Cl SO4 Research Articles

A study on the hydrogeology and hydrogeochemistry of groundwater from different depths in a coastal aquifer: Annamalai Nagar, Tamilnadu, India

Chemical characterization of groundwater is essential to bring out its nature and utility. Samples from shallow and deep ground water of the same location were collected and studied for their geochemical characteristics following standard procedures (APHA 1998). Sediment samples from different depths were collected and analysed for minerals using FTIR and SEM. Resisitivity logging was carried out in the bore well to understand the variations in depth to fresh water potential. The shallow ground water is dominated by Na–Cl–HCO3–SO4 and deeper groundwater by Na–HCO3–SO4–Cl types. It is observed that there is a significant ionic variation with depth. The ionic strength of the deeper samples is lesser than in the shallower samples. Wide pH variations in the shallow water samples are due to ion exchange process. Thermodynamic stability plot was used to identify the state of stability. It is inferred that there is no major significant difference in the thermodynamic state of stability in the shallow and the deeper aquifers as the aquifer matrix for the shallow and deeper aquifers are almost similar. Saturation index of Gibbsite, Kaolinite, Calcite, Dolomite and anhydrite, were studied for shallow and deep aquifers, to identify the difference in hydro chemical signatures. The Si/Al ratios of shallow samples are less when compared with the deeper samples. Leaching of secondary salts was the chief mechanism controlling the ground water chemistry of the region.

Modeling ferrous–ferric iron chemistry with application to martian surface geochemistry

The Mars Global Surveyor, Mars Exploration Rover, and Mars Express missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major recent mission findings are the presence of jarosite (a ferric sulfate salt), which requires formation from an acid-sulfate brine, and the occurrence of hematite and goethite on Mars. Recent ferric iron models have largely focused on 25 °C, which is a major limitation for models exploring the geochemical history of cold bodies such as Mars. Until recently, our work on low-temperature iron-bearing brines involved ferrous but not ferric iron, also obviously a limitation. The objectives of this work were to (1) add ferric iron chemistry to an existing ferrous iron model (FREZCHEM), (2) extend this ferrous/ferric iron geochemical model to lower temperatures (<0 °C), and (3) use the reformulated model to explore ferrous/ferric iron chemistries on Mars. The FREZCHEM model is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Ferric chloride and sulfate mineral parameterizations were based, in part, on experimental data. Ferric oxide/hydroxide mineral parameterizations were based exclusively on Gibbs free energy and enthalpy data. New iron parameterizations added 23 new ferrous/ferric minerals to the model for this Na–K–Mg–Ca–Fe(II)–Fe(III)–H–Cl–SO 4–NO 3–OH–HCO 3–CO 3–CO 2–O 2–CH 4–H 2O system. The model was used to develop paragenetic sequences for Rio Tinto waters on Earth and a hypothetical Martian brine derived from acid weathering of basaltic minerals. In general, model simulations were in agreement with field evidence on Earth and Mars in predicting precipitation of stable iron minerals such as jarosites, goethite, and hematite. In addition, paragenetic simulations for Mars suggest that other iron minerals such as lepidocrocite, schwertmannite, ferricopiapite, copiapite, and bilinite may also be present on the surface of Mars. Evaporation or freezing of the Martian brine led to similar mineral precipitates. However, in freezing, compared to evaporation, the following key differences were found: (1) magnesium sulfates had higher hydration states; (2) there was greater total aqueous sulfate (SO 4T = SO 4 + HSO 4) removal; and (3) there was a significantly higher aqueous Cl/SO 4T ratio in the residual Na–Mg–Cl brine. Given the similarities of model results to observations, alternating dry/wet and freeze/thaw cycles and brine migration could have played major roles in vug formation, Cl stratification, and hematite concretion formation on Mars.

Recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system, southwest of North China Plain

Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population, quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater was recharged by precipitation and was characterized by Ca–HCO3 type water with depleted δ18O and δD (mean value of −8.8‰ δ18O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex (Ca–Na–Mg–HCO3–Cl–SO4 type), and heavier δ18O and δD were observed (around −8‰ δ18O). Before the surface water with mean δ18O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ18O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal end of the fan. The groundwater underwent chemical evolution from Ca–HCO3, Na–HCO3, to Na–SO4. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical evolution, and groundwater flow paths in the complex alluvial fan aquifer system.

Hydrogeochemical investigation of Küçük Menderes River coastal wetland, Selçuk–Izmir, Turkey

Kucuk Menderes River forms a rich coastal wetland inside in the Selcuk plain. Three saline/brackish lakes, one swamp and Kucuk Menderes River are these wetlands’ components. Alkaline-slightly alkaline type lakes are recharged from precipitation and karstic springs that discharge from marble-schist and marble-alluvium contacts in the northern and southern parts of the study area. Water types of the wetland are Na–Cl and Na–Ca–Mg–HCO3–Cl in both rainy and dry seasons. Both seawater intrusion and evaporation, as being the sources of the ions, justify the presence of Na–Cl, Na–SO4 and Cl–SO4, in the wetland water. Environmental isotopes were used to identify the relationship between wetland and groundwater in the Selcuk plain. The δ18O and δD composition of wetland area samples have changed between −6.42 to −4.56‰, and −36.40 to −23.80‰, respectively. The lakes and rivers are plotted on the mixing line by slope of 5.2 and these data indicate that wetland is affected from seawater intrusion. The recharge area that was sampled in order to compare the wetland has Ca–HCO3 water type with a neutral-slightly alkaline pH values and the main hydrogeochemical process is weathering the different types of silicates. Iron, manganese and selenium are the dominant minor ions due to the high biological activities and organic matters in the lakes. There are two contamination risks for this wetland: (1) waste disposal site and (2) water treatment plant where the purified waters are released into the river. EC, Al, As, Cd, Cu, Fe and Zn values exceed those of aquatic life standards. In the near future these sites will pose a danger for wetland wild life and surrounding irrigation water suppliers.

Formation processes of thermal waters in Green Tuff: A geochemical study in the Hokuriku district, central Japan

Thermal waters from Green Tuff region in the Hokuriku district, central Japan were investigated to reveal formation process of water, based on the chemical and isotopic compositions of water and dissolved gases in water. The thermal waters of local meteoric origin are typical Green Tuff-type water, Na–Ca–Cl–SO 4-type or Na–Cl–SO 4-type, which well reacted by water–rock interaction and is found to be saturated with calcite and undersaturated with gypsum. The Green Tuff-type waters have relatively high 3He/ 4He ratio indicating high contribution of mantle-derived helium, and have extremely low total carbon/ 3He (Ct/ 3He) ratio compared with the ratio of MORB due to removal of carbon species from waters caused by calcite deposition. In contrast, a mineral spring water close to an active fault is found to be an immature water with less water–rock interaction containing a large amount of gaseous CO 2 and is undersaturated with both calcite and gypsum. This water has high 3He/ 4He ratio and Ct/ 3He ratio indicating the high contribution of mantle-derived helium and deep-seated CO 2, and likely provided through the fault. We proposed a chemical evolution model considering existence of both chemically immature CO 2 gas-rich water and mature carbon-poor water which well reacted with rocks. Deep-seated CO 2 and mantle-derived helium are upwelling via faults and are supplied to the groundwater of local meteoric origin, and an immature water containing high content of CO 2 and mantle-derived helium is formed. During the circulation of this immature water in the Green Tuff layers, water–rock interaction such as ion exchanges with minerals, dissolution of gypsum and deposition of calcite occurred. At the interaction with rocks, deposition of calcite occurs and results in a loss of Ca 2+, and decrease of Ca 2+ brings dissolution of gypsum and more calcite deposition. Consequently, almost all the supplied CO 2 is eliminated from the water. Furthermore, we made a quantitative evaluation of the chemical evolution of Green Tuff-type water using geochemical modeling code PHREEQC taking account of addition of gas components, and found the good agreement with observational results. This study reveals that the supply of large amounts of CO 2 and subsequent water–rock interaction are necessary for the formation of “Green Tuff-type” water with high 3He/ 4He ratio and extremely low Ct/ 3He ratio.

