Hydrogeochemistry and Origin of Thermal Groundwater in Bedrock Aquifers in Tianjin, China

Thermal groundwater resources were found to have occurred in deep-seated bedrock aquifers in the northeastern North China plain near Tianjin, China. Meso- to Neo-Proterozoic and Paleozoic carbonate rocks on the Cangxian uplift are capable of yielding 960-4 200 m 3/d of 60 to 96 ℃ water from the wells ranging in depth between 1 000 and 4 000 m. Conductive heat flow of 0.063 to 0.144 2 W/m 2 from the deep crust is responsible for this anomalous geothermal field. The water in the Ordovician aquifer is characterized by relatively high TDS, high concentrations of SO 4 and SO 4·Cl-Na·Ca type, but the waters from the Meso- to Neo-Proterozoic and Cambrian aquifers, by relatively low TDS, low concentrations of SO 4 and predominantly Cl·SO 4-Na type. It is noted that when the temperature of the waters increases at a rate of 10 ℃ in the range of 30-100 ℃, the content of SiO 2 increases at a rate of 12 to 15 mg/L, and fluoride concentration increases at a rate of 2.3 to 2.5 mg/L. Hydrochemical and isotopic data suggest that the thermal water in the bedrock aquifers is of meteoric origin and recharged in the northern mountain area to the north of the Baodi-Ninghe fault, and then flows laterally for a long distance from the north to the south to the city of Tianjin. Temperature of the waters increases because of heat exchange with the rocks and recharge by conductive heat flow from beneath.

Establishment of water source discrimination model in coal mine by using hydrogeochemistry and statistical analysis： a case study from Renlou Coal Mine in northern Anhui Province, China

The demand for energy consumption promotes to find more coal in deep underground up to 1 000 m and brings more serious situation of water disaster. As one of the major methods for water disaster control, hydrogeochemistry attracts a series of studies related to water source discrimination. In this paper, a simple method for constructing the water source discrimination model based on major ions and multivariate statistical analysis was reported using the following procedures： （1） collection of data and interpretation, （2） analysis of controlling factors based on the chemical composition of groundwater, （3） ＂pure＂ sample chosen, and （4） discrimination model establishment. After the processes, two functions and a diagram were established for three aquifers （the Quaternary, Coal bearing, and Taiyuan Fm.） from the Renlou Coal Mine in northern Anhui Province, China. The method can be applied in almost all coal mines and can be used for evaluating the contribution ratios if the water is collected from a mixing source.

Influence of cascade reservoirs on spatiotemporal variations of hydrogeochemistry in Jinsha River

River hydrogeochemistry offers necessary guidance for effective water environmental management.However,the influence of cascade reservoirs on river hydrogeochemistry remains unknown.In this study,the Jinsha River,the headwaters of the Yangtze River of China,was selected to investigate the spatiotemporal variations of hydrogeochemistry after the construction of six cascade reservoirs.Major ions,total dissolved solids,electrical conductivity,and pH values of sampled water in the upper natural reaches and lower reservoir-regulated reaches were analyzed in both flood and dry seasons.The results of Piper diagram and Gibbs plots showed that the hydrogeochemistry of the Jinsha River was naturally controlled by both evaporation-crystallization and carbonate weathering processes,but it was also artificially affected by reservoirs.The impoundment of cascade reservoirs affected the hydrodynamic condition of the river.The river flow in the flood season was reduced by approximately 24.5%,altering the proportions of water sources and leading to notable hydrogeochemical alterations in reservoir-regulated reaches.Conversely,river hydrogeochemistry generally remained unchanged in the dry season,owing to the insignificant effect of cascade reservoirs on river flow.In contrast to what has been observed in previous studies of individual reservoirs,the cumulative influence of cascade reservoirs on the Jinsha River flow regime did not cause abrupt hydrogeochemical changes between the upstream and downstream areas of each reservoir.Moreover,the water quality assessments revealed that the impoundment of cascade reservoirs improved downstream irrigational water quality,with lower Naþratio values in the flood season.This study provides the earliest evaluation of cascade reservoir influence on the hydrogeochemistry of the Jinsha River.The findings of this study can be used as a reference for scientific guidelines for future environmental management of cascade reservoirs in large rivers.

