中国岩溶

Estimation of the carbon sink of rock weathering by remote sensing and analysis of its spatiotemporal variations

ZHANG Yu, LUO Weiqun, LIU Meiling, LI Mengqi, ZHANG Li, CHEN Fangfang, ZHANG Yangcen, CHEN Rui

2024, 43(4): 727-741. doi: 10.11932/karst20240401

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As a type of natural carbon sink, rock weathering plays a critical role in the global carbon cycle by storing atmospheric carbon dioxide (CO₂). This process is particularly significant in mitigating climate change, although its contributions are often underestimated or overlooked in broader carbon calculation practices. The present study focuses on Guizhou Province, China, a region that is characterized by extensive karst landforms. These landforms are of particular interest because they are highly effective in capturing atmospheric CO₂ through rock weathering. This study aims to explore the spatiotemporal dynamics of the carbon sink of rock weathering from 2001 to 2020. This study integrates various data sources, including remote sensing data, meteorological records, and lithological information, to estimate the carbon sink capacity with the GEM-CO₂ model. This study also employs advanced analytical techniques such as Dynamic Time Warping (DTW) and statistical methods to analyze the spatiotemporal evolution of carbon sink. The findings of this study reveal that the rock type is a primary factor influencing the rate of rock weathering and CO₂ consumption, followed closely by annual precipitation. The temperature also plays a significant role, although the responses of its effects are observed to be lagged. This indicates that changes in temperature may affect CO₂ absorption rates several years after the initial temperature fluctuation occurred. This study identifies that the regions with the highest CO₂ consumption through rock weathering are predominantly concentrated in the northeastern, southwestern, southern, and southeastern parts of Guizhou Province. These areas are characterized by widespread formations of carbonate rocks and higher precipitation levels, which can jointly enhance the weathering process and increase carbon sequestration. In contrast, the northwestern regions, which are dominated by silicate rocks and receive lower levels of precipitation, exhibit the lowest levels of CO₂ consumption. This discrepancy underscores the importance of both lithological composition and climatic conditions in determining the effectiveness of natural carbon sink. From 2001 to 2020, the annual average karst carbon sink in Guizhou Province ranged from 0 to 1.04×10³ t C·km⁻²·a⁻¹. Although there was a general trend of fluctuation, the overall pattern showed an increase in carbon sequestration capacity. However, the analysis did not reveal any significant single trend over the two decades. This lack of a clear trend suggests a complex interplay between geological and climatic factors that influence carbon sequestration in karst landforms. The variability in carbon sink capacity observed in this study highlights the sensitivity of natural carbon sink to the changes in environmental conditions, particularly in precipitation and temperature.The spatial distribution of carbon sink closely mirrors the distribution of carbonate rocks in Guizhou Province. This correlation emphasizes the critical role that carbonate rocks play in the global carbon cycle due to their high solubility, which can accelerate the process of CO₂ absorption. Areas with more annual precipitation were found to have a greater capacity for carbon sequestration, and this result reinforces the importance of hydrological factors in the weathering process. This finding is particularly relevant for the regions that are expected to experience changes in precipitation patterns due to climate change, as it suggests that shifts in hydrological conditions could have a significant impact on the efficacy of natural carbon sink.In addition to these findings, this study also highlights the importance of both geological formations and climatic conditions when the carbon sequestration potential of different regions are estimated. The application of the GEM-CO₂ model in this study provides a robust framework for estimating the carbon sink at a regional scale. The effectiveness of this model in this context offers critical data that can be used to guide the development of carbon trading mechanisms and environmental policies aimed at enhancing the natural carbon sink. By integrating geological and climatic data, this model allows a more nuanced understanding of the factors that contribute to the carbon sequestration in karst landforms.The insights gained from this study are invaluable for informing carbon management strategies, particularly in regions with similar geological and climatic conditions. The findings of this study suggest that the carbon sequestration through rock weathering could be a viable component of mitigation efforts for climate change in a wider range. However, the fluctuating nature of carbon sink over the study period indicates that the natural carbon sink is highly sensitive to changes in environmental conditions. This sensitivity underscores the need for adaptive management strategies that can respond to changes in climate and ensure the continued effectiveness of natural carbon sink.Furthermore, this study lays the groundwork for future research to explore the further implications of rock weathering in global carbon cycles. It advocates a more integrated approach that considers both natural and human factors of mitigating climate change. As the climate change continues altering global weather patterns, understanding the role of natural processes like rock weathering in the carbon cycle will be increasingly important for us to develop effective strategies to manage and mitigate the impacts of climate change.

Rock weathering and carbon sink effects under exogenous acid action: A case study of the Yanggong river

LI Xueyan, LI Canfeng, YANG Kehao, CHEN Rui, XIONG Yinhong, WANG Xingrong, WANG Chuanyu

2024, 43(4): 742-752. doi: 10.11932/karst20240402

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Rock weathering in the river basin is not only an essential carbon source and sink mechanism, but also an important link in the global carbon cycle. Rivers are indispensable components of water bodies, and the hydrochemistry of rivers is a representation of the degree to which weathering and denudation occur at the surface of the river basin. Therefore, it is possible for us to collect information on rock weathering in the river basin by conducting an analysis of the chemical compositions of rivers. In turn, the analytical results can be used for the estimation of weathering rates and the amount of carbon dioxide that is consumed by the Earth's atmosphere. The presence of exogenous acids in the process of rock weathering in the river basin has an impact on the geochemical cycling of carbon as well as the carbon source/sink effect. The chemical weathering rate of carbonatite is accelerated by sulfuric acid, but the weathering does not consume atmospheric carbon dioxide. As a result, the effect of sulfuric acid on carbonatite weathering should be taken into consideration when the amount of atmospheric carbon dioxide that is consumed by rock weathering in the basin is calculated.The Yanggong river is a part of the Jinsha river system located in the upper reaches of the Yangtze river. The process of rock weathering and the influence of carbon sinks in the Yanggong river basin are not yet fully understood. As a result of climate warming, the considerable increase in water output from the high-altitude area of this basin has accelerated the water cycle there. This will undoubtedly exert a strong influence on rock weathering rates and geochemical cycling processes that occur within the Yanggong river basin. In addition, a large number of coal layers are distributed in this basin, so the sulfuric acid produced by sulfide oxidation or the dissolution of carbonate rocks by sulfuric acid caused by human activities would also alter rock weathering rates in this basin. For this reason, it is necessary for us to do more research in order to quantify the effect of exogenous acids on rock weathering as well as on the carbon source and sink in the Yanggong river basin.In this study, water samples from main streams and major tributaries of the Yanggong river were collected during the dry and rainy seasons of 2023. The major concentrations of anion and cation, metasilicic acid, and total dissolved solids (TDS) in these water samples were examined. Additionally, different types of rock weathering in the Yanggong river basin were analyzed by the water chemical equilibrium method and the Galy estimation model. Finally, the amount of carbon dioxide that was consumed by rock weathering under the combined effect of carbonic acid and sulfuric acid was estimated. The findings indicated that the ionic compositions of the water system in the Yanggong river basin were mostly derived from the weathering of silicate and carbonate rocks, and the hydrochemical types were either the HCO₃-Ca type or the HCO₃-Ca·Mg type. Sulfuric acid and carbonic acid worked together to contribute to the process of rock weathering in this basin. The atmospheric CO₂ consumption of rock weathering in this basin was 38.35 t CO₂·km⁻²·a⁻¹ when sulfuric acid was not taken into consideration. However, when sulfuric acid participation was taken into consideration, the carbon sink of rock weathering was reduced to 25.54 t CO₂·km⁻²·a⁻¹, with a reduction of approximate 33%, which significantly improved the accuracy of the calculation. The atmospheric CO₂ flux consumed by carbonatite weathering contributed 95.5% of the total, which indicated dominance of the atmospheric CO₂ flux consumed by carbonatite weathering in the Yanggong river basin. The quantity of atmospheric CO₂ consumed by rock weathering in the Yanggong river basin is 4.27×10⁴ t CO₂·a⁻¹, suggesting a process of carbon sink. That sulfuric acid participated in the process of rock weathering in the river basin changed the regional carbon cycle is a significant link that cannot be overlooked in the model of the global carbon cycle. Meanwhile, in studies on the carbon source/sink effect of rock weathering in the river basin, it was essential for us to consider the regional geological background, particularly the types of minerals rich in sulfides.

Spatiotemporal patterns of CO₂ efflux fluxes from the outflow of karst underground river: A case study of the Panyang river in Bama, Guangxi

XIAN Jinmei, SONG Xianwei, ZHANG Le, LIN Peixin, WEI Yuechun, YANG Qubao, GAN Wenjing, YANG Lu

