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1.
This study investigated the role of the solution composition on calcite precipitation induced by cyanobacteria. The precipitation of calcium carbonate was induced by addition of cyanobacterium cells Synechococcus strain PCC 7942 in two artificial solutions with a different composition at similar saturation states in respect to calcite. Ion‐selective electrodes for pH, Ca2+, and COequation/tex2gif-stack-1.gif monitored the experiments, and the morphology of precipitated crystals was analysed by scanning electron microscopy. The calcite precipitation was observed in all experiments after the addition of the cells. The composition of solution (the ratio of dissolved inorganic carbon to dissolved calcium) strongly influenced the calcite precipitation. Based on laboratory experiment results, a possible mechanism for precipitation induced by Synechococcus is proposed linking precipitation with the conditions near to cell walls rather than with the saturation conditions in the bulk solution.  相似文献   

2.
Calcite precipitation in spring 1988 in Lake Constance was studied by measuring physical, chemical and biological parameters in daily intervals. Algae triggering calcite precipitation in spring after an induction period of 1 day wereStephanodiscus hantzschii andChlorella spp. whereas no time lag concerning maximum saturation index was observed. Number and size distribution of crystals were determined by microscopical methods. Simple equations were given for estimation of the precipitated mass of calcite by approximating the volume of calcite crystals by simple geometric bodies and multiplying by crystal numbers. Particulate calcium was analysed after dissolving suspended matter and amounted to 90% of inorganic dry weight. Crystals were observed for the first time after dissolved phosphorus was no more detectable.  相似文献   

3.
To improve understanding of Ca isotope transport during water-rock interaction on the continents, we measured dissolved δ44Ca values along a 236 km flow path in the Madison aquifer, South Dakota, where fluids have chemically evolved according to dolomite and anhydrite dissolution, calcite precipitation, and Ca-for-Na ion-exchange over a timescale spanning ~ 15 kyr. We used a reactive transport model employing rate data constrained from major ion mass-balances to evaluate the extent to which calcite precipitation and ion-exchange fractionate Ca isotopes. Elevated δ44Ca values during the initial and final stages of water transport possibly result from calcite precipitation under supersaturated conditions and Ca-for-Na ion-exchange, respectively. However, for the bulk of the flow path, δ44Ca values evolve by mixing between anhydrite and dolomite dissolution, with no fractionation during calcite precipitation under saturated conditions. We attribute the absence of Ca isotope fractionation to the long timescale of water-rock interaction and slow rate of calcite precipitation, which have enabled fluids to chemically and isotopically equilibrate with calcite. We therefore conclude that the equilibrium Ca isotope fractionation factor between calcite and water (Δcal–w) is very close to zero. To the extent that the Madison aquifer typifies other groundwater systems where calcite slowly precipitates from solutions at or near chemical equilibrium, this study suggests that groundwater contributions to δ44Ca variability on the continents can be modeled according to simple mixing theory without invoking isotope discrimination.  相似文献   

4.
A theoretical model is derived in which isotopic fractionations can be calculated as a function of variations in dissolved carbonate species on CO2 degassing and calcite precipitation. This model is tested by application to a calcite-depositing spring system near Westerhof, Germany. In agreement with the model,13C of the dissolved carbonate species changes systematically along the flow path. The difference in δ values between the upper and lower part of the stream is about 1‰. The13C content of the precipitated calcite is different from that expected from the theoretical partitioning. The isotopic composition of the solid CaCO3 is similar to that of the dissolved carbonate, though in theory it should be isotopically heavier by about 2.4‰. The18O composition of dissolved carbonate and H2O is constant along the stream. Calculated calcite-water temperatures differ by about +5°C from the observed temperatures demonstrating isotopic disequilibrium between the water and precipitated solid. This is attributed to kinetic effects during CaCO3 deposition from a highly supersaturated solution, in which precipitation is faster than equilibration with respect to isotopes.Plant populations in the water have virtually no influence on CO2 degassing, calcite saturation and isotopic fractionation. Measurements of PCO2, SC and13C within a diurnal cycle demonstrate that metabolic effects are below the detection limit in a system with a high supply-rate of dissolved carbonate species. The observed variations are due to differences in CO2 degassing and calcite precipitation, caused by continuously changing hydrodynamic conditions and carbonate nucleation rates.  相似文献   

