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2023 Vol. 42, No. 2

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Research review on the application of microbial information technology to karst groundwater environment
LIU Dan, CHEN Xuequn, TIAN Chanjuan, ZHANG Wenjing, GUAN Qinghua
2023, 42(2): 185-192. doi: 10.11932/karst20230201
Abstract FullText HTML PDF(499KB) icon1832 icon79
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With the development of society and economy, the environmental problems of karst groundwater are increasingly prominent due to the influence of human activities. The unique heterogeneity of karst aquifer leads to the diversity of microbial community. With the continuous development of microbial information technology, its application to karst groundwater environment will be increasingly extensive. Therefore, the study of microbial information technology is of great significance to the development, utilization and protection of karst groundwater resources. In this study, the research on application of microbial information technology to karst groundwater environment is reviewed from the aspects of microbial sources, microbial tracing and monitoring technology in karst groundwater, and the application prospect in this regard is also offered. The heterogeneity of karst aquifer and the dual characteristics of microbial source recharge, including endogenous water and exogenous water, lead to the sensitivity and complexity of karst groundwater environment. The sources of microorganisms in karst groundwater are diverse, mainly including native and exotic microorganisms. The input of external microbial communities such as surface water and soil environment is the main source of microorganisms in karst groundwater. In addition, groundwater recharge and other human activities have a significant impact on microbial community characteristics. Because microbial tracer technology, in which the microorganism is used as a tracer indicator, has more advantages than the traditional indicator in the study on pollution and characteristics of pollutant environment in karst groundwater, this technology has become an important method of karst groundwater resource management. So far, many microorganisms, such as Escherichia coli and Bacteriophage, have been used as tracers in tracing tests. Escherichia coli can be used as a tracer to reflect the pollution degree of karst groundwater. Bacteroidetes are used to determine the pollution source and its contribution rate because of their host specificity. Having strong migration ability and being sensitive to changes in hydraulic conditions, Bacteriophages are non-toxic and non-pathogenic to other organisms. They are used as tracers in karst and fractured aquifers for the quantitative migration analysis of groundwater, the delineation of water flow path, etc. In addition, combined with microbial tracers and traditional tracers, the multi-tracking technology has the advantages of accuracy and operability. Because microorganisms are sensitive to the change of karst environment, their community structure and diversity are different, which can effectively indicate the change of karst groundwater environment. Different from hydrochemical index monitoring, microbial monitoring technology can indicate unknown components and provide more comprehensive information of groundwater environment. Its potential application to karst groundwater monitoring has been widely recognized.With the development of microbial information technology, the sources and distribution characteristics of microorganisms need to be further identified due to the complexity of karst aquifer and the variability of microorganisms. The pollution risk caused by the application of microbial information technology to karst groundwater environment needs to be further discussed. The microbial tracer technique in karst groundwater is still immature and more suitable microbial indicators need to be screened out. Biomonitoring techniques with molecular methods have not yet achieved the resolution and flux required for monitoring purposes, and the correlation between different environmental parameters and the characteristics of microbial community change needs to be further identified. However, the technology is being developed to provide reference for the development of microbial information technology and the development and protection of karst groundwater resources.
Effects of tourism activities on hydrochemical fingerprints in the karst underground river system
YANG Rui, HAN Zhijie, HAN Zhiwei, WU Qixin, WU Pan, HE Shouyang
2023, 42(2): 193-206. doi: 10.11932/karst20230202
Abstract FullText HTML PDF(3529KB) icon1178 icon61
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The underground river system is the main carrier of water resources and an important source of urban and rural water supply in karst areas, and is also an essential element of karst geological wonders. Nowadays, people are showing the increasing preference for the cultural tourism integrated with science and technology. Meanwhile, the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), a significant national science and technology infrastructure built at the special topography of karst, has become an aspiring destination for astronomy and tourism enthusiasts. However, pollutants from tourism activities will easily affect the water quality of underground river through the surface runoff via sinkholes, shafts and cracks. Using hydrochemical facies diagram (HFE-D), Gibbs models and coefficients of ion ratio, we have analyzed the characteristics and changes in water chemistry of wastewater from the tourist attraction and from the Dajing and Xiaojing underground river systems during different tourism periods in order to understand the periodic, concentrated and sudden effects of tourism activities on the water chemistry of underground river systems. The results show that: (1) The pH and conductivity values of the sewage from the tourist attraction varied little during the May Day holiday, ranging from 7.57 to 7.84 and 540.00 to 761.00 mS·cm−1, respectively. The sewage pH values during the National Day holiday ranged from 7.66 to 7.95 with an average value of 7.78; however, the conductivity varied greatly from 488.00 to 934.50 mS·cm−1. The water chemistry type of sewage is Ca−HCO3, and the values of K+, Na+, Cl− and ${\rm{NO}}_3^{-}$ subject to tourism activities fluctuated greatly. Their maximum values appeared on May 2 to May 3 and October 2 to October 4, which is consistent with the increasing number of tourists in the peak period of tourism. Compared with Dajing and Xiaojing underground river systems, increases of Na+, K+ and Cl− in the Durov diagram are responsible for domestic discharge and input from disinfection of Cl2 or NaClO in water treatment plants. (2) During the May Day holiday, the pH values of water from the inlet and outlet of the Dajing and Xiaojing underground river systems varied from 7.72 to 8.42 and 7.36 to 8.39, respectively. The water conductivity in the inlet ranged from 256.00 to 338.00 mS·cm−1 with an average of 281.79 mS·cm−1. The water conductivity in the outlet increased slightly, changing from 297.00 to 413.00 mS·cm−1 with an average of 313.59 mS·cm−1. Compared with the May Day holiday, the pH values of water from inlet to outlet of the Dajing underground river system increased slightly from 8.03 to 8.27 during the National Day holiday, while its conductivity values decreased slightly due to the dilution of rainfall, averaging between 317.51 mS·cm−1 and 265.11 mS·cm−1. Differently, the Xiaojing underground river system showed an increase in pH and conductivity vaules during both May Day holiday and National Day holiday, with the average of pH increasing from 7.66 to 8.02 and from 8.03 to 8.17, respectively. Average values of conductivity increased from 295.67 mS·cm−1 to 342.97 mS·cm−1 during the May Day holiday and from 307.63 mS·cm−1 to 359.72 mS·cm−1 during the National Day holiday, both of which were influenced by the urban or rural domestic discharges and the input from agricultural activities. (3) The water chemistry type of Dajing and Xiaojing underground river systems is Ca−HCO3, which is mainly controlled by karstification. The TDS increased from the inlet to the outlet as a result of sufficient water-rock interaction and effects of human activities. There are some differences in spatial variation of water chemistry between Dajing and Xiaojing underground river systems. Ca2+, Mg2+ and ${\rm{HCO}}_3^{-}$ produced by water-rock interaction in the Dajing underground river system gradually increased from inlet to outlet, while K+, Na+, Cl−, ${\rm{NO}}_3^{-}$ and ${\rm{SO}}_4^{2-}$ caused by human activities declined along groundwater. K+, Na+, Cl− and ${\rm{NO}}_3^{-}$ in Xiaojing underground river system increased from inlet to outlet. The value of ${\rm{NO}}_3^{-}$ fluctuated the most with a variation coefficient of 747.97. More fluctuations in water chemistry showed in Xiaojing underground river system due to the effect of urban or rural domestic discharges and input from agricultural activities. (4) Influenced by tourism activities, the HFE-D showed that continuous 5-day responses happened after the 24-days effect of tourism activities on the water chemistry in outlet of the Dajing underground river system. The response time lengthened 2 days compared with 3-day peak tourism in the May Day holiday. But the response duration prolonged more than 13 days during the National Day holiday. It can be contributed to a concentrated and explosive effect of tourism activities and needs an extended recovery time for the water chemistry values of the underground river system. The water chemistry at the inlet of Xiaojing underground river system had been affected before the peak of tourism no matter whether in the May Day holiday or National Day holiday, indicating that the water chemistry of the underground river is influenced not only by the sewage from tourist attraction, but also by the urban or rural domestics discharge and input from agricultural activities. The HFE-D indicates a 2-day response in water chemistry at the outlet of the Xiaojing underground river system 27 days after the May Day holiday. The poor continuity and regularity of the water chemistry response observed at the outlet of the Xiaojing underground river system during the National Day holiday may be related to multiple effects along the underground river. Both Gibbs model and analysis of ion ratio showed that the underground river system was influenced by the input of human activities such as urban domestic discharge, tourism and agriculture activities. Therefore, the human effect on water chemistry of the underground river system should be given adequate attention.
