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1.
This study was based on the analysis of isotopic compositions of hydrogen and oxygen in samples from precipitation, groundwater and stream water. In addition, parts of groundwater samples were dated by carbon-14 and tritium. These data are integrated to provide other views of the hydrologic cycle in the Hsinchu-Miaoli groundwater district. The groundwater district is principally composed of Pleistocene and Holocene aquifers. The Pleistocene aquifers are highly deformed by folding and faults into small sub-districts with areas of only tens of square kilometers. These aquifers are exclusively recharged by local precipitation. The Holocene aquifers cover narrow creek valleys, only tens of meters in thickness. The local meteoric water line (LMWL), constructed from rainfall samples in the Hsinchu Science Park, is described by the equation δD=8.02δ18O+10.16, which agrees with the global meteoric water line. In addition, the precipitation isotopic compositions can be categorized into two distinct end members: typhoon type and monsoon type. The groundwater isotopic compositions are perfectly located on an LMWL and can be considered a mixture of precipitations. Based on the mass balance of isotopic compositions of oxygen and hydrogen, infiltration is more active in the rainy season with depleted isotopic compositions. The amount of infiltration during May–September is roughly estimated to comprise at least 55% of the whole year’s recharge. The isotopic compositions of stream water are expressed by a regression equation: δD=7.61δ18O+9.62, which is similar to the LMWL. Although precipitation isotopic compositions are depleted during summer time, the isotopic compositions contrarily show an enriched trend in the upstream area. This is explained by the opposite altitude effect on isotopic compositions for typhoon-related precipitations.  相似文献   

2.
Detailed hydrogeochemical and isotopic data of groundwaters from the Hammamet–Nabeul unconfined aquifer are used to provide a better understanding of the natural and anthropogenic processes that control the groundwater mineralization as well as the sources of different groundwater bodies. It has been demonstrated that groundwaters, which show Na–Cl and Ca–SO4–Cl water facies, are mainly influenced by the dissolution of evaporates, the dedolomitization and the cation-exchange process; and supplementary by anthropogenic process in relation with return flow of irrigation waters. The isotopic signatures permit to classify the studied groundwaters into two different groups. Non-evaporated groundwaters that are characterized by depleted δ 18O and δ 2H contents highlighting the importance of modern recharge at higher altitude. Evaporated groundwaters with enriched contents reflecting the significance infiltration of return flow irrigation waters. Tritium data in the studied groundwaters lend support to the existence of pre-1950 and post-1960 recharge. Carbon-14 activities in shallow wells that provide evidence to the large contamination by organic 14C corroborate the recent origin of the groundwaters in the study area.  相似文献   

3.
Major ion geochemistry and environmental isotopes were used to identify the origins and the mineralisation processes of groundwater flowing within the three aquifer levels of the multilayer system of the Gafsa-south mining district (Southwestern Tunisia). It has been demonstrated that groundwaters are characterised by a Ca–Mg–SO4 water type. Geochemical pattern is mainly controlled by the dissolution of halite, gypsum and/or anhydrite as well as by the incongruent dissolution of dolomite. δ18O and δ2H values are much lower than the isotopic signature of regional precipitation and fall close to the meteoric water lines, indicating that groundwaters have not been significantly affected by evaporation or mineral–water reactions. The distribution of stable and radiogenic isotopes (δ18O, δ2H, δ13C and 14C) within the aquifer levels suggests that the deep confined aquifer receives a significant modern recharge at higher altitudes, while, the shallow unconfined aquifer has been mainly recharged under cooler paleoclimatic condition, likely during Late Pleistocene and Early Holocene humid periods. However, waters from the intermediate confined/unconfined aquifer have composite isotopic signatures, highlighting that they are derived from a mixture of the two first end-members.  相似文献   

