHAO Xiaoqing, PU Junwei, SHI Xiaoqian, FENG Yan, ZHOU Shijie

2024, 43(2): 379-391. doi: 10.11932/karst20240205

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As a kind of land degradation phenomenon, rocky desertification is one of the main ecological problems in karst areas in Southwest China. The key to the effective control of rocky desertification is to explore the distribution law and influence mechanism of rocky desertification. Taking three typical experimental areas in the karst mountainous area of southeast Yunnan as the research subjects, we extracted rocky desertification degrees and slope position factors as variables, and analyzed the correlation mechanism between these two variables. We also explored the roles of terrain factors such as slope gradients, slope aspects, terrain cutting depths, etc. in the correlation mechanism in order to further clarify the distribution law of different degrees of rocky desertification at different slope positions under the natural conditions as well as under the human interference. This study provides support for the case study on distribution and influence mechanism of rocky desertification in karst mountainous areas, and provides scientific basis for monitoring and restoring the regional ecological environment.The results show as follows: (1) The area of rocky desertification decreased gradually from ridge to valley, mainly distributed in the areas in high slope positions. Accordingly, the area of non-rocky desertification increased gradually. Slight rocky desertification mostly occurs along the ridge and on the uphill slope, while moderate rocky desertification mostly occurs at the ridge, and on the uphill and downhill slopes. The heavy rocky desertification is distributed in a uniform way in each slope position. (2) Slope positions are significantly correlated with degrees of rocky desertification, and directly affect the distribution law of rocky desertification. At the same time, the effect of slope positions on rocky desertification is indirectly enhanced by slope gradients and terrain cutting depths. (3) The correlation mechanism between slope positions and degrees of rocky desertification is demonstrated below. If the area is dominated by natural evolution, slope positions are negatively correlated with degrees of rocky desertification. The higher the slope position is, the greater the slope gradient and the deeper the terrain cutting will be. In this case, the increasing frequency of material migration in the area of high slope position will intensify the degree of rocky desertification. Conversely, the lower the slope position is, the smaller the slope gradient and the terrain cutting will be. In this case, human activities will become more convenient and frequent, which may consume the accumulated materials from the high slope position to the low and intensify the rocky desertification.The implications of research findings indicate that the geomorphic structure of the karst area is relatively complex according to the field investigation, and relevant research should be carried out based on the geographical environment of the study area. Most studies on rocky desertification have been conducted at a large or medium scale such as at a scale of the river basin or of the administrative unit, and the driving factors of different research scales have different influences on the degrees of rocky desertification. In addition, degrees of rocky desertification in different slope positions are significantly different. In the natural distribution, materials are lost along the ridge and accumulate in the valley. In rocky desertification areas, soil and other materials are lost along the ridge, and some remain in the valley. Furthermore, rocky desertification degrees are significantly correlated with slope positions, and the internal correlation mechanisms between rocky desertification degrees and slope positions are different under different intensities of human activity. Human interference is also an important factor affecting the correlation between slope positions and rocky desertification degrees. The research results can provide reference for in-depth analysis of the comprehensive influencing mechanism of rocky desertification degrees in karst mountainous areas, and provide basis for rocky desertification control and ecological restoration in mountainous areas.

