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2022 Vol. 41, No. 3

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2022, 41(3): 329-330.
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Study on ecological restoration strategy of karst spring region in north China:Taking Jinci spring as an example
WANG Yanxin
2022, 41(3): 331-344. doi: 10.11932/karst20220301
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In northern China, karst is widely distributed and rich in karst spring water resources. It is a high-quality water supply source for industry, agriculture and residents’ life in karst areas. However, under the superposition of global climate change, coal mining and other strong human activities, the flow of karst springs in northern China has declined, the water quality has deteriorated, and the ecological environment function of karst springs has declined. Therefore, how to take reasonable measures, strengthen the natural recovery function of karst springs through appropriate manual intervention, and finally realize the ecological environment restoration of spring area is the leading area and key field of ecological civilization construction in China. On the basis of analyzing and studying the causes of Jinci spring cutoff, the paper puts forward and scientifically evaluates a series of measures and expected results, such as strengthening leakage recharge of Fenhe ReservoirⅡ, closing and pressure mining of karst water in spring area, water conservation and limited mining in coal mine area, near source ecological water replenishment and far source river leakage recharge, in order to promote the fundamental improvement of karst groundwater ecological environment in Jinci spring area. The research work of this paper is expected to form a demonstration effect on the ecological restoration of karst springs in northern China, and provide a scientific basis for curbing the ecological deterioration in karst areas in China.
Research progress and prospect of carbon sink in karst region of China
JIANG Zhongcheng, ZHANG Cheng, LUO Weiqun, XIAO Qiong, WU Zeyan
2022, 41(3): 345-355. doi: 10.11932/karst20220302
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In the 1990s, karst scientists in China took the lead in the study of karst processes and carbon cycle. Based on systematically summarizing research progresses of the carbon cycle and carbon sink in the karst regions, this paper illustrates the principle of the karst carbon sink, puts forward the six kinds of carbon cycle models on the base of the earth system science idea, reveals the stability of karst carbon sink and answers the question of some geological scholars about karst carbon sink, and proposes a new idea to explore carbon sink potential of karst regions from the carbon cycle angle among earth atmosphere, biosphere, hydrosphere and lithosphere. Based on the review of research progresses on carbon sink in the karst regions, the carbon sink potential and shortage of the artificial intervention measure on the comprehensive treatment of rocky desertification, improvement of karst soil, carbon sequestration of aquatic plants and accelerating of karst processes have been analyzed. In the last of the paper, the development direction on investigation, researches and monitoring of carbon sink and technological innovation in the karst basins are given, meanwhile, the working idea for test and demonstration of carbon sequestration and carbon sink increase in karst basin are proposed.
An overview on the development of science and ecological hydrology of the earth critical zones in karst area
CHEN Xi, ZHANG Zhicai
2022, 41(3): 356-364. doi: 10.11932/karst20220303
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In view of the evolution history of ecology and environtment in karst area of sourthwest China and the challenges under the new situation,in this paper, the results of observation experiments on vegetation,hydrology,soil and dissolution test in three stages of vegetation degradation,artificial restoration and natural succession are systematically summarized, the development and existing problems of karst eco-hydrological model are expounded.The structure and composition of the atmosphere-vegetation-soil-rock system and the concept of co-evolution in karst area are put forward based on the scientific system thinking of the earth critical zones and the multidisciplinary comprehensive research paradigm.The research approaches of the co-evolution of eco-hydrology and carbon,water,and calcium cycles are discussed from the perspective of interdisciplinary,systematic observation and model intergration.Based on this,this paper puts forward suggestions to promote the development of karst eco-hydrology,so as to provide scientific support for the restoration of ecology and environment in karst area under the situation of global climate change and green development.
Karst ecosystem and its plants
CAO Jianhua, YUAN Daoxian, YANG Hui, HUANG Fen, ZHU Tongbin, LIANG Jianhong, ZHOU Mengxia, LUO Qukan, WU Xia
2022, 41(3): 365-377. doi: 10.11932/karst20220304
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Karst ecosystem is a vulnerable ecosystem constrained by a karst environment that is characterized as being rich in calcium, short of soil resources and insufficient for water resources (less surface water and rich groundwater water). Compared with silicate rocks, carbonate rocks are soluble, rich in calcium and magnesium, but lacking silicon, iron and aluminum. Carbonate rocks averagely contain 27.30%-54.33% of CaO, 0.49%-19.66% of MgO, and 0.41%-10.53% of insoluble matter. Thus, the vulnerability of karst ecosystem is ascribed to these geological properties. With the long-term interaction between plants and karst environment, surviving plants finally evolve into unique karst plants, featuring xerophyte, calciphilia and chomophyte.CALCIPHILIA of karst plants is demonstrated by Calciphile plants only growing on substrates rich in calcium carbonate and limestone soils, and Calcicole plants growing very well in Calcareous soil, but worse in acidic soil. Tolerance, exclusion and blocking mainly contribute the adaptation of karst plants to rich calcium environment. As relatively high free carboxyl existing in the intercellular space of plants, tolerance has high cation exchange capacity. Karst plants can accommodate a high content of calcium. There are two approaches in terms of exclusion. One is to improve the calcium protease activity, such as the cytoplasm membrane Ca2+-ATPase (ATPase) activity. Exclusion can transport calcium from cytoplasm out of the cell, and then store calcuim in the cell-wall. By another approach, excess calcium is ejected out of the cell through calcium channels, calcium secretion glands and even stoma. Blocking refers to a phenomenon that karst plants immobilize excess calcium around the rhizosphere to form calcified roots and restrict the transport of excess calcium to the living bodies mentioned above.CHOMOPHYE