International Research Center on Karst under the Auspices of UNESCO

Guilin, China

International Research Center on Karst under the Auspices of UNESCO

Guilin, China
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Ren K.,Chinese Academy of Geological Sciences | Ren K.,International Research Center on Karst under the Auspices of UNESCO | Ren K.,Southwest University | Shen L.,Southwest University | And 5 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2016

The high CO2 concentration in Xueyue cave, Chongqing, is rare at home and abroad. However, the circulation characteristics of carbon and its controlling factors in this cave system remain unknown. PCO2-soil, PCO2-cave, PCO2-eq, SIc, and δ13CDIC of subterranean stream were analyzed to investigate the laws of CO2 concentration variations in Xueyu cave and its contolling factors, as well as the impact on carbon cycle in this cave by subterranean stream. It is found that soil PCO2 mainly controlled by precipitation in subtropical areas was higher in rainy season than that of dry season. Cave air PCO2 exhibited seasonal variations, high cave air PCO2 typically occurred during warm periods, and low cave air PCO2 were typical of cold periods. It was ventilation driven by the temperature difference between cave and outside air that resulted in a sharp transition of cave air PCO2. Meanwhile, cave air PCO2 could rise to high level in a short period of time because of CO2 degassing from subterranean stream. Due to soil CO2 effect, groundwater became more mineralized water with low SIc and high water PCO2-eq, and dissolution in some months in rainy season. With the reduction of soil CO2 and precipitation, groundwater had low degree of mineralization with high SIc and low water PCO2-eq in dry season. © 2016, Editorial Department of Earth Science. All right reserved.

Pu J.,Chinese Academy of Geological Sciences | Pu J.,International Research Center on Karst Under the Auspices of UNESCO | Yuan D.,Chinese Academy of Geological Sciences | Yuan D.,International Research Center on Karst Under the Auspices of UNESCO | And 4 more authors.
Environmental Earth Sciences | Year: 2012

Groundwater quality in karst regions is largely controlled by natural processes and anthropogenic activities. Over the past 10 years, dissolved Sr and its radiogenic isotope, 87Sr/86Sr, were widely used to trace the sources of solutes in groundwater. However, there is little research about hydrogeochemistry and Sr isotopic compositions of the karst groundwater in Chongqing karst area. In this paper, thirty-five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types. Hydrochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO3 type or Ca(Mg)-HCO3 type. The dissolved Sr concentrations of the studied groundwater ranged from 0. 57 to 15. 06 μmmol/L, and the 87Sr/86Sr varied from 0. 70751 to 0. 71627. The groundwater samples from different aquifers and land use types showed distinctive dissolved Sr concentrations and 87Sr/86Sr. The very positive relationship between Ca/Sr and Mg/Sr in dolomite and limestone aquifers suggests that Ca, Mg and Sr element come mainly from the release of carbonate rock under the groundwater-rock-CO2 gas interaction. According to the 87Sr/86Sr ratio, the Sr element in karst groundwater in Chongqing was controlled by the weathering of limestone, dolomite and silicate rock (allogenic water in a non-karst area). The relationship 87Sr/86Sr versus Sr2+/[K+ + Na+] shows that the anthropogenic inputs also obviously contribute to the Sr contents. The research results show that the karst groundwater in Chongqing is facing serious crisis of water quality, and needs to be protected further. © 2012 Springer-Verlag.

Qingyu Z.,Wuhan University | Qingyu Z.,Chinese Academy of Geological Sciences | Qingyu Z.,International Research Center on Karst Under the Auspices of UNESCO | Bin L.,Chinese Academy of Geological Sciences | And 10 more authors.
Environmental Earth Sciences | Year: 2016

In the Lunnan area of the Tarim Basin, the fracture cave system of the Ordovician carbonate paleokarst, with strongly heterogeneous well-developed corrosion pores, caves, fissures, and a large underground water system, is buried at depths of 5068.51–5709.74 m. There has been little research on the carbon and oxygen isotopic characteristics of the cave fills of the middle–lower Ordovician karst within this area, and little is known about the regional karst developmental stages and their filling environments. In this work, systematic geochemical studies were conducted on the carbon and oxygen isotopes of 47 karst fill samples, based on which the developmental stages of the paleokarst and their characteristic filling environments were determined. Four different karstification stages were identified together with their filling environments. The results revealed δ13C (PDB) values within the range of 6.06 to −8.69 ‰ with an average of −1.40 ‰ and δ18O values within the range of −5.78 to −17.28 ‰ with an average of −10.74 ‰. The calculated deposition temperatures of the karst fracture caves were between 2.24 and 55.84 °C with an average of 22.06 °C. The Z values of the characteristic medium salinity were between 104.33 and 133.47 with an average of 119.06. Both the δ13C and the δ18O values exhibited broad ranges, resulting in a large span of calculated temperature differences that drift to opposite ends, revealing the complex and multiphase nature of the carbonate karstification process and the respective filling environments within this area. © 2016, Springer-Verlag Berlin Heidelberg.

