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1.
Solute dynamics of meltwater of Gangotri glacier,Garhwal Himalaya,India   总被引：2，自引：0，他引：2  
The present study investigates solute dynamics of meltwater of Gangotri glacier system in terms of association of different chemical compounds with the geology of the area. In the meltwater, the presence of cations varied as c(Mg2+) > c(Ca2+) > c(Na+) > c(K+), while order of concentration of anions has been c(HCO3 −) > c(SO4 2−) > c(Cl−) > c(NO3 −) in years 2003 and 2004. The magnesium and calcium are found as the dominant cations along with bicarbonate and sulphate as dominant anions. The high ratios of c(Ca2+ + Mg2+)/total cations and c(Ca2+ + Mg2+)/c(Na+ + K+) indicate that the meltwater chemistry of the Gangotri glacier system catchment is mostly controlled by carbonate weathering. Attempts are made to develop rating curves for discharge and different cations. Sporadic rise in discharge without corresponding rise in concentration of most of cations is responsible for their loose correlation in a compound valley glacier like Gangotri glacier.  相似文献   

2.
This study focused on the chemical compositions of the rivers around Yulong Mountain, one of the typical monsoonal temperate glacier regions in China. Water samples were collected from Baishui, Sanshu and Geji hydrological stations around Mt. Yulong during rainy season. The chemical analyses indicated that the river water around Mt. Yulong was characterized by high pH values (>8.0) and EC values varied from 36.4 to 71.7 μS/cm with an average of 52.6 μS/cm. Ca2+ and Mg2+ were the dominant cations, together accounting for about 90 % of the total cations. HCO3 ?, followed by SO4 2?, was the dominant anion. Obvious variations had been perceived during the rainy season. River water chemistry in rainy season was mainly influenced by precipitation and rock weathering. The proportions of Na+, K+, Ca2+, Mg2+ and SO4 2? from precipitation in river water were 23.44, 9.66, 3.10, 17.81 and 10.48 %, respectively. In addition, the ion characteristics of river water were mainly influenced by carbonate weathering. The human activities should not be ignored though its influence was little.  相似文献   

3.
In this study, 92 groundwater samples were collected from the Attica region (Greece). Moreover, geographical information system database, geochemistry of groundwater samples and statistics were applied. These were used for studying the chemical parameters (NO3 −, Mg2+, Ca2+, Cl−, and Na+) and conductivity spatial distribution and for assessing their environmental impact. The ranges of chemical parameters of the water samples (in mg L−1) are: NO3 − 1–306, Mg2+ 2–293, Ca2+ 3–453, Cl− 5–1,988, and Na+ 4–475. The elevated concentrations of sodium, Mg2+, Cl− are attributed to natural contamination (seawater intrusion). On the other hand, NO3 − elevated concentrations are attributed to anthropogenic contamination (nitrate fertilizers). The results of the GIS analysis showed that elevated values of Na+, Mg2+, Cl− are related to shrubby and sparsely vegetated areas, while elevated values of NO3 − are connected with urban and agricultural areas.  相似文献   

