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Papers by Zaihua Liu

Chinese Science Bulletin

DIC fertilization of primary production in karst lake-reservoirs and its effects on carbon seques... more DIC fertilization of primary production in karst lake-reservoirs and its effects on carbon sequestration and mitigation of eutrophication

Elementa: Science of the Anthropocene, 2021

During the past century, many lacustrine environments have changed substantially at the ecosystem... more During the past century, many lacustrine environments have changed substantially at the ecosystem level as a result of anthropogenic activities. In this study, the distributions of n-alkane homologues, carbon isotopes (δ13Corg), organic carbon, and the C/N atomic ratio in two sediment cores from Fuxian Lake (Yunnan, southwest China) are used to elucidate the anthropogenic impacts on this deep, oligotrophic, freshwater lake. The carbon preference index (CPI) of long-chain components, average chain length (ACL), proportion of aquatic macrophytes (Paq), and terrigenous/aquatic ratios (TAR) show different temporal patterns that reflect variations in biological production. Notably, the n-alkane homologues are shown to be more sensitive to environmental changes than δ13Corg and the C/N ratio. Prior to the 1950s, minor variations in the sedimentary geochemical record were likely caused by climate changes, and they represent a natural stage of lake evolution. The onset of cultural eutrophic...

Scientific Data, 2020

An amendment to this paper has been published and can be accessed via a link at the top of the pa... more An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Hydrogeology Journal, 2020

This study compares and analyzes high-frequency hydrochemical data from three karst catchments in... more This study compares and analyzes high-frequency hydrochemical data from three karst catchments in the mountainous Gadenalpe (GAC, Austrian Alps), Tsanfleuron-Sanetsch (TSC, Swiss Alps), and Banzhai (BZC, SW China) regions, to differentiate the effects of temperature, runoff, and land-cover on carbonate weathering. The results show that when bare rock dominates in the recharge area, as in the GAC and TSC, the seasonal discharge variations account for the most significant change in HCO 3 − concentration. In these two alpine catchments, maximum HCO 3 − concentrations occurred in the cold season when the areas were covered by snow and discharge was low, whereas minimum HCO 3 − concentrations occurred in the warm season, when snowmelt and/or glacier melt caused higher discharge and dilution. In contrast, control by the strong seasonal variation in soil respiration in the subtropical catchment (BZC), caused by the well-developed forest cover, exceeded the negative impact of temperature on carbonate weathering. This led to higher HCO 3 − concentrations during the summer growing season than in the winter dormant season. This study demonstrates that the occurrence of different soils/vegetation has a profound impact on the behavior of carbonate weathering on land, from negative temperature- and discharge-driven correlations in alpine catchments to positive soil CO 2 -driven correlation in subtropical catchments. Based on the equilibrium modeling of HCO 3 − concentration for a global temperature range, it is predicted that under future global warming, karst regions in cold climates with vegetation cover will have increasing CO 2 consumption potential, whereas karst regions in warm climates will have decreasing CO 2 consumption potential. Cette étude compare et analyse des données hydrochimiques à haute fréquence de trois bassins versants karstiques dans les régions montagneuses du Gadenalpe (GAC, Alpes autrichiennes), du Tsanfleuron-Sanetsch (TSC, Alpes suisses), et de Banzhai (BZC, Sud-Ouest de la Chine), pour différentier les effets de la température, du ruissellement, et de l’occupation du sol sur l’altération des carbonates. Les résultats montrent que lorsque la roche nue est dominante dans la zone de recharge, comme c’est le cas pour GAC et TSC, les variations saisonnières du débit expliquent le changement le plus significatif des concentrations d’HCO 3 − . Dans ces deux bassins versants alpins, les concentrations d’HCO 3 − les plus élevées prennent place au cours de la saison froide lorsque les régions sont couvertes par la neige et que le débit est faible, alors que les concentrations les plus faibles se produisent lors de la saison chaude, lorsque la fonte des neiges et/ou la fonte des glaciers entraîne un débit et une dilution plus élevés. En revanche, le contrôle par la forte variation saisonnière de la respiration du sol dans le bassin versant subtropical (BZC), causée par le couvert forestier bien développé, a dépassé l’impact négatif de la température sur l’altération des carbonates. Il en résulte des concentrations plus élevées d’HCO 3 − au cours de la saison de croissance estivale que pendant la saison de repos hivernale. Cette étude démontre que la présence de sols/végétation différents a un impact conséquent sur le processus d’altération des carbonates sur le terrain, de corrélations négatives liées à la température et au débit dans les bassins versants alpins à des corrélations positives liées au CO 2 du sol dans les bassins versants subtropicaux. Sur la base de la modélisation à l’équilibre de la concentration d’HCO 3 − pour une gamme de température à l’échelle mondiale, les prévisions indiquent que les régions karstiques sous climat froid avec un couvert végétal auront un potentiel de consommation de CO 2 en augmentation, tandis que les régions karstiques sous climat chaud verront leur possibilité de consommation de CO 2 diminuer. En este estudio se comparan y analizan los datos hidroquímicos de alta frecuencia de tres cuencas kársticas de las regiones montañosas de Gadenalpe (GAC, Alpes austríacos), Tsanfleuron-Sanetsch (TSC, Alpes suizos) y Banzhai (BZC, China occidental), para diferenciar los efectos de la temperatura, el escurrimiento y la ocupación del terreno en la meteorización del carbonato. Los resultados muestran que cuando la roca desnuda domina en la zona de recarga, como en el GAC y el TSC, las variaciones estacionales de descarga son las responsables del cambio más significativo en la concentración de HCO 3 − . En estas dos cuencas alpinas, las concentraciones máximas de HCO 3 − se produjeron en la estación fría, cuando las zonas estaban cubiertas de nieve y la descarga era baja, mientras que las concentraciones mínimas de HCO 3 − se produjeron en la estación cálida, cuando el deshielo de la nieve y/o el deshielo de los glaciares provocaron una mayor descarga y dilución. En cambio, el control por la fuerte variación estacional de la respiración del suelo en la cuenca subtropical…