A geospatial investigation of interlinkage between basement fault architecture and coastal aquifer hydrogeochemistry

The Mahanadi delta,deposited on a series of horst and graben basement structures,is considered an extension of the East Lambert Rift of Antarctica.Current study is based on the hydrogeochemical assessment of this deltaic aquifer system and geospatial analysis thereof,to appreciate the basement structure influence on groundwater chemistry.Major ion chemistry of subsurface waters portrays a distinct saline contamination across the terrain and varied regimes of water types,specifically with respect to southern and northern parts of this aquifer system.Findings of the study indicate a general near surface saline horizon and significant fragmentation of the hydrostatic units.This,in turn,implies noteworthy influence of formational water to salinity regimes and basin structural changes for the escape of these waters to surroundings.A plot of recent low intensity earthquakes displays proximity of epicenters to the faults as well as striking similarity to the trend of terrestrial faults indicating multiple reactivations of the faults.To further corroborate the above findings,spatial pattern analysis of individual hydrochemical variables is carried out which reveals specific clusters of sources(groundwater mixing)and sinks(groundwater dispersion) in proximity to basement fault dispositions.While the faults can be disregarded as conduits or barriers owing to their great depth,the overlying sedimentary mass,particularly,the horizons with significant clayey content have been distorted due to post rift subsidence and fault reactivations.A proximity analysis of ionic clusters points towards a greater influence of longitudinal faults to that of the transverse ones on groundwater mixing or dispersion.

Groundwater Origin and Its Hydrogeochemistry through GIS Maps in Linares Region, Mexico

The North-East region of Mexican Republic has a semi-arid weather condition;this area covers partially Tamaulipas, Nuevo León and Coahuila states. Pablillo River Basin (PRB) is located close to Nuevo León south border and its catchment area involves Linares City (LC), Hualahuises City (HC) and Cerro-Prieto dam (CP). This reservoir captures drinking water to Monterrey Metropolitan Zone (MMZ) the major urban center on the north-east Mexican region. More than 50% of the potable water for LC comes from groundwater stockpiles. A combination of GIS maps and major ion chemistry analysis has been assessed, to know the origin, geochemical evolution, and hydraulic interconnection of groundwater. During 2008-2009, 46 groundwater samples were taken and analyzed around LC and HC. GIS technology was use to analyze the spatial distribution of the constituents of groundwater through thematic maps. The major ion analysis and its results suggest the presences of two aquifers;shallow porous aquifer on the top and fractured aquifer on the bottom. General water mineralization was discovered, including dissolution of halite, dolomites and carbonates through the aquifers. Water quality varies widely through the aquifers, and the general pathways go from southwest to northeast direction. The overexploitation of groundwater increases the water mixing of groundwater between shallow and deeper aquifers. Natural origin of groundwater and groundwater pollution by anthropogenic activities should be considered in the groundwater quality analysis for drinking water purpose.

Hydrogeochemistry of Thermal Waters of Baransky Volcano, Iturup Island (Southern Kurils)

Different types of groundwater manifestations occurring on modern structure of the Baransky volcano were studied. Volcanic and seismic activity influences strongly on hydrology and hydrochemistry of the groundwater of the watershed of Sernaya river. Three types of fluids have been established: volcanic-heated, steam-heated and mature. Existing model of hydrothermal system of Baransky volcano was confirmed using geothermometry and hydrochemical calculations. Thus Baransky volcano is a complex object with atmospheric recharge, deep diorite body as heat source and thick fractured altered andesitic water reservoir, where different types of water springs can emerge.

Long-term hydrochemical monitoring and geothermometry:understanding groundwater salinization and thermal fluid contamination in Mila’s basin,Northeastern Algeria