2024, 43(4): 753-765. doi: 10.11932/karst2024y009

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Karst basins are key regions for rock weathering and carbon sinks. Because water bodies in karst basins contain high concentrations of dissolved inorganic carbon (DIC), and can affect carbon cycle through both lateral migration of DIC and vertical efflux of CO₂, they become research hotspots for CO₂ efflux. Although there have been many studies on CO₂ efflux fluxes in karst rivers, our understanding is still limited in terms of the spatiotemporal variations in CO₂ efflux fluxes of water bodies from the outflow of karst underground rivers.In order to explore the spatiotemporal patterns of partial pressure of carbon dioxide (pCO₂) and CO₂ efflux flux from the outflow of karst underground rivers, this study focused on the Panyang river in Bama in the karst area of Southwest China. Monthly routine sampling of surface water and groundwater as well as sampling based on rainfall events was conducted from July 2022 to April 2023. The spatiotemporal variations of pH, alkalinity, total dissolved solids (TDS), DIC, dissolved organic carbon (DOC) and pCO₂ in both the surface water and underground water were explored. The relationships between DIC, DOC and pCO₂, as well as the relationships between TDS, alkalinity, and DIC, were also analyzed. The controlling factors of pCO₂ were discussed, and the CO₂ efflux flux was estimated.The results showed that alkalinity, TDS, DIC and pCO₂ of groundwater in the basin were significantly higher than those of surface water, indicating that karst carbonate weathering released a large amount of DIC into groundwater, and the outflow of groundwater resulted in the CO₂ efflux, reducing the DIC content and pCO₂ of surface water. There was no significant difference in DIC concentrations and pCO₂ of surface water from upstream to downstream, indicating that groundwater could release CO₂ into the atmosphere in a short time and quickly reached equilibrium. During the rainy season, DIC and pCO₂ of groundwater showed an increasing trend from upstream to downstream, while during the dry season, they showed a decreasing trend, indicating that rock weathering during groundwater recharge is an important source of inorganic carbon in groundwater. Alkalinity, TDS, DIC, pCO₂ and CO₂ efflux flux of surface water and groundwater during the dry season were significantly higher than those during the rainy season, mainly due to the dilution effect of rainwater during the rainy season. In addition, there were high DOC concentrations during the dry season, and the mineralization of DOC contributed directly to CO₂ production, which also led to higher pCO₂ in the dry season compared to the rainy season. Overall, there were no significant differences in pH, alkalinity, TDS, DIC, DOC and pCO₂ of surface water and groundwater under rainfall events, possibly due to insufficient rainfall or its short duration. However, several samples during rainfall events showed significantly higher pCO₂ than in the regular rainy seasons, because the continuous heavy rainfall likely raised the water level of underground rivers and supplied high CO₂ concentrations from groundwater to surface rivers. There was no significant correlation between DOC and pCO₂, possibly because the carbon input from other sources disrupted the coupling relationship between DOC and pCO₂. These sources include soil CO₂, organic carbon synthesized by CO₂ that was absorbed by photosynthesis of plants, and human activities. A large amount of carbonate and other salt-based ions released from carbonate rocks into groundwater through dissolution increased DIC content, TDS and alkalinity, which contributed to a significantly positive correlation between DIC and indicators such as alkalinity and TDS. The CO₂ efflux flux of surface water in the Panyang river basin during the dry season (2.05 ± 1.89 kg C m⁻² year⁻¹) was significantly higher than that during the rainy season (0.40 ± 0.30 kg C m⁻² year⁻¹), and the CO₂ efflux flux of groundwater during the dry season (4.72 ± 4.15 kg C m⁻² year⁻¹) was about 4.6 times higher than that during the rainy season (1.03 ± 0.74 kg C m⁻² year⁻¹). During the study period, the CO₂ efflux fluxes of surface water and groundwater in the Panyang river basin ranged from -0.10 to 9.20 kg C m⁻² year⁻¹ and -0.12 to 17.28 kg C m⁻² year⁻¹, with average CO₂ efflux fluxes of 1.06 ± 1.46 kg C m⁻² year⁻¹ and 2.40 ± 3.14 kg C m⁻² year⁻¹, respectively, which were much higher than the average CO₂ efflux fluxes of major global river basins (0.64 kg C m⁻² year⁻¹). Understanding the CO₂ efflux flux and its spatiotemporal variations in karst basins is of great significance for us to accurately assess the carbon budget of rivers and to evaluate the role of rock weathering as a carbon sink.

Analysis of development trend of karst carbon cycle and carbon sink effect based on Web of Science

ZHONG Liang, ZHANG Chunlai, HU Fen, CAO Jianhua

2024, 43(4): 766-779, 809. doi: 10.11932/karst20240403

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Karstification refers to the chemical dissolution of carbonate rocks by water and the deposition of calcium carbonate due to CO₂ degassing. In a macro sense, karstification can be divided into epikarstification and deep-seated (geothermal) karstification. Karst covers about 22 million km² all over the world, accounting for 15% of the land area, and is of enormous carbon sink potential. Therefore, to alleviate the pressure of carbon neutrality and help China achieve the "Dual Carbon" target, it is of great significance for us to accurately understand the relationship between karst and carbon cycle and the carbon sink effect of karst. As an important tool for us to comprehensively understand the research progress in a specific area, bibliometric analysis can measure the relationship and influence among publications through a series of mathematical and statistical tools, and hence has been applied in many research fields. In order to understand the research hotspots and the development directions in the field of karst carbon cycle and carbon sink effect, this study undertook bibliometric citation analysis on 573 contributions to the literature written from January the 1^st, 1991 to June the 6^th, 2017, based on the Web of Science core collection. CiteSpace was used to analyze keyword frequency and emergency, country (region) and institution, author impact, research hot spot, co-cited literature and evolution of research topics.In terms of the number of papers published every year, there were fewer papers published before 2007, with a slow increase from 2007 to 2014 and a significant increase after 2015. The analysis of papers published by national (region) found that the research on karst carbon cycle and carbon sink effect presented distinct regional characteristics, which was mainly led by China, followed by the United States, Europe and other regions. Cluster analysis on the top 100 keywords in 573 papers by CiteSpace software generated 11 clusters which could be summarized and integrated into 5 main clusters: 1) the carbon cycle and carbon sink of chemical weathering of carbonate rocks; 2) the carbon cycle and hydrochemical characteristics in karst water; 3) the soil carbon cycle and carbon sink in karst regions; 4) the impact of ecosystem services on karst carbon cycle and carbon sink; 5) the technology of stabilizing carbon isotopes. The analysis of authors and cited references found that the research team led by Liu Zaihua has inherited and developed the viewpoint put forward by Yuan Daoxian that karstification participates in the global carbon cycle and has a carbon sink effect. Besides, Liu Zaihua team proposed a coupled carbonate weathering model, which greatly promoted the research of karst carbon sink. The analysis of references with the strongest citation bursts shows that citations about coupled carbonate weathering model, impact of karst rocky desertification, climate change and change of land use, effects of sulfuric acid as well as ecological engineering on karst carbon sink have attracted widespread attention in a short term and can represent cutting-edge research hot spots. The time line map and the keyword time zone map of keyword clustering can clearly show the research development in the field of karst carbon cycle and carbon sink in three stages: 1) the initial stage from 1997 to 2006, in which relevant studies show that the global amount of atmospheric CO₂ uptake from weathering of carbonate rocks was estimated at 0.11–0.608 Gt C·a⁻¹, accounting for 15%–30% of global carbon leakage; 2) the stage of rapid development in research on the chemical weathering of carbonate rocks from 2007 to 2014, in which studies mainly focused on the impact of exogenous acids, runoff conditions, and vegetation cover on the weathering of carbonate rocks in different watersheds; 3) the new stage of research on carbon cycle and carbon sink after 2015, in which studies have been conducted under the guidance of karst critical zone theory based on the atmosphere–biology–soil–water–bedrock system, and they mainly focus on the effect of aquatic photosynthesis, considering the impact of climate change and land-use change.In the future, the research of carbon cycle and carbon sink in karst critical zones should be carried out under the guidance of earth system science theory. At a micro level, studies should focus on the catalysis of carbonic anhydrase in soil, microbial carbon sequestration, photosynthesis of aquatic plants and other biological carbon pumps to improve the potential of karst carbon sink. At a macro level, studies should pay attention to the impact factors such as climate change, change of land use, and change of ecosystem service functions under human activities.

Relationship between temperatures of karst caves and local average temperatures: Taking Pailong cave of Puzhehei, Yunnan as an example

YANG Mingfeng, YIN Jianjun

2024, 43(4): 780-795. doi: 10.11932/karst20240404

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Generally speaking, temperatures of karst caves are comparable to local annual average temperatures. However, the actual monitoring has found that the relationship between cave temperatures and local annual average temperatures varies in different regions. To understand the relationship between these two kinds of temperature, we monitored the temperatures of Pailong cave in Puzhehei, Yunnan Province, Southwest China. Our high-resolution monitoring discovered higher temperatures within the cave compared to the local annual average temperatures and the temperatures at the cave entrance. Temperatures at cave entrance were primarily affected by ventilation, while temperatures inside the cave were influenced by seasonal temperatures and precipitation. The monitoring revealed a stronger effect of ventilation in winter and a weaker one in summer at the cave entrance. Additionally, monthly temperatures exceeded local annual temperatures from April to October, and fell below them from November to March, indicating that longer and effective heat import and less heat loss led to higher temperatures inside the cave. Rainfall during the rainy season (May to October) formed a fast flow into the cave and transfers heat, further increasing cave temperatures. Thus, longer and effective heat import, less heat loss, and rainfall-induced heat import resulted in higher cave temperatures than local annual average temperatures.To validate our hypothesis, we collected 48 published data on cave temperatures from China and analyzed the temperature differences inside and outside the cave. Generally, the difference is positive in the north of the Yangtze River and negative in the south. It is positive in the east of longitude 110°E and negative in the west. Correlation analysis between cave temperatures and other influencing factors such as latitude, longitude, altitude, bedrock depth, and overlying vegetation index shows that there is a significant negative correlation between cave temperatures and factors of latitude, altitude, and overlying vegetation index. The same is true of the correlation between local annual average temperatures and these factors, suggesting that cave temperatures are primarily influenced by local annual average temperatures. Weak ventilation effects can be attributed to the large depth of caves, and thus resulting in a negative correlation between the temperature difference inside and outside the cave and the cave length. Interestingly, the temperature differences inside and outside the cave correlate positively with latitude and longitude. To explain this, we introduce the concept of temperatures in the warm season (April to October), when the monthly temperature minus the annual temperature is above zero. We found significantly positive correlations of temperatures in the warm season with latitude as well as with temperature difference inside and outside the cave, indicating a longer warm season and anomaly of higher temperatures in the warm season may contribute to the large temperature difference inside and outside the cave. Furthermore, the rainy season may also influence cave temperatures via heat that is generated by drip water and transported into the cave. Hence, the temperature difference inside and outside the cave is primarily influenced by heat distribution. For instance, temperatures in the warm season increase from Guilin of South China to Beijing of North China. Similarly, temperatures in the warm season also increase with longitude. For example, temperatures in the warm season increase from Wenshan of Southwest China to Guilin of South China. Although the overlying vegetation index negatively correlates with cave temperatures and local annual average temperatures, there is no significant correlation between the overlying vegetation index and the temperature difference inside and outside the cave, probably because the dense vegetation cover can reduce the heat transported to the cave and lower cave temperatures. However, the vegetation cover does not vary significantly with latitude. Additionally, differences in cave structure and environment also affect the temperature difference inside and outside the cave. For example, temperatures in the caves of Guilin are respectively equal to (e.g. Panlong cave), above (e.g. Shuinan cave), or below (e.g. Maomaotou Big cave) the local annual average temperatures. Thus, selecting appropriate caves will ensure the accuracy of statistical results in understanding the difference between cave temperatures and local annual average temperatures. Though some individual results may influence statistical results, the positive correlation between the temperature difference inside and outside the cave and latitude indicated by the 48 cave data will not change. Finally, the long-term monitoring in some closed cave systems at different latitudes can increase the precision of the results.Our study highlights the local seasonal heat distribution and heat transport in the cave as the primary factors that influence cave temperatures, and our study will contribute to a better understanding and protection of the karst cave environment.