of karst plants means there exists much more underground biomass in karst ecosystem. Results of underground biomass investigation of karst vegetation in Maolan Nature Reserve show that biomass of karst vegetation is lower than that of non-karst forest in the same latitude, and only equivalent to that of temperate forest. However, underground biomass, reaching 57.49-58.15 mg·hm-2, is not only higher than that of non-karst forests in the same latitude, but also higher than that of non-karst forests both in temperate and tropical regions, and the absolute amount is nearly twice as large as that of non-karst forests in temperate tropical regions. Limestone and dolomite are two major carbonate rocks. Limestone is more likely to dissolve to form karstic fissures and conduits which can provide greater physical space for the growth of woody plant roots. The low anti-solubility, the aptness to the well-distributed weathering, and the uniform surface soil covering of dolomite are conducive to the development of shallow root plants. Survey results of Puding county in Guizhou Province show the high woody plant coverage and strong vegetation activity, but low ecosystem productivity in the limestone-dominated area. However, herbaceous and bush vegetation coverage is high, and the vegetation activity is weak, but ecosystem productivity is high in the dolomite-dominated area. XEROSPHYTE is the property for karst plants to adapt themselves to karst drought, on account of the karst hydrogeological structure with double layers of the epikarst and underground river. Consequently, ecological water is insufficient to meet the needs of the karst plants in karst areas in the dry season. The adaptive mechanism of karst plants mainly includes ecological regulation and physiologic regulation. The regulation of ecological traits of karst plants primarily involves prolonging roots to absorb deep water from soil and rock fissure, even underground river; decreasing the diameter of ducts and enriching parenchyma in xylem to reduce moisture transpiration; decreasing stomatal index to shrink leaves, and thickening cuticles and waxy layers to lower water loss. The regulation of physiologic traits of karst plants mainly includes,(1) accumulating proline, soluble sugar and other organic osmotic regulators to regulate the osmotic potential of plasma membrane and maintain cell membrane stability. The more contents of superoxide dismutase (SOD) peroxidase (POD) and catalase (CAT) are, the more reactive oxyradicals are produced, and the lower degree of membrane lipid peroxidation is. (2) Improving the activity of carbonic anhydrase in leaves, converting intracellular bicarbonate ions into water and CO2, supplementing water shortage in leaves and reducing intercellular CO2 during the dry season. These methods of regulation can improve the adaptability of karst plants to drought and avoid harzards. The diversity of karst plants presents minor genera families and a small number of species genera and endemic species. For example, in Xishuangbanna, Yunnan Province, the karst terrain covers an area of 3,600 km2, accounting for 19% of the total land area. Results of the forest survey show that karst vegetation includes 153 families, 640 genera and 1,394 species of vascular plants, accounting for 77.7% of the total family, 56.1% of the genera and 37.9 of the species, respectively. In Guangxi, the karst terrain covers an area of 82,100 km2, accounting for 34.8% of the total land area. The forest survey reveals that karst vegetation includes 175 families, 662 genera and 1,500 species of vascular plants, accounting for 76.75% of the total family, 59.11% of the genera and 50.28% of the species, respectively. Karst plants growing in cave twilight zone give their increasingly weak luminous intensity. Preliminary results show their species composition of herbs (88%), shrubs (8%) and vines (4%). The most abundant families include Urticaria (73 species), Gesneriaceae (37 species), Begoniaceae (22 species), Pterophoraceae (20 species) and Pterophoraceae (20 species). The most abundant genera include Stairweeds (42 species), Begonias (22 species), Auricerns (19 species), Primula Nerneris (19 species) and Coldwater flowers (13 species). Karst plants growing in Tiankeng (big collapse doline) provide possible access to the understanding of a succession of regional plant communities. In Leye Tiankeng, 863 species of seed plants belonging to 445 genera and 137 families are found. Ratios of temperate to tropical components are 1:2.31 in families and 1:1.5 in genera inside Tiankeng. Ratios of temperate components inside to outside Tiankeng are 1:2.79 and 1:2.18 respectively, showing higer proportion temperate components inside Tiankeng. The results suggest that with global warming, tropical components of a vegetation community outside Tiankeng increase continuously, while those inside Tiankeng develop slowly. Plants are producers of ecosystem, and their importance lies in their productivity and ecological service function. In order to restore the degraded karst ecosystem, we should find a proper approach to develop eco-industries with a win-win strategy for both environment and economy, based on natural karst. We should practice the principle of "lucid waters and lush mountains are invaluable assets" in the karst area, and improve and solidify the theory of karst ecosystem in China.
Theory of karst dynamics and development of modern karst science
ZHANG Cheng
2022, 41(3): 378-383. doi: 10.11932/karst20220305
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The core of the theory of karst dynamics is the carbon-water-calcium cycle, which emphasizes the systematic thinking and global view, and puts forward the conceptual model, structure and function of the karst dynamic system. The new growing point of discipline resulted from karst dynamics research has a milestone significance for the formation and development of modern karst science. The concept of "karst feature complex" has laid a complete method system for the study of karst heterogeneity, classification of karst types and formation environment. The initiation study of karst carbon cycle and carbon sink effects has successfully introduced karstology study into the field of global change, which opens a window for recognizing the role of karst processes in the global carbon cycle. Moreover, extending the study of karst geochemistry to the integration of inorganic and organic processes provides a clearer idea and method for the restoration and protection of fragile karst environment. The implementation of karst IGCP project reflects the guiding significance of karst dynamics theory for the establishment of International Karst Research Center under the auspices of UNESCO, meanwhile, karst dynamics theory has laid a solid theoretical and method foundation for us to consciously integrate into the national "Belt and Road" initiative, ecological civilization development strategy and the goals of "double carbon".