The regular hydrochemical monitoring of groundwater in the Mila basin over an extended period has provided valuable insights into the origin of dissolved salts and the hydrogeochemical processes controlling water salinization.The data reveals that the shallow Karst aquifer shows an increase in TDS of 162 mg L^(-1) while the ther-mal carbonate aquifer that is also used for drinking water supply exhibits an increase of 178 mg L^(-1).Additionally,significant temperature variations are recorded at the sur-face in the shallow aquifers and the waters are carbo-gaseous.Analysis of dissolved major and minor elements has identified several processes influencing the chemical composition namely:dissolution of evaporitic minerals,reduction of sulphates,congruent and incongruent car-bonates’dissolution,dedolomitization and silicates’weathering.The hydrogeochemical and geothermometric results show a mixing of saline thermal water with recharge water of meteoric origin.Two main geothermalfields have been identified,a partially evolved water reservoir and a water reservoir whosefluid interacts with sulphuric acid(H_(2)S)of magmatic origin.These hot waters that are char-acterized by a strong hydrothermal alteration do ascend through faults and fractures and contribute to the contamination of shallower aquifers.Understanding the geothermometry and the hydrogeochemistry of waters is crucial for managing and protecting the quality of groundwater resources in the Mila basin,in order to ensure sustainable water supply for the region.A conceptual model for groundwater circulation and mineralization acquisition has been established to further enhance under-standing in this regard.

Hydrogeochemical Characterization of Groundwater from Fissured Aquifers in the Angovia Mine Operating Permit Area (Central-West Côte d’Ivoire)

The main objective of this study is to determine the hydrogeochemical specificities of the groundwater of the Angovia mine operating permit, located in the Yaouré mountains in the center-west of Côte d’Ivoire. To do so, descriptive and multivariate statistical analysis methods with the SOM (Self Organizing Maps) algorithm were applied to the physicochemical parameters of 17 boreholes using the calcite (ISC) and dolomite (ISD) saturation indices. The results obtained have shown that the groundwater in the Angovia mine operating permit area has an average temperature of 27.52°C (long rainy season) and 27.87&degC (long dry season) and has an average pH of 7.09 ± 0.35 during the main rainy season and 7.32 ± 0.35 during the main dry season. They are mineralized with an average electrical conductivity of 505.98 ± 302.85 μS/cm during the long rainy season and with 450.33 ± 233.74 μS/cm as average during the long dry season. The main phenomena at the origin of groundwater mineralization are water residence time, oxidation-reduction and surface inflow. The study of the relative age of the water shows that the groundwater in the Angovia mine operating permit area is mainly undersaturated with respect to calcite and dolomite. They are therefore very old in the aquifer with a slow circulation speed during the long rainy season and the long dry season.

Hydrogeochemical Studies in Drought Scenarios: Canelones, Uruguay Case Study

The water scarcity in quality and quantity is becoming more noticeable and an urgent concern around the world. In Uruguay, these issues become exacerbated by the need to obtain drinking water in coastal areas, influenced by the climate change. Basic and structural geologies are strong conditioners in heterogeneous coastal aquifers. The objective of this study is to characterize the hydrochemistry of the fractured aquifers after having identified the main bearing fractures and the causes of aleatoreous water scarcity and quality problems, for hydric resources sustainable management. Identification of water bearing fracture, hydrogeochemical analysis and water quality evaluation are specific objectives. Some strategies were performed: 1) a base map in QGIS Software;2) fracture photointerpretation;3) geological correlation;4) statistical analysis of the background geochemistry data;5) ions analysis of strategically located wells. There were found water bearing fractures corresponding to 28 m3/h maximum flow rate for the NW-SE and 12 m3/h maximum flow rate for the NE-SW fracture direction, respectively. Besides, there could be a problem related to the high Sodium (Na) and Chloride (Cl) levels. In this respect, having previous data from 25 well samples, ions geochemical analysis has been carried out for 14 wells from Costa Azul and surrounding to have a first approach about the possible cause for the high values of Na (max. 385 mg/L) and Cl (max. 381 mg/L). The selected area for this study has a particular characteristic, because it corresponds to a heterogeneous fractured aquifer, which makes it difficult to catch water with enough flow rates and water quality to meet the population demand.

