A Geochemical study of the groundwater in the Misli basin and environmental implications

The aim of this study was to determine geochemical properties of groundwater and thermal water in the Misli Basin and to assess thermal water intrusion into shallow groundwater due to over-extraction. According to isotope and hydrochemical analyses results, sampled waters can be divided into three groups: cold, thermal, and mixed waters. Only a few waters reach water–rock chemical equilibrium. Thermal waters in the area are characterized by Na⁺–Cl⁻–HCO₃⁻, while the cold waters by CaHCO₃ facies. On the basis of isotope results, thermal waters in the Misli basin are meteoric origin. In particular, δ¹⁸O and δ²H values of shallow groundwater vary from −10.2 to −12.2‰ and −71.2 to −82‰, while those of thermal waters range from −7.8 to −10.1‰ and from −67 to −74‰, respectively. The tritium values of shallow groundwater having short circulation as young waters coming from wells that range from 30 to 70 m in depth vary from 10 to 14 TU. The average tritium activity of groundwater in depths more than 100 m is 1.59 ± 1.16, which indicates long circulation. The rapid infiltration of the precipitation, the recycling of the evaporated irrigation water, the influence of thermal fluids and the heterogeneity of the aquifer make it difficult to determine groundwater quality changes in the Misli Basin. Obtained results show that further lowering of the groundwater table by over-consumption will cause further intrusion of thermal water which resulted in high mineral content into the fresh groundwater aquifer. Because of this phenomenon, the concentrations of some chemical components which impairs water quality in terms of irrigation purposes in shallow groundwaters, such as Na⁺, B, and Cl⁻, are highy probably expected to increase in time.     

A geoelectrical-hydrogeochemical investigation of shallow groundwater occurrence in Ibadan, southwestern Nigeria

 An integrated geological, geoelectrical and hydrochemical investigation of shallow groundwater occurrence in the Ibadan area, southwestern Nigeria, is presented. The primary objective was to characterise the groundwater in a typical low-latitude environment underlain by Precambrian crystalline basement complex rocks. The dominant rocks comprise suites of gneisses and quartzites. Chemical analyses of the groundwater show that the mean concentration of the cations is in the order Na>Ca>Mg>K while that for the anions is Cl>HCO₃>NO₃>SO₄. Statistical analyses, using the product-moment coefficient of correlation, indicate positive correlations between the following pairs of parameters: TDS and conductivity (r=0.96); Na⁺+Mg²⁺ and Cl^– (r=0.95); Na⁺+K⁺ and Ca²⁺ (r=0.43); Na⁺+K⁺ and HCO₃ ^– (r=0.17); Ca²⁺ and Mg²⁺ (r=0.74); Ca²⁺ and HCO₃ ^– (r=0.33); Ca²⁺+Mg²⁺ and HCO₃ ^– (r=0.31) and pH and HCO₃ ^– (r=0.54). A very weak negative correlation was recorded between pH and Cl^–, with r=–0.003. Five groundwater groups have been identified, namely, (1) the Na-Cl, Na-Ca-Cl, Na-Ca-(Mg)-Cl; (2) the Ca-(Mg)-Na-HCO₃-Cl, Na-Ca-HCO₃-Cl, and Ca-HCO₃-Cl; (3) the Ca-(Mg)-Na-HCO₃, Ca-Na-HCO_3; (4) Ca-Na-Cl-(SO₄)-HCO₃ and (5) the Ca-(Mg)-Na-SO₄-HCO₃. The different groups reflect the diversity of bedrock types and consequently also of the products of weathering. Most of the water sampled is unfit for drinking on account of the high NO₃ ^– content. It can, however, be used for irrigation purposes as the sodium hazard is low while the salinity hazard ranges from low to medium. Resistivity soundings indicate the presence of a thick weathering profile, which could be up to 60 m. Such sites should be the target for any long-term and sustainable groundwater development in the area. Received: 15 April 1998 · Accepted: 4 July 1998     

Spatial distribution characteristics of stable carbon isotope compositions in desert plant Reaumuria soongorica (Pall.) Maxim