Li R.,Southwest University | Li R.,International Research Center on Karst Under the Auspices of UNESCO | Xiao Q.,International Research Center on Karst Under the Auspices of UNESCO | Liu W.,Southwest University | And 6 more authors.
Huanjing Kexue/Environmental Science | Year: 2015

To reveal the temporal and spatial variation pattern of groundwater chemistry in Lihu Lake and explore the causes for the change of water quality through analysis of sulfur isotope and nitrogen-oxygen isotope, so as to provide scientific basis for reasonable exploitation and protection of karst water resources. Several groundwater samples, collected from January to December in 2010 and May, October in 2014 were monitored to analyze the chemical composition of conventional water and the characteristics of δ34S-SO42-, δ15N-NO3-, and δ18O-NO3-. The results showed that: (1) The hydrochemical type of the underground water was HCO3-Ca type and effected by the seasonal precipitation and human activity, the temporal and spatial variation of the main cations was obvious. (2) The sulfur concentration in the underground river was slightly decreased since the operation of the sewage plant, however, the sulfur concentration was still high. The nitrate pollution aggravated in the year 2014 compared to 2010. Impacted by human activity, the concentration of sulfur and nitrate was higher in the upstream Nandan river, Layi cave and the midstream Liangfeng cave, and Gantianba than in the downstream Xiaolong cave. (3) The δ34S-SO42- value ranged from -4.12‰ to -0.93‰. It was inferred that the emission of sulfur oxides through burning coal resulted in the rainwater acidification, which input a large amount of SO42- into the underground water in the form of acid rain. (4) The δ15N-NO3- value ranged from 0.26‰ to 11.58‰, with an average value of 7.61‰, the δ 18O-NO3- value ranged from -2.33‰ to 21.76‰, with an average value of 9.38‰. In combination of the composition analysis of nitrogen-oxygen isotope of nitrate, it was believed that soil organic nitrogen, manure and sewage were the main sources of nitrate in the groundwater and the main causes for aggravation of nitrate pollution of the underground water. ©, 2015, Huanjing Kexue/Environmental Science. All right reserved.

Zhang C.,Chinese Academy of Geological Sciences | Zhang C.,International Research Center on Karst under the Auspices of UNESCO | Wang J.-L.,Chinese Academy of Geological Sciences | Wang J.-L.,International Research Center on Karst under the Auspices of UNESCO | And 2 more authors.
Acta Geoscientica Sinica | Year: 2015

The study of diel variations can help to reveal biogeochemical processes that occur relatively rapidly in natural waters and also the main and important controlling factors that influence the changes of aqueous chemistry. Three-day monitoring with high resolution data logger and high frequency sampling with 1-hour interval were conducted in a typical karst spring-fed stream with abundant aquatic vegetation. Daily cycling of hydrochemistry and its changes along the stream flow were discussed and the influence of biogeochemical processes on hydrochemistry was analyzed. The results show that the changes in aqueous chemistry are closely associated with biogeochemical processes and featured as diel cycling. Concentrations of Ca2+ and DIC decrease during the daytime with an amplitude of 22.4%, which reflects the controls of photosynthesis of aquatic plants and suggests that the stream loses Ca2+, DIC and nutrients with downstream distance, but changes of various components along the stream flow are quite different. NO3- concentration also tends to decrease along the stream flow, which is consistent with plant assimilation and exhibits a slightly daytime increasing and nighttime decreasing cycling in a 24-hour time scale. The latter may be caused by nitrification in such a nutrient-rich stream. Data of DOC and TOC collected at hourly interval change quickly but still have a daytime increase and nighttime decrease cycling, with daily increases of as high as 100%. These diel DOC and TOC cycles are likely caused by metabolic processes. The study of diel hydrochemical cycling and biogeochemical processes in karst spring-fed streams will improve understanding of carbon conversion rate between DIC and DOC in karst aquatic environments and thus lead to better estimation of karst carbon sink. ©, 2015, Science Press. All right reserved.

