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2023 Vol. 42, No. 3

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2023, 42(3): 1-2.
Abstract FullText HTML PDF(451KB) icon38 icon42
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Ecological restoration scheme of lake basins on the karst plateau based on natural solution: Take nine lakes on the Yunnan Plateau as example
LI Qin, WANG Yu, LI Li, ZHANG Hua, WANG Bo
2023, 42(3): 391-401. doi: 10.11932/karst2023y012
Abstract FullText HTML PDF(2885KB) icon350 icon111
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There are 30 lakes with a perennial surface area of more than 1 km2 on the Yunnan Plateau, including the famous "Nine Major Plateau Lakes" such as Dianchi lake, Fuxian lake, Erhai lake and Lugu lake. Since the Holocene, the plateau uplift has gradually stabilized, and plateau lakes generally entered the stage of degradation. Consequently, resources and environmental enduring capacity have decreased, and ecological vulnerability, in turn, has increased. The severe ecological damage of basins and degradation of lake ecology caused by a heavy load of population and economy in lake basins on the plateau have led to the water quality deterioration due to the shortage of water resources and the severe pollution, the decline of ecological services caused by the ecosystem destruction, and the severe restriction of the implementation and sustainability of ecological protection and restoration due to the overload of territorial space. The lakes are all distributed on the plateau and along its edge, therefore, their ecological damage effect is directly transmitted to and affects the water environment of the Yangtze River, the Pearl River and other big rivers through the surface and underground rivers. Therefore, the ecological restoration of the plateau lake basins is of great significance to the regional water environmental and ecological security. Through the systematic investigation and research, we find that mainly developing in karst faulted basins with a complete geomorphic unit for each lake basin is the most important environmental feature of plateau lakes. The karst faulted basin can be divided into four geological zones in terms of ecological environment, mountain area, hilly area, flat land area, and lake area. The ecological and economic functions of the zones are shown as follows, mountain areas are mainly used for the ecological functions such as soil and water conservation, biodiversity protection, etc., and the development of mineral resources and energy; hilly areas are used for ecological barrier establishment, water and soil conservation, water resource regulation and storage, industrial development and leisure tourism; flat land areas are used for urban construction, economic and social development, and the ecological functions such as wetland restoration, wetland reconstruction, and mitigation of man-made and natural hazards. The lake areas have functions of buffer and isolation, biodiversity and habitat protection, water resources regulation and storage, water quality purification, as well as the economic value of aquatic product and tourism. The surface water and groundwater runoffs merge into lakes from high to low. All the adverse environmental effects caused by the ecological damage in the peripheral area are directly transferred to lakes by these runoffs as carriers. Therefore, ecological restoration should be carried out systematically in the basins. The ecological restoration scheme of plateau lakes should adhere to the principle of respecting and adapting to nature.According to the differential characteristics of ecological and geological environments of the plateau lake basins, the rule of water cycle and mass transport, as well as the conditions of resources and environment, we should conduct the zoning evaluation of ecological function and suitability in drainage basins, reveal the main ecological problems, and summarize experience, based on the succession law and the internal mechanism of nature. Finally, after determining ideas and principles based on natural solutions, we can work out ecological restoration schemes that are adapted to the conditions of resources and environment, and social realities of the plateau lake basins. In general, ecological restoration schemes should be deployed in a coordinated manner throughout the entire basin, targeting at the problems in different areas. The main ecological problems in mountain areas are vegetation degradation, biodiversity damage, soil erosion, rocky desertification and geological disasters. For these issues, ecological restoration should focus on the restoration of natural resources and the enhancement of ecological functions. The main ecological problems in hilly areas are vegetation destruction, excessive mountain reclamation, excessive mining of building materials, destruction of landform and landscape, pollution with multiple sources, and many other types of environmental and geological problems. For these issues, artificially assisted regeneration and ecological reconstruction should be adopted as the main ecological restoration methods. At the same time, ecological and economic functions should be improved. The main ecological problems in flat land areas are the overload of land space, the shortage of water resources, the heavy pollution issue, the serious destruction of the ecosystem, wetland loss due to excessive construction, destruction of vegetation, the intense transformation of natural flow fields, the poor quality of water environment, etc. For these issues, in order to effectively improve the economic and ecological functions of territorial space, ecological restoration should be focused on ecological reconstruction, comprehensive governance, transformation and utilization of land space, as well as pollution control. The main ecological problems in lake areas are as follows, intensive human activities, serious encroachment on the ecological land by the farmland and villages in the lakeside buffer zone, habitat damage, biodiversity reduction, attenuation or loss of the ecological barrier area around the lake, and serious water pollution. For these issues, ecological restoration should be focused on pollution interception and treatment, water quality restoration, and ecological reconstruction. Specifically, we should construct ecological banks and corridors, eliminate the stress factors of habitat fragmentation, improve and repair the water environment, and rebuild a sound ecosystem. In the past decade, a total area of 593 hm2 has been restored in the plateau lakes. The ecological restoration practice of the "Nine Major Plateau Lakes" proves that the ecological restoration scheme of lake basins on the karst plateau based on natural solutions is effective, and the ecological restoration of major plateau lakes has achieved significant results.
Study on the difference of water-bearing capacity of fault-controlled dolomites in Dengying Formation of a mining area in central Guizhou and its significance of water control
XIANG Gang, WANG Mingzhang, ZENG Mudan, WANG Jiaming, FAN Shanxing
2023, 42(3): 402-412. doi: 10.11932/karst2022y19
Abstract FullText HTML PDF(3470KB) icon2201 icon48
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The central region of Guizhou Province enjoys global fame of its areas with large-scale production rich in phosphorus. For a long time, the phosphate rock resources in this area have provided a reliable guarantee for the domestic economic development. At present, this region has also become an important raw material base of phosphate rocks and a production base of fine phosphate chemicals in China. After decades of mining, phosphorus mines in this area have gradually changed from open pits to underground ones and from shallow to deep, and thus the hydrogeological conditions of deposits become increasingly complex. Dengying Formation, the main aquifers of phosphate rocks, is composed of dolomite with the water-bearing medium of solution pores and cracks. It is a water-bearing formation comprised of pure carbonate rocks with medium to high water abundance. Consequently, the high cost of mine drainage has imposed a heavy burden on mining enterprises. In addition, mine water inrush has severely threatened the exploitation safety of phosphate rock resources in this region. Therefore, it is very important to research the characteristics of water abundance of the Dengying Formation. The phosphate mine of Dawan, a water-filling deposit with deeply covered karst, is located on the western flank of the Baiyan anticline. The high bearing capacity of groundwater and complicated hydrogeological conditions of Dengying Formation are representative and typical in the Baiyan anticline area. Due to the super large scale and high grade of phosphate ore resources, the phosphate mine of Dawan was listed as a key project of mineral resource exploration in Guizhou Province in 2020. During the exploration work, a large amount of geological data was obtained through surface surveys, geophysical and hydrological logging, drilling, and hydrogeological experiments. In this paper, a study on the water abundance of the Dengying Formation of the deposit has been conducted based on the data from the exploration of the phosphate mine as well as the anatomy of typical mining areas. The research results show that the phosphate mine in Dawan is a karst deposit with water-filled roof, and the lithology, structure and fracture structure of the Dengying Formation in the water-filled layer are the main factors controlling the water-filling condition of the deposit. With an obvious distribution law, the water content and permeability of Dengying Formation present obvious characteristics of "plane partition" and "vertical stratification". In the plane of exploration area, there is a significant difference in water abundance of the Dengying Formation near and far from the structural area. The differences in fault properties also result in different water abundance of the Dengying Formation. In the vertical direction, there is a weak permeable layer with poor water content and relative water resistance in the middle and lower parts of the Dengying Formation. The waterproof design of mine based on the characteristics of water abundance in Dengying Formation is of great significance to ensure the safe production of the phosphate mine in central Guizhou, and to reduce the cost of mining drainage.
Karst hydrogeological survey and tracing of Zhangyukeng phosphogypsum repository
ZHAO Zhihao, WANG Kongwei, ZHOU Zhun, LIU Shiyuan, ZHANG Kaiyuan, WANG Lan
2023, 42(3): 413-424. doi: 10.11932/karst2023y017
Abstract FullText HTML PDF(18714KB) icon2313 icon51
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The most effective treatment of phosphogypsum—the waste generated in the production of phosphoric acid—is centralized landfill. Given the stability of phosphogypsum landfill and possible pollution to groundwater, Zhangyukeng phosphogypsum repository, a typical phosphogypsum landfill site, should be established in accordance with strict requirements on the geological environment. In this study, based on the field geological survey, observation of drilling cores and interpretation of geophysical profiles, the tracer evaluation technology was used to evaluate karst development and to analyze characteristics of karst water runoff and discharge in the study area. The following conclusions are drawn as follows. Firstly, the gullies where Zhangyukeng phosphogypsum repository is located have no hydraulic connection with the adjacent valley; therefore, there will be no groundwater leakage to the adjacent valley. Secondly, NE karst pipelines control the runoff and discharge of karst water in Zhangyukeng area. The discharge channel is unique and the geological point (D5) is the contact-type descending spring existing in this area—the discharge channel of karst groundwater. Thirdly, the tracer curve is a unimodal one with trailing characteristics, and the type of underground karst pipeline is single with relatively simple structures, which shows that the underground karst in the experimental area is developed and there is a main path channel with smooth flow between two geological points from D2 to D5. In conclusion, from the perspective of hydrogeological conditions, the building of a phosphogypsum landfill should meet the requirements that there exists a relatively independent underground geological unit without the hydraulic connection with the adjacent valley, and the discharge channel is single and clear. The karst hydrogeological conditions of Zhangyukeng phosphogypsum repository basically satisfy the above requirements and meet the hydrogeological conditions for its construction.
