Sulfuric acid as a weathering agent of carbonate weathering constrained by δ~(13)C: Examples from Southwest China

Rock weathering by carbonic acid is one of the important atmosphere CO2 sequestration. Actually, it depends on whether carbonic acid or other acids as weathering agents, which is important to understand the model of global carbon cycle. For example, sulfu…     

Chemical composition of wet precipitation at a developing urban site in southeastern China

A comprehensive study on the chemical composition of wet precipitation was carried out from January 2004 to December 2004 at Jinhua, China. All samples were analyzed for pH, electrical conductivity and major ions （F, Cl, NO3,. SO4^2-, K^＋, Na^＋, Ca^2＋, Mg^2＋. and NH4^＋）. The results showed that SO4^2- is one of the dominant anions, accounting for 66.1% of the measured anions in precipitation, while NH4^＋ and Ca^2＋ account for 56.6% and 33.4% of the measured cations, respectively. Even though the concentrations of SO4^2- and NO3^- were not high relative to those in the northern areas of China, rainwater in the studied area is typically acidic with a volume-weighted mean pH of 4.54 due to the lack of neutralization in precipitation. The fractional acidity value suggested that about 76% of acid was neutralized by alkaline constituents. On the other hand, H^＋ showed no significant correlation with other ionic species, which indicates that its acidity might be attributed to the comprehensive effect of all the acidifying and neutralizing ions rather than one major ion in precipitation. A good correlation between Ca^2＋ and Mg^2＋, as well as between Na^＋ and Cl^-, indicated these ions are commonly of crustal and marine origin, respectively. Other relatively good correlations were observed between NH4^＋ and SO4^2-, Ca^2＋ and SO4^2-, Mg^2＋ and SO4^2-, Mg^2＋ and NO3^-, and Mg^2＋ and Cl^-. These results were attributed to the atmospheric chemical reactions of the acids H2SO4, HNO3 and HCl with alkaline compounds such as NH3 and/or carbonate materials. High enrichment factor of marine source for SO4^2-, Ca^2＋ and K^＋ indicated that large amounts of these ions came mainly from a non-marine source. Similarly, a high enrichment factor of soil for SO4^2-, NO3^- and CI also suggested that most of these ions did not come from soil source.     

Acid rain in China-Input-output budgets of major ions in four forested catchments

Acid rain is one of China＇s major environmental problems and emissions of sulphur and nitrogen are still increasing. The acid rain situation in China is somewhat different from what is seen in Europe and North America. Sulfur deposition is very high, but there is also very high deposition of calcium and other base cations. The sources of atmospheric Ca are not well understood, although it is important for understanding long term impacts of acid deposition. The fate of S, N and Ca^2＋ in the catchment is crucial for the future development of the acidification situation of soils and waters in China. Very few studies presenting catchment input-output ion budgets in Chinese natural environments exist and there are several unknown factors regarding processes. Here, we present annual input-output budgets for three years （2001-2003） for major ions for four forested catchments in China receiving different loads of acid deposition. For the two sites receiving the highest SO4^2- inputs, the input-output budget for the upper 50 cm of soil is approximately balanced. For the most remote site the soil is a net sink for SO4^2-, suggesting that the pool of adsorbed SO4^2- in the soil is building up. This is in agreement with the fact that the site so far has received only moderate SO4^2- inputs. For the southemmost, the subtropical site there is a loss of SO4^2- in the soil, which at least partly may be related to high uptake from the dense and highly productive forest at the site. The Ca^2＋ budgets for the upper 50 cm of soil show large variations both within and between sites. For most locations there is production of Ca^2＋ in the soil that can be explained by weathering, and variation between years related to hydrology that can be explained by ion exchange. However, at some plots at the site receiving very high inputs of both SO4^2- and Ca^2＋, there is an unknown sink of Ca^2＋ in the soil at some plots.     