Pu J.-B.,Chinese Academy of Geological Sciences | Pu J.-B.,International Research Center on Karst under the Auspices of UNESCO
Acta Geoscientica Sinica | Year: 2013

Karst groundwater constitutes the important water resources and life support systems in the karst areas, and its geochemical research is an indispensable method for karst aquifer protection. There are approximately 380 subterranean karst streams (SS) which are the important part of the groundwater resources in Chongqing City. The isotope geochemistry of 51 subterranean karst streams in Chongqing shows that all the SS waters originate from modern precipitation because their δ18O and δD values are distributed along the line of GMWL or LMWL, which shows that the evaporation of groundwater does not occur or is not strong. Under the control of movement of rain cloud cluster from south to north (atmospheric circulation effect) and the regional relief, the regional distribution of δ18O and δD for SS in Chongiqng in rain season is in order of northeastern Chongqing < western Chongqing, central area of Chongqing < southeastern Chongqing (the symbol "<" means "more minus"). In dry season, the regional distribution of δ18O and δD for SS is not clear due to the slower movement velocity in karst aquifer. Because of the slower movement velocity and longer staying time in karst aquifer in dry season, the d-excess value of SS in dry season is obvious smaller than that in wet season. Considering the relationship between the altitude and the mean value of δ18O for SS within 100 m altitude, the authors established the second order polynomial of karst groundwater between δ18O and altitude. According to the equations, the δ18O-elevation gradient of karst groundwater in Chongqing is -0.34 ‰/100 m in dry season and -0.31‰/100 m in wet season. These results are very useful to the study of the groundwater cycle in karst aquifers. The achievements obtained by the authors are applicable to the reasonable protection and exploitation of subterranean karst streams.

Pu J.,Chinese Academy of Geological Sciences | Pu J.,International Research Center on Karst under the Auspices of UNESCO | Cao M.,Southwest University | Zhang Y.,Southwest University | And 4 more authors.
Environmental Earth Sciences | Year: 2014

The application of combined isotopic and hydrochemical compositions may be useful for evaluating water quality problems in karst aquifers in which it is difficult to distinguish the sources of solutes from the natural background of those due to human activities. Multiple isotopes (δ13C-DIC, δ34S-SO4 2-) and chemical parameters were measured in rainwater, groundwater and sewage in order to elucidate the solute sources and impacts from human activities and natural background in the Laolongdong karst catchment in Chongqing Municipality, SW China. Overall, the dissolution of carbonate rock controls Ca2+, Mg2+ and HCO3 - content in rainwater and karst groundwater. SO4 2- originated mainly from gypsum dissolution in karst groundwater. Carbonate rocks in the studied site could be dissolved jointly by H2CO3 from the natural CO2-H2O reaction and other acids (organic acids and HNO3) from sewage and soils. Sewage discharge from urban areas and agriculture activities lead to the increase of NO3 -, PO4 3- and Cl- in karst groundwater. To protect and sustainably utilize the karst aquifer, sewage originating from urban areas must be controlled and treated and the use of fertilizer should be limited. © 2014 Springer-Verlag Berlin Heidelberg.

Guo F.,Institute of Karst Geology | Guo F.,International Research Center on Karst under the Auspices of UNESCO | Guo F.,Chang'an University | Jiang G.,Institute of Karst Geology | And 4 more authors.
Water Environment Research | Year: 2015

Changes of groundwater flow and quality were investigated in a subtropical karst aquifer to determine the driving mechanism. Decreases in groundwater flow are more distinct in discharge zones than those in recharge and runoff zones. Long-term measurement of the represented regional groundwater outlet reveals that groundwater discharge decrease by nearly 50% during the dry season. The hydrochemistry of groundwater in the runoff and discharge zones is of poorer quality than in the recharge zone. Indications of intensive land resource exploitation and changes in land use patterns were attributed to changes in groundwater conditions since 1990, but the influence of climate change was likely from 2001, because the water temperature exhibited increasing trends at a mean rate of 0.02 °C/yr even though groundwater depth was high in the aquifer. These conclusions imply the need for further groundwater monitoring and reevaluation to understand the resilience of aquifer during urbanization and development.