Analysis on D/18O and hydrochemical characteristics of karst groundwater in northwestern Hunan Province
LIAO Jia, ZHU Zhenhua, PENG Yi, WEI Shanhu, LUO Zhaohui, LIU Zhuang, XU Qiangqiang, XIE Gen
2023, 42(3): 425-435, 481. doi: 10.11932/karst2023y003
Abstract FullText HTML PDF(5029KB) icon1041 icon66
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Understanding hydrochemistry of karst water in northwestern Hunan is the foundation for reasonable utilization of water resources. The study on the causes of water sources and the evolution process of solute components is of great scientific value and practical significance. However, most of the research on this area has focused on the optimal allocation of water quantity and the evaluation of local water quality in the past few years. There is lack of research on hydrological geochemical characteristics and control factors based on groundwater systems, and hence a need of further research on the systematic understanding and utilization of local karst groundwater. This study takes the karst water system in northwestern Hunan Province as a case, aiming to reveal the characteristics, the evolution law and causes of hydrochemistry in this area. The research findings are hoped to play a positive guiding role in the sustainable development, and utilization and integrated management of regional groundwater resources.On the basis of hydrochemical and isotopic analyses of water samples collected in the study area, the source and composition origin of groundwater in this area have been explored with isotope D and 18O and with the comprehensive hydrogeochemical research method of multivariate statistics and hydrochemistry (piper trilinear diagram and ion scale coefficient). The results show that although there is little difference among three study zone on the whole, the sources and genesis of groundwater components are still quite different. According to the pipper three-line chart and the Gibbs chart, it can be seen that the main component of groundwater mainly derives from the dissolution and leaching of carbonate, accompanied by different degrees of the leaching of gypsum and other minerals. Concentrations of potassium, sodium ions and chloride ions are generally low, which is related to the low content of salt rocks in the carbonate formation and weak effect of evaporative concentration. Because the alternating adsorption of cations is weak, it is not the main influencing factor of the groundwater chemistry in the study area. Longshan area (Zone I), mainly presents the leaching of calcite/dolomite and gypsum. The water abundance in karst aquifers is high and the interaction between water and rock is rapid. In Yongshun-Fenghuang area (Zone II), groundwater in the Youshui basin mainly presents the leaching of dolomite and the concentrations of potassium and sodium ions are affected by the leaching of rock salt. In the Wushui basin, the joint leaching effect of limestone and dolomite that influences the concentrations of calcium and magnesium ions in groundwater, together with the leaching of silicate rock, augments the concentrations of potassium and sodium ions. In Shimen county (Zone III), the main source of ions comes from the leaching of limestone, and there are multiple sources of sodium, potassium, and chloride ions in groundwater. Besides, the recharge source of groundwater in the study area is mainly atmospheric precipitation, groundwater generally replenished directly through sinkholes, karst pipelines, karst funnels, etc. The isotope D and 18O of groudwater in the study area presents obvious continental and elevation effects. It is believed that springs show more closure properties compared with wells and underground river systems. Since the study area is a karst landform in an arc-shaped mountainous area, the terrain is severely cut, and the elevation of the sampling point is not very representative of the average supply elevation of springs and underground river systems. The deuterium surplus reflects that the spring system is the one with a faster cycle and shorter retention compared with the system of underground river. However, the underground river has a longer supply source, a wider range of replenishment, a longer movement time and a longer flow of water underground, and stronger water-rock interaction.
Geochemical characteristics and paleoenvironmental implications of carbonate rocks at the Givertian and Eifelian boundary in northeast Guangxi
LIU Shijie, GUAN Qi, PAN Ming
2023, 42(3): 436-447. doi: 10.11932/karst2023y019
Abstract FullText HTML PDF(2746KB) icon1189 icon35
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The Devonian period, marking the initial phase of the Late Paleozoic era, has garnered considerable attention in recent decades. This heightened interest stems from its intricate climatic fluctuations, recurrent global shifts in sea levels, and a series of consequential biological catastrophes. Of particular captivation is the upper Devonian-lower Carboniferous in northeastern Guangxi, characterized by a multifaceted paleogeographic configuration known as platform-trench-basin facies. Notably, the stratigraphic progression from basin facies to open platform facies displays a notable continuity, culminating in the formation of a substantial kilometer-thick carbonate rock layer. This unique geological foundation underpins the development of a renowned karst geomorphic landscape, which is globally significant.Furthermore, this distinctive karst landscape has facilitated the establishment of the international Devonian-Carboniferous boundary auxiliary layer profile, adding another layer of importance to the study of the Devonian system in this region. While prior investigations have primarily concentrated on sedimentary facies, paleontology, pivotal organisms, and event layers like the 'F-F' biological catastrophe event and the D/C boundary layer during the Late Devonian, certain critical events, notably the Kačak-Otomari event in the late middle Devonian, have received comparatively less attention. Moreover, a comprehensive global-scale comparative analysis has been lacking.Given these gaps, the present study investigates a critical juncture, the boundary between the Eiffelian and Givertian systems, situated in Longyankou village, Yangshuo county. A meticulous examination was carried out, involving the collection of ten carbonate rock samples from this specific section. Through a comprehensive analysis encompassing microscopic features, elemental compositions, ratios, as well as carbon and oxygen isotope data, the study aimed to elucidate and discuss the ancient oceanic sedimentary environments in proximity to this location. Our findings can be summarized as follows:(1) The presence of Polygnathus intermedius, a conodont fossil, is observed within the YS3 sample layer, attributed to the late Eifelian period. This fossil aids in establishing a precise temporal boundary for both the carbon isotope migration event and the Kačák event within this stratum. (2) By employing Wilson's established microfacies sedimentary model in conjunction with lithological traits, four distinct microfacies types, SMF23, SMF16, SMF4, and SMF15, have been successfully distinguished. (3) Through meticulous geochemical analysis, we draw several significant conclusions regarding the sedimentary environment during various stages: The sedimentary environment during the YS1 to YS2 transition demonstrates rapid deepening of sedimentary water and a consistent material source supply. This mirrors the geological process of swift transformation from limited platform facies to slope facies during the initial transgression phase; the low terrigenous component content during YS3 and YS4 stages indicates a distant shoreline sedimentary environment with deep waters and relatively elevated sea levels. Notably, this stage is characterized by widespread hypoxia, displaying global uniformity; Geochemical indicators for YS5 to YS10 stages exhibit minor fluctuations. Notably, the terrigenous component content gradually increases, while the appearance of radial oolitic limestone signifies a low-energy environment. Simultaneously, the sedimentary area witnesses a significant sea level decline, characterized by thicker upward progradational sequences that provide excellent sedimentary responses. (4) Reconstructing the paleoseawater temperature evolution curve based on oxygen isotope data reveals an average seawater temperature of 21 ℃ during the studied period. This temperature profile reflects a warm subtropical climate, aligning with the paleogeographic proximity to the equator. (5) The observed negative migration of carbon isotopes corresponds with the E/G boundary stratotype profile in Morocco and the carbon isotope curve characteristics observed in Canada within the same horizon as sample YS3. In summary, these findings emphasize the prevalence of a deep-water and anoxic sedimentary environment amidst a global-scale transgressive backdrop.
Research progress on the effect of moss crust on the weathering of carbonate rocks
YANG Tao, GUO Hui, ZHOU Jinxing, PENG Xiawei
2023, 42(3): 448-455. doi: 10.11932/karst2021y36
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The exposed area of carbonate rocks in the karst region of Southwest China reaches 550,000 km2, which is the largest area with the most developed karst in the world and also the most severely desertified area in the world. Therefore, the origin of soil in karst ecosystems and the process of carbonate rock weathering have always been scientific issues of great concern. Mosses coexist with algae, bacteria, and fungi on the exposed calcareous rocks, forming a moss crust. The moss crust can not only survive and reproduce on the surface and crevices of rocks under severe conditions of water shortage and nutrient deficiency, but also accelerate the weathering of carbonate rocks through organic acid secretion, CO2 release, and mechanical action. The accumulated organic matter can develop the soil parent material on the surface of carbonate rocks into shallow primitive soil, playing an irreplaceable role in the restoration of degraded ecosystems in karst regions, and is known as "the engineer of desert ecosystem". Among the components of moss crust, the volume of microorganisms is at the micrometer scale, and people's understanding of the microbial population growing with moss on rocks is mainly obtained through morphological observations. Many microorganisms are too small to be cultivated, so it is impossible to obtain information on the entire microbial population in this habitat, and thus their functional knowledge has been ignored. Therefore, in order to provide a theoretical basis and technical support for ecological management in desertification areas, this article summarizes the previous studies on moss crust in recent years in desertification areas, clarifies the rock weathering and soil formation process in which various components of moss crust (microorganisms and moss plants) participate, and their application in desertification control.
