The CO2 Discharge in the Boundary Fault Areas of the Sichuan-Yunnan Block and Its Sources

A large number of CO2 springs outcrop along the boundary faults of the Sichuan-Yunnan block and in their neighboring areas.These springs are of a roughly similar distribution as the epicenters of strong earthquakes since 1900.This similarity indicates that the CO2 discharges could be directly related to the modern seismic activity in that area.The evidences of stable carbon and oxygen isotopes indicate that an overwhelming majority of the CO2 released from modern active faults is derived from the deep earth crust.There are 2 main mechanisms of CO2 discharge.Modern active faults are able both to produce directly a lot of CO2 due to thermodynamic metamorphism and to provide passages for the CO2 constituent coming from the lower crust or upper mantle.By continuously monitoring the dynamic changes of CO2 discharges,it would be possible to obtain the information of earthquake precursors that reflect the physical and chemical changes of the earthquake sources.     

Hydrologic and geologic control of carbonate water chemistry in the subarctic nahanni karst,canada

There are six classes of water and five geologic environments in the subarctic Nahanni karst. During the summers of 1972 and 1973, 214 water samples were collected from 15 of the 30 hydrogeologic categories. Linear discriminant function analysis, using five measured and two derived chemical variables, indicates that there are statistically significant (0.005 level) differences in water chemistry between similar waters in different geologic environments, between waters in the same geologic environment, and between waters in different hydrogeological categories. Geological environment labels a natural water because it determines the availability of soil CO₂ and of soluble minerals. Measurements indicate that mean soil log PCO₂ is greatest in areas of shale mantled by till (?2.39), and least in areas of sandy fluvioglacial drift (?3.27). Low values on the sandy drift are due to the sparse shrub vegetation, and to the high degree of soil aeration; soils in areas of shale are clay-rich and support a dense boreal forest. Hydrology influences water chemistry because it determines how much CO₂ natural waters pick up from the environment and how much they subsequently lose to the atmosphere, and as a result, whether they dissolve or deposit soluble materials. The similarity between mean calculated log PCO₂ in natural waters (?2.92) and mean measured soil log PCO₂ (?2.80) suggests that natural waters in Nahanni are dose to equilibrium with mean soil CO₂ levels.     

Timing the transport of water through the upper vadose zone in a Karstic system above a cave in Israel

Chemical and isotopic analysis of karst water dripping over a one year period from seeps in a cave above the Cenomanian aquifer in the Judea hills of Israel lead to several conclusions: (i) The tritium ages and the chemical composition of water from different seeps in a karstic cave vary greatly, (ii) The reservoirs in the upper part of the vadose zone hold water for up to several decades, (iii) Some of the cave seeps are mixtures of the old and more recent meteoric water from paths of different length, (iv) The history of storm events can only be traced in some of the seeps, (v) For most dripping seeps there is no immediate response of seepage discharge to the rainfall intensity and quantity—i.e. the seepage discharge is fairly constant.     

汕头东山湖热矿水的物理化学动态及其与地震的关系

文章概述了汕头东山湖高热水化学观测井的地质、水文地质等环境条件，并据实测资料分析认为，该井是震兆反映较灵敏的进中孔，其水化学灵敏震兆组分为Cl^-、HCO3^-、He、H2等多项组分。     

Compositional multivariate statistical analysis of thermal groundwater provenance: A hydrogeochemical case study from Ireland

Thermal groundwater is currently being exploited for district-scale heating in many locations world-wide. The chemical compositions of these thermal waters reflect the provenance and circulation patterns of the groundwater, which are controlled by recharge, rock type and geological structure. Exploring the provenance of these waters using multivariate statistical analysis (MSA) techniques increases our understanding of the hydrothermal circulation systems, and provides a reliable tool for assessing these resources.Hydrochemical data from thermal springs situated in the Carboniferous Dublin Basin in east-central Ireland were explored using MSA, including hierarchical cluster analysis (HCA) and principal component analysis (PCA), to investigate the source aquifers of the thermal groundwaters. To take into account the compositional nature of the hydrochemical data, compositional data analysis (CoDa) techniques were used to process the data prior to the MSA.The results of the MSA were examined alongside detailed time-lapse temperature measurements from several of the springs, and indicate the influence of three important hydrogeological processes on the hydrochemistry of the thermal waters: 1) salinity and increased water-rock interaction; 2) dissolution of carbonates; and 3) dissolution of sulfides, sulfates and oxides associated with mineral deposits. The use of MSA within the CoDa framework identified subtle temporal variations in the hydrochemistry of the thermal springs, which could not be identified with more traditional graphing methods, or with a standard statistical approach. The MSA was successful in distinguishing different geological settings and different annual behaviours within the group of springs. This study demonstrates the usefulness of the application of MSA within the CoDa framework in order to better understand the underlying controlling processes governing the hydrochemistry of a group of thermal springs in a low-enthalpy setting.     