Variation characteristics of stable hydrogen and oxygen isotopes in precipitation of Longtan trough valley and Maoba syncline in Youyang, Chongqing

SUN Tingting, YANG Yan, JIANG Xiuyang, LUO Zhenyu, TANG Yueer

2024, 43(4): 796-809. doi: 10.11932/karst2024y013

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This study aims to explore the characteristics and influencing factors of δ¹⁸O and δD in precipitation in two adjacent topographic areas of Longtan trough valley and Maoba syncline in Wuling mountain, southeastern Chongqing. Based on the sampling data about δ¹⁸O and δD in precipitation of Maoba syncline (altitude of 1,140 m) and Longtan trough valley (altitude of 330 m) in Youyang county of Chongqing in two hydrological years from June 2020 to May 2022, the meteoric water lines of the two studies areas were established, and the variation characteristics and influencing factors of hydrogen and oxygen stable isotopes in precipitation in these areas were also analyzed. The results show as follows. (1) The slopes and intercepts of meteoric water lines in Longtan trough valley and Maoba syncline exceeded those of the global meteoric water lines. The values of δ¹⁸O in precipitation in these two study areas show a significant effect of precipitation, while the influence of temperature effect is relatively weak. (2) The slope and intercept of the meteoric water line in Longtan trough valley were smaller than those in the Maoba syncline. The difference between the meteoric water lines in these two study areas was mainly controlled by the temperature and evaporation conditions during water vapor condensation. (3) The average values of δ¹⁸O and δD in precipitation in Longtan trough valley were more positive than those in Maoba syncline. The results of d-excess showed that there was a weak sub-cloud secondary evaporation of δ¹⁸O and δD in Longtan trough valley. The values of δ¹⁸O and δD in precipitation in Longtan trough valley and Maoba syncline exhibited significant seasonal changes, with negative values during the rainy season (May to October) and positive values during the dry season (November to the following April). (3) The values of δ¹⁸O in precipitation in Longtan trough valley and Maoba syncline showed a significant precipitation effect, while the influence of temperature effect is weak. During the same precipitation event, the values of δ¹⁸O in precipitation in Longtan trough valley were generally more positive than those in Maoba syncline, indicating that δ¹⁸O values in precipitation in Longtan trough valley and Maoba syncline were influenced by elevation effects. (4) The interannual variations of δ¹⁸O in precipitation in Longtan trough valley and Maoba syncline were mainly affected by the change of the proportion of water vapor transported from Indian Ocean. In the summer of 2020, the proportion of water vapor from the Indian Ocean to the study areas reached 76%, with negative δ¹⁸O in precipitation. However, the proportion decreased to 52% in the summer of 2021, with positive δ¹⁸O in precipitation. This study is of great significance for the understanding of the water cycle process in the karst trough valley areas of Southwest China and for future studies on the eco-hydrological process of Longtan trough valley and Maoba syncline.

Daily dynamics effects of microclimate of two underlying surfaces in rocky desertification areas

WANG Jia, LI Sheng, ZHENG Yanhong, PAN Wen, SUN Yan

2024, 43(4): 810-821, 853. doi: 10.11932/karst2024y023

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As an ecologically vulnerable area with the strongest karst development in the world, the karst area in Southwest China exceeds 540,000 km². Long-term human activities and frequent extreme climate have accelerated soil erosion, causing large areas of bedrock to be exposed on the surface; consequently, a rocky desert landscape with severely degraded vegetation came into being. Under the influence of the hot and humid monsoon climate, carbonate rocks underwent dissolution, which formed various heterogeneous underlying surfaces such as earth flatland and stone surface. The local microclimate differences caused by different underlying surfaces play an important role in regional vegetation restoration and ecosystem reconstruction. Current research on environmental factors in rocky desertification areas mainly focuses on water, soil and other aspects, while there is still a lack of research on microclimate of underlying surfaces.Taking two typical underlying surfaces (earth flatland and bare land) as the research objects, this study aims to explore the microclimate effects of heterogeneous underlying surfaces in rocky desertification areas. A long-term quantitative comparison in daily dynamics of near-surface temperature and humidity of these two underlying surfaces were conducted through simulation experiments. In rocky desertification areas, earth flatland is composed of polygonal rock masses exposed on the surface and patches of soil distributed inside, while bare land is normal land with no exposed rocks and no vegetation coverage. This study area is located in Puding county, Anshun City, Guizhou Province, where karst is strongly developed. The karst landform accounts for 84.27% of the county area with 60.55% of rocky desertification. The county has humid monsoon climate on the north subtropical plateau, with an annual average temperature of 15.1 °C and an annual rainfall of 1,378.2 mm. The annual total solar radiation fluctuates from 85.71 to 458.81 MJ·m⁻².Preliminary field surveys found that there were large parameter variations in rock mass shape and size, and orientation of earth flatland. In order to improve the reliability and accuracy of the observation results, this study adopted in-situ limestone and concrete pouring technology to conduct simulation construction based on the average parameters of 30 earth flatlands that have been investigated. There were three replicates for each of the two underlying surfaces. To carry out long-term monitoring of temperature and relative humidity, high-resolution iButton DS1923 temperature and humidity recorders were installed at different heights (2 cm, 40 cm and 80 cm) above the surface of the two underlying surfaces. All data analyses were performed in the R version 4.2.3. The functions of tapply and bartlett.test/var.test were used to test data normality and homogeneity of variances. If the data passed the test, one-way ANOVA would be used to conduct multiple comparisons of air temperature and humidity at different spatial heights. An independent sample t-test was used to compare the air temperature and humidity at the same spatial height on earth flatland and bare land. If the test failed, multiple sets of data would be applied for non-parametric testing and multiple comparisons through the kruskal.test function and PMCMRplus package. These two groups of data were applied for the wilcoxon rank sum test by the wilcox.test function.Daily dynamics of microclimate of bare land and earth flatland obviously differed on the spatial and temporal scales. When solar radiation was the strongest in summer, temperature at each spatial height of earth flatland was significantly higher than that of bare land (P<0.05), and the relative humidity was significantly lower than that of bare land (P<0.05), which led to warming and dehumidifying conditions. However, air temperature in the bottom space of earth flatland was significantly lower than that in bare land (P<0.05), and the relative humidity was significantly higher than that of bare land (P<0.05) from 10:00 to 16:00 in winter, which resulted in cooling and humidifying effects. The daily variation degree of microclimate in bare land and earth flatland was significantly different in response to different seasons. The daily temperature range of the upper layer of earth flatland was significantly higher than that of bare land (P<0.05) in summer, indicating that the earth flatland intensified the daily change of air temperature. However, the daily temperature and humidity range of the lower layer of the earth flatland was significantly lower than that of the bare land (P<0.05) in winter, showing that the earth flatland buffered the daily change of the microclimate.At present, bedrock-exposed areas of rocky desertification are under a more severe and changeable microclimate change background. Therefore, based on the differences in the microclimate effects of heterogeneous underlying surfaces, priority should be given to introduce early fast-growing karst plants to accelerate surface vegetation coverage and improve local microclimate conditions, which would play a positive role in buffering microclimate changes in rocky desertification areas and accelerating vegetation restoration.

Vulnerability assessment of karst groundwater in the Jinci spring area and the zoning of protected areas for water quality

ZHAO Chunhong, SHEN Haoyong, LU Haiping, WANG Zhiheng, LIANG Yongping, TANG Chunlei

2024, 43(4): 822-830. doi: 10.11932/karst2024y034

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Jinci spring is a famous karst spring in Shanxi Province, and its backflow is an ecological restoration goal of the Shanxi Provincial government. Composed of Nanlao spring, Shengmu spring, and Shanli spring, Jinci spring is exposed at the foot of Xuanweng mountain in the western mountains of Taiyuan, twenty-five kilometers away from the city center, and it is a concentrated discharge point for karst water in the Jinci spring area. Karst water in the spring area is mainly supplied by atmospheric precipitation infiltration and leakage from rivers and reservoirs. Karst water in the Jinci spring area is an important water source for people's life and industrial and agricultural production in Taiyuan City. In recent years, with the intensification of climate change, large-scale development of karst water, coal mining and other human activities, especially after the construction of the second reservoir of the Fenhe river, the karst hydrogeological conditions in the spring area have undergone fundamental changes, with the spring area expanding from 2,030 km² to 2,713 km², which has affected the evaluation, management and protection of karst water resources in the spring area. The original zoning of protected areas can no longer meet the needs of water resource management and protection. Therefore, it is urgent to re-zone the protected areas and formulate corresponding protection measures. In terms of the problems on water quality and quantity, there exist differences in the causes, regions, and protective measures, and thus LIANG Yongping et al. proposed the concepts of "water quantity vulnerability" and "water quality vulnerability", as well as a method of "first classifying, and then grading" for the zoning of karst aquifer protected areas.This study focuses on the hydrogeological conditions of special recharge, runoff, and discharge in the karst water system of North China, as well as the main influencing factors of the antifouling performance of karst aquifer systems. It combines European methods and "water vulnerability assessment" to evaluate the antifouling performance. Based on infiltration duration of karst water in the unsaturated zone, leakage of rivers and reservoirs, precipitation infiltration in different regions, and replacement of karst aquifer media structure with water abundance, this study selects four factors to evaluate the antifouling performance of karst aquifers in North China, including the thickness of unsaturated zone, the amount of infiltration recharge, the lithology of overlying strata, and the water abundance of karst aquifers. Taking the newly divided karst water system in the Jinci spring area as the evaluation object, this study aims to evaluate the vulnerability of karst water system in the spring area and to zone the protected areas.The results show as follows, (1) The protected areas are mainly distributed in Jinci park and its surrounding areas. (2) The first-class protected areas are mainly distributed in the main stream of the Fenhe river, the exposed areas of carbonate rocks in the front of western mountains of Taiyuan, and the leakage sections of carbonate rocks in Tunlanchuan, the Tianchi river and the Liulin river. (3) The second-class protected areas are mainly distributed in the north of the spring area and the north bank of the Fenhe river. (4) The quasi-protected areas are mainly distributed in the south bank of the Fenhe river and the Taiyuan basin in the southeast. The newly zoned protected areas for spring water quality can provide a basis for the rational protection and scientific utilization of karst water resources in the Jinci spring area.