The hydrogeochemistry of the Wujiang River drainage system in Guizhou, China (Ⅰ)——U-Ca-Sr system in karst river water

TRACE element concentrations in river water are controlled by a number of factors, such as lithology,weathering processes or adsorption. Further investigations on trace elements, especially heavy andtransition metals, allow us to evaluate the impact on the environment by human activities. Chinese scholars focus their research on the geochemistry of river water of the Changjiang River and Huanghe River. A number of scholars have conducted research on the uranium geochemistry in river water in orderto know the variation of input of U from rivers to oceans, and to get better understanding of the geochemistry of uranium series in marine geochemistry. Moreover, the presence of uraninite in sediments has beenproposed as an indicator of atmospheric oxidation and reduction levels. Plamer and Edmond

Hydrogeochemistry of toxic metals in Au-As-Hg-Tl mineralized area in southwest Guizhou Province, China

THE environmental geochemistry problems during the processes of mining activities are intensively considered by scientists worldwide, and the hydrogeochemistry presents an important implication of toxic metalcontamination related to mining activities. The hydrogeochemistry due to mining activities and naturalmineralized processes present some differences whose comparison can indicate a good understanding of theinfluence of mining on the environment. This ongoing study aims at the hydrogeochemistry of toxic metals in the Au-As-Hg-Tl metallogenicbelt of Huijiabao anticline in southwest Guizhou, China. The presently-mined Lanmuchang mercury-thallium deposit with a Hg-mining history of about 350 years containing one of the world’s highest concentration of thallium and the to-be-mined Yanshang gold deposit enriching high concentration of toxic metals have been chosen to study the hydrogeochemistry of toxic metals. The groundwater samples werecollected from the shallow aquifer in terms of spring, domestic well and karstic cave whereas the surfacewater was only sampled downside the surface drainage leaching the mine waste at Lanmuchang. All

Ecological and geochemical aspects of interlayer water use for potable water supply of urban population:a case study in the Dnieper–Donetsk aquifer system,Ukraine

The article is devoted to the study of ecological and geochemical features of interlayer waters of the Dnieper–Donetsk aquifer system in Ukraine,used for the potable water supply of Kyiv.A wide range of methods was used,including Microsoft Excel,Statistica,and Attestat software packages,MapInfo Professional 6.5 and ArcGIS-ArcMap 9.3 programs;the method of mass spectrometry with inductively coupled plasma(ICP-MS)and GEMS software were performed.Monitoring study results(during 2007–2023)were analyzed for two interlayer aquifers—Cenomanian-Callovian groundwater complex and Bajocian aquifer.It was determined that the normalized value of mineralization increased with a decrease in water intake during 1980–2010,which indicates a relative increase in the content of mineral substances during longterm exploitation.A high negative correlation(Kcor.=-0.54 to-0.86)is also typical for normalized values of oxidizability,total hardness,pH,Ca,Mg,and Cl content.Comparative analysis of two different aquifers revealed that the macrocomponent composition of Bajocian aquifer remains stable,once for Cenomanian-Callovian groundwater complex,there is a tendency to decrease hydrogen carbonates and increase chlorides and sulfates,whereas the cation composition remains relatively stable.A significant increase(by 55%)of the total mineralization in the representative well located on the right bank of the Dnieper River was found.There is also a significant increase(by more than 5 times)in the iron content,which the authors associate with the unsatisfactory technical condition of the well casing pipes.Physico-chemical modeling of trace elements,performed for investigated aquifers,shows that both aquifers are characterized by the predominant migration of the following metals in the cationic form(aqua-ions):Ca,Mg,Na,Ba,Co,Cu,Mn,Ni,Sr,Zn.It was found that the predominant migration forms of metals in the studied interlayer waters are free uncomplexed ions,carbonate,and hydroxo complexes.

Assessment of Groundwater Quality for Drinking and Irrigation Uses in the Samba Dia Area, Central West Senegal

In the Sahelian zone in Africa, groundwater is the main source of drinking water for domestic, industrial, and agricultural uses. The groundwater of the Samba Dia sandy aquifer was assessed for understanding processes controlling the hydrogeochemistry and its drinking and irrigation suitability, on the basis of various water quality parameters. For the present study, thirty-three groundwater samples were collected in wells of the study area during the dry season in March 2021 and subjected to analysis for chemical characteristics (major ions), pH, electrical conductivity (EC), and total dissolved solids (TDS). Gibbs plot depicts that the process of ionic exchange is mainly due to the dissolution of water-rock interaction. The Piper diagram indicates a largely dominant sodium chloride facies with 70% of the groundwater samples followed by calcium chloride facies (18%) than calcium bicarbonate facies (12%). Analytical results of hydrogeochemical parameters of groundwater samples reveal that the majority of samples are within the World Health Organization safety range for drinking water. TDS and electrical conductivity (EC) values of groundwater indicate that 70% and 61% are safe for drinking water, respectively. Sodium percentage (% Na), Sodium Adsorption Ratio (SAR) values, and Ca/Mg ratio were calculated and compared with the standard guideline values recommended by the World Health Organization and agricultural water standards. This study shows that the groundwater in the area is mostly chemically suitable for drinking and irrigation, although some wells at the edge of the area exhibit signs of progressive salinization and traces of pollution.

