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1.
Cave air CO2 is a vital part of the cave environment. Most studies about cave air CO2 variations are performed in caves with no streams; there are few studies to date regarding the relationship of cave air CO2 variations and drip water hydrochemistry in underground stream–developed caves. To study the relationship of underground stream, drip water, and cave air CO2, monthly and daily monitoring of air CO2 and of underground stream and drip water was performed in Xueyu Cave from 2012 to 2013. The results revealed that there was marked seasonal variation of air CO2 and stream hydrochemistry in the cave. Daily variations of cave air CO2, and of stream and drip water hydrochemistry, were notable during continuous monitoring. A dilution effect was observed by analyzing hydrochemical variations in underground stream and drip water after rainfall. High cave air CO2 along with low pH and low δ13CDIC in stream and drip water indicated that air CO2 was one of the dominant factors controlling stream and drip water hydrochemistry on a daily scale. On a seasonal scale, stream flows may promote increased cave air CO2 in summer; in turn, the higher cave air CO2 could inhibit degassing of drip water and make calcite δ13C more negative. Variation of calcite δ13C (precipitated from drip water) was in reverse of monthly temperature, soil CO2, and cave air CO2. Therefore, calcite δ13C in Xueyu Cave could be used to determine monthly changes outside the cave. However, considering the different precipitation rate of sediment in different seasons, it was difficult to use stalagmites to reconstruct environmental change on a seasonal scale.  相似文献   

2.
High temporal resolution (15 min) measurements of stage, pH, electric conductivity, temperature, and other hydrochemical parameters of groundwater at two sites in the Jinfo Mountain Nature Reserve of China were collected using automatic data loggers. Bitan Spring (BS 700 m a.s.l.) sits in subtropical climate zone, while Shuifang Spring (SS 2,060 m a.s.l.) is located in plateau temperate climate. The data show that hydrochemistry of epikarst springs at different altitudes is very sensitive to the changes of their physical environment, especially two factors: air temperature and soil CO2 concentration. Springs at lower altitude are associated with higher air temperature and soil CO2 concentration, thus more likely leading to more active karst processes than those at higher elevation. Water temperature and pH of BS showed a noticeable diurnal circle with high values in daytime and low values at night. The data also indicate that at least there are two effects that could impact the variations of groundwater hydrochemistry during flood pulse: dilution effect and CO2 effect.  相似文献   

3.
Cave dripwater hydrochemistry responds to environmental changes, both within and outside of the cave, and thereby conveys this information to any stalagmite fed by the drips. As stalagmites are important archives of climate proxy information, understanding how dripwater hydrochemistry responds to environmental forcing is critical. However, despite the large number of speleothems in SW China, the response of dripwater to regional climate variability is not yet adequately understood. A 3‐year study of three drip sites in Xueyu Cave, Chongqing Municipality, SW China, revealed the most important mechanisms controlling dripwater chemical variability. The principal chemical indices (pH, specific conductivity, Ca2+, Mg2+, Sr2+ and ) in collected dripwaters and the local climate data were analysed in this study. The principal controls on the hydrochemistry were found to be the external climate and its changes, groundwater residence time, cave ventilation and prior calcite precipitation (PCP) processes. Dripwater hydrochemistry showed strongly coherent seasonal patterns despite the fact that all sites are Ca–HCO3 type waters and supersaturated with calcite. Seasonal changes in dripwater hydrochemistry were influenced by the soil and vadose zone CO2 content as well as groundwater residence time in the upper karst zone. Cave‐air CO2 seasonal variations were consistent with changes in dripwater PCO2 and cave ventilation. Trace element ratios (Mg/Ca and Sr/Ca) of dripwater were controlled by PCP processes. Seasonal variations in dripwater Mg/Ca and Sr/Ca ratios in Xueyu Cave showed inverse changes with the Asia Monsoon Index during the monitoring period, reflecting the seasonal climate changes that may have been recorded in the speleothems. Based on a linear regression of PCO2 and the Ca2+ data in the cold–dry winter season, a 130‐ppm shift in cave‐air PCO2 results in a 1‐ppm shift in dripwater Ca2+ concentration in Xueyu Cave. This study illustrates the importance of understanding factors controlling the changes in the composition of dripwater before it reaches the speleothem.  相似文献   