Stable isotopes （S, Cl） and hydrochemical variations in a karstic ground water system, Guiyang, SW China

A groundwater system in a karstic terrain is easily subject to pollution and its remediation is difficult once contaminated by human activities. The groundwater samples collected in both winter and summer seasons at Guiyang, SW China, show a wide range of variations in chemical composition and dominance of Ca^2＋, Mg^2＋, SO4^2-, and HCO3^- ions. The anthropogenic inputs include Cl^-, NO3^-, SO4^2-, Na^＋, and K^＋, as judged from the relationships between different elemental ratios and sewage samples. Cl^- concentrations of all water samples in the study area vary from 0 to 3.9 mmol/L in winter and are higher than in summer. In most of the samples, SO4^2- concentrations are high, ranging from 0.1 to 11 mmol/U The studies show that the cycling of sulfur plays an important role in controlling water chemistry and fate of contaminants in groundwater. In order to understand the source of SO4^2- and the geochemical cycling of some elements in the karstic groundwater environment, we have carried out a study on the variations of S and Cl isotope compositions, in addition to other isotopic tracers such as ^87Sr/^86Sr and δ^13C studied previously. The δ^37Cl values of the groundwater samples present a seasonal variation, ranging from 0.00‰ to ＋2.03‰ in winter and from -1.46‰ to ＋0.29‰ in summer. The surface water samples show a similar range of variations as observed for groundwater. Two rainwater samples collected at Guiyang have a distinct isotopic signature （mean value is -3‰） compared to the δ^37Cl values reported in literature. These results indicate that ground water is mainly derived from precipitation and suggest a fast recharge of the karst system by surface water.     

Major ions characteristics in a disturbed aquifer of an oceanic island——Sipadan, Malaysia

The Sipadan island is the only oceanic island found in Malaysia, and is popularly known for its beautiful corals and diving activities. The aquifer of the island is affected by seawater intrusion associated with groundwater exploitation. Geologically, the aquifer is composed of several series of Quaternary bioherm facies, and its recharge merely depends on rainfall. This research attempts to understand the chemical changes of the groundwater attributed to the salinization processes based on major ion composition （Ca^2＋, Mg^2＋, Na^＋, K^＋, HCO, SO, Cl^-）. The initial assessments were done in years 1993 - 1994, followed by subsequent assessment in years 2004-2005. Methods of analyses were adopted from APHA （1995）. The hydrogeochemical saturation indices （SI） were computed using the PHREEQC program in order to assess the state of equilibrium between groundwater and the minerals present. The results of analyses indicated that the groundwater has been highly enriched in Na^＋, SO and CI, reflecting an encroachment of saline water into the aquifer. The groundwater facies can be classified as sodium chloride （Na-Cl） water type. There are positive correlations （moderate to strong）, except HCO3^-, between the studied parameters. The weak and inconsistent correlation of HCO3^- with the cations and anions related to dissolved salts suggests that saltwater intrusion has an insignificant impact on the chemistry of HCO3^- in the groundwater. Strong correlations （r 〉0.70） exist among the major elements （Na^＋, Mg^2＋, K^＋, Cl^- and SO4^-） and salinity （EC）. These relationships clearly identify the main elements contributing to the groundwater salinity and their tendency to depict a similar trend of salinization pattern. Chloride has a major influence on the salinity of groundwater based on the positive and strong correlation that exist between Cl^- and EC （r=0.97）.     

Variability of aquatic chemistry in central Guizhou karst region, China

It is necessary to understand the aquatic chemical characterstics of natural surface fresh water for water quality assessment.The chemical data from different kinds of water in the central Guizhou karst area showd that spring water from carbonate rock cracks(crack-water)is of neutrality or meta-alkalinity and [C] Ca II type.The amounts of all ions and the concentrations of HCO3^- and Ca^2 were higher in the autumn than in the spring,The crack-water was influenced by the infiltration of surface water in the process of erosion and /or trans-portation with decreasing HCO3 and increasing pH,SO4^2-,Cl^-,K^ and Na^ during running in a certain distance on the land surface .In particular,the chemical compositions of the waters at Tianxingqiao(upper-stream),Shuiliandong(mid-waterfall)and Luoshuitan(down-pool)near the Huangguoshu Waterfall were much different from those of the crack-water.The concentration of SO4^2-,Na^ ,Fe^3 and NO3^- varied closely with seasons.The CaCO3 deposited violently with CO2 release in the spring ,In Lake Hongfeng the HCO3^-/SO4^2- equivalent ratios were only 2.1-2.4 ,but Ca^2 /Mg^2 up to 2.4-4.2.The Cl^- concentration increased by a factor of 1 and Na^ by order of magnitude relative to the spring water.These indicated the increase in artificial pollutant discharge in the Lake Hongfeng watershed.In addition,Proewater in the soils covering carbonate rocks belongs to strongly mineralized water,The obvious differences in water quality were controlled by carbonate deposition,sulphate mineralization and nitrogen fixation as well as ammonification.It is indicated thaty the chemical compositions in the waters from the karst region were unstable and changeable.     