An isopiestic study of aqueous NaBr and KBr at 50 °C: Chemical equilibrium model of solution behavior and solubility in the NaBr–H 2O, KBr–H 2O and Na–K–Br–H 2O systems to high concentration and temperature

The isopiestic method has been used to determine the osmotic coefficients of the binary solutions NaBr–H 2O (from 0.745 to 5.953 mol kg −1) and KBr–H 2O (from 0.741 to 5.683 mol kg −1) at the temperature t = 50 °C. Sodium chloride solutions have been used as isopiestic reference standards. The isopiestic results obtained have been combined with all other experimental thermodynamic quantities available in literature (osmotic coefficients, water activities, bromide mineral’s solubilities) to construct a chemical model that calculates solute and solvent activities and solid–liquid equilibria in the NaBr–H 2O, KBr–H 2O and Na–K–Br–H 2O systems from dilute to high solution concentration within the 0–300 °C temperature range. The Harvie and Weare [Harvie C., and Weare J. (1980) The prediction of mineral solubilities in naturalwaters: the Na–K–Mg–Ca–Cl–SO 4–H 2O system from zero to high concentration at 25 °C. Geochim. Cosmochim. Acta 44, 981–997] solubility modeling approach, incorporating their implementation of the concentration-dependent specific interaction equations of Pitzer [Pitzer K. (1973) Thermodynamics of electrolytes. I. Theoretical basis and general equations. J. Phys. Chem. 77, 268–277] is employed. The model for binary systems is validated by comparing activity coefficient predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solutions model due to data insufficiencies are discussed. This model expands the variable temperature sodium–potassium model of Greenberg and Moller [Greenberg J., and Moller N. (1989) The prediction of mineral solubilities in natural waters: a chemical equilibrium model for the Na–K–Ca–Cl–SO 4–H 2O system to high concentration from 0 to 250 °C. Geochim. Cosmochim. Acta 53, 2503–2518] by evaluating Br − pure electrolyte and mixing solution parameters and the chemical potentials of three bromide solid phases: NaBr–2H 2O (cr), NaBr (cr) and KBr (cr).

Modeling of Bovine Type‐I Collagen Fibrils: Interaction with Pickling and Retanning Agents

Bovine Type I collagen was investigated, building on a large scale computer model of a collagen fibril in water, and focusing on two stages of the leather manufacturing process. The effects of different salts (NaCl, CaCl(2), and Na(2)SO(4)) on the swelling behavior of collagen at low pH (the pickling process) were studied. The salts suppress the swelling of the fibrils at low pH and we find specific stabilizing influences for CaCl(2) and Na(2)SO(4), due to weak Ca(2+)/Cl(-) and strong SO(4) (2-)/lysine/arginine interactions, respectively. Using state-of-the-art sampling techniques, such as the metadynamics algorithm, to allow an efficient exploration of configuration space, we were able to investigate the effect of polyacrylate and poly(methyl acrylate) - two polymeric retanning agents - on the fibril. Both polymers interact with the ammonium groups on the surface, but polyacrylate shows significantly stronger interactions. We suggest that it is this stronger interaction that contributes to the reduced suitability of PAA as a tanning agent.

Hydrochemistry and isotope compositions of groundwater from the Shihongtan sandstone-hosted uranium deposit, Xinjiang, NW China

Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO 3 type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ 18O of − 8.3‰, δD of − 48.2‰,δ 11B of 1.5‰, and 87Sr/ 86Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO 4 type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ 18O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ 11B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and 87Sr/ 86Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO 4 type water with the highest TDS (249.1 g/l, brine) and has δ 18O of − 2.8‰, δD of − 45.8‰,δ 11B of 21.2‰, and 87Sr/ 86Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ 11B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.