Water quality analysis and evaluation of irrigation applicability in Nandong underground river basin, Southwest China
LI Jun, YANG Guoli, ZHU Xiuqun, XU Li, ZHU Danni, ZHAO Yi, LI Yanqing, LAN Funing
2023, 42(2): 207-219. doi: 10.11932/karst20230203
Abstract FullText HTML PDF(1744KB) icon1390 icon57
Abstract:
The karst surface water and groundwater of Nandong underground river basin are vital water sources for agricultural and industrial production, and lives of residents in Honghe Hani and Yi Autonomous Prefecture in Yunnan, Southwest China. With a growing public awareness of water environment and water safety, the evaluation of karst water quality and irrigation applicability especially in agricultural regions is becoming increasingly necessary. In this study, 32 samples of karst surface river water and 24 samples of underground river water were collected from Nandong underground river basin during dry and rainy seasons. 11 inorganic regular ions (i.e., K+, Na+, Ca2+, Mg2+, Cl−, ${\rm{SO}}_4^{2-}$, ${\rm{HCO}}_3^{-}$, ${\rm{NO}}_3^{-}$, NO$_2^{−}$, NH$_4^{+}$, and F−) and 9 heavy metals (i.e., Al, Cu, Pb, Zn, Cr, Cd, Ni, Mn, and As) were analyzed in these samples to investigate the water quality and irrigation applicability. Based on the measured concentrations of the hydrochemical composition, the Nemerow composite index in combination with the four irrigation assessment systems of sodium concentration (SC), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), and permeability index (PI) were applied to evaluate the karst water quality and irrigation applicability, respectively. Results show that Ca2+ and ${\rm{HCO}}_3^{-}$ were identified as the major ions in both karst surface water and karst groundwater, indicating weakly alkaline karst water in the study area. For karst surface water, among the 11 inorganic regular ions, only NH$_4^{+}$ was found exceeding the maximum acceptable level for drinking water recommended by General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China. Meanwhile, among the 9 heavy metals, the concentrations of Al, Pb, Mn, and As were evaluated as exceeding the maximum acceptable level. Moreover, the rates of measured ions exceeding permitted levels in the dry season were generally higher than those in the rainy season. For karst groundwater, the concentrations of Al, Pb, Zn, Cr, Mn, and As exceeded the maximum acceptable levels, and the rates of these metals exceeding permitted levels in the rainy season were generally higher than those in dry season. The nitrogen synthetic fertilizers might be a main cause of the increase of NH$_4^{+}$ concentration in karst surface water. High concentration of Al, Mn, and Cd in karst water were mainly caused by large amounts of discharge from metal smelting, waste residue of mining, and open-pit mining. Furthermore, an exposed surface environment of bedrock in some parts of this study area might be responsible for these components exceeding the permitted levels due to the lack of surface decontamination of pollutants. The karst water quality belonging to the good grade or above accounted for 89.29% and 85.71% of the total water samples collected during the dry season and the rainy season, respectively, and the quality belonging to poor grade or below accounted for 7.14% and 14.29%, respectively. Hence, the karst water quality in Nandong underground river basin was generally high based on the results of the assessment of karst water quality. However, some cases of poor-quality karst water were found in parts of our study area (e.g., G1 and S4 sampling sites in the dry season and G1, G2, and G3 sampling sites in the rainy season), accompanied by the seasonal differences in karst water pollution. According to the permitted level for irrigation water and the results of SC, SAR, RSC, and PI assessments, most of the karst water in Nandong underground river basin was generally suitable for irrigation. However, it is noted that the concentration of As (54.70 μg·L−1) in the sampling site of surface water (i.e., S3) exceeded the permitted level for the irrigation of vegetables and water crops in the dry season, thereby being no longer suitable for irrigation. Our results suggest that the high concentrations of metal compositions (e.g., Al, Pb, Mn, and As) should be controlled by some targeted measures to prevent further metal pollution in karst water of Nandong underground river basin. Our study also provides an integrated method for the comprehensive understanding of water quality in karst surface water and groundwater.
Hydrochemical characteristics and water quality evaluation of karst water in Jinan City
LIU Wenyue, GAO Zongjun, XU Yuan, HAN Cong, LUO Zhenjiang, ZHAO Zhenhua
2023, 42(2): 220-232, 244. doi: 10.11932/karst20230204
Abstract FullText HTML PDF(1399KB) icon2304 icon75
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Karst groundwater is an important source recharge for springs in Jinan, and its water quality directly affects the effectiveness of spring protection work in this city. In this study, a total of 128 groundwater samples (64 each in the wet season and the dry season) were collected from the main karst hydrogeological units in Jinan—Changxiao karst water system, Baotu Spring karst water system and Baiquan karst water system in May (the dry season) and September (the wet season), and their water quality was tested. By means of mathematical statistics, correlation analysis, Piper three-line diagram, Gibbs model and ion ratio, the hydrochemical characteristics of groundwater in the study area were analyzed. Besides, the groundwater quality in this area was evaluated comprehensively by fuzzy evaluation method. The analysis may provide a basis for the hydraulic connection of the three karst water systems. Results show that groundwater in the three karst water systems of Changxiao, Baotu Spring and Baiquan are all weakly alkaline water with low hardness, and TDS values are less than 1,000 mg·L−1, among which TDS value and TH value show as Changxiao>Baiquan>Baotu Springs. The ion concentrations are as follows: Ca2+>Na+>Mg2+>K+, ${\rm{HCO}}_3^{-}$>${\rm{SO}}_4^{2-}$>Cl −>${\rm{NO}}_3^{-}$. The water quality of the three karst water systems is worse in the dry season than in the wet season. The chemical types of water in Changxiao, Baotu and Baiquan are roughly the same, mainly calcium type and bicarbonate-mixed water. The Changxiao karst water system and Baotu Spring karst water system are mainly of SO4·Cl-Ca·Mg type, and the Baiquan karst water system is mainly of HCO3-Ca·Mg type. According to the piper three-line diagram and the Gibbs diagram, the main groundwater ions in the three karst water systems of Changxiao, Baotu Spring and Baiquan mainly come from rock weathering. It can be seen from the ion ratio diagram that the main hydrochemical effects in the study area are from the weathering and dissolution of carbonate rocks and evaporite salts and cation exchange. More than 50% of the water in the three karst water systems falls into Grade III in both the dry season and the wet season, indicating that the karst groundwater in the study area is less polluted. Compared with the water collected from sample points in two seasons, the water quality in the wet season is better than that in the dry season. The Baotu Spring karst water system has the best water quality, followed by the Baiquan karst water system.In this study, suggestions on the environmental protection of karst water resources are put forward: (1) The government should standardize the management of industrial water use, implement a quota system, and avoid unreasonable use of water resources. (2) Transporting sewage channels, pipelines and oil pipelines through protection area of water source should be prohibited. (3) The construction of oil depots in protection areas should be prohibited. (4) The government and institution should gradually improve the irrigation system in agriculture, and actively introduce new technologies and techniques to save water. (5) The government and related institutions should heighten citizens' awareness of water conservation and water resources protection, and promote standardized water resources management.
Recharge characteristics and protection of karst groundwater in major leakage area of Yufu river in Jinan
GUAN Qinghua, WANG Yujing, CHEN Xuequn, ZENG Guihua, XIN Guangming
2023, 42(2): 233-244. doi: 10.11932/karst2022y23
Abstract FullText HTML PDF(7579KB) icon1780 icon67
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Jinan, called as "the city of thousands of springs", is famous for its large number of springs. The saying "the seventy-two famous springs in Jinan top those elsewhere" reflects a profound spring culture with a long history. Therefore, spring water conservation and research are very important. However, in Baotu Spring Group, the reduction of water level and spring flow in the dry season have to be faced with . The direct recharge area and the major leakage zone in the region of Baotu Spring are important recharge areas for karst groundwater. Especially, the major leakage zone is an important supply channel for spring water. As a natural river leakage zone with a large watershed area and better inflow conditions, the Yufu river is one of the major leakage zones in the region of Baotu Spring. Besides, by increasing the water replenishment capacity of major leakage zones with external water replenishment, the water system connection project of Wohushan Reservoir and Jinxiucheng Reservoir can transport and replenish water to the Yufu river.Taking the main river as a research focus, we delimited the protection range of the major leakage zone of the Yufu river. In order to finish the delimitation, we analyzed the water replenishment function of leakage and adopted the techniques such as RS, GPS, GS, geophysical surveys and hydrogeological tests and LSDPV method. Meanwhile, the calculation by the method of variation parameters shows that the average recharge of nature groundwater in the major leakage zone of the Yufu river has reached 12.90 million m3 for recent years, becoming an important recharge source for karst groundwater. The water replenishment effect in the major leakage zone of the Yufu river has been achieved mainly by raising the karst groundwater level in the western area so as to prevent the westward diversion of groundwater in the northern runoff process in the southern mountainous area of Baotu Spring. In this process, the groundwater is concentrated in the spring outcropping area, and hence the spring discharge may increase. On the condition of protecting the nature infiltration of leakage zone, we can fully explore the water replenishment function and increase the replenishment of major leakage zones of the Yufu river by water diversion, ecological restoration and pollution control. The research finding shows that delimiting major protection areas for leakage zones is important for us to ensure the continuous gushing of springs. This study also provides a basis for the accurate and scientific protection of springs as well as technical support for urban development planning and protection of the famous springs in Jinan.