4.
About 24 samples from hand-dug wells and boreholes were used to characterize concentrations of the main inorganic ions in a laterite environment under semi-arid climatic conditions in Tikaré, northern Burkina Faso. It was found that the most represented groundwater anion in groundwater was HCO3 − with average levels of 49.1 mg/L in the dry season and 33.5 mg/L in the rainy season. The most represented cation was Ca2+ with mean concentrations of 13.7 and 9.5 mg/L, respectively. The main processes, which influence the concentrations of these ions, are evaporation (dry season), local enrichment of recharge water in some elements, ion exchange and fixation by clay minerals (in case of K+). The best correlations were found between Ca2+ and Mg2+ (r = 0.95), Cl− and Na+ (r = 0.95), HCO3 − and Mg2+ (r = 0.89), HCO3 − and Ca2+ (r = 0.89), and between HCO3 − and Na+ (r = 0.80). In general, the quality of the groundwater from the different wells sampled for this study was good enough to serve as drinking water. However, there were situations where the quality of water was polluted because of anthropogenic contaminants (mainly NO3 −, K+, Cl−) from septic tanks and manure pits located in the vicinity of some sampled wells. In addition, application of fertilizers also represents a potential anthropogenic contamination source with regard to SO4 2−, Ca2+, K+, Na+, and Mg2+. Considering the high concentrations of SO4 2−, Mg2+, Na+ and Ca2+ found in one borehole, the deeper, fractured aquifers were also likely to be enriched in these elements. In contrast, the shallow aquifers are likely to be contaminated with Cl−, NO3 − and K+. Cl− and K+ seem to be locally present in recharge water as shown by their relative higher mean concentrations in the rainy season samples.  相似文献   

5.
Hydrogeochemical investigations are carried out in the different blocks of Burdwan district, West Bengal, India in order to assess its suitability for drinking as well as irrigation water purpose. Altogether 49 representative groundwater samples are collected from bore wells and the water chemistry of various ions viz. Ca2+, Mg2+, Na+, K+, CO32−, HCO3−, Cl−, SO42− and NO3− are carried out. The chemical relationships in Piper and Gibbs diagram suggest that the groundwater mainly belongs to alkali type and Cl− group and are controlled by rock dominance. A comparison of groundwater quality in relation to drinking water quality standards proves that most of the water samples are suitable for drinking water purpose whereas groundwater in some areas of the district has high salinity and high sodium adsorption ratio (SAR), indicating unsuitability for irrigation water and needs adequate drainage.  相似文献   

6.
In India, the quantity and quality of water available for irrigation is variable from place to place. Assessment of water quality has been carried out to determine the sources of dissolved ions in groundwater. Quality of groundwater in a 398 km2 Peddavanka watershed of a semi-arid region of south India is evaluated for its suitability for drinking and irrigation purposes. The middle Proterozoic Cuddapah Supergroup and Kurnool Group of rocks underlie most of the watershed. The main lithologic units consist chiefly of quartzite, limestone, and shale. Seventy-six water samples were collected from open-wells and bore-holes. Water samples were collected representative of the post-monsoon (winter) and pre-monsoon (summer). The quality assessment is made through the estimation of Ca2+, Mg2+, Na+, K+, Cl−, SO42−, CO32−, HCO3−, total hardness as CaCO3, TDS, EC, and pH. Based on these analyses, parameters like sodium adsorption ratio, % sodium, residual sodium carbonate, non-carbonate hardness, potential salinity, Kelley’s ratio, magnesium ratio, index of base exchange and permeability index were calculated. According to Gibbs‘ ratio samples in both seasons fall in the rock dominance field. The overall quality of waters in the study area in post-monsoon season is high for all constituents ruling out pollution from extraneous sources.  相似文献   

7.
This paper reports original data on the physical and chemical parameters of precipitation, river water and groundwater in and around the Longhushan Nature Reserve Area, located in southwestern China karst region, and provides a preliminary characterization of the hydrogeochemical process governing the natural water evolution in this area. The rainfall and river water mainly pertain to the HCO3 −–Ca2+ type and groundwater mainly pertain to the HCO3 −–Ca2+ + Mg2+ type. The HCO3 − was the predominant anion and Ca2+ was the predominant cation in all waters, respectively. The Gibbs Boomerang Envelop model, the 1:1 relationship of Na+ plus K+ versus Cl− as well as the 1:1 relationship of Ca2+ plus Mg2+ versus HCO3 − all suggested geochemical weathering is the main controlling factor for the geochemical compositions of this natural water. In surface water, the Mg2+/Ca2+ ratios ranged from 0.32 to 0.42 and the Na+/Ca2+ varied between 0.04 and 0.05. In the groundwater, the Mg2+/Ca2+ ratios varied from 0.37 to 0.62 and were below the ideal ratio of 0.8. These ratios showed the presence of a dolomite source. Analysis of trace elements showed that As, B, Pb, Se, Sr, V and Zn elements were abundant in the natural water during summer in this region.  相似文献   