The effect of acid deposition on base cation cycling in a karstic-forested catchment： Evidence from strontium isotopes

Bedrock weathering and atmospheric deposition are the two primary sources of base cations （K^＋, Na^＋, Ca^2＋ and Mg^2＋） to forest ecosystems. Therefore, the key problem is to understand the relative inputs from these two sources and the cycling in the ecosystem. This study focuses on the effects of acid deposition on cation cycling in a small-forested karstic catchment in Guizhou Province. Sr isotope ratios were used as a tracer for understanding the transport process between the different cation pools： rock, soil, surface water, atmospheric deposition and plant. The samples of wet deposition, total deposition, throughfall, surface and ground waters, vegetation, and soil were monthly collected. The exchangeable Sr^2＋ and Ca^2＋ in soil samples were extracted by using 1 M ammonium acetate. The leaf-tissue samples were ashed at 550℃, and the residue was digested in ultrapure HClO4 and HNO3. All water samples were filtrated through 0.45 μm aperture filter paper. Base cation concentrations and Sr isotopic composition were analyzed for all the samples. The results show that acid deposition （average pH 4.9） frequently occurred in the studied region. Cation abundance follows an increasing manner from rainwater, throughfall, to surface water or ground water samples, suggesting that acid deposition at first eiuviates Ca^2＋ , Mg^2＋ and Sr^2＋ from leaf, then the exchangeable cations from soil, and at last cations accumulate in surface water or ground water.     

Chemical and Isotopic Characteristics of the Water and Suspended Particulate Materials in the Yangtze River and Their Geological and Environmental Implications