Flood hydrological process and its effective control measures in the high-altitude depressions of peak-cluster areas in Lijiang River

PU Zhenggong, HUANG Qibo, WU Huaying, LI Tengfang, ZOU Changpei, LIAO Hongwei

2024, 43(4): 831-842. doi: 10.11932/karst2024y004

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With a length of 83 km and an area of about 624 km², the high-altitude karst depressions in peak-cluster areas are mainly distributed in the middle reaches of the Lijiang River from Daxu town to Yangshuo county, Guilin. There are thousands of depressions in this area, with sufficient nutrients in soil. Large depressions with flat terrain are concentrated with villages, but land resources are scarce. The frequent alternation of droughts and floods has seriously affected not only the local economic development and rural revitalization but also the improvement of landscape resources, which is the main bottleneck restricting the development and protection of natural landscape resources in these depressions. Previous studies mainly focused on the geomorphological origins and geological structures of depressions, but there is little research on the flood formation conditions and hydrological processes.In this study, the Andang depression in the peak-cluster area of Lijiang River basin was selected as a study area in the analysis of flood water cycle, About 3.5 km away from the Lijiang river, the study area is located on the west bank of the Lijiang River, with a catchment area of 2.3 km². Rainfall mainly recharges the karst underground river channels through A01, A02, A03 and A04 sinkholes in north-south alignment in the central part of the depression, then discharges to the surface at Guanyan village on the west bank of the Lijiang river, and finally flows into the Lijiang River. The elevation of the Andang depression (150 m) is higher than that of the Lijiang river (130 m). A calcite vein about 20 m wide developed in the middle of the depression was mined in the early years. The slag was piled up in Sinkhole A01, resulting in the blockage of underground channels and limited water discharge capacity. Consequently, floods are likely to occur due to the poor drainage system when it rains heavily. With flooding depths of 3–10 m, floods take place 3 or 4 times every year in the depressions, lasting 5–10 days each time, even one month for the longest. A large area of cultivated land in the depression has been deserted due to years of waterlogging.This study established real-time monitoring stations for atmospheric rainfall, surface water level, groundwater level, and outlet flow in the depression to analyze the conditions and causes of floods. The main drainage outlets (A01 and A03 sinkholes) in the depressions were widened and dredged to increase their drainage capacity, which was effective for the control of flood and waterlogging. The results showed that the depression were highly subject to flooding after rainfall. The water depth in the depression could reach the maximum within 12–24 h after the rainfall. If the daily rainfall exceeded 50 mm or the cumulative rainfall exceeded 90 mm in 72 h, the depression was prone to flood. A total of 8 floods occurred in the depression area from April to July, 2023, with a flooding time of 417.5 h (18.6 d). The discharge at the outlet of the Yudang underground river reached 77.77% and 87.32% of the rainfall recharge, which was the total groundwater discharge outlet of the Andang depression. The four sinkholes A01, A02, A03 and A04 were discharge outlets for the central section of the underground river. The water discharge rates of these four sinkholes formed four flow peaks at the outlets. Because the hydraulic gradient in Sinkhole A01 was small, and the karst channels of the lower section were blocked by calcite slag, the water discharge speed was slow. Renovating Sinkhole A01 is not an effective way to control flooding in the depressions. Located on the south side of the calcite lode, Sinkhole A03 and Sinkhole A04 were not affected by the blockage of calcite slag; therefore, groundwater discharged smoothly. The dredging of Sinkhole A04 and water diversion from the south of Gucan depression to Sinkhole A03 reduced the flooding time to 66.71 h (2.8 d). Therefore, constructing the south drainage system, diverting water from the south Gucan depression to Sinkhole A03, and discharging water from Sinkhole A04 to the outlet of the Yudang underground river are crucial for further control of flood hazards in the Andang depression.

Response characteristics of groundwater level dynamics to precipitation based on continuous wavelet-cross correlation analysis: A case study of the Guiyang karst basin

WANG Ying, SONG Xiaoqing, WANG Fei, PENG Qin, CAO Zhendong, PU Xiuchao

2024, 43(4): 843-853. doi: 10.11932/karst20240410

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Precipitation is the main source of water supply for most groundwater systems; therefore, its spatiotemporal distributions will, to some extent, determine the dynamic characteristics of groundwater levels. Hence, conducting research on groundwater level dynamics is of great significance for the sustainable development and utilization of groundwater resources, regulation and management of surface–groundwater resources, and determination of floating resistance and anti-floating water levels in engineering construction. The Guiyang karst basin is located within the construction scope of the main urban area of Guiyang City. In order to further understand the nonlinear process of groundwater level dynamics in the karst basin area, and help improve the management of groundwater resources in this area, we collected the observation data and precipitation data of seven observation points of groundwater levels in the Guiyang karst basin in different periods from 2007 to 2021. Besides, to analyze the groundwater level dynamics on different time scales and the response of the dynamics to precipitation in the Guiyang karst basin, we adopted the continuous wavelet analysis that can quantitatively judge the periodicity of precipitation and groundwater levels, and the correlation analysis that can quantitatively calculate the lag relationship between groundwater and precipitation. The results show as follows. (1) According to the groundwater level data from monitoring holes in the study area, the water level variations of the monitoring holes located inside the Guiyang karst basin is relatively small, with a maximum annual water level variations of about 2–7 m, because this basin, featuring relatively flat terrain, is a discharge area of the groundwater system. The edge of the Guiyang karst basin is controlled by the terrain and topography, with significant undulations. The water levels of monitoring holes located at the edge of the basin vary greatly, with the maximum variations of water level about 10–20 m over the years. In terms of the continuous wavelet transform analysis of the response characteristics of groundwater levels to precipitation in the study area, it can be concluded that the main oscillation period of precipitation is 256–512 days, which passed 95% of the red noise tests from January 2008 to January 2017, indicating significant periodic characteristics. Due to the influence of hydrogeological conditions and human activities around monitoring holes, the oscillation periods of different observation points varied. However, the groundwater level dynamics in the Guiyang karst basin were significantly controlled by precipitation, showing discontinuous and short oscillation periods in high-frequency areas, with an overall main oscillation period of 256 to 512 days. (2) In the study area, there is a significant time lag between groundwater level variation and precipitation. That is, the longer a groundwater runoff distance is, the more hysteretic the response of groundwater level to precipitation becomes. The groundwater level variation in the runoff–discharge area lags behind precipitation by 2.66–7.7 days, by 1.25–8.04 days in the discharge area. Because the regional hydrogeological conditions of the two groundwater systems in the study area are different, the responses of the two groundwater systems in the north and south to precipitation are also different. In the southern groundwater system, the time lag of the response of groundwater level variations to precipitation gradually increases from the runoff–discharge area to the discharge area. In the northern groundwater system, due to the effect of the long-distance precipitation recharge from upstream, the groundwater level of runoff–discharge area changes more slowly than that of discharge area with multiple sources of recharge.

Sources and pathways of arsenic pollution in the karst water source area in the west of Jinchengjiang district, Hechi City

LIU Weiwei, JIA Long, LIU Chang, ZHOU Fubiao

2024, 43(4): 854-862, 875. doi: 10.11932/karst20240405

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Karst groundwater is an important water resource in karst areas of China and even the world, which plays an important role in people's life and industrial and agricultural production. A karst aquifer is composed of interconnected karst pores, cracks, caves, pipelines and other multiple media, which has strong capabilities for water collection, storage and drainage. Because soil layers in karst areas are generally thin, pollutants can directly enter groundwater aquifers through soil layers, sinkholes and karst cracks, which makes karst groundwater extremely vulnerable to pollution. Due to several reasons in the past, some old industrial slag yards were built on karst caves and cracks, but no effective anti-seepage measures were taken. Many incidents of karst groundwater pollution caused by leakage of slag piles occurred in China.In order to study the characteristics of sources and transporting routes of pollutants in karst underground water sources, this study took the karst water source of Chengxi water plant in Jinchengjiang district, Hechi City as a study area. By investigating the causes of arsenic anomalies in this plant and conducting hydrogeological analysis, this study identified pollution sources and sampled in the contaminated site to assess the arsenic pollution sources. The sources of arsenic pollution were found out, that is, the former site of arsenic factory and the karst depression to its east in Sanjing village, Wuxu town, Jinchengjiang district. The waste slag piled on the site of Sanjing arsenic factory was alluvial with the flood in the gully and bottom depression. Under the long-term action of rain, sunlight, air and microorganisms, the waste residue underwent complex chemical reactions, releasing heavy metal ions. Leachate seeped into groundwater through sinkholes and karst cracks, forming pollution sources. Arsenic concentrations in the contaminated site range between 7.17 and 25,200 mg·kg⁻¹, with an average concentration of 1,296.3 mg·kg⁻¹. The area where the arsenic concentration is higher than the risk control value of other agricultural land (120 mg·kg⁻¹) covers about 22,297 m², with an average thickness of 2.5 m. The volume of arsenic contaminated soil is 55,742.5 m³.Two tracing tests of underground water found that arsenic flows to Chengxi water plant through underground karst runoff, and the pathway is as follows: karst depression in the east of Sanjingcun arsenic factory → Xingdong in Xingdong village of Liuwei town → Fandong → Oudong → Nalong reservoir (underground runoff zone) → Chengxi water plant. The runoff is 12.25 km long with a groundwater flow rate of 0.86 km·d⁻¹ and a permeability coefficient of 0.995 cm·s⁻¹.The long-term monitoring of water quality shows that the arsenic content of Chengxi water plant is at risk of exceeding the permitted level of Class III (0.01 mg·L⁻¹) during the flood season. Therefore, it is necessary to control the pollution source (karst depression in the east of the arsenic factory) and to strengthen the monitoring of groundwater quality in the water source area of Chengxi water plant by setting up monitoring points for long-term observation of water quality at key points in the runoff area. For example, new monitoring points can be established at Lingxiao spring, estuary of Dula underground river, Xingdong skylight and Fandong skylight.The pollution source is located outside the quasi-protected area of the water source of Chengxi water plant. Considering that the water source mainly consists of karst water, and the groundwater primarily flows through karst pipelines, the pollutant runoff path is long and the attenuation is slow, it is suggested to expand the quasi-protected area of the water source of Chengxi water plant, with the southern boundary defined by groundwater divide of Longjiang karst groundwater system and Diaojiang karst groundwater system.