Seasonal variation characteristics of dissolved organic matter composition and cycle process in caves
LIU Yugang, HE Qiufang, SHEN Licheng, FAN Jiaxin
2023, 42(3): 456-471. doi: 10.11932/karst2023y23
Abstract FullText HTML PDF(3208KB) icon122 icon50
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Dissolved organic matter (DOM) is the key part and important carbon source of karst carbon sink. The migration and degradation of DOM in karst aquifers is an important carrier of material and energy transfer. However, due to the lack of long-term and in-depth research on the content, composition and migration process of DOM in karst groundwater, the transfer and metabolism process of organic carbon in cave water system and its impact on karst carbon sink process are still unclear. Colored dissolved organic matter (CDOM), a colored soluble component in DOM, is often used to characterize DOM in marine and freshwater systems. It is also used to characterize the composition and change process of organic matter in the study of karst groundwater. 16S rDNA high-throughput sequencing, a commonly used method for the detection of non-cultured microorganisms, can comprehensively detect and analyze the bacterial community composition and species abundance in environmental samples. This study collected samples from the underground river in Fengdu Xueyu Cave, Chongqing on a quarterly basis, analyzed their hydrochemical indexes and organic carbon content, and characterized the changes in the composition and structure of organic carbon using CDOM fluorescence and UV-visible spectrum information. Combined with 16S rDNA high-throughput sequencing, this study also analyzed the structural characteristics of bacterial communities in groundwater and the metabolic function genes of microorganisms based on Pecrust2 prediction. According to the metabolism and transformation process of organic carbon in cave water and its response to the external input of organic matter, we can understand the migration and transformation process of organic carbon in karst groundwater, and provide scientific information for the carbon cycle and carbon sink process of karst groundwater system.Xueyu Cave is located in the Longjiang Gorge in Fengdu county, Chongqing, the southwest karst region. The cave opening is exposed at the mid-mountain elevation of 340 meters. Affected by the subtropical monsoon climate, there are relatively obvious dry seasons with low precipitation (from October to April of the next year) and rainy seasons with high precipitation (from May to September). The flow of underground river in the cave is controlled by precipitation which is much higher in the rainy season than in the dry season. This study collected water samples from the deep part of the cave and at the mouth of the cave in the Xueyu Cave underground river on a quarterly basis in 2018 and analyzed their hydrochemical characteristics. It is found that the chemical type of the underground river water is a typical HCO3-Ca type, with high pH, high DIC and high Ca. PCA analysis shows that the hydrochemical indicators are mainly controlled by precipitation, and present a two-level distribution in the dry season and the rainy season. δD and δ18O content indicates that the evaporation effect and retention time of groundwater in the dry season are higher than those in the rainy season. Three CDOM components are found in the underground water of Xueyu Cave by CDOM three-dimensional fluorescence EEM parallel factor analysis, C1 is an endogenous tryptophan-like substance of microbial origin; C2 is an endogenous humic acid or fulvic acid of microbial origin; C3 is an exogenous humic acid component. The results of UV-visible absorption spectrum parameters and fluorescence spectrum parameters are similar, both of which indicate that the DOM components in the Xueyu Cave underground water are affected by inputs both from internal and external sources. The internal organic matter is mainly small molecular endogenous organic matter, accounting for 61%-77%. PCA analysis of organic carbon content and CDOM related indicators shows no obvious seasonal changes in terms of DOC and TOC content, while CDOM components, fluorescence spectrum parameters and absorption spectrum parameters demonstrate obvious seasonal differences. The fluorescence intensity and proportion of exogenous C3 in the rainy season are much higher than those in the dry season, while the proportions of endogenous C1 and C2 in the dry season are higher. In the fluorescence parameters, HIX indicates the humification degree of CDOM, with the average value of 1.89 in the dry season, lower than the average value of 2.00 in the rainy season. On the contrary, BIX indicates the contribution of endogenous DOM in the new generation. The mean value in the dry season is 0.88, higher than that in the rainy season. 16Sr DNA analysis of bacterial community diversity shows that the Xueyu Cave underground water is dominated by heterotrophic microorganisms, and there is a large difference in the microbial community structure between the rainy season and the dry season. The gene abundance of metabolic function predicted by Pecrust 2 demonstrates that the functional gene abundance related to the degradation of aromatic substances in the rainy season is 30%-56%, higher than that in the dry season. The above analyses show that the input of exogenous organic carbon introduced by rainfall is the main control factor of organic carbon composition and carbon metabolism process in karst groundwater. During the rainy season from May to September in the karst area of Southwest China, exogenous organic matter enters karst groundwater with rainstorms, and hence its content increases. The proportions of exogenous components in CDOM and the indexes of HIX, FI and other related spectral also increase. The change of organic matter compositions takes place with the change of bacterial community diversity. The abundance of functional genes that metabolize exogenous aromatic substances in underground water increases, so does the content of exogenous organic carbon output from underground water to the outside of the cave. During the dry season from October to April of the next year, the rainfall is about 1/4 of the rainy season. While the input of exogenous organic matter decreases, the retention time of karst groundwater is longer, and the process of microbial degradation and metabolism is more sufficient. Therefore, the CDOM spectrum of groundwater reflects stronger endogenous characteristics of microorganisms with higher proportion of endogenous CDOM components exported by karst groundwater to the outside of the cave. The study results show that the main source of organic carbon in karst groundwater is controlled by rainfall, and the input amount in the rainy season is higher than that in the dry season. The full degradation and metabolism of organic matter in groundwater by microorganisms in the dry season causes the endogenous enhancement in groundwater system, which has an important impact on the process of karst underground carbon sink.
Chemical properties of leaf litter among tree species with different mycorrhizal types in southern subtropical China
CHAO Lin, LI Zhongguo, MO Zhenzhen, HUANG Huilian, WANG Aihua, ZHANG Jianbing, HU Baoqing, LIU Yanyan
2023, 42(3): 472-481. doi: 10.11932/karst2023y009
Abstract FullText HTML PDF(917KB) icon2461 icon45
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The sample plot is located in the Experimental Center of Tropical Forestry, Chinese Academy of Forestry, the southwest of Guangxi, China. In a typical southern subtropical monsoon climate, the annual temperature of this area averages at 21 ℃ with the lowest average at 12.5 ℃ in January and the highest at 27 ℃ in July. The average annual precipitation is between 1,200 to 1,500 mm, and shows obvious seasonality with the wet season from April to September and the dry season from October to March in the following year. The area is characterized by a typical landform with peak-cluster depression at the elevation ranging from 150 to 800 m. The main soil type in this area is red soil developed from carbonatite.Taking the leaf litter of 24 tree species with different mycorrhizal types (respective eight species for arbuscular mycorrhizal fungi, ectomycorrhizal fungi and nitrogen-fixers) as the research object, we measured the chemical properties of leaf litter (non-structure carbohydrate, water-soluble carbon, lignin, cellulose, hemicellulose and tannin) and nutrient concentration (N, P, K, Ca, Mg and Mn), analyzed the relationships of these properties, and explored the effects of different mycorrhizal types on the chemical properties. The results indicate that the chemical properties of leaf litter exhibited a fair degree of variation in carbon-related properties, nutrient contents and stoichiometric properties. There were no significant differences in carbon-related chemical properties among tree species with different mycorrhizal types (P>0.05). However, the nutrient content (N, P and Mg) and stoichiometry properties of leaf litter (C/P and N/P) were significantly different among mycorrhizal types. Nitrogen-fixer trees showed a significantly higher leaf litter N (16.1 g·kg−1) than the trees with arbuscular mycorrhizal (10.1 g·kg−1) and ectomycorrhizal fungi (10.7 g·kg−1). However, tree species with arbuscular mycorrhizal fungi (0.4 g·kg−1) exhibited a significantly higher P concentration than the trees with ectomycorrhizal fungi (0.1 g·kg−1) and N-fixer (0.08 g·kg−1) trees. The concentration of Mg (0.51 g·kg−1) in the tree species with ectomycorrhizal fungi was significantly higher than the trees with arbuscular mycorrhizal fungi (0.19 g·kg−1) and N-fixer trees (0.03 g·kg−1). In addition, the C/P and N/P of N-fixer trees were significantly higher than the tree species with arbuscular. Hence the differences in the chemical properties of leaf litter among different mycorrhizal types should be considered during the restoration of degraded ecosystems, and appropriate tree species for restoration will be selected according to the strategies of nutrient utilization.
Changes and driving factors of psychrophilic diatom community structure of algal mats in Huanglong Scenic Area
RAO Hanyun, DONG Faqin, LIU Mingxue, AN Dejun, DAI Qunwei, LI Qiongfang, ZHANG Qiang, LIU Yifan, LIU Zeling, ZHANG Yuting
2023, 42(3): 482-494. doi: 10.11932/karst20230301
Abstract FullText HTML PDF(2453KB) icon95 icon40
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Huanglong Scenic Area, located in Songpan county, Sichuan Province, China, is listed as the World Natural Heritage, and is covered with travertine landscape at an altitude of about 3,145-3,588 m. With the plateau temperate sub-frigid monsoon climate, the melt water from snow mountains, the atmospheric precipitation and the underground karst water are the main water sources of Huanglong Scenic Area. In addition, covered by ice and snow at extremely low temperatures, Huanglong Scenic Area has a half-year-long freezing period with an annual average temperature of only 1.1℃. A large number of algae, mainly psychrophilic diatoms, grow in the water coverage of the travertine deposition area in the scenic area. The diatom community, an indicator of water quality change, is very sensitive to environmental changes in natural rivers. At present, there are still few studies related to this alpine karst area. In order to explore the structure of algal mats as well as the relationship between the community structure of psychrophilic diatoms in algal mats and environmental variables in Huanglong Scenic Area, we analyzed water samples and algae mats from 8 typical scenic spots in October 2021. The water temperature (T), pH and conductivity (Ec) as well as the concentrations of ${\rm{HCO}}_3^{-}$ and ${\rm{CO}}_3^{2-}$ of the sampling points were measured on site. At the same time, the geographic data of the sampling points were recorded. The concentrations of dissolved silicon (Dsi), cations (Ca2+, Mg2+, Al3+, K+), anions (Cl−, ${\rm{NO}}_3^{-}$, ${\rm{SO}}_4^{2-}$), TN and TP were determined in the laboratory. The structural compositions of the algal mats and the characteristics of the diatom community structure were analyzed. The main driving factors affecting the water of Huanglong Scenic Area were judged by Principal Component Analysis (PCA), and one of the two environmental variables with greater correlation was eliminated by Spearman Correlation Analysis. After Detrend Correspondence Analysis (DCA) of diatom species abundance in algal mats, Redundancy Analysis (RDA) was selected to analyze the relationship between environmental variables and diatom communities. The results show that the concentrations of Ca2+ and ${\rm{HCO}}_3^{-}$ in the waterbody is high, and water mainly belongs to the HCO3-Ca type, followed by the HCO3-Ca-Mg type. The algal mats are mainly composed of travertine particles, filamentous algae and diatoms. The study area is an alpine karst micro-ecosystem with travertine as the base and filamentous algae as the skeleton, inhabiting a large number of diatoms. 72 species of diatoms from 25 genera are identified from algal mats, among which 16 species have a total relative abundance greater than 2%. The genus Cymbella (14 species), Diatoma. (8 species), Cymbopleura (7 species), Caloneis (4 species) and Synedra (4 species) contribute the most. There are 13 dominant species of diatoms in Huanglong Scenic Area. 4 species from the genus Cymbella have absolute advantage (Ytotal = 0.132) at the genus level. At the species level, there is little difference in the dominance index of each dominant species (0.023≤Y≤0.053), among which the dominance index of Diatoma vulgaris is the largest, and that of Cymbopleura linearis is the smallest. In terms of the diversity index, there are some differences in the Shannon-Weiner index, Simpson diversity index and Pielou index at various sampling points. As the altitude decreases, the diversity index from #1 to #8 fluctuates, rising and then falling repeatedly. This may be related to the water circulation system of Huanglong Scenic Area. The analyses of the relationship between environmental variables and diatom communities by RDA show that the eigenvalues of the first two axes are 0.43 and 0.24, respectively, explaining 67.68% of the cumulative variance of data about diatom community species. The correlation between environmental variables and diatom community structure in algal mats is T>DSi>pCO2>TN> Mg2+>Ca2+>altitude, and the three environmental variables of Cl−, ${\rm{NO}}_3^{-}$ and ${\rm{SO}}_4^{2-}$ are excluded because of the low correlations. The significance test of the influence degree of each factor by Monte Carlo test finds that T (F=2.8, P=0.02) and DSi (F=2.3, P=0.04) are environmental variables that significantly affect the algae community structure of the algal mats. In addition, although TN is not the most significant driving factor affecting diatoms of the algal mats in Huanglong Scenic Area, there is a trend of eutrophication in the waterbody of the scenic spot, which will affect the algal community structure, so TN may be a potential driving factor. The above conclusions can provide a basis for the establishment of the diatom species bank in Huanglong Scenic Area and the monitoring and management of the river water environment in the plateau karst area.