Geothermal reservoir structure and heat flow characteristics of proterozoic metamorphic rock series of Dahongshan group in Honghe river basin
LI Chuanwei, WANG Yu, ZENG Wei, WANG Jiaxing, ZHUANG Haijun
2022, 41(3): 384-394. doi: 10.11932/karst20220306
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Hot mineral water for development and utilization has been drilled from the metamorphic rock series of Dahongshan group of paleoproterozoic in the Gasa basin in the middle part of the Honghe river basin through geothermal geological survey, geophysical exploration and analysis. The exploration hole depth is 2,200.71 m, and the water intake target layer of 4th to 5th section of Dahongshan group (Pt1dhs4-5) thermal reservoir is rich in water with 1,089 m3·d−1 of borehole water inflow, 84.3 ℃ of borehole bottom temperature and 9,777 mg·L−1 of degree of mineralization of geothermal water.The hydrochemistry type is Cl-Na type, and the hydrochemistry composition is complex. The successful exploration revealed the thermal reservoir characteristics and geothermal resource potential of Dahongshan metamorphic rock series, and expanded a new field of geothermal water exploration and development. The terrestrial heat flow value of the study region is 73.3 mW·m−2. Hot springs are sparsely distributed along the Honghe fault zone,and the water temperature is generally 25 ℃ to 40 ℃. The current fault activity is relatively weak. Due to the continuous activity of the fault, the brittle dolomite marble and schist in the metamorphic rock series of the Dahongshan group distributed in the Jiasa area have formed a water-bearing fissure zone, forming a deep permeable rock zone. The overlying Quaternary loose layers and Triassic clastic rock layers are soft and flexible rock layers in the Jiasa valley basin, with good structural plane closure and poor permeability, and the thermal conductivity of rocks is as low as 2.4 W·(m·k)−1 to 2.6 W·(m·k)−1, making the layer a good thermal reservoir caprock. The high-density cold water formed by Ailao mountain and the deep structural fissure water are exchanged in the layer, forming the geothermal water of the target mining layer. The content of cation Na+ in geothermal water is significantly higher than that of K+、Ca2+、Mg2+, the milliequivalent content is 88.3%, the anion content is mainly Cl− which accounts for 81.47% of the components;the pH value is 8.14, the content of SiO2 is 75.65 mg·L−1, and the content of ion F− is 7.46 mg·L−1. The degree of mineralizationand the content of ionic components of waterare high, indicating that the metamorphic rock series with salt-bearing minerals and metamorphic minerals in the geothermal water circulation route has dissolved a large amount of minerals through deep circulation. The Cl− and Na+ ions in the thermal fluid are mainly derived from chlorapayite and sodalite in the first to third volcanic lava section of Dahongshan group(Pt1dhs4-5). The heat source in the study area mainly comes from the rising heat flow along the fault zone and regional geothermal heating. Near the Honghe fault, which penetrates deep into the mantle,the groundwater communicates smoothly with the deep heat source, absorbing the energy released by the deep magma, radioactive decay and tectonic movement, forming underground hot water. Under the action of water pressure difference and density difference, geothermal water migrates to the shallow part along the Ailao mountain piedmont fault, Shuitang-Yuanjiang fault, fault of heat conduction and water conduction such as F1, and structual fracture zone. When geothermal water migrates through the soluble rocks and the rock strata with hard brittle fracture in the metamorphic rock series of the Dahongshan group, it forms a thermal reservoir, and the water-bearing voids are mainly joint fractures.
Carbon sink of microalgae in karst lakes under the influence of the extracellular of carbonic anhydrase
LI Haitao, WU Yanyou, FU Bing
2022, 41(3): 395-400, 440. doi: 10.11932/karst20220307
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Carbonic anhydrase is a metal enzyme which contains Zn. It has the characteristics of catalyzing the mutual conversion between CO2 and HCO3− with high efficiency and specificity. It plays an important role in promoting the global carbon cycle, such as carbonate dissolution, photosynthesis of plants and atmospheric CO2 hydration reaction.Karst carbon sink refers to the biological carbon sequestration process which is the aquatic organisms represented by microalgae absorb and utilize inorganic carbon represented by HCO3− from carbonate karst erosion. In karst lake, under the catalytic action of carbonic anhydrase, it can greatly accelerate the dissolution process of carbonate rock, significantly affect the pH and the concentration of HCO3− of karst lake water,and promote the growth of microalgae. Correspondingly, the karst carbon sink capacity of microalgae increased with the increasing of biomass. And on this basis, the life activities of microalgae can promote the dissolution process of the karstification. Finally, it forms an aquatic photosynthetic carbon cycling system between carbonate rocks and atmosphere with the participation of microalgae.Isotopes are different atoms of the same element with the same number of protons but different numbers of neutrons. Isotopes in nature can be divided into radioisotopes and stable isotopes according to their stability. Stable isotope analysis is accurate, pollution-free and non-destructive, which can be used to study the interaction between organisms and the environment. It has been widely used in the field of plant ecology.Stable isotopes were used in this study.Microalgae is the primary producer of aquatic ecosystem, which refers to a class of microscopic plants living in water and living in a planktonic lifestyle. The character of microalgae in karst lakes have typical seasonal fluctuation and spatial heterogeneity. The activity of carbonic anhydrase was different significantly among various microalgae. In spring and summer, green algae dominated with strong carbonic anhydrase activity and fast growth; while in autumn and winter, the dominated algae is the diatoms which with weak carbonic anhydrase activity and slow growth. In conclusion, the activity of carbonic anhydrase determines the ability of microalgae to obtain inorganic carbon, which brings about great differences in the growth of various microalgae,and then affects a huge impact in the capacity of photosynthetic carbon sink in microalgae.Acetazolamide (AZ) belongs to the sulfonamide group which is a specific inhibitor about the extracellular of carbonic anhydrase. Its substrate is CAex, and it has a good inhibitory effect on CAex.In this study, the microalgae in Hongfeng lake, a karst plateau lake,was taken as the research object, we simulated karst condition in laboratory by adding different inorganic carbon labeled. In addition, different concentrations of AZ were added to simulate the difference of carbonic anhydrase extracellular enzyme activity of different microalgae of karst lakes. By monitoring the protein content and stable carbon isotope composition of microalgae, the proportion of absorption and utilization of inorganic carbon from different sources was calculated. The carbon sink of microalgae with different extracellular enzyme activities were calculated based on the biomass growth index of microalgae and the above proportion. The results showed that the carbon sink capacity of microalgae with high activity of carbonic anhydrase was 5 times higher than that of microalgae without carbonic anhydrase in natural water of karst lake. The extracellular carbonic anhydrase had significant effects on the photosynthetic carbon sink capacity of microalgae.Although the content of native bicarbonate is high in karst lake water, inorganic carbon utilized by microalgae mainly comes from atmospheric carbon dioxide (photosynthetic carbon sink), and only a small amount of native bicarbonate (karst carbon sink) is utilized in karst lake water. The main contribution of carbonic anhydrase extracellular enzyme is accelerating the absorption, utilization and conversion efficiency of atmospheric carbon dioxide by microalgae, and finally promoted the growth of microalgae, carbon sequestration and increase sink. It is of great significance for scientific selection of human using microalgae with strong extracellular enzyme activity of carbonic anhydrase to increase carbon sink and serve the national strategy of "carbon neutrality".