Overview on karst geology of Vietnam

WEI Yanlan, LI Wenli, HUANG Chenhui, ZHOU Lixin, YANG Xiangpeng

2024, 43(2): 392-405. doi: 10.11932/karst20240206

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Karst is widely distributed in Vietnam, covering almost 60,000 km², approximately 20% of the total area of Vietnam. Most karst rocks crop out in North and Central Vietnam. Karst developed with peak-clusters, peak-forests, caves, etc. is sparsely distributed in the south of Vietnam. Based on previous research, the geological map of karst distribution in Vietnam was drawn up, combined with remote sensing image, geological map, and cave atlas. In terms of geological structure, lithology combination, hydroclimate in Vietnam, conditions of karstification in this country were analyzed. From the perspective of regional geology, the characteristics of karst geology and geomorphology, karst distribution and the present situation of karst resources in Vietnam were investigated. Karst in Vietnam is distributed in the tropical karst belt, with similar origins of karst in South China. The distribution law of karst in Vietnam is mainly controlled by stratigraphic lithology and tectonic movement. Karst is developed in all the pre-Cambrian and Holocene strata and the pure limestone strata of Carboniferous, Permian and Triassic with a thickness of 1,000–2,000 m are the main beds of karst development. The warm and rainy climate and rich biological diversity accelerate karstification. There are four major karst zones in Vietnam, including peak-clusters and peak-forests in the northeast, peak-forests in Ha Long Bay and karst mountain along Truong Son Ra karst in the northwest. The karst area in northeast is an extension of the karst from South China, with the development of alpine karst landforms, peak-forests, peak-clusters, large drainage gullies and sinkholes. Sinkholes are extremely developed, with an average 1.4 sinkholes per square kilometer. The karst landforms vary from plateaus to depressions and hills and finally to plains from northwest to southeast, showing a complete evolution of tropical karst geomorphology. There are karst landforms such as large and deep poljes, deep gullies and caves. The vertical distance of Conh Nuoc cave, the deepest cave, is 600 m. The peak-forest along Ha Long Bay is an extension of the peak-forest of South China. In the central part, karst is distributed along the Truong Son Ra. Phong Nha Cave currently known as the longest cave in Vietnam is located in the famous karst area of Phong Nha-Ke Bang. The Phong Nha cave system is composed of 20 caves, more than 60 km in length, where is located the longest river cave and the cave with the largest passage in the world. Vietnam is rich in karst water, karst mineral and karst landscape resources. At present, karst water has become the main water source for industry, agriculture and life in Vietnam, but water supply is in serious shortage, especially in the dry season. Vietnam is at an advanced level in the exploitation of karst mineral resources and is currently the eighth largest cement producer in the world. Remarkable achievements have been made in balancing regional economic development and ecological protection, and a series of world geological heritage reserves and national ecological reserves have been established in karst areas.

Development mechanism of covered karst collapses induced by groundwater drawdown

LI Jingtian, ZHU Kai, XIAO Xianxuan, YIN Yan, LIU Hao, XU Mo, HE Zhipan

2024, 43(2): 406-420. doi: 10.11932/karst2024y010

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With continuous development of society and economy, acceleration of urbanization, increase of water consumption in industry and agriculture and improvement of people's life, the interference and destruction of environment caused by human activities and engineering construction are increasingly serious, and the number of karst collapses is rising day by day. As a major type of geological disaster in karst areas, karst collapses threaten local people's life and property because of their suddenness and covertness. Therefore, it is of great significance to study the induced factors and development mechanism of karst collapses. Since the construction of the diversion tunnel of Chemabi reservoir in 2017, a large number of ground collapses have occurred in Malong district of Qujing City. The field geological investigation found that there is a Quaternary overburden layer with sandy clay–clay–sand structure in the study area in which occur strong karst development and frequent groundwater activities. Karst collapses in the study area are mainly distributed near rivers. In this study, we took karst collapses in the east of Malong district, Qujing City as the research objects. On the basis of fully understanding the geological conditions, hydrodynamic conditions and geological prototypes of collapses in the study area, we took the collapses of multi-structure overburden as examples, among which we selected a typical karst collapse as the prototype. Then we scaled down the geological prototype in equal proportion under the principle of similarity. Meanwhile, we prepared the materials similar to the physical parameters of the soil samples from overburden layers of the geological prototype, and constructed a geophysical model consistent with the prototype in the laboratory. Subsequently, according to the water discharge of the construction near the subsidence area and the data of observation well, we estimated the rate of groundwater drawdown, and monitored the pore water pressure in the overburden layer, the vacuum pressure in the karst cave and the cumulative displacement of the overburden soil. Finally, we carried out the experiments of karst collapses triggered by the groundwater drawdown under two typical working conditions. According to the experiment data, we put forward the collapse mechanism of the overburden layer, and the evolution characteristics of karst collapses with permeable layer–aquiclude–permeable layer. The results show as follows: (1) Negative pressure zones in covered layers and karst caves may occur because of groundwater drawdown. Due to the air recharge caused by relatively closed aquitards and the water-holding effect of the soil in overburden layers, the pore water pressure in overburden layers and vacuum pressure in karst caves will increase to the maximum with the fluctuation of groundwater discharge. The faster the rate of groundwater drawdown becomes, the greater the growth rate and peak of pressure will be. (2) According to the evolution characteristics of pressure and the deformation quantity of overburden layer, the collapse evolution can be divided into 3 stages: the stage of development of soil caves with rapid pressure increase but small displacement of overburden surface, the stage of soil cave expansion with the reducing growth rate of pressure but a rapid increase of displacement of overburden surface and the stage of instability and collapse of overburden layers when both pressure and displacement of the overburden surface reach the maximum. At the first stage, upper aquitards and middle strong permeable layers, i.e. the soil above the water level, are subjected to the erosion of pore water and the vacuum suction effect of pore water pressure generated in the negative pressure zone within the overburden layer. At the second and third stages, the vacuum pressure in the karst cave plays a leading role in the vacuum suction erosion of the entire overburden soil. (3) The rapid decrease of groundwater level is the main factor leading to the collapses in the study area. When the rate of groundwater drawdown is relatively small, the overburden soil may undergo minor deformation but will not collapse. However, when the rate of groundwater drawdown in Malong district reaches 0.1 cm·min⁻¹ (1.44 m·d⁻¹), the vacuum pressure can provide the force of vacuum suction erosion. Together with osmotic pressure, this force is large enough to generate collapses. The research can provide reference for the prevention and early warning of collapse disaster in Malong district.