Water chemistry and tufa deposition on the restored dam of Huohua Lake in the Jiuzhai Valley
LIU Qin, YAN Hao, XIAO Weiyang, XIAO Yao, ZHOU Lyu, XIE Yao, QIAO Xue, TANG Ya
2023, 42(3): 495-508. doi: 10.11932/karst20230302
Abstract FullText HTML PDF(5998KB) icon105 icon26
Abstract:
In 2017, an Ms 7.0 earthquake breached the tufa dam of Huohua Lake in the Jiuzhai Valley, resulting in the lake drainage. Exposed to the atmosphere, the tufa dam collapsed due to continued physical and chemical weathering. To prevent further collapse, the dam of Huohua Lake was restored by using the modified glutinous rice mortar and local limestone rocks. After the restoration, we monitored the chemical and isotopic compositions of surface water and tufa to answer the following questions.Does the surface water after the earthquake tend to conserve the tufa dam and precipitate tufa? Does the modified glutinous rice mortar have a significant impact on the surface water in the lower part of Huohua Lake? Does new tufa deposit on the restored dam? What are the characteristics and main sources of newly-deposited tufa? Are there any differences between the old tufa on the natural tufa dam and the newly-formed tufa on the restored dam?The characteristics of surface water and tufa samples were investigated. First, from September 2020 to September 2021, the surface water of Huohua Lake was monitored once a month. The parameters included pH, conductivity, temperature, alkalinity, turbidity, DO, K+, Ca2+, Na+, Mg2+, ${\rm{SO}}_4^{2-}$, ${\rm{NO}}_3^{-}$, NH$_4^{+}$, dissolved organic carbon (DOC), and calcite saturation index (SIC). We also compared these parameters between the values before and after the earthquake. Second, to examine the physical and chemical characteristics of tufa, we used the scanning electron microscope (SEM) and X-Ray Diffractomer (XRD) for tufa samples and analyzed the elemental compositions (Ca, Mg, Al, Si, P, S, K, Fe and Ba), organic matter, and carbon and oxygen isotopes in the modified glutinous rice mortar, tufa samples, and surface water. Third, the characteristics of microorganisms in the tufa samples were quantified by using the high-throughput sequencing technology.The SIc values of surface water after Huohua Lake restoration were 0.77 ± 0.11, indicating that the surface water tended to precipitate CaCO3. From the upstream to downstream of Huohua Lake, there were no significant changes in Ca2+, ${\rm{SO}}_4^{2-}$, NH$_4^{+}$, ${\rm{NO}}_3^{-}$, PO$_4^{3-}$, DOC, and other water chemistry parameters (P>0.05), indicating that the dam restoration materials had no significant influence on the surface water. The concentrations of ${\rm{HCO}}_3^{-}$ were 94-291 mg·L−1 before the earthquake, 189-338 mg·L−1 after the earthquake but before the restoration, and 157-212 mg·L−1 after the restoration. The concentrations of ${\rm{NO}}_3^{-}$ increased after the earthquake, and the DOC concentrations after the earthquake were 0.8-2.05 mg·L−1. At the same time, the lake turbidity generally increased after the earthquake. The changes of these hydrochemical indicators were most likely due to the vegetation damage caused by the earthquake, which further intensified soil erosion. After the dam restoration, newly-deposited tufa was observed on the top of dam, and the brown color generally reflected the high content of organic matter, Si, Al, K, Fe, and Ba from enhanced soil erosion. On the side surface of the repaired dam, tufa was white and contained much lower amount of organic matter compared to that of the tufa collected on the top of dam. The main mineral composition of tufa from both the restored dam and the natural dam is calcite, but was quite different from the modified glutinous rice mortar. The δ13C values of newly-deposited tufa on the restored dam were between those of surface water and the tufa of natural dam, but were much lower than those of modified glutinous rice mortar. These results suggest that CaCO3 of newly-deposited tufa was likely mainly from surface water. The bacteria biodiversity indices (Chao1, PD, Shannon, and Simpson) were higher in the tufa of natural dam than in the newly-deposited tufa. Compared with the newly-deposited tufa on the top of repaired dam, the old natural tufa was richer in organic matter and more porous.Our results show that the SIc values of surface water were larger than zero, indicating that the water tended to precipitate CaCO3 and was beneficial for tufa dam conservation. The newly-formed tufa on the top of dam was likely from surface water according to the mineralogical characteristics, carbon and oxygen isotopes, and elemental compositions. The composition of newly-deposited tufa was affected by soil erosion. The old tufa of natural dam and the new tufa of restored dam showed differences in the physical structure and the trace elemental content. In addition, the organic matter content and the bacterial biodiversity were relatively lower in the new tufa, probably due to the fact that the natural restoration of vegetation and microorganism community may require a relatively longer time. Continuous monitoring is required to better understand the future evolution of the restored dam.
Spatial variation of limestone soil minerals in a karst area of northwestern Guangxi
YU Yuefeng, ZENG Chengcheng, SONG Tongqing, PENG Wanxia, HE Tieguang
2023, 42(3): 509-516, 527. doi: 10.11932/karst20230303
Abstract FullText HTML PDF(873KB) icon77 icon23
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As extremely important components of soil and constitutors of soil skeleton, soil minerals account for over 95% of the solid mass of soil. They directly participate in the entire process of soil weathering, soil formation, and plant growth and development, impacting significantly on the internal structure, exchange capacity, and fertility status of soil. Studying the spatial distribution of soil mineral elements is of great significance for understanding and mastering soil development, physical and chemical properties, and the supply status of plant nutrients. Because of the special formation matrix and ecological environment conditions of carbonate rock—the parent material of limestone soil in karst areas, soil in karst areas presents a high degree of spatial heterogeneity. At the same time, the shortage of mineral nutrients may be an important limiting factor for the growth and restoration of vegetation in mountainous areas of carbonate rock in southwestern China. However, the spatial distribution characteristics of soil minerals on a large scale in the karst area of northwestern Guangxi are currently unclear. Clarifying the spatial variation characteristics of limestone minerals in the karst area of northwestern Guangxi can provide reference for the effective utilization of mineral resources and ecological restoration and reconstruction. In order to explore the distribution pattern of the main soil mineral components in the karst area of northwestern Guangxi and to guide vegetation restoration and ecological reconstruction in the relevant area, the spatial heterogeneity of mineral components (SiO2, Fe2O3, CaO, MgO, Al2O3, and MnO) in surface soil (0-15 cm) and its influencing factors were studied by the methods of classical statistics and geostatistics. The soil samples were collected by the grid method based on the whole karst regional scale in northwestern Guangxi. The results show that the content differences and variance coefficients of six mineral components in limestone soil of karst area in northwestern Guangxi are large. The average content of SiO2 is up to 55.72%, while the variance coefficient is the smallest (37.50%). The sum of SiO2 and Al2O3 accounts for 85.22% of the total six mineral components. The spatial patterns of the six mineral components are quite different from each other, and fit different models of mineral components. The spatial autocorrelation of SiO2 is medium, but the autocorrelations of Al2O3 and MnO are weak, and their ranges are long in good spatial continuum. CaO, Fe2O3 and MgO are characterized by strong spatial autocorrelations with short ranges. The spatial distribution of minerals is closely related to the main nutrients and topographic characteristics. The spatial variation of Al2O3 and Fe2O3 is mainly affected by the altitude. The bare rock rate is the main topographic factor affecting the spatial variation of SiO2, MnO and MgO, and the gradient is the main factor affecting the spatial distribution of CaO. A principal component analysis show that the soil mineral is an important factor affecting the spatial variation of limestone soil, especially SiO2. On a large regional scale, various topographic factors affect the spatial variation limestone soil minerals, and hence impacting the spatial distribution of limestone soil.
A review of karst collapse mechanisms
JIANG Xiaozhen, FENG Tao, ZHENG Zhiwen, LEI Mingtang, ZHANG Wei, MA Xiao, YI Xiaojuan
2023, 42(3): 517-527. doi: 10.11932/karst20230304
Abstract FullText HTML PDF(837KB) icon185 icon85
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Karst collapse is a global geohazard and has been reported to occur in 23 countries, including China, the United States of America, Canada, South Africa, Italy, France, the United Kingdom, Germany, Russia, and Turkey. The mechanism of karst collapse is the basis for its monitoring, early warning, prevention and treatment. For a long time, studies on the mechanism of karst collapse have been mainly based on the qualitative speculation of the investigation after karst collapse, involving geological conditions and influencing factors of the collapse. They lack support of scientifically defensible data, hence resulting in the hypothetical stage of current studies on karst collapse mechanism. This has become a technical bottleneck in the prediction and prevention of karst collapse hazard.Karst collapse hazards are characterized by concealment and suddenness. Among the existing collapse events in China, more than 90% are soil collapse. Studies on karst collapse in China started in the 1980s and have gone through approximately four phases, (1) The sporadic karst collapse research in selected mines; (2) The karst collapse inventory and small-scale physical modeling in Yangtze River Basin, and representative mines and railroads; (3) The karst collapse reconnaissance and large-scale physical modeling in urban areas including Wuhan, Yulin, Tangshan, Tongling, Guilin, and Shenzhen; (4) The systematic nation-wide karst collapse reconnaissance. Since 2000, National Natural Science Foundation of China has increased investment in the studies on karst collapse involving groundwater pumping, foundation piling, tunneling, drainage in mines, and train vibration and in the studies on karst collapse mechanisms induced by extreme climate. At present, there are about eight karst collapse mechanisms according to previous studies, such as subduction, vacuum negative pressure, pressure difference, hydraulic fracturing, gas explosion, chemical dissolution, resonance, liquefaction, etc. These processes are closely associated with changing underground hydrodynamic conditions.With a profound analysis of definitions and theoretical basis of karst collapse mechanism, this study proposes that most of the above mechanisms can be attributed to seepage deformation of soil. This means, under the action of groundwater seepage force or dynamic water pressure, some particles of the whole soil mass will move, causing deformation and destruction of soil or rock mass. During the formation of karst collapse, the action mode and direction of groundwater seepage force on karst cavities roof soil will be different because of the change of groundwater dynamic conditions. The limit equilibrium theory of soil mechanics considers the roof stability of karst cavities, which is the last stage in the development of karst collapse; the effect of surface load is only to shorten the time of ground collapse.Finally, it is pointed out that due to the practicability of water-air pressure with high-frequency sampling, accelerometer and acoustic wave sensors, the research direction on collapse mechanisms will be changed from hydrostatic pressure to hydrodynamic pressure, a challenge that should be faced with. The cavitation damage and resonance damage caused by pressure pulsation will also be the future research focus, and the corresponding critical seepage deformation or damage indicators need to be further studied the prevention and control of geological disasters of karst collapse.