In order to investigate the distribution characteristics of stable carbon isotope ratios (δ ¹³C) in the desert plant Reaumuria soongorica, the δ ¹³C values of leaves were measured in 407 individuals of 21 populations. Soil physicochemical properties including soil water content, soil total dissolved solids, soil total nitrogen, soil total phosphorus and soil organic content were also analyzed in order to survey the major factors influencing δ ¹³C values on spatial variation. Leaves and soil samples were simultaneously collected from the ten major distribution areas in Northwest China at altitudes from 394 m to 1 987 m above sea level, at latitudes from 36°10′N to 44°33′N, and at longitudes from 81°43′E to 106°37′E. These ten areas include Shihezi, Baicheng, Yiwu areas in Xinjiang Uygur Autonomous Region; Anxi, Zhangye, Baiyin, Lanzhou areas in Gansu Province; Shapotou, Yinchuan areas in Ningxia Hui Autonomous Region; and Alashan County in Inner Mongolia Autonomous Region. The results show that the δ ¹³C value of R. soongorica ranges from −22.77‰ to −29.85‰ with an average of −26.52‰. Foliar d13C values in R. soongorica are not significantly correlated with altitude, latitude or longitude, and a spatial distribution trend of d13C values of R. soongorica is not obvious on a large scale. However, when d13C values of two R. soongorica populations under the same climate conditions are compared, δ ¹³C values increase obviously from east to west and from north to south. As none of the soil total dissolved solids, soil total nitrogen, soil total phosphorus, and soil organic content shows a uniform trend from east to west and from north to south, we suppose that the small-scaled spatial distribution pattern of δ ¹³C values of R. soongorica is mainly controlled by the soil water content. Translated from Quaternary Sciences, 2006, 26(6): 947–954 [译自: 第四纪研究]     

Hydrogeochemical processes in the groundwater environment of Heihe River Basin,northwest China

The Heihe River Basin is a typical arid inland river basin for examining stress on groundwater resources in northwest China. The basin is composed of large volumes of unconsolidated Quaternary sediments of widely differing grain size, and during the past half century, rapid socio-economic development has created an increased demand for groundwater resources. Understanding the hydrogeochemical processes of groundwater and water quality is important for sustainable development and effective management of groundwater resources in the Heihe River basin. To this end, a total of 30 representative groundwater samples were collected from different wells to monitor the water chemistry of various ions and its quality for irrigation. Chemical analysis shows that water presents a large spatial variability of chemical facies (SO₄ ²⁻–HCO₃⁻, SO₄ ²⁻–Cl⁻, and Cl⁻–SO₄ ²⁻) as groundwater flow from recharge area to discharge area. The ionic ratio indicates positive correlation between the flowing pairs of parameters: Cl⁻ and Na⁺(r = 0.95), SO₄ ²⁻ and Na⁺ (r = 0.84), HCO₃ ⁻ and Mg²⁺(r = 0.86), and SO₄ ²⁻ and Ca²⁺ (r = 0.91). Dissolution of minerals, such as halite, gypsum, dolomite, silicate, and Mirabilite (Na₂SO₄·10H₂O) in the sediments results in the Cl⁻, SO₄ ²⁻, HCO₃ ⁻, Na⁺, Ca²⁺ and Mg²⁺ content in the groundwater. Other reactions, such as evaporation, ion exchange, and deposition also influence the water composition. The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification and the Wilcox diagram. The results show that most of the groundwater samples are suitable for irrigation uses barring a few locations in the dessert region in the northern sub-basin.     

Hydrochemical appraisal of groundwater and its suitability in the intensive agricultural area of Muzaffarnagar district,Uttar Pradesh,India

Muzaffarnagar is an economically rich district situated in the most fertile plains of two great rivers Ganga and Yamuna in the Indo-gangetic plains, with agricultural land irrigated by both surface water as well as groundwater. An investigation has been carried out to understand the hydrochemistry of the groundwater and its suitability for irrigation uses. Groundwater in the study area is neutral to moderately alkaline in nature. Chemistry of groundwater suggests that alkaline earths (Ca + Mg) significantly exceed the alkalis (Na + K) and weak acids exceed the strong acids (Cl + SO₄), suggesting the dominance of carbonate weathering followed by silicate weathering. Majority of the groundwater samples (62%) posses Ca–Mg–HCO₃ type of hydrochemical species, followed by Ca–Na–Mg–HCO₃, Na–Ca–Mg–HCO₃, Ca–Mg–Na–HCO₃–Cl and Na–Ca–HCO₃–SO₄ types. A positive high correlation (r ² = 0.928) between Na and Cl suggests that the salinity of groundwater is due to intermixing of two or more groundwater bodies with different hydrochemical compositions. Barring a few locations, most of the groundwater samples are suitable for irrigation uses. Chemical fertilizers, sugar factories and anthropogenic activities are contributing to the sulphate and chloride concentrations in the groundwater of the study area. Overexploitation of aquifers induced multi componential mixing of groundwater with agricultural return flow waters is responsible for generating groundwater of various compositions in its lateral extent.     