Philosophical cognition and prospect of karst research in China
LI Yuhui, ZHANG Cheng, ZHUANG Xiaodong, DING Wenrong, YU Xiaoya
2022, 41(3): 401-413. doi: 10.11932/karst20220308
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The scientific term of Karst in Europe and Yanrong in China is originated from the cognitive history and different orientation of the same objective entity (carbonate topography). The progress of Yanrong research in China has shifted from focusing on the deconstructive engineering properties and resource utilization by karst dissolution dynamics to the systematic construction of karst dynamics, karst biogeochemistry and karst ecosystem productivity. In the process of serving the needs of social and economic development, Chinese karst studies have discovered and improved the contradictory movement mechanism of "deconstruction" and "construction" of karst system and its space-time scale and effect changed by human activities, which have been transformed into the theory and technology serving for regional resource environmental management and sustainable development, including controlling karst rocky desertification. In-depth research on the movement law of opposition and unity between erosion base level evolution that controls the deconstruction of karst ecosystem in small watershed and vegetation succession that improves the construction of karst ecosystem will contribute to the construction of ecological community of karst mountain, water, fields, forests, lakes and grass and serve for sustainable development and coping with global change.
Review and prospect of modern monitoring and paleoclimate research in Xueyu cave group, Fengdu, Chongqing
CAO Min, JIANG Yongjun, HE Qiufang, YIN Jianjun, YANG Yan, LI Tingyong
2022, 41(3): 414-428. doi: 10.11932/karst20220309
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Karst caves are well developed due to karstification in carbonate reservoirs. Speleothems in the caves are of great significance to evaluate the evolutionary history of past climate and environment as speleothems record all climatic and environmental information when they were formed. A comprehensive link between paleoclimate change and modern climate based on detailed monitoring, precise chronology and high-resolution records is essential to explore the correlation and interaction between climate and the earth system in the geological history. Here, we review a series of modern monitoring and stalagmite-based Asian Summer Monsoon (ASM) records spanning the past 120 thousand years (ka B.P.) from Xueyu cave group, southwestern China. The Xueyu cave group includes Yangzi cave, Xueyu cave, and Shuiming cave, Xueyu cave is also a famous show cave. The three caves are all located in the Triassic limestone strata on the left bank of the Dragon river, which is the tributary of the Yangzi river, Fengdu, Chongqing. The overlying vadose zone is thick, and the elevations of the three caves are 10-100 m above the level of the Dragon river. Yangzi cave, Xueyu cave and Shuiming cave are respectively located at high-, middle- and low-elevation. These caves from different altitudes are excellent for modern monitoring and paleoclimate reconstruction. Since 2008, regular modern process monitoring has been carried out in the Xueyu cave to observe the transmission, transformation, and recording process of climate and environmental information. External air, overlying vegetation and soil, rock, precipitation, cave atmosphere (temperature, humidity, CO2, etc.), hydrochemical properties of the subterranean river, drip water, and cave deposits are monitored to understand the detailed mechanisms connecting cave environmental variables and properties of cave deposits. A monitoring program conducted from 2009 to 2016 recorded the characterization of external air temperature, precipitation, and the subterranean water temperature and PCO2 dynamics in the cave. Monthly measurements of cave air CO2 in the Xueyu cave show regular seasonal variations. High-resolution monitoring of cave air CO2 revealed the effects of rainfall events and tourist activities. Precipitation is one of the main factors responsible for transferring the CO2 signal from the soil to the cave. On a short time scale, PCO2 is significantly affected by tourist activities, but the magnitude is far less than that caused by seasonal or rainstorm-driven variation. Cave drip-water flow can be classified into two types-'fast flow' and 'slow flow', which reflects climatic events in different ways and may result in distinct speleothem paleoclimate records. Variations in drip water chemistry (Mg/Ca, and Sr/Ca) indicate that the Prior Calcite Precipitation (PCP) may occur when drip rates are slow. Only the 'slow flow' could reflect wet-dry variations as the drip rate variability can provide the primary control on trace element variations that are finally trapped in speleothems. The deposition rates are relatively high in winter, which could reach up to 0.33 mm·a−1. The isotopic and chemical variability observed in Xueyu cave drip waters also support previous interpretations of speleothem records from Yangzi cave and Shuiming cave where a series of stalagmite proxies is published. The stalagmite records of the Shuiming cave and Yangzi cave indicate that the stalagmites in this area have fast depositional rates. From 120 ka B.P. to 3 ka B.P., the variation of δ18O is basically consistent with the change curve of solar radiation at 65°N.The resolution of the dating in some periods was 269a, while the time resolution of isotopic composition is close to 88a, which successfully records some abrupt climate events at the scale of hundreds of or thousands of years , such as the Heinrich event, the 7.2 ka event, and the Little Ice Age. δ13C records of the stalagmite confirmed that the ''7.2 ka event'' started from 7.29±0.03 ka B.P. and its summit was 7.1±0.04 ka B.P. and the main drought period sustained about 50a. During the Little Ice Age, especially from 1,400-1,650 AD, δ18O records of stalagmites showed severe fluctuation, which indicated Asian summer precipitation was also in the fluctuating period. To sum up,the comprehensive comparison of paleoclimate changes based on accurate chronology and high-resolution records has good research potential in the Xueyu cave group.