5.
This study is undertaken to understand how calcite precipitation and dissolution contributes to depth-related changes in porosity and permeability of gas-bearing sandstone reservoirs in the Kela 2 gas field of the Tarim Basin, Northwestern China. Sandstone samples and pore water samples are col-lected from well KL201 in the Tarim Basin. Vertical profiles of porosity, permeability, pore water chem-istry, and the relative volume abundance of calcite/dolomite are constructed from 3600 to 4000 m below the ground surface within major oil and gas reservoir rocks. Porosity and permeability values are in-versely correlated with the calcite abundance, indicating that calcite dissolution and precipitation may be controlling porosity and permeability of the reservoir rocks. Pore water chemistry exhibits a sys-tematic variation from the Na2SO4 type at the shallow depth (3600-3630 m), to the NaHCO3 type at the intermediate depth (3630―3695 m),and to the CaCl2 type at the greater depth (3728―3938 m). The geochemical factors that control the calcite solubility include pH, temperature, pressure, Ca2 concen-tration, the total inorganic carbon concentration (ΣCO2), and the type of pore water. Thermodynamic phase equilibrium and mass conservation laws are applied to calculate the calcite saturation state as a function of a few key parameters. The model calculation illustrates that the calcite solubility is strongly dependent on the chemical composition of pore water, mainly the concentration difference between the total dissolved inorganic carbon and dissolved calcium concentration (i.e., [ΣCO2] -[Ca2 ]). In the Na2SO4 water at the shallow depth, this index is close to 0, pore water is near the calcite solubility. Calcite does not dissolve or precipitate in significant quantities. In the NaHCO3 water at the intermedi-ate depth, this index is greater than 0, and pore water is supersaturated with respect to calcite. Massive calcite precipitation was observed at this depth interval and this intensive cementation is responsible for decreased porosity and permeability. In the CaCl2 water at the greater depth, pore water is un-der-saturated with respect to calcite, resulting in dissolution of calcite cements, as consistent with microscopic dissolution features of the samples from this depth interval. Calcite dissolution results in formation of high secondary porosity and permeability, and is responsible for the superior quality of the reservoir rocks at this depth interval. These results illustrate the importance of pore water chemis-try in controlling carbonate precipitation/dissolution, which in turn controls porosity and permeability of oil and gas reservoir rocks in major sedimentary basins.  相似文献   

6.
In the present paper, we describe the genetic mechanism that causes the precipitation of raft cones in caves. These speleothems usually form in a hydrothermal and epiphreatic environment where dripwater, dripping repeatedly over the same spot, sinks calcite rafts that were floating on the water surface of a cave pool. In particular, the paper describes a new variety of raft cones that were recently discovered in the Paradise Chamber of the Sima de la Higuera Cave (Murcia, south‐eastern Spain) based on their morphological and morphometric characteristics. These speleothems, dubbed ‘double‐tower cones’, have a notch in the middle and look like two cones, one superimposed over the other. The genetic mechanism that gave rise to the double‐tower cones must include an intermediate stage of rapid calcite raft precipitation, caused by a drop in the water table and by changes in cave ventilation leading to greater carbon dioxide (CO2) degassing and evaporation over the surface of the thermal lake where these speleothems formed. Calcite rafts were deposited in Paradise Chamber, completely covering many of the cones. Later, conditions for slower calcite raft precipitation were restored and some of the cones continued to grow at the same points. When the water table finally fell below the level of Paradise Chamber, the tower cones became exposed, as the incongruent deposits of calcite rafts were dissolved and mobilized to lower cave levels. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
Grotta di Ernesto is a cave site well suited for palaeoclimate studies because it contains annually laminated stalagmites and was monitored from 1995 to the end of 2008 for microclimate, hydrology and hydrochemistry. Long‐term monitoring highlighted that cave drips show three different hydrological responses to rainfall and infiltration: (1) fast seasonal drips in the upper part of the cave, which are mostly fed by fractures, (2) slow seasonal drips, located at mid‐depth in the cave characterized by mixed feeding and (3) slow drips, mostly located in the deeper gallery, which are fed by seepage flow from bulk porosity with a minor fracture‐fed component. The slow drips display daily cycles during spring thaw. Monitoring also indicated that drip waters are only slightly modified by degassing within the soil zone and aquifer and by prior calcite precipitation. Hydrochemical studies show a clear seasonality in calcite saturation index, which results in most cave calcite precipitation occurring during late autumn and winter with similar amounts of precipitated calcite on most stalagmites, regardless of drip rate (discharge) differences. Drip rate, and drip rate variability, therefore, has a minor role in modulating the amount of annual calcite formation. In contrast, drip rate, when associated with moderate reduction in calcite saturation index, clearly influences stalagmite morphology. Increasing drip rate yields a passage from candle‐, to cone‐ to dome‐shaped stalagmites. Very high drip rates feed speleothems with flowstone morphology. In summary, monitoring provides information about the karst aquifer and how hydrology influences those physical and chemical characteristics of speleothems which are commonly used as climate proxies. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Irrigation, urbanization, and drought pose challenges for the sustainable use of ground water in the central Couloir sud rifain, a major agricultural region in north-central Morocco, which includes the cities of Fès and Meknès. The central Couloir is underlain by unconfined and confined carbonate aquifers that have suffered declines in hydraulic head and reductions in spring flow in recent decades. Previous studies have surveyed ground water flow and water quality in wells and springs but have not comprehensively addressed the chemistry of the regional aquifer system. Using graphical techniques and saturation index calculations, we infer that major ion chemistry is controlled (1) in the surficial aquifer by cation exchange, calcite dissolution, mixing with deep ground water, and possibly calcite precipitation and (2) in the confined aquifer and warm springs by calcite dissolution, dolomite dissolution, mixing with water that has dissolved gypsum and halite, and calcite precipitation. Analyses of 2H and 18O indicate that shallow ground water is affected by evaporation during recharge (either of infiltrating precipitation or return flow), whereas deep ground water is sustained by meteoric recharge with little evaporation. Mechanisms of recharge and hydrochemical evolution are broadly consistent with those delineated for similar regional aquifer systems elsewhere in Morocco and in southern Spain.  相似文献   