Scientific Data, 2020

Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, gro... more Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset’s coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a...

Nature Communications, 2019

The response of carbonate weathering carbon-sink flux (CCSF) to its environmental drivers is stil... more The response of carbonate weathering carbon-sink flux (CCSF) to its environmental drivers is still not well understood on the global scale. This hinders understanding of the terrestrial carbon cycle. Here, we show that there is likely to be a widespread and consistent increase in the global CCSF (ranging from + 9.8% (RCP4.5) to + 17.1% (RCP8.5)) over the period 1950–2100. In the coming years the increasing temperature might be expected to have a negative impact on carbonate weathering. However, the increasing rainfall and anticipated land-use changes will counteract this, leading to a greater CCSF. This finding has been obtained by using long-term historical (1950–2005) and modeled future (2006–2100) data for two scenarios (RCP4.5 and RCP8.5) for climate and land-use change in our CCSF equilibrium model. This study stresses the potential role that carbonate weathering may play in the evolution of the global carbon cycle over this century.

Chinese Science Bulletin, 2017

Acta Geochimica, 2019

Biological carbon pumping (BCP) is a key process in which dissolved inorganic carbon in terrestri... more Biological carbon pumping (BCP) is a key process in which dissolved inorganic carbon in terrestrial aquatic ecosystems is utilized by aquatic autotrophs for photosynthesis and transformed into autochthonous organic matter (AOC). However, the mechanisms underlying BCP and the amount of generated AOC deposited effectively, are still poorly understood. Therefore, we conducted a systematic study combining modern hydrochemical monitoring and a sediment trap experiment in Fuxian Lake (Yunnan, SW China), the second-deepest plateau, oligotrophic freshwater lake in China. Temperature, pH, EC (electrical conductivity), DO (dissolved O 2), [HCO 3-], [Ca 2? ], SI c , partial CO 2 (pCO 2) pressure, and carbon isotopic compositions of HCO 3-(d 13 C DIC) in water from Fuxian Lake all displayed distinct seasonal and vertical variations. This was especially apparent in an inverse correlation between pCO 2 and DO, indicating that variations of hydrochemistry in the lake water were mainly controlled by the metabolism of the aquatic phototrophs. Furthermore, the lowest C/N ratios and highest d 13 C org were recorded in the trap sediments. Analyses of the C/N ratio demonstrated that the proportions of AOC ranged from 30% to 100% of all OC, indicating that AOC was an important contributor to sedimentary organic matter (OC). It was calculated that the AOC flux in Fuxian Lake was 20.43 t C km-2 in 2017. Therefore, AOC produced by carbonate weathering and aquatic photosynthesis could potentially be a significant carbon sink and may have an important contribution to solving the lack of carbon sinks in the global carbon cycle. Keywords Carbonate weathering Á Hydrochemical variation Á Biological carbon pump effect Á Sediment trap Á Autochthonous organic carbon Á Carbon sink & Zaihua Liu

Global and Planetary Change, 2016

Chinese Science Bulletin, 2017

Geochimica et Cosmochimica Acta, 2015

Conventional carbonate-water oxygen isotope thermometry and the more recently developed clumped i... more Conventional carbonate-water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials. In spite of a large number of studies, however, there are still large uncertainties in both d 18 O-and Δ 47-based temperature calibrations. For this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates. In this study we analyzed oxygen, carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines, tufa and cave deposits from natural springs and wells. Together these samples cover a temperature range from 6 to 95°C. Travertine samples were collected close to the vents of the springs and from pools, and tufa samples were collected from karstic creeks and a cave. The majority of our vent and pool travertines and tufa samples show a carbonate-water oxygen isotope fractionation comparable to the one of Tremaine et al. (2011) with some samples showing higher fractionations. No significant difference between the calcite-water and aragonite-water oxygen isotope fractionation could be observed. The Δ 47 data from the travertines show a strong relationship with temperature and define the regression Δ 47 = (0.044±0.005 x 10 6) / T 2 + (0.205±0.05047). The pH of the parent solution, mineralogy and precipitation rate do not appear to significantly affect the D 47-signature of carbonates, compared to the temperature effect and the analytical error. The tufa samples and three biogenic calcites show an excellent fit with the travertine calibration, indicating that this regression can be used for other carbonates as well. This work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6ºC to 95ºC.