4.
Stable isotopes (δ18O, δ2H and 13C) and radioactivity (3H, 14C) have been used in conjunction with chemical data to evaluate the processes generating the chemical composition, reconstruct the origin of the water and groundwater residence time. The Aleppo basin is comprised of two main limestone aquifers: the first one is unconfined of Paleogene age and the second is confined of Upper Cretaceous age. The chemical data indicate that the dissolution of minerals and evaporation are the main processes controlling groundwater mineralization. The groundwater from the two aquifers is characterized by distinctive stable isotope signatures. This difference in water isotopes is interpreted in terms of difference origin and recharge period. Fresh and brackish shallow groundwater were mostly recharged during the Holocene period. The presence of 3H in several groundwater samples of this aquifer gives evidence that groundwater recharge is going on. Brackish water of the deep confined aquifer has depleted stable isotope composition and very low 14C activity that indicates recharge during the late Pleistocene cold period.  相似文献   

5.
Unplanned exploitation of groundwater constitutes emerging water-related threats to MayoTsanaga River Basin. Shallow groundwater from crystalline and detrital sediment aquifers, together with rain, dams, springs, and rivers were chemically and isotopically investigated to appraise its evolution, recharge source and mechanisms, flow direction, and age which were used to evaluate the groundwater susceptibility to contamination and the basin’s stage of salinization. The groundwater which is Ca–Na–HCO3 type is a chemically evolved equivalent of surface waters and rain water with Ca–Mg–Cl–SO4 chemistry. The monsoon rain recharged the groundwater preferentially at an average rate of 74 mm/year, while surface waters recharge upon evaporation. Altitude effect of rain and springs show a similar variation of −0.4‰ for δ18O/100 m, but the springs which were recharged at 452, 679, and 773 m asl show enrichment of δ18O through evaporation by 0.8‰ corresponding to 3% of water loss during recharge. The groundwater which shows both local and regional flow regimes gets older towards the basins` margin with coeval enrichment in F− and depletion in NO3 −. Incidentally, younger groundwaters are susceptible to anthropogenic contamination and older groundwaters are sinks of lithologenic fluoride. The basins salinization is still at an early stage.  相似文献   

6.
Hydro- and isotope geochemistry are used to refine groundwater conceptual models in two areas of central Italy (Acque Albule Basin and Velino River Valley) affected by extensional Quaternary tectonics, where deep and shallow groundwater flow systems are interacting. The role of geology, of recent deposits filling the plains and of main tectonic features controlling groundwater flowpaths and deep-seated fluids emergences are investigated and discussed. Environmental isotopes (2H and 18O) confirm recharge in the surrounding carbonate aquifers, and meteoric origin of both shallow and deep groundwater. Major ion chemistry indicates a mixing between shallow Ca-HCO3 groundwater from carbonate aquifers and deep Ca-HCO3-SO4 groundwater, characterised by higher salinity and temperature and high concentration in sulphates. Isotopic composition of dissolved sulphates (δ 34S and δ 18O) and dissolved inorganic carbon (δ 13C), henceforth indicated as DIC, are used to verify the presence of different sources of groundwater, and to validate the mixing model suggested by the major ion analyses. Sulphate isotope composition suggests a marine origin for the groundwater characterised by elevated sulphate concentration, whose source is present in the deep buried sequences. Carbon isotope composition confirms the role of a DIC source associated to CO2 degassing of a deep reservoir. Groundwater conceptual models are improved underlining the importance of Plio-Pleistocene sequences filling the tectonic depression. In the Acque Albule area, the travertine plateau represents a mixing stratified aquifer, where deep groundwater contribution is spread into the shallow aquifer. The alluvial–clastic–lacustrine leaky aquifer of Velino Valley enables a complete mixing of shallow and deep groundwater allowing spot-located discharge of deep groundwater along tectonic patterns and facilitating sulphate reduction in the lacustrine sediments, explaining locally the presence of H2S.  相似文献   