Zoning of early warning for karst collapses in the Jingquan area of Shandong Province

FENG Yawei, MAO Ningli, LI Weili

2024, 43(2): 421-431. doi: 10.11932/karst20240207

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As one of the most common geological disasters in the Jingquan area, covered karst collapses mostly occurred in the dry seasons from 2015 to 2017. With the frequent occurrence of karst collapses, the sustainable development of economy and the safety of people's lives and property are threatened. Therefore, it is urgent for us to find out the current situation of karst collapses, analyze their influencing factors and distribution rules, and carry out the research on the zoning of early warning for karst collapses under different environmental conditions, in order to provide a decision-making basis for carrying out targeted prevention and control. In view of the frequent occurrence of covered karst collapses in the Jingquan area, based on the exploration data of karst collapses in this area, this study analyzes and studies the background conditions and influencing factors of collapse formation with methods such as mathematical statistics, numerical simulation and comprehensive evaluation model. Through numerical simulation and fuzzy mathematical methods, the zoning of early warning for karst collapses under different environmental conditions (rainfall frequency of 20%, 50%, 80% and 95%, and the increase of mining volume of 30%, 50% and 70%) is studied, and targeted prevention and control measures are put forward. The research conclusions mainly include the following four aspects: (1) The aquifer system in the Jingquan area can be generalized into three aquifer groups as a whole. The first layer—the shallow aquifer group—includes pore water in the Quaternary coverage area and shallow water in the exposed bedrock area. The second layer—the weakly permeable aquifer group—includes the Quaternary clay layer and the fractured deep aquifers of Cambrian and Ordovician in a certain depth range. The third layer—the deep aquifer group—includes Ordovician aquifers of carbonate fissure karst water and Cambrian aquifers of carbonate karst water. (2) In this study, the lower boundary of the water flow system has been set at the buried depth of 200 m in the Jingquan area. The atmospheric precipitation infiltration and the lateral runoff supply of groundwater are the main supply sources of groundwater in the study area. The main discharge of groundwater in the area is the exploitation of groundwater. The exploitation amount of the water source has been obtained through monitoring data, and the scattered exploitation amount has been obtained through investigation and statistics. (3) Given that other environmental conditions remain unchanged, the area of the red-early-warning area gradually increases with the continuous reduction of precipitation, and the degree of early warning gradually decreases from southwest to northeast. The denser the pumping wells are, the likelier karst collapses occur. The increase of karst water exploitation and the change of rainfall are the main causes of karst collapses. (4) In order to prevent karst collapses in this area, we should strengthen the management of water resources and make rational use of groundwater resources. We should also strengthen the monitoring of karst collapses in the red-warning area, and adopt a variety of engineering measures to change the geological background conditions of karst collapses to the greatest extent.

