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WATSPEC: A computer program for determining the equilibrium speciation of aqueous solutions
... Many mathematical methods were tested to solve the set of nonlinear algebraic equations describing thermodynamic equilibrium: Zero-order methods such as the continuous fractions method [48], the Simplex method ( [32]) which do not use the derivative of the objective function. The latter methods converge more slowly [31], but are sometimes considered more robust than first-order methods. ...
... Positive continuous fraction method PCF The continuous fraction method (CF) has been used to solve thermodynamic equilibrium in the computer code WATSPEC [48], or for preconditioning of the Newton-Raphson method for the major species in the PHREEQC code [33]. This method, which only needs one computation of the approximate thermodynamic equilibrium per iteration, is the cheapest zero-order method. ...
... Often, the component H + has a zero total concentration and is associated with negative stoichiometric coefficients. In the code WATSPEC [48], the pH value must be imposed to find the thermodynamic equilibrium. Hydrogen and oxygen are excluded from the continuous fraction preconditioning in the code PHREEQC [33]. ...
The modeling of thermodynamic equilibria leads to complex nonlinear chemical systems which are often solved with the Newton-Raphson method. But this resolution can lead to a non convergence or an excessive number of iterations due to the very ill-conditioned nature of the problem. In this work, we combine a particular formulation of the equilibrium system called the Positive Continuous Fraction method with two iterative methods, Anderson Acceleration method and Vector extrapolation methods (namely the reduced rank extrapolation and the minimal polynomial extrapolation). The main advantage of this approach is to avoid forming the Jacobian matrix. In addition, a strategy is used to improve the robustness of the Anderson acceleration method which consists in reducing the condition number of matrix of the least squares problem in the implementation of the Anderson acceleration so that the numerical stability can be guaranteed. We compare our numerical results with those obtained with the Newton-Raphson method on the Acid Gallic test and the 1D MoMas benchmark test case and we show the high efficiency of our approach.
... The CO 2 partial pressure (pCO 2 ) and calcite saturation index (SI C ) were calculated according to the WATSPEC program (Wigley 1977). The batch data of pH, T, and the concentrations of seven major ions were used as inputs. ...
... where the brackets denote the bicarbonate/calcium concentrations in mg L −1 and EC represents the electrical conductivity in μS cm −1 at 25°C. ] were inputted to the WATSPEC program (Wigley 1977) to calculate pCO 2 and SI C (Liu et al. 2007). ...
... The pH and SI C values range from 7.06 to 8.46 and − 0.91 to 0.77, with mean values of 7.79 and 0.03, respectively. In general, pH and SI C exhibited temporal variations that are higher If SI > 0, supersaturation occurs and calcite may deposit; if SI < 0, water is aggressive to calcite; and if SI = 0, the equilibrium is reached b Calculated CO 2 partial pressure of water by WATSPEC (Wigley 1977) Environ Sci Pollut Res (2020) 27:13142-13154 in warm rainy seasons and lower in cold dry seasons. In warm rainy seasons, pH and SI C increase gradually as the discharge increases, implying the dilution effect (Fig. 3). ...
The coupled carbonate weathering represents a significant carbon sink and can be controlled by the riverine hydrochemical variations. However, magnitudes, variations, and mechanisms responsible for the carbon sink produced by coupled carbonate weathering are unclear. In view of this, temperature, pH, dissolved oxygen, turbidity, electrical conductivity, and discharge of the Xijiang River at Wuzhou Hydrologic Gauging Station was recorded during October 2013 to September 2015 to elucidate the temporal variations in riverine hydrochemistry and their controlling mechanisms. To obtain the complete carbon sink flux (CSF) produced by coupled carbonate weathering with terrestrial aquatic photosynthesis in the river basin, the fluxes of dissolved inorganic carbon (DIC), autochthonous organic carbon (AOC, sourced from the transformation of DIC via aquatic photosynthesis), and sedimentary AOC were all considered. The results show that seasonal hydrochemical variations in the Xijiang River were related not only to dilution effects but also aquatic primary production. These results demonstrate that the variations in discharge caused by rainfall played a dominant role in controlling the variations in the CSF due to the chemostatic behavior of DIC and dissolved organic carbon (DOC). The CSF of the Xijiang River produced by coupled carbonate weathering was calculated as 11.06 t C km⁻² a⁻¹, including DIC carbon sink flux of 6.56 t C km⁻² a⁻¹, AOC flux (FAOC) of 2.25 t C km⁻² a⁻¹, and sedimentary AOC flux (FSAOC) of 2.25 t C km⁻² a⁻¹. The FAOC and FSAOC together accounted for approximately 69% of DIC carbon sink flux, or approximately 41% of the CSF, indicating that the riverine AOC flux may be high and must be considered in the estimation of rock weathering-related carbon sinks.
... Since the first approach [12], Newton method (usually Newton-Raphson) has been proposed and it has been adopted by quite all the equilibrium [13,14] and reactive transport codes [15,16]. Even if the pioneer [12] did not report convergence problem, further authors mentioned these difficulties and proposed some solutions [17][18][19]. Some authors have tested other methods such as continuous fraction, secant, monotone sequences, Steffensens [17] or Quasi-Newton, Gauss-Newton, Levenberg-Marquardt and the Nelder-Mead Simplex method [20] but none of these methods overpassed the Newton Raphson one. ...
... where ̃is the stoichiometric matrix of species Δ in the reaction . (19) can be written in matrix form Δ ⇄ 0. ...
... The partial pressure of CO 2 (pCO 2 ), and saturation index of calcite (SIc) in water were calculated using the hydrochemical data sets (pH, water temperature and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− , and HCO 3 -) in the WATSPEC program (Wigley, 1977) (Text S1 in Supporting Materials). The main species of DIC include CO 2 * (dissolved CO 2 (CO 2aq ) and H 2 CO 3 ), HCO 3 -, and CO 3 2- ...
... The hydrochemical parameter, i.e., pH, water temperature and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl -, SO4 2and HCO3were processed with the program WATSPEC (Wigley, 1977) to calculate pCO2 and saturation index of clcite (SIc). pCO2 is assumed to be in equilibrium with the sampled waters by the equation: ...
Most reservoirs in subtropical areas experience periodic variations in the thermal structure of their water columns, with times of strong thermal stratification being succeeded by periods of mixing, over the course of the year. Understanding of the transport and transformation of dissolved inorganic carbon over such thermal cycles in artificial reservoirs remains poor. To address this problem, this study examined the spatiotemporal behavior of dissolved inorganic carbon (DIC), the partial pressure of CO2 (pCO2), carbon isotope ratios (δ¹³CDIC), and CO2 emission (FCO2), from 2014 to 2018 in a subtropical, groundwater-fed reservoir in southern China. It was found that CO2 emissions during mixing periods are much higher than in thermally stratified periods (particularly during transition from stratified to mixing) as a result of upwelling and release of dissolved CO2 (CO2aq) accumulated in the hypolimnion. CO2 emission fluxes at the water-gas interface accounted for only a small proportion of the DIC in the reservoir. The relationships between of DIC and δ¹³CDIC displayed two distinct modes, due to spatial differences in water depths and to strong thermal stratification during warmer seasons: (1) DIC concentrations increase and δ¹³CDIC values decrease from epilimnion to hypolimnion, and (2) δ¹³CDIC values decrease with increasing DIC concentrations but δ¹³CDIC is progressively enriched near the bottom during periods of thermal stratification. In addition, this study found three distinct processes of DIC accumulation and consumption in the reservoir: (1) DIC accumulated in the hypolimnion during thermal stratification periods, due to carbon retention but (2) DIC was substantially consumed in the epilimnion during such periods, and (3) average DIC concentrations and pCO2 increased significantly from upstream to downstream along the reservoir, while average δ¹³CDIC values became lighter. These results highlight that carbon behavior in groundwater‑fed reservoirs is often controlled by a combination of biogeochemical processes and seasonal variations in thermal structure. Sampling and monitoring strategies should consider these factors in order to accurately estimate carbon budgets in reservoirs, lakes or ponds.
... Hydrochemical and isotopic results were evaluated using Schoeller, Piper, δ 18 O-δ 2 H, Na-K-Mg Giggenbach, Wilcox, United States Salinity Laboratory, and mineral saturation index diagrams. Mineral saturation index values were calculated using WATSPEC software (Wigley 1977). The suitability of the groundwater for irrigation was determined by calculating the permeability index (PI), soluble sodium percentage (SSP), the Kelley ratio (KR), sodium adsorption ratio (SAR), sodium percentage (Na %), and residual sodium carbonate (RSC) indices. ...
... The WATSPEC computer program (Wigley 1977) was used to calculate the saturation index values (SI) of a number of mineral phases in the water samples. When SI is negative, the mineral is considered undersaturated, when SI is positive then the mineral is oversaturated and when SI = 0, the mineral is in equilibrium in the water. ...
In this study, the chemical characteristics, isotopic compositions (δ18O, δ2H), geothermal properties, and suitability for irrigation of groundwater resources were explored in Çubuk-Melikşah (Ankara/Turkey). Water types present in the study area were mainly CaMgHCO3 and NaHCO3, with isotope compositions ranging from − 10.6 to − 9.06 for δ18O and from − 75.62 to − 61.93 for δ2H. The mineral saturation index showed that samples were saturated with respect to aragonite, calcite, and dolomite, while anhydrite and gypsum were undersaturated. Reservoir temperatures, computed from silica geothermometers were 60–75 °C for Melikşah thermal water. Based on the sodium adsorption ratio, residual sodium carbonate, soluble sodium percentage, permeability index, sodium percentage, boron and electrical conductivity values, waters examined in the study area were generally considered to be suitable for irrigation purposes.