Discussions on the disciplinary system of modern karstology-To commemorate the sixth anniversary of the publication of the academic book of Modern Karstology
PU Junbing
2022, 41(3): 429-440. doi: 10.11932/karst20220310
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As an important part of modern earth science, karstology (karst science) has always been considered as a cross and marginal discipline between geology, geography, environmental science and ecology, but has not established its own independent discipline system. According to the latest statistics, 15.2% of the global ice-free continental land is characterized by the presence of carbonate rock. The extent of carbonate rocks displaying distinctive karst landforms, which is part of important landscape types on the earth’s surface. However, for a long time, dominated research ideas and methods in karstology are mainly originated from geology, geography, hydrology, environmental science, ecology and other disciplines. In some research fields in karstology, interdisciplinary research has become the dominated characteristic, so the disciplinary systems of karstology itself is submerged in the interdisciplinary research background, which leads to the problems of incomplete disciplinary system, unclear characteristics, inaccurate orientation and so on, and has a certain adverse impact on the sustainable development of the karstological discipline. The widespread karst landform is a fragile ecological environment region with various and complex eco-environmental problems, which is also closely related with the economic and social development. For resolving these problems, it needs to utilize new scientific theory and technique. Based on a brief review of the karstology development at home and abroad, this paper analyzes the development of karstology and its related disciplines in the past 30 years, and discusses an important problem on constructing the disciplinary system of modern karstology under the guidance of earth system science and karst dynamics theory. According to the four functions of karst dynamic system (to drive the formation of karst features, to regulate greenhouse gas in atmosphere, thus mitigate environmental acidification, to drive the movements of elements, thus influence life and bring about formation of mineral deposits, and to record environmental changes) and the related resources, environment and ecological problems in karst area, this paper attempts to establish the disciplinary system of modern karstology on the basis of some views from geology, geography, geochemistry, ecology, environment and hydrology. The main subdisciplines in modern karstoloy include the following nine subdisciplines: karst geology, karst geomorphology, karst hydrogeology, karst environmental science, karst engineering geology, karst ecology, karst resource science, karstic global change science, and speleology. This paper also briefly discusses the scientific connotation and orientation of each branch subject. Karst geology discipline mainly studies the geological process and evolution of various karst phenomena, including petrology and lithofacies paleogeography of various soluble rocks (carbonate rocks, sulphate rocks, halide rocks, etc.), formation environment of strata containing soluble rocks and its formation process, geological structure and processes, development history of karst, etc. Karst geomorphology mainly studies the characteristics, genesis, distribution and evolution of various karst landforms or features on the earth’s surface and their relationship with the formation environment. Karst hydrogeology mainly studies the storage, distribution and movement of karst groundwater, the spatio-temporal variations and evolution of karst groundwater quantity and quality, the mutual transformation between surface water and karst groundwater, the evaluation, exploitation and utilization of karst groundwater resources and the protection of water environment in karst areas under the influences of natural environment and anthropogenic activities. Karst environmental science mainly focuses on the characteristics, interaction relationship and evolution rules of material and energy cycle of the lithosphere, atmosphere, hydrosphere and biosphere constrained by karst around human beings. It also studies various environmental problems in karst areas and proposes corresponding solutions. Karst engineering geology is a science that studies the interaction and mutual influence between engineering construction activities and geological environment in karst areas, and solves engineering geological problems by using the techniques and methods of modern karstology and other related disciplines to ensure the smooth run of construction works and the safe operation of various engineering. Karst ecology mainly studies the structures, functions, operation mechanisms of ecosystem constrained by karst environment and its interaction between ecosystem and human activities. Karstic global change science mainly studies the relationship between the operation processes of karst dynamic system and the source and/or sink of global greenhouse gases (mainly CO2) and the interpretation of high resolution global or regional environmental information in karst speleothems. Karst resource science mainly studies the theories and rules of formation, occurrence, evolution and distribution of various resources (mainly natural resources) related to karst system and the theories, techniques and methods of protection, exploitation and sustainable utilization of related resources. Speleology is the science of caves accessible to human, which main studies cave formation, cave landform and related geological processes, the genesis, processes and environmental significance of cave speleothems (sediments) and various cave features, cave physical, chemical, hydrological and meteorological processes, cave biology and microorganism, cave paleontology and archaeology, cave culture and art, cave surveying and mapping technology, cave exploitation, utilization and protection, cave tourism, cave health care, etc. The establishment of these sub-discipilines reflects the unity of independence and interdisciplinarity of related research directions and disciplinary development in international karstological research, and also reflects the current situation and future trend in international karstological research, which have great significance to the development of international karstology.