Earth-Science Reviews, 2015

Studies conducted over several decades have shown that solubility trapping in karst areas is an i... more Studies conducted over several decades have shown that solubility trapping in karst areas is an important component of the "missing carbon" in the global carbon cycle. Chinese researchers have taken advantage of their natural geography that includes numerous karst areas, representing approximately 1/7 of the global karst area, to conduct studies of solubility trapping. This paper reviews over 30 years of research progress on solubility trapping by China's researchers and summarizes the following five findings: (a) water plays an important role in the karst solubility trapping, regardless of its role as reactant or carrier; (b) the CO 2 concentration gradient in the soil environment, which contains biological activity, organic matter content, pH, and temperature, affects the karst solubility trapping; (c) transfer rules for CO 2 in the karst system are influenced by different land cover/land use; (d) relationships between biological metabolism and karst solubility trappings are analyzed; and (e) multiple models have been established to estimate the regional and global karst solubility trapping. This review concludes with proposals for future solubility trapping research.

Environmental Earth Sciences, 2011

About two hydrological years of continuous data of discharge, temperature, electrical conductivit... more About two hydrological years of continuous data of discharge, temperature, electrical conductivity and pH have been recorded at the Glarey spring in the Tsanfleuron glaciated karst area in the Swiss Alps, to understand how glaciated karst aquifer systems respond hydrochemically to diurnal and seasonal recharge variations, and how calcite dissolution by glacial meltwater contributes to the atmospheric CO 2 sink. A thermodynamic model was used to link the continuous data to monthly water quality data allowing the calculation of CO 2 partial pressures and calcite saturation indexes. The results show diurnal and seasonal hydrochemical variations controlled chiefly by air temperature, the latter influencing karst aquifer recharge by ice and snowmelt. Karst process-related atmospheric CO 2 sinks were more than four times higher in the melting season than those in the freezing season. This finding has implication for understanding the atmospheric CO 2 sink in glaciated carbonate rock terrains: the carbon sink will increase with increasing runoff caused by global warming, i.e., carbonate weathering provides a negative feedback for anthropogenic CO 2 release. However, this is a transient regulation effect that is most efficient when glacial meltwater production is highest, which in turn depends on the future climatic evolution. Keywords Hydrochemical variation Á Glaciated karst aquifer Á Temperature-controlled recharge Á Karst process Á Atmospheric CO 2 sink Á Switzerland Á Alps

Science in China Series D: Earth Sciences, 2000

Taking Huanglong Ravine and Kangding, Sichuan, and Xiage, Zhongdian, Yunnan, as examples, the aut... more Taking Huanglong Ravine and Kangding, Sichuan, and Xiage, Zhongdian, Yunnan, as examples, the authors summarize the hydrogeochemical and carbon stable isotopic features of the geothermal CO 2-water-carbonate rock system and analyze the CO 2 sources of the system. It was found that the hydrogeochemical and carbon stable isotopic features of such a system are different from those of shallow CO 2-water-carbonate rock system, which is strongly influenced by biosphere. The former has higher CO 2 partial pressure, and is rich in heavy carbon stable isotope. In addition, such a geothermal system is also different from that developed in igneous rock. The water in the latter system lacks Ca 2+ , and thus, there are few tufa deposits on ground surface, but it is rich in light carbon stable isotope. Further analysis shows that CO 2 of the geothermal CO 2-water-carbonate rock system is a mixture of metamorphic CO 2 and magmatic CO 2 .

Science in China Series B: Chemistry, 2001

Techniques of rotating-disk and catalyst were used in investigating the kinetics of dolomite diss... more Techniques of rotating-disk and catalyst were used in investigating the kinetics of dolomite dissolution in flowing CO 2-H 2 O system. Experiments run in the solutions equilibrated with various CO 2 partial pressures () from 30 to 100000 Pa. It shows that dissolution rates of dolomite are related with rotating speeds at conditions far from equilibrium. This was explained by modified diffusion boundary layer (DBL) model. In addition, the dissolution rates increase after addition of carbonic anhydrase (CA) to solutions, where the CA catalyzes CO 2 CO P 2 conversion. However, great differences occur among various CO 2 partial pressures. The experimental observations give a conclusion that the modified DBL model enables one to predict dissolution rates and their behaviour at various with satisfactory precision at least far from equilibrium.

Karst flow systems formed in carbonate rocks have been recognized as a sink for atmospheric carbo... more Karst flow systems formed in carbonate rocks have been recognized as a sink for atmospheric carbon that originates as gaseous carbon dioxide and ends up as dissolved aqueous carbon, primarily as bicarbonate. While measurements of the magnitude of the sink associated with carbonate rock dissolution have assumed that half of the dissolved inorganic carbon leaving a given catchment comes from the mineral and half from the atmosphere, consideration of the kinetics of carbonate mineral dissolution in acid solutions suggests that the ratio is enriched in mineral-source carbon to an extent that depends on the geochemical environment of mineral/fluid contact. After developing a methodology for precise field measurement of both the magnitude of this sink as well as the partitioning of inorganic carbon sources in south central Kentucky, in 2001 we initiated a long-term project to improve understanding and estimates of the sink with a global monitoring network. The first two new stations and m...