... The historical approach [12,34,37,40,[42][43][44][45][46][47] involves the resolution of the system (6) with the Newton-Raphson method using [X k ] and [Cp i ] as primary unknowns. This formulation has some weaknesses that are explained later (see Section 3.1). ...
... However, other classes of preconditioners may be more efficient. (iv) Previous works have addressed the use of methods to solve geochemical equilibria other than the Newton-Raphson method [17,44,49,67]. It has been shown [17] that an efficient algorithm can be obtained by combining a zero-order method with the Newton-Raphson approach. ...
Equilibrium chemistry computations and reactive transport modelling require the intensive use of a linear solver under very specific conditions. The systems to be solved are small or very small (4 × 4 to 20 × 20, occasionally larger) and are very ill-conditioned (condition number up to 10¹⁰⁰). These specific conditions have never been investigated in terms of the robustness, accuracy, and efficiency of the linear solver. In this work, we present the specificity of the linear system to be solved. Several direct and iterative solvers are compared using a panel of chemical systems, including or excluding the formation of mineral species. We show that direct and iterative solvers can be used for these problems and propose computational keys to improve the chemical solvers.
... The resolutions are 6 and 1 mg/l, respectively (Liu et al. 2007). To understand t�e general c�emistry, waters at t�e sampling sites were collected mont�ly by syringes wit�, were processed t�roug� t�e program WATSPEC (Wigley 1977), w�ic� calculates CO 2 partial pressure (pCO 2 ) and calcite saturation index (SI C ) for eac� record (Liu et al. 2007). PCO 2 is calculated from: ...
... 10) for special study. Because CO 2 is t�e key parameter w�ic� links temperature, aquatic plants and calcite dissolution/precipitation, we concentrated on t�e control of temperature and aquatic plants on pCO 2 , w�ic� �as been calculated using WATSPEC (Wigley 1977). The temperature control was estimated t�roug� t�e influence of water temperature on Henry's constant (Lu et al. 2006). ...
UDC 556.34:54(510) Haijing Wang, Zaihua Liu, Jinliu Zhang, Hailong Sun, Dejun An, Ruxian Fu & Xiaoping Wang: Spatial and temporal hydrochemical variations of the spring-fed travertine-depositing stream in the Huanglong Ravine, Sichuan, SW China Automatic hydrochemical logging and in situ titration combined with laboratory analysis were used to understand the spatial and temporal hydrochemical variations of the springfed, travertine-depositing stream in celebrated Huanglong Ravine, Sichuan, SW China. This is essential for protection of the Huanglong World Natural Heritage travertine landscape. It was found that the deposition of travertine was due to very strong CO(2) degassing from the water, leading to decrease in pCO(2) and specific conductivity (SpC), and increase in pH and Sic downstream from the Spring. However, regular downstream hydrochemical evolution was interrupted by dilution with snow-melt water and by renewed CO, from some downstream springs. The chemistry of Huanglong Spring itself was stable at a diurnal scale though it was altered by the great Wenchuan earthquake of May 12 2008. However, in spring-fed pools downstream, pCO(2) and SpC were lower, and pH and Sic were higher in daytime than at night, which indicates that the deposition of travertine was faster during the daylight hours. This was due to the combined effects of higher water temperatures and higher aquatic algae photosynthesis. In addition, it was found that the phosphate concentration in the stream increased remarkably downstream in the tourist midseason, indicating water pollution by tourism activities. The increase of phosphate (an inhibitor of calcite precipitation) may be one of the reasons for the decrease in travertine deposition rates and accelerated propagation of discoloration by diatoms during the past decades, which needs to be given more comprehensive study and tackled in future for the protection of these world famous travertine deposits.
... The HCO 3 and CO 3 were analyzed by routine titration methods in the field. The partial pressure of CO 2 , P CO2 , in groundwater was calculated using the WATSPEC program (Wigley, 1977). SiO 2 contents were measured using ultraviolet-visible spectrophotometry. ...
Chemical weathering of rocks largely determines sources of groundwater hydrochemical components, but the superposition of processes removing cations leads to a wide variability of elemental ratios. In this study, potassium (K) isotopes are used for the first time to quantify the roles of silicate dissolution, clay incorporation and clay adsorption in subsurface K cycle. We investigate the behavior of K isotopes in groundwater with contrasting ages from a sandstone aquifer in the Ordos Basin, NW China. For modern groundwater (< 50 yrs) in the recharge area with abundant CO 2 , the silicate-derived K has been largely removed by 10-year-scale clay incorporation, generating low [K]/[Na] ranging between 0.026 and 0.048 and extremely high δ 41 K varying between 0.57‰ and 0.69‰; our calculations reveal that 92% of total K released from silicate dissolution has been removed by clay incorporation, suggesting that using measured [K] alone would underestimate the degree of silicate dissolution. For fossil groundwater (~10 4 yrs) in the discharge area, clay adsorption during long-time circulation leads to extremely low [K]/[Na] ranging from 0.001 to 0.011 and much lower δ 41 K varying from-0.32‰ to 0.37‰; as a result of the combined effect of clay incorporation and clay adsorption, up to 99.2% of silicate-derived K has been removed from the dissolved load. This study provides novel insights into the complex processes controlling the K cycle in groundwater and highlights the potential of K isotopes in understanding subsurface weathering and associated elemental cycles.
... The saturation indices (SI = the degree of saturation of minerals in aqueous solutions with respect to given minerals) were calculated by using the WATSPEC (Wigley, 1977) computer program with respect to water compositions. The results show that all waters are undersaturated with anhydrite and gypsum. ...
Geochemical investigations carried out on thermal waters over the Erzin-Hatay area allowed the collection of a suite of 9 samples from natural springs and one well characterized by outlet temperatures in the range from 19.6 to 31.5 °C. All of the springs have slightly acidic pH (in the range of 6) but one sample was marked by a pH value >11 as a consequence of serpentinization processes. The water chemistry denotes water/rock interactions with either magmatic or carbonatic rocks in a water reservoir equilibrated at temperatures estimated to be in the range of 58–162 °C. The stable isotope composition of the collected waters, in terms of dD and d18O, denotes a recharge from local meteoric waters. The dissolved gases denote the contribution of no atmospheric components. CO2 is the dominant dissolved component for most of the sample, while methane is the major component for the thermal water involved in serpentinization. Besides the main components CO2 and CH4, the dissolved gases show significant concentrations of He, H2, and CO. The isotopic composition of helium shows 3He/4He ratios well above that of Air Saturated Waters (ASW = 1.39 × 10–6) clearly indicating a significant contribution of 3He of mantle origin. Taking into account the location of some sampling sites nearby the Düziçi- İskenderun Active Fault Zone and the associated mantle helium contribution, we propose that fluids/faults relationships have to be considered as responsible for the feeding of deep-originated fluids to the shallow groundwater. As mantle-derived fluids are also carriers of thermal energy, the collected results strongly suggest improving the knowledge of the study area, where hydrological and geochemical considerations coupled with the tectonic setting of the area should focus on the geothermal potential of the circulating waters.
... The water temperature, pH and concentrations of Ca 2+ , Mg 2+ , K + , Na + , Cl − , HCO3 − and SO4 2− were processed with the program WATSPEC [33] to calculate the partial pressure value of CO2 (pCO2) and the saturation indexes of calcite (SIC) and dolomite (SID) in spring water. pCO2 is assumed to be in equilibrium with the sampled spring waters and was calculated using the following equation: ...
Accurate estimate of carbonate weathering and the related carbon sink flux induced by anthropogenic H2SO4 is of great significance for improving understanding of the hydrogeochemical evolution and the global carbon cycle. Here, to quantitatively evaluate the influence of anthropogenic H2SO4 on different lithological carbonate weathering and the related carbon sink budget, karst spring water in the typical limestone and mixed limestone–dolomite catchments in Yaji and Beidiping affected by acid precipitation in southwest China were sampled monthly for the analysis of hydrochemical and δ13CDIC characteristics. Results show for the period of sampling (August 2013 to December 2014) that the average contribution rates of atmospheric inputs and carbonate weathering to total dissolved cations are 2.24% and 97.8%, and 3.09% and 96.9% in Yaji and Beidiping, respectively. The δ13CDIC values (−17.0% to −14.7‰) and the [Ca2+ + Mg2+]/[HCO3−] (0.98 to 1.25) and [Ca2+ + Mg2+]/[HCO3− + SO42−] (approximately 1) equivalent ratios of samples prove that H2CO3 and H2SO4 simultaneously participate in carbonate weathering. The contribution rates of H2SO4 to [Ca2+ + Mg2+] and [HCO3−] produced by carbonate weathering in Yaji and Beidiping are 0–30% and 0–18%, and 0–37% and 0–23%, with average values of 14% and 7%, and 19% and 11%, respectively, suggesting that the influence of H2SO4 on different lithological carbonate weathering is different. H2SO4 precipitation participating in carbonate weathering increases the weathering rate by 14–19%, whereas it decreases the flux of karst carbon sink by 7–11% in Southwest China. Therefore, anthropogenic acids have influenced the global carbon cycle and climate change by carbonate weathering due to the large karst areas in the world, and their influences on different lithological carbonate weathering should not be ignored in the regional and global carbon cycles in future studies.
