中国岩溶

Thinking and practice on the research direction of karst water in northern China

LIANG Yongping, SHEN Haoyong, ZHAO Chunhong, WANG Zhiheng, TANG Chunlei, ZHAO Yi, XIE Hao, SHI Weizhi

2021, 40(3): 363-380.

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The carbonate aquifer in northern China is an important water resource of the country with large thickness and wide distribution. The karst water in this vast region has the functions in water resources，tourism and ecology. It plays an important role in the construction of national economy，especially in the construction of urban water supply and energy infrastructures. In the past 50 years，due to the influence of large-scale development and other high-intensity human activities，karst water environment problems in northern China have become prominent and brought a series of negative effects，which seriously restrict sustainable utilization of water resources. Under the background of ecological civilization construction vigorously advocated by the state，how to coordinate well the development of resources and environment in the northern karst areas is an issue that needs to rethought by the hydrogeological work industry. Starting from the national demand，this paper points out that the ecological reflow of cutoff karst springs，the pollution prevention and control of the acid "old kiln water" in closed coal mines，and the development and utilization of deep karst water and thermal resources should be taken as the key research directions of karst water in the future in northern China. At the same time，this paper briefly presents the results of investigations and research on these issues in recent years.

Distribution of soluble rock strata and development of karst landforms in the Batang area, west Sichuan plateau

KANG Xiaobing, YANG Sifu, GUAN Zhende, ZHANG Wenfa, XU Mo

2021, 40(3): 381-388.

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This paper focuses on Batang county and Baiyu county， west Sichuan plateau. Based on data from field investigations， we analyze the geological background， topography， lithologic characteristics and distribution of carbonate rocks in exposed strata from Triassic to Cambrian， especially rock composition， structural characteristics and the distribution of karst development in the study area. The features of carbonate strata and law of karst development in the study area are systematically summarized. Results show that the soluble strata in the study area are distributed in a NW-SE direction， indicating an obvious control of regional geological structure. The karst landform development in the study area is consistent with that in the main areas of Tibetan plateau， belonging to the paleokarst formed by the exposed surface of the cover-type karst， which developed and evolved in a tropical-subtropical environment during Tertiary time with many karst types and distinct morphology and scales. Statistics of the karst development degrees of different carbonate rock formations shows that the Devonian depression occupies the largest area， and the Triassic and Silurian carbonate strata have more depressions， but their development density is lower than the Devonian. The number and area of Permian depressions are the smallest. The density of the Carboniferous karst depressions is the largest because of their relatively high purity and concentrating exposure.

Distribution, genesis and age of travertine at Hongshan, Jiexiu, Shanxi Province

WEI Rongzhu, HAN Ying, XU Qinmian, WEI Yunfeng, DU Yanwei, FAN Junhui

2021, 40(3): 389-397.

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In Shanxi Province，besides the travertine scenic spots in Niangziguan，the travertine scenery in Hongshan town，Jiexiu，located at the foot of Huqi mountain，is another potential karst landscape with great geologicaltourism value. It has relatively large exposure range， stable thickness and beautiful forms. Systematic geological investigations and profile measurement have been made to the Hongshan travertine. Research has been conducted on its distribution，occurrence，rock characteristics，petrochemical characteristics and isotopic chronology. In light of the karst water cycle，this work then analyzed the formation mechanism，influencing factors and generation age of the travertine，providing a geologic basis for the protection and landscape development of travertine in the area.

Hydrochemical characteristics and genesis of karst groundwater in the Baiquan spring catchment

WANG Rui, LI Xiaohan

2021, 40(3): 398-408.