8.
A water quality investigation was carried out in the Deoria district, Ganga plain, to assess the suitability of surface and groundwaters for domestic, agricultural, and industrial purposes. As much as 50 representative samples from river and groundwater were collected from various stations to monitor the water chemistry of various ions, comprising Ca2+, Mg2+, Na+, K+, HCO3 −, SO4 2−, NO3 −, Cl−, F−, and trace metals, such as Fe, Cu, Mn, Zn, Cd, and Pb. The results showed that electrical conductance (EC), total dissolved solids (TDS), HCO3 −, Mg2+, Na+, and total hardness (TH) are above the maximum desirable limit, and apart from Fe and Mn all other trace metals are within the maximum permissible limit for drinking water. The calculated values for sodium absorption ratio (SAR), salinity, residual sodium carbonate (RSC), and permeability index (PI) indicate well to permissible use of water for irrigation. High values of Na%, RSC, and Mg-hazard (MH) at some stations restrict its use for agricultural purpose. Anthropogenic activities affect the spatial variation of water quality. Economic and social developments of the study area is closely associated with the characteristics of the hydrological network.  相似文献   

9.
A long mining history and unscientific exploitation of Jharia coalfield caused many environmental problems including water resource depletion and contamination. A geochemical study of mine water in the Jharia coalfield has been undertaken to assess its quality and suitability for domestic, industrial and irrigation uses. For this purpose, 92 mine water samples collected from different mining areas of Jharia coalfield were analysed for pH, electrical conductivity (EC), major cations (Ca2+, Mg2+, Na+, K+), anions (F−, Cl−, HCO3 −, SO4 2−, NO3 −), dissolved silica (H4SiO4) and trace metals. The pH of the analysed mine water samples varied from 6.2 to 8.6, indicating mildly acidic to alkaline nature. Concentration of TDS varied from 437 to 1,593 mg L−1 and spatial differences in TDS values reflect the variation in lithology, surface activities and hydrological regime prevailing in the region. SO4 2− and HCO3 − are dominant in the anion and Mg2+ and Ca2+ in the cation chemistry of mine water. High concentrations of SO4 2− in the mine water of the area are attributed to the oxidative weathering of pyrites. Ca–Mg–SO4 and Ca–Mg–HCO3 are the dominant hydrochemical facies. The drinking water quality assessment indicates that number of mine water samples have high TDS, total hardness and SO4 2− concentrations and needs treatment before its utilization. Concentrations of some trace metals (Fe, Mn, Ni, Pb) were also found to be above the desirable levels recommended for drinking water. The mine water is good to permissible quality and suitable for irrigation in most cases. However, higher salinity, residual sodium carbonate and Mg-ratio restrict its suitability for irrigation at some sites.  相似文献   

10.
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.  相似文献   

11.
Urban and industrial development and the expansion of irrigated agriculture have led to a drastic increase in the exploitation of groundwater resources. The over-exploitation of coastal aquifers has caused a seawater intrusion and has seriously degraded groundwater quality. The shallow coastal aquifer of the Djeffara plain, southeastern Tunisia constitutes an example of water resource suffering an intensive and uncontrolled pumping for irrigation. Intensive exploitation of the aquifer and climate aridity caused a decrease in piezometric level and an increase in salinity. According to the hydrochemical data (Cl−, SO4 2−, NO3 −, HCO3 −, Br−, Ca2+, Mg2+, Na+, K+) and the stable isotope composition (oxygen-18 and deuterium content), groundwater salinization in the investigated system is caused by three main processes: (i) salts dissolution especially in the central part of Jerba and around Medenine plain; (ii) evaporation process; and (iii) seawater intrusion which caused the increase in salinity in the peninsula of El Jorf, in Jerba and in the North of Ben Gardane.  相似文献   