9.
The precipitation of freshwater carbonates (tufa) along karstic rivers is enhanced by degassing of carbon dioxide (CO2) downstream of karstic springs. However, in most karstic springs CO2 degassing is not enough to force the precipitation of tufa sediments. Little is known about the role of dissolution of gypsum or dolomite in the hydrochemistry of these systems and how this affects the formation of tufa deposits. Here we present a monitoring study conducted over a year in Trabaque River (Spain). The river has typical karst hydrological dynamics with water sinking upstream and re‐emerging downstream of the canyon. Mixing of calcium–magnesium bicarbonate and calcium sulphate waters downstream of the sink enhances the dissolution of carbonates and potentially plays a positive role in the formation of tufa sediments. However, due to the common‐ion effect, dissolution of dolomite and/or gypsum causes precipitation of underground calcite cements as part of the incongruent dissolution of dolomite/dedolomitization process, which limits the precipitation of tufa sediments. Current precipitation of tufa is scant compared to previous Holocene tufa deposits, which likely precipitated from solutions with higher saturation indexes of calcite (SIcc values) than nowadays. Limited incongruent dissolution of dolomite/dedolomitization favours higher SIcc values. This circumstance occurs when waters with relatively high supersaturation of dolomite and low SO42? composition sink in the upper sector of the canyon. In such a scenario, the process of mixing waters enhances the exclusive dissolution of limestones, preventing the precipitation of calcite within the aquifer and favouring the increase of SIcc values downstream of the springs. Such conditions were recorded during periods of high water level of the aquifers and during floods. This research shows that the common‐ion effect caused by the dissolution of gypsum and/or dolomite rocks can limit [or favour] the precipitation of tufa sediments depending on the occurrence [or not] of incongruent dissolution of dolomite/dedolomitization. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