Pu J.,Chinese Academy of Geological Sciences | Pu J.,International Research Center on Karst under the Auspices of UNESCO | Yuan D.,Chinese Academy of Geological Sciences | Yuan D.,International Research Center on Karst under the Auspices of UNESCO | And 3 more authors.
Environmental Earth Sciences | Year: 2014

The role of CO2 in karst has been of interest for decades, and emphasized by IGCP 379, International Geoscience Programme, UNESCO started in 1995. There are still open questions about the dynamics of carbon in karst systems, particularly the flux of carbon between the surface and subsurface and between different components in the karst subsurface. This research report focuses on the variations of hydrochemistry and PCO2 (partial pressures of carbon dioxide) in subtropical karst groundwater, using high-resolution auto-monitoring hydrochemical data (15-min intervals). The aim of this study was to understand how hydrochemistry and PCO2 in karst systems respond to recharge over different time scales and what the controlling factors are. An auto-monitoring hydrochemistry station was installed about 300 m upstream from the exit in the active stream channel of Xueyu Cave, a typical subtropical karst cave. Four years of high-resolution continuous pH, specific conductivity (Spc), temperature and water-level data were collected. A thermodynamic model was used to link the continuous data to monthly water quality data, allowing the calculation of CO2 partial pressures and calcite saturation (SIc) levels on a continuous basis. Seasonal, diurnal and storm-scale variations were captured in the hydrochemistry and calculated PCO2 records, indicating that the cave stream is a dynamic and variable system. Seasonal features (higher specific conductivity and lower pH in summer; lower specific conductivity and higher pH in winter) tend to covary with temperature which influences the production of CO2 in soils, thus being the driving force for the variations (the soil CO2 effect). Due to the buffer effect of a thick vadose zone and large void cave space, diurnal variations are not obvious compared with epikarst springs in SW China. Storm-scale fluctuations due to storm events occur during the summer rainy season. Piston flow effects, dilution and soil CO2 effects determine the variations in different storm events. At the beginning of the rains, the piston effect drives the variations, characterized by increase in Spc, SIc and pH in the cave stream and decrease in PCO2. With heavy rainfall, decrease in Spc shows control by the dilution effect, while decrease in SIc and pH and increase in PCO2 indicates the greater influence of soil CO2. These results imply that the soil and cave voids are important factors influencing the hydrochemical evolution of karst groundwater. Future works need to use such high-resolution technology widely for tracing the PCO2 and hydrochemical variations in different karst aquifers. © 2013 Springer-Verlag Berlin Heidelberg.

Pu J.,Chinese Academy of Geological Sciences | Pu J.,International Research Center on Karst under the Auspices of UNESCO | Yuan D.,Chinese Academy of Geological Sciences | Yuan D.,International Research Center on Karst under the Auspices of UNESCO | And 4 more authors.
Environmental Earth Sciences | Year: 2013

Groundwater from karst subterranean streams is among the world's most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are affected by both natural environment and people. Therefore, the study of karst groundwater hydrochemistry and its solutes' sources is very important to ensure the normal function of life support systems. This paper focused on the major ion chemistry and sulfate isotope of karst groundwater in Chongqing for tracing the sulfate sources and related hydrochemical processes. Hydrochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO3 type or Ca(Mg)-HCO3 type. However, some hydrochemical types were the K + Na + Ca-SO4 type (G25 site) or Ca-HCO3 + SO4 type (G26 and G14 sites), indicating that the hydrochemistry of these sites may be strongly influenced by anthropogenic activities or unique geological characteristics. The δ34S-SO4 2- of collected karst groundwater sample fell into a range of -6. 8 to 21. 5 ‰, with a mean value of 5. 6 ‰. In dolomite aquifer, the δ34S-SO4 2- value ranges from -4. 3 to 11. 0 ‰, and in limestone aquifer, it ranged from -6. 8 to 21. 5 ‰. The groundwater samples from different land use types showed distinctive δ34S-SO4 2- value. The δ34S-SO4 2- value of groundwater samples had range of -6. 8 to 16. 7 ‰ (mean 4. 0 ‰, n = 11) in cultivated land areas, 1. 5-21. 5 ‰ (mean 7. 2 ‰, n = 20) in forested land areas, and -4. 3 to 0. 8 ‰ (mean -1. 7 ‰, n = 2) in coalmine areas. The δ34S-SO4 2- values of groundwater samples collected from factory area and town area were 2. 2 and 9. 9 ‰, respectively. According to the δ34S information of potential sulfate sources, this paper discussed the possible sulfate sources of collected karst groundwater samples in Chongqing. The variations of both δ34S and 1/SO4 2- values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sulfide mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) contributed to sulfate in karst groundwater. The influence of oxidation of sulfide mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread. For protecting, sustaining, and utilizing the groundwater resources, the sewage possibly originating from urban, mine or industrial area must be controlled and treated, and the use of fertilizer should be limited. © 2012 Springer-Verlag.

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