Mapping of groundwater quality in the Turonian aquifer of Oum Er-Rabia Basin, Morocco: a case study

This study takes the groundwater of the Moroccan limestone aquifer of Oum Er-Rabia as an example of statistical and cartographical approaches in water resources management. Statistical analyses based on frequency distribution and PCA methods revealed the homogeneity of waters with the existence of abnormal points and have helped to assess correlations between the studied variables. The mapping approach illustrated that waters are influenced by the lithology of the surrounding rocks and are of Ca–Mg–HCO3, Ca–Mg–Cl–SO4, and mixed types according to the Piper classification. The quality of water is of high to medium, north of the basin, but it is of medium to bad, NE and south, due to excessive contents of chloride, sulfate and nitrate. According to the US Salinity Laboratory classification, water used for irrigation in the eastern and the southern parts of the basin should take into consideration the drainage conditions, the nature of plants and the addition of gypsum doses.

Processes of water–rock interaction in the Turonian aquifer of Oum Er-Rabia Basin, Morocco

Possible water–rock interaction processes, in the Moroccan basin of Oum Er-Rabia, were discussed by a geochemical study of groundwater from the Turonian limestone aquifer, the most important water resource in the region. Different types of water according to the classification of Piper were defined. Waters have shown an evolution from dominant CHO3–Ca–Mg type through mixed to SO4–Cl–Ca–Mg type. The use of geochemical diagrams and chemical speciation modeling method has shown that water–rock interaction is mainly controlled by carbonate and anhydrite dissolution, ion exchange and reverse ion exchange processes. Water–rock equilibrium conditions are favorable for the precipitation of calcite, dolomite, kaolinite and magnesian smectite.

Synthesis of highly substituted meso-tetraarylporphyrins

meso-Tetraphenylporphyrin (and its derivatives), in the reaction with fuming yellow nitric acid ( d=1.53), form either 5-(4-nitroaryl)-10,15,20-triarylporphyrin, 5,10-bis(4-nitroaryl)-15,20-diarylporphyrin, or 5,10,15-tris(4-nitroaryl)-20-arylporphyrin, depending on the reaction temperature (0–20 °C), amounts of the acid used, and reaction time. The above nitroporphyrins react, in the presence of a base ( t-BuOK) at 0 °C, with carbanions (which bear nucleophugal groups at the carbanionic center: −CH(Cl)SO 2Tol, −CH(Br)SO 2Tol, and −CH(Cl)SO 2NMe 2), leading to the nucleophilic substitution of hydrogen in one or more of the meso-nitroaryl rings. By this route, the preparation of the highly substituted ‘synthetic’ porphyrins (bearing up to ten O-, N-, Cl-, or C-substituents) was demonstrated.

Use of reaction path modeling to identify the processes governing the generation of neutral Na–Cl and acidic Na–Cl–SO 4 deep geothermal liquids at Miravalles geothermal system, Costa Rica

The EQ3/6 Software Package was used to investigate the irreversible water–rock mass exchanges governing the production of neutral Na–Cl and acidic Na–Cl–SO 4 geothermal liquids circulating at depth into the Miravalles geothermal system. First, we reconstructed the in-situ reservoir composition, including pH, we evaluated the boundary conditions ( P CO 2 , P H 2S , and/or P O 2 ), which are necessary for the implementation of reaction path modeling, we estimated the thermodynamic affinity of the reservoir liquids with respect to relevant hydrothermal solid phases, and we identified possible compositions of the initially acidic meteoric–magmatic liquids. Then we modeled both the interaction between meteoric–magmatic fluids and calc–alkaline volcanic rocks and the interaction between neutral Na–Cl waters and highly altered volcanic rocks. Reaction path modeling was performed through a purely stoichiometric approach without considering the kinetics of irreversible mass exchanges. Results of reaction path modeling suggest that the neutral Na–Cl liquids hosted in the Miravalles geothermal reservoirs are produced through interaction between initially acidic, magmatic–meteoric aqueous solutions and volcanic rocks and represent the final product of this process. However, the deep acid Na–Cl–SO 4 liquids of Miravalles are not intermediate products in this process. They are instead generated through interaction of neutral Na–Cl waters with volcanic rocks affected by advanced argillic alteration, representing old solfataras buried by later volcanics, as suggested by Robert O. Fournier about 10 years ago.