7.
The need for more agricultural or residential land has encouraged reclamation at the coastal areas of Korea since 1200 ad (approximately). The groundwaters of these reclaimed areas could be expected to reveal hydrogeochemical properties different from those of areas directly affected by seawater intrusion. The purpose of this study, therefore, was to examine the salinization of shallow groundwater in a coastal reclaimed area and to identify the effect of land reclamation on groundwater quality. Major cations and anions, iodide, total organic carbon, δD, δ 18O and δ 13C were measured to assist the hydrogeochemical analysis. Chloride, δD and δ 18O data clearly show that the Na–Cl type water results from mixing of groundwater with seawater. In particular, the δD and δ 18O of Ca+Mg–Cl+NO3 type groundwaters are close to the meteoric water line, but Na–Cl type waters enriched in chloride are 18O-enriched with respect to the meteoric water line. Meanwhile, carbon isotopic data and I/Cl ratios strongly suggest that there are various sources of salinity. The δ 13C values of Na–Cl type groundwaters are generally similar to those of Ca+Mg–Cl+NO3 type waters, which are depleted in 13C with respect to seawater. I/Cl ratios of Na–Cl type groundwater are 10–100 times higher than that of seawater. Because the reclamation has incorporated a large amount of organic matter, it provides optimum conditions for the occurrence of redox processes in the groundwater system. Therefore, the salinization of groundwater in the study area seems to be controlled not only by saltwater intrusion but also by other effects, such as those caused by residual salts and organic matter in the reclaimed sediments.  相似文献   

8.
The occurrence of fluoride in groundwaters can be influenced by many factors. In Korea, the fluoride-rich groundwaters are normally associated with rock types, especially granite and gneiss. In Gimcheon, high-fluoride groundwaters (up to a maximum of 2.15 mg/L) were observed with bimodal distribution of concentrations. The groundwater in this area showed relatively high concentrations of anthropogenic chemicals such as nitrate, chloride, and sulfate. Statistical analysis showed that fluoride is positively correlated with pH, alkalinity, sodium, and lithium, indicating that the interaction with granite is the main cause enriching its concentration. In Gimcheon, δ18O data of groundwater showed a negative correlation with nitrate and can be used as an indicator of groundwater age. The four samples of fluoride-rich groundwater were plotted in the light δD and δ18O region, showing that they were the result of long water–rock reaction. However, other groundwater with a low-fluoride concentration was evenly distributed throughout all δD and δ18O ranges and did not show a statistically significant correlation with nitrate, indicating possible mixing with another source of fluoride. Considering the influence from the surface on the geochemical characteristics of groundwater in this area, anthropogenic sources including phosphate fertilizer containing fluoride and pesticides may also have partly contributed to the concentrations of fluoride in the low-fluoride groundwater. The scattered distribution of fluoride-rich groundwater and the significant correlation with lithium suggest that pegmatite is the main rock type increasing fluoride concentration in this area.  相似文献   

9.
Changes in the climatic conditions during the Late Quaternary and Holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the Great Lakes region. Increased hydraulic gradients from melting of kilometer-thick Pleistocene ice sheets reorganized regional-scale groundwater flow in Paleozoic aquifers in underlying intracratonic basins. Here, we present new elemental and isotopic analyses of 134 groundwaters from Silurian-Devonian carbonate and overlying glacial drift aquifers, along the margins of the Illinois and Michigan basins, to evaluate the paleohydrology, age distribution, and geochemical evolution of confined aquifer systems. This study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the Midcontinent region, and extends into deeper portions of the Illinois and Michigan basins, focused on the freshwater-saline water mixing zones. In addition, the hydrogeochemical data from Silurian-Devonian aquifers were integrated with deeper basinal fluids, and brines in Upper Devonian black shales and underlying Cambrian-Ordovician aquifers to reveal a regionally extensive recharge system of Pleistocene-age waters in glaciated sedimentary basins. Elemental and isotope geochemistry of confined groundwaters in Silurian-Devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals, dissolution of halite and anhydrite, cation exchange, microbial processes, and mixing with basinal brines. Carbon isotope values of dissolved inorganic carbon (DIC) range from −10 to −2‰, 87Sr/86Sr ratios range from 0.7080 to 0.7090, and δ34S-SO4 values range from +10 to 30‰. A few waters have elevated δ13CDIC values (>15‰) from microbial methanogenesis in adjacent organic-rich Upper Devonian shales. Radiocarbon ages and δ18O and δD values of confined groundwaters indicate they originated as subglacial recharge beneath the Laurentide Ice Sheet (14-50 ka BP, −15 to −13‰ δ18O). These paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake-bed clays and/or shales. The presence of isotopically depleted waters in Paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional-scale groundwater flow. Modern groundwater flow in the Great Lakes region is primarily restricted to shallow unconfined glacial drift aquifers. Recharge waters in Silurian-Devonian and unconfined drift aquifers have δ18O values within the range of Holocene precipitation: −11 to −8‰ and −7 to −4.5‰ for northern Michigan and northern Indiana/Ohio, respectively. Carbon and Sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions (δ13CDIC = −14.7 to−11.1‰ and 87Sr/86Sr = 0.7080-0.7103). The distinct elemental and isotope geochemistry of Pleistocene- versus Holocene-age waters further confirms that surficial flow systems are out of contact with the deeper basinal-scale flow systems. These results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes, which are important for determining the sustainability of present-day water resources and stability of saline fluids in sedimentary basins.  相似文献   