4.
Hourly resolved cave air PCO2 and cave drip water hydrochemical data illustrate that calcite deposition on stalagmites can be modulated by prior calcite precipitation (PCP) on extremely short timescales. A very clear second-order covariation between cave air PCO2 and drip water Ca2+ concentrations during the winter months demonstrates the effects of degassing-induced PCP on drip water chemistry. Estimating the strength of the cave air PCO2 control on PCP is possible because the PCP signal is so clear; at our drip site a one ppm shift in Ca2+ concentrations requires a PCO2 shift of between 333 and 667 ppm. This value will undoubtedly vary from site to site, depending on drip water flow rate, residence time, drip water-cave air PCO2 differential, and availability of low PCO2 void spaces in the vadose zone above the cave. High-resolution cave environmental measurements were used to model calcite deposition on one stalagmite in Crag Cave, SW Ireland, and modelled growth over the study period (222 μm over 171 days) is extremely similar to the amount of actual calcite growth (240 μm) over the same time interval, strongly suggesting that equations used to estimate stalagmite growth rates are valid. Although cave air PCO2 appears to control drip water hydrochemistry in the winter, drip water dilution caused by rain events may have played a larger role during the summer, as evidenced by a series of sudden drops in Ca2+ concentrations (dilution) followed by much more gradual increases in drip water Ca2+ concentrations (slow addition of diffuse water). This research demonstrates that PCP on stalactites, cave ceilings, and void spaces within the karst above the cave partially controls drip water chemistry, and that thorough characterisation of this process at individual caves is necessary to most accurately interpret climate records from those sites.  相似文献   

5.
Globally, it is possible that up to 25% of the world’s population depends on karst water supplies. In karst areas, a high degree of groundwater and surface water linkage often results in the direct recharge of groundwater with polluted run-off following rainfall. In order to reveal the hydrochemical variations after rainfall, especially real-time variation of pollutants, high-resolution auto-monitoring techniques were used at the outlet of Qingmuguan subterranean stream (QSS), which is influenced by agricultural activities. In addition to rainfall, high-resolution measurements of pH, water level, electrical conductivity (Ec) and NO3 − concentration were recorded in the monsoon season and fertilizer application period using a data logger with time intervals of 15 min. In the six observed rainfall events, the pH value was mainly controlled by acidic rainfall inputs. The pH showed sharp decline after the rainfall event, and then increased. The Ec was impacted by the rainfall chemistry, dilution effect of rainfall and agricultural wastewater. NO3 − derived from agricultural activities was less impacted by rain chemistry; and its variations were mainly affected by the dilution effect of rainfall and agricultural wastewater. Under the influences of the R1 rainfall, the rapid changes of Ec and NO3 − were opposite in direction. As the rain continued, both the Ec and NO3 − rapidly changed in synchronization within the shortest period of 5 h and the longest of 27 h because of the impact of the agricultural wastewater. The groundwater quality changed due to the influx of agricultural wastewater over the entire monitoring period. According to the National Groundwater Quality Standard, People’s Republic of China (GB/T14848-9), the groundwater quality of the QSS moved through the following grades during the monitoring period: Grade III → Grade IV → Grade V → Grade IV → Grade V → Grade IV → Grade V → Grade IV → Grade III. Traditional sampling methods did not reveal accurate hydrochemistry changes of the QSS, and even generated misleading results. Consequently, the high-resolution auto-monitoring technique is necessary for the future protection and sustainable use of karst aquifer in Southwest China.  相似文献   

6.
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 CO2 sink. 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 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 CO2 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 CO2 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 CO2 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.  相似文献   