Groundwater contamination with arsenic in Sherajdikhan,Bangladesh: geochemical and hydrological implications

An integrated study has been carried out to elucidate the distribution and occurrence of arsenic in selected groundwater samples in the area of Sherajdikhan, Bangladesh. Arsenic and other parameters (T, pH, EC, Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃ ⁻, SO₄ ²⁻, HCO₃ ⁻, PO₄ ³⁻, Fe, Mn and DOC) have been measured in groundwater samples collected from shallow/deep tube wells at different depths. Hydrogeochemical data suggest that the groundwaters are generally Ca–Mg–HCO₃ and Mg–Ca–HCO₃ types with bicarbonate (HCO₃ ⁻) as the dominant anion, though the other type of water has also been observed. Dissolved arsenic in groundwater ranged from 0.006 to 0.461 mg/l, with 69% groundwater samples exceeded the Bangladesh limit for safe drinking water (0.05 mg/l). Correlation and principal component analysis have been performed to find out possible relationships among the examined parameters in groundwater. Low concentrations of NO₃ ⁻ and SO₄ ²⁻, and high concentrations of DOC, HCO₃ ⁻ and PO₄ ³⁻ indicate the reducing condition of subsurface aquifer where sediments are deposited with abundant organic matter. Distinct relationship of As with Fe and Mn, and strong correlation with DOC suggests that the biodegradation of organic matter along with reductive dissolution of Fe–Mn oxyhydroxides has being considered the dominant process to release As in the aquifers studied herein.     

Tracing the sources of nitrate in karstic groundwater in Zunyi,Southwest China: a combined nitrogen isotope and water chemistry approach

Nitrate (NO₃ ⁻) is major pollutant in groundwater worldwide. Karst aquifers are particularly vulnerable to nitrate contamination from anthropogenic sources due to the rapid movement of water in their conduit networks. In this study, the isotopic compositions (δ¹⁵N–NO₃ ⁻, δ¹⁵N–NH₄ ⁺) and chemical compositions(e.g., NO₃ ⁻, NH₄ ⁺, NO₂ ⁻, K⁺) were measured in groundwater in the Zunyi area of Southwest China during summer and winter to identify the primary sources of contamination and characterize the processes affecting nitrate in the groundwater. It was found that nitrate was the dominant species of nitrogen in most of the water samples. In addition, the δ¹⁵N–NO₃ ⁻ values of water samples collected in summer were lower than those collected in winter, suggesting that the groundwater received a significant contribution of NO₃ ⁻ from agricultural fertilizer during the summer. Furthermore, the spatial variation in the concentration of nitrate and the δ¹⁵N–NO₃ ⁻ value indicated that some of the urban groundwater was contaminated with pollution from point sources. In addition, the distribution of δ¹⁵N–NO₃ ⁻ values and the relationship between ions in the groundwater indicated that synthetic and organic fertilizers (cattle manure) were the two primary sources of nitrate in the study area, except in a few cases where the water had been contaminated by urban anthropogenic inputs. Finally, the temporal and spatial variation of the water chemistry and isotopic data indicated that denitrification has no significant effect on the nitrogen isotopic values in Zunyi groundwater.     

National scale evaluation of groundwater chemistry in Korea coastal aquifers: evidences of seawater intrusion