Effect of soil-rock structures on the characteristics of rainfall-runoff responses in epikarst zones

XU Zifan, CHEN Xi, LIU Weihan, LIU Hao, ZHANG Zhicai

2024, 43(4): 863-875. doi: 10.11932/karst20240406

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This study was conducted at the Puding Karst Ecosystem Research Station, Chinese Academy of Sciences. Three square columns were set up in the experiment to simulate different soil-rock structures. Each column has a cross-sectional area of 1 square meter and a height of 2 meters. The station is located in a warm, humid mid-subtropical monsoon climate zone, with an average annual rainfall of 1,315 mm and an average annual temperature of 15.1 ℃. The soil-rock structures in this area are diverse, mainly comprising limestone, dolomite, and associated soils.This study aims to reveal the impact of complex soil-rock structures on hydrological processes in the karst areas of Southwest China. In this study, physical models of three typical soil-rock structures (Column a: thin limestone soil over limestone blocks; Column b: thin limestone soil over dolomite gravel; Column c: thick soil over limestone gravel) were constructed, the underground runoff processes formed by natural rainfall were observed, and the water balance and runoff response characteristics under different soil-rock structures were compared. The research findings provide scientific insights into better understanding of the transformation and effective utilization of water resources in karst areas.Three square columns were used as experimental devices in this study to simulate different types of soil-rock structures (combinations of limestone, dolomite, overlying lime soil, and yellow soil). During natural rainfall events, evaporation and runoff of the soil columns with different soil-rock structures were compared and analyzed. Various methods of statistical analysis were employed to quantitatively assess the impact of these structures, revealing the hydrological processes of the complex soil-rock structures in epikarst zones.The main results are as follows. (1) Water Balance: As soil thickness increased (20 cm, 23 cm, 85 cm), evaporation increased and runoff decreased. Dolomite gravel (Column b) retained more water than limestone blocks (Column a), leading to higher evaporation and lower runoff. Seasonal runoff variability was significant in areas covered with thinner soil, in which flood and drought are prone to occur. (2) Rainfall-Runoff Relationship: Linear regression revealed a threshold-linear two-stage pattern. Runoff started after reaching a threshold, becoming linear beyond that. The increase of soil thickness raised the rainfall threshold for runoff formation. Column a had the highest runoff efficiency, while Column c had the lowest. The specific surface area of the gravel in Column b is larger, so its evaporation is twice as much as that of Column a, and the regression slope is lower. (3) Impact of Rainfall Patterns: Small-event rainfall (Patterns B and D) caused higher peaks in Column a, while large-event rainfall (Patterns A and C) caused higher peaks in Column b. Thicker soil in Column c delayed initial runoff and peak flow, especially in small events. Additionally, the initial runoff response time of soil-rock structures with thin soil layers depends on the rainfall process, while the initial runoff response time of soil-rock structures with thick soil layers is negatively correlated with soil moisture content.This study reveals the significant impact of different soil-rock structures on hydrological processes in the karst areas of Southwest China. The physical properties of soil-rock structures (e.g., soil thickness and characteristics of underlying rocks) not only affect the water balance but also determine the rainfall-runoff relationship and runoff characteristics under different rainfall patterns. Firstly, the soil layer thickness is a key factor influencing water balance and underground runoff response. Thicker soil can significantly delay the response time of underground runoff, reduce peak flow, and increase the rainfall threshold required for runoff generation. Additionally, the physical properties of rock fractures affect the water balance, with dolomite gravel under the soil having a higher water retention capacity than limestone blocks, leading to higher evaporation losses and lower runoff. Lastly, the response of water balance and underground runoff to different rainfall patterns varies significantly with soil-rock structures. Low-fracture limestone blocks beneath the soil (fracture porosity of 8%) have high water conductivity, allowing small rainfall to easily infiltrate and form substantial peak flows. In contrast, dolomite gravel beneath the soil, with a higher water storage capacity (fracture porosity of 40%), facilitates the accumulation of infiltrated water during heavy rainfall, leading to larger peak flows.

Genesis model of geothermal fields in Yangmeichong, Guangxi

WANG Xinwei, ZHANG Lili, Li Shanmin

2024, 43(4): 876-888, 921. doi: 10.11932/karst20240407

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Hezhou in Guangxi is rich in geothermal resources with great development prospects and research value. However, there are problems to be addressed in terms of supply sources, cyclic evolution processes, and genesis mechanisms of geothermal resources in this region. Through geothermal geological surveys and analyses of geophysics, geochemistry, and environmental isotopes, this study has explored thermal storage characteristics, supply sources, circulation depths, and genetic models of the geothermal fields in Yangmeichong, Hezhou. A geological geophysical model and a convective geothermal model of uplift mountain faults have been preliminarily established, whose geological parameters such as temperature, composition, depth, and magnetism of geothermal resources are consistent with the understanding of geology. The thermal reservoir of geothermal fields in Yangmeichong is belt shaped and composed of the Yanshanian granite fracture zone. The Guposhan Fault (F₁) is the main water conducting and heat controlling structure in the geothermal fields in Yangmeichong. The source of geothermal heat flow in the geothermal fields is the heat from the upper mantle and deep crust (mantle heat flow), as well as the heat generated by the decay of radioactive elements in the shallow crust (crust heat flow), providing a heat source for the formation of deep circulating groundwater. Temperatures and geothermal gradients gradually increase from the western boundary (F_1-1) to the eastern boundary (F₁) and from the northern boundary to the southern boundary of the geothermal fields in Yangmeichong. In the vertical direction, geothermal gradients increase with the increase of depths. Temperatures within the depth range of 800–1,200 m are 53.5–73.0 ℃, and the geothermal gradient is 4.88 ℃/100 m. The deep thermal storage temperatures of the Yangmeichong geothermal fields have been measured by both silicon dioxide geothermal temperature scale and potassium magnesium geothermal temperature scale, and temperatures are 92.24 ℃ and 87.22 ℃, respectively. Accordingly, the depths of underground thermal mineral water circulation are 3,292 m and 3,069 m, respectively. The hydrochemical type of geothermal fluid in the geothermal fields in Yangmeichong is HCO₃-Na. Due to the leaching effect of deep groundwater on granite bodies, the contents of silicic acid and sodium ions in underground hot water are relatively high. The isotopic detection results indicate that the supply of geothermal water in the area comes from precipitation infiltration, and the tritium content of geothermal water is less than 2 TU. It is speculated that geothermal water in Yangmeichong was formed by atmospheric precipitation before 1960. The geothermal energy in Yangmeichong is a fault convection geothermal model. Geothermal water is directly supplied by atmospheric precipitation with fault zones and rock pores as water channels, and it flows deep by both hydraulic and thermal forces. After alternating water thermal convection, geothermal water is formed. Subsequently, the convection of geothermal water took place along the fault of Gupo mountain from deep to shallow and from north to south, which formed the fault convective geothermal model in Yangmeichong. The research results provide a theoretical basis for the exploration and rational utilization of geothermal resources in Yangmeichong, Guangxi.

Source characteristics and influencing factors of groundwater hydrochemistry in the karst areas of central Guizhou