Hydrogeochemical Characteristics and Groundwater Inrush Source Identification for a Multi-aquifer System in a Coal Mine

Correct identification of water inrush sources is particularly important to prevent and control mine water disasters.Hydrochemical analysis,Fisher discriminant analysis,and geothermal verification analysis were used to identify and verify the water sources of the multi-aquifer groundwater system in Gubei coal mine,Anhui Province,North China.Results show that hydrochemical water types of the Cenozoic top aquifer included HCO3-Na+K-Ca,HCO3-Na+K-Mg and HCO3-Na+K,and this aquifer was easily distinguishable from other aquifers because of its low concentration of Na++K+and Cl-.The Cenozoic middle and bottom aquifers,the Permian fissure aquifer,and the Taiyuan and Ordovician limestone aquifers were mainly characterized by the Cl-Na+K and SO4-Cl-Na+K or HCO3-Cl-Na+K water types,and their hydrogeochemistries were similar.Therefore,water sources could not be identified via hydrochemical analysis.Fisher model was established based on the hydrogeochemical characteristics,and its discrimination rate was 89.19%.Fisher discrimination results were improved by combining them with the geothermal analysis results,and this combination increased the identification rate to 97.3%and reasonably explained the reasons behind two water samples misjudgments.The methods described herein are also applicable to other mines with similar geological and hydrogeological conditions in North China.

Identifying the Sources of Solutes in Karst Groundwater in Chongqing,China:a Combined Sulfate and Strontium Isotope Approach

Groundwater from karst subterranean streams is among the world＇s most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are impacted by both natural environment and people. Therefore, the study of hydrochemistry and its solutes＇ sources is very important to ensure the normal function of life support systems. In this paper, thirty-five representative karst groundwater samples were collected from different aquifers （limestone and dolomite） and various land use types in Chongqing to trace the sources of solutes and relative hydrochemical processes. Hydrogeochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO3 type or Ca （Mg）-HCO3 type. However, some hydrochemical types of karst groundwater were the K＋Na＋Ca-SO4 type （G25 site） or Ca-HCO3＋SO4 type （G26 and G14 site）, indicating that the hydrochemistry of these sites might be strongly influenced by anthropogenic activities or unique geological characteristics. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 ~tmmol/L, and the STSr/S6Sr varied from 0.70751 to 0.71627. The j34S-SO42- fell into a range of-6.8%o-21.5%o, with a mean value of 5.6%o. The variations of both 87Sr/S6Sr and Sr values of the groundwater samples indicated that the Sr element was controlled by the weathering of limestone, dolomite and silicate rock. However, the figure of STSr/S6Sr vs. Sr2＋/[K＋＋Na＋] showed that the anthropogenic inputs also obviously contributed to the Sr contents. For tracing the detailed anthropogenic effects, we traced the sources of solutes collected karst groundwater samples in Chongqing according to the j34S value of potential sulfate sources. The variations of both j34S and 1/ SO42- values of the groundwater samples indicated that the atmospheric acid deposition （AAD）, dissolution of gypsum （GD）, oxidation of sulfide mineral （OS） or anthropogenic inputs （SF： sewage or fertilizer） have contributed to solutes in karst groundwater. The influence of oxidation of sulfide mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread.