10.
The Feldberger Haussee, a highly eutrophic stratified hard-water lake located in the eastern part of Germany's Baltic lake district, was selected for a restoration programme combining external nutrient loading reduction and long-term biomanipulation. In 1980 the external phosphorus loading (1.8 g TP m−2 a−1) decreased by 90%, but water quality did not improve significantly within the following 6 years. In 1985 biomanipulation was initiated, with manual removal of cyprinid fish coupled with piscivore introductions as the principal measures. The expected changes in the pelagic community and improvements of water quality occurred after a delay of several years. Despite intensive manual removal of cyprinids and stocking of piscivores, standing stocks of cyprinid fish remained relatively high (130-260 kg ww ha−1) after some years of decline. Compared to the pre-biomanipulation period, mean seasonal (May-September) Daphnia spp. biomass roughly doubled (0.037 g C m−3vs. 0.084 g C m−3). However, the predominance of small (<1 mm) D. cucullata throughout the whole investigation period indicated that planktivory was still substantial. Paired observations between edible phytoplankton biomass and Daphnia spp. indicated that a significant decline in algal stocks would only occur if herbivorous biomass was above a certain threshold (0.2 g C m−3). Reduced external and internal loading in concert with pelagic calcite precipitation were most likely responsible for the decline in lake phosphorus concentrations, thereby substantially improving the water quality of Feldberger Haussee. Although this is not supported by quantitative evidence, we hypothesize that resource-related water quality improvements were caused by changes in the structure of the pelagic community leading to increased calcite precipitation. In agreement with the results of other investigations, we conclude that because stabilising mechanisms such as macrophyte growth were lacking in Feldberger Haussee, biomanipulation in stratified lakes may not be as successful as has been observed in shallow lakes. However, in hard-water lakes, calcite precipitation may act as another stabilising resource-related mechanism. Phosphorus associated with sedimenting calcite particles is insensitive to redox-conditions and may therefore not be re-mobilised from lake sediments even if hypolimnetic oxygen is depleted.  相似文献   

11.
The ecosystem dynamics in the vadose zone, the unsaturated layer between the surface and the groundwater table, was studied in five caves located in northwestern Romania. Hypogean and epigean copepod assemblages collected in drip water and in the associated pools were analyzed over a period of 12 and 7 months, respectively. The temporal variation of fauna in both habitats was related to a series of environmental parameters (pH, temperature, electrical conductivity, forest cover, precipitation, type of limestone, hydrographic basin, substrate and volume of the pools). Canonical Correspondence Analysis was used to explore the relationships. Over the year, total abundances in pools were much lower than the abundances observed in drips and showed steep raising values in December only. It is shown that forest cover might be one of the most important driving factor influencing the copepod diversity and abundance. Occurrence of epigean species underground was influenced by precipitation and drip rates. The occurrence of hypogean species was related to electrical conductivity, as an indicator of residence time of water in the vadose zone. Pools on limestone harbored a more diverse and abundant fauna than those with clay sediments. Pools with calcite precipitation were preferred by hypogean species.  相似文献   

12.
Annual growth rates and the ratio of dark to light-colored calcite within single annual laminae in three contemporaneously deposited Holocene speleothems from Grotta di Ernesto, an Alpine cave in northern Italy, respond to changes in surface temperature rather than precipitation. Based on monitoring of present-day calcite growth, and correlation with instrumental data for surface climatic conditions, we interpret a higher ratio of dark to light-colored calcite and the simultaneous thinning of annual laminae as indicative of colder-than-present winters. Such dark and thin laminae occur in those parts of the three stalagmites deposited from AD 1650 to 1713 and from AD 1798 to 1840, as reconstructed through lamina counting. These periods correspond to the well-known Maunder and Dalton Minima of solar activity. An 11-yr cyclicity in growth rate, coupled with reduced calcite deposition during the historic minima of solar activity, is indicative of a solar influence on lamina thickness. Spectral analysis of the lamina thickness data also suggests that the North Atlantic Oscillation variability influenced winter temperatures. Based on the present-day controls on cave calcite formation, we infer that high-frequency changes in solar activity modulated the seasonal duration of soil CO2 production.  相似文献   

13.
A calibration study of oxygen and hydrogen isotopic composition from precipitation and cave dripwater was conducted in west‐central Florida at Legend Cave during 2007–2008. This study was performed to better understand how modern precipitation patterns can be discerned through examination of cave dripwater and speleothem calcite for paleoclimate reconstruction. The ‘amount effect’ was shown to be a dominant control on the oxygen isotopic composition of precipitation for the study area. A meteoric water line with a slope of 6·7 suggests evaporative effects occur either during precipitation or subsequent hydrological processes. However, δ18O values of cave dripwater averaged near the mean annual amount‐weighted average of precipitation, suggesting that the isotopic composition of dripwater tracks the long‐term average of rainfall. An observed weak seasonal influence occurred in the d‐excess values, with summer precipitation being more enriched due to increased evaporative effects. Comparison of precipitation δ18O values to synoptic weather data shows the dominant amount effect influence occurs due to strong convective storms producing highly 18O‐depleted rainfall at greater amounts during the year. Constant δ18O values of the dripwater indicate that paleoclimate reconstructions using speleothems from this area would record changes in annual to interannual shifts in precipitation amount above the cave. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