12.
We have investigated the geochemistry of supraglacial streams on the Canada Glacier, Taylor Valley, Antarctica during the 2001–2002 austral summer. Canada Glacier supraglacial streams represent the link between primary precipitation (i.e. glacier snow) and proglacial Lake Hoare. Canada Glacier supraglacial stream geochemistry is intermediate between glacier snow and proglacial stream geochemistry with average concentrations of 49.1 μeq L−1 Ca2+, 19.9 μeq L−1 SO42−, and 34.3 μeq L−1 HCO3−. Predominant west to east winds lead to a redistribution of readily soluble salts onto the glacier surface, which is reflected in the geochemistry of the supraglacial streams. Western Canada Glacier supraglacial streams have average SO42−:HCO3− equivalent ratios of 1.0, while eastern supraglacial streams average 0.5, suggesting more sulfate salts reach and dissolve in the western supraglacial streams. A graph of HCO3− versus Ca2+ for western and eastern supraglacial streams had slopes of 0.87 and 0.72, respectively with R2 values of 0.84 and 0.83. Low concentrations of reactive silicate (> 10 μmol L−1) in the supraglacial streams suggested that little to no silicate weathering occurred on the glacier surface with the exception of cryoconite holes (1000 μmol L−1). Therefore, the major geochemical weathering process occurring in the supraglacial streams is believed to be calcite dissolution. Proglacial stream, Anderson Creek, contains higher concentrations of major ions than supraglacial streams containing 5 times the Ca2+ and 10 times the SO42−. Canada Glacier proglacial streams also contain higher concentrations (16.6–30.6 μeq L−1) of reactive silicate than supraglacial streams. This suggests that the controls on glacier meltwater geochemistry switch from calcite and gypsum dissolution to both salt dissolution and silicate mineral weathering as the glacier meltwater evolves. Our chemical mass balance calculations indicate that of the total discharge into Lake Hoare, the final recipient of Canada Glacier meltwater, 81.9% is from direct glacier runoff and 19.1% is from proglacial Andersen Creek. Although during a typical, low melt ablation season Andersen Creek contributes over 40% of the water added to Lake Hoare, its overall chemical importance is diluted by the direct inputs from Canada Glacier during high flow years. Decadal warming events, such as the 2001–2002 austral summer produce supraglacial streams that are a major source of water to Lake Hoare.  相似文献   

13.
Water resources are a key factor, particularly for the planning of the sustainable regional development of agriculture, as well as for socio-economic development in general. A hydrochemical investigation was conducted in the Friuli Venezia Giulia aquifer systems to identify groundwater evolution, recharge and extent of pollution. Temperature, pH, electric conductivity, total dissolved solids, alkalinity, total hardness, SAR, Ca2+, Na+, K+, Mg2+, Cl−, SO4 2−, NO3 −, HCO3 − , water quality and type, saturation indexes and the environmental stable isotope δ18O were determined in 149 sampling stations. The pattern of geochemical and oxygen stable isotope variations suggests that the sub-surface groundwater (from phreatic and shallow confined aquifers) is being recharged by modern precipitations and local river infiltrations. Four hydrogeological provinces have been recognised and mapped in the Friuli Venezia Giulia Plain having similar geochemical signatures. These provinces have different degrees of vulnerability to contamination. The deep confined groundwater samples are significantly less impacted by surface activities; and it appears that these important water resources have very low recharge rates and would, therefore, be severely impacted by overabstraction.  相似文献   