... where IAP is the ion activity product and K is the temperaturedependent equilibrium constant of calcite dissolution. The hydrochemical data sets, including T, pH, and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− , and HCO 3 − were processed with the program WATSPEC to calculate pCO 2 and SIc in river water (Wigley, 1977;Zhang et al., 2017). Riverine ionic concentration for the two catchments has been described in our previous studies (Yu et al., 2019(Yu et al., , 2021a. ...
Dissolved inorganic carbon (DIC) fluxes account for over one-third of the total carbon transported in most rivers. The DIC budget for glacial meltwater of the Tibetan Plateau (TP), however, is still poorly understood, despite the fact, the TP has the largest glacier distribution outside of the Poles. In this study, the Niyaqu and Qugaqie catchments in the central TP were selected to examine the influence of glaciation on the DIC budget in vertical evasion (CO2 exchange rate at the water-air interface) and lateral transport (sources and fluxes) from 2016 to 2018. Significant seasonal variation in DIC concentration was found in the glaciated Qugaqie catchment, but was absent in the not glaciated Niyaqu catchment. δ13CDIC showed seasonal changes for both catchments, with more depleted signatures during the monsoon season. The average CO2 exchange rates in river water of Qugaqie were ~8 times lower compared to Niyaqu with values of -1294.6 ± 438.58 mg/m2/h and -163.4 ± 581.2 mg/m2/h, respectively, indicating that proglacial rivers can act as a substantial CO2 sink due to CO2 consumption by chemical weathering. DIC sources were quantified via the MixSIAR model using δ13CDIC and ionic ratios. During the monsoon, the contribution from carbonate/silicate weathering driven by atmospheric CO2 was 13-15 % lower, while biogenic CO2 involved in chemical weathering was 9-15 % higher, indicating a strong seasonal control on weathering agents. Carbonate dissolution driven by H2SO4/HNO3 was the most important contributor to DIC in both catchments (40.7 ± 2.2 % in Niyaqu and 48.5 ± 3.1 % in Qugaqie). The net CO2 consumption rates of chemical weathering in Niyaqu and Qugaqie were -0.07 ± 0.04 × 105 mol/km2/y and -0.28 ± 0.05 × 105 mol/km2/y, respectively. The negative CO2 consumption flux was significant in the glaciated Qugaqie catchment. Extrapolating these data to glacial areas of the whole TP, the potential CO2 release flux could counteract the long-term carbon sink effect of silicate weathering of the largest Tibetan river, the Yarlung Tsangpo (-2.4 × 1010 mol/y versus 1.8 × 1010 mol/y). This study highlights that chemical weathering in small glaciated catchments may lead to hitherto overlooked substantial releases of CO2 to the atmosphere.
... The HCO 3 − and CO 3 2− of groundwater were analyzed by titration in the field. The partial pressure of CO 2 , P CO2 , in groundwater was calculated by the WATSPEC program (Wigley, 1977). The Cl − , SO 4 2− and NO 3 − were analyzed by ion chromatography (ICS-900, Dionex), and Na + , K + , Mg 2+ and Ca 2+ were measured by inductively coupled plasma (ICP-OES-900, Thermo) at the Ministry of Education Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences. ...
... The resolutions of the pH, T, EC, and DO measurements were 0.01, 0.01 • C, 0.01 µs cm −1 , and 0.01 mg/L, respectively. The pCO 2 (CO 2 partial pressure) and SIc (calcite saturation index) were calculated using the WATSPECT program [42]. A blood counting chamber was used to determine the amount of biomass in the water samples. ...
The molecular composition of the lipid biomarkers in the surface water, water column, and surface sediments collected along the Pearl River was investigated to identify the mechanisms of the delivery and preservation of autochthonous organic carbon (AOC) and to estimate its contribution to the carbon sink. The spatial distribution of these lipid biomarkers showed that samples collected at high-DIC-concentration sites (DIC: dissolved inorganic carbon) had prominent aquatic autochthonous signatures, while samples collected at low-DIC-concentration sites showed greater terrestrial contributions, which were described as the DIC fertilization effects. In the summer, typically, intense precipitation and flood erosion diluted the biogeochemical composition and carried terrestrial plant detritus. Therefore, the percentage of AOC (auto%) was higher in the winter than in the summer. According to the calculation of the lipid biomarkers, the values of the auto% were 65% (winter) and 54% (summer) in the surface water, 55.9% (winter) and 44.6% (summer) in the below-surface water, and 52.1% (winter) and 43.9% (summer) in the surface sediment, which demonstrated that AOC accounted for a major portion of the TOC. Vertical variability was mainly present in sites with intense flood erosion, which resulted in the mixing and deposition of resuspended sediments. There was a positive correlation of the clay content with the auto% value and the biogeochemical composition, showing that clay adsorbed the organic carbon in the water, vertically deposited it into the sediment, and was the dominant mechanism of the vertical delivery of organic carbon (OC). According to the new karst carbon sink model, based on coupled carbonate weathering and aquatic photosynthesis, the karst carbon sink flux (CSF) in the Pearl River was 2.69 × 106 t/a which was 1.7 times the original estimation (1.58 × 106 t/a), and this did not consider the formation of AOC. This indicated that previously, the contribution of the riverine system to the global karst carbon sink may have been highly underestimated.
... The HCO 3 and CO 3 were analyzed by routine titrimetric methods in the field. The partial pressure of CO 2 , P CO2 , in groundwater was calculated by the WATSPEC program (Wigley, 1977). The Cl, SO 4 , and NO 3 were analyzed by ion chromatography (ICS-900, Dionex), and Na, K, Mg, and Ca were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES-900, Thermo) at the MOE Key Laboratory of Groundwater Circulation and powders and then were analyzed using a D/MAX2500 Xray diffractometer at the Xi'an Center of Geological Survey to determine the mineral modes. ...
Lithium (Li) isotopes have shown large potential in tracing weathering in various water bodies, but there is limited study on Li isotopes in subsurface conditions where CO2 has been largely consumed. In this study, we use a thick sandstone aquifer in the Ordos Basin, NW China, as a natural setting to investigate the behaviors of Li isotopes in hydrogeochemical conditions with different concentrations of dissolved CO2. For young groundwater in the recharge area (group R) where CO2 is abundant (mean PCO2 = 10-2.5 atm), clay formation accompanying with weathering leads to the enrichment of ⁷Li in groundwater. The four deep samples in the recharge area have uniform Li/Na ratios (with a mean of 2.52 μmol/mmol) and δ⁷Li (with a mean of 25.0‰), corresponding to a mean Li removal rate of 81.2% compared with the sandstone leachate. For groundwater in the shallow part of the discharge area (group D1), Li was firstly removed by clay formation during weathering in the recharge area and was later removed by physisorption when CO2 becomes much lower (mean PCO2 = 10-3.1 atm). Different degrees of weathering lead to a wide range of δ⁷Li varying from 19.7‰ in the deepest well to 33.0‰ in the shallowest well. The proportion of Li removal caused by physisorption is found to increase with groundwater age. After the stage of Li removal by adsorption, Li was released in the deeper part of the discharge area (group D2), and the positive correlation of δ⁷Li versus Li/Na is explained by a ternary mixing model. The endmember of water brought by cation exchange is inferred to have a heavier δ⁷Li than sandstone leachate, demonstrating that cation exchange could cause an enrichment of ⁷Li in water. This study enhances our understanding of the controlling factors of Li isotopes in deep groundwater with low dissolved CO2, which have implications for the application of Li isotopes in subsurface water.
... General algorithms and/or numerical methods for geochemical speciation modeling are widely recognized as very challenging due to the non-linearity of the mathematic system, the very large range of magnitude of the chemical species concentrations and the equilibrium constants. Since first works, [14][15][16] many authors worked on improving these algorithms and/or numerical methods. 8,[17][18][19][20][21][22][23][24][25][26][27][28] An examination of these articles shows that all these codes include one or more activity correction models. ...
Reactive transport softwares are today one of the cornerstones of environmental research. They contain multiphysics with very complex algorithms, including flow, transport, chemical, and sometimes heat transport, mechanical, and/or biological algorithms. Because of this complexity, some parts of these algorithms still have not been sufficiently studied. In this work, we focus on algorithms for activity correction, a specific subset of equilibrium chemistry algorithms. We show that the most used algorithm (the inner fixed‐point algorithm) or the most rigorous algorithm (the full Newton) might not be the most efficient, and we propose a new one, the outer fixed‐point algorithm, which is more robust and faster than other algorithms.
... The δ 13 C DIC was measured by a GasBench II interfaced with a Finnigan MAT-253 mass spectrometer (Thermo Fisher Scientific, USA), and the result was reported at the V-PDB scale with a precision better than ± 0.1‰. The saturation index of calcite (SIc) and the partial pressure of CO 2 (pCO 2 ) in the studied groundwater was calculated using the program WATSPEC (Wigley, 1977). ...