Hydrological Processes, 2004

High-resolution measurements of rainfall, water level, pH, conductivity, temperature and carbonat... more High-resolution measurements of rainfall, water level, pH, conductivity, temperature and carbonate chemistry parameters of groundwater at two adjacent locations within the peak cluster karst of the Guilin Karst Experimental Site in Guangxi Province, China, were made with different types of multiparameter sonde. The data were stored using data loggers recording with 2 min or 15 min resolution. Waters from a large, perennial spring represent the exit for the aquifer's conduit flow, and a nearby well measures water in the conduit-adjacent, fractured media. During flood pulses, the pH of the conduit flow water rises as the conductivity falls. In contrast, and at the same time, the pH of groundwater in the fractures drops, as conductivity rises. As Ca 2C and HCO 3 were the dominant (>90%) ions, we developed linear relationships (both r 2 > 0Ð91) between conductivity and those ions, respectively, and in turn calculated variations in the calcite saturation index SI C and CO 2 partial pressure P CO 2 of water during flood pulses. Results indicate that the P CO 2 of fracture water during flood periods is higher than that at lower flows, and its SI C is lower. Simultaneously, P CO 2 of conduit water during the flood period is lower than that at lower flows, and its SI C also is lower. From these results we conclude that at least two key processes are controlling hydrochemical variations during flood periods: (i) dilution by precipitation and (ii) water-rock-gas interactions. To explain hydrochemical variations in the fracture water, the water-rock-gas interactions may be more important. For example, during flood periods, soil gas with high CO 2 concentrations dissolves in water and enters the fracture system, the water, which in turn has become more highly undersaturated, dissolves more limestone, and the conductivity increases. Dilution of rainfall is more important in controlling hydrochemical variations of conduit water, because rainfall with higher pH (in this area apparently owing to interaction with limestone dust in the lower atmosphere) and low conductivity travels through the conduit system rapidly. These results illustrate that to understand the hydrochemical variations in karst systems, considering only water-rock interactions is not sufficient, and the variable effects of CO 2 on the system should be evaluated. Consideration of water-rock-gas interactions is thus a must in understanding variations in karst hydrochemistry.

Geochimica et Cosmochimica Acta, 1995

Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates al... more Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates along the flow path of the Huanglong Ravine, located in northwestern Sichuan province, China, on an altitude of about 3400 m asl. Due to outgassing of CO, the mainly spring-fed stream exhibits, along a valley of 3.5 km, calcite precipitation rates up to a few mm/year. We have carried out in situ experiments to measure calcite deposition rates at rimstone dams, inside of pools and in the stream-bed. Simultaneously, the downstream evolution of water chemistry was investigated at nine locations with respect to Ca2+, Mg'+, Na+ , Cl ~, SO:-, and alkalinity. Temperature, pH, and conductivity were measured in situ, while total hardness, Ca,, and alkalinity have been determined immediately after sampling, performing standard titration methods. The water turned out to be of an almost pure Ca-Mg-HCO, type. The degassing of CO, causes high supersaturation with respect to calcite and due to calcite precipitation the Ca2+ concentration decreases from 6. lo-? mole/l upstream down to 2.5. lo-" mole/l at the lower course. Small rectangular shaped tablets of pure marble were mounted under different flow regimes, i.e., at the dam sites with fast water flow as well as inside pools with still water. After the substrate samples had stayed in the water for a period of a few days, the deposition rates were measured by weight increase, up to several tens of milligrams. Although there were no differences in hydrochemistry, deposition rates in fast flowing water were higher by as much as a factor of four compared to still water, indicating a strong influence of hydrodynamics. While upstream rates amounted up to 5 mm/year, lower rates of about 1 mm/year were observed downstream. Inspection of the marble substrate surfaces by EDAX and SEM (scanning electron microscope) revealed authigeneously grown calcite crystals of about 10 pm. Their shape and habit are indicative of a chemically controlled inorganic origin. By applying a mass transfer model for calcite precipitation taking into account the reaction rates at the surface given by Plummer et al. (1978), slow conversion of CO2 into H+ and HCO.: , and diffusional mass transport across a diffusion boundary layer, we have calculated the deposition rates from the hydrochemistry of the corresponding locations. The calculated rates agree within a factor of two with the experimental results. Our findings confirm former conclusions with respect to fast flow conditions: reasonable rates of calcite precipitation can be estimated in reducing the PWP-rate calculated from the chemical composition of the water by a factor of about ten, thus correcting for the influence of the diffusion boundary layer.