JIANG Feng, JIQIN Kebuzi, CAO Jianwen, WANG Ruofan, ZHAO Liangjie

2024, 43(4): 889-899. doi: 10.11932/karst2024y028

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Based on the results of regional hydrogeological and environmental geological surveys, this study conducted comprehensive water sampling and testing at 43 groundwater points across the karst areas of central Guizhou during the dry and wet seasons. The study utilized three widely-used geochemical diagrams—Piper trilinear plots, Gibbs diagrams, and ion ratio diagrams (including relationships like HCO$_3^{-}$-(Mg²⁺/Ca²⁺ and [SO$_4^{2-}$/HCO$_3^{-}$]-[Ca²⁺+Mg²⁺]/HCO$_3^{-}$) to identify the sources and characteristics of hydrochemical indicators of groundwater in the karst areas of central Guizhou. In addition to these geochemical methods, principal component analysis (PCA) was performed separately on the results of water quality tests completed from the dry and wet seasons to further clarify and verify the characteristics of groundwater sources during these two seasons, and to pinpoint specific water quality indicators influenced by various environment and human factors in the karst areas.The research findings reveal that the hydrochemical characteristics and influencing factors of groundwater in the study area are relatively consistent during the dry and wet seasons. Hydrochemical types of groundwater in this area is predominantly characterized by HCO₃(SO₄)-Ca(Mg). The Gibbs diagrams show that the groundwater chemistry across the study area aligns closely with the rock weathering type, with only minor deviations of a single mine water sample (H6). A comprehensive analysis using Gibbs diagrams confirms that karst groundwater in the study area is primarily of a rock weathering type, with its hydrochemical composition predominantly derived from rock weathering and leaching dissolution processes. Further analysis using the [(Ca+Mg)/HCO₃]-[SO₄/HCO₃] diagrams indicates that the molar ratio of [Ca²⁺+Mg²⁺]/HCO$_3^{-}$ in groundwater during both the wet and dry seasons is largely below 0.5. This finding is particularly concentrated in the areas dominated by carbonate rocks, with some samples showing a trend towards gypsum dissolution. Particularly, certain samples, such as Spring S214 in Yongjing town of Xifeng county, and Spring C8 in Longyanpo village of Jinzhong town, Kaiyang county, are located either to the right or near the gypsum dissolution line. These positions indicate a significant influence of gypsum dissolution on groundwater chemistry, suggesting gypsum dissolution plays a crucial role in shaping the hydrochemical profile in parts of the areas. A comprehensive analysis of ion ratio correlations suggests that the soluble carbonate rocks in the study area are primarily affected by carbonate weathering and erosion processes. However, significant impacts from gypsum dissolution are also observed in some samples. This suggests that while the majority of the groundwater chemistry is shaped by carbonate dissolution, there are distinct pockets where gypsum dissolution contributes markedly to the groundwater composition. During the wet season, groundwater composition is mainly influenced by three principal factors: water-rock interactions (PC1), human activities (PC2), and industrial production (PC3). Together, these factors explain 83.7% of the variance in groundwater chemical composition. In contrast, during the dry season, groundwater is primarily influenced by water-rock interactions (PC1*) and human activities (PC2*), jointly accounting for 85.1% of the chemical composition variance. This seasonal variation highlights the dynamic nature of groundwater chemistry in response to both natural and human factors. Water-rock interactions emerge as the predominant factor influencing the hydrochemical composition of groundwater in the study area. These interactions significantly affect the concentrations of major ions such as potassium, sodium, calcium, magnesium, bicarbonate, total phosphorus, fluoride, and silica. Human activities, particularly agricultural and domestic activities, mainly influence the concentrations of ammonium, chemical oxygen demand (COD_Mn), and chloride. Additionally, the impact of phosphate mining is evident in its contribution to elevated sulfate ion concentrations, particularly in areas near mining operations. The research findings provide valuable insights into the complex hydrochemical dynamics of karst groundwater in central Guizhou. The consistent hydrochemical characteristics observed during the dry and wet seasons, alongside the predominant influence of rock weathering and dissolution processes, underscore the importance of geological factors in shaping groundwater chemistry in karst areas. However, the notable influence of gypsum dissolution in certain samples also highlights the need to consider localized geological variations when groundwater quality and developing management strategies are assessed. Moreover, the identification of human activities and industrial production as significant secondary influences on groundwater quality points to the need for targeted management interventions. These interventions should aim to mitigate the impacts of human activities on groundwater resources, particularly in the areas where agricultural runoff, domestic wastewater discharge, and industrial effluents contribute to the groundwater contamination.Overall, this study enhances our understanding of the hydrochemical characteristics of karst groundwater in central Guizhou, revealing the sources of groundwater ion components and their influencing factors. The findings have significant implications for the rational development and conservation of groundwater resources in karst areas. Effective management strategies should consider both natural geological processes and human influences identified in this study to ensure the sustainable use and protection of groundwater resources in the karst areas in central Guizhou. By integrating hydrogeological surveys with geochemical and statistical analyses, this study provides a comprehensive framework for understanding groundwater systems in karst environment, offering valuable guidance for future research and water resource management.

Water eco-physiological adaptability of Hemiboea subcapitata in heterogeneous habitats in the Dehang karst valley

WANG Chenyao, ZHANG Ting, ZENG Dewu, LI Long, YE Qingzi, TIAN Xiangrong

2024, 43(4): 900-910. doi: 10.11932/karst2024y031

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The Dehang canyon of Xiangxi UNESCO Global Geopark is cut by the runoff of streams. As a unique karst landform, it is an ideal area for studying plant species diversity and ecological adaptability. Collecting the clone plants, Hemiboea subcapitata, as samples from the Dehang karst valley in Xiangxi Global Geopark, this study measured their growth, morphology, and photosynthetic and water physiological indicators. On this basis, this study explored the water eco-physiological adaptability of the plants to three types of heterogeneous habitats formed during the evolution of the Dehang karst valley. These three habitats are canyon karst walls slightly weathering after water erosion without soil covering, bank weathered rocks with little soil covering and bank soil organic horizons highly weathering with soil covering.The results show as follows. (1) There was only a small difference (< 2%) in the natural water content in ramet leaves of H. subcapitata in heterogeneous habitats, while there is no significant difference in terms of relative water content and natural saturation deficit. It is proved that they not only have a strong water maintenance mechanism but also have no obvious difference in their recovery ability after drought. The lowest water potential of canyon karst walls was -1.630 ± 0.047 Mpa, and the highest water potential of bank soil organic horizons was −0.705 ± 0.025 Mpa. It is obvious that, in heterogeneous habitats, the water demand of ramet leaves increased significantly with the decrease of the matrix water content, but the water potential of leaves decreased significantly. (2) There was a significant difference in ramet growth but no significant difference in total biomass. For example, the plant heights and leaf areas of ramets on the surfaces of canyon karst walls were significantly higher than those in bank soil organic horizons, but there was no significant difference in the cumulative height and leaf area of total population. (3) The morphological changes of ramets were significant. Values of lengths, diameters and root densities of stolons were listed as: canyon karst walls>bank weathered rocks>bank soil organic horizons. The leaf thickness on canyon karst walls was nearly 60 μm thicker than that in bank soil organic horizons, while the specific leaf area (SLA) decreased to 78.2%, and the stomatal density significantly reduced to 66%. The highest stomatal density was 2,299 ± 158 mm² in the habitats of bank soil organic horizons, and the lowest stomatal density was 1,518 ± 98 mm² in the habitats of canyon karst walls. (4) In terms of photosynthetic parameters, stomatal limit values of leaves increased significantly with the decrease of leaf water potential in different habitats, but stomatal conductance increased significantly at the same time, so the intercellular CO₂ concentration did not change significantly. However, the net photosynthesis of ramet leaves on bank soil organic horizons only reached 69.6% of that in bank soil organic horizons. (5) The water use efficiency (WUE) of the habitats of bank soil organic horizons was the highest (4.134 ± 0.333 μmol CO₂·mmol⁻¹ H₂O). When the water deficit of leaves on canyon karst walls was the highest, the water use efficiency was the lowest (3.029 ± 0.461 μmol CO₂·mmol⁻¹ H₂O), only 73% of that in bank soil organic horizons. These results indicate that H. subcapitata can ensure the relative water stability of ramets in karst heterogeneous habitats through its own water maintenance mechanism. H. subcapitata can be adapted to the habitats of arid karst rock walls by increasing root density, stolon length, leaf thickness and weight, and by reducing stomatal density and other morphological plasticity. It can also keep intercellular CO₂ concentration by increasing stomatal conductance to maintain transpiration pull. At last, it can be adapted to water heterogeneous habitats in karst river valleys by relatively stable growth with higher water consumption.

Genetic models and influence factors of karst collapses in Loudi City of central Hunan, China

GUO Jiehua, JIANG Zhongcheng, LIU Xinjian, LIAO Hongwei, LI Cheng

2024, 43(4): 911-921. doi: 10.11932/karst20240408

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Loudi City in central Hunan has recorded 281 karst collapse incidents and tens of thousands of collapse pits, which made it one of the cities in China experiencing the most serious karst collapses. Among all these karst collapses, 222 karst collapses occurred in mining areas, accounting for 79% of the total. In addition, some karst collapses were caused by foundation engineering or by rainfall infiltration and erosion. By sorting out the temporal and spatial relationship between karst collapse events, karst collapses and collapse pits, it is concluded that karst collapses in Loudi City can fall into four occurrence modes, namely, vacuum erosion, floating–softening, load vibration and seepage erosion, and each mode has four collapse processes. Among them, vacuum erosion collapses and floating–softening collapses are mainly caused by mining activities, which are induced by drainage from the mining area and backwater after the mine has been closed; load vibration collapses are mainly induced by external dynamic loads such as pile foundation construction; seepage erosion collapses are natural collapses mostly induced by heavy rainfall. The influencing factors of karst collapses include basic factors and inducing factors. The basic factors include stratum lithology, karst landform, karst water abundance, correlation with mining areas, etc., which constitute the key influencing factors in karst collapse-prone areas; the inducing factors mainly include drainage in mining areas, backwatering in closed mines, engineering vibration, rainfall, etc., and the intensities of these factors can affect the time, scope and scale of karst collapses.In order to strengthen the risk management of karst collapses, it is recommended to establish a monitoring and early warning system for karst collapses, and scientifically develop risk assessment, prevention and control plans and disaster emergency response plans for karst collapses. Besides, controlling the area, method and intensity of engineering construction, prohibiting or limiting the mining of coal, gypsum, groundwater, etc. in karst areas, and maintaining the dynamic balance between rock, soil, cave, water and air are effective measures to prevent and control karst collapses. In this paper, the distinction between the basic factors and inducing factors of karst collapses can provide a scientific basis for their effective prevention and control in karst areas, and can provide a reference for the construction of harmonious and beautiful villages.

Influence of water level dropping rates on the collapse of karst soil caves

CHEN Xuejun, XUE Mingming, SONG Yu

2024, 43(4): 922-936. doi: 10.11932/karst20240409

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The change of water-gas pressure caused by the rise and fall of water level will lead to the collapse of karst soil caves. In this study, we combined the physical model test and FLAC3D numerical simulation to simulate the soil cave collapse caused by water level fluctuation under the same water supply rate and different drainage rates. Besides, we also analyzed the influence of different drainage rates on the variation of water-gas pressure, soil pressure of the overlying soil layer and deformation of soil caves during the fluctuation. We also established the relationship between water-gas pressure and variables such as drainage rates, overburden deformation and cave, and put forward the action law of water level fluctuations on the collapse of soil cave. The results show as follows. (1) The influence of drainage rates on the variation of water-gas pressure is basically the same, but with different degrees. The change degree and response time of water-gas pressure are positively correlated with the drainage rate. (2) The change of overburden deformation and soil pressure is positively correlated with the change of water-gas pressure, but with different influence degrees. The drainage rate can only accelerate the change degree. (3) Degrees of deformation and collapse of soil caves are caused by comprehensive factors. The speed of the drainage rate and the number of water level fluctuations influence the changes of water-gas pressure in different degrees in soil caves and also influence the soil deformation caused by water level fluctuations. (4) The numerical simulation results are basically consistent with the results of laboratory model test. These results provide important theoretical support for further research on the laws of hydrodynamic factors affecting karst collapse and provide a basis for rational prevention and prediction of karst collapse.