Accurate estimate of carbon sink flux resulted from carbonate weathering in the karst area is of great significance for advancing the current understanding of the global carbon cycle and climate change. However, the carbon sink flux may be overestimated when the natural reaction with carbonic acid is influenced by protons of anthropogenic sulfuric and nitric acids, which can reduce the carbon sink flux during carbonate weathering. Here, we quantitatively evaluated the impact of anthropogenic sulfuric and nitric acids on carbonate weathering and carbon sink flux under base flow condition based on the stoichiometry of chemical compositions of groundwater from a typical karst catchment (Guohua), Guangxi, southwestern China. Seventy groundwater samples were analyzed for the characteristics of hydrochemistry and carbon isotopes of dissolved inorganic carbon (δ¹³CDIC) during the dry season in 2015. The results show that: (1) Ca²⁺ and Mg²⁺ dominate 92.4%-99.7% of the total cations, while HCO3⁻ accounts for 83.0%-97.4% of total anions, indicating that the compositions of groundwater are primarily controlled by carbonate weathering; (2) The [Ca²⁺+Mg²⁺]/[HCO3⁻] equivalent ratios (1.00 to 1.41) and the corresponding δ¹³CDIC values (-16.8‰ to -8.1‰) of groundwater are all distributed between carbonate weathering by carbonic acid, and carbonate weathering by sulfuric and nitric acids. Meanwhile, the [Ca²⁺+Mg²⁺]/[HCO3⁻+SO4²⁻+NO3⁻] ratios of groundwater are about 1, and the [Ca²⁺+Mg²⁺] equivalent concentrations have a good positive correlation with [HCO3⁻+SO4²⁻+NO3⁻] and [SO4²⁻+NO3⁻], suggesting that sulfuric and nitric acids, in addition to carbonic acid, have been involved in carbonate weathering; (3) The contribution of sulfuric and nitric acids involved in carbonate weathering to (Ca²⁺+Mg²⁺) and HCO3⁻ in groundwater varies from 0.6% to 58.0% (mean value of 20.9%) and from 0.3% to 40.9% (mean value of 12.2%), respectively. The carbonate weathering rate has increased by 20.9% while the karst carbon sink flux has decreased by 12.2%. Therefore, the carbon sink flux produced by carbonate weathering should be carefully evaluated when anthropogenic sulfuric acid and/or nitric acid are involved and the role of sulfuric and nitric acids in carbonate weathering could not be ignored in the global carbon cycle.
... The sensitivity of cationic and anionic measurement is 0.001 mg/L and 0.01 mg/L with an accuracy of ±2% and ±5%, respectively. Saturation of calcite, dolomite, and gypsum are calculated from hydrochemical data (water temperature, pH, and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− , and HCO 3 − ) using the modified program WATSPEC (Wigley, 1997). ...
The uplift of the Tibetan Plateau (TP) not only may enhance physical denudation and chemical weathering but also makes this area contain the largest glacier storage outside the polar regions. There is an argument on whether glaciation favours chemical weathering and carbon sequestration. To explore chemical weathering processes and intensities in the cold glacial region of the central TP, hydrochemistry of the river water in two catchments, i.e. the Qugaqiong and Qugaqie, was monitored from April to September 2018 with high-frequency sampling. These two catchments share similar geographical features except there are some cold glaciers in the upper reaches of the Qugaqie. The results of chemical composition show that the river water of the Qugaqie has a lower proportion of Ca²⁺ and HCO3⁻ but higher SO4²⁻ and K⁺+Na⁺ compared with the Qugaqiong. The seasonal variation of ionic concentration in the Qugaqie is significant but minor in the Qugaqiong. Those differences highlight the glacial impact in the Qugaqie compared with the non-glacierized Qugaqiong. Solutes in the glacial runoff of the Qugaqie mainly derive from sulfide oxidation. Its contribution to cations in the runoff of the Zhadang glacier and the Hanging glacier reaches 39% and 36%. The second most important contribution is carbonate dissolution (32% for both glacial runoffs). Silicate weathering provides fewer solutes and its contribution is only 20% and 11% in the two glacial runoffs, respectively. River water of the Qugaqiong shares similar hydrochemical characteristics with the non-glacial tributaries draining granodiorite/biotite adamellite in the Qugaqie. The contribution of sulfide oxidation to solutes in those rivers decreases to 10% while carbonate dissolution increases to 50%. Glacial comminution exposed trace sulfide minerals, thus made sulfide oxidation became pretty active due to this reaction is much faster than other mineral dissolution. The carbonate weathering rate (CWR) and silicate weathering rate (SWR) in the Qugaqie catchment are 9.7 t/km²/y and 6.7 t/km²/y. In comparison, values in the Qugaqiong catchment are 6.9 t/km²/y and 3.8 t/km²/y, respectively, which means CWR and SWR is 1.4 and 1.8 times higher in the Qugaqie catchment, respectively. Higher runoff and physical erosion rates are considered as the main reasons for higher chemical denudation rates in the Qugaqie catchment. The drainage system of the glaciers is dominated by the distributed pattern, which caused longer residences time of water, thus further promoted chemical weathering in the glacierized region. Our observation supports the idea that glaciation in the glacierized catchment of the central TP enhances chemical weathering, especially for SWR. Chemical denudation rates in the Qugaqie catchment remain at a moderate level compared with other glacierized catchments in the world and lithology and runoff are important factors to cause this spatial heterogeneity.
... The results of δ 13 C analysis were reported relative to the V-PDB standard and the overall experimental accuracy for δ 13 C measurements was ±0.2‰. The pCO 2 of water were calculated based on hydrochemical data, including water temperature, pH and concentrations of seven major ions (K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− and HCO 3 − ), by using the modified program WATSPEC (Wigley, 1977) (Eq. (1)). ...
The cycling of carbon (C) and nitrogen (N) in karst aquatic systems has been shown to be closely related, with coupled control of dissolved organic carbon (DOC) concentrations through the metabolic pathways of subaquatic communities. However, the coupled CN cycling involving in the transformation of dissolved inorganic carbon (DIC) into DOC has not been well-explored. In this study, we chose the Lijiang River, a typical karst aquatic system in Southwest China as our study area and documented its diurnal and seasonal variations in terms of several hydrochemical and isotopic parameters to identify how to couple cycling for C and N. The results of the Bayesian stable isotope-mixing model showed that approximately 50% and 72% of the total DOC formed in summer and winter, respectively, represented autochthonous organic carbon in the Lijiang River. Diurnal monitoring results revealed that DIC and NO3⁻ transformations were primarily controlled by metabolic processes (photosynthesis and respiration) of subaquatic communities, accompanying DOC formation, in the Lijiang River. The consumption of DIC and NO3⁻ by aquatic photosynthesis was in the ratio of 9:1 (mol/mol) to produce autochthonous DOC, accompanying the enriched δ¹³CDIC, δ¹⁵N-NO3⁻ and δ¹⁸O-NO3⁻, with a daily variation of 7.9‰, 10.6‰ and 11.2‰, respectively. On the diurnal scale, 6.2% of the total DIC and 7.1% of the total NO3⁻ were consumed by metabolic processes of subaquatic communities and these values were consistent with their corresponding values on the interannual scale. However, the proportions of DIC and NO3⁻ utilized in the dry season were higher than those in the wet season. Approximately 1.18 × 10⁷ kg C/yr of DIC and 1.64 × 10⁶ kg N/yr of NO3⁻ were converted into organic matter by the aquatic photosynthesis, with 80% and 79% of the total DIC and NO3⁻ consumption respectively occurring in the wet season. Furthermore, the coupled CN cycling involving DIC and NO3⁻ can promote the production of autochthonous DOC, constituting a relatively long-term natural C and N sinks in karst aquatic systems.
... Since the host rocks in the study region are limestone and dolomite, intercalated with gypsum strata, Ca 2+ , Mg 2+ , HCO 3 − and SO 4 2− are the major ions. With the recorded temperature and pH, as well as the measured ion concentrations, calculations of pCO 2 and SI C were processed through the program WATSPEC (Wigley, 1977) based on the following equations: ...
δ¹³C and D¹⁴C measurements on dissolved inorganic carbon (DIC), particulate organic carbon (POC) and aquatic plants from a karst spring and two spring-fed ponds in Laqiao, Maolan Township, Libo County, southeastern Guizhou of China in January, July and October of 2013 have been carried out to understand the roles of aquatic photosynthesis through DIC uptake in surface karst waters. The mean D¹⁴C and δ¹³C values of DIC for the spring, midstream pond (MP) and downstream pond (DP) are -26±36‰ and -13±2‰, 6±56‰ and -12±3‰, and 0±64‰ and -9±2‰, respectively. The carbon source for the DIC is mainly from biogenic CO2 rather than the dissolution of limestone rock as the D¹⁴C and δ¹³C of limestone are about -1000‰ and 2‰, respectively. The enrichment trend of D¹⁴CDIC and δ¹³CDIC from the spring to the DP indicates CO2 exchange between atmospheric CO2 and DIC, because D¹⁴C and δ¹³C values of atmospheric CO2 are ca. 50‰ and -8‰, respectively. The average D¹⁴CPOC values in the spring, MP and DP were -325‰, -123‰ and -158‰, respectively, which are all lower than these of the DIC in each reservoir. The lower D¹⁴C values of the POC may be caused by older soil carbon from surface runoff and dust fall. More aquatic algae were formed through photosynthesis in the stream ponds, especially in summer, shown by strongly increased D¹⁴CPOC and evidence of growth in EDS/SEM analyses. Furthermore, the D¹⁴C values of the submerged aquatic plants range from -153‰ to -26‰, reflecting that the aquatic plants used DIC for photosynthesis. The D¹⁴C value of an emergent plant which uses atmospheric CO2 during photosynthesis is 52.5±0.3‰, equivalent to the atmospheric D¹⁴C. Seasonal variations of D¹⁴CDIC and δ¹³CDIC are influenced by soil CO2 input, primary productivity in the ponds, and CO2 exchange; hydrochemical condition show lower D¹⁴C values but higher δ¹³C values in cold/dry season, and vice versa in summer rainy season. A simple mass balance calculation indicates ∼90% of carbon for the spring DIC is from biogenic CO2, with higher contribution in summer due to higher productivity. Although this simple calculation may overestimate the biogenic CO2, it indicates that organic decomposition is a major carbon source for DIC in the karst hydrological system. The results of the present study have implications for ¹⁴C dating on aquatic plant remains, regional and perhaps global carbon budgets, and the different behaviors of ¹³C and ¹⁴C in karst systems.