7.
There are very few process studies that demonstrate the annual variation in cave environments depositing speleothems. Accordingly, we initiated a monitoring program at the Obir Caves, an Austrian dripstone cave system characterized by a seasonally changing air flow that results in a predictable pattern of high pCO2 during summer and low pCO2 in winter. Although similar seasonal changes in soil pCO2 occur, they are not directly connected with the changes in the subsurface since the dripwaters are fed from a well-mixed source showing little seasonal variation. Cold season flushing by relatively CO2-poor air enhances degassing of CO2 in the cave and leads to a high degree of supersaturation of dripwater with regard to calcite. Forced calcite deposition during the cold season also gives rise to a pronounced pattern of synchronous seasonal variations in electrical conductivity, alkalinity, pH, Ca and δ13CDIC which parallel variations recorded in δ13Ccave air. Chemical components unaffected by calcite precipitation (e.g., δD, δ18O, SiO2, SO4) lack a seasonal signal attesting to a long residence in the karst aquifer. Modeling shows that degassing of CO2 from seepage waters results in kinetically-enhanced C isotopic fractionation, which contrasts with the equilibrium degassing shown from the Soreq cave in Israel. The Obir Caves may serve as a case example of a dripstone cave whose seepage waters (and speleothems) show intra-annual geochemical variability that is primarily due to chemical modification of the groundwater by a dynamic, bidirectional subsurface air circulation.  相似文献   

8.
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 impacted by both natural environment and people. Therefore, the study of hydrochemistry and its solutes’ sources is very important to ensure the normal function of life support systems. In this paper, thirty?five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types in Chongqing to trace the sources of solutes and relative hydrochemical processes. Hydrogeochemical types of karst groundwater in Chongqing were mainly of the Ca?HCO3 type or Ca (Mg)?HCO3 type. However, some hydrochemical types of karst groundwater were the K+Na+Ca?SO4 type (G25 site) or Ca?HCO3+SO4 type (G26 and G14 site), indicating that the hydrochemistry of these sites might be strongly influenced by anthropogenic activities or unique geological characteristics. 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 δ34S?SO42? fell into a range of ?6.8‰?21.5‰, with a mean value of 5.6‰. The variations of both 87Sr/86Sr and Sr values of the groundwater samples indicated that the Sr element was controlled by the weathering of limestone, dolomite and silicate rock. However, the figure of 87Sr/86Sr vs. Sr2+/[K++Na+] showed that the anthropogenic inputs also obviously contributed to the Sr contents. For tracing the detailed anthropogenic effects, we traced the sources of solutes collected karst groundwater samples in Chongqing according to the δ34S value of potential sulfate sources. The variations of both δ34S and 1/SO42? values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sul?de mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) have contributed to solutes in karst groundwater. The influence of oxidation of sul?de mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread.  相似文献   

9.
Diurnal variations of hydrochemistry were monitored at a spring and two pools in a travertine-depositing stream at Baishuitai, Yunnan, SW China. Water temperature, pH and specific conductivity were measured in intervals of 5 and 30 min for periods of 1 to 2 days. From these data the concentrations of Ca2+, HCO3−, calcite saturation index, and CO2 partial pressure were derived. The measurements in the spring of the stream did not show any diurnal variations in the chemical composition of the water. Diurnal variations, however, were observed in the water of the two travertine pools downstream. In one of them, a rise in temperature (thus more CO2 degassing) during day time and consumption of CO2 due to photosynthesis of submerged aquatic plants accelerated deposition of calcite, whereas in the other pool, where aquatic plants flourished and grew out of the water (so photosynthesis was taking place in the atmosphere), the authors suggest that temperature-dependent root respiration underwater took place, which dominated until noon. Consequently, due to the release of CO2 by the root respiration into water, which dominated CO2 production by degassing induced by temperature increase, the increased dissolution of calcite was observed. This is the first time anywhere at least in China that the effect of root respiration on diurnal hydrochemical variations has been observed. The finding has implications for sampling strategy within travertine-depositing streams and other similar environments with stagnant water bodies such as estuaries, lakes, reservoirs, pools and wetlands, where aquatic plants may flourish and grow out of water.  相似文献   