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Karst groundwater in the Baiquan spring catchment is the main water supply source for industrial and agricultural production and urban and rural life in Xingtai City，Hebei Province. In recent years，influenced by changes of natural conditions and human activities，the groundwater flow field in this spring catchment has changed obviously，while the evolution mechanism of its hydrochemical field remains unclear. To solve this problem，on the basis of hydrogeological surveys and sample collection and testing，this work used statistical methods（descriptive statistics，Person correlation coefficient），saturation index calculation and hydrochemical methods（piper diagram，stiff diagram，Gibbs diagram，coefficients of ion proportion）to study the hydrochemical characteristics of karst groundwater in the spring catchment. The results show that the karst water in this area is weak-alkaline fresh water，in which Ca2+，Mg2+，HCO3- and SO42- are the main ions，mainly resulted from the weathering dissolution of calcite，dolomite and gypsum，and Na+ and Cl- are mainly from the dissolution of halite. Calcite changes from a dissolution state to an equilibrium state along the flow direction，while dolomite，gypsum and halite are always in a dissolution state. Karst groundwater in the recharge area and northern runoff area are basically the HCO3-Ca·Mg type. In addition to HCO3-Ca·Mg type，types of HCO3·SO4-Ca，HCO3·Cl-Ca·Mg and HCO3·SO4-Ca·Mg also occur in the karst groundwater near the Qili river，Sha river and coal-iron mine areas in the south. The increase of SO42- in the karst groundwater near the mine areas is attributed to the mixture of mine drainage with high SO42- content. Evaporation is only obvious in the discharge area with shallow water level and relatively slow groundwater flow. The Baiquan spring in the discharge area is HCO3·SO4·Cl-Ca·Mg type. In addition，industrial and agricultural activities have changed the runoff conditions and water quality of groundwater，resulting in rise of the content of NO3-，Cl-，Fe and total hardness in local karst groundwater or even exceeding the standards .

Characteristics, formation models and water cycle differences of ten major spring groups in Jinan City

SUN Bin, XING Liting, PENG Yuming, LI Changsuo

2021, 40(3): 409-419.

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The purpose of this work is to systematically and comprehensively understand the ten major spring groups in Jinan City. By comparison， characteristics of the distribution，flow，landscape and water quality of these spring groups are revealed. Through fine description of hydrogeological structure and analysis of spring discharge conditions，the genetic differences of the spring groups are further clarified，the formation modes of spring water are summarized，and the differences of water cycles are clarified. The results show that the ten spring groups can be roughly divided into two categories，six ascending spring groups in the drainage area and four descending spring groups in the southern supply area. Their formation models can be divided into five types：structural uplift and limestone "sky light"，structural uplift and crack connection，shallow multi-layer sand layer and high permeability clay conduction， crack cutting and erosion overflow. Macroscopically，the water circulation of the ten spring groups in Jinan is controlled by the northward inclined monocline structure，in which the input conditions，transport systems and output modes have small differences. On a micro scale，there are obvious differences in the way of spring water output among the six pressure spring groups， of which the type，thickness，permeability of limestone overburden and burial depth of limestone roof vary greatly，resulting in different spring water outflow forms，flow and water quality，forming their own unique landscapes. The detailed study on the micro genesis of karst springs can provide an important geological basis for the classified protection of the ten spring groups in Jinan.

Dynamic characteristics and influence factors of discharge of the Longzici karst spring in Shanxi Province

WANG Dawei, QIAO Xiaojuan, GAO Bo, JIA Xiaojun

2021, 40(3): 420-429.