Process and mechanism of microbial induced carbonate precipitation
GAO Xubo, PAN Zhendong, GONG Peili, JIANG Yu, LI Chengcheng, LI Hongyu
2022, 41(3): 441-452. doi: 10.11932/karst20220311
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At present, the global ecological environment and geological environment situation is very serious. For environmental heavy metal remediation, traditional physical and chemical remediation methods have been widely used, but the traditional remediation methods have disadvantages such as high cost, high energy consumption, and the use of a large number of chemicals. As a kind of bionic engineering, the principle of biological method is that microorganism fix or degrade pollutants in the environment by microbial metabolic activity.Compared with the traditional physical and chemical methods, biological repair method has lower cost, higher efficiency, and the advantages of green environmental protection,which has been repeatedly proved that can effectively reduce the concentration of heavy metals in the soil and water. Biological mineralization is a kind of biological method, and its main mechanisms include: (1) biologically controlled mineralization; (2) biologically mediated mineralization; (3) biologically induced mineralization, in which Microbially Induced Calcium Carbonate Precipitation (MICP) is one of the main biologically induced mineralization. It is very common in various environments of seawater and sediment, fresh water and soil, and it is a biological mineralization process that exists widely in nature. At the same time, the process has the characteristics of fast reaction speed, low requirements for environmental conditions, wide application range and significant greenhouse gas emission reduction effect, so that it has been widely concerned and popularized in many fields of geology, civil engineering, water conservancy and environment. The research in this field covers the intersection of biological science and inorganic chemistry, biophysics and materials science, etc. The research on biologically induced mineralization and its application in various fields are very remarkable, especially the biologically induced mineralization provides a new idea for environmental remediation. The microbial-induced precipitation of calcium carbonate has been proved for many times to effectively reduce the concentration of heavy metal elements in the environment, and its main action process is as follows: microorganisms produce metabolite CO32− through metabolic activities, and interact with Ca2+ in the environment to form calcium carbonate precipitation under appropriate environmental conditions, and fix heavy metal ions in the environment during the formation of calcium carbonate.Based on the analysis of relevant research results at home and abroad, this paper summarizes the pathway and mechanism of calcium carbonate mineralization induced by various microorganisms, such as denitrification process, sulfate reduction and urea decomposition. In the process of mineralization induced by urea decomposing bacteria, urea is hydrolyzed into carbamate and ammonia under the action of urea decomposing bacteria, and then carbamate spontaneously decomposes to produce ammonia and carbonic acid. The ammonia generated in the reaction hydrolyzes and generates OH−, which increases the pH of the water environment and causes the hydrolysis balance of carbonic acid to move towards the direction of generating carbonic acid, resulting in a large number of carbonic acid ions, which react with the calcium ions existing in the environment and form calcium carbonate precipitation in the supersaturated state. Compared with other MICP mechanisms, urea decomposition process has the advantage of not relying on additional nutrients and producing high concentration of calcium carbonate in a short period of time, so it has attracted more attention and research.It is important to note that minerals induced by microbial mineralization are influenced by environmental factors. In this paper, represented by urea decomposers, the effects of environmental factors such as calcium source, ambient temperature, pH condition and ion concentration on minerals produced by MICP were discussed. The following conclusions are summarized :(1) calcium source affects the morphology, crystal size and morphology of carbonate precipitation and mineral deposition rate; (2) The optimum temperature for the formation and precipitation of urea decomposing bacteria mainly depends on the optimum temperature for bacterial growth and metabolism, which is usually between 20 ℃ and 40 ℃; (3) pH influences the plasma concentrations of HCO3−, CO32− and NH4+ to change the precipitation rate, which directly determines the size of mineral crystals; (4) The presence of other ions in the environment, such as Mg, Ni and Sr, will affect the formation of minerals.Finally, the effects and mechanisms of MICP on reducing the concentration of heavy metal elements in various environments are summarized in this paper. Research show that the process of calcium carbonate induced by urea decomposition can effectively reduce the concentration of heavy metals in the environment, and the fixation rate of copper, cadmium, zinc and other elements is above 90%. The mechanism of action is mainly divided into two kinds, for the heavy metal element like Cu2+, Pb2+ and Zn2+, they are fixed by forming precipitation directly with CO32− or replacing calcium ions in calcium carbonate, while for As and Cr, they will form complex anions such as arsenate in water environment, and will be fixed by substituting carbonate ions from calcium carbonate into the solid. As a simple and efficient geological environment process, MICP has broad application prospects in the field of ecological environment remediation.
Review and prospect of research on the role of micro-organisms in karst carbon cycle
KANG Weihua, CHENG Congyu, LI Wei, YU Longjiang
2022, 41(3): 453-464. doi: 10.11932/karst20220312
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Abstract:
The issue of global climate change has drawn much attention to the research on the carbon cycle of karst systems. Carbonate rock is the largest known carbon pool on the earth. It is easy to make CO2 in the atmosphere sink continuously through karstification, and enter into the pedosphere and hydrosphere in the form of inorganic carbon, and actively participate in the global carbon cycle through a series of dynamic processes such as migration and transformation, resulting in carbon sink effect. On the other hand, under the catalysis and regulation of organisms during the geological history, the deposition of carbonate rocks can also absorb atmospheric CO2 and produce a huge sink effect. Therefore, strengthening the study of weathering and depositional processes of carbonate rocks will help to study the karst carbon cycle and increase the karst carbon sink.Various microscopic organisms are distributed on the surface of carbonate rocks, and they have strong adaptability, which can affect the weathering and deposition processes of carbonate rocks through their own metabolism and the interactive network within the community. Carbonic Anhydrase (CA) is a zinc containing metalloenzyme, and it can efficiently catalyze the hydration of CO2 (CO2+H2O↔HCO3−+H−). CA and CA producing microorganisms are widely distributed in the soil and water in the karst area, and CA has good relative stability in the karst environment. CA and CA producing microorganisms can significantly promote the dissolution of carbonate rocks, and can also significantly promote the deposition of carbonate rocks under certain conditions. At present, more and more researchers begin to pay attention to how to use CA or CA producing micro-organisms to increase the carbon storage in the karst area, so as to increase the karst carbon sink.At present, some studies have proved that bacteria, fungi, actinomycetes and microalgae isolated from karst areas can participate in the process of karst carbon cycle. A large number of studies have found that micro-organisms such as bacillus, phosphorus dissolving bacteria, microalgae and their CA can promote the weathering of carbonate rocks. At the same time, atmospheric CO2 as a carbon source can be used by aquatic photosynthetic organisms, resulting in the migration and transformation process of "inorganic carbon → organic carbon → inert organic carbon", and finally forming a long-term stable carbon sink. Based on the results of the field in-situ soil column experiment and the indoor soil column simulation experiment, we