Chinese Science Bulletin

DIC fertilization of primary production in karst lake-reservoirs and its effects on carbon seques... more DIC fertilization of primary production in karst lake-reservoirs and its effects on carbon sequestration and mitigation of eutrophication

Elementa: Science of the Anthropocene, 2021

During the past century, many lacustrine environments have changed substantially at the ecosystem... more During the past century, many lacustrine environments have changed substantially at the ecosystem level as a result of anthropogenic activities. In this study, the distributions of n-alkane homologues, carbon isotopes (δ13Corg), organic carbon, and the C/N atomic ratio in two sediment cores from Fuxian Lake (Yunnan, southwest China) are used to elucidate the anthropogenic impacts on this deep, oligotrophic, freshwater lake. The carbon preference index (CPI) of long-chain components, average chain length (ACL), proportion of aquatic macrophytes (Paq), and terrigenous/aquatic ratios (TAR) show different temporal patterns that reflect variations in biological production. Notably, the n-alkane homologues are shown to be more sensitive to environmental changes than δ13Corg and the C/N ratio. Prior to the 1950s, minor variations in the sedimentary geochemical record were likely caused by climate changes, and they represent a natural stage of lake evolution. The onset of cultural eutrophic...

Scientific Data, 2020

An amendment to this paper has been published and can be accessed via a link at the top of the pa... more An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Hydrogeology Journal, 2020

This study compares and analyzes high-frequency hydrochemical data from three karst catchments in... more This study compares and analyzes high-frequency hydrochemical data from three karst catchments in the mountainous Gadenalpe (GAC, Austrian Alps), Tsanfleuron-Sanetsch (TSC, Swiss Alps), and Banzhai (BZC, SW China) regions, to differentiate the effects of temperature, runoff, and land-cover on carbonate weathering. The results show that when bare rock dominates in the recharge area, as in the GAC and TSC, the seasonal discharge variations account for the most significant change in HCO 3 − concentration. In these two alpine catchments, maximum HCO 3 − concentrations occurred in the cold season when the areas were covered by snow and discharge was low, whereas minimum HCO 3 − concentrations occurred in the warm season, when snowmelt and/or glacier melt caused higher discharge and dilution. In contrast, control by the strong seasonal variation in soil respiration in the subtropical catchment (BZC), caused by the well-developed forest cover, exceeded the negative impact of temperature on carbonate weathering. This led to higher HCO 3 − concentrations during the summer growing season than in the winter dormant season. This study demonstrates that the occurrence of different soils/vegetation has a profound impact on the behavior of carbonate weathering on land, from negative temperature- and discharge-driven correlations in alpine catchments to positive soil CO 2 -driven correlation in subtropical catchments. Based on the equilibrium modeling of HCO 3 − concentration for a global temperature range, it is predicted that under future global warming, karst regions in cold climates with vegetation cover will have increasing CO 2 consumption potential, whereas karst regions in warm climates will have decreasing CO 2 consumption potential. Cette étude compare et analyse des données hydrochimiques à haute fréquence de trois bassins versants karstiques dans les régions montagneuses du Gadenalpe (GAC, Alpes autrichiennes), du Tsanfleuron-Sanetsch (TSC, Alpes suisses), et de Banzhai (BZC, Sud-Ouest de la Chine), pour différentier les effets de la température, du ruissellement, et de l’occupation du sol sur l’altération des carbonates. Les résultats montrent que lorsque la roche nue est dominante dans la zone de recharge, comme c’est le cas pour GAC et TSC, les variations saisonnières du débit expliquent le changement le plus significatif des concentrations d’HCO 3 − . Dans ces deux bassins versants alpins, les concentrations d’HCO 3 − les plus élevées prennent place au cours de la saison froide lorsque les régions sont couvertes par la neige et que le débit est faible, alors que les concentrations les plus faibles se produisent lors de la saison chaude, lorsque la fonte des neiges et/ou la fonte des glaciers entraîne un débit et une dilution plus élevés. En revanche, le contrôle par la forte variation saisonnière de la respiration du sol dans le bassin versant subtropical (BZC), causée par le couvert forestier bien développé, a dépassé l’impact négatif de la température sur l’altération des carbonates. Il en résulte des concentrations plus élevées d’HCO 3 − au cours de la saison de croissance estivale que pendant la saison de repos hivernale. Cette étude démontre que la présence de sols/végétation différents a un impact conséquent sur le processus d’altération des carbonates sur le terrain, de corrélations négatives liées à la température et au débit dans les bassins versants alpins à des corrélations positives liées au CO 2 du sol dans les bassins versants subtropicaux. Sur la base de la modélisation à l’équilibre de la concentration d’HCO 3 − pour une gamme de température à l’échelle mondiale, les prévisions indiquent que les régions karstiques sous climat froid avec un couvert végétal auront un potentiel de consommation de CO 2 en augmentation, tandis que les régions karstiques sous climat chaud verront leur possibilité de consommation de CO 2 diminuer. En este estudio se comparan y analizan los datos hidroquímicos de alta frecuencia de tres cuencas kársticas de las regiones montañosas de Gadenalpe (GAC, Alpes austríacos), Tsanfleuron-Sanetsch (TSC, Alpes suizos) y Banzhai (BZC, China occidental), para diferenciar los efectos de la temperatura, el escurrimiento y la ocupación del terreno en la meteorización del carbonato. Los resultados muestran que cuando la roca desnuda domina en la zona de recarga, como en el GAC y el TSC, las variaciones estacionales de descarga son las responsables del cambio más significativo en la concentración de HCO 3 − . En estas dos cuencas alpinas, las concentraciones máximas de HCO 3 − se produjeron en la estación fría, cuando las zonas estaban cubiertas de nieve y la descarga era baja, mientras que las concentraciones mínimas de HCO 3 − se produjeron en la estación cálida, cuando el deshielo de la nieve y/o el deshielo de los glaciares provocaron una mayor descarga y dilución. En cambio, el control por la fuerte variación estacional de la respiración del suelo en la cuenca subtropical…