Detection of karst collapses through microtremor surface waves based on windowing cross-correlation function

SONG Tong, LI Xinxin, ZHANG Wei, HU Tao, ZHENG Xiaohui

2024, 43(4): 937-947. doi: 10.11932/karst20240415

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The study area is located in the karst development area of Pingxiang in the west of Jiangxi Province, China. The landform of this area is complex, low in the northwest and high in the southeast. The fold action and gravitational sliding action led to the development of faults and extensional sliding nappe structures in the area, accompanied by magmatic intrusion activities, which has formed multi-phase superimposed complex structures. Atmospheric precipitation and groundwater in the upstream limestone areas constitute the main water source in the study area. Meanwhile, karst collapses may cause the formation of holes below the surface, seriously endangering people's life and property. Therefore, finding out the geological situation of the collapse area can provide a reference for the understanding of the geological characteristics and the groundwater system in this area.Microtremor is a kind of persistent weak vibration signal observed on the surface caused by industrial vibrations, traffic noises, tidal currents, atmospheric activities and other activities on the earth. Surface waves are formed by vertical waves and transverse waves interfering on the surface. They have the characteristics of low speed, low frequency and frequency dispersion, which lay a foundation for the detection of underground structure. The method of microtremor surface waves survey utilizes various types of vibrations that continuously exist in nature as signal sources. It extracts the information on seismic surface wave field from microtremor records and uses this type of information for imaging underground media. The steps include microtremor signal acquisition in the study area, data preprocessing, empirical Green function calculation, extraction of surface wave dispersion curves and inversion of velocity structure for transverse waves. Among these steps, the empirical Green function is obtained through the cross-correlation operation of the microtremor signals recorded by two detectors, and calculating the empirical Green function is the key to obtain the surface wave information.This study detects the karst collapses in the study area by using microtremor surface waves. However, the surface wave signals are affected by uneven distribution of natural noise sources and random noises, which may cause the low signal-to-noise ratio of the Green function. Therefore, the direct use of the empirical Green function for subsequent data processing may get the dispersion energy spectrum with low resolution, which is not conducive to the subsequent extraction of high-quality dispersion curves and accurate inversion.Due to the above shortcomings, this study first optimized the window function for the cross-correlation function of microtremor signals to improve the signal-to-noise rate of microtremor data, and to enhance the resolution of energy spectrum of microtremor surface wave dispersion. Then, the extraction of dispersion curves and inversion of the virtual source surface record of each group in the study area were conducted to obtain the transverse wave velocity structure of each point along the measurement line. Finally, the distribution positions and depths of karst collapses in the study area were revealed, according to the the transverse wave velocity section below the measurement line generated by inversion as well as the geological interpretation of drilling data. The results show as follows, (1) The selection of window function in the cross-correlation function calculation will affect the resolution of the dispersion energy spectrum, and the window function should be tested in processing the microtremor data. (2) The processing and optimizing of window function for the cross-correlation function can effectively improve the signal-to-noise rate of microtremor surface wave and the resolution of the dispersion energy spectrum, widen the frequency band range of dispersion curves, and improve the accuracy of the inversion. (3) The method of microtremor surface waves survey is highly applicable to karst collapse detection, and the optimization of the window function can determine the range of underground hazards in a more accurate way.

Genesis of topography and regional distribution of the concealed red karst landform in the adjoining area of Hunan–Hubei–Chongqing–Guizhou

JIANG Fuwei, LAI Haiqing, YANG Qingkun, CHEN Youzhi, YU Ning, YANG Tao

2024, 43(4): 948-956. doi: 10.11932/karst20240411

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Red karst is a concealed landform that has been newly discovered and is buried beneath soil, characterized by its red color and unique shapes. It is widely distributed in the area of Wuling mountain of Hunan, Hubei, Chongqing and Guizhou in China. Compared with common karst landforms, red karst landforms have four basic characteristics: red color, stratified convex morphology, landform lithology of argillaceous limestone, and different dissolution causes in soil environment. Because of its bright red color and unique appearance, red karst is very ornamental and has great tourism economic value. The morphological origin of red karst has been discussed from the perspective of macroscopic geological conditions and tectonic forces, but its mechanism of microscopic morphological formation and shaping process have not been deeply analyzed. In addition, as a concealed landform, it is difficult to be found on the surface, so determining its distribution is of great significance for the relevant investigation and research. Therefore, this paper discusses the formation mechanism and shaping process of the concealed red karst landform from the microscopical point of view, and determines the distribution range of the red karst in the adjoining area of Hunan, Hubei, Chongqing and Guizhou. It can provide the basis for the future investigation and development of red karst.Material composition differences, joint fissure cutting and differential dissolution are the key factors in the formation of red karst geomorphology. The main reasons are as follows: (1) The content of soluble matter on the convex surface of red karst landform gradually increases from top to bottom, while the content of soluble matter on the concave surface is the highest and that on the convex surface is the lowest. This shows that the difference of soluble material content is the material basis for the formation of convex and convex forms of red karst landform. (2) The joint fissure is a good transport channel for water required by dissolution, which can greatly improve the weathering and denudation efficiency of karst geomorphic area and lays a prototype for the evolution of geomorphic form. (3) When the content of soluble components in the parent rock is high, the dissolution rate is fast and concave, and on the contrary, it is convex, which causes differential dissolution. During the formation of red karst landform, the difference of material composition horizontally leads to differential dissolution, and the decrease of erosion vertically leads to differential dissolution. Therefore, the difference of soluble material content in rock composition and the layered rhythmic layer are the material conditions that lead to the diversity of red karst geomorphology, and the dynamic conditions are the cleavage of structural joints and the differential dissolution of rock mass.The evolution of red karst morphology mainly goes through four basic stages: the formation stage of material conditions for morphological development, the emergence stage of dissolved rock layers, the formation stage of erosive groundwater in weathered soil, and the stage of differential dissolution in soil. The formation of red karst mainly goes through three key geological processes: (1) joint fissure cutting; this effect has mainly shaped the outlines of trapezoids and cylinders. (2) rock and soil interface corrosion; due to the undulating rock surface, the rock and soil interface corrosion makes erosive groundwater with fast dissolution rate accumulate in the low concave of the surface, often forming a conical or sharp rock mass. (3) dissolution of joint fissure surface; vertically, due to the continuous consumption of erosive H⁺ ions, both the dissolution ability and dissolution rate decrease, with the increase of depth, forming an approximate V-shaped grike; at the same time, the erosive groundwater dissolves the rock wall on both sides of the joint fissure surface in the transverse direction, and is controlled by the difference of soluble material composition, forming the concave-convex interlayer.According to the definition of red karst geomorphology and the field investigation by the research team, five factors such as color, morphology, lithology, exposure and geomorphology conditions are selected as the criteria for determining red karst geomorphology. The rock composition of the red karst geomorphology in Hunan, Hubei, Chongqing and Guizhou is more dependent on the stable distribution of purplish red nodular limestone and argillaceous limestone in Dawan Formation, supplemented by the purplish red carbonate rock in Guniutan Formation or the Cross Pu Formation, in which the outcrop area of Dawan Formation is the key development area. According to 1∶200,000 geological map, the potential distribution area of concealed red karst geomorphology in the adjoining area of Hunan–Hubei–Chongqing–Guizhou covers 3,433.83 km², and it is distributed in a narrow strip or partially distributed in a patch in SW–NE direction.

Research advance for uranium isotope as a quantitative proxy for paleo-oceans anoxic or oxic environment

LUO Qukan, CAO Jianhua, ZHONG Liang, BAI Bing, WANG Qigang, LIAO Hongwei, ZONG Keqing, QIN Hanlian

2024, 43(4): 957-968. doi: 10.11932/karst20240412

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Compared with other elements that are sensitive to redox environments (U, Mo, V, S, Fe, Cu, Zn, Ni), uranium isotopes have the advantage to quantitatively reflect long-term and global-scale paleoredox of oceans, due to its uniform composition in the oceans globally, and quantitative relationship with the proportion of the anoxic seafloor areas in ancient oceans. Therefore, uranium isotopes are widely used in the events such as the Late Ediacaran, Early Cambrian, Ordovician/Silurian, Late Devonian, Devonian/Carboniferous, Permian/Triassic, Triassic/Jurassic, and OAE 2 (Oceanic Anoxic Event 2). Through a review of previous papers, the author has systematically summarized the principles, methods, and results of using uranium isotopes for quantitative analysis of paleoredox. It has found that the core of current uranium isotopes quantitative method is the mass balance box model of seawater uranium (mass balance box model) and its isotopes and the related variants. By simplifying the uranium mass balance box model based on the proportion and fractionation coefficient of different types of uranium sinks, the redox environment and duration of ancient oceans can be quantitatively reflected. However, there may be ambiguity in the interpretation regarding whether the marine environment contains sulfur or not. In addition, by reviewing previous papers, the author has set up a preliminary coupling relationship among the proportion of anoxic seafloor area (%) reflected from uranium isotopes, atmospheric oxygen concentration, and oceanic anoxic or biological events. It has found that: (1) the uranium isotope analysis results were highly consistent with the occurrence time and extent of various anoxic or biological events, especially being coincident with the events that occurred in the Late Ediacaran, Late Ordovician, Late Devonian Frasnian-Famennian, Devonian/Carboniferous, Permian/Triassic, and Triassic/Jurassic periods, indicating that uranium isotopes are indeed an effective global scale and deep-time scale proxy for quantitative analysis on paleoredox of oceans. (2) The trend of anoxic seafloor expansion is not completely consistent with the trend of the atmospheric oxygen concentration changes. Usually, there is a lag. Only the trend of atmospheric oxygen concentration changes in the Triassic/Jurassic period is similar to the trend of oceanic redox environment changes. Analysis suggests that uranium isotope analysis results indicate the proportion of anoxic seafloor area, that is, the proportion of anoxic bottom seawater area, which is actually the change of redox environment of oceanic bottom water. At first, the change in atmospheric oxygen concentration affects shallow seawater, which first responds to the changes in the atmospheric redox environment, and then gradually affects the biological productivity of the seawater, gradually transmitting the environmental changes caused by redox evolution to the bottom water, and thus leading to a lag reaction of anoxic seafloor's expansion or shrink; or due to climatic changes, sea level rise and fall can cause changes of ocean internal circulation (such as thermohaline ocean circulation), leading to changes in productivity and causing anoxic seafloor area expansion or shrink, which may also result in hysteresis effects. There should be a kind of coupling relationship between the atmospheric redox evolution and ocean redox evolution, it deserves to be paid more attention for further study in future. In addition, through a review and analysis of previous research results, the author believes that there are several problems with the quantitative analysis of global scale paleoredox environments of oceans by using uranium isotopes, such as low accuracy, ambiguity, and the representativeness of samples. It is suggested to improve this method from the following two aspects further: (1) although uranium isotopes have been widely used in many important biological events or oceanic anoxic events since the Ediacaran period, the representativeness of sampling sites for some research results still needs to be improved. Although uranium isotopes are assumed to have global homogeneity theoretically, this assertion has not fully considered the influence of post-diagenesis, weathering and alteration in each sampling site on the uranium isotope composition that reflects the original seawater features. It is necessary to calibrate and verify the analysis results of different samples from different sampling sites of the same period to improve the quantitative analysis accuracy further. (2) The single proxy analysis results of uranium isotopes provides a wide range of anoxic seafloor area proportion, showing insufficient accuracy. It is necessary to carry out comprehensive multi-proxy isotopic quantitative analysis, by adding the results of isotopes like Mo, Tl, and others, which is believed could effectively improve the analysis accuracy for the same event. Finally, the author believes that if the accuracy of uranium isotopes method for quantitative analysis could be improved by comprehensive analysis with combination of other isotopes analysis, it is necessary to find out the coupling relationship between atmospheric redox evolution and marine redox evolution, especially the time effects of marine redox evolution to the atmospheric evolution. Hence, it is also possible to find out the response mechanism of oceanic redox conditions to the atmospheric redox evolution. The coupling relationship and the response mechanism may help the related researchers to predict the impact range and extent of oceanic redox evolution after a certain periods of lagging to the atmospheric redox evolution that is caused by natural and human factors. The results may provide great support for addressing global climate change.