Numerical simulation of crystallization blocking in tunnel drainage pipes based on dynamic mesh and level set
MAO Chengjun, YANG Yun, WU Jianfeng, DONG Ping, WU Jichun
2023, 42(2): 245-256. doi: 10.11932/karst2021y37
Abstract FullText HTML PDF(2466KB) icon1008 icon36
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The complex hydrogeological conditions in karst areas lead to frequent water seepage and water gushing disasters in tunnels, which often require supporting drainage systems to prevent and control water hazards. When the karst groundwater with high salinity enters the tunnel drainage pipe, the solubility of soluble salt ions in water changes with the variation of external temperature and pressure conditions, forming saturated solution. Ions crystallize and precipitate, sticking to the inner wall of the drainage pipe, which will contribute to decreasing its flow area. If not treated, in the long run, the drainage pipe will be blocked, resulting in the increase of water pressure in the tunnel lining. Consequently, it is likely to occur a series of tunnel water hazards such as water leakage, water gushing, mud outburst, lining damage, etc., which may seriously threaten the safety of tunnel construction and operation.For quantitative research on the crystallization blocking process of tunnel drainage system, we constructed the blocking model of karst water crystallization in drainage pipes for the first time, coupling with the pipeline hydrodynamic field, the concentration field and the chemical reaction field. Meanwhile, with methods of dynamic mesh and level set, we quantitatively expounded the crystallization blocking process in the tunnel drainage system. We also carried out a comparative study on different simulation technologies to analyze the influence of such factors as temperature, velocity, solute concentration, etc. on the blocking of crystallization. The results show that: (1) Both of the two methods can simulate and predict the crystallizing process, among which the dynamic mesh method is simpler and its solving accuracy is relatively higher, and the level set method can be used to simulate the further deposition after the topological shape has been changed (i.e., completely blocked). (2) Crystallization blocking mainly occurs in the transverse tube, where more crystalline precipitates are developed, because the flow velocity in the longitudinal tube is generally higher than that in the transverse tube, and the CaCO3 crystal concentration in the transverse tube is higher than that in the longitudinal tube. (3) Temperatures and solution concentrations are positively correlated with the crystallization rate, while the flow rate is negatively correlated with it. (4) Given the coupling of hydrodynamic reaction with chemical reactions, the numerical model of crystallization blocking can provide technical support for the early identification and safety evaluation of geological hazards of karst tunnels.
Dynamic research on source and distribution of PAHs in the Qingshuiquan underground river
WANG Zhe, LI Jiang, LU Li, XIA Riyuan, CAO Jianwen, ZHAO Liangjie, LUAN Song
2023, 42(2): 257-265. doi: 10.11932/karst2022y15
Abstract FullText HTML PDF(2032KB) icon1360 icon35
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In recent years, the groundwater pollution of polycyclic aromatic hydrocarbons (PAHs) in Nanning City has been increasingly serious due to the acceleration of urbanization in this city and its dual water-bearing structure of underground and surface as well as the properties of PAHs. As a major source of drinking water for the city, the Qingshuiquan underground river plays an important role in the local economic and social development. Therefore, more research on PAHs pollution in Naning City is needed.Covering an area of about 55.3 km2, the Qingshuiquan underground river is located in the northwest of Nanning. The strata distributed in the area are mainly upper Carboniferous (C3), Lower Cretaceous (K1) and Paleocene (E1), and the lithology is mostly thick bedded limestone. There are two underground river pipelines in the area. The groundwater mostly flows from east to west in the way of pipeline flow, and is discharged from the surface in the form of underground river outlet at S15 and flows into the Bachi river. At present, with an annual water supply capacity of 19 million square meters, the Qingshuiquan underground river provides drinking water for Yongning district of Nanning City, and is an important source of drinking water in Nanning City. In the upper reaches of the system, pollution is mainly from agricultural and domestic pollutants. In its middle and lower reaches, pollution is mainly generated from industrial enterprises, including cement plants, paper mills, quarries and gas stations.Based on the previous test data and the sampling data of this study, the research is mainly focused on the distribution rule of PAHs with the Qingshuiquan underground river as the research object. The statistics method, isomer ratio method, distribution coefficient method and others were adopted to analyze the content, distribution characteristics and source change of PAHs in water environment over the years. Results showed that, (1) The PAHs content with different ring numbers in groundwater were in the order of 4>3>5>2>6, mainly with low ring (2-3); the content of PAHs with different ring numbers in sediment were in the order of 4>5>3>6 >2, mainly with high ring (4-6). The PAHs content in groundwater experienced an increase after a decrease, but the content in sediment saw a gradual increase, which reflected different dynamic characteristics of PAHs content in groundwater and sediment due to the urbanization and industrialization in Nanning City. (2) The spatial distribution of PAHs content in water environment was listed as follows, upstream content<middle stream content<downstream content, which may be caused by the increase of industrial pollution sources as well as PAHs emissions from upstream to downstream. The variation trend of PAHs content in groundwater in different regions was different. The content of PAHs in groundwater increased gradually in the upstream, stabilized initially and then increased sharply in the middle, and decreased first and increased afterward in the downstream. The content of PAHs in sediments of different regions presented the same trend of a gradual increase, but the increase rate was different. (3) There are also differences between the change rules over the years. The PAHs sources at upstream reaches has been generated by biomass burning, and have changed from petroleum source to the mixed one at middle reaches. At downstream, the PAHs sources has changed from fossil fuel combustion to primarily mixed source. These changes are mainly attributed to different types of pollution sources and their emissions in different areas. (4) Kp values of different ring numbers were in the order of 6>5>4>3>2. Kp values gradually increased with rise of ring numbers, and PAHs with larger ring numbers tended to be adsorbed by sediments. The lgKoc values of PAHs at S11-S15 sampling sites all exceeded the upper limit and were distributed in downstream, showing a strong adsorption capacity of PAHs on particulate matter. The lgKoc values of the remaining sampling sites are below the upper limit, reflecting the influence of dissolved organic matter on the distribution of PAHs.
Numerical simulation of karst groundwater in Dajing basin of Guizhou Province based on MODFLOW-CFP
DANG Zhiwen, SHAO Jingli, CUI Yali, LI Jun, GONG Zhiqiang, ZHAO Liangjie, LIANG Yongsheng
2023, 42(2): 266-276. doi: 10.11932/karst2023y002
Abstract FullText HTML PDF(1932KB) icon2600 icon53
Abstract:
China is a country with the most widely distributed karst, and the karst is extensively developed in its southwesten part where 2,836 underground rivers are distributed with about 1,847.8×108 m3·a−1 of karst groundwater resources and a total discharge of 479.7×108 m3·a−1 in the dry season. These underground rivers become the main water source for people's life as well as the development of industry and agriculture in Southwest China. However, water shortage has often occurred in recent years, due to the unreasonable development and utilization of karst water resources. How to make scientific, reasonable and effective use of karst water resources has become a difficult problem in tackling water resource crisis. In this paper, we have studied the hydrological process and numerical simulation of groundwater in karst areas from the perspective of groundwater science, which is of great significance to the accurate evaluation, and rational development and utilzation of karst water resources.In this study, we take Dajing basin, a typical karst peak-cluster depression area in southern Guizhou Province, as the study area. Water-bearing media in karst areas often include karst pipelines with high permeability and dissolved gaps with low permeability. The flow mechanism of groundwater in these two media is quite different. The groundwater in the gap mainly accords with Darcy’s law and the laminar flow mechanism, while the groundwater in the karst pipeline is mostly in the turbulent state due to the large flow rate. In the actual situation, the two media are independent of each other, but there is an interrelated process of hydraulic exchange on the boundary. Based on this, we adopt MODFLOW-CFP coupling model to carry out a numerical simulation of Dajing basin. MODFLOW-CFP is a dual-system coupling model based on dual structure theory. MODFLOW-CFP model contains three groundwater flow simulation methods. In this study, CFPM1, the most basic model, is adopted. In this pattern, the traditional groundwater flowing model is coupled with a specific pipeline model. The main purpose is to depict caves, cracks in interstitial space and basaltic aquifer pipes in karst aquifers, where groundwater can be fully or partially filled and flow patterns can be laminar or turbulent. Therefore, a complete simulation of the hydrological process of karst groundwater may help us to grasp the law of groundwater movement in Dajing basin, accurately evaluate karst water resources, and thus promote the rational development and utilization of the resources.The process of using MODFLOW-CFP to establish a mathematical model of groundwater in Dajing basin includes the establishment of porous media model in MODFLOW and pipeline model in CFP. Subsequently, the two models are combined together to identify the model and analyze the water balance, based on the coupling model. Finally, the water resources are evaluated and the mechanism of groundwater migration is studied. In this study, it is found that Dajing basin is a groundwater system with complete recharge, runoff and drainage conditions, and the North-South and the Northeast-Southwest trending structures control the distribution of regional karst aquifers and the development of karst. According to the buried conditions of groundwater and the practical significance of water supply, the main source of recharge in this area is atmospheric rainfall, and the main discharge is the outflow from the southern Dajing basin. Meanwhile, the simulation results show that the exchange capacity between pipes and porous media is 6,719.1 m3·a−1, mainly in the upper and middle reaches of Dajing basin. The total recharge water in the study area is 10,977.3×104 m3·a−1, and the recharge module is 133.495 m3·km−2·a−1. The rainfall inflow and infiltration accounts for 81.35% of the total recharge, and the total discharge is 10,813.47×104 m3·a−1, mainly from the outlet of the underground river. Based on the research findings, the migration mechanism of groundwater in Dajing basin is clarified, and new development and utilization of water resources are put forward to address the shortage of local water resources.