... This study calculated the partial pressure of CO 2 (pCO 2 ) and saturation index of calcite (SIc) in river water using the hydrochemical datasets, including pH, water temperature and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− , and HCO 3 by the program WATSPEC (Wigley, 1977). This study obtained the Revelle factor and the DIC species including HCO 3 -, CO 3 2− and dissolved CO 2 using CO 2 SYS program based on the water temperature, alkalinity and pH (Pierrot et al., 2006). ...
Estimates of CO2 flux from rivers are uncertain due to limited measurements at high-resolution. In addition, precipitation may impact diurnal variation of riverine CO2 flux but the processes controlling those impacts are unknown. Here, we examine the diurnal characteristics of some physicochemical parameters, meteorological parameters, water level, δ¹³CDIC values, and the CO2 emission flux at two transects (DM and PY) of a typical karst river (Lijiang River, LJR), southwest China, during May 13–16, 2017. Our results show significant correlations between CO2 flux, DO, pCO2, and δ¹³CDIC and reflect control of CO2 flux diel pattern (decreasing during daytime and increasing at night) by metabolic processes of aquatic plants. The amplitude of CO2 flux diel pattern is weakened at DM. In contrast, diurnal pattern are interrupted at PY by the precipitation, and afterwards controlled by water level due to the significant positive correlation between water level and CO2 flux. Certainly, this amplitude will return to prestorm values as the water level recovered. We suggest that effects of precipitation on regional CO2 efflux estimate require scaling water level and CO2 flux with a linear relationship, and converting hourly flux to daily flux (α values) to improve the estimate of CO2 flux diel cycle. These methods will optimize sampling monitoring strategies and provide more reliable estimates of regional riverine CO2 emissions.
... In addition, the water CO 2 partial pressure (pCO 2 ) and calcite or dolomite saturation index (SI c or SI d ) were calculated based on the concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− , and HCO 3 − , as well as pH and water temperature (Liu et al. 2007;Zeng et al. 2016). Here, the geochemical program WATSPEC (Wigley 1977) was used to calculate the water pCO 2 , SI c , and SI d using the continuous logged or calculated water temperature, pH, and concentrations of Ca 2+ , Mg 2+ , and HCO 3 − from the three catchments. ...
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.
... The hydrochemical datasets, including pH, water temperature and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− , and HCO 3 -, were processed with the program WATSPEC (Wigley, 1977) to calculate the partial pressure of CO 2 (pCO 2 ) and saturation index of calcite (SIc) in river water. The DIC (including species HCO 3 -, CO 3 2-, CO 2 aq, and total DIC) was calculated by the CO 2 SYS procedure using the alkalinity and pH (Pierrot et al., 2006). ...
The important flux estimate of carbon exchange across the water–air interface in river systems of the global carbon cycle are being increasingly recognized. However, these estimates have large uncertainty due to the incomplete temporal and spatial coverage of CO2 flux. Here, we evaluated the seasonal and spatial dynamics and controlling factors of CO2 exchange across the water–air interface and their potential role in regional and global carbon budgets in 25 river transects along Guijiang River (GJR), southwestern China, in July and December 2016. These river transects were divided into upstream (US), middle (MS), and downstream (DS) reaches in non-karst, karst and mixed areas, respectively. The riverine CO2 fluxes showed obvious seasonal variations, ranging from 5.62 ± 5.93 g/(m².d) in summer to 1.25 ± 4.02 g/(m².d) in winter, with an average value of 3.44 ± 5.48 g/(m².d). The riverine CO2 fluxes exhibited significant spatial patterns, where the highest and lowest averaged CO2 fluxes occurred at MS in summer and winter, respectively. Generally, the river was a carbon source with respect to the atmosphere throughout the year. However, the CO2 fluxes were obviously restrained by aquatic metabolism and the carbonate buffer system in winter. Additionally, the absorbed CO2 at MS was due to strong photosynthetic and carbonate buffer activities. Carbon loss via atmospheric exchange in the GJR river basin was 0.032 ± 0.047 Tg C/yr, which accounted for 20.1% of the riverine dissolved carbon fluxes (0.160 ± 0.075 Tg C/yr). Thus, 0.128Tg C yr⁻¹ was sequestered in the GJR basin. Our results demonstrate the need to emphasize the importance of aquatic photosynthesis and the carbonate buffer system in restraining CO2 degassing in karst rivers. It is important to underscore the detailed spatiotemporal changes in CO2 flux to reduce uncertainty in current estimates of global riverine CO2 emissions.
... The relative impact of both contributions can be evaluated if melt waters are fully analysed for anionic species. The analyses of total alkalinity and pH reported here allow a full description of the dissolved carbonate speciation, 38 by solution of the carbonate equilibria using the computer programme WATSPEC (Wigley, 1977) . ...
Variations in dissolved cations, total alkalinity, sulphate, and field pH are recorded for samples of precipitation, supraglacial melt, and bulk melt waters (those emerging at the portal) from Fjallsjökull (south-east Iceland). The composition of supraglacial melt indicates derivation from precipitation by the acquisition of solutes from the weathering and dissolution of rock debris, in a system open to atmospheric carbon dioxide. Bulk melt waters have variable compositions, approaching saturation with calcite, which can be derived from supraglacial melt water by continued solute acquisition in a system closed to atmospheric carbon dioxide. Solute–discharge relationships suggest that chemical evolution of the bulk melt waters occurs when aggressive englacial waters are mixed with the solute and sediment-rich subglacial component. Simple mixing behaviour occurs over intermediate discharges as long as variations in the extent of post-mixing evolution are small compared to changes in the mixing ratio.
... All laboratory analyses were carried out in the Environmental and Geochemical Analysis Laboratory at the Institute of Karst Geology, Chinese Academy of Geological Science. The hydrochemical data sets, including pH, water temperature and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2 − and HCO 3 − were processed with the program WATSPEC (Wigley, 1977) to calculate partial pressure of CO 2 (pCO 2 ) and saturation index of calcite (SIc) in river water. pCO 2 is assumed to be in equilibrium with the sampled waters by the equation: ...
CO2 fluxes across water-air interfaces of river systems play important roles in regulating the regional and global carbon cycle. However, great uncertainty remains as to the contribution of these inland water bodies to the global carbon budget. Part of the uncertainty stems from limited understanding of the CO2 fluxes at diurnal and seasonal frequencies caused by aquatic metabolism. Here, we measured surface water characteristics (temperature, pH, and DO, DIC, Ca2 + concentrations) and CO2 fluxes across the air-water interface at two transects of Guijiang River, southwest China to assess the seasonal and diurnal dynamics of fluvial carbon cycling and its potential role in regional and global carbon budgets. The two transects had differing bedrock; DM transect is underlain by carbonate and detrital rock and PY is underlain by pure carbonate. Our results show that the river water both degasses CO2 to and absorbs CO2 from the atmosphere in both summer and winter, but the degassing and absorption varied between the two transects. Further, CO2 fluxes evolve through diurnal cycles. At DM, the river evaded CO2 from early morning through noon and absorbed CO2 from afternoon through early morning. At PY in summer, the CO2 evasion decreased during the daytime and increased at night while in winter at night, CO2 uptake increased in the morning and decreased in the afternoon but remained relatively stable at night. Although the river is a net source of carbon to the atmosphere (~ 15 mM m− 2 day− 1), the evasion rate is the smallest of all reported world's inland water bodies reflecting sequestration of atmospheric carbon through the carbonate dissolution and high primary productivity. These results emphasize the need of seasonal and diurnal monitoring of CO2 fluxes across water-air interface, particularly in highly productive rivers, to reduce uncertainty in current estimates of global riverine CO2 emission.
... , Na ? , Ca 2? , Mg 2? , Cl -, and SO 4 2were processed with the program WATSPEC (Wigley 1977), which calculates groundwater PCO 2 . PCO 2 was assumed to be in equilibrium with the sampled waters using the following equation: where parenthesis denotes species activity in mol/L, and K 1 and K h are the first dissociation constants for CO 2 gas in water and temperature-dependent Henry's Law, respectively. ...
Cave CO2 is an important part of the carbon cycle in a karst system. From 2008 to 2009 the partial pressure of CO2 (PCO2) of the cave air and cave water (cave stream and dripwater) in Xueyu Cave was studied. The PCO2 for cave air and cave water over two years showed that CO2 concentrations vary seasonally in all field sites, with higher CO2 concentrations in the wet season and lower concentrations in the dry season. These seasonal CO2 variations of cave air and cave water are attributed to seasonally variable soil CO2 production that is controlled by outside temperature fluctuations. Cave ventilation controls synchronous sharp variations of PCO2 from wet season to dry season or dry season to wet season in cave water and cave air. In the wet season, there were no obvious spatial differences of mean PCO2 in cave stream and cave air from upstream to downstream cave. Conversely, there were significant spatial differences of mean PCO2 in cave stream and cave air from upstream to downstream cave in the dry season because of cave ventilation. Mean dripwater PCO2 in D1 site where near cave entrance is much higher than that of the D2 and D3 sites where located in inner cave because D1 has a shorter flowpath from cave ceiling to soda-straw tip and lesser CO2 degassing along the flowpath. Further work in Xueyu Cave needs to clarify the quantitative relationship of CO2 cycle between cave air CO2 and cave water and focus on the influence of CO2 cycle on speleothem form.