estimated the annual increase in soil carbon storage caused by soil micro-organisms and their CA in the karst area of southwest China. The results showed that it was equivalent to the carbon emissions of China's thermal power plants in 2015 (the data came from the China Statistical Yearbook). It was considered that the soil micro-organisms and their CA in the karst area had the potential of carbon sequestration that could not be ignored. Micro-organisms promote the weathering of carbonate rocks mainly through mechanical and physical action, chemical degradation and enzymatic action such as production and secretion of CA. On the other hand, some micro-organisms such as cyanobacteria, bacillus, microalgae and their CA can also use atmospheric CO2 and Ca2+ in the environment to induce calcium carbonate deposition, thereby realizing the capture of atmospheric CO2. Micro-organisms promote the deposition of carbonate rocks mainly by capturing and adhering, performing metabolic activities to change environmental conditions, and producing biological enzymes such as secretions and CA. In addition, the weathering and deposition of carbonate rocks promoted by micro-organisms is a complex process involving multiple factors, which is related to the types of micro-organisms and the substances they secrete (enzymes, peptides, proteins, etc.), environmental conditions (pH, temperature, ion concentration, etc.), and various mechanisms can also interact. Researchers need to integrate various factors to reveal the mechanisms of micro-organisms promoting the weathering and deposition of carbonate rocks.At present, studies on the effects of micro-organisms and their CA on weathering and deposition carbon sinks of carbonate rocks are mainly based on laboratory simulation experiments, and mainly focused on the promotion of micro-organisms and their CA on weathering or deposition of carbonate rocks to increase karst carbon sinks. Therefore, this paper reviews the research results on the role and mechanisms of micro-organisms and their CA in weathering and deposition of carbonate rocks, and points out that in the future, it is necessary to quantitatively study the impact of micro-organisms and their CA on enhancement of carbon sinks in karst ecosystems in combination with different karst ecological environments. This review provides a reference for in-depth study of the contribution of micro-organisms and their CA to karst carbon sinks, and to increase the carbon sink capacity of karst ecosystems to help achieve carbon neutrality.
Biogeochemical cycles of karst systems and their response to global change
LIU Xin, LI Siliang, YUE Fujun, ZHONG Jun, QIN Caiqing, DING Hu
2022, 41(3): 465-476. doi: 10.11932/karst20220313
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Abstract:
Biogeochemical cycles are the core of matter cycling in the earth system, and are critical to sustaining ecosystem stability and the development of human society. However, climate change and excessive human interference may significantly alter biogeochemical cycles in surface earth systems, especially fragile karst ecosystem. Meanwhile, the special porous critical zone structure in karst regions accelerates the material circulation and its response to the change of external environment, which affects the circulation of matter and biogeochemical process at different scales. Thus, this review mainly emphasized the effects of environmental changes on biogeochemical cycles in karst regions at macroscale (climate change), mesoscale (human activities), and microscales (microbial activities). The main contents are as follow.(1) Climate change (including climate warming and precipitation anomaly) is a direct representation of global change, which not only influence the stability of ecosystem in the karst regions, but also determine local biogeochemical process and material circulation. Although climate warming may enhance the carbon sink function of the aquatic ecosystem in karst region, the watershed carbon sink effect would change with the increase of the warming degree. Moreover, disasters and extreme climate have a strong impact on the ecologically fragile karst regions, but sometimes also have important negative feedback significance to the restoration and reconstruction of regional ecosystem. Furthermore, climate warming can directly or indirectly promote soil respiration intensity by improving biological factors (e.g., physiological activity of underground roots) and abiotic factors (e.g., enzyme activity), but whether it can offset the weakening of soil respiration caused by the decrease of soil moisture content should be further studied. In addition to climate warming, precipitation anomaly also significantly affects soil respiration and watershed nutrient fluxes in karst critical zone, which have important impacts on global carbon cycle and local aquatic ecosystem security. Significantly, due to the coupling relationship between temperature and precipitation, single-factor analysis may not be able to comprehensively assess the impact of climate change on biogeochemical cycles. Therefore, laboratory and field experiments should be combined to comprehensively evaluate the impact of climate change on biogeochemical cycles and feedback on ecosystem stability in karst regions in future work.(2) The impact of human activities on the environment and biogeochemical cycles in karst regions is multi-dimensional, especially land use change, urbanization and water conservancy projects. Land use conversion and vegetation cover change not only change the structure and function of the ecosystem in karst regions, but also change the nutrient cycling process of the ecosystem, thereby affecting the local biogeochemical cycling process. Moreover, urbanization in karst regions will significantly increase the carbon storage in urban systems. Therefore, a coupling system of urban-suburb-rural ecosystem should be established to formulate appropriate environmental management policies through reasonable allocation and sharing of resources in the future. Furthermore, the construction of water conservancy projects in karst watershed not only change the transportation and transformation processes of river particles and nutrients, but also change the geochemical behavior of Dissolved Inorganic Carbon (DIC) in river water, thus affecting the watershed carbon cycle. As we know, human activities have greatly changed the biogeochemical cycles in karst regions and led to new ecological and environmental problems. Therefore, reasonable measures should be taken under the premise of scientific evaluation in order to achieve ecological protection and sustainable development in karst regions.(3) Microbes drive biogeochemical cycles through metabolic activities and respond rapidly to changing environmental conditions to maintain global ecosystem stability. Compared to non-karst regions, the unique karst structure changes the diversity and abundance of microbes. As we know, biodiversity is changing at an unprecedented rate as a result of global change. Climate change affects biogeochemical cycles through controlling microbial community structure and biomass in karst regions. In addition, nutrients addition caused by human activities also affected the functional diversity and community structure of soil microbes in karst regions. And long-term fertilization not only significantly changed the availability of carbon and nitrogen in soil profile in karst regions, leading to differentiation of soil microbial community, but also changed the coupling relationship among different elements (e.g., C, N, P, S). Microbes play a vital role in biogeochemical cycles, which should be further studied in the future under the circumstances of climate change and intensified human activities.As above, multi-factor changes have strongly influenced the matter cycling in karst regions, climate change, human activities, microbial activities and their coupling relationship are vital to regulate biogeochemical cycles. Meanwhile, we also stressed the limitations of existing research and pointed out the challenges and direction of future research. In the future, we should combine multi-scale monitoring-analysis and integrated model research from the perspective of system research (e.g., earth critical zone), so as to establish a multi-source and multi-scale coupling process and system model. Through the above methods, the evolution rules and dynamic mechanism of karst system are clarified, and the theoretical basis for ecological protection and high-quality development in karst regions are provided.