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The Longzici spring is located in front of the Xishan mountains, 13 km southwest of Linfen City, Shanxi Province. The spring area is 2,250 km2. The exposed strata are dominated by Cambrian and Ordovician, Carboniferous Permian, Triassic and Cenozoic Quaternary. Overall, the geological structure of the spring area is featured by uplift on the north and south sides, and a depression in the central part. The north is the Longzici syncline, which forms syncline mountains in topography, and the south is an underground structure sloping to the north or northeast. The recharge in this area is dominated by precipitation infiltration in the exposed carbonate rock area, followed by surface runoff infiltration recharge from the Carboniferous-Permian sand shale area. The aquifer is dominated by the Cambrian-Ordovician carbonate water-bearing rock group.In order to explore the spatial-temporal variation characteristics and response laws of spring dynamics in karst water-bearing systems, this paper uses a 65-year time series of spring water flow and precipitation monitoring data from 1954 to 2018 and mining data from 1990 to 2018, and employs the stepwise analysis of multiple regression methods to establish the response relationship models of spring discharge, precipitation and mining in stages. Then using the models we simulate and predict spring discharge over a long time sequence. The research results of this paper can provide data support for the prevention and control of the flow attenuation in the Longzici spring area. The conclusions of this article are as follows，(1) The precipitation ranges 287.2-868.7 mm with a multi-year average 541.1 mm in the spring area. More precipitation occurred after 1990 than before, and there was a four-month time lag in the response of spring flow to precipitation replenishment during the year. The average extraction volume of karst water for many years is 3.233 million cubic meters, and the average extraction volume of pore water in the piedmont area is 8.243 million cubic meters. When the extraction volume remains at a relatively high level, the spring flow generally shows a significant downward trend.(2) The spring flow fluctuates between 2.94-8.39 m3·s-1, and the multi-year average flow is 4.74 m3·s-1. Before 1990, the average flow was 5.61m3·s-1, while after 1990 it was 3.68 m3·s-1. In addition to factors such as mining and precipitation that affect spring flow, local coal mining activities also affect spring flow dynamics, which need to be analyzed in subsequent studies.(3) The results of multiple regression show that the main influencing factors of spring flow in the first stage (1954-1989) were the precipitations of the previous year and the previous two years. In the second stage (1990-2018), the spring flow was restricted by both precipitation and mining and was negatively correlated with the mining volume of the year, most strongly affected by it; followed by the precipitation of the previous year and the previous two years. Error analysis shows that the flow error in the entire time series is 11.62%, implying a good simulation effect.

Relationship between the surface water system structure and the flood peak in the Xiangxi river karst basin

FAN Wei, CHEN Zhihua, NIU Junqiang, LI Wei, WANG Liang, HUANG He

2021, 40(3): 430-438.

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The Xiangxi river basin is located in the mountainous area of western Hubei Province with an area of about 3，211 km2. The basin hosts a tectonic erosion and dissolution landform, with gentle elevation variations. The terrain is generally high in the north and low in the south. The Xiangxi river is a large tributary close to the Three Gorges Dam, with a length of 97 km and an average annual flow 40.6 m3·s-1. The Nanyang river, Gufu river and Gaolan river are the major tributaries of the Xiangxi river, covering an area of 678 km2, 1,183 km2 and 928 km2, respectively. The strata are well exposed in the basin, except for the absence of carboniferous and Cretaceous strata, from the metamorphic rocks of Shuiyuesi group of Archean to the loose rocks of Quaternary system. The study area is basically an exposed karst area, where carbonate rocks are widely distributed, which generally reflects the characteristics of the transition zone between north and south karst, and groundwater flows from north to south on the whole.The purpose of this work was to study the structural characteristics of the surface water system and the attenuation process of flood peak flow in the karst area. The drainage structure of typical sub-basins was analyzed by a statistical method, and the drainage attenuation equation was used to examine the typical dewatering process. The results show that topographic slope affects the development of the water system by affecting the erosion ability of slope runoff. The greater the slope is, the stronger the scouring force of surface runoff is, and the more developed the water system. The stratigraphic lithology is an important factor affecting the development of the water system. Karst development, water system density, river frequency and other water systems in the carbonate river basin are small in number, but the water system length is large. The attenuation rate of surface water flux is variable, and the dewatering coefficient decreases with time. There are several sub-dynamic state in the flow attenuation process of surface water. The water distribution ratio of each sub-dynamic state is taken as the characteristic value to describe the characteristics of flood peak, and the number ratio of the water system and length ratio of water system are taken as the characteristic values to describe the structure of the water system for correlation analysis. The results show that the ratio of water length in the karst area has a high correlation with the ratio of the water volume in the first and third sub-dynamic states, with a correlation coefficient as high as 0.84. The ratio of water length in the karst area can better characterize the structure of the water system.

Causes of drought and models of drilling wells for water exploration in the Gexiang river basin of the Wumeng mountains

CAO Jianwen, ZHAO Liangjie, WANG Zhe, LUAN Song, ZHANG Qingyu, YI Rui

2021, 40(3): 439-448.