The chemical and isotopic characteristics of the water and suspended particulate materials（SPM） in the Yangtze River were investigated on the samples collected from 25 hydrological monitoring stations in the mainsteam and 13 hydrological monitoring stations in the major tributaries during 2003 to 2007. The water samples show a large variation in both δD（ 30‰ to 112‰） and δ18O（ 3.8‰ to 15.4‰） values. Both δD and δ18O values show a decrease from the river head to the Jinsha Jiang section and then increase downstream to the river mouth. It is found that the oxygen and hydrogen isotopic compositions of the Yangtze water are controlled by meteoric precipitation, evaporation, ice（and snow） melting and dam building. The Yangtze SPM concentrations show a large variation and are well corresponded to the spatial and temporal changes of flow speed, runoff and SPM supply, which are affected by the slope of the river bed, local precipitation rate, weathering intensity, erosion condition and anthropogenic activity. The Yangtze SPM consists of clay minerals, clastic silicate and carbonate minerals, heavy minerals, iron hydroxide and organic compounds. From the upper to lower reaches, the clay and clastic silicate components in SPM increase gradually, but the carbonate components decrease gradually, which may reflect changes of climate and weathering intensity in the drainage area. Compared to those of the upper crust rocks, the Yangtze SPM has lower contents of SiO2, CaO, K2 O and Na2 O and higher contents of TFe2 O3 and trace metals of Co, Ni, Cu, Zn, Pb and Cd. The ΣREE in the Yangtze SPM is also slightly higher than that of the upper crust. From the upper to lower reaches, the CaO and MgO contents in SPM decrease gradually, but the SiO2 content increases gradually, corresponding to the increase of clay minerals and decrease of the carbonates. The δ30SiSPM values（ 1.1‰ to 0.3‰） of the Yangtze SPM are similar to those of the average shale, but lower than those of the granite rocks（ 0.3‰ to 0.3‰）, reflecting the effect of silicon isotope fractionation in silicate weathering process. The δ30SiSPM values of the Yangtze SPM show a decreasing trend from the upper to the middle and lower reaches, responding to the variation of the clay content. The major anions of the river water are HCO 3, SO 4 2, Cl, NO 3, SiO 4 4 and F and the major cations include Ca2＋, Na＋, Mg2＋, K＋ and Sr2＋. The good correlation between HCO3-content and the content of Ca2＋may suggest that carbonate dissolution is the dominate contributor to the total dissolved solid（TDS） of the Yangtze River. Very good correlations are also found among contents of Cl, SO4 2, Na＋, Mg2＋, K＋and Sr2＋, indicating the important contribution of evaporite dissolution to the TDS of the Yangtze River. High TDS contents are generally found in the head water, reflecting a strong effect of evaporation in the Qinghai-Tibet Plateau. A small increase of the TDS is generally observed in the river mouth, indicating the influence of tidal intrusion. The F and NO3 contents show a clear increase trend from the upstream to downstream, reflecting the contribution of pesticides and fertilizers in the Chuan Jiang section and the middle and lower reaches. The DSi shows a decrease trend from the upstream to downstream, reflecting the effect of rice and grass growth along the Chuan Jiang section and the middle and lower reaches. The dissolved Cu, Zn and Cd in the Yangtze water are all higher than those in world large rivers, reflecting the effect of intensive mining activity along the Yangtze drainage area. The Yangtze water generally shows similar REE distribution pattern to the global shale. The δ30SiDiss values of the dissolved silicon vary from 0.5‰ to 3.7‰, which is the highest among those of the rivers studied. The δ30SiDiss values of the water in the Yangtze mainsteam show an increase trend from the upper stream to downstream. Its DSi and δ30SiDiss are influenced by multiple processes, such as weathering process, phytolith growth in plants, evaporation, phytolith dissolution, growth of fresh water diatom, adsorption and desorption of aqueous monosilicic acid on iron oxide, precipitation of silcretes and formation of clays coatings in aquifers, and human activity. The δ34SSO4 values of the Yangtze water range from 1.7‰ to 9.0‰. The SO4 in the Yangtze water are mainly from the SO4 in meteoric water, the dissolved sulfate from evaporite, and oxidation of sulfide in rocks, coal and ore deposits. The sulfate reduction and precipitation process can also affect the sulfur isotope composition of the Yangtze water. The87Sr/86Sr ratios of the Yangtze water range from 0.70823 to 0.71590, with an average value of 0.71084. The87Sr/86Sr ratio and Sr concentration are primary controlled by mixing of various sources with different87Sr/86Sr ratios and Sr contents, including the limestone, evaporite and the silicate rocks. The atmospheric precipitation and anthropogenic inputs can also contribute some Sr to the river. The δ11B values of the dissolved B in the Yangtze water range from 2.0‰ to 18.3‰, which is affected by multifactors, such as silicate weathering, carbonate weathering, evaporite dissolution, atmospheric deposition, and anthropogenic inputs.     

Hydrogeochemistry of karst underground waters at shallow depth in Guiyang City, Guizhou Province

The aim of this study is to shed light on the hydrogeochemical characteristics of karst underground waters at shallow depth in Guiyang City, Guizhou Province with an emphasis on the geochemistry of major elements. Guiyang City bears abundant underground waters and it is also an important representative of the karst areas throughout the world. Ca^2 and Mg^2 are the dominant cations, accounting for 81% -99.7% of the total, and HCO3^- and SO4^2- are the dominant anions. Weathering of limestones and dolostones is the most important factor controlling the hydrogeochemistry of underground waters, and weathering of sulfate and evaporite rocks is less important. Moreover, the precipitation and human activities also have a definite influence on the hydrogeoehemistry of underground waters in the region studied.     