14.
The response of a climate proxy against measured temperature, rainfall and atmospheric circulation patterns at sub-annual resolution is the ultimate test of proxy fidelity but very few data exist showing the level of correspondence between speleothem climate proxies and the instrumental climate record. Cave sites on the Gibraltar peninsula provide a unique opportunity to calibrate speleothem climate proxies with the longest known available precipitation isotopes and instrumental records. An actively growing speleothem sampled from New St. Michaels Cave in 2004 is composed of paired laminae consisting of light columnar calcite and a darker microsparitic calcite. Stable isotope analysis of samples micromilled in 100 μm steps at the equivalent of bi-monthly intervals reveals fabric-correlated annual cycles in carbon isotopes, oxygen isotopes and trace elements responding to seasonal changes in cave microclimate, hydrology and ventilation patterns. Calcite δ13C values reach a minimum in the light columnar fabric and evidence from trace element behaviour and cave monitoring indicates that this grows under cave ‘winter’ conditions of highest pCO2, whereas the dark microsparitic calcite, characterised by elevated δ13C and δ18O values grows under low ‘summer’ pCO2 conditions. Drip water δ13CDIC reaches a minimum in March–April, at which time the attenuated δ18O signal becomes most representative of winter precipitation. An age model based on cycle counting and the position of the 14C bomb carbon spike yields a precisely dated winter oxygen isotope proxy of cave seepage water for comparison with the GNIP and instrumental climate record for Gibraltar. The δ18O characteristics of calcite deposited from drip water representing winter precipitation for each year can be derived from the seasonally resolved record and allows reconstruction of the δ18O drip water representing winter precipitation for each year from 1951–2004. These data show an encouraging level of correspondence (r2 = 0.47) with the δ18O of rainfall falling each year between October and March and on a decadal scale the δ18O of reconstructed winter drip water mirrors secular change in mean winter temperatures.  相似文献   

15.
《水文科学杂志》2013,58(6):1230-1240
Abstract

This study aims to identify the hydrogeochemical processes influencing the high fluoride concentrations in groundwater of the Nairobi area, Kenya. For this purpose 16 groundwater samples were collected and analysed. Fluoride concentrations above the WHO standard are found in the downstream areas. The high F? concentrations are correlated with high sodium and pH and low Ca2+ concentrations. Weathering of sodium-rich alkaline igneous rocks causes a pH increase resulting in an increase in HCO3 ? and CO3 2- by dissolution of CO2. Groundwater becomes oversaturated compared to calcite and calcite precipitation occurs, leading to a decrease in Ca2+. This causes a sub-saturation with respect to fluorite and dissolution of fluorite increases the F? concentration. These reactions were modelled using the PHREEQC model and the results showed a good agreement with the measured groundwater quality, indicating that the proposed reactions are plausible for explaining the observed concentrations in groundwater.  相似文献   

16.
Affected by structural uplift,the Ordovician carbonate rockbed in the Tarim Basin,China,was exposed to dissolution and reformation of atmospheric precipitation many times,and formed a large quantity of karst caves serving as hydrocarbon reservoir.However,drilling in Tahe area showed that many large karst caves,small pores and fractures are filled by calcite,resulting in decrease in their reservoir ability.Calcite filled in the karst caves has very light oxygen isotopic composition and87Sr/86Sr ratio.Its 18OPDB ranges from 21.2‰to 13.3‰with the average of 16.3‰and its87Sr/86Sr ratio ranges from0.709561 to 0.710070 with the average of 0.709843.The isotope composition showed that calcite is related to atmospheric precipitation.Theoretic analyses indicated that the dissolving and filling actions of the precipitation on carbonate rocks are controlled by both thermodynamic and kinetic mechanisms.Among them,the thermodynamic factor determines that the precipitation during its flow from the earth surface downward plays important roles on carbonate rocks from dissolution to saturation,further sedimentation,and finally filling.In other words,the depth of the karstification development is not unrestricted,but limited by the precipitation beneath the earth surface.On the other hand,the kinetic factor controls the intensity,depth,and breadth of the karstification development,that is,the karstification is also affected by topographic,geomorphologic,climatic factors,the degree of fracture or fault,etc.Therefore,subject to their joint effects,the karstification of the precipitation on the Ordovician carbonate rocks occurs only within a certain depth(most about 200 m)under the unconformity surface,deeper than which carbonate minerals begin to sedimentate and fill the karst caves that were formed previously.  相似文献   