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Groundwater is an important drinking water source in the Gexiang river basin of the Wumeng mountains area. Because of the complex development law of groundwater and the huge topographic relief, the development and utilization of groundwater are facing big difficulties, resulting in water shortage in the vast area. To solve this problem, the hydrogeological investigation team of Institute of Karst Geology used the comprehensive investigation, exploration and the evaluation method of karst groundwater and the combination method of effective geophysical exploration of "three determinations" to clarify the occurrence and development law of groundwater in the study area, reveal the genetic mechanism of frequent droughts in the basin, establish four types of water storage structure models, summarize five types of locations with rich water, and effectively apply them to severe droughts in the water shortage area. The success rate of well location increased more than 70%, which has solved the problem of drinking water for more than 20,000 people in the basin, and effectively aided in the effort of poverty alleviation.

Spatial estimation model and migration analysis of soil total calcium content in the Maolan karst area, Guizhou Province

YANG Shengtian, LI Xi, LOU Hezhen, LUO Ya, LI Chaojun, WANG Pengfei, WU Xijin, ZHANG Jun

2021, 40(3): 449-458.

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Calcium is an important element in the karst environment. In this work，we collected soil total calcium data in Libo-Maolan Nature Reserve in Guizhou，a world natural heritage site， and analyzed the effectiveness of spatial analysis in the geographic weighted regression（GWR）method. Through identifying the main factors affecting the spatial distribution of soil total calcium，a calculation model for the spatial distribution of soil total calcium in the karst area was established to obtain basic data for studying the spatial distribution of soil total calcium. The soil erosion status was calculated by the soil erosion equation（USLE），and the spatial correlation between soil total calcium and soil erosion was comparatively analyzed to reveal the spatial migration law of soil total calcium. Results show that，（1） under the condition of consistent lithology，the relative height difference and slope are the dominant factors affecting the spatial distribution of total calcium in the soil. （2）The prediction accuracy of the GWR model is better than the global regression（OLS），of which the correlation coefficients are 0.41 and 0.39，respectively. （3）The spatial distribution characteristics of soil total calcium in the study area were calculated by the spatial estimation model of soil total calcium， yielding soil total calcium ranging from 0 to 37.68 g?kg-1. Research suggests that in the karst region with humid climate，despite the large vegetation coverage，the spatial distribution of total soil calcium is still highly affected by the soil-forming parent material. Karst peak forests have high soil erosion intensity，high soil total calcium content，and material migration is dominated by loss. The soil in peak clusters and depressions has low soil erosion intensity and low total calcium content， where the material migration is dominated by leaching loss.

Response traits of the chlorophyll a fluorescence to saturation and subsequent continuous dehydration in five karst plants

XING Deke, YU Rui, CHEN Lu, WU Yanyou, ZHAO Yuguo, LI Lin, FU Weiguo

2021, 40(3): 459-465.

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The heterogeneity of karst habitat together with the diversity of plant adaptive mechanism makes the reasonable allocation of pioneer plant in karst regions very difficult， which affects the efficient governance of the degraded karst ecosystem. Research on the diversity of plant photosynthetic adaptive mechanism can help complete the anchorage of plants and heterogeneous karst drought habitats. In this work， the naturally-grown leaves of five karst plants were selected as materials and treated with saturation and subsequent continuous dehydration. The chlorophyll fluorescence parameters were determined， and the response traits of photosynthetic process were investigated， which provides a basis for the rapid evaluation of plant drought resistance. The results indicate that the leaf photosynthetic process of Rhus chinensis exhibits better adaptability to great variation of leaf water content， and the activity of PSII reaction center and electron transport rate are inhibited by high water stress. However， the stable light energy conversion can help maintain the photochemical efficiency， which is attributed to the increasing chlorophyll concentration. The leaf water retention capacities of Broussonetia papyrifera and Lonicera japonica are relatively high， the chlorophyll concentration increases with water losing and maintains stable subsequently. The PSII reaction center of Broussonetia papyrifera is sensitive to water loss， but the activity of PSII reaction center and light energy conversion efficiency show adaptability to the long-term continuous dehydration. The photosynthetic structure of Lonicera japonica is not damaged seriously， and the activity of PSII reaction center is stable. The leaf water retention capacity of Pyracantha fortuneana is worse than that of other plants， but the chlorophyll concentration increases significantly from the fourth hour. The stability of photosynthetic structure， electron transport rate and the portion of light energy absorbed by leaf that is used for photochemistry are better than that in Lonicera japonica under continuous dehydration conditions. Myrica rubra is a non-karst plant， of which the chlorophyll concentration decreases under long-term dehydration. The activity of the PSII reaction center is inhibited， and the photosynthetic structure is damaged. Meanwhile， the electron transport rate of Myrica rubra is too low to show significant variation as water losing continues， and the photochemical efficiency would be inhibited by the low electron transport rate.