Sodic metasomatism in a dacite weathering profile in Pinxiang, Guangxi, China

The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron oxide minerals, quartz, and a small amount of illite, montmorillonite and vermiculite. In going downwards the red clay zone gives way to a saprolite zone in which plagioclase pseudomorphs have been well preserved although replaced by kaolinite. Beneath the saprolite zone is the saprock zone characterized by less weathering for dacite. At the bottom of the weathering profile is the parent material, dacite, which is composed mainly of plagioclase, quartz, K-feldspar and biotite which have been largely altered into chlorite owing to submarine extrusion of dacite lavas. Some layers in the weathering profile show obvious sodium enrichment and potassium depletion relative to others. In the Al2O3-(CaO* Na2O)-K2O triangular diagram, the weathering trends of these layers in the middle stage are remarkably deviated from normal ones. Both mineralogy and micro-morphology of these layers indicate such deviation resulted from sodic metasomatism of orthoclase.     

Carbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang, China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (-1‰ to -2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (-7‰ to -8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between -1‰ and -5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg-calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg-calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.     

On the Origin of Petroleum Hydrocarbon Gases

The compositional variation of oil-soluble gaseous hydrocarbons in high-pressure in-place oil from more than 40 oil wells in the Northern Jiangsu oil field, China, was studied. Samples in which the effects of the factors of pressure and biodegradation had been got rid of were chosen as the representatives that could really reflect the original composition of hydrocarbon gases. Such samples were compared compositionally with their corresponding hydrocarbons formed by decarboxylation of volatile low-molecular fatty acids. Thus highly correlative regularities were found to exist between them. The numerical values of both are graphically expressed. The two curves on the diagram are very similar. These two sets of values have a simple correlation coefficient of 0.9935, which presents their genetic relation.Based on the study of the formation of gaseous hydrocarbons from decarboxylation of volatile fatty acids, the following regularities of the isomers are revealed:1) n-butyric acid + isobutyric acid = propane:2) 1 2 isopentanoic acid(2-methyl-butyric acid) + n-pentanoic acid = n-butane; and3) 1 2 isopentanoic acid(3-methyl-butyric acid) = isobutane.The thermodynamics of decarboxylation was analysed and the enthalpy change △H, entropy change △S and Gibbs free energy change △G in the following reaction were calculated:CH_3COOH(1)--CH_4(g) + CO_2(g).Thus the author considers that the reaction for the formation of hydrocarbons due to the decarboxylation of fatty acids is an exothermic one with increased entropy and decreased free energy as well as a spontaneous one. According to the CRC rule, the resultant Gibbs free energy change △G is approximately-41.84 kJ/mol, which is well within the range of the energy levels of biophysiological changes.According to the changes in odd-carbon preference in n-alkanes of petroleum and sediments and the analysis of fatty acids and amino acids, it is considered that hydrocarbon gases do not originate from pyrolysis or thermal degradation but from decarboxylation of organisms. But this biological reaction is not ordinary biochemical reaction in the artificial fermentation for generating marsh gas. On the basis of the change tendency of the fatty acid content in the fermentation liquor for marsh gas generation and the change tendency of the carbon isotopes in methane and carbon dioxide in the marsh gas, it can be judged that the biochemical reaction for forming hydrocarbon gases is a special biological one occurring after the fermentation.     

Carbon Fluxes and Sinks: the Consumption of Atmospheric and Soil CO2 by Carbonate Rock Dissolution

Carbonate rock outcrops cover 9%–16% of the continental area and are the principal source of the dissolved inorganic carbon (DIC) transferred by rivers to the oceans, a consequence their dissolution. Current estimations suggest that the flux falls between 0.1–0.6 PgC/a. Taking the intermediate value (0.3 PgC/a), it is equal to 18% of current estimates of the terrestrial vegetation net carbon sink and 38% of the soil carbon sink. In China, the carbon flux from carbonate rock dissolution is estimated to be 0.016 PgC/a, which accounts for 21%, 87.5%–150% and 2.3 times of the forest, shrub and grassland net carbon sinks respectively, as well as 23%–40% of the soil carbon sink flux. Carbonate dissolution is sensitive to environmental and climatic changes, the rate being closely correlated with precipitation, temperature, also with soil and vegetation cover. HCO3- in the water is affected by hydrophyte photosynthesis, resulting in part of the HCO3? being converted into DOC and POC, which may enhance the potential of carbon sequestration by carbonate rock dissolution. The possible turnover time of this carbon is roughly equal to that of the sea water cycle (2000a). The uptake of atmospheric/soil CO2 by carbonate rock dissolution thus plays an important role in the global carbon cycle, being one of the most important sinks. A major research need is to better evaluate the net effect of this sink in comparison to an oceanic source from carbonate mineral precipitation.     