Pollution of groundwater by seawater intrusion poses a threat to sustainable agriculture in the coastal areas of Korea. Therefore, seawater intrusion monitoring stations were installed in eastern, western, and southern coastal areas and have been operated since 1998. In this study, groundwater chemistry data obtained from the seawater intrusion monitoring stations during the period from 2007 to 2009 were analyzed and evaluated. Groundwater was classified into fresh (<1,500 μS/cm), brackish (1,500–3,000 μS/cm), and saline (>3,000 μS/cm) according to EC levels. Among groundwater samples (n = 233), 56, 7, and 37% were classified as the fresh, brackish, and saline, respectively. The major dissolved components of the brackish and saline groundwaters were enriched compared with those of the fresh groundwater. The enrichment of Na⁺ and Cl⁻ was especially noticeable due to seawater intrusion. Thus, the brackish and saline groundwaters were classified as Ca–Cl and Na–Cl types, while the fresh groundwater was classified as Na–HCO₃ and Ca–HCO₃ types. The groundwater included in the Na–Cl types indicated the effects of seawater mixing. Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ²⁻, and Br⁻ showed good correlations with Cl⁻ of over r = 0.624. Of these components, the strong correlations of Mg²⁺, SO₄ ²⁻, and Br⁻ with Cl⁻ (r ≥ 0.823) indicated a distinct mixing between fresh groundwater and seawater. The Ca/Cl and HCO₃/Cl ratios of the groundwaters gradually decreased and approached those of seawater. The Mg/Cl, Na/Cl, K/Cl, SO₄/Cl, and Br/Cl ratios of the groundwaters gradually decreased, and were similar to or lower than those of seawater, indicating that Mg²⁺, Na⁺, K⁺, SO₄ ²⁻, and Br⁻, as well as Cl⁻ in the saline groundwater can be enriched by seawater mixing, while Ca²⁺ and HCO₃ ⁻ are mainly released by weathering processes. The influence of seawater intrusion was evaluated using threshold values of Cl⁻ and Br⁻, which were estimated as 80.5 and 0.54 mg/L, respectively. According to these criteria, 41–50% of the groundwaters were affected by seawater mixing.     

Effects of groundwater level fluctuation on its chemical composition in karst soils of Lithuania

Groundwater regime and mineralization process in moraine sandy loam and peat soils of the active sulphatic karst zone (karst processes develop in the Upper Devonian gypsum–dolomites) in Lithuania and the dependence of chemical compounds concentrations on water level fluctuations are reviewed. According to ion sum, groundwater mineralization in peat soil is 1.1–1.3 times higher than in loam soil. Based on this result, lower levels of groundwater predetermine a more intensive mineralization process. A stronger correlation was determined between groundwater levels and concentrations of chemical compounds (Ca²⁺, Mg²⁺, SO₄ ²⁻ and HCO₃ ⁻) enhancing groundwater mineralization. In mineral soil (sandy loam) nitrate (NO₃)⁻ concentration is highly influenced by changing stages of groundwater level as well as by nearby sinkholes.     

Evaluation of groundwater quality with emphasis on fluoride concentration in Nalbari district,Assam, Northeast India

This study was carried out to analyze groundwater quality in selected villages of Nalbari district, Assam, India, where groundwater is the main source of drinking water. 40 groundwater samples collected from hand pumps and analyzed for pH, EC, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ⁻, SO₄ ²⁻, Cl⁻ and F⁻. Chemical analysis of the groundwater showed that mean concentration of cations in (mg/L) is in the order Ca²⁺ > Mg²⁺ > Na⁺ > K⁺ while for anions it is HCO₃ ⁻ > Cl⁻ > SO₄ ²⁻ > F⁻. Fluoride concentration was recorded in the range of 0.02–1.56 mg/L. As per the desirable and maximum permissible limits for fluoride in drinking water recommended by WHO and by Bureau of Indian Standards (BIS), which is 1.5 mg/L, the groundwater of about 97% of the samples were found to be suitable for drinking purpose. The suitability of the groundwater for irrigation purpose was investigated by some determining factors such as sodium adsorption ratio, soluble sodium percentage, Kelly’s ratio and electrical conductivity. The value of the sodium absorption ratio and electrical conductivity of the groundwater samples were plotted in the US Salinity laboratory diagram for irrigation water. Most of the groundwater samples fall in the field of C2S1 and C3S1 indicating medium to high salinity and low sodium water, which can be used for irrigation on almost all types of soil with little doubt of exchangeable sodium. The hydrochemical facies shows that the groundwater is Ca-HCO₃ type.     