Relationship between surface soil pollen and modern vegetation in karst trough area of Zhongliang mountain, Chongqing City, SW China

WANG Qirong, JIANG Yongjun, HAO Xiudong, MA Lina, ZHANG Caiyun, QIN Linjuan, ZHENG Yang, QIU Hua

2021, 40(3): 466-475.

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The objective of this work was to ascertain the sources of pollen in the karst depression of the Zhongliang mountains，Chongqing. On samples of surface soil and moss polsters from a karst trough in this area， we examined the relationship between pollen assemblages and modern vegetation by pollen analysis. The result show that the pollen assemblages have a good correspondence to each vegetation type. Cultivated areas，abandoned areas，shrub lands，pinus massoniana forests and bamboo forests can better reflect the composition of the parent vegetation community. The mixed forest and the parent vegetation community have a poor correspondence，and the main sporepollen types show adaptability to the karst environment feature. Depression surface samples can reflect regional vegetation more than other samples due to convergence of the depression. Among the pollen of depression surface zones，pinus pollen is over-representative，which is from the Zhongliang mountains area and the southwest wind area. Quercus，Alnus，Pterocarya and Humulus can partly reflect the vegetation，which mostly come from the vegetation in the surrounding mountains. Poaceae has a low-representative feature，of which the sources are relatively complex. These results will provide useful information for the study of Quaternary paleovegetation，paleoclimate as well as paleoenvironment using palynology in this area.

Temporal and spatial differentiation of the ecosystem service value in typical fault-depression basins

LIANG Jintao, DENG Yan, CAO Jianhua, JIN Zhenjiang, LI Xuyao

2021, 40(3): 476-486.

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A typical fault-depression basin—the Xiaojiang river basin is chosen as the research area in this work. Based on the three-phase land-use data of 1982, 2003, and 2016, the Costanza ecosystem service value formula is used to evaluate the ecosystem service value. “Spatial-temporal” characteristics of ecosystem service values are described under coexisting geologically differentiated structures. The results show that， (1) the Xiaojiang river basin is dominated by farmland ecosystems, and the ecosystem pattern was generally stable during the study period. The cultivated land, construction land, forest land, and garden land increased to varying degrees, while the area of unused land decreased, and the water area was largely unchanged. (2) From 1982 to 2016, the total value of ecosystem services in the study area showed an upward trend. The total value of ecosystem services in 1982, 2003, and 2016 were 90.11 × 108 yuan, 105.65 × 108 yuan, and 136.81 × 108 yuan, respectively. The ecosystem service value of the forest land, forest land, garden land and water area increased as a whole, while that of the unused land decreased. (3) On the whole, the ecosystem service value of the southern and eastern Xiaojiang river basin increased significantly, while the ecosystems of the central and western regions increased significantly. The service value showed a gradual change or continuous decline. The ecosystem service value of the Xiaojiang karst valley area was the highest, while the ecosystem service value density of the sedimentary flat dam area was the lowest, which was the unique decline ecosystem service function area. (4) During the study period, the value of various ecosystem services in the Xiaojiang river basin showed an upward trend, and the regulation services were dominant, and the service value of climate regulation was the highest. The value of ecosystem services in the Xiaojiang river basin lacked elasticity, and changes in the area of water ecosystems amplified the variations in ecosystem values in the study area. The implementation of comprehensive rock desertification management projects such as mountain closure and forestation, returning farmland to forests, and small watershed management projects can enhance the value of ecosystem services.

Photosynthetic characteristics of Broussonetia papyrifera and Morus alba under rock outcrop habitat in karst area

LI Huan, WU Yanyou, WU Yansheng

2021, 40(3): 487-494.