Analysis of tunnel inflow conditions based on the characteristics of typical tight-narrow monoclinic karst water system in the central Yunnan Province, China
HUANG Shengcai, CHENG Jianmei, BA Jinghui, LI Zhongxia, XU Wenjie, WANG Yan
2023, 42(3): 528-537. doi: 10.11932/karst20230305
Abstract FullText HTML PDF(2210KB) icon100 icon62
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The southwest China is covered by large areas of carbonate rock strata, in which the movement of many terranes results in strong folds and rock fractures. The spatial structure diversity of strata and tectonics has formed various complex and distinctive karst water systems. Therefore, tunnels for traffic lines and water diversion projects are often built in southwest China, but when tunnels cross karst water systems, the tunnel inflow conditions are difficult to be identified due to the complexity of water inflow, which has been a challenge in tunnel construction projects. In the Xiaopu tunnel area of the central Yunnan Province, linear extension and closely interbedded soluble and non-soluble rock strata are developed, forming a typical tight-narrow monoclinic karst water system. Since the tunnel construction, the water inrush has respectively occurred in Section 1 and Section 2 with large and long-lasting water inflow. The complexity of the water inflow brings a great challenge for the tunnel construction. Therefore, it is urgent to find out the source and mode of water inflow in Xiaopu tunnel. Focusing on specific engineering problems, this study carefully sorts out the controlling factors of the characteristics of the tight-narrow monoclinic karst water system in Xiaopu tunnel. The division of the karst water system is reduced to a small scale, and the water inflow conditions of the tunnel are identified according to the groundwater monitoring data as well as the inflow conditions such as the hydrochemical characteristics and hydrogen and oxygen isotopes of water inflow.The results show that the tight-narrow monoclinic structure affects the spatial pattern of karst development, the runoff and the transformation mode of groundwater. This structure also controls the characteristics of aquifer media development and groundwater recharge, runoff and discharge distribution. Hence, the study area can be subdivided into four small-scale karst water systems with different characteristics, i.e., the bare-covered fissure flow and conduit flow with concentrated discharge, bare conduit flow with concentrated discharge, the bare-covered fissure flow with multiplex discharge, and the bare fissure flow with concentrated discharge. The hydrochemical type of groundwater in the Duimen-Daliyuan-Niuliancun karst water system, which is crossed by the Section 1 of Xiaopu tunnel, is mainly HCO3·SO4-Ca·Mg. And the concentration of Ba2+ in groundwater is higher than that in other karst water systems due to the dissolution of barite minerals in the strata of the Weining group of the middle Carboniferous and the upper Devonian. The hydrochemical type of groundwater in the Piantoushan-Lunacun-Jinxiandong karst water system crossed by Section 2 is HCO3-Ca·Mg, indicating relatively pure karst water. This shows that dolomite dissolution is the main hydrochemical process for controlling water quality. Due to the slow flow of the karstic fracture network, the groundwater has a long residence time in the runoff path, and the water-rock interaction and evaporation are relatively strong, thus the heavy hydrogen and oxygen isotopes are more enriched. Huge differences in hydrogen and oxygen isotope composition also rule out the possibility of surface water flooding into the tunnel. It is concluded that the water inflow in Section 1 is caused by the uncovering of the underground conduit and the interception of the discharge spring of the shallow karst downstream. The karst conduit developed in the contact zone of igneous rock constitutes the main water inflow channel, in which the groundwater in the conduit is the water source with a recharge elevation of 2,165.4 m, mainly located in the karst depression in the north of Wangjiawan. The water inflow in Section 2 is caused by the exposure of karst fissures. The fissure network constitutes the main water flow passage, and the groundwater in Dengying formation is the water source, with a recharge elevation of 2,234.6 m, mainly located in the slope area on the north ridge of Piantou mountain.The groundwater in different karst water systems has experienced different water-rock interaction and evaporation processes. Therefore, the hydrochemistry and stable hydrogen and oxygen isotopes of groundwater are good natural tracers for tracing the source of water inflows in tunnels crossing different karst water systems. Comprehensive utilization of multiple approaches and information verification can improve the accuracy of identifying tunnel water inflow conditions, which may provide a basis for the subsequent design of tunnel drainage projects and the prevention of water inrush disasters in the tunnel.
Simplified design method of reinforcement treatment for karst subgrade collapse
WU Di, LI Aiwen, LI Dan, JIA Long, WEI Xueying, WU Jianjian
2023, 42(3): 538-547. doi: 10.11932/karst2023y001
Abstract FullText HTML PDF(1114KB) icon791 icon52
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Karst areas are widely distributed in China, especially in South China. With the proposal of the Belt and Road Initiative, a large amount of infrastructure has to be built in the karst area. However, the diversity of structure and mechanical properties of karst make it difficult for us to construct roads on karst foundations. In recent years, the frequent occurrence of settlement and even collapse of the road surface caused by karst foundations under soil layers of roads has threatened the safety of urban transportation and the development of economy. Therefore, the treatment of karst collapse has become an urgent engineering problem. For the controlling of karst collapse under a complex urban road environment, the treatment of karst collapse by the method of backfilling and compacting is economical in construction and can be finished in short time, but collapses are prone to happen again after treatment. In this case, the treatment can be carried out with geosynthetics, namely filling the geotextile in the subsidence area during the backfilling and compacting process. This kind of treatment utilizes not only the reinforcement effect of geotextiles to achieve the self-stability of the entire reinforced soil system, but also utilizes the filtration performance of geotextiles to prevent the loss of soil particles backfilled, thus addressing both the symptoms and root causes of the collapse. However, the interface interaction between reinforcement and soil is so complex in this method that the corresponding design method of reinforcement is still not clear. In previous studies, the design method of reinforcement focuses on the prevention of collapse before its occurrence. In this kind of method, reinforcement materials are generally used with sufficient anchoring length for full paving. As for the design method of treatment after collapse, there are few studies on the range selection of paving reinforcement. In addition, the maximum tensile force of geotextile will affect its strength design and then impact the overall strength of the reinforced body. Therefore, the previous studies on anchoring length and the lack of theories on calculating reinforcement force have restricted the application of reinforcement in engineering practice.In order to accurately calculate the maximum tensile force of the reinforcement and to study the anchoring length of the geotextile, a design method for reinforced treatment of karst roadbed collapse was proposed. Firstly, the simplified Bishop's strip method was used to analyze the soil force. According to the characteristics of tension action between reinforcement and soil, the calculation formula of the reinforcement force in subsidence areas and stability areas was deduced by assuming that the deformation of the reinforcement was catenary. Meanwhile, with the assumption that the anchoring force of the reinforced body was greater than the maximum tensile force to ensure the settlement stability of the subsidence area, a calculation formula for the reasonable anchoring length of the reinforcement was worked out and the relevant design procedure of the anchor length was sorted out. Additionally, based on the test results of existing models and the comparison with previous calculation methods, the calculation method of adding reinforcement tension and of the reasonable anchoring length was verified, on this basis of which the parameter design was conducted according to the relevant experimental results. It was assumed that the vertical stress in the stability area was roughly distributed in a decreasing exponential form. Finally, the effects of collapse width and maximum deflection of the reinforcement on the tensile force and on reasonable anchoring length were analyzed. The results show that firstly, a design method of anchoring length of geotextile reinforced cushion for treating urban road collapses in karst areas has been established in this study. In order to ensure the reliability of the proposed design method of reinforcement, the methods of determining values involving the vertical stress distribution function P(x) of the tensile force reinforcement should be taken into account, one is the value determination by model tests or numerical means; another is the value estimation according to the classical earth arch theory. Meanwhile, when determining the anchoring length, it is necessary for us to introduce the corresponding factor of safety in combination with the actual situation to ensure the project quality. Secondly, the calculation results by the design method in this study are more consistent with the test results of other methods, which suggests that the proposed method not only increases the safety of preventing karst subgrade collapse, but also effectively improves the utilization effect of reinforcement. The result is of referential value for engineering practice. Moreover, the design method in this study also shows that both the anchoring length and the tensile force of reinforced body demanded by geotextile are big when the range of subgrade collapse is large. Thirdly, the collapse width is the main factor affecting the force of the reinforced body and the reasonable anchoring length. But the maximum deflection of the reinforced body has little effect on the reasonable anchoring length. Therefore, it is necessary to choose the anchoring length of the geosynthetics for the subgrade with a high standard required by the tendency to road deformation.