Soil properties of carbonate rocks under different vegetation types
LUO Mei, ZHOU Yunchao, TANG Fenghua
2023, 42(2): 277-289. doi: 10.11932/karst2022y17
Abstract FullText HTML PDF(1552KB) icon2718 icon103
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Guizhou Province is located in the largest continuous karst area in the world. The karst landform accounts for 73.8% of the province's land area where 88% of its rural population live. The exposed area of carbonate rocks developed in karst reaches 130,000 km2, accounting for 73% of land area in this province. Soil erosion leads to the exposure of carbonate rocks on the surface, aggravates the process of karst rocky desertification, and causes a series of ecological and environmental problems, all of which seriously affect the development of local economy and people's life. The research on the comprehensive prevention and control of karst rocky desertification has become a scientific problem that needs to be solved urgently. In addition, bedrock and vegetation play a prominent role in soil development and formation. In different soil development stages, bedrock and vegetation types have an important impact on the soil physical and chemical properties. However, the current research on karst soils mainly focuses on the soil properties of limestone-formed soils. There is still a lack of research on the characteristics of soil developed by carbonate rock and the effects of their interactions on soil in karst areas from the perspective of vegetation-soil-bedrock system.Taking the soil developed by carbonate rock (limestone, calcareous dolomite and dolomite) as the research object, this study aims to explore the distribution characteristics and influencing factors of the soil developed by carbonate rock under different vegetation conditions in karst areas, and analyze the effects of different vegetation types, bedrock types and soil layers on soil properties. The study area is located in Huaxi district, Guiyang City, Guizhou Province. It has a subtropical monsoon climate with an average annual temperature of 14.9 ℃ and an average annual precipitation of 1,229 mm. Three representative plots in Huaxi district were selected, including Huaxi Reservoir, Huaxi TV Tower, and the area near the southern Guizhou University, and a total of 60 soil samples were collected from these three sample plots of different carbonate rock types. The main tree species in the study area are Cupressus funebris, Quercus, and Myrsine Africana, and grass species are Stipa bungeana and Cynodon dactylon. The soil physicochemical properties were determined by potentiometric method, Kjeldahl method, alkaline hydrolysis diffusion method, molybdenum antimony anti-colorimetric method (sodium bicarbonate extraction), and potassium dichromate oxidation with an external heating method. The particle size distribution of soil was determined by the hydrometer method. In SPSS24 software, Shapiro-Wilk test was used to test the normality of the data. Mann-Whitney U test and Kruskal-Wallis H test (multiple comparison, Bonferroni method) were used to test the difference of soil properties with different sampling depths, vegetation types and bedrock types. Scheirer-Ray-Hare test was used to determine whether vegetation type, bedrock type, soil layer, and their interactions had a significant effect on soil particles and fertility. Permutation multivariate analysis of variance (PERMANOVA) was used to analyze whether there were significant differences between two or three groups of data. Non-metric multi-dimensional (NMDS) was used to analyze the particle and fertility indexes of the soil developed by different bedrock types in the 0-20 and 20-40 cm soil layers. Redundancy analysis (RDA) was used to analyze the effects of vegetation type, bedrock type, and soil layer on changes in soil properties. These analyses were performed in the R version 4.0.3.The bedrock and vegetation types are the main factors affecting the development of carbonate rocks into soil, followed by soil layers. In 0-20 and 20-40 cm soil layers, the fertility and particles of the soil developed by limestone, limy dolomite and dolomite are significantly different. However, between the 0-20 and 20-40 cm soil layers, there is no significant difference in the nature of the soil developed from the same bedrock except the differences between gravel content (SLC) and fine particle ratio (<0.002 mm) of limestone-developed soil and the differences between available phosphorus (AP) and organic matter (SOM) content of dolomite-developed soil. In the 0-40 cm soil layer, the bedrock type significantly affects the distribution of soil pH, AP, SLC, AN, total nitrogen (TN), SOM, and 0.2-0.25 mm and 0.002-0.02 mm particles. Vegetation type significantly affects the pH value, AP, TN content of limestone-developed soil, pH, SLC, coarse particles (0.25-2 mm) and fine particles of dolomite-developed soil, and available nitrogen (AN), SOM, coarse and fine particles of soil developed by limestone dolomite. The soil layer significantly affects the distribution of SLC, coarse and fine particles in limestone-developed soil and AP in dolomite-developed soil.At present, the soil under the abandoned grassland slope and grass cover and the limestone-developed soil in the study area are likely being damaged by erosion. Therefore, according to the lithology of the parent rock, moderately changing the planting structure of vegetation on soil has a positive effect on improving soil nutrients and soil particle composition, and enhancing soil erosion resistance. Besides, the interaction of bedrock-vegetation-soil system and human activities should be comprehensively considered in the prevention and control of soil erosion in karst areas.
Nutrient characteristics and differences of forest soil in rocky desertification areas of Southwest China
CHEN Qiufan, LU Qi, WANG Yan, LIU Yungen
2023, 42(2): 290-300. doi: 10.11932/karst2022y24
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In this study, papers related to vegetation restoration and soil in rocky desertification area since 1990s have been retrieved. Based on nutrient grading standards of two national soil censuses, the soil nutrient improvement and soil stoichiometry characteristics have been explored, which can provide theoretical foundation for the ecological restoration effect and model screening of rocky desertification. Results are shown as follows, (1) The mean values of total organic carbon (TOC) and total nitrogen (TN) in the forest soil of rocky desertification areas of Southwest China are higher than those of Grade Ⅰ of two national soil censuses. Total phosphorus (TP) falls into Grade Ⅱ, with obvious soil nutrient improvement, while the total potassium (TK) concentration falls into the GradeⅤ of the low potassium area. (2) According to the soil censuses, TOC and TN rank top among the five provinces/regions/cities, and TP and TK fall into Grade Ⅱ and Grade Ⅳ, respectively in Guangxi Zhuang Autonomous Region, which can show the most significant increase in soil nutrient concentration. In Guizhou Province, TOC and TN are higher than those of grade Ⅰ by 34% and 37%, respectively, and TP falls into Grade Ⅱ and TK Grade Ⅴ, reflecting obvious nutrient improvement of forest soil in rocky desertification areas of this province. In Yunnan Province, TOC and TP are higher than those of Grade I by 9% and 21% respectively. TN falls into Grade II and TK Grade V. These indexes show that soil nutrients has been improved to different degrees. TOC in Chongqing City is higher than that of Grade I by 1.75%. Both TN and TP fall into Grade Ⅱ. TK, ranking top among the five provinces/regions/cities, falls into Grade IV, showing less improvement compared with that of the other three provinces. In Hunan Province, TOC, TN, TP and TK fall into Grades Ⅱ, Ⅱ, Ⅴ, and Ⅴ respectively, suggesting that Hunan Province should focus on controlling rocky desertification. (3) Indicators of TOC and TN in the soil of rocky desertification areas in Southwest China are positively correlated, and the growth of vegetation is limited by potassium. TOC, TN and TP are stored quickly in Guangxi with significant soil improvement. The soil carbon sequestration capacity of Guizhou Province is higher than that of national average. In rocky desertification areas of Yunnan Province, low TK has posed a bad effect on vegetation growth. The high concentration of TK in Chongqing is not related to TOC, TN, and TP, but nitrogen limits the growth of plants. Phosphorus and potassium elements should be supplemented in growing vegetation in Hunan Province. In conclusion, potassium should be supplemented in growing pants in rocky desertification areas of Southwest China. In addition, phosphorus and nitrogen should be supplemented in Hunan Province and Chongqing City. To strengthen the ecological management of rocky desertification and bring the management into full play, Yunnan, Hunan and Chongqing should learn the experience of ecological restoration from Guangxi.