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Taking the karst-adaptable plant species， Broussonetia papyrifera as the target， and the non-karst-adaptable plant （Morus alba） as the contrast， this study compared photosynthetic responses of different plant species to rock outcrop habits. Research suggests that the soil in a rock outcrop habit has higher water content and more organic matter than that in a non-rock outcrop habit. The light response curve and carbon dioxide response curve of photosynthesis， chlorophyll fluorescence parameters， water potential （LWP） and carbon stable isotope values （δ13C） of leaves were measured. Results show that there is no significant difference in LWP and δ13C between different habitats in the two plant species， while there exists a significant difference in chlorophyll fluorescence parameters of the same plant species except for the initial fluorescence parameter （F0）. The respiration rate and carboxylation efficiency （CE） of Broussonetia papyrifera do not change significantly in different habitats， while that of Morus alba growing in the soil of rock outcrop habit are significantly higher than those growing in the soil of non-rock outcrop habit. Broussonetia papyrifera can maintain stable CE at the expense of carbon in the plant， thus maintaining stable photosynthetic capacity under water deficit of a non-rock outcrop habit. The karst-adaptable plant species， Broussonetia papyrifera， is more adaptable to the karst environment than Morus alba.

Pollution characteristics and risk assessment of heavy metals in soils along the upper reaches of the Duliu river

ZHANG Guangyin, WU Linna, OUYANG Kunchang, WU Pan

2021, 40(3): 495-503.

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Sixty-two soil samples were collected from the karst area along the upper reaches of the Duliujiang river，Guizhou Province. The purpose was to study the cumulative pollution characteristics and spatial pattern of potential ecological risks of five heavy metals，Sb，Cd，As，Cr and Pb by comprehensive utilization of the geo-accumulation index，potential ecological risk index and Kriging interpolation methods. The results show that the average contents of Sb and Cd in the soil of the study area exceed the environmental background values of Guizhou Province by 4.085 times and 1.876 times，respectively.In terms of spatial distribution，the local serious pollution area of Sb element accounts for 37.87% of the total，which is mainly controlled by the distribution of Wangchengpo formation，Yaosuo formation and Jiwozhai formation，the ore-bearing strata in the area.However，the proportion of slightly accumulated pollution area of Cd element is 59.76%，and the distribution of carbonate rocks is the main influencing factor for its general enrichment.The potential ecological risk in the study area is of a low level，but the probability of single potential ecological risk with medium or above Cd and Sb is relatively high. The highest probability risk group of Cd is mainly distributed in the strata of Shiniulan formation and Bangzhai formation，while that of Sb is distributed in the strata of Bangzhai formation，Jiwozhai formation and Dushan formation.Therefore，special attention should be paid to the prevention and control of potential ecological risks of soil Cd and Sb in the strata of Shiniulan formation，Bangzhai formation，Jiwozhai formation and Dushan formation in karst areas.

Influence of geological and geomorphologic features on karst rocky desertification in northwestern Hunan Province：A case study of Zhangjiajie City

GONG Shuhua, ZHU Lifen

2021, 40(3): 504-512.

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This work made an overlay analysis using geographic information technology （GIS）， DEM，geological structure，lithological characteristics and geomorphological data. The objective was to examine the influence of geological and geomorphological factors on the distribution of karst rocky desertification in the Zhangjiajie area， northwestern Hunan Province. The results show that the occurrence rate of karst rocky desertification in this area exhibits the characteristics of hilly>depressions> low mountains> middle mountains> high mountains. In terms of slope，the occurrence rate of rocky desertification is the highest among the grade II slopes，and the rocky desertification area is sunny. The distribution is featured by slope>semi-shady slope>shady slope>semi-sun slope，and with the slope direction from cloudy to sunny，the proportion of karst rocky desertification area of various grades gradually increases. In terms of stratum lithology，carbonate and clastic interbedded rock formations are more prone to karst rocky desertification. In terms of geological structure，the spatial distribution of rocky desertification is in the same direction as the fault structures，and the influence of faults on rocky desertification is mainly reflected in the impact on the two walls in the IB fault. The differences in lithology and strata pose influence on the development and distribution of water systems.