Hydrogeochemistry, groundwater ages and sources of salts in a granitic batholith on the Canadian Shield, southeastern Manitoba

The hydrogeochemistry of the Lac du Bonnet granitic batholith has been determined for the region of the Whiteshell Research Area (WRA) in southeastern Manitoba, Canada. This work forms part of the geosciences studies performed for the Canadian Nuclear Fuel Waste Management Program over the period 1980–1995 by Atomic Energy of Canada Limited (AECL). Knowledge of the variation of groundwater chemistry and its causes is useful in assessing the performance and safety of a nuclear fuel waste vault located at depths of up to 1000 m in a crystalline rock formation of the Canadian Shield. Groundwaters and matrix pore fluids have been obtained by standard sampling methods from shallow piezometers in clay-rich overburden, from packer-isolated borehole zones intersecting fractures or fault zones in the bedrock, and from boreholes in unfractured rock in AECL's Underground Research Laboratory (URL). Eighty-six individual fracture groundwaters have been sampled and analysed from permeable zones in 53 boreholes drilled to depths of up to 1000 m in the Lac du Bonnet batholith. In addition, 28 groundwaters from piezometers in a large wetland area near the URL have been sampled and analysed to determine the influence of clay-rich overburden on the bedrock hydrogeochemistry. Analyses have been made for major and minor ions, pH, Eh, trace metals, and stable and radioactive isotopes, to characterise these groundwaters and relate them to their hydrogeologic regimes. Shallow groundwaters in the fractured bedrock are generally dilute (TDS <0.3 g/l), Ca–Na–HCO 3 waters and show little indication of mixing with Ca–Mg–HCO 3–SO 4 groundwater from overburden sediments. The near-modern levels of 3H and 14C, and a warm-climate 2H/ 18O signature in these groundwaters, indicates that the upper ∼200 m of fractured bedrock contains an active groundwater circulation system with a residence time of tens to hundreds of years. Deeper fracture groundwaters (200–400 m depth) in recharge areas, are more alkaline, Na–Ca–HCO 3 waters and evolve to Na–Ca–HCO 3–Cl–SO 4 waters with increasing distance along the flow path. Isotopic data indicate the presence of a glacial melt-water component suggesting that the residence times of these waters are 10 3–10 5 a. These waters form a transition zone between the upper, advective flow regime and a deeper regime in sparsely fractured rock where groundwater in fractures and fracture zones is largely stagnant. At these depths (> 500 m), Na–Ca–Cl–SO 4 waters of increasing salinity (up to 50 g/l) with depth are found and in some fractures the waters have evolved to a Ca–Na–Cl composition. Isotopic data indicate that these waters are warm-climate and pre-glacial in origin, with residence times of over 1 Ma. Pore fluids observed to drain from the unfractured rock matrix in the URL facility are almost pure Ca–Cl in composition, ∼90 g/l salinity, and have a 2H/ 18O composition displaced well to the left of the global meteoric water line, about which all other WRA groundwaters lie. This information indicates that these pore fluids have undergone prolonged water-rock interaction and have residence times of 10 1–10 3 Ma. Most of the deeper fracture groundwaters and pore fluids have low Br/Cl ratios and moderate to high δ 34S values of dissolved SO 4 which indicates that their salinity could be derived from a marine source such as the basinal sedimentary brines and evaporites to the west of the batholith. These fluids may have entered the batholith during early Paleozoic times when sedimentary rocks were deposited over the granite and were driven by a hydraulic gradient resulting from higher ground in western Canada. The hydrogeochemical data and interpretations show that below ∼500 m in the WRA, fracture-hosted groundwaters are very saline, reducing and old, and are, therefore, indicative of stagnant conditions over the period of concern for nuclear waste disposal (1 Ma). The intact rock matrix at these depths is extremely impermeable as indicated by the presence of pore fluids with unusual geochemical and isotopic characteristics. The pore fluids may represent basinal brines that have evolved geochemically and isotopically to their current composition over periods as long as 10 3 Ma.