Effects of rock tablet lithology difference on estimation of rock dissolution rate and carbon flux
ZHANG Xiaoqin, LUO Weijun, WANG Yanwei, CAI Xianli, LYU Yina, WANG Shijie
2022, 41(3): 477-487. doi: 10.11932/karst20220314
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Abstract:
Under the control of subtropical humid monsoon climate, karstification is very strong in the karst area of southern China. At the same time, a lot of researches indicate that the carbon sink formed by karstification in southern China may be an important part of the global missing carbon sink. At present, there are many research methods to estimate the intensity of karst carbon sink. The carbonate rock tablet test is one of the main traditional research methods to estimate the karst carbon flux. The main principle of this method is based on the chemical reaction of water-CO2-carbonate rock. The specific operation is to bury the carbonate rock test piece with the same size under the soil, then take them out and weigh them after a certain time, use the dissolution amount of rock tablets to calculate the dissolution rate and karst carbon flux in study area. Finally, the regional karst carbon sink can be estimated according to"point by area". In the study of estimating karst carbon sink in China, previous scientists used pure limestone from Rongxian formation of Devonian System in Guilin. However, the geological background of different regions is quite different, and the composition and structure of bedrock are different, so that the estimation results of standard carbonate rock tablets (pure limestone) may be also different from the actual dissolution amount of local bedrock tablets, resulting in great uncertainty in the estimation of karst carbon sink in the region. Based on this, in this study, we chose Puding county, Guizhou Province as the study area. The main bedrock types (limestone and dolomite) of this place are made into standard size rock tablets, and buried them in the typical land use types (secondary forest, shrub, grassland, dry land and paddy field) in the study area. After monitoring for four hydrological years, the dissolution rate and karst carbon flux were calculated, then compared them with the previous research results using the standard carbonate rock tablet (pure limestone) in the same study area, and the following results are obtained; (1) Under the same climatic conditions and soil environmental conditions, lithology has a significant impact on the dissolution rate of carbonate rock tablets, and the dissolution rate has a positive correlation with CaO content in the rock tablets and a negative correlation with MgO content in the rock tablets; (2) The difference of dissolution rate between limestone and dolomite is controlled by land use types and soil depths. Without considering the influence of environmental factors, on the whole, the dissolution rate of limestone is 14% higher than that of dolomite; (3) The karst carbon sink intensity estimated by different lithology carbonate rock tablets varies greatly. The estimated result of standard limestone tablets is higher than that of local tablets in this study. Therefore, when using the carbonate rock tablet method to estimate the regional karst carbon flux, we should consider the lithology of the bedrock where the rock tablet is buried, or correct the estimation results based on the standard carbonate rock tablet, so as to accurately obtain the real karst carbon flux on the regional scale.
Analysis of influencing factors on mineral morphology of active speleothem-A case study of Furong cave in Chongqing
HUANG Yangyang, LI Tingyong, XIAO Siya, CHEN Chaojun, HUANG Ran, WANG Tao, WU Yao, XU Yuzhen, QIU Haiying, YANG Yan, LI Junyun
2022, 41(3): 488-500. doi: 10.11932/karst20220315
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Abstract:
Stalagmites, secondary mineral deposits forming in karst caves, record much paleo-climate and paleo-environment information. In stalagmites, the mineral forms of calcium carbonate are aragonite and calcite. It is considered that the properties of bedrock, discharge of drip water, pH, and the Mg/Ca ratios of drip water are the important factors affecting the crystal morphology. In addition, the changes of mineral morphology in stalagmites are thought to indicate the changes of paleo-climate and paleo-environment. At present, most studies focus on inferring the change of paleoclimate through the crystal morphology in stalagmites, while there are few studies on analyzing the mineral crystal morphology of active speleothem (AS) according to modern cave monitoring data. In this study, in order to collect active speleothem and drip water samples during 2017-2018, glass plates were placed under 3 drip water sites (MP2, MP5, MP9) in Furong Cave located in Wulong District, Chongqing. The mineral crystal morphology of AS was identified by polarizing microscope. Systematic monitoring was performed on Mg/Ca ratios, pH, the discharge of drip water, the cave environment, as well as δ18O, δ13C and Mg/Ca ratios of the active speleothem deposited on the front and back sides of glass plates. The results suggest that, (1) The mineral crystal morphology of active speleothem that deposit on both sides of glass plates at MP2 is calcite. There are calcite and aragonite-calcite mixture on the front side of glass plates at MP5 and MP9. However, aragonite-calcite crystals deposit on the back side of the glass plates, and there are more aragonites than those on the front sides. (2) The Mg/Ca ratios of drip water collected from MP2 is less than the ratios from MP5 and MP9, which indicates that the Mg/Ca ratio of drip water is an important factor affecting the mineral morphology of active speleothem. And the effect of pH values of drip water on AS mineral crystal morphology is different at different drip sites. (3) Regardless of the front or back side of glass plates, the δ18O and δ13C of AS mixed with aragonite-calcite are more positive than the calcite-dominated AS, which suggests that changes in the AS mineral morphology will lead to changes in δ18O and δ13C. The systematic monitoring and analysis in Furong Cave show that the mineral form of AS is closely related to the surface environment and the karst hydrogeological conditions in the upper part of the cave, and it has been verified that the mineral form of AS in caves has important influence on the δ18O and δ13C of stalagmites.

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