Water chemical behavior at Yangtze （Changjiang） River estuary

Geochemical cycling has received wide attention due to the need to understand the pathways of pollutants through our present environment. In this regard the Yangtze River plays a significant role in putting those pollutants into the East China SeafWorld Oceans. The Yangtze River is of high sedimentation rate and water discharge. The watershed covers variable climate regions from temperate to subtropical and from semiarid to humid. Twenty three （23） sampling locations at the estuary have been selected for understanding the dynamic relationships. The elements （Cl^-, SO4^2-, Na^＋, K^＋, and Ca^2＋） show conservative behavior during mixing of fresh water with saline water whereas Mg^2＋, Mn^2＋ show a non-conservative pattern . The relationships between Na^＋/SO4^2- and Cl^-/SO4^2- molar ratios show a mixing of more than two water sources.     

Carbon and Oxygen Isotopic Composition of Surface‐Sediment Carbonate in Bosten Lake (Xinjiang,China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (?1‰ to ?2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (?7‰ to ?8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between ?1‰ and ?5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg–calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg–calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.     

Role of Carbonic Anhydrase as an Activator in Carbonate Rock Dissolution and Its Implication for Atmospheric CO_2 Sink

The conversion of CO2 into H+ and is a relatively slow reaction. Hence, its kinetics may be rate determiningin carbonate rock dissolution. Carbonic anhydrase (CA), which is widespread in nature, was used to catalyze the CO2 conversion process in dissolution experiments of limestone and dolomite. It was found that the rate of dissolution increases by a factor of about 10 after the addition of CA at a high CO2 partial pressure (Pco2) for limestone and about 3 at low Pcoj for dolomite. This shows that reappraisal is necessary for the importance of chemical weathering (including carbonate rock dissolution and silicate weathering) in the atmospheric CO2 sink and the mysterious missing sink in carbon cycling. It is doubtless that previous studies of weathering underestimated weathering rates due to the ignorance of CA as an activator in weathering, thus the contribution of weathering to the atmospheric CO2 sink is also underestimated. This finding also shows the need to examine the situ distribution and activ     

Geochemical characteristics and source analysis of inflow of mine water in Wang＇ershan Gold Mine, Shandong

Through a systematic observation of water level and temperature, and a comprehensive analysis of the data on major/trace elements, nitrite, hydrogen-oxygen isotopes, the conclusion has been drawn that there are two relatively independent groundwater systems （cool water and hot water）, and the geochemical indicators of hot/cool waters are described. The cool water system is relatively enriched in Ca^2＋, Mg^2＋ and HCO3^-. Its TDS is relatively low, about 1400-1800 mg/L. The hot water system is relatively enriched in K^＋, Na^＋, Cl^- and SO4^2-. Its TDS is relatively high, about 2200-2300 mg/L. The cool water system is enriched in Ba, Ga, Cd, and the hot water system is enriched in B, Ti, Cr, Ni, Cu, Mo, Rb, and Cs, relatively. Especially, the contents of Rb and Cs in the hot water system are more than five times as high as those in the cool water system. The NO3^- contents of cool water discharged from the gold mine are relatively high, and those of hot water are extremely low. The 8D and 8-80 values follow an increasing order of surface water〉mine cool water〉mine hot water. The cool water comes mainly from the lateral supply of phreatic water, while the hot water comes mainly from the vertical supply of deeply circulating structure-fracture water. The ratio of cool water over hot water was estimated to be about 1：1 by a water quality model..     