Application of comprehensive geophysical prospecting method to water detection in the clastic rock area of Dalubian village, Xuanwei, Yunnan Province

ZHENG Zhijie, ZENG Jie, GAN Fuping, CHEN Jili, LU Xiuhua

2024, 43(2): 432-440. doi: 10.11932/karst2024y008

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The development of fractured and fissured zones characterized by strong water abundance is limited in the clastic rock aquifer with generally poor water-rich properties. Additionally, the small contrast in electrical properties between the water storage structures and the clastic rock makes water detection difficult. In order to explore the effectiveness of geophysical methods in water detection in clastic rock areas, the high-density resistivity method, combined with profile method and audio frequency magnetotelluric method (EH4) are used to study the water detection in clastic rock strata in Dalubian village, Xuanwei, Yunnan Province. The study findings may provide a theoretical basis for the selection of geophysical methods under the same site condition and the same geological background so as to avoid blind method selection and to save time and cost.The study area is located in Xuanwei county, Yunnan Province, belonging to the Beipan river basin. The terrain is low in the north and high in the south, with large undulations and a height difference of 150–250 m. The terrain falls into the type of the eroded middle-mountain trough valley. The exposed strata in the study area are purplish red or greyish-green sandy mudstone, mudstone, sandstone interbedded with limestone, mudstone, etc. of the lower Triassic Feixianguan Formation(T₁f). The study area is located in the northwest wing of Tianba syncline, about 1 km away from the core. The core is composed of the Feixianguan Formation (T₁f) of the lower Triassic, and the two wings are composed of the Carboniferous (C) to Permian (P) strata. The main aquifer in the study area is composed of purplish red or greyish green sandy mudstone, mudstone, and sandstone layers of the Feixianguan Formation (T₁f) in the lower Triassic, with fractures as the main aquifer medium. The fractured aquifer is mainly composed of insoluble hard and brittle rock layers in clastic rocks, igneous rocks, and metamorphic rocks. Interbedded fractured aquifers, fractured aquifers, and weathered fractured aquifers are commonly present. Atmospheric precipitation infiltrates along cracks and joints to recharge groundwater, with runoff direction from south to north, and is ultimately enriched in valleys. The study area is located near the core of the Tianba syncline, with well-developed joints and fractures, and a large storage space for groundwater.The results show that the clastic rocks of Feixianguan Formation (T₁f) in the upper Triassic system are at medium-level water abundance, with uniform water content. Constrained by the narrow ground, the lengths of survey lines in high-density electrical method and the combined profiling method are limited, and hence the small detecting depths. Affected by the small resistivity of clastic rocks, the effect of using high-density electrical method and combined profile method in water detection is not good, because it is difficult to identify effective anomalies such as bedrock fractures within the detectable depth range by these methods. Therefore, it is necessary for us to combine other geophysical methods to effectively distinguish the anomalies. The audio frequency magnetotelluric method with high lateral resolution can effectively identify the development sections of structural fault fracture zones and fracture zones in clastic rocks. The anomaly is characterized by relatively low resistance. The apparent resistivity sounding curve, with a high vertical resolution and good indication significance for fracture, can effectively distinguish the structure of rock and soil layers at different depths. To carry out water detection in the clastic rock area with relatively narrow ground site, the audio frequency magnetotelluric method combined with apparent resistivity sounding curve can achieve good results. The audio frequency magnetotelluric method can determine the location of fracture development zone in clastic rock areas, and apparent resistivity sounding curve can determine the depth of fracture development zone.

Application of high-density resistivity method and audio-frequency magnetotelluric method in the detection of landslide structure in Houchang town

LIU Yongliang, ZHANG Wei, LIU Zhenyu, YI Lianxing, WU Qiuju, LIANG Nan, GAN Fuping, WU Jianqiang, HAN Kai