14.
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.  相似文献   

15.
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.  相似文献   

16.
There are 19 sub-tropical temperate glaciers on Mount Yulong, the southernmost currently glacier-covered area in Eurasia, controlled by the south-western monsoon climate. In the summer of 1999, a firn core, 10.10 m long, extending down to glacier ice, was recovered in the accumulation area of the largest glacier, Baishui No.1. Periodic variations of climatic signals above 7.8 m depth were apparent, and net accumulation of four years was identified by the annual oscillations of isotopic and ionic composition. The boundaries of annual accumulation were confirmed by higher values of electrical conductivity and pH, and by dirty refreezing ice layers at the levels of summer surfaces. Calculated mean annual net accumulation from 1994/95 to 1997/98 was about 900 mm water equivalent. The amplitude of isotopic variations in the profile decreased with increasing depth, and isotopic homogenization occurred below 7.8 m as a result of meltwater percolation. Variations of δ18O above 7.8 m showed an approximate correlation with the winter climatic trend at Lijiang station, 25 km away. Concentrations of Ca2+ and Mg2+ were much higher than those of Na+ and K+, indicating that the air masses for precipitation were mainly from a continental source, and that the core material accumulated during the winter period. The close correspondence of Cl − and Na+ indicated their common origin. The decreasing trend of Na+/Cl− ratios with increasing depth further reflects a progressive homogenization process caused by meltwater percolation. Concentrations of SO42− and NO3− in the core are quite low. The mean annual net accumulation in the core and the estimated ablation indicate that the average annual precipitation above the glacier's equilibrium line is 2400–3100 mm, but this needs to be confirmed by long-term observation of mass balance.  相似文献   

17.
To properly interpret climatic and environmental information recorded in ice cores retrieved in the temperate-glacier region, the post-depositional processes, especially the meltwater percolation, need to be well understood. From late April to mid-July 2006, two successive snow pits, site P1 located at 4,750?m a.s.l. in the ablation zone and site P2 at 4,900?m a.s.l. in the accumulation area at Baishui Glacier No. 1, Mt. Yulong, southeastern Tibetan Plateau, were excavated. Changes in soluble ions (K+, Na+, Ca2+, Mg2+, Cl?, NO3 ? and SO4 2?) and stable oxygen isotopes (??18O) in the snow pits were investigated. Before the melting period, soluble ions and ??18O exhibit pronounced seasonal variations, with high values in the upper snow-firn layer (accumulated in winter/spring season) and relatively low values in the lower firn layer (deposited in summer season), reflecting seasonal shift in the Indian summer monsoon and winter westerlies over the region. During the melting period, most ions in the upper snow-firn layer were leached with different efficiencies. Although no significant changes in ion concentrations in the lower firn layer were observed, the impurities in the upper snow-firn layer could be eluted down into the lower firn layer. However, the pre-melting isotopic stratigraphy remained relatively unchanged during the observation period, indicating that the influence of meltwater percolation on stable isotopes is less significant than that on soluble ions. This understanding is crucial for the interpretation of ice-core records in the monsoon temperate-glacier region.  相似文献   

18.
The thermal expansion of gehlenite, Ca2Al[AlSiO7], (up to T=830 K), TbCaAl[Al2O7] (up to T=1,100 K) and SmCaAl[Al2O7] (up to T=1,024 K) has been determined. All compounds are of the melilite structure type with space group Thermal expansion data was obtained from in situ X-ray powder diffraction experiments in-house and at HASYLAB at the Deutsches Elektronen Synchrotron (DESY) in Hamburg (Germany). The thermal expansion coefficients for gehlenite were found to be: α1=7.2(4)×10−6 K−1+3.6(7)×10−9ΔT K−2 and α3=15.0(1)×10−6 K−1. For TbCaAl[Al2O7] the respective values are: α1=7.0(2)×10−6 K−1+2.0(2)×10−9ΔT K−2 and α3=8.5(2)×10−6 K−1+2.0(3)×10−9ΔT K−2, and the thermal expansion coefficients for SmCaAl[Al2O7] are: α1=6.9(2)× 10−6 K−1+1.7(2)×10−9ΔT K−2 and α3=9.344(5)×10−6 K−1. The expansion-mechanisms of the three compounds are explained in terms of structural trends obtained from Rietveld refinements of the crystal structures of the compounds against the powder diffraction patterns. No structural phase transitions have been observed. While gehlenite behaves like a ’proper’ layer structure, the aluminates show increased framework structure behaviour. This is most probably explained by stronger coulombic interactions between the tetrahedral conformation and the layer-bridging cations due to the coupled substitution (Ca2++Si4+)-(Ln 3++Al3+) in the melilite-type structure. Electronic Supplementary Material Supplementary material is available for this article at  相似文献   