Groundwater chemistry within a plateau neighboring Matsumoto city,Japan

The change in groundwater chemistry along the groundwater flow path in the Matsumoto tunnel vicinity was studied, and the origin of the groundwater and dissoluted substances was determined. The relationship between the concentration of HCO₃ ^–, Ca²⁺, and Na⁺, and CO₂ gas pressure in the groundwater indicated that the HCO₃ ^–, Ca²⁺, and Na⁺ were produced by the reaction of the CO₂ gas in the groundwater and feldspar in the rocks. The relationship between the concentration of NO₃ ^– and the Eh and pH values in the groundwater indicated that in an oxidative condition, ammonia-oxidizing and nitriteoxidizing bacteria used NH₄ ⁺ and produced NO₃ ^– and H⁺, and in a reductive condition, denitrifying bacteria used NO₃ ^– and produced N₂ gas and OH^–. The stable hydrogen and oxygen isotopic ratio in the groundwater and precipitation indicated that the groundwater originated from precipitation that had fallen on the area. The concentration of³H and the stable hydrogen and oxygen isotopic ratios in the groundwater suggested that it has been getting warmer climatically for more than 60 years. The stable carbon isotopic ratio indicated that the HCO₃ ^– in the groundwater, excluding deep well water, originated from CO₂ gas produced by organic matter in the soil. The deep well water, which had a higher concentration of HCO₃ ^– than the other groundwater sampled, was thought to have acquired HCO₃ ^– though contact with rocks. The³⁶Cl/Cl ratio indicated the recharge age of the deep well water sampled at a depth of 760 m at the foot of the plateau was recent.     

Effects of poor quality irrigation waters on the nutrient leaching and groundwater quality from sandy soil

Sodium (Na⁺) in poor quality irrigation water participate in ion-exchange processes results in the displacement of base cations into solution and a raised concentration in groundwater. Knowledge of the rate of decrease of nutrients from soils resulting from poor water quality application is essential for long-term planning of crop production while minimizing the impact on groundwater quality. In this study, we examined the effect of sodium adsorption ratio (SAR) of irrigation water on nutrients leaching and groundwater quality in columns of sandy soil. Three types of irrigation waters at three NaCl–CaCl₂ solutions with the following levels of SAR (5, 15, and 30) were synthesized in laboratory. With the application of solutions, exchange occurred between solution Na⁺ and exchangeable cations (Ca²⁺, Mg²⁺, and K⁺), resulting in the displacement of these cations and anions into solution. Increasing the level of SAR from 5 to 15 and 30 resulted in increase in the average exchangeable sodium percentage (ESP) of the soil from 10.4 to 20.3, and 32.5, respectively. Adverse effect of high Na⁺ concentration in the solutions on raising ESP was less pronounced in solution having low SAR. Leaching of Ca²⁺, Mg²⁺, K⁺, and P from soil with the application of solutions represents a significant loss of valuable nutrients. This sandy soil showed the high risk for nutrients transfer into groundwater in concentrations exceeding the groundwater quality standard. Irrigation with poor quality water, which is generally more sodic and saline than regional groundwater, increases the rate of sodification and salinization of shallow groundwater.     

Hydrochemical evaluation of groundwater quality in the Çavuşçayı basin, Sungurlu-Çorum, Turkey

The purpose of this study is to investigate the quality and usage possibility of groundwater in the Çavuşçayı basin and suggest the best water structure for the groundwater use. Results from hydrochemical analyses reveal that groundwater is mostly affected by salty (Na⁺–Cl⁻) waters of the Incik Formation and brackish (Ca²⁺, Mg²⁺–SO ₄ ²⁻ ) waters of the Bayındır Formation. The Alibaba saltpan discharged (2 l/s) from the Incik Formation is used for salt production. In the basin, salinity risk increases with depth and along the groundwater flow direction. Therefore, shallow water and trenches opened in the alluvium aquifer at the east of the basin were determined to yield suitable water with no Na⁺ and Cl⁻ contamination. Following the heavy rainy period, waters of less salinity and conductivity are possibly used for agriculture.     