2024, 43(2): 441-453. doi: 10.11932/karst20240208

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The frequent occurrence of landslides in China has done great harm to people's lives and property. In the stability analysis of landslides and the design of treatment scheme, the application of geophysical technologies has become a frontier research field in engineering and environment in terms of interdisciplinary development and application. The Houchang landslide in Weining county, Bijie City, Guizhou Province is a typical karst landslide. The landslide area is dominated by karst peak-cluster depressions or gullies, in which limestone strata are widely distributed, and karst is strongly developed. Since the collapse and landslide in 2006, the scale of tensile cracks in rock mass has gradually increased. In order to explore the causes of collapse, scholars have deduced the collapse process, established the conceptual model of landslide and studied the karst hydrogeological conditions. However, due to the lack of detection data, the structural characteristics of landslides have not been fully understood. In this study, the high-density resistivity method and audio-frequency magnetotelluric method were used to detect the landslide area, and the structural characteristics of landslides were revealed from the development of shallow karst and cracks, and the bottom interface of karst landslide. The stratigraphic structure of landslide area was divided by audio-frequency magnetotelluric method, and the lithologic interface between Qixia–Maokou Formation and Liangshan Formation was defined according to the electrical characteristics of different lithologic strata. Furthermore, the clastic rocks of Liangshan Formation in some areas were divided into shale, carbonaceous shale and coal seam. It is found that there are two layers of karst development: one is the karst fracture zone in the shallow part of the karst mountain, which is filled with mud and other low-resistivity substances, and the development depth of the karst layer gradually increases from northeast to southwest; the other is the deep karst fracture zone at the bottom interface of limestone in Qixia–Maokou Formation, which is mainly developed in the southern part of the landslide mountain, showing low-resistance characteristics. These two layers of karst structures provide a weak layer for landslide regeneration. Cracks and karst development areas have been detected by high-density resistivity method. There are three mountain cracks in the landslide mountain, including one with a large front edge and two secondary cracks at the rear edge. The cracks show the characteristics of "local high-resistance zone in the low-resistance layer on the surface and vertical low-resistance zone in the underground high-resistance rock mass". In addition, some shallow vertical karst fracture zones were detected, which destroyed the integrity of karst mountain. With the development of karst, karst mountain deteriorated into scattered fragments, which may gradually collapse or landslide under some extreme conditions. It is considered that the development of karst, especially the deep karst at the interface between limestone and shale, is one of the key factors leading to landslides. Together with the goaf formed by coal seam mining, karst development is the background condition that may trigger landslides, which in turn can deteriorate karst mountains into scattered blocks and gradually into collapses and landslides. The combination of audio-frequency magnetotelluric method and high-density electrical method can effectively detect the structural characteristics of karst landslides, and can comprehensively obtain the characteristics of karst spatial development, crack location and distribution of landslide bottom interface, which can provide an important basis for in-depth and comprehensive analysis of landslide stability.

Field experiment on the attenuation rule of main frequency for mining blasting vibration in the karst area

TANG Lingming, HUANG Xiang, LI Hongming, LI Jiaming, CAO Xianfa, CHEN Xuejun, LU Lixia

2024, 43(2): 454-462. doi: 10.11932/karst2024y014

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The study area is located within the Gudan lead-zinc mining region of Rong'an county, Guangxi. This area falls under the subtropical monsoon climate zone, experiencing four distinct seasons with abundant rainfall. It is characterized by a karst landscape of peak-cluster valleys, with undulating topography and a relative elevation difference of about 300 m. The study area is located in the gently flexural fold structure of rock strata from Siding to Tunqiu in a nearly north-south direction. The secondary small-scale fold structures are developed in a normal way, but fault structures are well developed, consisting of two main groups in north–south and north–east directions. The overlying soil layer mainly consists of clay soil, while the underlying bedrock is made up of sandstone, quartz sandstone, dolomite and gray rock. Karst is well developed primarily in exposed form, followed by buried type. The distribution trend of karst is in accordance with the fault structure of the area. Karst development is subject to lithology, and slows down with the increase of depth. Many surface collapses have occurred on a large scale in the study area. Karst fissure water is the primary groundwater, mainly existing in the limestone of Donggangling Formation (D₂d) of the Middle Devonian. Groundwater is recharged by atmospheric precipitation and replenished vertically through surface weathering fissures, karst caves, funnels and sinkholes. The karst fissures well developed at the shallow part serve as conduits for groundwater recharge and karst formation. This paper presents an analysis of the relationship between the main frequency for mining blasting vibration and various influencing factors in the karst area. The attenuation patterns of the main frequency of blasting vibration in collapse areas, backfilled areas, and non-collapse areas have been investigated, with the aim of providing suggestions for the prevention and control of surface subsidence in the karst mining area. The field data on blasting vibration were collected with the use of the engineering exploration detector of SWS-type multi-wavelength digital image and the ABEM Terrafo Mark6 seismometer. To determine the main frequency of blasting vibration at different measurement points under different conditions, the collected data were analyzed by WinWave software from Guilin University of Technology, supplemented by Matlab software. This facilitated the establishment of the relationship between the main frequency for mining blasting vibration and the influencing factors of mining in the karst area.The results indicate that the properties of the rock and soil have a significant effect on the main frequency of blasting vibration, which can be manifested that the looser the structure is, the larger the porosity becomes, and the smaller the compactness is, and thus the faster the attenuation of the main frequency and vibration energy of blasting vibration will be. In addition, the main vibration frequency f tends to decrease with the increase of epicentral distance R in the outer subsidence area and the subsidence backfill area. However, the main vibration frequency shows a fluctuation and a slight upward trend within the subsidence area. Furthermore, the frequency formula of blasting vibration was verified that this formula is of high reference value for testing mining blasting vibration in karst collapse areas. In collapse and non-collapse areas, the main frequency of blasting vibration decreased with the increase of epicenter distance and dosage of explosive. Under the same vibration load, the attenuation rate of the main frequency of blasting vibration in the collapse is significantly higher that than that in the non-collapse area. The impact of explosive dosage on the attenuation rate of the main frequency of blasting vibration is greater in the collapse area compared to the non-collapse area.