The use of hydrogeochemical analyses and multivariate statistics for the characterization of thermal springs in the Constantine area, Northeastern Algeria

This paper deals with the results of a hydrogeochemistry study on the thermal waters of the Constantine area, Northeastern Algeria, using geochemical and statistical tools. The samples were collected in December2016 from twelve hot springs and were analyzed for physicochemical parameters(electric conductivity, p H,total dissolved solids, temperature, Ca, Mg, Na, K, HCO_3,Cl, SO_4, and SiO_2). The waters of the thermal springs have temperatures varying from 28 to 51 °C and electric conductivity values ranging from 853 to 5630 l S/cm. Q-mode Cluster analysis resulted in the determination of two major water types: a Ca–HCO_3–SO_4 type with a moderate salinity and a Na–K–Cl type with high salinity. The plot of the major ions versus the saturation indices suggested that the hydrogeochemistry of thermal groundwater is mainly controlled by dissolution/precipitation of carbonate minerals, dissolution of evaporite minerals(halite and gypsum), and ion exchange of Ca(and/or Mg) by Na. The Gibbs diagram shows that evaporation is another factor playing a minor role. Principal Component Analysis produced three significant factors which have 88.2% of totalvariance that illustrate the main processes controlling the chemistry of groundwaters, which are respectively: the dissolution of evaporite minerals(halite and gypsum), ion exchange, and dissolution/precipitation of carbonate minerals. The subsurface reservoir temperatures were calculated using different cation and silica geothermometers and gave temperatures ranging between 17 and 279 °C. The Na–K and Na–K-Ca geothermometers provided high temperatures(up to 279 °C), whereas, estimated geotemperatures from K/Mg geothermometers were the lowest(17–53 °C). Silica geothermometers gave the most reasonable temperature estimate of the subsurface waters overlap between 20 and 58 °C, which indicate possible mixing with cooler Mg groundwaters indicated by the Na–K–Mg plot in the immature water field and in silica and chloride mixing models. The results of stable isotope analyses(δ^(18) O and δ~2 H) suggest that the origin of thermal water recharge is precipitation, which recharged from a higher altitude(600–1200 m) and infiltrated through deep faults and fractures in carbonate formations. They circulate at an estimated depth that does not exceed 2 km and are heated by a high conductive heat flow before rising to the surface through faults that acted as hydrothermal conduits.During their ascent to the surface, they are subjected to various physical and chemical changes such as cooling by conduction and change in their chemical constituents due to the mixing with cold groundwaters.

Geochemical modeling of groundwater in southern plain area of Pengyang County,Ningxia,China

The purpose of this paper is to examine the evolution mechanisms of a hydrochemical field and to promote its benefits to the living standards of local people and to the local economy in the southern plain area of Pengyang County, in Ningxia, China. Based on understanding of the hydrogeological conditions in Pengyang County, the chemical evolution characteristics of groundwater in the plain area were analyzed. PHREEQC geochemical modeling software was used to perform hydrochemical modeling of water-rock interaction and to quantitatively analyze the evolution processes and the formation mechanisms of the local groundwater. Geochemical modeling was performed for two groundwater paths. The results showed that, along path 1, Na＋ adsorption played the leading role in the precipitation process and its amount was the largest, up to 6.08 mmol/L; cation exchange was significant along path 1, while along simulated path 2, albite accounted for the largest amount of dissolution, reaching 9.06 mmol/L, and the cation exchange was not significant. According to the modeling results, along the groundwater flow path, calcite and dolomite showed oversaturated status with a precipitation trend, while the fluorite and gypsum throughout the simulated path were not saturated and showed a dissolution trend. The total dissolved solids （TDS） increased and water quality worsened along the flow path. The dissolution reactions of albite, CO2, and halite, the exchange adsorption reaction of Na＋, and the precipitation of sodium montmorillonite and calcite were the primary hydrogeochemical reactions, resulting in changes of hydrochemical ingredients.

Hydrogeochemical characteristics of hot springs exposed from fault zones in western Guangdong and their ^(14)C age correction