Phosphorus adsorption and desorption in soil under different land use types in karst wetlands
CHEN Rongshu, LYU Yuanfei, WANG Shan, HUANG Zuoshui, CAI Weihao, ZHONG Rongrong, XUAN Lizhen, YAN Shenyan, QIN Yingfeng, LIANG Jianhong, HUANG Huimin, ZHU Jing
2023, 42(2): 301-310. doi: 10.11932/karst2022y26
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The adsorption and desorption of phosphorus (P) in soil are the main factors controlling the P availability and leaching risk. Soils in karst wetlands are characterized as being rich in calcium with pH close to neutral. However, it still lacks a systematic evaluation on the characteristics of P adsorption and desorption in the soil under different land use types in karst wetlands. Meanwhile, exploring the main influencing factors of P adsorption and desorption can provide a scientific basis for the prevention and control of surface source pollution in karst wetlands. This study investigated the characteristics of P adsorption and desorption in surface soils (0-20 cm) and deep soils (20-40 cm) under different land use types, namely, farmland, orchard and barren land, as well as river sediment in Huixian karst wetland, Guilin, China. Langmuir adsorption isotherm equation was applied to reveal the maximum P adsorption capacity (Qm), energy of adsorption (K) and maximum buffering capacity (MBC). In addition, the desorption rate of adsorbed P was estimated through curve fitting. The relationship of the indices of P adsorption and desorption and soil physiochemical features were analyzed to reveal the impact of human activities.The results are shown as follows, (1) The barren soils had greater P adsorption rate than the soils from farmland, orchard and river sediment. The P adsorption rates of deep soils were higher than those of surface soils when the low P concentration (below 2,500 mg·kg−1) was added.(2) Langmuir equation showed good fits to the curves of soil adsorbed P contents and the corresponding P concentrations in the equilibrated solution of all soils (R2=0.91-0.98, p<0.01). The characteristics of P adsorption in soil varied greatly among different land use types. The river sediment had the largest Qm (4,961.61 mg·kg−1)) but very low K, resulting in a relatively low MBC. To the contrary, the surface soil of the barren land had the smallest Qm (359.71 mg·kg−1) but largest K, leading to the largest MBC among all soils. The indices of P desorption characteristics of the rice paddy land and orchard soil were in-between of the above two soils.(3) The P desorption rate of river sediment (11.9%) was higher than those of the other soils. Among all surface soils, the barren land had the lowest desorption rate (4.5%). The desorption rates of all deep soils were lower than those of the surface soils, indicating a greater P sequestration capability of the deep soils in karst wetlands.(4) In terms of the surface soil of farmlands and orchards, Qm increased by 286.11% and 1,025.80%; K decreased by 79.41% and 95.49%; desorption increased by 75.56% and 33.33% respectively, compared with the wasteland. This indicates that anthropogenic tillage raised the phosphorus adsorption sites in the soil. However, the binding energy between soils and the adsorbed P decreased. Therefore, the adsorbed P did not convert into a stable form. Under high external P load, it would enter into the phase of fast P desorption. In comparison, even though the river sediment had a great Qm, its K value was the lowest, leading to a small MBC and the greatest P desorption rate. This result indicates that the weakly bound iron/aluminum-P in the karst soil reduced and released P under anaerobic condition. Even though the barren soil had a low Qm value, but its P adsorption and buffering capability was the greatest; therefore, the potential risk of P leaching was the lowest in this kind of soil.(5) The Pearson's correlation and principal component analysis (PCA) suggests that the indices of P desorption (Qm, K and MBC) were closely correlated with soil texture and pH, suggesting that land use change would affect the characteristics of P adsorption through changing soil physiochemical features. The P desorption rate was significantly correlated with soil available P, suggesting that the equilibrium of P desorption is the major control of available P content of soil. This study concludes that the characteristics of P adsorption and desorption are affected by different land uses in karst wetlands. The soils of farmland and orchards adsorb great amount of P, but with great potential risk for P leaching due to the weak retention strength. The barren soil retains P and plays an important role in reducing the risk for eutrophication owing to a high water connectivity in karst wetlands. The river sediment releases P easily, and therefore functions as a long-term P source for waterbody eutrophication.
Effect of land utilization patterns on total and easy-to-use components of soil carbon, nitrogen and phosphorus in the karst area of Pingguo, Guangxi
SU Tongqing, CUI Tingting, ZHANG Jianbing, LUO Weiqun, HU Baoqing
2023, 42(2): 311-320. doi: 10.11932/karst20230205
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Soil carbon, nitrogen and phosphorus are important factors of soil quality, which play important roles in increasing soil nutrient storage, improving soil fertility and promoting plant growth. A large number of studies have shown that returning cultivated land back to forest and grassland and converting land use patterns will lead to changes in soil nutrient status and stoichiometry. However, systematic studies on total and easy-to-use components of soil carbon, nitrogen, and phosphorus are relatively few in Pingguo karst area of Youjiang River Valley in central Guangxi. In this study, plots of three types of land use (the restored forest and grassland from cultivated land and cultivated land for sugarcane and maize) inside and near Pingguo National Field Observation and Research Station of Karst Ecosystem, Guangxi were taken as research objects, and 0-15 cm surface soil was sampled in March, 2021. The physical and chemical properties of soil, total and easy-to-use components of carbon, nitrogen and phosphorus and their relationships were analysed in order to better understand the effects of returning cultivated land back to forest and grassland and converting land utilization patterns on total and easy-to-use components of carbon, nitrogen and phosphorus of soil in karst areas. The results showed as follows: 1) Compared to cultivated land, the soil pH values of the restored forest and grassland from cultivated land increased significantly. The macro-aggregates of restored forest and grassland (42.82%, 57.11% respectively) were significantly higher than those of cultivated land for sugarcane (16.94%) and maize (5.49%), and their micro-aggregates (4.58%, 1.76% respectivey) were significantly lower than those of cultivated land for sugarcane (12.42%) and maize (16.34%). Meanwhile, compared to cultivated land for sugarcane (103.39 mg·kg−1, 3.22 mg·kg−1) and that for maize (105.02 mg·kg−1, 3.07 mg·kg−1), available nitrogen of restored forest and grassland significantly increased to 156.55 and 166.49 mg·kg−1, repectively, while available phosphorus significantly decreased to 0.41 and 0.30 mg·kg−1, respectively. 2) Compared to cultivated land, the organic carbon, microbial biomass carbon and total nitrogen of soil in restored forest and grassland increased significantly. The values of soil organic carbon of restored forest and grassland (34.12 g·kg−1, 32.45 g·kg−1respectively) were 1.98 and 1.88 times of cultivated land for sugarcane (17.26 g·kg−1), and 2.15 and 2.04 times of cultivated land for maize (15.89 g·kg−1), respectively. The values of microbial biomass carbon of soil in restored forest and grassland (985.35 mg·kg−1, 1,110.04 mg·kg−1repectively) were 2.71 and 3.05 times of cultivated land for sugarcane (364.07 mg·kg−1), and 3.14 and 3.54 times of cultivated land for maize (313.92 mg·kg−1), respectively. The values of total nitrogen of soil in restored forest and grassland (4.14 g·kg−1, 4.10 g·kg−1respectively) were 2.48 and 2.46 times of cultivated land for sugarcane (1.67 g·kg−1), and 2.19 and 2.16 times of cultivated land for maize (1.89 g·kg−1), respectively. The total value of phosphorus in restored grassland was the highest (1.04 g·kg−1), followed by that of cultivated land for maize (0.81 g·kg−1), and the values of dissolved phosphorus of cultivated land for sugarcane and maize were significantly higher than those of restored forest and grassland. The values of stoichiometry of carbon, nitrogen, and phosphorus, OC/TP, TN/TP of soil in restored forest were significantly higher than those of restored grassland and cultivated land, and the values of restored grassland and cultivated land did not show significant difference. 3) Soil bulk density, aggregate structure, pH value, available nitrogen and available phosphorus were significantly correlated with total and easy-to-use components of carbon, nitrogen and phosphorus of soil. Properly speaking, soil pH value, large macro-aggregates, and available nitrogen showed a significantly positive correlation with organic carbon, microbial biomass carbon, total nitrogen and microbial biomass nitrogen of soil, and a significantly negative correlation with dissolved phosphorus. Meanwhile, bulk density, micro-aggregates, and available phosphorus of soil showed a significantly negative correlation with organic carbon, microbial biomass carbon, total nitrogen and microbial biomass nitrogen of soil, and a significantly positive correlation with dissolved phosphorus. The results indicated that the measures of returning cultivated land back to forest and grassland and converting land use patterns significantly improved soil carbon, nitrogen and soil quality in karst areas. These two measures are important and effective ways to control rocky desertification and protect ecological environment in karst areas.