Risk assessment of water inrush disasters of karst tunnels based on variable weight-cloud model: A case study of Zhongliangshan tunnel
LI Hui, WEI Xingping, LIU Cheng, LI Liangxin
2023, 42(3): 548-557, 572. doi: 10.11932/karst20230306
Abstract FullText HTML PDF(2180KB) icon136 icon41
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In order to solve the uncertainty and complexity of risk factors and the subjectivity of risk assessment of water inrush disasters in karst tunnels, the risk of water inrush disaster has been scientifically assessed. According to the Zhongliangshan karst tunnel project on the middle route of Chengdu-Chongqing, the study constructed a risk assessment model of water inrush disasters in karst tunnels based on variable weight-cloud model. First of all, referring to the research methods of Wu Xin, Liu Dunwen and others, and consulting professors in the field of geological disasters and engineers from tunnel construction and inspection units, a total of 8 experts determined the grade and classification standard of each influencing factor on water inrush disasters of karst tunnels, and clarified the parameter value of each influencing factor of Zhongliangshan tunnel on the middle route of Chengdu-Chongqing. In this study, five influencing factors were selected to construct an index system of risk assessment of the water inrush in karst tunnels. These five factors include formation lithology (calcium carbonate content in strata and rock structure), geologic structures (water-conducting fault structure, water-blocking fault structure and fold structure), surface catchment conditions, tunnel spatial locations and alternating conditions of groundwater circulation. In addition, the grading standards of water inrush disasters were determined, and accordingly the disasters were divided into five risk levels, low, mild, moderate, high and highest.Firstly, the cloud model was used to determine digital characteristics of the risk level of each index. The diagram of membership cloud of each influencing factor was drawn by MATLAB. The single factor membership degree (μj(x)) of each influencing factor was calculated according to parameter values of water inrush disasters in karst tunnels. Secondly, the analytic hierarchy process (AHP) was used to determine the constant weight. In order to avoid the situation that the constant weight does not change with the state value of the index to be evaluated, the punitive variable weight method was used to determine the variable weight vector (W(x)) and the comprehensive membership degree (U). Finally, according to the principle of maximum membership degree, risk levels of water inrush disasters in karst tunnels were calculated, and water inrush disaster situations of 7 sections in Zhongliangshan Tunnel on the middle route of Chengdu-Chongqing were determined. The results show that water inrush disasters in Zhongliangshan tunnel are between level III and level VI, with a high risk. Among them, DK15 + 630-DK15 + 680 and DK16 + 750-DK16 + 78 are the sections with a moderate risk; DK16 + 020-DK16 + 460 are of high risk; DK14 + 720-DK15 + 630, DK15 + 680-DK16 + 020, DK16 + 460-DK16 + 750 and DK16 + 785-DK17 + 380 are the sections with a highest risk. Water inrush disasters of karst tunnels can be attributed to a variety of influencing factors. The parameter value of each influencing factor of the high-risk section is higher than that of the low-risk section, and the risk of water inrush disasters in a transition zone between a karst area and a non-karst area is the highest. With the large porosity, the developed karst, and active groundwater, the soluble rock stratum is a three-medium system of pores, fissures and pipelines, which provides conditions for the occurrence of water inrush disasters and thus increases disaster possibility.The assessment result is in consistency with the actual situation of water inrush and tunneling. The consistency indicates that the risk assessment index and its system are applicable to water inrush assessments in karst tunnel areas. The cloud model intuitively reflects a fuzzy membership of risk; the variable weight theory constructs an equilibrium function, and each index is weighted according to the specific situation. It is a good solution to the problem of mutual neutralization between the indexes in the risk assessment of water inrush in karst tunnels, which is conducive to observing the change range and relative importance of each index. The risk assessment method of water inrush disasters of karst tunnels constructed in this paper can realize the objectivity of risk classification of water inrush disasters in tunnels from a multiple decision-making perspective, which is applicable to the risk assessment of karst tunnels and provides reference for the tunnel quality control and life assessment in the future.
Monitoring subsidence characteristics of Baishazhou karst area in Wuhan with Sentinel-1 images from 2015 to 2019
YANG Chen, DENG Fei, SHI Xuguo
2023, 42(3): 558-564. doi: 10.11932/karst2023y018
Abstract FullText HTML PDF(1537KB) icon1533 icon38
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The karst region of southwest China includes , Guizhou, Yunnan, Guangxi, Sichuan, Hunan, Hubei, Guangdong and Chongqing. The region has a warm and humid climate with heavy rain, making it a zone of high incidence of geological disasters. China experienced 6,181 geological disasters in 2019, up 108.4% from 2,966 in 2018. These disasters caused the direct economic loss of 1.7 billion yuan, accounting for 61.4% of the total in China. Two hundred and twenty-four people are dead and missing, with 98 people in the karst mountainous areas of Chongqing, Sichuan, Guizhou, and Yunnan.Numerous Chinese cities, including Guiyang, Guilin, Wuhan, Shenzhen, Guangzhou, etc., are situated in karst regions. According to statistics, more than 30 large and medium-sized cities and 420 counties and cities in China are located in high-risk locations for ground collapse. One of the primary causes of geological disasters like ground collapse and ground deformation in cities is the development of subsurface karst, abundant karst groundwater, and a specific thickness of soil layer. In Wuhan, there is a sizable region of covered karst with extremely complicated geological conditions that are primarily distributed in an NWW-SEE direction. The Yangtze River is crossed by several karst belts. Consequently, karst environmental geological problems are widespread in this region, and karst geological disasters have resulted in considerable financial losses. The survey data shows that there have been more than 40 karst collapses since 1994. Human engineering activities have increased in intensity with the ongoing urbanization. Geological disasters have been happening more frequently year after year.The technologies such geological radar detection, the automatic monitoring of sensor for water pressure dynamic change in karst pipeline system, the survey monitoring with the precise level, GPS monitoring, Interferometric Synthetic Aperture Radar (InSAR), etc. are used to monitor surface deformation in karst areas. Among them, InSAR has been widely used as a method to monitor wide-range deformation with high precision in recent years. InSAR shows its advantages of all-weather, all-time, extensive spatial coverage, weather durability, and high precision, compared to other conventional monitoring techniques. In this study, the researchers used InSAR technology to conduct time series analysis on the data of Synthetic Aperture Radar (SAR) such as TerraSAR-X, COSMOSkyMed, Sentinel-1, Radarsat-2, etc. This data was obtained in Wuhan at different time periods, which can indicate that the subsidence mainly occurred in soft soil areas and karst areas with intensified human activities.Situated in Wuhan at 30° 28′ 0′′–30° 32′ 24′′ north latitude and 114° 12′ 30′′–114° 18′ 45′′ east longitude, the study area covers the embankment of the Yangtze River and the Zhoutou sub-district in Hanyang district, Baishazhou sub-district in Wuchang district, and Zhangjiawan sub-district and Qingling sub-district in Hongshan district, in which the alluvial lacustrine plain and the denudation accumulation hillock are dominant landforms and the terrace is developed in the river valley. Holocene loose sediments from the Quaternary primarily cover the surface. Clayey soil makes up the higher portion of the lithology, and silty fine sand makes up the lower portion. The risk of a karst collapse is high because the loose deposits are buried beneath soluble carbonate rocks. The historical karst collapse spots in the study area, mainly situated in the alluvial lacustrine plain. Due to intensified human activities, the incidence of karst collapse has also been increasing year by year, which can be indicated by 23 karst collapses between 1931 and 2019.In this study, the elevated orbit Sentinel-1 SAR data set covering the high incidence area of karst collapse in Baishazhou, Wuhan, was analyzed with the time series of InSAR. Additionally, the land subsidence in the study area was identified and analyzed from April 2015 to September 2019. In the study area, the surface is mainly covered by loose deposits of the Quaternary Holocene, with cohesive soil in the upper part and fine sand in the lower part. The underlying soluble carbonate rocks under loose deposits may pose a high risk of karst collapse. Land subsidence resulted from the weight of the Quaternary soil covering the karst area has significantly increased by the concentrated summer rain. At high incidence zones of karst collapse in Baishazhou sub-district and Zhangjiawan sub-district, seasonal deformation signals connected to rainfall are discovered based on time series analysis, and the deformation rate is roughly 15 mm·a−1. Attributed to human construction activities, ground subsidence with a maximum deformation rate of 30 mm·a−1 was also discovered in the depot of Metro Line 6 and Qingling sub-district. This study establishes the value of InSAR technology in identifying geological risks in karst regions. A significant amount of SAR data can be offered for geological disasters in karst areas thanks to the development of Sentinel-1 and the upcoming NISAR mission of the United States. It is anticipated that, in the future, land subsidence monitoring products with large range, high precision and hightime-resolution will be available for the prevention and control of geological disasters.
Influence of the Xuzhou paleochannel alluvium on karst collapse and engineering construction
WEI Yongyao, JIANG Guoqing, HUANG Jingjun, XU Shiyin, WU Xin
2023, 42(3): 565-572. doi: 10.11932/karst2021y35
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According to historical records, from 1128, when the Yellow River encroached the Huai river to flood the Sishui river, to 1855, when the Yellow River flowed through Xuzhou, the Yellow River flooded many times, causing several changes in the direction of the surface water system and the repeated scouring and burying of the paleochannel, which has contributed to the complexity of today's paleochannel in terms of its direction, burial depth and stratigraphic structure, over these seven hundred years.In this paper, the characteristics of changes, erosion, identification, depth and stratigraphic structure of the Xuzhou paleochannel are analyzed through data collection, field exploration, drilling, geophysical exploration and other geological methods, and the influence of alluvium formed by the paleochannel on karst collapse and engineering construction has been studied. It is concluded that since the late Pleistocene, a total of 5 rivers have flowed through Xuzhou. Among them, there are 2 paleochannels in late Pleistocene, both originating in Shandong and entering Xuzhou City from north, and 3 in the Holocene, namely, the ancient Sishui river, the ancient Bianshui river and the ancient Yellow River. Besides, the strata of the Xuzhou paleochannel were firstly formed by the flood of the Bianshui river and the Sishui river, and then by the alluviation of the Yellow River. Therefore, the strata are characterized by "new" (The age is young, mainly formed by the flooding of the Yellow River.), "soft" (Many strata present the large compressibility with high water content), "miscellaneous" (The strata contain bricks, tiles, stones and pottery of the underground ancient city.), "changing" (The large area of cover caused by the flooding of the Yellow River not only buried the ancient city, but also changed the landform). Furthermore, the paleochannel has created favorable geological structure for the formation of karst collapse because the formation of superimposed silt and silt deposits as well as the scouring to the old clay that is steadily distributed formed a replenishment skylight of underlying karst aquifer. This is also the main reason why the collapse points are densely distributed near the paleochannel. Finally, due to the strong water abundance near the paleochannel, the construction of the subway shield is subject to the sand inrush caused by silt and mealy sand. At the same time, the special stratigraphic structure and engineering geological characteristics of the paleochannel will have a great influence on the stability of foundation pit engineering and shallow foundation buildings, and hence corresponding engineering measures should be taken during the project construction.