19.
The thermal expansion of gehlenite, Ca2Al[AlSiO7], (up to T=830 K), TbCaAl[Al2O7] (up to T=1100 K) and SmCaAl[Al2O7] (up to T=1024 K) has been determined. All compounds are of the melilite structure type with space group Thermal expansion data were obtained from in situ X-ray powder diffraction experiments in-house and at HASYLAB at the Deutsches Elektronen Synchrotron (DESY) in Hamburg (Germany). The thermal expansion coefficients for gehlenite were found to be: α1=7.2(4)×10−6×K−1+3.6(7)×10−9ΔT×K−2 and α3=15.0(1)×10−6×K−1. For TbCaAl[Al2O7] the respective values are: α1=7.0(2)×10−6×K−1+2.0(2)×10−9ΔT×K−2 and α3=8.5(2)×10−6×K−1+2.0(3)×10−9ΔT×K−2, and the thermal expansion coefficients for SmCaAl[Al2O7] are: α1=6.9(2)×10−6×K−1+1.7(2)×10−9ΔT×K−2 and α3=9.344(5)×10−6×K−1. The expansion mechanisms of the three compounds are explained in terms of structural trends obtained from Rietveld refinements of the crystal structures of the compounds against the powder diffraction patterns. No structural phase transitions have been observed. While gehlenite behaves like a ‘proper’ layer structure, the aluminates show increased framework structure behavior. This is most probably explained by stronger coulombic interactions between the tetrahedral conformation and the layer-bridging cations due to the coupled substitution (Ca2++Si4+)–(Ln 3++Al3+) in the melilite-type structure. This article has been mistakenly published twice. The first and original version of it is available at .  相似文献   

20.
Present study is an effort to distinguish between the contributions of natural weathering and anthropogenic inputs towards high salinity and nutrient concentrations in the groundwater of National Capital Territory (NCT) Delhi, India. Apart from the source identification, the aquifer of entire territory has been characterized and mapped on the basis of salinity in space and water suitability with its depth. Major element chemistry, conventional graphical plots and specific ionic ratio of Na+/Cl−, SO4 2−/Cl−, Mg2+/Ca2+ and Ca2+/(HCO3 − + SO4 2−) are conjointly used to distinguish different salinization sources. Results suggest that leaching from the various unlined landfill sites and drains is the prime cause of NO3 − contamination while study area is highly affected with inland salinity which is geogenic in origin. The seasonal water level fluctuation and rising water level increases nutrients concentration in groundwater. Mixing with old saline sub-surface groundwater and dissolution of surface salts in the salt affected soil areas were identified as the principle processes controlling groundwater salinity through comparison of ionic ratio. Only minor increase of salinity is the result of evaporation effect and pollution inflows. The entire territory has characterized into four groups as fresh, freshening, near freshening and saline with respect to salinity in groundwater. The salinity mapping suggests that in general, for drinking needs, groundwater in the fresh, freshening and near freshening zone is suitable up to a depth of 45, 20 and 12 m, respectively, while the saline zones are unsuitable for any domestic use. In the consideration of increasing demand of drinking water in the area; present study is vital and recommends further isotopic investigations and highlights the need of immediate management action for landfill sites and unlined drains.  相似文献   

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