Isotope hydrochemical approach to understand fluoride release into groundwaters of Ilkal area,Bagalkot District,Karnataka, India

Isotope and hydrochemical investigations have been carried out in the Ilkal area of Karnataka, India, in order to determine the source and mechanism of fluoride release into groundwaters and to understand groundwater hydrochemistry. Agriculture, granite quarrying and rock-polishing industries are the main occupations in this area. Closepet granite, Peninsular gneiss and Dharwar schists are the major geological formations. Results show that the fluoride concentration in groundwater is 0.3–6.5 mg/L and it is found to increase from recharge area to discharge area. Fluoride variability is found to be influenced by the geology of the area and depth wise correlation was not observed. Water samples are unsaturated with respect to fluorite, indicating the possibility of further increase in fluoride in groundwater. Positive correlations between fluoride with sodium and bicarbonate in groundwater show that high fluoride content and alkaline sodic characteristics are the result of dissolution of fluoride bearing minerals, possibly derived from weathered granite and gneiss. A positive correlation between fluoride and δ¹⁸O, and the presence of high tritium in fluoride-contaminated groundwater, point to contribution from surface waters, contaminated by anthropogenic activities. Dumping of rock wastes that are rich in fluoride into the streams by the rock-polishing industries plays a significant role in contaminating groundwater.     

Evaluation of sea water ingress into an Indian atoll

Groundwater is the prime source of fresh water in most part of world. The groundwater floats in the form of thin lens which is vulnerable to various stresses such as tide, cyclone, draught, abstraction, etc. The problem of getting this meager resource of fresh groundwater sustained for longer time, becomes more difficult task on tiny atoll with large population depending on it. In order to develop sustainable management scheme and identify vulnerable part of aquifer, systematic assessment of groundwater quality on such island have become imperative. Detailed hydrochemical study has been carried out to identify potential fresh groundwater resources on Andrott Island, UT of Lakshadweep, India. The analysis has given an early signal of deterioration in groundwater quality in some parts of the island during non-monsoon period, whereas the quality becomes slightly better during monsoon period. The study suggests immediate measures for arresting the deterioration in groundwater quality as well as augmentation for restoration of aquifer in some parts of the island.     

Deep groundwater flow and geochemical processes in limestone aquifers: evidence from thermal waters in Derbyshire, England, UK

Thermal waters potentially provide information on geochemical processes acting deep within aquifers. New isotopic data on groundwater sulphate, inorganic carbon and strontium in thermal and non-thermal waters of a major limestone aquifer system in Derbyshire, England, UK, are used to constrain sulphate sources and groundwater evolution. Shallow groundwaters gain sulphate from oxidation of sulphide minerals and have relatively ¹³C-depleted dissolved inorganic carbon (DIC). Thermal waters have relatively high Sr/Ca and more ¹³C-enriched DIC as a result of increased water–rock interaction. In other respects, the thermal waters define two distinct groups. Thermal waters rising at Buxton have higher Mg, Mn and ⁸⁷Sr/⁸⁶Sr and lower Ca and SO₄, indicating flow from deep sandstone aquifers via a high permeability pathway in the limestone. By contrast, Matlock-type waters (97% of the thermal flux) have elevated sulphate concentrations derived from interaction with buried evaporites, with no chemical evidence for flow below the limestone. About 5% of the limestone area's groundwater flows to the Matlock group springs via deep regional flow and the remainder flows via local shallow paths to many non-thermal springs. Gypsum dissolution has produced significant tertiary porosity and tertiary permeability in the carbonate aquifer and this is an essential precursor to the development of karstic drainage.

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Resumen Las aguas termales potencialmente proporcionan información sobre procesos geoquímicos que actúan a profundidad en acuíferos. Nuevos datos isotópicos de sulfatos, carbón inorgánico y estroncio en aguas termales y no-termales de un acuífero importante de caliza en Derbyshire, Inglaterra se utilizan para delinear las fuentes de sulfato y la evolución de aguas subterráneas.Las aguas subterráneas no muy profundas adquieren sulfato a través de la oxidación de minerales de sulfuro y poseen carbón inorgánico disuelto (DIC) relativamente deplatado de ¹³C. Las aguas termales muestran un ratio Sr/Ca relativamente alto y poseen (DIC) más enriquecido en¹³C, como resultado de la mayor interacción de roca-agua. En otros aspectos, los aguas termales definen dos grupos distintivos. Las aguas termales que ascienden en Buxton tienen mas Mg, Mn y ⁸⁷Sr/⁸⁶Sr y menos Ca and SO₄, indicando flujo de acuíferos de areniscas profundas por un sendero de alta permeabilidad en la caliza.En contraste el tipo de agua - Matlock (97% del flujo termal) posee altas concentraciones de sulfato, derivado por interacción con evaporitas enterradas, sin evidencia química de flujo debajo de la caliza. Aproximadamente 5% del agua del área de la caliza se fluye al grupo de manantiales de Matlock a través de un flujo regional profundo y el resto fluye por senderos locales poco profundos a muchos de los manantiales no-termales. La disolución de yeso ha producido porosidad terciaria importante así como permeabilidad en el acuífero de carbonato y este es un precursor esencial del desarrollo de drenaje kárstico.