Scientific Data, 2020

Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, gro... more Karst aquifers provide drinking water for 10% of the world’s population, support agriculture, groundwater-dependent activities, and ecosystems. These aquifers are characterised by complex groundwater-flow systems, hence, they are extremely vulnerable and protecting them requires an in-depth understanding of the systems. Poor data accessibility has limited advances in karst research and realistic representation of karst processes in large-scale hydrological studies. In this study, we present World Karst Spring hydrograph (WoKaS) database, a community-wide effort to improve data accessibility. WoKaS is the first global karst springs discharge database with over 400 spring observations collected from articles, hydrological databases and researchers. The dataset’s coverage compares to the global distribution of carbonate rocks with some bias towards the latitudes of more developed countries. WoKaS database will ensure easy access to a large-sample of good quality datasets suitable for a...

Nature Communications, 2019

The response of carbonate weathering carbon-sink flux (CCSF) to its environmental drivers is stil... more The response of carbonate weathering carbon-sink flux (CCSF) to its environmental drivers is still not well understood on the global scale. This hinders understanding of the terrestrial carbon cycle. Here, we show that there is likely to be a widespread and consistent increase in the global CCSF (ranging from + 9.8% (RCP4.5) to + 17.1% (RCP8.5)) over the period 1950–2100. In the coming years the increasing temperature might be expected to have a negative impact on carbonate weathering. However, the increasing rainfall and anticipated land-use changes will counteract this, leading to a greater CCSF. This finding has been obtained by using long-term historical (1950–2005) and modeled future (2006–2100) data for two scenarios (RCP4.5 and RCP8.5) for climate and land-use change in our CCSF equilibrium model. This study stresses the potential role that carbonate weathering may play in the evolution of the global carbon cycle over this century.

Chinese Science Bulletin, 2017

Acta Geochimica, 2019

Biological carbon pumping (BCP) is a key process in which dissolved inorganic carbon in terrestri... more Biological carbon pumping (BCP) is a key process in which dissolved inorganic carbon in terrestrial aquatic ecosystems is utilized by aquatic autotrophs for photosynthesis and transformed into autochthonous organic matter (AOC). However, the mechanisms underlying BCP and the amount of generated AOC deposited effectively, are still poorly understood. Therefore, we conducted a systematic study combining modern hydrochemical monitoring and a sediment trap experiment in Fuxian Lake (Yunnan, SW China), the second-deepest plateau, oligotrophic freshwater lake in China. Temperature, pH, EC (electrical conductivity), DO (dissolved O 2), [HCO 3-], [Ca 2? ], SI c , partial CO 2 (pCO 2) pressure, and carbon isotopic compositions of HCO 3-(d 13 C DIC) in water from Fuxian Lake all displayed distinct seasonal and vertical variations. This was especially apparent in an inverse correlation between pCO 2 and DO, indicating that variations of hydrochemistry in the lake water were mainly controlled by the metabolism of the aquatic phototrophs. Furthermore, the lowest C/N ratios and highest d 13 C org were recorded in the trap sediments. Analyses of the C/N ratio demonstrated that the proportions of AOC ranged from 30% to 100% of all OC, indicating that AOC was an important contributor to sedimentary organic matter (OC). It was calculated that the AOC flux in Fuxian Lake was 20.43 t C km-2 in 2017. Therefore, AOC produced by carbonate weathering and aquatic photosynthesis could potentially be a significant carbon sink and may have an important contribution to solving the lack of carbon sinks in the global carbon cycle. Keywords Carbonate weathering Á Hydrochemical variation Á Biological carbon pump effect Á Sediment trap Á Autochthonous organic carbon Á Carbon sink & Zaihua Liu

Global and Planetary Change, 2016

Chinese Science Bulletin, 2017

Geochimica et Cosmochimica Acta, 2015

Conventional carbonate-water oxygen isotope thermometry and the more recently developed clumped i... more Conventional carbonate-water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials. In spite of a large number of studies, however, there are still large uncertainties in both d 18 O-and Δ 47-based temperature calibrations. For this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates. In this study we analyzed oxygen, carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines, tufa and cave deposits from natural springs and wells. Together these samples cover a temperature range from 6 to 95°C. Travertine samples were collected close to the vents of the springs and from pools, and tufa samples were collected from karstic creeks and a cave. The majority of our vent and pool travertines and tufa samples show a carbonate-water oxygen isotope fractionation comparable to the one of Tremaine et al. (2011) with some samples showing higher fractionations. No significant difference between the calcite-water and aragonite-water oxygen isotope fractionation could be observed. The Δ 47 data from the travertines show a strong relationship with temperature and define the regression Δ 47 = (0.044±0.005 x 10 6) / T 2 + (0.205±0.05047). The pH of the parent solution, mineralogy and precipitation rate do not appear to significantly affect the D 47-signature of carbonates, compared to the temperature effect and the analytical error. The tufa samples and three biogenic calcites show an excellent fit with the travertine calibration, indicating that this regression can be used for other carbonates as well. This work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6ºC to 95ºC.