Bibliometric analysis of the current research focus on vegetation restoration in karst areas
NING Jing, YANG Lei, CAO Jianhua, LI Liang
2023, 42(2): 321-336. doi: 10.11932/karst2022y25
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Vegetation plays an important role in the flow of material energy and nutrient cycle in the ecosystem. Karst vegetation is one of the main factors to maintain the stability of karst ecosystem function. At the same time, as a medium connecting soil, atmosphere and rock, plants not only present the characteristics of water balance in hydrologic and ecological processes, but also are an important link in regional vegetation restoration which is the basis of ecological construction and rocky desertification control in karst areas. In order to comprehensively understand the research progress, development trend and hot issues of karst vegetation restoration at home and abroad, literature related to this topic from 1985 to 2021 was retrieved from the Web of Science Core Collection Database (WoS) and China National Knowledge Infrastructure (CNKI) in this study. Based on high-frequency keyword analysis, keyword co-occurrence and cluster analysis, time evolution analysis of research subject, etc., the focuses and trends of karst vegetation restoration were analyzed. The results show that 319 and 351 related articles were collected respectively in WoS and CNKI databases from 1985 to 2021, and the number of articles published in 37 years experienced an increase with fluctuation. The publishing of these articles could be divided into three stages, the first stage (before 2005), an initiation stage of the research, in which the number of articles published was small; the second stage (2005-2015), a stage with a significant increase of literature due to great attention from domestic and foreign scholars to the ecological reconstruction of karst areas; the third stage (2015-2021), a rapid development stage, in which the number of international publications saw a continuous increase, while the domestic number showed a rise with fluctuation, and the growth rate of domestic research is significantly higher than that of international research.Rocky desertification, vegetation succession, soil nutrients and species diversity are high-frequency keywords in the literature, reflecting the common concerns of domestic and foreign research. Among them, vegetation succession law, soil nutrients and species diversity are the core issues in studies on karst rocky desertification areas. International studies on karst vegetation restoration pay more attention to ecosystem services and climate change, while domestic studies mainly focus on vegetation restoration in karst rocky desertification areas in the early stage, and pay more attention to the effects of vegetation restoration on soil properties and plant community composition in the later stage. In recent years, the diverse configuration of karst vegetation restoration technology and mode, for example, Huajiang Mode, Pingshang Mode, Huanjiang Mode, Pingguo Mode, etc. put forward through test, research and development, has become one of the research focuses. In addition, environmental benefits of vegetation restoration (moisture, nutrients, soil and water loss, etc.), soil seed banks, microbe and plant functional groups, vegetation restoration and forestry industry (understory economy and ecological industry), karst plant restoration and karst carbon sink, etc. have gradually become new hot issues in the research field of karst vegetation restoration. In the research of "vegetation restoration", the issues about industrial development such as fruit forest for ecological economy, governance and management modes for ecological economy, etc. have also been taken into account. In recent years, the restoration of karst vegetation (the control of rocky desertification) in China is closely related to the projects of poverty alleviation and elimination, for example, Huajiang Mode—the establishment of comprehensive management of industry for ecological environment in medium-intensity rocky desertification areas in karst plateau canyon, Pingshang Mode—the facilitation of vegetation restoration by planting honeysuckle in the rocky desertification control of Zhenfeng county, Huanjiang Mode characterized with ecological migration, and the Pingguo Mode characterized with the dragon fruit planting in Pingguo county.Due to the slow soil formation rate, thin soil layer and easy soil erosion, the karst area falls into a typical vulnerable ecosystem in the world, and the vegetation restoration in this area is very difficult. Therefore, the vegetation restoration mode is selected for the purpose of improving soil structure and coordinating the balance among soil water, fertilizer, air and heat. In order to promote the development of karst vegetation restoration research, it is suggested to strengthen domestic and international cooperation, and to set up some observation points in the field to observe and compare the dynamics of karst vegetation restoration in different regions for a long time. By comparing the spatio-temporal changes of large scale at home and abroad, the function and significance of vegetation restoration process on ecological restoration in karst areas can be analyzed through monitoring data. Through the restoration technology, model and evaluation method of karst vegetation system, the construction of karst ecosystem and the multi-scale pattern of vegetation diversity from the perspective of life community of mountain, forest, field, lake and grass and the perspective of rural industry can be further revealed. By comparing the research at home and abroad, some new ideas will be provided for ecological restoration in karst areas.
Flow attenuation analysis and inorganic carbon flux estimation of surface karst spring in rocky desertification control area: A case study at Laoquan spring in the Longtan trough valley, Youyang county, Chongqing City, China
LUO Zhenyu, YANG Yan, LI Ji, XIAO Wenjie, SUN Tingting, YE Zhimao
2023, 42(2): 337-350, 381. doi: 10.11932/karst2023y011
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The rational utilization of groundwater resources is the key to achieving the carbon peaking and carbon neutrality goals, strengthening the comprehensive control of karst rock desertification and soil erosion in the ecological environment. On the southern wing of Tongmaling anticline in southeast Chongqing, Longtan trough valley—a part of Wuling Mountain area—is located in Youyang county, Chongqing City, China. The karst development is strong in the trough valley area, and the distribution of groundwater is extensive. At the same time, the problem of rocky desertification is severe in this area, so the efficient utilization of water resources and ecological restoration are especially important. The objective of this study is to explore the flow characteristics of karst spring and structure types of aquifer medium, and to further analyze the variation characteristics of inorganic carbon flux in the ecological restoration area of rock desertification control. In this study, the flow attenuation equation and hydrochemical runoff method are used to estimate and analyze attenuation process and inorganic carbon flux of Laoquan spring based on the re-vegetation in a karst rocky desertification area in Longtan trough valley in Youyang county, Chongqing City, Southwest China. The results show that: (1) The flow attenuation process of Laoquan spring is divided into two sub-dynamics with attenuation coefficients of 0.0892 and 0.0196, respectively. The attenuation process of this spring mainly occurs on the first sub-dynamics. In the aquifer medium of groundwater system, the ratio of pipeline to fissure is significant. The strong water conduction effect of aquifer medium leads to the weak capacity of Laoquan spring to regulate and store rainfall infiltration water. (2) The variation process of the carbon flux of Laoquan spring during the rainstorm period is divided into four stages, and the carbon flux has obvious variation characteristics with the flow. The carbon flux during the rainstorm period is 97.64 kg·km−2·d−1. In the summer drought period (from the end of July to the end of August), the carbon flux of Laoquan spring has obvious diurnal variation characteristics, low at night and high in the day. The soil CO2 concentration, water CO2 concentration and carbon flux of Laoquan spring are synchronized in the diurnal variation, and the carbon flux in the summer drought period is 18.23 kg·km−2·d−1. (3) The climate instability can affect the carbon flux of Laoquan spring. The precipitation of this spring in summer is positively correlated with the carbon flux (R=0.78), and the evaporation is negatively correlated with the carbon flux (R=−0.36). The change of land use mode has a significant effect on the carbon flux of Laoquan spring. The correlation coefficient between ${\rm{HCO}}_3^{-}$ concentration and soil CO2 concentration based on the monthly mean value of Laoquan spring is 0.64, indicating that ${\rm{HCO}}_3^{-}$ in Laoquan spring sensitively responds to the change of soil CO2. The correlation coefficient between the annual spring carbon flux and the annual soil CO2 concentration is 0.90, and the average annual δ13CDIC shows an obvious negative trend, indicating that land use change (Vegetation Restoration) is conducive to the increasing of soil CO2 concentration and carbon flux. (4) From 2018 to 2021, the carbon flux in Laoquan spring was 11.66, 10.33, 21.31 and 16.9 t·km−2·a−1, respectively, showing an increasing trend with fluctuation. The annual inorganic carbon flux is 15.05 t·km−2·a−1(CO2). The carbon sink capacity should be enhanced by the improvement of comprehensive control measures of rocky desertification. Therefore, in the process of rocky desertification control, it is necessary to make scientific use of karst water resources and heighten the awareness of karst environment protection, especially the scientific use and management of water resources in summer rainstorm and summer drought. In addition, it is necessary to boost regional carbon sink capacity by restoring natural dominant vegetation in rocky desertification control areas.