Response of cave air and hydrogeochemistry of drip water to local climate in the Liangfeng cave，Guilin City

WU Xia, PAN Moucheng, YIN Jianjun, WANG Zhijun, ZHU Xiaoyan, YANG Hui, ZHANG Meiliang, CAO Jianhua

2021, 40(3): 513-520.

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he hydrogeochemistry of cave drip water is an important environmental index in cave systems, to which the monitoring may be an essential solution for paleoclimate reconstruction. In this study, we collected samples from three drip points in the Liangfeng cave of Guilin City, southwest China, from January to December 2017. During the monitoring period, we measured the hydrogeochemical properties of the drip water (electrical conductivity, pH, Ca2+, HCO3-), and CO2 concentration was simultaneously collected at the same monitoring points. Then these monitoring proxies were compared with regional atmospheric temperatures and precipitation amounts. Results show that the hydrogeochemical index exhibits seasonal variations as water transforms from precipitation to cave drip water. Under the influence of the CO2 in the overlying soil layer on the top of the cave, the cave CO2 and δ13CCO2 present obvious seasonal variation patterns of high and light in summer, and low and heavy in winter, respectively. Differences in monitoring site CO2 and δ13CCO2 values are caused by the barrier of inner structure of the cave and retention time difference in epikarst. However, δ13CCO2 amplitude relative to the CO2 response is more sensitive to outside atmosphere environment, and cave CO2 the major influence factors are obviously different in different seasons. The major influence factor is soil CO2 in summer, while atmospheric CO2 is the major influence factor in winter. The hydrochemical index of drip water shows obvious seasonal variation. Although the precipitation amount increases in summer which bring more soil CO2 into the pipes or fissures of the cave, the mixing of precipitation with "old water" in the surface karst zone makes it rise slowly as a whole. The decrease of seepage water supply caused by seasonal drought in the Guilin area leads to the relative decrease of the dissolution of surrounding rock, which makes it become a hydrochemical index. In addition, the variation of the hydrochemical index of each drip point is mainly due to its different runoff paths.

Seasonal variations and sources of dripping CO2 in karst caves: A case study of the Dafeng cave, Guizhou Province

TANG Yuntao, ZHOU Zhongfa, WANG Yanlin, ZHANG Jie, TIAN Zhonghui, XUE Bingqing

2021, 40(3): 521-530.

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The purpose of this work was to clarify the characteristics of CO2 changes and its sources in the dripping water of the Dolomite caves. Taking the Dafeng cave，part of the Shuanghe cave system，as the research object， monitoring， sampling and laboratory analysis were conducted to cave air CO2 concentration （pCO2（c）），soil CO2 concentration （pCO2（soil）），cave drip CO2 partial pressure（pCO2（w）），and cave dripping hydrochemical environment for 15 months（January 2016 to March 2017）. Then principal component analysis was performed on each monitoring index using the statistical analysis method. Results show that，（1）pCO2（w） and pCO2（c）have obvious seasonal variations，which are characterized by summer-autumn> winter-spring. pCO2（soil）is affected by rainfall and cave ventilation，which is the main source of pCO2（w） in caves.（2）Water-rock interactions of osmotic water flowing through caves over the karst zone，especially the hydrochemical environment and its HCO3- change are one of the main factors affecting pCO2（w）， an important contribution to the pCO2（w）.（3）Using principal component analysis（PCA），the contribution of each factor to cave drip is as follows，HCO3->pCO2（s）>Soil 1#>pCO2（w）>Soil 2#. The contribution comparison of each factor to pCO2（w） is as follows：deep karst on the surface > soil air environment on the cave > cave air environment.（4）The conceptual model on the source of pCO2（w）suggests that during the rainy season，the rainfall is large，the soil is infiltrated quickly，the groundwater is fully replenished，but the stagnation time is short，the reaction with the surrounding rock is insufficient in the seepage zone，and the PCP process is weak， posing a big influence on pCO2（w），while the dry season is the opposite. These research results have certain theoretical and practical significance for the protection of cave stalagmites and stalactite sediments. It is of great significance to the development and utilization of cave tourism and the study of karst carbon cycle.