Earth-Science Reviews, 2015

Studies conducted over several decades have shown that solubility trapping in karst areas is an i... more Studies conducted over several decades have shown that solubility trapping in karst areas is an important component of the "missing carbon" in the global carbon cycle. Chinese researchers have taken advantage of their natural geography that includes numerous karst areas, representing approximately 1/7 of the global karst area, to conduct studies of solubility trapping. This paper reviews over 30 years of research progress on solubility trapping by China's researchers and summarizes the following five findings: (a) water plays an important role in the karst solubility trapping, regardless of its role as reactant or carrier; (b) the CO 2 concentration gradient in the soil environment, which contains biological activity, organic matter content, pH, and temperature, affects the karst solubility trapping; (c) transfer rules for CO 2 in the karst system are influenced by different land cover/land use; (d) relationships between biological metabolism and karst solubility trappings are analyzed; and (e) multiple models have been established to estimate the regional and global karst solubility trapping. This review concludes with proposals for future solubility trapping research.

Environmental Earth Sciences, 2011

About two hydrological years of continuous data of discharge, temperature, electrical conductivit... more About two hydrological years of continuous data of discharge, temperature, electrical conductivity and pH have been recorded at the Glarey spring in the Tsanfleuron glaciated karst area in the Swiss Alps, to understand how glaciated karst aquifer systems respond hydrochemically to diurnal and seasonal recharge variations, and how calcite dissolution by glacial meltwater contributes to the atmospheric CO 2 sink. A thermodynamic model was used to link the continuous data to monthly water quality data allowing the calculation of CO 2 partial pressures and calcite saturation indexes. The results show diurnal and seasonal hydrochemical variations controlled chiefly by air temperature, the latter influencing karst aquifer recharge by ice and snowmelt. Karst process-related atmospheric CO 2 sinks were more than four times higher in the melting season than those in the freezing season. This finding has implication for understanding the atmospheric CO 2 sink in glaciated carbonate rock terrains: the carbon sink will increase with increasing runoff caused by global warming, i.e., carbonate weathering provides a negative feedback for anthropogenic CO 2 release. However, this is a transient regulation effect that is most efficient when glacial meltwater production is highest, which in turn depends on the future climatic evolution. Keywords Hydrochemical variation Á Glaciated karst aquifer Á Temperature-controlled recharge Á Karst process Á Atmospheric CO 2 sink Á Switzerland Á Alps

Science in China Series D: Earth Sciences, 2000

Taking Huanglong Ravine and Kangding, Sichuan, and Xiage, Zhongdian, Yunnan, as examples, the aut... more Taking Huanglong Ravine and Kangding, Sichuan, and Xiage, Zhongdian, Yunnan, as examples, the authors summarize the hydrogeochemical and carbon stable isotopic features of the geothermal CO 2-water-carbonate rock system and analyze the CO 2 sources of the system. It was found that the hydrogeochemical and carbon stable isotopic features of such a system are different from those of shallow CO 2-water-carbonate rock system, which is strongly influenced by biosphere. The former has higher CO 2 partial pressure, and is rich in heavy carbon stable isotope. In addition, such a geothermal system is also different from that developed in igneous rock. The water in the latter system lacks Ca 2+ , and thus, there are few tufa deposits on ground surface, but it is rich in light carbon stable isotope. Further analysis shows that CO 2 of the geothermal CO 2-water-carbonate rock system is a mixture of metamorphic CO 2 and magmatic CO 2 .

Science in China Series B: Chemistry, 2001

Techniques of rotating-disk and catalyst were used in investigating the kinetics of dolomite diss... more Techniques of rotating-disk and catalyst were used in investigating the kinetics of dolomite dissolution in flowing CO 2-H 2 O system. Experiments run in the solutions equilibrated with various CO 2 partial pressures () from 30 to 100000 Pa. It shows that dissolution rates of dolomite are related with rotating speeds at conditions far from equilibrium. This was explained by modified diffusion boundary layer (DBL) model. In addition, the dissolution rates increase after addition of carbonic anhydrase (CA) to solutions, where the CA catalyzes CO 2 CO P 2 conversion. However, great differences occur among various CO 2 partial pressures. The experimental observations give a conclusion that the modified DBL model enables one to predict dissolution rates and their behaviour at various with satisfactory precision at least far from equilibrium.