Research on the law of water inrush disasters in pipeline-type karst tunnels under the coupling effect of stress-seepage-damage
MENG Jie, LIN Zhibin, LIN Peizhong
2023, 42(2): 351-360. doi: 10.11932/karst20230206
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With the strategy of "advancing the development of China's western regions", the construction of tunnels in karst areas has increased significantly. Among these tunnels, the karst pipeline is a kind of structure prone to disasters caused by the filling which is developed under the action of surface rainfall and groundwater dissolution. Generally, this kind of structure is small with sufficient water supply, so it is not easy to be found in the early geological survey. Once the karst pipeline is exposed by tunnel excavation, under the combined action of groundwater pressure and construction disturbance stress, the filling medium in the karst pipeline will be damaged, resulting in the decrease of its anti-sliding force and the increase of permeability. Consequently, it is easy to cause an accident of water and mud inrush. However, previous research rarely focuses on the sudden change of mechanical and permeability properties of surrounding rock and pipeline filling medium after the rock and medium have been damaged. This is inconsistent with the actual complex evolution process of water inrush disasters in pipeline-type karst tunnels. Aiming at water inrush disasters in pipeline-type karst tunnels, some scholars take the influence of tunnel excavation disturbance into consideration, and study the evolution process and disaster mechanism of water inrush disasters in pipeline-type karst tunnels through theoretical analysis, physical model test and numerical simulation. Taking the different occurrence forms of karst pipelines into account, some other scholars analyze the influence of the location and size of karst pipeline development as well as the influence of the water level of water-bearing body on the safety of karst tunnel excavation by establishing a geological model of water inrush in karst pipelines. These research results greatly ensure the excavation safety of pipeline-type karst tunnels. However, they rarely focus on the mechanical and permeability properties of the surrounding rock and pipeline filling medium after they have been damaged. In this study, we took Dazhai Tunnel in Bijie City as an example and took the stress-seepage-damage coupling effect of surrounding rock into consideration to explore the law of water inrush disasters in pipeline-type karst tunnels. Furthermore, using FLAC 3D, we studied the displacement of surrounding rock, the plastic zone, the permeability coefficient and the variation law of water inrush during the tunneling process of pipeline-type karst tunnels. On this basis, we conducted a comparative study of the effects of karst-free pipelines and different karst water pressures on the characteristics of water inrush disasters in tunnels. The numerical simulation results show that: (1) When the tunnel face is more than 4 m away from the karst pipeline, the maximum displacement of surrounding rock on the left wall, right wall, bottom arch, top arch and tunnel face will be stabilized at 25.0 mm, 24.5 mm, 14.1 mm, 18.2 mm and 34.1 mm respectively. However, once the karst pipeline is completely exposed by tunnel excavation, the filling rock body inside the karst pipeline will be prone to plastic yielding, and thus cause the overall slipping and instability. This phenomenon will result in accidents of water and mud inrush in tunnels. The result is consistent with the actual engineering situation, indicating the rationality of the mathematical model established under the coupling of stress-seepage-damage in this study. (2) The amount of water inflow during the tunneling process of the pipeline-type karst tunnel roughly changes in an "s-shaped" curve, showing strong suddenness and a large volume. When some karst pipelines are exposed by tunnel excavation, water inflow increases from 5.9 m3·h−1 to 256.0 m3·h−1; when all karst pipelines are exposed by tunnel excavation, water inflow reaches 588.7 m3·h−1. (3) If there are no karst pipelines, large displacement as well as large water inflow will not be generated by tunnel excavation through the karst cave when it is far away from the tunnel. This result indicates that the existence of karst pipelines provides a potential water-conducting channel for water inrush from karst cave to tunnel. (4) There is a starting pressure when a water inrush occurs from the karst pipeline to the tunnel. Only when the starting pressure is exceeded, will an accident of water and mud inrush occur in the tunnel, and the water inrush amount presents an obvious exponential increasing relationship with the karst water pressure.
Evolution and monitoring of karst ground collapse in the Zhifang-Miaoshan paleo-clay area of Wuhan
CHEN Biaodian, LI Xi, XIONG Qihua, LI Yulei, TU Jing, LIU Pengrui, Ye Jiang
2023, 42(2): 361-369. doi: 10.11932/karst20230207
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This study is aimed at finding out the disaster mechanism of karst ground collapse in the Zhifang-Miaoshan paleo-clay area of Wuhan and selecting appropriate methods for the monitoring and early warning, so as to effectively reduce the harm caused by karst ground collapse. Through a special karst survey, we have identified the distribution and geological structure of soluble rocks, analyzed the formation and evolution process of karst ground collapse and selected monitoring methods for different collapse stages in the study area. The survey results show that the study area is mostly distributed by paleo-clay with single-layered structure. According to the upper and lower stacking relationship of overburden cohesive soil, soft soil and non-soluble rock (red layer), the geological structure distribution of soluble rock can be divided into three categories (①, ② and ③). In the structure of class ①, the upper part is composed of cohesive soil; the lower part is soluble rock. The cohesive soil is mostly composed of paleo-clay with the value of cohesion C mainly from 42 kPa to 70 kPa, and the φ value mostly from 10.3° to 19.1°. The free movement of the soil particles is limited, and soil holes are usually formed at the bottom of the soil layer in the soil body. In the structure of class ②, the upper part is composed of cohesive soil; the middle part is soft soil (residual red clay in the shape of soft plastic-flow plastic); the lower part is composed of soluble rock, in which the red clay—weathering residues of the limestone surface—is prone to soften in the shape of soft-fluid plastic in water. Mainly distributed in solution grooves with uneven thicknesses, the red clay usually loses with the action of gravity or suction force, and hence is developed into soil holes. In the structure of class ③, the upper part is composed of cohesive soil; the middle part is the red layer (K2E1g red sandstone); the lower part is soluble rock. In this structure, soil holes are difficult to form due to the barrier of red layer; therefore, karst ground collapse is not likely to occur under the natural condition. According to the different physical and mechanical characteristics of soil bodies, the process mechanism of karst ground collapse is various in different geological structures. Soil-hole collapse mainly occurs in the structure of class ①.The disaster evolution process can be summarized as follows: (A) In the undisturbed stage, the karst water level drops little, and the small value of the suction negative pressure leads to the failure of soil denudation caused by insufficient suction force. Therefore, there is no significant change in the soil body. (B) Affected by the repeated fluctuations of karst groundwater level or human engineering activities, the soil hole is developed initially along the surface of the open karst cave, when the corrosion absorption force is greater than the collapse resistance force of the soil itself. Then the soil of the cave roof collapsed, and the continuous collapse upward contributes to the expanding of the soil hole and the thinning of its roof. (C) The hole continues to expand upwards, and the roof of the soil hole keeps balanced under the friction force generated by the lateral pressure of soil around it. In the early stage of imminent collapse, the ground surface often presents a small amount of subsidence deformation. (D) Induced by natural or man-made factors, the surrounding friction can not balance the gravity of the roof of soil hole. Consequently, the roof may collapse quickly. In the structure of class ②, there mainly occurs compound collapse of mud flow+soil hole. The process of disaster formation and evolution can be summarized as follows: (A) Thick layers of soft soil and cohesive soil are developed on the upper soluble rock. The karst opening is in the stable stage due to the blockage of the cohesive soil. (B) Affected by fluctuations of karst groundwater level or human engineering activities, the soft soil flows and loses to the cave fissure, which forms the mudflow hole, and the hole quickly expands to the top of the soft soil. (C) The soil hole continues to expand upward in the layer of cohesive soil, and the roof of the soil hole keeps balanced under the friction force generated by the lateral pressure of soil around it. In the early stage of imminent collapse, the ground surface often presents a small amount of subsidence deformation. (D) Induced by natural or man-made factors, the surrounding friction can not balance the roof of soil hole (dead weight+loading); consequently, the roof collapsed quickly. Besides, the quick loss of red clay in shapes of soft plastic-fluid plastic accelerates karst ground collapse. In the structure of class ③, it is unlikely to occur collapse because the barrier of red layer makes it difficult to form the cohesive soil. Combined with the formation mechanism of collapse, the formation and evolution of soil hole can be monitored by optical fiber, and induced factors such as groundwater levels and water pressures should also be monitored. During the deformation and collapse stage, precise leveling or GPS monitoring can be used to monitor surface deformation because the ground surface often presents a small amount of subsidence deformation before the imminent collapse.