Impact of virtual tourism experience on travel intentions of karst tourism destinations: Take Wulong karst tourist zone as an example

LI Yuping, LIU Ya'nan, YANG Xiaoxia

2024, 43(2): 463-475. doi: 10.11932/karst2024y016

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The study on the impact of virtual tourism experience on travel intentions of karst tourist destinations is of great significance to enhance tourists' intentions of on-the-spot travel and to promote the development of karst tourist destinations. The virtual tourism market is increasingly expanded because the application of virtual reality technology to tourism industry makes people's travel experience abundant and interesting. At present, some scholars have conducted research on the application of virtual tourism in the fields of hotel management, cultural heritage protection, museum protection, etc. However, there are few studies on the application of virtual tourism in natural landscapes, let alone on the combination of karst tourist destinations with virtual tourism. Taking karst tourist destinations as research objects, this paper explores the marketing effect of virtual reality technology on karst tourist destinations, which can supplement the content of quantitative research on virtual tourism in karst tourist destinations and enrich the theoretical exploration of factors influencing tourists' behavioral intentions. In order to deeply explore the flow state of tourists after their virtual tourism experience in karst tourist destinations and its impact on travel intentions on the spot, and the marketing effect of virtual tourism on karst tourism destinations, this paper takes the model path of "environment–cognition–behavior" in Social Cognitive Theory as the theoretical basis and introduces Flow Theory. Structural Equation Model (SEM) is used to verify the hypotheses and give some suggestions.Wulong karst tourist zone of Chongqing is chosen as the research object because of its high typicality and representativeness, and it is an important part of the World Natural Heritage of "South China Karst", a typical representative of the world canyon karst system. Besides, Wulong karst tourist zone is one of the best examples of karst landforms with high tourism resource value. At the same time, the official page "3D·VR panoramic exhibition of Wulong karst tourist zone" shows it from all directions and different angles. Directly using their mobile phones and computers, people can visit Wulong karst tourist zone, which makes traveling more convenient. According to the previous research, this paper summarizes the theoretical framework of virtual tourism experience, flow experience and on-the-spot travel intentions, and puts forward the relevant hypotheses of virtual tourism in karst tourist destinations. Virtual tourism experience includes four dimensions: system quality, webpage design, information quality and interaction. Flow experience includes three dimensions: focused attention, telepresence and temporal distortion. A questionnaire has been designed, including eight dimensions and 29 items. The second part of the questionnaire investigates the background information of the subjects for their demographic characteristics. In order to reduce homology bias during the questionnaire design process, explanations and relevant definitions are provided at the beginning of the questionnaire.In this study, descriptive statistical analysis, reliability and validity testing, structural equation model fitting and intermediary effect analysis have been carried out to verify the proposed research hypotheses, and the research conclusions have been drawn according to the empirical research results and the validity of the hypotheses. The results show that the virtual tourism experience of karst tourist destination, which consists of system quality, webpage design, information quality and interaction, has significant positive effects on the three dimensions of flow experience (focused attention, telepresence and variation of temporal sense) and on on-the-spot travel intention. Among the three dimensions of flow experience, only focused attention has a significant positive impact on on-the-spot travel intention, playing a partial intermediary role in the transition from virtual tourism experience to on-the-spot travel intention, while telepresence and variation of temporal sense have no significant impact on the on-the-spot travel intention. In the future, we can develop Wulong karst tourism zone from the following aspects: optimizing the virtual technology and creating a more realistic virtual tourism experience, providing comprehensive and high-quality tourism information to reduce the cost of tourist information collection, and strengthening the publicity of virtual tourism to win more potential tourists. Future research topics should also be focused on questionnaire design of virtual tourism, influence of demographic characteristics on variables in the model, and comparison of virtual tourism between different karst landscapes.