The threshold value of epikarst runoff in forest karst mountain area

Hydrochemical investigations were carried out in Damagh area, Hamadan, western Iran, to assess chemical composition of groundwater. Forty representative groundwater samples were collected from different wells to monitor the water chemistry of various ions. Chemical analysis of the groundwater showed that the mean concentration of the cations is in the order Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, while that for anions was HCO₃⁻ > Cl⁻ > SO₄^{2 −} > NO₃⁻. All of the investigated groundwaters present two different chemical facies (Ca–HCO₃ and Na–HCO₃) which is in relation with their interaction with the geological formations of the basin, cation exchange between groundwater and clay minerals and anthropogenic activities. The principal component analysis (PCA) performed on groundwater identified three principal components controlling their variability in groundwater. Electrical conductivity, Mg²⁺, Na⁺, SO₄²⁻, and Cl⁻ content were associated in the same component (PC1) (salinity), determined principally by anthropogenic activities. The pH, CO₃^{2 −}, HCO₃⁻, and Ca²⁺ (PC2) content were related to the geogenic factor. Finally, the NO₃⁻, Cl⁻ and K⁺ (PC3) were controlled by anthropogenic activity as a consequence of inorganic fertilizers.     

Enrichment of fluoride in groundwater under the impact of saline water intrusion at the salt lake area of Yuncheng basin,northern China

Long-term intake of high-fluoride groundwater causes endemic fluorosis. This study, for the first time, discovered that the salt lake water intrusion into neighboring shallow aquifers might result in elevation of fluoride content of the groundwater. Two cross-sections along the groundwater flow paths were selected to study the geochemical processes controlling fluoride concentration in Yuncheng basin, northern China. There are two major reasons for the observed elevation of fluoride content: one is the direct contribution of the saline water; the other is the undersaturation of the groundwater with respect to fluorite due to salt water intrusion, which appears to be more important reason. The processes of the fluorine activity reduction and the change of Na/Ca ratio in groundwater induced by the intrusion of saline water favor further dissolution of fluorine-bearing mineral, and it was modeled using PHREEQC. With the increase in Na concentration (by adding NaCl or Na₂SO₄ as Na source, calcium content kept invariable), the increase of NaF concentration was rapid at first and then became slower; and the concentrations of HF, HF₂⁻, CaF⁺, and MgF⁺ were continuously decreasing. The geochemical conditions in the study area are advantageous to the complexation of F⁻ with Na⁺ and the decline of saturation index of CaF₂, regardless of the water type (Cl–Na or SO₄–Na type water).     

Groundwater depletion and quality deterioration due to environmental impacts in Maheshwaram watershed of R.R. district,AP (India)

Maheshwaram watershed is situated in Ranga Reddy district of Andhra Pradesh at a distance of about 30 km south of Hyderabad, capital of Andhra Pradesh. The watershed has an area of 60 km² and has hard rock aquifers with semi-arid climate. The study area has been expanding at a fast pace and now has the distinction of being one of the fastest growing urban centers facing the problem of groundwater depletion and quality deterioration due to the absence of perennial source of surface water and also due to over exploitation. Human activities involving industrial and agricultural development and the inadequate management of land and water resources have, directly or indirectly resulted in the degradation of environment viz. water and soil. In the present study chemical analysis of groundwater samples of the study area, collected during pre- and post-monsoon seasons of 2007–2008 has been carried out. The analyzed data are utilized to characterize the hydro chemical process dominant in the area. Various classification methods such as Piper, Back and Hanshaw, Wilcox, USA. Salinity Laboratory are employed to critically study the geochemical characteristics of groundwater of the study area. Finally, principal component analysis (PCA) is also employed to the chemical variables of groundwater to characterize the hydro chemical process that is dominant in the area. In the analysis four principal components emerged as significant contributors to the groundwater quality. The total contribution of these four components is about 85–87%. The contribution of the first component is about 49–50% and has significant positive loadings of Ca²⁺, Mg²⁺, Na⁺, and Cl⁻ ions. The second, third, and fourth principal components have significant positive loadings of F⁻, NO₃ ⁻, SO₄ ²⁺, and HCO₃ ⁻ ions.     

Elastic properties and stability of coexisting 3T and 2M 1 phengite polytypes

The elastic properties of coexisting natural 3T and 2M ₁ phengite samples (Cima Pal, Sesia Zone; Val Savenca; Western Alps, Italy) with similar chemical compositions have been studied by room temperature–high pressure powder diffraction, using synchrotron radiation on the ID9A beam-line at ESRF (Grenoble, France). The P–V curves have been modelled by the Birch–Murnaghan model; a third-order expansion fitted to the experimental data yields for 3T and 2M ₁ K ₀=60.4(±0.7) GPa, K′=5.79(±0.11) at V ₀=703.8851 ų, and K ₀=57.3(±1.0) GPa, K′=6.97(±0.24) at V ₀=938.8815 ų, respectively. The relative stability of 3T vs. 2M ₁ has been explored as a function of pressure and temperature in terms of configuration and deformation contributions to the Gibbs energy, using the elastic properties determined here and other thermodynamic parameters from earlier investigations. The results presented agree with the hypothesis of stability of the 3T polytype in the high pressure regime.     