Hydroclimate variability in early stage of late Holocene recorded by stalagmite from Southern Thailand
YIN Jianjun, XU Qi, SIRIPORNPIBUL Chaiporn, SIRIPATTARAPUREENON Russarint, WU Xia, TANG Wei, CHENG Hai, NING Youfeng, QIN Zhengfeng
2023, 42(3): 573-581. doi: 10.11932/karst20230307
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The climate change during the transition of the middle-to-late Holocene (4.2 ka event) is linked to the collapse of many paleo-cultures worldwide. However, it is still controversial in the following two questions, Is the 4.2 ka event global, and what is the relationship between the climate change and its societal effect? Though it is difficult to identify the relationship, we can construct paleoclimate records from different places all over the world to identify whether the 4.2 ka event is global. In the karst survey in 2019, we found many ancient cultural remains in caves of Southern Thailand, and the time span of many remains covers the 4.2 ka event. However, there are relatively few records on the 4.2 ka event with high precision and high resolution that can reveal the climate and environment in this area. To better understand the 4.2 ka event, we choose the stalagmite record from Phet Cave in Southern Thailand to verify the event in a tropical area.The climate in Southern Thailand is dominated by the tropical monsoon system. The mean values of annual temperature and precipitation are 27.1 ℃ and 2,390 mm, respectively. Precipitation in the rainy season from May to November accounts for 76% of the annual value. The Phet Cave (8°23′36″N, 98°46′26″E, 54 m a.s.l.) is a dry underground river cave developed along the local fault, and the cave environment is relatively stable. The stalagmite D008-05 is a pure aragonite stalagmite with a length of about 18 cm and a diameter of 5-6 cm. To determine the age of the stalagmite, 10 powder subsamples were collected for 230Th/U dating through the Neptune MC-ICP-MS in the Isotope Laboratory of Xi'an Jiaotong University. We got the dating results with relatively high precision-high uranium and low 232Th concentration. The age model was constructed through the StalAge. We confirm that the stalagmite grew in the early stage of the Late Holocene, from 3,738 a B.P. to 3,906 a B.P., and the mean growth rate was 0.95 mm·a−1. We drilled the δ18O and δ13C samples from the top of the stalagmite with an interval of 1 mm, and a total of 160 samples were collected. Then we obtained an annual resolution for the high growth rate. The δ18O and δ13C were analyzed through a MAT 253 mass spectrometer equipped with a Kiel IV carbonate device at the Institute of Karst Geology, Chinese Academy of Geological Sciences. Previous studies suggest that the moisture source of precipitation in the rainy season of Southern Thailand is mainly from the Bay of Bengal, and the precipitation δ18O in this area is mainly influenced by the local convective activity and rainfall amount. Therefore, we suggest that the stalagmite δ18O can be used to reflect the rainfall amount in this area. The synchronous variation of δ18O and δ13C also suggests that both the δ18O and δ13C can be used to reflect the hydroclimate change in Southern Thailand. The relationship between precipitation and stalagmite δ18O and δ13C is shown as follows,heavy precipitation is correlated with lower δ18O in precipitation/stalagmite, and lower soil CO2 δ13C, and no prior calcite deposition (PCP) occurs in the aquifer, and thus leading to higher stalagmite δ13C, and vice versa for low precipitation. The decreasing trend of δ18O and δ13C of the overall stalagmite D008-05 is following the decline of Asian summer monsoon intensity, which is dominated by the decrease of north hemispheric summer insolation in the tropical area. Two decadal-scale drought events were identified between 3,850-3,840 a B.P. and 3,805-3,795 a B.P. The spatial comparison result indicates that these two events happened in many places in the Asian monsoon region. In addition, we found the hydroclimate change in Southern Thailand is dominated by the south-north movement of the Intertropical Convergence Zone (ITCZ), and it is also influenced by the solar activities and El Niño-Southern Oscillation (ENSO) state in the interannual-to-decadal timescales. Strong solar activates will produce more summer monsoon rainfall in Southern Thailand, whereas weak solar activities will induce less summer monsoon rainfall in Southern Thailand. Different from solar activities, the relationship between the ENSO state and summer monsoon rainfall is as follows: in the El Niño state, the summer monsoon rainfall is suppressed, and in the La Niña state, the summer monsoon rainfall is enhanced. We found that the dry trend during the 4.2 ka event had a potential effect on the paleo-culture in Southeast Asia, which caused the change of subsistence pattern from hunting and gathering to crop cultivation and domesticating pigs. As the decrease of precipitation and sea level, more land was outcropped near the river, seacoast, and river delta, which provided more land for rice planting. Besides, the improvement of production tools by culture exchanges also led to life style change in Southeast Asia.
Variation of stalagmite growth rate and its paleoclimatic significance in Sanbao cave, Hubei Province over the past 640,000 years
JIANG Ying, WEI Wei, FENG Xiaoyi, ZHANG Han, ZHU He, DONG Jinguo
2023, 42(3): 582-589. doi: 10.11932/karst2021y31
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In the past few decades, great progress has been made in the study of stalagmite paleoclimate. Compared with the geochemical indicators such as stalagmite δ18O, the average growth rate of stalagmite is a physical indicator, which can directly reflect the wet and dry changes of the external climate, and is one of the important means to reconstruct the past regional hydrological changes.Sanbao cave (31°40′N, 110°27′E), the study area, is located in Shennongjia National Nature Reserve, Hubei Province, on the north bank of the Three Gorges of the Yangtze River and adjacent to the southern edge of the Loess Plateau. Mainly affected by the East Asian summer monsoon, the average annual temperature in this area is 8-9℃ with the annual precipitation of 2,000 mm. In summer, warm and humid air from the equatorial ocean enters the hinterland of the mainland, bringing about 60% of the annual precipitation. In winter, the dry and cold air from Siberia controls the climate in Shennongjia area, so it is particularly sensitive to the seasonal advance and retreat of East Asian summer monsoon. Sanbao cave, 1,900 m above sea level, is located on the northern slope of Shennongjia Mountain in Hubei Province, covered with limestone layer about 300 m thick. The thickness of the surface layer is about 2-3 m, mainly distributed with trees, shrubs and weeds. The research objects are five stalagmites (numbered SB12, SB14, SB32, SB58 and SB61) from Sanbao Cave, with a cumulative height of about 2.991 m, of which SB61 was deposited in 229.4-384 ka B.P., corresponding to MIS8-MIS10; SB14 grew and developed from 299.6-622.8 ka B.P., spanning from MIS9 to MIS15; SB12 and SB58 were respectively deposited at 425.1-462.7 ka B.P. and 426.7-464.7 ka B.P., corresponding to MIS12; SB32 grew from 514.3-638.2 ka B.P., and spanned from MIS13 to MIS15. 167 230Th age data of these five stalagmites was obtained by the analytical instruments of Thermo-Finnigan Element and Thermo-Finnigan Neptune in Minnesota Isotope Laboratory, the USA. The age analysis error was ±2σ measurement statistical error with the error accuracy of 0.5-2.0 ka. For the calculation of average growth rates of stalagmites, firstly, the data of stalagmite age reversal in stratigraphy has been excluded. Then, the curve of the measured age point of stalagmite and its corresponding growth depth has been established. The new results are basically consistent with the growth rate curve in the original literature. Finally, the average growth rates of stalagmites have been obtained by dividing the depth difference between two adjacent points by the measured age difference.Based on 167 230Th age data from 5 stalagmites spanning 220,000 to 640,000 years in Sanbao cave, and combined with the past work, this paper has reconstructed the precipitation change process of East Asian summer monsoon (EASM) in the middle and lower reaches of the Yangtze River over the past 640,000 years in the late Pleistocene. The results show that the growth rates of stalagmites in Marine Isotope Stages (MIS) 1, 5.3, 5.5, 7.3, 7.5, 9, 15.1, 15.5 increased significantly, indicating that the intensity of EASM increased significantly with more precipitation in the interglacial stage. On the contrary, the slow or undeveloped growth rates in the glacial stage indicate the weakening of the summer monsoon intensity with less precipitation. Based on statistical analysis of the growth rates of 22 stalagmites, we hold that the average growth rate index cannot quantitatively indicate the change of the monsoon intensity. Moreover, when the stalagmite growth rate is less than 10 µm·a−1, it also cannot effectively indicate the glacial-interglacial change. On the orbital scale, the glacial-interglacial fluctuation revealed by the average growth rate may be attributed to the joint action of global ice and solar radiation. Finally, it should be noted that in different time scales, the controlling factors of stalagmite growth rate are complicated, and the noise generated by the environment difference inside the cave may cover up or weaken the transmission of the climate signal from the outside to the inside. Therefore, the possible influencing factors must be carefully considered when we reconstruct the paleoenvironment by using the average growth rates of stalagmites.