17.
The sediment budget of the small research catchment of Cal Parisa (Vallcebre, Eastern Pyrenees) was studied by hydrological monitoring and assessment of the erosion rates in the major sediment sources. This area is characterized by clayey mudrock prone to landsliding and badland erosion, but the catchment was selected in an area free of major badland features, as a representative of middle mountain regions where a system of terraces and drainage ditches had been built for agricultural use but is now abandoned. Streamwater chemistry is dominated by Ca2+ and HCO3− at concentrations close to calcite saturation. Total dissolved solids show dilution during runoff peaks and positive hysteresis loops that support a slow contribution of subsurface water. Relative dissolved ion concentrations are different for each event analysed. Particulate sediment yield is very low and represents only about 1 per cent of gross erosion in the catchment. Mineralogical analysis of suspended sediments shows an enrichment in calcite because of precipitation. Chemical analysis of suspended sediments, using common one-litre water samples, shows higher contents of Ca, P and Mn in transported sediment than in sediment source areas, attributed to the precipitation of calcite, and enrichment in organic particulate matter during events respectively for the two first elements, whereas enrichment in Mn remains uncertain. Solid matter yield is therefore clearly dominated by dissolved transport as a result of both high calcium bicarbonate concentrations in runoff waters and strong suspended sediment conveyance discontinuities. Land conservation structures are very effective because they are in good condition whereas the soil is covered by dense permanent vegetation. Nevertheless, this state is unstable because the network of drainage ditches needs maintenance; its spontaneous breakdown after abandonment may result in the rearrangement of the elementary stream network and gullying of old fields in hollows. © 1997 John Wiley & Sons, Ltd.  相似文献   

18.
Gottfried Proft   《Limnologica》2003,33(4):359-372
The CO2 content, air saturation and calcite equilibrium of the River Ilm and some of its tributaries were analysed. CO2 content was measured by degasing the CO2 from water. The CO2 level is a very sensitive indicator for a low pollution in oxygen saturated waters. Clean running waters have a CO2 content close to the air saturation of 0.1–0.3 mg C l−1. Ground water and springs are rich in CO2. Polluted waters are characterised by higher CO2 contents, also organic pollution can result in high values of CO2. Carbon dioxide concentration of streams and brooks is limited by re-aeration.

The headwater region (softwater) of the River Ilm is unsaturated, the hard water in the middle- and underflow is oversaturated. In summer and autumn high saturation could be found, but without autochthonous calcite precipitation like in hard water lakes.  相似文献   


19.
To understand the role played by microorganisms in the formation of cold seep carbonates, we conducted an integrated microbial, mineralogical and organic geochemical study of methane-related authigenic carbonate crusts formed on eastern Mediterranean mud volcanoes. We show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane. Combined lipid biomarker analysis and 16S rRNA gene surveys identified a highly diversified methane-consuming archaeal community possibly comprising novel species, implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation. Moreover, pore-water sulphate gradients produced by co-occurring methane-based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation. We propose that this may be the dominant mode of carbonate crust formation at cold seeps world-wide, in agreement with aquatic chemistry predictions and explaining carbonate mineralogy.  相似文献   

20.
《水文科学杂志》2013,58(6):1149-1162
Abstract

Groundwater quality problems have emerged in many geographical areas due to natural environmental processes and human intervention in the geosystems. Hydrogeochemical appraisal of fluoride contaminated groundwater in Mehsana District, Gujarat State, India is carried out by means of groundwater quality investigations together with X-ray diffraction analysis of soil samples in the delineated high fluoride areas. Results show that fluoride has negative relationships with calcium, whereas relationships with sodium, alkalinity and sulphate are positive. Results obtained from aqueous speciation modelling using PHREEQC reveal that the groundwater is undersaturated with fluorite and oversaturated with calcite. The factor analysis indicates that sodium plus potassium bicarbonate groundwater have high factor loading for fluoride, whereas that for calcium chloride and magnesium chloride groundwater is low. The plausible geochemical reactions in the study area are precipitation of calcite and dissolution of dolomite, carbon dioxide and sulphate minerals with ion exchange.  相似文献   

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