The crater lake and hydrothermal system of Mount Pinatubo, Philippines: evolution in the decade after eruption

The June 1991 eruption of Mount Pinatubo, Philippines breached a significant, pre-eruptive magmatic-hydrothermal system consisting of a hot (>300 °C) core at two-phase conditions and surrounding, cooler (<260 °C) liquid outflows to the N and S. The eruption created a large, closed crater that accumulated hydrothermal upwellings, near-surface aquifer and meteoric inflows. A shallow lake formed by early September 1991, and showed a long-term increase in level of ~1 m/month until an artificial drainage was created in September 2001. Comparison of the temporal trends in lake chemistry to pre- and post-eruptive springs distinguishes processes important in lake evolution. The lake was initially near-neutral pH and dominated by meteoric influx and Cl–SO4 and Cl–HCO3 hydrothermal waters, with peaks in SO4 and Ca concentrations resulting from leaching of anhydrite and aerosol-laden tephra. Magmatic discharge, acidity (pH~2) and rock dissolution peaked in late 1992, during and immediately after eruption of a lava dome on the crater floor. Since cessation of dome growth, trends in lake pH (increase from 3 to 5.5), temperature (decline from 40 to 26 °C), and chemical and isotopic composition indicate that magmatic degassing and rock dissolution have declined significantly relative to the input of meteoric water and immature hydrothermal brine. Higher concentrations of Cl, Na, K, Li and B, and lower concentrations of Mg, Ca, Fe, SO4 and F up to 1999 highlight the importance of a dilute hydrothermal contribution, as do stable-isotope and tritium compositions of the various fluids. However, samples taken since that time indicate further dilution and steeper trends of increasing pH and declining temperature. Present gas and brine compositions from crater fumaroles and hot springs indicate boiling of an immature Cl–SO4 geothermal fluid of near-neutral pH at approximately 200 °C, rather than direct discharge from magma. It appears that remnants of the pre-eruptive hydrothermal system invaded the magma conduit shortly after the end of dome emplacement, blocking the direct degassing path. This, along with the large catchment area (~5 km2) and the high precipitation rate of the area, led to a rapid transition from a small and hot acid lake to a large lake with near-ambient temperature and pH. This behavior contrasts with that of peak-activity lakes that have more sustained volcanic gas influx (e.g., Kawah Ijen, Indonesia; Poas and Rincon de la Vieja, Costa Rica).

Use of hydrochemical parameters for the identification of fresh groundwater resources, Potharlanka Island, India

A hydrochemical study has been carried out on the fresh groundwater resources of Potharlanka, Krishna Delta, India. Groundwater samples were collected at 58 sites and analyzed in June and December 2001. The groundwater is mildly alkaline with a pH of 7.2–8.2, electrical conductivity (EC) varies from 645–4,700 μS/cm in June 2001 (pre-monsoon) and from 605–5,770 μS/cm in December 2001 (post-monsoon). More than 75% of the samples have >1000 mg/l TDS which is higher than the maximum permissible limit for potable water. Na and Cl are the dominating cations and these are directly proportional to TDS. Extremely low HCO3 /Cl and variable high Mg/Ca (molar ratios) indicated the transformation of the fresh groundwater aquifer systems to saline. Groundwater of this island is classified as Na–Cl, Na–Ca–Cl–HCO3, Na–Mg–Cl–SO4 and mixed types. A high percentage of mixed water types indicates the possibility of simultaneous fresh groundwater dilution activity along with a seawater ingression/intrusion process. Low rainfall and excessive withdrawal of groundwater has caused the increase of saline water intrusion.