Construction of karst cave rescue system: A case study of Guizhou Province

LUO Shuwen, WU Kehua, HE Wei, LUO Shiqin, ZHOU Wenlong, MAO Yongqin, YANG Tao, LI Po, ZHANG Yuanhai, DENG Yadong, LIU Yuxuan, Jean Botazzi, ZHANG Hongzhi, QIAN Zhi, WANG Deyuan

2024, 43(2): 476-490. doi: 10.11932/karst20240209

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Abstract:
Since the 1980s, with the development of joint spelunking activities between China and other countries, modern spelunking activities and techniques have been introduced and gradually promoted in China. Spelunking is now emerging as a popularized activity, which has been integrated into sports and tourism industries. Guizhou is located in the core area of the largest contiguous karst area of the world; therefore, cave resources in Guizhou have become an important part of China's economic development. However, cave accidents have occurred frequently, showing an increase in recent years. Establishing a sound cave rescue system is of great practical significance to support the construction and development of economy in sports industry and tourism industry in Guizhou. The cave environment is one of the most risky and challenging environments for human activities, and cave rescue has gradually attracted people's attention. As early as 1935, the world's first famous cave rescue organization was established in Yorkshire, England, and subsequently, cave rescue organizations have also sprung up in the United States, France, Italy, Belgium and other western countries. On 13–15 August, 1963, the first cave rescue conference was held in Bruxelles and Han-sur-Lesse, Belgium. Cave rescue manuals have been consecutively compiled and cave rescue websites have also been set up in Europe. At present, China's cave accidents mostly handled by rescue teams temporarily deployed from relevant personnel, mainly from the fire brigade. Most of the rescuers are cave professionals and enthusiasts lacking professional skills for cave knowledge and standardized training to carry out rescue operations. Consequently, it is difficult to achieve consistent and orderly rescue, which may even cause secondary injuries or delay in rescue. Based on the achievements of cave rescue and cave rescue manuals overseas, we analyzed cave rescue elements and summarized the composition of cave rescue in this paper. Taking Guizhou Province as an example, we analyzed the current types of cave accidents and rescue in China, on the basis of which we constructed a cave rescue system by combining the composition of rescue subjects and cave technical talents in China. It is believed that the cave rescue system consists of the following parts: (1) Under the leadership of the two functional departments—the Emergency Management Department and the fire brigade, the command center for cave rescue can be established responsible for alarm receiving and rescue dispatch. (2) At the same time, in cooperation with Guizhou Institute of Mountain Resources and Guizhou Cave Association, Technology Research and Development Center for Cave Rescue is expected to be set up for rescue personnel training, accreditation of rescue qualification, technology research and development, etc. Norms such as standardization of rope technology, training of rope technology and system of qualification accreditation, codes of conduct for cave rescue personnel, etc. should be established. (3) According to the distribution characteristics and main elements of caves in Guizhou, a provincial team deployed by Technology Research and Development Center for Cave Rescue in Guiyang should be established in charge of the cave rescue in complex situations of Guizhou and the training of provincial cave rescue team. With the fire brigade as the main body, this team consists of cave routing group, stretcher group, communication group, medical group, underwater diving group, explosion group and ventilation group. In Liupanshui City, Zunyi City, Bijie City, Anshun City, Tongren City, Qiannan Buyi and Miao Autonomous Prefecture, Qianxinan Buyi and Miao Autonomous Prefecture and Qiandongnan Miao and Dong Autonomous Prefecture, rescue teams consisting of routing group, stretcher group and medical group should be deployed in charge of the city's ordinary cave rescue. The rescue force composed of cave clubs and civil organizations of cave enthusiasts and individuals in different cities should be made full use of under the leadership of Guizhou Cave Association. (4) By Guizhou Cave Association and Cave Rescue Center, a database of cave rescue experts can be established under the leadership of Cave Rescue Center to form a rescue system with top-down linkage and official and civil interaction.

2024 Vol. 43, No. 2

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