... = 0 for H+, PHREEQE solves a set of non-linear equations using a combination of two techniques: (1) a continued fraction approach, as in Wigley (1977), is used for mass balance equations, and (2) All other unknowns, activities of other aqueous species, activity coefficients, molalities, and the activity of water are calculated from these independent variables. The activities of aqueous species are calculated from their mass action equations, which involve only master species and an equilibrium constant. ...
... The hydrochemical data sets, including pH, water temperature and concentrations of K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− and HCO 3 were processed with the program WATSPEC (Wigley, 1977) to calculate partial pressure of CO 2 (pCO 2 ) in stream waters and saturation index of calcite (SIc). pCO 2 is assumed to be in equilibrium with the sampled waters by the equation: ...
... As stated in [Morad. S. 1990], the model presented in [Egeberg and Aagaard 1988] lates activities of the various ions of formations waters using ion association model (originally described in [Wigley 1977]). The thermodynamics data used are given in [Helgeson and Kirkham 1974], [Helgeson and Kirkham 1974], [Helgeson and Kirkham 1976], [Walter and Helgeson 1977], [Helgeson H. C and [Helgeson H. C. and Flowers 1981]. ...
A geochemical speciation modelling software is responsible for calculating the distribution of dissolved species between solutes and aqueous complexes, and also computes saturation indexes for different minerals. In this work we introduce SHPECK, a software developed to model geochemical equilibrium systems using the mass-balance conditions based on the phase rule concept [Garrels and Christ 1965]. Our software accepts any general combination of elements, species, and reactions, allowing the user to create different environments, simulations and, therefore, fully control any aspect and configuration of the model. It provides an interactive and intuitive user interface as well as the support of a built-from-the-ground database structure that handles the management of the whole thermodynamic data used for the geochemical modeling. We present a thorough computer science based review about the available geochemical modeling software (only programs that provide speciation modeling), expressing relevant particularities as: input and output options; user interaction; file formats ; and software environment together with installation procedures; Finally, we validate SHPECK by modeling the diagenetic reactions observed in a sandstones' reservoir and performing a comparative study with the previously discussed software. In addition to this, a database comparison was addressed and the results demonstrate a substantial improvement on the performance by the use of the SHPECK 's relational database.
... The cations were analyzed through ICPeOES Vista MPX (Varian, USA). Ion concentrations were used to calculate the CO 2 partial pressure (pCO 2 ) and calcite saturation index (SIc) from a geochemical model with pH, temperature, and seven major ions concentrations using the WATSPECT program (Wigley, 1977). Chl a was concentrated from water sample through filtration with vacuum filtration and then extracted using an acetone 90% solution. ...
The photosynthetic conversion of dissolved inorganic carbon (DIC) into organic carbon (OC) by using aquatic phototrophs in rivers may serve as a potential carbon sink, especially in the carbonate rock areas, thereby offering a clue for finding the missing carbon sink. However, primary-produced autochthonous OC is erroneously considered as terrestrial-derived allochthonous OC. Thus, carbonate weathering-related carbon sink is underestimated if only DIC concentrations sampled at river mouths are considered , and the transformation of DIC to autochthonous OC is neglected. Therefore, distinguishing sources of autochthonous and allochthonous OC is vital in the assessment of carbon sink. In this study, source-specific biomarkers, in association with chemical compositions and phytoplankton proxies in water samples collected from the Pearl River, were analyzed to determine OC sources. Results showed that biomarkers in the Pearl River were quite abundant, and the calculated average autochthonous OC was approximately 65% of the total OC, indicating intense in-river primary productivity. Moreover, phyto-plankton biomass and DIC concentration were positively related, indicating the DIC fertilization effect on aquatic photosynthesis. High total suspended solid (TSS) on the water surface blocked the sunlight and then reduced phytoplankton production. However, in situ photosynthesis of phytoplankton could also produce autochthonous OC, even larger than the allochthonous source at sites with high DIC, and even with higher TSS concentrations. These findings comprehensively elucidated the formation of autoch-thonous OC based on the coupling action of rock weathering and photosynthetic activity in the riverine system, suggesting a potential direction for finding the missing carbon sink.
... The saturation index (SI) values with respect to the minerals calcite and dolomite were calculated using the WATSPEC computer program [33]. The SI values calculated for common mineral dissolution are plotted in Figure S1(a,b) (SM) for dry and wet periods, respectively. ...
... The saturation index (SI) values with respect to the minerals calcite and dolomite were calculated using the WATSPEC computer program [33]. The SI values calculated for common mineral dissolution are plotted in Figure S1(a,b) (SM) for dry and wet periods, respectively. ...
The thermal fluids vented over Eskisehir province have been investigated for their origin and to estimate the geothermal potential of the area. Thermal waters as well as bubbling and dissolved gases were collected and analysed for their chemical and isotopic features. Their isotopic composition varies in the range from −11.5 to −7.7 ‰ for δ 18 O, −84 and −57 ‰ for δ 2 H, and 0–7.2 TU for tritium. The gases (bubbling and dissolved) are mostly N 2-dominated with a significant amount of CO 2. The helium isotopic ratios are in the range of 0.2–0.66 R/Rac, indicate remarkable mantle-He contribution ranging between 2 and 10 % in the whole study area. Considering the estimated geothermal gradient about three times higher than the normal gradient, and the reservoir temperatures estimated to be between 50 and 100 °C using quartz and chalcedony geothermometers, a circulation model was built where possible mixing with shallow waters cool down the uprising geothermal fluids. ARTICLE HISTORY
... Li et al. [2008Li et al. [ , 2010 found that δ 13 C-DIC values and major elements ratios might be shifted when CO 2 degassing/secondary calcite precipitation occurred. The partial pressure of CO 2 (PCO 2 ) and calcite saturation index (SIc) in the Wujiang River are calculated using the WATSPEC software [Wigley, 1977]. The average calcite saturation index (SIc) is 0.23 (Table S1), slightly oversaturated with respect to calcite. ...
Multiple isotopes (13C-DIC, 34S and 18O-SO42−, 15N and 18O-NO3−) and water chemistry were used to evaluate weathering rates and associated CO2 consumption by carbonic acid and strong acids (H2SO4 and HNO3) in a typical karst watershed (Wujiang River, Southwest China). The dual sulfate isotopes indicate that sulfate is mainly derived from sulfide oxidation in coal stratum and sulfide-containing minerals, and dual nitrate isotopes indicate that nitrate is mainly derived from soil N and nitrification. The correlation between isotopic compositions and water chemistry suggests that sulfuric and nitric acids, in addition to carbonic acid, are involved in carbonate weathering. The silicate and carbonate weathering rates are 7.2 t km−2 yr−1 and 76 t km−2 yr−1, respectively. In comparison with carbonate weathering rates (43 t km−2 yr−1) by carbonic acid alone, the subsequent increase in rates indicates significant enhancement of weathering when combined with sulfuric and nitric acids. Therefore, the role of sulfuric and nitric acids in the rock weathering should be considered in the global carbon cycle.
... In a spreadsheet program it is easy to modify data, including equilibrium constants, and to include new reactions. Some widely used equilibrium programs [18][19][20][21][22][23] include all reactions as statements in the program code. To consider a new reaction or to change equilibrium constants, the user must modify the source code and recompile it. ...
Spreadsheets can automate any chemical equilibrium calculation that can be performed by hand.
Lotus 1‐2‐3 ® worksheets for calculating the calcite saturation index (SI) and calcium carbonate precipitation potential of a water sample are described. A simplified worksheet illustrates the principles of the method, and a more complex worksheet suitable for modeling most potable water sources is briefly described. Both worksheets include ion pairing and adjustments of equilibrium constants for temperature and ionic strength. For several test cases with a wide range of temperature, alkalinity, pH, and calcium concentration, the worksheet SI values differed <1 percent from those computed by WATEQX. For water quality modeling, spreadsheets have several advantages compared with large equilibrium codes: flexible input and output, ease of maintaining the thermodynamic database, and relatively small memory and mass‐storage requirements. Modeling of archived chemical data is possible through the combination of database management and computational capabilities of many commercially available programs. The worksheets can be obtained from the authors.
The significance of CO2 emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO2 emission flux in a catchment, little research has been carried out to investigate the spatio-temporal variations in CO2 emissions in view of a water continuum. Here, we systematically compared the differences and control factors of CO2 degassing across the water–air interface of a spring–river–lake continuum in the discharge area of Baotuquan Spring in July 2017, which is a typical temperate karst spring area in Jinan city, northern China, using hydrogeochemical parameters, stable carbon isotope values, and CO2 degassing flux. Affected by the pCO2 concentration gradient between the water and ambient air, the spring water showed a high CO2 degassing flux (166.19 ± 91.91 mmol/(m2 d)). After the spring outlet, the CO2 degassing flux in the spring-fed river showed a slight increase (181.05 ± 155.61 mmol/(m2 d)) due to river flow rate disturbance. The river flow rate was significantly reduced by the “blockage” of the lake, which promoted the survival and reproduction of phytoplankton and provided favorable conditions for aquatic plant photosynthesis, increasing the plankton biomass in the lake to 3383.79 × 104/L. In addition, the significant decrease in the dissolved inorganic carbon (DIC) concentration and the increase in the δ13CDIC values in the lake also indicated that the photosynthesis of the lake’s aquatic plants resulted in a significant decrease in the pCO2 concentration, thus limiting the amount of CO2 off-gassing (90.56 ± 55.03 mmol/(m2 d)).