Hot springs are natural exposed points of the hydrothermal system. The hydrogeochemistry of hot springs can be used to interpret the formation of the hydrothermal system; and the ^(14)C dating can be used to evaluate the renewability of the hydrothermal system. The hot springs exposed from fault zones in western Guangdong are classified as granite fissure water and clastic rock fissure water, which are sampled and tested. The results of water chemistry analysis show that hot spring water is mainly HCO_3-Na type in the beginning, while the mixing of seawater leads to the increase of Cl^-. Hydrogen and oxygen isotopes indicate that these hot springs mainly come from atmospheric precipitation, and water-rock interactions produce oxygen isotope exchange reactions, where a significant "oxygen drift" phenomenon can be observed. The relationship between δ^(13)C and HCO_3^- indicates that there is a deep source of CO_2 "dead carbon" in hot spring water. This systematic error is not considered in the existing ^(14)C dating correction models. The ^(14)C age of the deep source "dead carbon" correction proposed in this paper is close to the ^(14)C age of the reverse chemical simulation correction, the Gonfiantinie model, and the Mook model. The deep source "dead carbon" correction method can improve the systematic error. Therefore, the ^(14)C age corrected by the deep source "dead carbon" may be more representative in terms of the actual age of geothermal water.

Hydrogeochemical characteristics of groundwater and pore-water and the paleoenvironmental evolution in the past 3.10 Ma in the Xiong’an New Area,North China

The groundwater level has been continuously decreasing due to climate change and long-time overexploitation in the Xiong’an New Area,North China,which caused the enhanced mixing of groundwater in different aquifers and significant changes in regional groundwater chemistry characteristics.In this study,groundwater and sediment pore-water in drilling cores obtained from a 600 m borehole were investigated to evaluate hydrogeochemical processes in shallow and deep aquifers and paleo-environmental evolution in the past ca.3.10 Ma.Results showed that there was no obvious change overall in chemical composition along the direction of groundwater runoff,but different hydrochemical processes occurred in shallow and deep groundwater in the vertical direction.Shallow groundwater(<150 m)in the Xiong’an New Area was characterized by high salinity(TDS>1000 mg/L)and high concentrations of Mn and Fe,while deep groundwater had better water quality with lower salinity.The high TDS values mostly occurred in aquifers with depth<70 m and>500 m below land surface.Water isotopes showed that aquifer pore-water mostly originated from meteoric water under the influence of evaporation,and aquitard pore-water belonged to Paleo meteoric water.In addition,the evolution of the paleoclimate since 3.10 Ma BP was reconstructed,and four climate periods were determined by theδ18O profiles of pore-water and sporopollen records from sediments at different depths.It can be inferred that the Quaternary Pleistocene(0.78‒2.58 Ma BP)was dominated by the cold and dry climate of the glacial period,with three interglacial intervals of warm and humid climate.What’s more,this study demonstrates the possibilities of the applications of pore-water on the hydrogeochemical study and further supports the finding that pore-water could retain the feature of paleo-sedimentary water.

Hydrogeochemical evaluation and statistical analysis of groundwater of Sylhet, north-eastern Bangladesh

To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and analyzed for temperature, pH, Eh, EC,DO, DOC, Na^+, K^+, Ca^(2+), Mg^(2+), Cl^-, SO_4^(2-), NO_3^-,HCO_3^-, SiO_2^-, Fe, Mn and As. Besides, 12 surface water samples from Surma and Kushiyara Rivers were also collected and analyzed to understand the influence into aquifers. Results revealed that, most of the groundwater samples are acidic in nature, and Na–HCO_3 is the dominant groundwater type. The mean value of temperature, EC,Na^+, K^+, Ca^(2+), Mg^(2+), Cl^-, NO_3^- and SO_4^(2-) were found within the range of permissible limits, while most of the samples exceeds the allowable limits of Fe, Mn and As concentrations. However, relatively higher concentration of Fe and Mn were found in deep water samples and reverse trend was found in case of As. The mean concentrations of As in shallow, intermediate and deep wells were 39.3, 25.3and 21.4 lg/L respectively, which varied from 0.03 to148 lg/L. From spatial distribution, it was found that Fe,Mn and As concentrations are high but patchy in northern,north-western, and south-western part of Sylhet region. The most influential geochemical process in study area were identified as silicate weathering, characterized by active cation exchange process and carbonate weathering, which thereby can enhance the elemental concentrations in groundwater. Pearson's correlation matrix, principal component analysis and cluster analysis were also employed to evaluate the controlling factors, and it was found that, both natural and anthropogenic sources were influencing the groundwater chemistry of the aquifers. However, surface water has no significant role to contaminate the aquifers,rather geogenic factors affecting the trace elemental contamination. Thus it is expected that, outcomes of this study will provide useful insights for future groundwater monitoring and management of the study area.