Climatic and environmental changes during Heinrich 6 recorded by δ13C in stalagmites from Jinfo Cave, Chongqing
Zulisaisi, YANG Xunlin, WANG Yong, HU Mingguang, XU Yibin
2023, 42(3): 590-602. doi: 10.11932/karst2023y008
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Of the six Heinrich events (H event for short) occurring during the last glacial period, H6 event has been less studied due to its earliest occurrence time. However, using high-resolution stalagmite records to study climate and environmental changes during H6 event can help people understand the response of climate change at high and low latitudes to the H events. In recent years, much progress has been made in terms of studies on paleoclimate and environmental changes with use of stalagmite δ13C records. Besides, some stalagmite δ13C records have been used to study the climate change of the events on a millennium scale during the last glacial period, but there is no detailed record of the high-resolution climate change in Southwest China during the H6 event. In this case, the JF2017 stalagmite δ13C may provide an excellent proxy for exploring the climate and environmental change during H6 event. Based on the dating data of uranium series and carbon isotope data of JF2017 stalagmite in Jinfo Cave, we analyzed the climate significance indicated by stalagmite δ13C, and reconstructed the evolution process of the monsoon climate environment in Southwest China during H6 event.Developed from the Jinfo-Yangzi Cave system, Jinfo Cave is located in Jinfo Mountain, Nanchuan district, Chongqing, Southwest China, with an altitude of 2,080 m. The Jinfo Mountain area belongs to subtropical humid monsoon climate, which is jointly affected by the Indian Summer Monsoon and the East Asian Summer Monsoon (ASM). In this study, the age samples of stalagmites were tested by Neptune Plus Multi-receiver Plasma Inductively Coupled Mass Spectrometry (MC-ICP-MS), and the carbon isotopes of stalagmites were tested by Delta-V-Plus gas isotope ratio mass spectrometer and carbonate automatic sampling device Kiel-IV online. The experimental results are based on Vienna Pee Dee Belemnite (V-PDB) with δ13C experimental analysis error<0.06 ‰(2σ). According to data analysis, the variation range of stalagmite JF2017 δ13C is from -1.44 ‰ to -4.92 ‰, with an average value of -3.40 ‰. JF2017 stalagmite δ13C fluctuates significantly, and change amplitude is -3.48 ‰. JF2017 stalagmite δ13C records show that the value mainly presents a negative-positive-negative-positive trend during the period of 63,000-58,000 a B.P. Due to the complex influence factors of stalagmite δ13C, we compared JF2017 stalagmite δ13C records with JFYK7 stalagmite δ18O records in Yangkou Cave which belongs to the same cave system as Jinfo Cave in order to further analyze the climate significance of stalagmite JF2017 δ13C. The comparison indicates a similar variation between the stalagmite stable isotope records of Yangkou Cave and JF2017 stalagmite δ13C records. Through previous research, JFYK7 stalagmite δ18O is indicative of variations in ASM intensity, and the positive shift in stalagmite δ18O corresponds to weakened ASM. In this study, we observed that the stalagmite JF2017 δ13C value was slightly positive, corresponding to the positive JFYK7 stalagmite δ18O. Therefore, under the background of weakening ASM, JF2017 stalagmite δ13C records can reflect the change of ecological environment caused by the change of regional hydrological climate. In addition, the comparison between JF2017 stalagmite and the stalagmites from other caves indicate that JF2017 stalagmite δ13C records were comparable with other climate records during H6 event. From 61,811 a B.P.to 60,848 a B.P., the values gradually became heavier, reaching to the maximum, and then fluctuated on a short-time scale. Finally, from 60,848 a B.P. to 59,716 a B.P., they became slightly lighter to the end of H6 event. The comparison between JF2017 stalagmite δ13C and other relevant records in the rest of the world shows fluctuations in the stalagmite δ13C record, so do the corresponding ITCZ and AMOC.This study shows that the stalagmite JF2017 δ13C value was significantly heavier during the 61,811 ± 204 a B.P.-59,716 ± 159 a B.P. period, lasting for about 2,095 a, which may suggest that the monsoon weakened and the ecological vegetation degraded during this period. This result corresponds to the North Atlantic H6 event. During H6 event, stalagmite JF2017 δ13C records became heavy to the maximum value during the period of 61,811-60,848 a B.P., followed by the fluctuation change on the short-time scale. During the period of 60,848-59,716 a B.P., the values slowly became lighter to the end of the H6 event. The trend of becoming light after a gradual increase of weight and a climate shock inside on a centennial scale indicate that the local climate was unstable during H6 event. The monsoon climate change on a centennial scale recorded by stalagmite JF2017 may be closely related to the Intertropical Convergence Zone (ITCZ) and the North Atlantic meridional overturning circulation (AMOC).
Study on the prioritization of stakeholders engaging in educational tourism of karst cave with methods of AHP and Grey Clustering: A case study of Furong Cave in Chongqing
ZHOU Yanling, YANG Xiaoxia
2023, 42(3): 603-615. doi: 10.11932/karst20230308
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With the deep integration of culture and tourism, educational tourism has developed rapidly in China. As a tourism product integrating education, educational tourism is helpful to promote the upgrading of cave tourism so that precious cave resources can be developed scientifically and reasonably. Educational tourism can also enhance the value of resources, and extend the life cycle of cave tourism destinations. At the same time, cave educational tourism can enrich educational tourism products, help to cultivate students' core geographical literacy, and guide them to actively participate in the practice of ecological civilization construction. In recent years, products of karst cave educational tourism, a kind of characteristic tourism, have been increasing. As the cave educational tourism is an interdisciplinary and integrated new business form, many stakeholders participate in it. But the difference of stakeholders' demands may affect the healthy and sustainable development of the karst cave educational tourism. In order to solve the current development dilemma, it is necessary for us to define and sort out different stakeholders and list the order of their importance.Situated in Wulong district of Chongqing in China, Furong Cave is affiliated with Wulong Karst Tourist Area in which some famous scenic spots such as Fairy Maiden Mountain, Three Natural Bridges, and Longshui Gorge are located. Chongqing, where Furong Cave is located, is an experimental zone of educational tourism approved by the Ministry of Education and the only one at a provincial level in China. Wulong district is an experimental district of both social practice and educational tourism for primary and secondary schools in Chongqing. In recent years, relying on tourism resources, Wulong district has endeavored to plan and develop educational tourism. The district has issued a number of policies and documents supporting the development of educational tourism, and planned to transform Furong Cave into an educational tourism base featuring karst heritage and culture. At the same time, Furong Cave was also selected as "2021 National Top Five Caves for Educational Tourism" by Committee on Cave Research, Geological Society of China.Based on the stakeholder theory and gray system theory, this study is focused on the prioritization and classification of stakeholders engaging in educational tourism of Furong Cave with methods of qualitative and quantitative research, such as analytic hierarchy process, gray clustering method, and Mitchell subdivision method. Firstly, through news mining, telephone interviews and literature analysis, stakeholders were selected. Secondly, based on the stakeholder classification as well as the actual situation of educational tourism of Furong Cave, indexes were determined to build the evaluation model for the importance of educational tourism of Furong Cave. Then, by collecting expert evaluation data and performing the gray clustering model based on the central point mixed whitening weight function, the prioritization of stakeholders were obtained and classified. The study results show that,(1) Ten types of stakeholders engage in the educational tourism of Furong Cave, including managers of Furongdong Scenic Area, government departments, enterprises supported by tourism, institutions of educational tourism, primary and secondary schools, students, tutors of educational tourism, students' parents, associations and experts in tourism industry, and public media. There are differences among stakeholders in power, economic dependence, influence of social interests, urgency of demand and initiative of taking risk. Different stakeholders exert different influences on educational tourism in scenic spots.(2) The prioritization in a descending order of stakeholders engaging in educational tourism of Furong Cave is listed as follows, managers of Furongdong Scenic Area, government departments, institutions of educational tourism, primary and secondary schools, enterprises supported by tourism, tutors of educational tourism, associations and experts in tourism industry, students' parents, students, and public media.(3) According to the ranking of tourism industry, the relevant stakeholders can be divided into core stakeholders (managers of Furong Cave Scenic Area, government departments, institutions of educational tourism, and primary and secondary schools), important stakeholders (enterprises supported by tourism, tutors of educational tourism, and associations and experts in tourism industry) and general stakeholders (students' parents, students and public media).According to the study results, it is suggested that the managers and operators of scenic spots of karst cave should pay attention to the changes in the demands of various stakeholders, organize and manage stakeholders in an orderly and classified manner with the principle of differential order, and cooperate with them to promote the healthy and sustainable development of educational tourism of karst cave.
Cave expedition and histoplasmosis, a kind of cave disease
SUN Chenghang
2023, 42(3): 616-626. doi: 10.11932/karst2023y016
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Histoplasmosis is an invasive fungal infection, which might breakout among people who are exposed to the Histoplasma capsulatum, usually, Histoplasma capsulatum var. capsulatum. This disease is an occupational disease of cave explorers, but many cavers or cave managers have never learned, or known very little about it. In order to popularize the disease and its prevention among karst cave geologists, cave explorers and managers, this review introduced histoplasmosis through seven sections following the introduction of histoplasmosis as one of the threats faced by cavers during cave survey in the preface. The first section retrospect research history about the discovery of histoplasmosis and its pathogenic fungus, Histoplasma capsulatum, on the basis of papers published by US scientists, Samuel T. Darling in 1906 and 1908, William DeMonbreun in 1934 and 1939, as well as Chester W. Emmons in 1947 and 1948. The second section introduced definition of cave sickness and investigation on the source of infection in cave. The third section summarized the research evidence how bat spread Histoplasma capsulatum to caver, some important papers published in Science by Martha H. Shacklette in 1962 and Marinkelle C J in 1965 were cited in the section. The fourth and fifth section discussed geographical distribution of histoplasmosis in the world and in China, respectively. Furthermore, in the fifth section, the analysis of histoplasmosis cases in China from three different groups in different period, such as case statistics of 1990-2011 by Pan Bo from Shanghai Changzheng Hospital, case statistics of 2001-2014 by Yu Jie from Huashan Hospital and case statistics of 2001-2019 by LYU Xin from Xiangya Hospital, all data showed Yunnan, Hubei, Hunan, Chongqing, Jiangsu, Guangdong, Sichuan, Zhejiang,Shanghai,Guangxi, most cases came from in China. Meanwhile, in the fifth section, the earliest histoplasmosis cases in China in 1950s were looked back. On the basis of histoplasmosis outbreaks in China and the World, the sixth section summarized the knowledge on how to protect cavers from histoplasmosis infection during cave exploration and provided suggestion about how to prevent histoplasmosis outbreaks for cave managers and local health authorities. In addition, a real story on an outbreak of febrile histoplasmosis among Chinese manganese-mine workers in cooperative Republic of Guyana in 2019 was stated on the basis of two papers published in China CDC Weekly, 2019 and Chinese Journal Infection Chemotherapy, 2020 and one thesis published by Chongqing Medical University in 2021. In the final section, it was emphasized how to prevent to carry unintentionally Histoplasma capsulatum through the caving equipment during international visit for joint expedition.

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