Chemical composition of brine inclusions in halite fromclayey salt (zuber) facies from the Upper Tertiary (Miocene) evaporite basin (Poland)

The chemistry of the primary brines for halites from the upper part of the Wieliczka deposit and the clayey salt (zuber) unit of the Bochnia deposit has been investigated. The results evidenced that the brines belong to the Na K Mg Cl SO 4 type and the proportion of the ions was similar tothe concentration in recent seawaters but depleted in S04 ion.

Anionic ligand effect on the nature of epoxidizing intermediates in iron porphyrin complex-catalyzed epoxidation reactions.

We have studied an anionic ligand effect in iron porphyrin complex-catalyzed competitive epoxidations of cis- and trans-stilbenes by various terminal oxidants and found that the ratios of cis- to trans-stilbene oxide products formed in competitive epoxidations were markedly dependent on the ligating nature of the anionic ligands. The ratios of cis- to trans-stilbene oxides obtained in the reactions of Fe(TPP)X (TPP = meso-tetraphenylporphinato dianion and X(-) = anionic ligand) and iodosylbenzene (PhIO) were 14 and 0.9 when the X(-) of Fe(TPP)X was Cl(-) and CF(3)SO(3)(-), respectively. An anionic ligand effect was also observed in the reactions of an electron-deficient iron(III) porphyrin complex containing a number of different anionic ligands, Fe(TPFPP)X [TPFPP = meso-tetrakis(pentafluorophenyl)porphinato dianion and X(-) = anionic ligand], and various terminal oxidants such as PhIO, m-chloroperoxybenzoic acid (m-CPBA), tetrabutylammonium oxone (TBAO), and H(2)O(2). While high ratios of cis- to trans-stilbene oxides were obtained in the reactions of iron porphyrin catalysts containing ligating anionic ligands such as Cl(-) and OAc(-), the ratios of cis- to trans-stilbene oxide were low in the reactions of iron porphyrin complexes containing nonligating or weakly ligating anionic ligands such as SbF(6)(-), CF(3)SO(3)(-), and ClO(4)(-). When the anionic ligand was NO(3)(-), the product ratios were found to depend on terminal oxidants and olefin concentrations. We suggest that the dependence of the product ratios on the anionic ligands of iron(III) porphyrin catalysts is due to the involvement of different reactive species in olefin epoxidation reactions. That is, high-valent iron(IV) oxo porphyrin cation radicals are generated as a reactive species in the reactions of iron porphyrin catalysts containing nonligating or weakly ligating anionic ligands such as SbF(6)(-), CF(3)SO(3)(-), and ClO(4)(-), whereas oxidant-iron(III) porphyrin complexes are the reactive intermediates in the reactions of iron porphyrin catalysts containing ligating anionic ligands such as Cl(-) and OAc(-).

Biophysical analysis of natural, double-helical DNA modified by a dinuclear platinum(II) organometallic compound in a cell-free medium.

Modifications of natural DNA by the dinuclear platinum(II) organometallic complex [[Pt(Me)Cl(Me(2)SO)](2)(mu-N-N)] [where N-N=H(2)N(CH(2))(6)NH(2)] (ORGANObisPt) were studied by methods of molecular biophysics. These methods include DNA binding studies using atomic absorption spectrophotometry, HPLC analysis of enzymatically digested DNA, interstrand cross-linking employing gel electrophoresis under denaturing conditions, DNA unwinding studied by gel electrophoresis, mapping of DNA adducts by transcription assay, DNA melting curves measured by absorption spectrophotometry and conformational analysis of platinated DNA by differential pulse polarography. The results indicate that the complex ORGANObisPt binds irreversibly to DNA. Its DNA binding mode is, however, different from that of the formally equivalent [[cis-PtCl(NH(3))(2)](2)(mu-N-N)] (1,1/c,c), which exhibits antitumor activity including that in the tumor cells resistant to cisplatin. Interestingly, ORGANObisPt binds to DNA considerably faster than 1,1/c,c and cisplatin. In addition, when ORGANObisPt binds to DNA it exhibits a strong base sequence specificity to guanine residues. ORGANObisPt forms mainly monofunctional adducts on double-helical DNA. It forms also a small amount of DNA interstrand cross-links (approximately 2%), i.e. a radically smaller amount in comparison with the complex 1,1/c,c. Importantly, these interstrand cross-links of ORGANObisPt are capable of terminating RNA synthesis in vitro, while its major monofunctional adducts are not. In addition, the adducts of ORGANObisPt affect the conformation of DNA, but in a different way than its dinuclear analogue 1,1/c,c or cisplatin. Some structural features of ORGANObisPt, such as the charge or nature of the trans and cis activating groups relative to the labile chloride, might be responsible for the altered DNA binding mode and biological activity in comparison with the 1,1/c,c compound.