The acid neutralizing capacity （ANC） of South Africa＇s freshwater ecosystems

Acidification is considered the most important one of the primary chemical stress factors that impact on freshwater ecosystems. In unpolluted freshwater systems, the primary controls on the degree of acidification are factors such as the geological substrate of the catchment area, the presence of organic acids secreted by vegetation in the river system, and equilibrium exchange of carbon dioxide with the atmosphere. Anthropogenic factors that can impact on the degree of acidification of freshwater systems include agricultural, mining and industrial activities, either through direct runoff into river systems or through deposition of atmospheric pollutants from these sources. The capacity factors alkalinity and acidity, which represent the acid- and base-neutralizing capacity （ANC and BCN） of an aqueous system, have been used as more reliable measures of the acidic character of freshwater systems than pH. Unlike pH, ANC and BNC are not affected by parameters such as temperature and pressure. Therefore, ANC has been employed as a predictor of biological status in critical load assessments. Freshwater systems with ANC＇s eq/L isμeq/L are considered sensitive to acidification, ANC=0 μbelow 150 commonly used as the predictor for fish species such as trout in lakes, and an eq/L as more realistic for streams. Acid-neutralizing capacity μANC value of 40 （ANC） can be determined by titration with a strong acid to a preselected equivalence point. Alternatively, it can be calculated as the difference between base cations （[BC]） and strong acid anions （[SAA]）： ANC=[BC]- [SAA]=[Ca^2＋]＋[Mg^2＋]＋[Na^＋]＋[K^＋]-[SO4^2-]-[NO3^-]-[Cl^-] To date, there has been no attempt to establish the ANC of South Africa＇s freshwater ecosystems or variability therein, despite the fact that long-term water quality monitoring data exist for all the parameters needed to calculate it according to the above equations. As a result, the relationship between the acid neutralizing capacity of freshwater ecosystems in South Africa and biodiversity factors, such as fish status, is unknown. Results of the first comprehensive （country-wide scale） evaluation of the acid neutralizing capacity of river systems in South Africa will be presented. Long-term monitoring data obtained from the Department of Water Affairs and Forestry （DWAF） from most of South Africa＇s river systems were used to establish geographic and temporal variabilities in ANC. The results show that the Berg and Breede River systems are most susceptible to acidification, and that geological substrate appears to explain most of the geographic variabilities observed.     

Transformation of organic carbon and its potential impact on lead weathering in firing range soils

Lead （Pb） is normally considered as a trace element in soils and sediments for geochemical study. However, the concentration of Pb in firing range soils is generally so high that it should be considered as a major element during the evaluation of the soil geochemical properties. Soil organic matter （SOM） has been reported as one of the major factors to expedite the corrosion of metallic lead （Pb） in acidic and organic-rich soils. The main impacts of SOM on the fate and transport of Pb in firing range soils lie in the following two aspects; （1） the complexation of organic matter with Pb, which has received lots of attention, and; （2） changes in soil redox potential due to the transformation of SOM and its subsequent impact on Pb speciation, which has rarely been investigated. Soils from 6 different firing ranges are selected for this study. These samples have been stored under a closed condition for more than 3 years. The soil moisture contents were well-retained, as all the samples were kept in closed plastic buckets. The analytical data showed that the summation of the soil total organic carbon content （TOC） and inorganic carbon contents （TIC） were consistent with soil total carbon contents （TC） measured in previous years, although the TOC and TIC contents have changed respectively after years of storage. In general, it is observed that the soil TOC decreased against an increase of TIC. The mass balance on such a transformation suggested a major conversion of organic carbon （Corg） to inorganic carbon （CO3^2-） in the stored soils.     

Hydrogeochemistry of Wujiang River Water in Guizhou Province,China

The chemical composition of Wujiang River water represents that of river water from the typical carbonate areas.Ite hydrogeochemical characteristics are different from those of global major rivers.The Wujiang River and its tributaries have high total dissolved solid concentrations,with Ca^2 and HCO3^- being dominant,Mg^2 and SO4^2- coming next.Both Na^ K^ and Cl^- Si account for 5%-10% of the total cations and anions,respectively,These general features show the chemical composition of river water is largely controlled by carbonate weathering,with the impact of silicate and evaporate weathering being of less importance.Production activity,minin practice and industrial pollution also have some influence on the chemical composition of rive water.