Karst flow systems formed in carbonate rocks have been recognized as a sink for atmospheric carbo... more Karst flow systems formed in carbonate rocks have been recognized as a sink for atmospheric carbon that originates as gaseous carbon dioxide and ends up as dissolved aqueous carbon, primarily as bicarbonate. While measurements of the magnitude of the sink associated with carbonate rock dissolution have assumed that half of the dissolved inorganic carbon leaving a given catchment comes from the mineral and half from the atmosphere, consideration of the kinetics of carbonate mineral dissolution in acid solutions suggests that the ratio is enriched in mineral-source carbon to an extent that depends on the geochemical environment of mineral/fluid contact. After developing a methodology for precise field measurement of both the magnitude of this sink as well as the partitioning of inorganic carbon sources in south central Kentucky, in 2001 we initiated a long-term project to improve understanding and estimates of the sink with a global monitoring network. The first two new stations and m...

Hydrological Processes, 2004

High-resolution measurements of rainfall, water level, pH, conductivity, temperature and carbonat... more High-resolution measurements of rainfall, water level, pH, conductivity, temperature and carbonate chemistry parameters of groundwater at two adjacent locations within the peak cluster karst of the Guilin Karst Experimental Site in Guangxi Province, China, were made with different types of multiparameter sonde. The data were stored using data loggers recording with 2 min or 15 min resolution. Waters from a large, perennial spring represent the exit for the aquifer's conduit flow, and a nearby well measures water in the conduit-adjacent, fractured media. During flood pulses, the pH of the conduit flow water rises as the conductivity falls. In contrast, and at the same time, the pH of groundwater in the fractures drops, as conductivity rises. As Ca 2C and HCO 3 were the dominant (>90%) ions, we developed linear relationships (both r 2 > 0Ð91) between conductivity and those ions, respectively, and in turn calculated variations in the calcite saturation index SI C and CO 2 partial pressure P CO 2 of water during flood pulses. Results indicate that the P CO 2 of fracture water during flood periods is higher than that at lower flows, and its SI C is lower. Simultaneously, P CO 2 of conduit water during the flood period is lower than that at lower flows, and its SI C also is lower. From these results we conclude that at least two key processes are controlling hydrochemical variations during flood periods: (i) dilution by precipitation and (ii) water-rock-gas interactions. To explain hydrochemical variations in the fracture water, the water-rock-gas interactions may be more important. For example, during flood periods, soil gas with high CO 2 concentrations dissolves in water and enters the fracture system, the water, which in turn has become more highly undersaturated, dissolves more limestone, and the conductivity increases. Dilution of rainfall is more important in controlling hydrochemical variations of conduit water, because rainfall with higher pH (in this area apparently owing to interaction with limestone dust in the lower atmosphere) and low conductivity travels through the conduit system rapidly. These results illustrate that to understand the hydrochemical variations in karst systems, considering only water-rock interactions is not sufficient, and the variable effects of CO 2 on the system should be evaluated. Consideration of water-rock-gas interactions is thus a must in understanding variations in karst hydrochemistry.

Geochimica et Cosmochimica Acta, 1995

Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates al... more Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates along the flow path of the Huanglong Ravine, located in northwestern Sichuan province, China, on an altitude of about 3400 m asl. Due to outgassing of CO, the mainly spring-fed stream exhibits, along a valley of 3.5 km, calcite precipitation rates up to a few mm/year. We have carried out in situ experiments to measure calcite deposition rates at rimstone dams, inside of pools and in the stream-bed. Simultaneously, the downstream evolution of water chemistry was investigated at nine locations with respect to Ca2+, Mg'+, Na+ , Cl ~, SO:-, and alkalinity. Temperature, pH, and conductivity were measured in situ, while total hardness, Ca,, and alkalinity have been determined immediately after sampling, performing standard titration methods. The water turned out to be of an almost pure Ca-Mg-HCO, type. The degassing of CO, causes high supersaturation with respect to calcite and due to calcite precipitation the Ca2+ concentration decreases from 6. lo-? mole/l upstream down to 2.5. lo-" mole/l at the lower course. Small rectangular shaped tablets of pure marble were mounted under different flow regimes, i.e., at the dam sites with fast water flow as well as inside pools with still water. After the substrate samples had stayed in the water for a period of a few days, the deposition rates were measured by weight increase, up to several tens of milligrams. Although there were no differences in hydrochemistry, deposition rates in fast flowing water were higher by as much as a factor of four compared to still water, indicating a strong influence of hydrodynamics. While upstream rates amounted up to 5 mm/year, lower rates of about 1 mm/year were observed downstream. Inspection of the marble substrate surfaces by EDAX and SEM (scanning electron microscope) revealed authigeneously grown calcite crystals of about 10 pm. Their shape and habit are indicative of a chemically controlled inorganic origin. By applying a mass transfer model for calcite precipitation taking into account the reaction rates at the surface given by Plummer et al. (1978), slow conversion of CO2 into H+ and HCO.: , and diffusional mass transport across a diffusion boundary layer, we have calculated the deposition rates from the hydrochemistry of the corresponding locations. The calculated rates agree within a factor of two with the experimental results. Our findings confirm former conclusions with respect to fast flow conditions: reasonable rates of calcite precipitation can be estimated in reducing the PWP-rate calculated from the chemical composition of the water by a factor of about ten, thus correcting for the influence of the diffusion boundary layer.