10.
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.  相似文献   

11.
为探究白云岩洞穴滴水中CO2来源及变化特征,以贵州省绥阳双河洞洞穴系统中的大风洞为研究对象,对洞穴空气CO2浓度（pCO2（c））、洞穴上覆土壤CO2浓度（pCO2（soil））、洞穴滴水CO2分压（pCO2（w））、以及洞穴滴水水化学环境进行了为期15个月（2016年1月-2017年3月）的监测、采样和室内实验分析,运用统计分析方法对各监测指标进行主成分分析。结果表明:（1）pCO2（w）、pCO2（c）具有明显的季节性变化特征,表现为雨季>旱季。pCO2（soil）受降雨、洞穴通风效应的影响,季节性波动较大,是洞穴pCO2（w）的重要来源;（2）深层岩溶作用中渗透水在流经洞穴上覆表层岩溶带发生的水-岩相互作用及其产生的水化学环境,特别是变化,是影响pCO2（w）的主要因素之一,对pCO2（w）具有重要贡献;（3）运用主成分分析法（PCA）得出各因素对洞穴滴水的相对方差贡献率依次为:HCO3- >pCO2（s）>Soil 1#>pCO2（w）>Soil 2#。各因子对pCO2（w）的贡献率依次为:地表深层岩溶作用>洞穴上覆土壤空气环境>洞穴空气环境;（4）pCO2（w）来源概念模型表明,雨季时,降雨量大,土壤水下渗快,地下水得到充分补充,但停滞时间较短,在渗流带中与围岩反应不充分,PCP过程较弱,对pCO2（w）影响较大;旱季则相反。研究结果对洞穴石笋、石钟乳沉积物的保护具有一定意义,对洞穴旅游开发、管理及岩溶碳循环研究具有重要意义。   相似文献   

12.
利用HOBO小型自动气象站、WGZ21型光电数字水位计和CTDP300型在线水质监测仪,对典型岩溶槽谷地下河系统暴雨条件下水文水化学动态变化进行了连续监测,运用WATSPAC软件计算方解石饱和指数(SIc)和CO2分压(PCO2)。分析了降雨过程中,地下河系统水文水化学动态变化特征。结果表明:在降雨过程中,地下河系统总体以稀释效应为主,对降雨的响应速度快。其中,地下河入口水化学变化受降雨稀释效应和外界环境因素共同影响,变化复杂。出口水化学变化以稀释效应为主,较入口规律。强降雨初期主要由来自中下游岩溶裂隙和洼地对地下河管道的快速补给;降雨后期和降雨过程结束后主要由来自上游岩口落水洞的注入补给。青木关流域岩溶发育程度高,岩溶管道流畅通性良好。强降雨形成的短时地表产流集中注入、降雨入渗经裂隙的快速补给对地下河水质的好坏造成直接影响。  相似文献   

13.
Nongla, a typical karst dynamic system (KDS) monitoring site, is located at Nongla Village, Mashan County, Guangxi, China. The data from a Greenspan CTDP300 multichannel data logger indicates that the KDS is highly sensitive to environmental changes. Multi-day and diurnal physico-chemical composition of epikarst spring water is quite different under different climatic conditions. During a day with no rainfall, water temperature and air temperature have similar variations. Electrical conductivity (EC) has good positive correlation with pH value and water temperature. During rainstorms, the physico-chemical composition of the spring water is initially strongly effected by dilution, pH and EC drop rapidly. However, half to one hour later, EC returns to normal and the CO2 effects will be the dominant physical effect. This is due to the high fissure rates and high permeability in the epikarst zone. Dilution effects were observed during the entire rainstorm event,whereas, it only acts during the earliest period of light rain. Therefore, it is necessary to examine the water–rock–CO2 combination as a whole system to explain the hydrochemical behavior of epikarst processes.  相似文献   