Accurately quantifying the carbon sink effect resulting from chemical weathering caused by anthropogenic H2SO4 is imperative to improve the assessment of the global carbon budget. Nevertheless, there is still a lack of precise understanding regarding the impact of anthropogenic H2SO4 on CO2 consumption during chemical weathering. Here, spring water samples were collected monthly from three catchments with distinct bedrock lithologies affected by severe acid precipitation in Southwest China for analyses of hydrogeochemistry and δ13CDIC to quantitatively estimate the effect of anthropogenic H2SO4 on the weathering carbon sink budget. The results show that carbonates contribute 97.4 %, 95.0 % and 88.8 % of the total cationic load using a straightforward method in the Beidiping carbonate catchment, as well as in the Shegengyan and Bianyan silicate catchments, respectively. The [Ca2++Mg2+]/[HCO3 − ] (0.98–1.19) and [Ca2++Mg2+]/[HCO3 − +SO4 2− ] (approximately 1) equivalent ratios, and δ13CDIC values (− 16.8 to − 8.0 ‰) of the samples suggest that besides H2CO3, H2SO4 is involved in carbonate weathering. The stoichiometry of the chemical compositions of spring water indicates that the presence of H2SO4 enhances carbonate weathering rates by 14.8 %, 8.1 % and 7.5 % while decreasing the CO2 consumption by 8.2 %, 4.3 % and 4.0 % in Beidiping, Shegengyan and Bianyan, respectively. Thus the reduced proportion of karst carbon sink in the carbonate catchment is approximately 2 times that in the silicate catchment, suggesting that carbonate weathering in the karst catchment is more sensitive to acid precipitation. The impact of acid precipitation on rock weathering in the silicate catchment is constrained by the soil buffering effect. Our study highlights the important role of anthropogenic H2SO4 in carbonate weathering, which should be critically evaluated in regional and global carbon cycles in future studies.
The chemical equilibrium equations utilized in reactive transport modeling are complex and nonlinear, and are typically solved using the Newton-Raphson method. Although this algorithm is known for its quadratic convergence near the solution, it is less effective far from the solution, especially for ill-conditioned problems. In such cases, the algorithm may fail to converge or require excessive iterations. To address these limitations, a projected Newton method is introduced to incorporate the concept of projection. This method constrains the Newton step by utilizing a chemically allowed interval that generates feasible descending iterations. Moreover, we utilize the positive continuous fraction method as a preconditioning technique, providing reliable initial values for solving the algorithms. The numerical results are compared with those derived using the regular Newton-Raphson method, the Newton-Raphson method based on chemically allowed interval updating rules, and the bounded variable least squares method in six different test cases. The numerical results highlight the robustness and efficacy of the proposed algorithm.
This study was undertaken in the Banzhai, a small groundwater-fed stream flowing over carbonate karst terrain in the southwest of Guizhou, China. To assess the biogeochemical processes behind carbon fluxes and sinks and calculate the end-member contribution to the geological carbon sink, samples were collected at a 2-h sampling interval during a two-day period, and the diel-variation of δ13CDIC, δ13CPOC, and C/N were analyzed. During the sampling period, temperature, pH, electrical conductivity (EC), dissolved oxygen (Do), and chlorophyll were measured at a 15-min interval using in situ sensors. The results showed that (1) the hydro-chemical variations reflected the photosynthesis of subaquatic plants and degassing. These processes likely turned a part of HCO3- to organic carbon, which subsequently precipitated. (2) The 13C isotope ratios indicated a varying intensity of photosynthesis and degassing during the HCO3- migration process. Moreover, subaquatic plants changed their metabolic pathway from C3 to C4 carbon fixation due to the lack of CO2 in the water and utilized HCO3- in the water as their carbon source. (3) The net carbon sink flux was 1784.54 kg CO2, where carbonate weathering, the biological carbon pump, and weathering of silicate rocks accounted for 85.80 %, 13.64 %, and 0.56 %, respectively. (4) In the Banzhai ground river, the DIC during the migration process was mainly lost through degassing, allogenic acid, and consumption by photosynthesis of subaquatic plants.
Cette thèse est consacrée à l’étude du transport réactif dans les réserves en eaux. Elle est structurée en deux parties distinctes : la première porte sur l’élaboration de solveurs chimiques et la seconde sur l’étude mathématique d’une classe de modèles décrivant des écoulements en eaux peu profondes en interaction avec les eaux de surface.Dans la première partie du travail, on s’intéresse à la résolution numérique des équilibres thermodynamiques qui conduisent à des systèmes non linéaires complexes et très mal conditionnés. Dans ce travail, on combine une formulation particulière du système d’équilibre chimique, appelée la méthode des fractions continues positives, avec deux méthodes numériques itératives, la méthode d’Accélération d’Anderson et des méthodes d’extrapolation vectorielle, à savoir les méthodes MPE (minimal polynomial extrapolation) et RRE (reduced rank extrapolation). Le principal avantage de ces approches est d’éviter de former la matrice jacobienne et donc d’éviter les problèmes liés aux mauvais conditionnements de la matrice. Des tests numériques sont faits, notamment sur le cas test de l’acide gallique et sur le cas test 1D de référence du benchmark MoMas. Ces essais illustrent la grande efficacité de cette approche par rapport aux résolutions classiques résultant de la méthode de Newton-Raphson. Dans la seconde partie de la thèse, on introduit et étudie des modèles de type Richards-Dupuit pour décrire les écoulements dans des aquifères peu profonds. L’idée est de coupler les deux types d’écoulements principaux présents dans l’aquifère : celui de la partie insaturée avec celui de la partie saturée. Le premier est décrit par le problème classique de Richards dans la frange capillaire supérieure.Le second résulte de l’approximation de Dupuit après intégration verticale des lois de conservation entre le fond de l’aquifère et l’interface de saturation. Le modèle final consiste en un système fortement couplé d’edp de type parabolique qui sont définies sur un domaine dépendant du temps. Nous montrons comment la prise en compte de la faible compressibilité du fluide permet d’éliminer la dégénérescence présente dans la dérivée temporelle de l’équation de Richards. Puis nous utilisons le cadre général des équations paraboliques dans des domaines non cylindriques introduit par Lions pour donner un résultat d’existence global en temps. Nous présentons l’analyse mathématique du premier modèle qui correspond au cas isotrope et non conservatif. Puis nous généralisons l’étude au cas anisotrope et conservatif.
The chief constituents in water samples are obtained by the geochemical analysis. The results are then studied for various utility purposes, such as domestic, drinking, and agriculture. The results are also studied for understanding the thermodynamic states to determine geochemistry and the nature of the reactions. There are several software's available for this purpose, but still they do not include all the required parameters for the classification purpose or all the popular diagrams basically required for the study. In this context a software was coded in C++ and compiled in Visual C for the basic interpretation of the geochemical data, considering the utility thermodynamic nature and classification of water. The input data includes Ca, Mg, Na, K, Cl, HCO3, SO4, F, NO3, Si, TDS, EC, pH and Temperature. The output of the software presents the parameters like I.B.E. (Index to Base Exchange), Schollers water type, R.S.C. (Residual sodium carbonate), S.A.R. (Sodium Adsorption Ratio), N.C.H. (Non Carbonate Hardness), P.I, (Permeability Index), K.R. (Kellys Ratio), P.S. (Potential Salinity), M.H. (Magnesium hazard), S.S.P. (Soluble Sodium Percentage) and Na% (Sodium Percentage). The software also calculates the Scholler Classification, Corrositvity ratio, Chloride Classification, Cation, Anion facies and Handas Classification for each sample. The corrosive nature of the water sample is also determined by the software by calculating Puckorius Scaling index, Ryznar stability index, Larson-Skold index, Langelier saturation index and Aggressive index for each sample. Activity coefficient, Ionic activity and silicate stability diagrams were designed in the output. Later the total number samples were grouped based on the standard classification adopted for each calculated parameter. Standard diagrams like USSL, Johnsons plot, Gibbs, Doneens, other thermodynamic plots for Na, K, Mg for silicate system also form the output of the software. The output are saved in different files as opted during the execution of the program.
The pollution of karst aquifers by acid mine drainage (AMD) waters is increasing. Major and minor ions (Ca²⁺, Mg²⁺, HCO3⁻, SO4²⁻, F⁻, and Fe), stable sulfur and oxygen isotopes of dissolved sulfates (δ³⁴SSO4 and δ¹⁸OSO4) and oxygen isotope of water (δ¹⁸OH2O), were analyzed in rainwater, surface water, groundwater, and AMD water sampled from the Babu subterranean stream watershed, in Southwest China. The principal aim of this study was to explore the impact of AMD waters on the evolution of karst aquifers. Based on hydrogeochemistry and stable isotopes (δ¹⁸OH2O, δ¹⁸OSO4 and δ³⁴SSO4): (1) the chemistry of AMD waters was primarily controlled by pyrite oxidation, karst conduit water by AMD waters and mixing with calcite and dolomite dissolution, and spring water by atmospheric precipitation and carbonate dissolution; (2) contamination of the karst conduit water was mainly attributed to the input of AMD waters, resulting in a shift of δ³⁴SSO4 towards more negative values (from 3.4‰ to −13.2‰); (3) the quality of karst conduit water changed from suitable to unsuitable for irrigation and drinking, particularly due to the increase in total Fe, SO4²⁻, and F⁻ concentrations, reflecting the cumulative effect of AMD waters derived from tailings dumps; this influence was enhanced during rainstorm/drought and anthropogenic activities; and (4) the flow of contaminated groundwater through the conduit promoted the dissolution of carbonates, especially during the dry season due to the greater proportion of AMD in the groundwater. This released more CO2 to the atmosphere. We believe that analysis of stable isotopes (δ¹⁸OH2O, δ¹⁸OSO4, and δ³⁴SSO4), combined with hydrogeochemistry, is effective for exploring the impact of AMD on karst aquifers. Therefore, reasonable treatment methods should be taken to reduce the negative impacts of tailings dumps on karst aquifers.