Overview of karst geology in Turkey

QIN Zhengfeng, XU Qi, XIE Yincai, BI Xueli

2024, 43(4): 969-981, 990. doi: 10.11932/karst20240413

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Turkey is distributed with karst up to about 40% of its land area, in which karst is developed under typical Mediterranean climate. According to the structural characteristics, Turkey is divided into four different karst areas from north to south, among which the Taurus mountains is the largest and most developed karst area in this country and even in the Mediterranean region; therefore, karst in Turkey is of high research value. Based on the systematic collection of geological, structural and hydrogeological data, this study compiles a 1∶100,000,000 karst geological map of Turkey, analyzes the factors affecting karst development, and summarizes the distribution law of karst in Turkey, the main karst phenomena and the current situation of resource exploitation and utilization.Many external and internal factors contribute to the type and the degree of karstification of carbonate rocks. However, the basic fact is that the geological structure, the orogeny, and the connected tectonics provide the basic framework that permits, enhances, or impedes the processes of karstification. The Alpineorogeny and the following epiorogenic movements in Turkey have become important factors in karstification. This type of karstification of carbonate rocks is distributed almost everywhere in Turkey.According to the structural characteristics, karst areas in Turkey can be divided into four units: the karst area of the Taurus mountains, the karst area of southeast Anatolia, the karst area of central Anatolia, and the karst area of northwest Anatolia. The region of the Taurus mountains is the largest and most developed karst area in Turkey and even in the entire Mediterranean region. Carbonate rocks developed from the Cambrian to the Neogene are mainly distributed in Mesozoic and Cenozoic strata, and are the most developed in the Jurassic and Cretaceous strata. In some places, the total thickness of carbonate rocks is more than 1,500 m. The most notable karst geomorphic features are karst caves, sinkholes, dissolution funnels, poljes, karst depressions, karst canyons, karst springs, underground rivers or lakes and submarine springs. From the Mesozoic to the Holocene, limestone was deposited by thrust-nappe effect on the strata with extremely low permeability such as schist, sandstone, shale, etc. Numerous fractures generated by tectonic movements became water channels. Many large-scale karst springs composed of Mesozoic limestone, Tertiary limestone and conglomerate were developed on the contact surface between limestone and impermeable strata, which made the area home to the world’s largest karst aquifer and karst hot springs.Carbonate caves in Turkey are mainly concentrated in the Taurus mountains near the Mediterranean Sea, the central and western karst areas of the Black Sea, and the karst areas of Thrace. Although gypsum caves are developed in the central region of Anatolia, the number is limited and the scale is small. Due to differences in geological and climatic conditions, caves in the Mediterranean region and caves in the Black Sea region show different morphological characteristics.(1) The karst area of Thrace is dominated by ancient karst, with single-layer horizontal caves at altitudes of 40–60 m and multi-layer horizontal caves at altitudes of 240–450 m.(2) Dolomite and volcanic rocks are widely distributed in the karst area of the western Black Sea, in which karst is not developed vertically and multi-stage horizontal caves are mainly developed below the altitude of 350 m.(3) Vertical caves are mainly developed in the karst area of central Black Sea, some of which are more than 200-meter deep, but the deepest cave is less than 300 m, due to the thin limestone thickness.(4) In the karst area of the Taurus mountains near the Mediterranean Sea, overthrust faults are developed, and the thicknesses of carbonate rocks in some areas are more than 1,000 m, in which vertical caves are mostly developed. Both the longest cave and the deepest one in Turkey are located in this karst area.By the end of 2019, there were 52 caves in Turkey with a depth of more than 200 m, 43 of which were located in the karst area of the Taurus mountains near the Mediterranean Sea, and 7 in the karst area of central Black Sea. There were 62 caves with a length of more than 1,000 m, 34 of which were located in the karst area of the Taurus mountains near the Mediterranean Sea, 16 in the karst areas of central and western Black Sea and Thrace.Turkey is rich in karst resources such as marble, geothermal, oil, natural gas, etc., and it has abundant karst landscapes including large springs, caves, canyons, and travertine. The potential for development and utilization is vast, and there is an urgent need to conduct detailed karst hydrogeological surveys.

Design and implementation of karst geological data management and sharing system

YANG Chen, BI Benteng, ZHOU Lixin

2024, 43(4): 982-990. doi: 10.11932/karst20240414

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Distributed in almost all provinces, karst areas in China cover approximately one-third of the national land area. Therefore, scientific research in the field of karst is one of the hotspots of geological studies. Since its establishment, the Karst Geological Research Institute has conducted hydrogeological surveys, environmental geological surveys, karst subsidence, ecological environment, geological relics, oil and gas resources, karst landscapes, and other investigations in karst areas. This institute has completed over 1,500 scientific research projects of the Ministry of Science and Technology, the National Natural Science Foundation of China, the Ministry of Land and Resources, the Guangxi Science and Technology Department, and other departments, as well as technical service projects in local economic construction, with over 100,000 archives and data. These long-term accumulated geological data and scientific and technological achievements are a giant treasure containing meaningful and valuable knowledge and rules for us to develop. In order to tap its potential value, it is necessary for us to integrate and realize resource sharing services, improve data accessibility, break down various barriers to data utilization, and establish an integrated data resource management system. We should improve the utilization value of various data resources, and classify and organize electronic resources on a large scale and in a standardized way. We should also unify scheduling and resource management, and realize the classification, retrieval, download, and use of various data resources. Because by doing so, we can provide data support for researchers and technicians in the field of karst research and survey through improving their efficiency in data utilization.Taking SQL Server as the relational database and ArcGIS Server as the spatial map service engine, the data layer of the service system for karst geological data management has been developed by open-source technology frameworks such as ASP NET CORE 6.0 MVC framework, C#, JavaScript, HTML language, integrated WebGIS technology, Echart, jieba word segmentation, etc. The main functional modules include data statistics, data uploading, comprehensive table query module, directory query based on word segmentation technology, one map module for karst geological data, and modules of map service, map sheet conversion, borrowing management, user management, etc. based on ArcGIS JS.The data statistics module displays the quantity statistics results of various data categories in the system. In order to visually display the data, the bar chart and line chart drawing functions of open-source framework have been used to design a set of visual interfaces, with the data category as the horizontal axis and the data quantity as the vertical axis. This module facilitates users to quickly understand the quantity of various karst geological data.The comprehensive table query module of geological data has been developed based on open-source tables. By feat of powerful interaction and capabilities of displaying various geological data information to users that DataTables has, this module can display various information on geological data to users, and provide functions such as fuzzy retrieval, advanced retrieval, sorting, and data export. According to their needs, users can obtain data by selecting different attribute sorting, setting the numbers of pages and multi-attribute joint query conditions, etc. Through multi-attribute conditional joint query, the data query range can be narrowed down, and the query results can be accurately obtained, solving the problem of large data retrieval.The directory query module can realize the retrieval of geological data based on the content input by users. This module decomposes the query statement input by users, queries word by word to improve the query accuracy, and facilitates users to obtain the required data. Based on the results of word segmentation query, users can further filter data by data category, scale, and administrative region, and the keywords searched are highlighted in the query results. Users can click on the title to enter the page for data details.With the use of spatial information on geological data, the one map module for karst geological data can realize the map spatial retrieval of various geological data, based on spatial topology. Users can choose to query data categories and scales, and obtain data information through various methods such as inputting map sheet numbers, dragging boxes, and polygon queries. The map displays the location of the data, and the list on the right displays the name of the data. If users click on the spatial position of the data on the map or the name of the data in the query results list, the data information window will display for users to enter the page for data details.The map service module can realize the online viewing and attribute query of professional map elements. Users can select the professional geological map layer to be queried according to their needs, switch between vector maps, remote sensing images, terrain, and other base maps, view the legend, adjust the layer transparency, and use point selection, line selection, and surface selection to query attribute information.These modules use various ways to display the spatial, temporal, related attributes, and other metadata information of karst geological data to users, realizing the informationization of geological data management services and improving the efficiency of data query and access.

Current Issue
2024 Vol. 43, No. 4

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Submission Guide

Current Issue 2024 Vol. 43, No. 4

Archive

Submission Guide

Current Issue
2024 Vol. 43, No. 4