14.
Water temperature, dissolved oxygen (DO), pH, and specific conductivity (spc) were measured in a time interval of 15 min in a karst spring and the spring-fed pool with flourishing submerged plants in Guilin, SW China under dry weather for periods of 2 days. Measurements allowed calculation of calcium and bicarbonate concentrations ([Ca2+] and [HCO3 −]), and thus CO2 partial pressure ( ) and saturation index of calcite (SIc). Results show that there were not any diurnal variations in the physico-chemical parameters of the water for the spring. However, during daytime periods, pool water decreased to far less than the spring water in a few hours, pH and SIc increased to greater than the spring, and [Ca2+] and [HCO3 −] decreased to less than the spring. During nighttime periods, pool water returned to or even increased to greater than the spring, pH and SIc decreased to less than the spring, and [Ca2+] and [HCO3 −] increased to greater than the spring. The decrease in [Ca2+] and [HCO3 −] to less than the spring during daytime periods implies daytime deposition of calcium carbonate, while the increase in [Ca2+] and [HCO3 −] to greater than the spring during nighttime periods implies nighttime dissolution of calcium carbonate. The direction of the observed changes depended essentially on the illumination, indicating that daytime photosynthetic and nighttime respiratory activities in the pool aquatic plant ecosystem, which were further evidenced by the increase and decrease in DO during daytime and nighttime periods respectively, were the main processes involved. The large variations of the components of the carbonate system imply considerable changes of the capacities of CO2 and O2 in water. The finding has implications for water sampling strategy in slow-flowing karst streams and other similar environments with stagnant water bodies such as estuaries, lakes, reservoirs, and wetlands, where aquatic plant ecosystem may flourish.  相似文献   

15.
The terrestrial carbon cycle and the role of atmospheric CO2 concentrations in controlling global temperatures can be inferred from the study of ancient soils (paleosols). Soil-formed goethite and calcite have been the primary minerals used as a geochemical proxy for reconstructing atmospheric pCO2 from ancient terrestrial records. In the case of goethite, optimum sampling strategies for reconstructing pCO2 focus on the portion of the soil profile that displays steep gradients in both soil CO2 concentration and δ13C values of soil CO2 such that a keeling plot can be developed for a given soil and atmospheric pCO2 can be calculated from it. We report data from a Carboniferous paleosol that depart from the expected linear trends. The results indicate that pedogenic goethite is sensitive to variations in the isotopic composition of soil CO2, over a range of timescales, and can record these variations in the carbon isotope composition and mole fraction of Fe(CO3)OH in solid solution with goethite. We explore possible environmental conditions that can drive these changes as a function of either moisture controlled variations in soil respired CO2 or in the residence time of carbon in soils. The implications of this result are overestimation of paleoatmospheric pCO2 from pedogenic goethite.  相似文献   

16.
桂林盘龙洞岩溶表层带土壤CO2浓度的季节变化研究   总被引：5，自引：2，他引：3  
以桂林盘龙洞岩溶实验场为例,选择岩溶洼地里的坡地和洼地2个样地,通过长期定时监测土壤CO2浓度变化,表明:(1)土壤CO2浓度具有明显的季节性变化特征,夏季(6-8月)土壤CO2浓度是其它时期的2～3倍,并显示与气温、降水和生物活动密切相关;(2)洼地地段土壤CO2浓度比坡地地段要高,尤其夏季时洼地比坡地高近1000mg/m2;(3)在垂直剖面上,大多数的情况下土壤CO2浓度随土壤深度的递增而升高,但在雨季时坡地(-50cm与-80cm处)和洼地(-80cm与-100cm处)的土壤CO2浓度随深度的增加而降低。   相似文献   