Study on the developmental characteristics and mechanism of ectopic stone flower at Duoleyuan karst caves in Yunnan

WU Guangfen, WANG Jiaxue, YANG Li

2021, 40(3): 531-538.

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Stone flowers （calcite flower， aragonite flower and gypsum flower） are a kind of common secondary chemical sediment in karst caves， which widely distribute on the wall of caves， stalactites， stalagmites and the surface of collapse accumulation bodies，and their shape is varied with different causes of formation.The stone flower on the surface of some high-hanging secondary chemical sediments at the Duoleyuan karst caves in Yunnan is found to be an ectopic stone flower. The cause of formation is that ectopic stone flower was formed by the synergistic action of dripping and splashing during the formation of stone pillars， then the ancient river deposits below the stone pillars were eroded and transported， some stone pillars were suspended to form new stalactites or stalactites-like sediment， hence，the stone flower attached to the bottom of stone pillars were relatively raised and exposed. The ectopic stone flower was firstly discovered in Yunnan，which could be used as an important basis for indicating the evolution of micro-geomorphology in karst caves.

Features of geological relics and genesis of the Chanjiayan Tiankeng group in Ningqiang, Shaanxi Province

REN Juangang, HONG Zenglin, ZHANG Jing, TANG Li, LIU Xiaofeng, QIN Zhen, WANG Peng, WANG Yan

2021, 40(3): 539-547.

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Abstract:
The Tiankeng group in Hanzhong, Shaanxi Province is located in the northernmost of the humid tropics and subtropics between 32°N to 33°N, adjacent to the Hanzhong basin and the Qinling orogenic belt in the north and the central Sichuan uplift belt in the south. It is a unique and typical window karst type with complete karst system, good ecological environment and unique landscape. It is praised as "the great geographical discovery of the 21st century" by National Geography of China. This geologic feature has important scientific values for the comparative analysis of paleogeographic environments and climate change in north and south China and even in the world.The Tiankeng group of Chanjiayan in Ningqiang , Shaanxi Province is one of the four relatively independent karst systems in the Tiankeng group of Hanzhong, which lies in the northern margin of the Yangtze block. Bounded by the Dazhuba-Xinji fault (F1), in the north it belongs to the foreland thrust fold zone of Longmen mountains in Ningqiang; and in the south, it is part of the thrust syncline fold belt with nearly EW-trending Liping fault in the Hannan-Micangshan uplift area, which hosts various geological relics in complex geomorphology. Through a lot of field investigations, this paper sorts out the distribution characteristics of the geological relics and analyzes the basic characteristics and the causes of the main geological relics to reveal the formation and evolution mechanism of karst under the canyon landform in the north-south transitional zone. Results show that， (1) The geological relics of the Tiankeng group in the Chanjiayan area can be classified into 2 major groups, 4 types and 5 sub-types, which are characterized by Tiankeng, platforms, karst caves, canyons and secondary chemical sediments. (2)The karst landform is typical, in which Tiankeng and karst cave developed very well. (3) Affected by deep canyons, there are four surface karst platforms in the study area, all of which have relatively independent karst hydrogeological characteristics, and the Tiankeng and shaft have entered the degradation period. (4)Tiankeng was generated during the Neotectonics under the action of strata, lithology and structure.

Construction of a karst knowledge discovery system based on knowledge graph

YANG Chen, BI Benteng, ZHOU Lixin

2021, 40(3): 548-554.

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Abstract:
The karst field has accumulated a large number of outcome resources through geological surveys and scientific research. The relationship between resources is more complex，and the traditional keyword retrieval model cannot meet the needs of users to acquire knowledge. In order to realize data retrieval at the knowledge level，data mining technology is used to extract and calculate karst entity relations. With karst terminology as the core，a karst knowledge discovery system is constructed based on the knowledge graph. Intelligent semantic search for and related navigation to karst geological results，journals，papers，books，standards，projects，experts and other entities are realized to maximize the potential of data mining. It provides users with precise knowledge services and improves the user experience.

2021 Vol. 40, No. 3

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