The hydro geochemical characterization of ground waters in Tunisian Chott’s region.

Tunisian Chott’s region is one of the most productive artesian basins in Tunisia. It is located in the southwestern part of the country, and its groundwater resources are developed for water supply and irrigation. The chemical composition of the water is strongly influenced by the interaction with the basinal sediments and by hydrologic characteristics such as the flow pattern and time of residence. The system is composed of an upper unconfined “Plio-Quaternary” aquifer with a varying thickness of 20–200 m, an intermediate confined/unconfined “Complex Terminal” aquifer about 100 m in thickness and a deeper “Continental Intercalaire” aquifer about 150 m in thickness separated by thick clay and marl layers. The dissolution of evaporites and carbonates explains part of the contained Na⁺, Ca²⁺, Mg²⁺, K⁺, SO₄²⁻ and Cl^-, but other processes, such carbonate precipitation, also contributes to the water composition. The stable isotope composition of waters establishes that the deep groundwater (depleted as compared to present corresponding local rainfall) is ancient water recharged probably during the late Pleistocene and the early Holocene periods. The relatively recent water in the Plio-Quaternary aquifer is composed of mixed waters resulting presumably from upward leakage from the deeper groundwater.     

Influence of hydrogeochemical processes on temporal changes in groundwater quality in a part of Nalgonda district, Andhra Pradesh, India

Geochemical processes that take place in the aquifer have played a major role in spatial and temporal variations of groundwater quality. This study was carried out with an objective of identifying the hydrogeochemical processes that controls the groundwater quality in a weathered hard rock aquifer in a part of Nalgonda district, Andhra Pradesh, India. Groundwater samples were collected from 45 wells once every 2 months from March 2008 to September 2009. Chemical parameters of groundwater such as groundwater level, EC and pH were measured insitu. The major ion concentrations such as Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, and SO₄ ²⁻ were analyzed using ion chromatograph. CO₃ ⁻ and HCO₃ ⁻ concentration was determined by acid–base titration. The abundance of major cation concentration in groundwater is as Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ while that of anions is HCO₃ ⁻ > SO₄ ²⁻ > Cl⁻ > CO₃ ⁻. Ca–HCO₃, Na–Cl, Ca–Na–HCO₃ and Ca–Mg–Cl are the dominant groundwater types in this area. Relation between temporal variation in groundwater level and saturation index of minerals reveals the evaporation process. The ion-exchange process controls the concentration of ions such as calcium, magnesium and sodium. The ionic ratio of Ca/Mg explains the contribution of calcite and dolomite to groundwater. In general, the geochemical processes and temporal variation of groundwater in this area are influenced by evaporation processes, ion exchange and dissolution of minerals.     

Statistical analysis of groundwater chemistry of the Tarim River lower reaches,Northwest China

This study applied a comprehensive quantitative approach including statistical, principal component and gray relation analyses to assess the groundwater chemistry based on monitored data from 840 samples collected from the lower reaches of Tarim River from 2000 to 2009. The main findings were: (1) there were six types of groundwater chemistry in the lower reaches of Tarim River where Cl·SO₄–Na·Mg was the dominant type accounting for 73.57% in all samples. There were linear relationships among chemical parameters, where TDS had significant multiple correlations with Na⁺, K⁺, Mg²⁺, Ca²⁺ and Cl⁻, respectively. (2) Three principal components (PC1, PC2 and PC3) were extracted. They included comprehensive measurements for salinization, alkalinity and pH, respectively. Most parameters showed decreasing trends during the period of 2000–2009, as well as the scores on PC1, because the concentrations of various chemical substances were diluted due to the uplift of the groundwater table in the lower reaches and the implementation of the ecological water delivery project in 2000. (3) HCO₃ ⁻ was the most sensitive chemical parameter affected by the groundwater table followed by TA, Mg²⁺, TH, SO₄²⁻, K⁺, TDS and TS. PC2 was the most sensitive principal component to the change of the groundwater table followed by PC1 and PC3.