17.
Wet season hydrochemistry of Bribin Cave in Gunung Sewu Karst, Indonesia   总被引：1，自引：0，他引：1  
This research was conducted on the Bribin River, the most important underground river in the Gunung Sewu Karst, Gunung Kidul, Java, Indonesia. The main purpose of this study was to define the wet-season hydrochemistry of this river. This research also focuses on identifying the relationship between hydrochemical parameters to provide better aquifer characterization. Water-level monitoring and discharge measurements were conducted over a 1-year period to define the discharge hydrograph. Furthermore, baseflow-separation analysis is conducted to determine the diffuse-flow percentage throughout the year. Water sampling for hydrogeochemical analysis is taken every month in the wet season and every 2?hours for two selected flood events. To describe the hydrogeochemical processes, a bivariate plot analysis of certain hydrochemical parameters is conducted. The results show that the diffuse-flow percentage significantly controls the river hydrochemistry. The domination of diffuse flow occurs during non-flooding and flood recession periods, which are typified by a high value of calcium and bicarbonate and low CO2 gas content in water. Conversely, the hydrochemistry of flood events is characterized by the domination of conduit flow and CO2 gas with low calcium and bicarbonate content. According to the wet-season hydrochemistry, it seems that the small- and medium-sized fractures in the Bribin aquifer still provide storage for the diffuse and fissure flows, although the conduit fracture is already developed.  相似文献   

18.
Saturation index with respect to calcite (SIc) and equilibrium CO2 partial pressure are important parameters to study groundwater in limestone aquifers. Aside from their use in time series, CO2 and SIc are used to estimate the baseline of CO2 in the vadose zone. The objective of this paper is to present conceptual examples on the use of the CO2–SIc relationship to have new information from usual parameters. Case study was considered as an example of use from Cussac site, a limestone aquifer in southwest of France. The result showed that CO2 baseline in unsaturated zone is found close to 25,000 ± 1,000 ppm.  相似文献   

19.
The modelling of CO2 intrusion into virtual freshwater aquifers after a leakage from CO2 storage formations is a well-established approach for the identification of monitoring parameters and for the risk assessment. At presence, standard or close-to-standard conditions in terms of temperature (T), i.e. 25?°C and pressure (P), i.e. 1?C5?bar, are assumed. This approach neglects the fact that temperature and pressure conditions change with the depth of the freshwater aquifer. This study tests the accuracy of T?CP corrections of the geochemical constants in the system gaseous CO2?Cwater?Cmineral which are performed by the simulators PhreeqC (Parkhurst and Appelo in User??s guide to phreeqc (version 2)??a computer program for speciation, batch reaction, one-dimensional transport, and inverse geochemical calculations. Technical report, US Department of the Interior, 1999) and TOUGHREACT (Xu et?al. in Toughreact user??s guide: a simulation program for non-isothermal multiphase reactive geochemical transport in variably saturated geologic media. Technical report, Lawrence Berkeley National Laboratory, 2004). It further identifies the impact of T and P variations on the predicted concentrations of the monitoring parameters pH and total inorganic carbon (TIC) and on the predicted concentration of the trace metal lead (Pb) in 3D multiphase-multicomponent simulations of virtual aquifers. The results reveal a strong imprecision in the correction of kinetic rates of mineral dissolution and a lack of corrections of sorption equilibrium states. The predicted pH and concentrations of TIC and lead depend strongly on the assumed T and P conditions. It is concluded that a neglect of T and P effects results in inaccurate predictions of groundwater chemistry. The impact assessment and monitoring strategies based on currently available modelling results consequently require strong improvements.  相似文献   

20.
The direction and intensity of karst processes can be deeply affected by soil physical and chemical variations which were resulted from land use. Taking Nongla Fengcong depression area, Mashan County, Guangxi as an example, authors discussed the impact of land use on karst processes based on the data of field limestone tablet. The results showed that the corrosional rates at varied soil depth are quite different. Corrosional rate in woodland and orchard is mostly bigger than 20 mg/a, which is much higher than that in tilled land and shrub. Generally, corrosional rate decreased from orchard, woodland, tilled land, fallow land and shrub successively, in which soil organic matter (OM) and soil pH are two major controlling factors: corrosion process is controlled remarkably by soil OM in woodland and orchard. The higher the organic matter content is and the less the pH value is, the higher the corrosional rate is. Owing to lower organic matter content, the corrosional rate is mainly affected by soil CO2 in tilled land and shrub.  相似文献   

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