Hillslope geo-hazard susceptibility assessment in Pingguo City based on coupling of CF information value and MLPC classifier model
WANG Xinwei, ZHANG Lili, MO Deke, YE Zongda, JIANG Fan
2023, 42(2): 370-381. doi: 10.11932/karst20230208
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Abstract:
Frequent geological hazards in Pingguo City, Guangxi Province, seriously restrict the engineering construction in this area. Through the remote sensing interpretation and field investigation, 251 hillslope geological hazards, including 189 collapses and 62 landslides in Pingguo City are determined. All hazard points are randomly split into two subsets with 80% (200) and 20% (51) respectively for training and validation purposes. In addition, an equal number of non-hazard points were randomly selected from the hazard-free areas and then divided into a training dataset and a validation dataset. The hazard point is denoted as 1 and the non-hazard point is denoted as 0. Then, based on the geological environment conditions of Pingguo City, nine factors including elevation, slope angle, slope aspect, curvature, engineering geology groups, distance from faults, soil thickness, distance from rivers and rainfall are selected as hazard evaluation factors. Elevation, slope angle, slope aspect and curvature are topographic factors, which are produced from Advanced Land Observing Satellite (ALOS) digital surface model (DSM) with a resolution of 12.5 m. Distance from rivers is one of hydrological variables, also produced from the ALOS DSM. Engineering geology groups and distance from faults are geological factors, which are produced from a geological map at a scale of 1:200,000 provided by the China Geological Survey. Soil thickness is one of the factors related to land use, which is derived from domestic high resolutions remote sensing data such as Gaofen No.2 and Beijing No.2. Rainfall is an environmental factor, which is collected from the China Meteorological Administration. All relevant factors are converted into raster format with a 12.5-m resolution of ArcGIS software. Among these nine factors, engineering geology group is a categorical factor, whereas the other factors are continuous factors. In this study, continuous factors are reclassified into categorical factors based on natural breaks or equal interval methods. The tolerance (TOL) and variance inflation factor (VIF) are used to detect multicollinearity of all the factors. Generally, a VIF of less than 10 or a TOL of more than 0.1 indicates that all the factors are independent. Then, combined with the advantages of information value (IV) and multi-layer perceptron classifier (MLPC), the coupling model of IV and MLPC is used to evaluate the susceptibility of hillslope geo-hazard in Pingguo City, and the results are classified into five classes: very low, low, moderate, high, and very high. Finally, the receiver operating characteristic curve (ROC) and the area under the ROC curve are applied to carry out accuracy verification of the model.The main conclusions include: (i) Rainfall has the highest VIF value (1.163) and the lowest TOL value (0.86), both of which do not exceed the critical threshold values (TOL>0.1 or VIF<10). Thus, there are no severe collinearity problems among the 9 conditioning factors. (ii) The information values of the factor classes show that certain classes are conducive to the occurrence of hazards. The factor classes mostly prone to the occurrence of hazards are the elevation with 250-350 m, slope angle with 40°-50°, south slope, curvature less than -0.05, limestone and dolomite, 0-500 m from the faults, soil thickness with 0-1m, the area 0-250 m from the rivers and rainfall with 1,373-1,428 mm. (iii) The zoning map of hillslope geo-hazard susceptibility in Pingguo City shows that the areas with very high, high, moderate, low and very low susceptibility respectively account for 25.39%, 3.49%, 4.34%, 30.54% and 36.24% of the total area of the city. The areas with very high susceptibility are mainly distributed in the junction of steep mountains and plains, such as Liming town, Tonglao town and Bangwei town in the north of the study area, Haicheng town, Tonglao town and Pozao town in the middle and Xin'an town in the south. The hillslope geo-hazards in these five susceptible areas cover proportions of 64.54%, 8.37%, 1.59%, 21.91%, and 3.59%, respectively, which indicates that the evaluation results of hazard susceptibility are highly consistent with the distribution of historical collapse and landslides, and the mapping results of hazard susceptibility are reliable and accurate. (iv) The frequency ratio of each susceptibility zone can be obtained by calculating the ratio of hazard point proportion and area proportion of each susceptibility class. The frequency ratio increases from the very low susceptibility area to the very high susceptibility area, which indicates that the coupling model can effectively determine the different susceptibility levels in the study area. (v) The performance of the model is comprehensively compared through the AUC and ROC curves with validation datasets. The AUC value for the IV-MLPC model is 0.809, showing that the model exhibits a satisfactory performance (AUC>0.8) in collapse and landslide spatial prediction. The research results can provide a scientific basis for the risk assessment and disaster prevention of collapse and landslide in the study area.
Case study on super high-rise foundation design of the deep-buried beaded karst cave
XIAO Hongbin, JIN Yaomin
2023, 42(2): 382-390. doi: 10.11932/karst20230209
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Abstract:
In 2007, a super high-rise building was proposed in a city. A detailed survey revealed the distribution of deep-buried beaded karst cave in the stratum under the surface of 80 meters. The construction of the proposed super high-rise building highly requires foundation stability, bearing capacity and deformation. The geological conditions of the site are complex because the site is irregularly distributed with deep-buried beaded karst caves with thin roofs in multiple layer. Geophysical exploration was conducted to prove that the burial depth of karst caves is likely to be deepened. There are many uncertainties in the horizontal and vertical distribution and connectivity of beaded karst caves. Because of the deep burial depth, the situation of groundwater cannot be accurately identified. If the foundation is shallowly buried and meets the demand of stability, its bearing capacity will not satisfy the requirement. Besides, the effective pile length is very limited, and the bearing capacity of a single pile cannot meet the design requirements. If the foundation is deeply buried, foundation piles will be fixed crossing the karst cave in each layer and entering the lower stable bedrock. Before design and construction, the construction survey should be conducted pile by pile, and foundation treatment such as grouting should be carried out for the karst cave in each layer within the range of pile shaft. However, the site survey has indicated that the recovery of 80-meter casing pipe was very difficult and even impossible for many pipes. The indeterminacy in vertical and horizontal distribution and in connectivity of karst caves was relatively large, leading to the inaccurate estimation of grouting volume, poor construction feasibility, and unavailability of managed cost. In order to address the indeterminacy of karst cave distribution—the biggest construction difficult, the shallow-buried design principle of the foundation was finally determined. According to the idea that the foundation should be shallowly buried and meet the requirement of bearing capacity as well, in the aspect of survey, the precondition for the foundation stability requirement—the deepest burial depth of each unit—was preliminary determined. Based on the distribution characteristics of karst caves, roof thicknesses and cavity distribution depths of different units, the survey was carried out by qualitative method and semi-quantitative method. It was also recommended to transform the foundation stability problem into an uneven foundation problem according to the normative framework. In terms of structural design, the foundation stability scheme was further defined through calculation, and accordingly the structure was redesigned to determine the structure model. From the perspective of architectural design, the professional scheme was revised to reduce the burial depth of the basement from the original 20 m to 12 m according to the shallow burial depth. The difficulty of shallow-buried scheme was focused on the bearing capacity of a single pile, and hence this problem was discussed in terms of architectural design. In order to reduce the bearing capacity of a single pile, the team for architectural design decided to use steel structure frame to reduce the upper load. In terms of structural design, the steel-framed shear wall and light-weight partition wall were used to reduce the wall thickness and structural dead weight and other loads. Two layers of reinforcement were adopted to increase the overall structural stiffness so as to control the uneven settlement. Although the design scheme was revised repeatedly to minimize the bearing capacity of a single pile, it still could not meet the design requirements; consequently, the construction was postponed. In order to successfully solve the problem of bearing capacity of a single pile, we visited the survey expert for foundation scheme and were recommended the new process of post-grouting for cast-in-place piles, which was still an innovation in 2007. In this process, the grouting of pile ends and pile sides after piling reinforces the soil around the ends and sides, and thus effectively increasing their resistance. In this way, this process greatly improved the bearing capacity of a single pile, and at the same time controlled the uneven settlement. The project of super high-rise building was finally carried forward in 2010.After the first phase of the project was completed, the average settlement and uneven settlement of Tower I well met the design requirements according to the settlement observation data during and after the construction. This complex project involved multi-disciplinary technical linkage including the deep integration of professional expertise from architectural design, survey, structural design and construction, which is a successful attempt on technology integration of survey, design and construction. Compared with the current integration of management progress, this technology is more complex and forward-looking. It is not only an innovation in the construction management process, but also shows a development direction for the future integration of technology optimization.

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