In karst regions, soil CO2 is a major chemical driving force for the karst processes and finally has a significant impact on the hydrochemical processes of karst underground river. Hydrochemical features, soil and climatic parameters with a high-temporal resolution have been monitored on different scales (daily scale, seasonal scale and interannual scale, storm scale) in the Xueyu Cave watershed from 2009 to 2015. The aim of this study is to understand how cave stream pCO2 and hydrochemistry respond to overlying soil carbon recharge on different time scales. The results show that the variational amplitudes of the hydrochemistry in Xueyu Cave underground river (XUR) tend to be in the order: storm-scale > seasonal > interannual > daily scale. Soil CO2, pCO2 (CO2 partial pressure in the XUR) and Spc (specific conductivity) were higher in summer and autumn than those in winter and spring. The synchronous variations of XUR pCO2 with soil CO2 concentrations in the same order of magnitude confirm the “soil CO2 effects” on the formation of XUR hydrochemical features. The storm-scale fluctuations of hydrochemistry in XUR water are especially depending on the intensities of rainfalls that determine whether the “dilution effects” or the “CO2 effects” are predominant in the stream during rainfall events. At the same time, soil moisture and soil CO2 work as important factors for controlling pCO2 variations in the XUR. The identified relationship of soil-XUR pCO2 suggests a temperature control on carbonate weathering on daily and seasonal scale but a rainfall/soil moisture control on storm and annual scale. The combined effect of point and diffused infiltration that delays the arrival of storm flows determines the fluctuations of the discharge and pCO2 variation. Defining relationships between CO2 from overlying soils and groundwater offers the chance to explore the processes at different time scales, potentially increasing our ability to understanding the carbon dynamics in karst systems.
Although ²¹⁰Pb dating has been successfully used in speleothems, the understanding of the factors impacting ²¹⁰Pb variations in modern calcite depositions in karst caves is poor due to the lack of in situ monitoring. Here, we studied the ²¹⁰Pb variations in drip water and modern calcite depositions at five sampling sites in Maomaotou Big Cave in Guilin, south China, through more than three years of in situ monitoring. In this work, the air ²²²Rn concentrations, weights and ²¹⁰Pb-specific radioactivity of modern calcite depositions showed significant temporal and spatial variations. The modern calcite deposition weights and ²²²Rn concentrations in the air of Maomaotou Big Cave ranged from 0.02 to 6.04 g and 62.9–628 Bq.m⁻³ (higher values in summer-autumn and lower values in winter–spring), respectively, while the ²¹⁰Pb-specific radioactivities in calcite depositions varied from 7.33 to 658.52 Bq•kg⁻¹, with lower values reported in summer–autumn and higher values in winter–spring. The opposite seasonal trends observed for the ²²²Rn concentrations and ²¹⁰Pb-specific radioactivity indicated that the air ²²²Rn concentration was not the dominant factor influencing the ²¹⁰Pb-specific radioactivity in the modern calcite depositions. This study concluded that ²¹⁰Pb-specific radioactivity in modern calcite depositions is mainly carried by drip water; further, the remarkable negative correlation between deposition weight and ²¹⁰Pb-specific radioactivity in modern calcite depositions suggests that the Constant Initial Concentration model (CIC) is fit for recent speleothem dating in a closed system. Such important information may provide a scientific basis for cave deposition dating using ²¹⁰Pb.
The Kucaj-Beljanica massif represents a complex hydrological karst system that possesses enormous potential for further groundwater extraction and regional water supply uses. In this paper, the influencing factors on groundwater quality in this area were discussed using hydrochemical analysis and the factor analysis method with 123 water and 20 rain/snow water samples. Hydrochemical analysis of the cation composition of cold springs, thermal springs/wells and sinkhole waters in the test area indicates that Ca²⁺ and Mg²⁺ are the dominant cations, representing 73–98% of ion equivalent. The anion composition of water indicates that HCO3⁻ is the dominant anion, represented by 73–91% of ion equivalent. Only in the No. 30 thermal spring is characterized by K⁺ + Na⁺ and HCO3⁻ + SO4²⁻. The PCO2 of thermal springs/wells, cold springs and sinkhole waters decreases gradually by an average of 10,247, 3444, 319 ppmv (part per million of volume ratio), respectively. The average δ¹³CDIC of thermal springs/wells, cold springs and sinkhole waters is − 6.56‰, − 10.19‰ and − 13.46‰, respectively. Corresponding to δ¹³CDIC, the mole ratios of (Ca²⁺ + Mg²⁺)/HCO3⁻ are 0.48, 0.55 and 0.60, respectively. Factor analysis identifies 3 sources of solutes: (a) precipitation; (b) water–rock interactions; and (c) soil leaching. Ions of Na⁺, K⁺, Cl⁻ and SO4²⁻ indicate the predominant influence of atmospheric precipitation, but the No. 30 thermal spring sample is probably the result of deep water–rock interaction (volcanic rock) or is influenced by connate water mixed with shallow karst water. The dissolution of carbonate rocks is the primary factor affecting the Ca²⁺, Mg²⁺ and HCO3⁻ contents of groundwater, and soil leaching is the primary factor controlling the concentration of NO3⁻ in water. These results provide a scientific basis for rational exploitation, protection and land use planning in the test area.
Metabolic processes of the submerged aquatic community (photosynthesis and respiration) play important roles in regulating diel cycles of dissolved inorganic carbon (DIC) and sequestering carbon in a karst stream. However, little is known of whether diel DIC cycling occurs during rainfall in a karst groundwater-fed stream, even though this question is critical for the accurate estimation of what may be a major terrestrial carbon sink. Here, we measured diel variations of water chemical composition in a small karst groundwater-fed stream in southwest China during a rainfall event to assess the influences of rainfall and rising discharge on DIC diel cycling and the potential carbon sink produced by in-stream metabolism. Our results show that water chemical composition at the source spring (CK site) is relatively stable due to chemostatic behavior during rising discharge after a rainfall period. This site lacked submerged aquatic vegetation and, thus, had no diel variations in water chemistry. However, diel cycles of all hydrochemical parameters occurred at a site 1.3 km downstream (LY site). Diel variations in pH, DO, and δ¹³CDIC were inversely related to diel changes in SpC, DIC, Ca²⁺, and pCO2. These results indicated that diel cycling of DIC due to in-stream metabolism of submerged aquatic community was still occurring during elevated discharge from rainfall. We estimate the carbon sink through the in-stream metabolism of the submerged aquatic community to be 5.6 kg C/day during the studied rainfall event. These results imply that submerged aquatic communities in a karst stream can significantly stabilize carbon originating from the carbonate rock weathering processes in karst areas.
A hydrogeochemical and isotopic study was conducted on the subterranean karst stream, namely the Guancun subterranean stream (GSS). The hydrogeochemical processes of the GSS were controlled through calcite dissolution and precipitation and were driven by the concentration of CO2, which controlled changes in the pH and of PCO2 in the water. The δ¹⁸O and δD values of the GSS were within the global meteoric water line and the local meteoric water line, thereby indicating that the water of the GSS comes from precipitation. Certain abnormal δ¹⁸O and δD values suggest the effect of evaporation on the GSS given its use in a particular irrigation system, wherein the GSS in transformed into a surface stream and flows for a relatively long time on the surface during the wet season. The δ¹³CDIC values of the GSS range from −13.5 to −11.3‰ in the dry season and from −13.9 to −9.5‰ in the wet season, thereby indicating that the GSS belongs to a semi-open system. The δ¹³CDIC values in the GSS were formed by the δ¹³CDIC values of the soil CO2 and carbonate dissolution at different proportions. According to the simplified mass balance formula, the contributions of carbonate dissolution to the dissolved inorganic carbon (DIC) of the GSS were calculated to be 50.2–58.3% and 48.7–64.7% in the dry and wet seasons, respectively, thereby indicating a less than 50% carbonate dissolution contribution during the formation of DIC in karst groundwater. Moreover, sulfuric acid and nitric acid were observed to participate in karst processes.
The studies on geochemistry of the karstic waters, especially, those related to the classic system of chemical reactions CO2-H2O-CaCO3, have been fully developed in different karstic areas around the world, many of them to disembowel the mechanism and processes of the karstification. Some significant contributions, among others, developed in the tropical mountain karst of western Cuba are: studies about the chemico-physical behavior of the karstic waters of different hydrogeological natures and their typologies; studies about the chemical evolution of the karstic waters and the empiric relations among variables, parameters and physico-chemical indexes; quantitative estimations about the chemical denudation; the “prompt” work of hydrogeologic, chemico-physical and isotopic monitoring of the karstic waters in different hydrodynamic zones of the karst. This work offers information and brief analyses about the above mentioned, and pay attention to some cardinal problems, totally or partially not yet solved.
Two new expressions for the pH of saturation (pH//s) were derived. One is a simplified equation developed from an aqueous carbonate equilibrium system in which correction for ionic strength was considered. The other is a more accurate quadratic formula that involves computerized calculation of pH//s and takes into account ionic speciation and an activity correction factor. Different methods of determining pH//s of 155 water samples were compared using the Langelier equation, the Larson-Buswell formula, the two pH//s equations derived in this study, two mathematical models obtained from multivariate analysis, the WATSPEC2 computer program, and Caldwell-Lawrence diagrams.
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