Thermodynamic study of the KMgAlClSO 4H 2O system at the temperature 298.15 K

The Pitzer ion-interaction model has been used for thermodynamic simulation of the binary AlCl 3H 2O, Al 2(SO4) 3H2O, ternary KClAlCl 3H 2O, K 2SO 4Al 2(SO 4) 3H 2O, MgCl 2AlCl 3H 2O, MgSO 4Al 2(SO 4) 3H 2O, and the quaternary KClMgCl 2AlCl 3H 2O systems at T=298.15 K. The optimum values of the binary parameters of ionic interactions for aluminum solutions have been calculated using activity data up to saturation of solutions. The ternary parameters have been chosen on the basis of the compositions of saturated ternary solutions taking into account the unsymmetrical mixing terms. Good agreement between experimentally determined and calculated solubilities has been found. Important thermodynamic characteristics (thermodynamic solubility product, standard molar Gibbs energy of formation) of the solid phases (simple and double salts) crystallizing in the systems under consideration are determined.

Tracing regional flow paths to major springs in Trans-Pecos Texas using geochemical data and geochemical models

San Solomon, Giffin, and Phantom Lake Springs, located in Trans-Pecos Texas, have a high TDS, Na–Cl–SO 4 baseflow component derived from a regional flow system and a low TDS, mixed cation–mixed anion stormflow component derived from local precipitation events. The hypothesis that the regional flow system maintaining baseflow spring discharge originates in the Salt Basin and flows through the Apache Mountains towards the springs is tested with historical geochemical data from wells and springs. Data from over 1400 wells in the study area over a 50-year period were analyzed and used to delineate 11 hydrochemical facies based on the predominant ions. Geochemical data from samples along the hypothesized regional flow path indicate a trend of increasing dissolved solids and Cl–HCO 3 ratios and decreasing Na–Cl ratios. These are consistent with evolution of groundwater in an unconfined regional system dominated by carbonates and evaporites. In the bicarbonate facies, the waters represent recent recharge modified by mineral dissolution and cation exchange. In the sulfate zones, the hydrochemical facies are controlled by gypsum, anhydrite, and halite dissolution, cation exchange, and mixing with Na–Cl waters. In the chloride zones, the hydrochemical facies are controlled by halite dissolution and irrigation return flow. Spring discharge chemistry is most similar to chloride zone waters; Na–Cl and Ca–SO 4 ratios suggest that baseflow is derived from the chloride zone waters upgradient along the hypothesized flow path. PHREEQC modeled groundwater evolution along the hypothesized flow path and spring discharge under stormflow and baseflow conditions. Results indicate that: (1) hydrochemistry along the regional flow path is controlled by dissolution of halite, gypsum, dolomite, and CO 2 and by precipitation of calcite; (2) baseflow spring discharge is derived primarily from this regional flow system; and (3) spring discharge after major storm events can constitute as much as 72% local recharge that is further modified by dissolution of calcite, gypsum, and CO 2. Data analysis and model results suggest that cave formation in this system is occurs during major storm events.