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Résumé Les eaux thermales peuvent apporter des informations sur les processus géochimiques dans les aquifères profonds. De nouvelles données isotopiques sur les sulfates présents dans les eaux souterraines, le carbone inorganique et le strontium dans les eaux thermales et non thermales d'un système aquifère calcaire majeur dans le Derbyshire, Angleterre, Royaume Uni, sont utilisées pour comprendre les sources de sulfates et l'évolution des eaux souterraines. Les eaux souterraines phréatique s'enrichissent en sulfate via l'oxydation des minéraux sulfatés et ont un Carbone Inorganique Dissous (DIC) relativement appauvri en¹³C. Les eaux thermales ont un rapport Sr/Ca relativement plus élevé et un DIC plus enrichi en¹³C, du fait de l'interaction accrue des eaux avec les roches. En d'autres mots, les eaux thermales définissent deux groupes distincts. Les eaux thermales remontant à Buxton ont un Mg, un Mn et un rapport ⁸⁷Sr/⁸⁶Sr plus hauts, mais un Ca et SO₄ plus faible, indiquant un écoulement à travers les zones perméables des aquifers gréseux. Par contraste, les eaux du type de Matlock (97% du flux thermique), possèdent des concentrations élevées en sulfates, provenant de l'interaction des eaux avec les évaporites enfouies, tandis qu'il n'existe aucune évidence chimique d'un écoulement sous les calcaires. Sur environ 5% de la surface des calcaires, les eaux souterraines alimentent des sources non-thermales. La dissolution du Gypse a produit une porosité tertiaire significative et une perméabilité dans les aquifères calcaires, et ceci est un précurseur essentiel au développement du drainage karstique.

     

Occurrence of soluble salts and moisture in the unsaturated zone and groundwater hydrochemistry along the middle and lower reaches of the Heihe River in northwest China

Deforestation, over-development of water resources and population growth have contributed to degeneration of vegetation in the Heihe River Basin in northwest China. Salts and water contents are the most important factors affecting the growth of vegetation in this arid area. This study was conducted to determine soluble salt levels of soils in the unsaturated zone and the hydrochemistry of groundwater at 14 sites in this region. Concentrations of soluble ions in the soils deceased with depth. Soil ion contents increased at depths below the root system of native plants. Sulfate was the dominant anion in both the unsaturated zone and the groundwater. Total dissolved solids (TDS) in groundwater ranged from less than 1 g/L in the middle reaches of the watershed to about 10 g/L in the arid lower reaches. In the middle and upper reaches of the watershed, salinity in soil and groundwater decreased. Groundwater was highly variable in hydrochemistry. The lower reaches was predominated by SO₄–Na•Mg and SO₄–Mg•Na type water, whereas in the middle reaches groundwater is characterized by lower TDS and HCO₃-dominated type water. Evapotranspiration is responsible for occurrence of the soluble salts in the soil profiles. Dissolution is the dominant chemical process in the middle reaches, whereas evapotranspiration prevails in the lower reaches of the Heihe River.     

Hydrogeological and hydrochemical features of an area polluted by heavy metals in central Nicaragua

Geophysical and hydrochemical surveys were used to investigate the hydrogeological conditions in one of the Río Sucio microbasins, in central Nicaragua. Zones of vertical structures (i.e. fractures and quartz veins) and weathering were mapped using Continuous Vertical Electrical Soundings (CVES), as such zones are of major importance for groundwater transport. Water from the springs was analysed to determine concentrations of major ions and heavy metals. Low ion concentrations and ¹⁸O analyses indicate that the springs occur close to their recharge areas and there is a relatively rapid groundwater circulation. Mercury (Hg) content in the springs was low, while comparatively high amounts of lead (Pb) were found. The results presented here demonstrate the important function of weathering and tectonics in the occurrence of groundwater systems in the basin. Hg and Pb found in the springs’ water reveal the existence of an increase in pollution sources disseminating in the area. More than 100 years of using mercury in the gold-mining industry and releasing wastes into rivers has affected water quality and ecosystems. Further investigations are needed in this area to determine the groundwater vulnerability to this pollution as this resource may be needed in the future.