10.
The 18O and 2H (HDO) compositions are summarized for sampled springs (n = 81) within the Elwha watershed (≈692 km2) on the northern Olympic Peninsula. Samples, collected during 2001–2009, of springs (n = 158), precipitation (n = 520), streams (n = 176), and firn (n = 3) assisted the determinations for meteoric composition of recharge waters. The local mean water line (LMWL) is defined as δ2H = 8.2δ18O − 9.3 for the watershed. Recharge history is surmised from groundwater ages ranging from 5 ± 3 years (apparent 85Kr) to 9,490 ± 420 14C cal years BP. About 56% of the springs were recharged over the last 1,000 years while 13% of springs were recharged over 5,000 years ago. Spring HDO values fluctuate between −11.8 to −15.6‰ δ18O and −90.9 to −119.4‰ δ2H. Deuterium excess values predominate around 4–6‰. The HDO proxy records from springs suggest a pronounced paleoclimate shift in air masses near 5,000 year BP on the Peninsula.  相似文献   

11.
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12.
The ionic and isotopic compositions (δD, δ18O, and 3H) of urban groundwaters have been monitored in Seoul to examine the water quality in relation to land-use. High tritium contents (6.1–12.0 TU) and the absence of spatial/seasonal change of O–H isotope data indicate that groundwaters are well mixed within aquifers with recently recharged waters of high contamination susceptibility. Statistical analyses show a spatial variation of major ions in relation to land-use type. The major ion concentrations tend to increase with anthropogenic contamination, due to the local pollutants recharge. The TDS concentration appears to be a useful contamination indicator, as it generally increases by the order of forested green zone (average 151 mg/l), agricultural area, residential area, traffic area, and industrialized area (average 585 mg/l). With the increased anthropogenic contamination, the groundwater chemistry changes from a Ca–HCO3 type toward a Ca–Cl(+NO3) type. The source and behavior of major ions are discussed and the hydrochemical backgrounds are proposed as the basis of a groundwater management plan.  相似文献   

13.
In the Djerid-Nefzaoua region, southern Tunisia, about 80% of agricultural and domestic water supply is provided by the complex terminal (CT) aquifer. However, 20% of this demand is provided by other hydraulically connected aquifers, namely the continental intercalaire (CI) and the Plio-Quaternary (PQ). Overexploitation of the CT aquifer for agricultural practices has contributed to the loss of the artesian condition and the decline of groundwater level which largely increased the downward leakage from the shallow PQ aquifer. Excess irrigation water concentrates at different rates in the irrigation channels and in the PQ aquifer itself. Then, it returns to the CT aquifer and mixes with water from the regional flow system, which contributes to the salinization of the CT groundwater. A geochemical and isotopic study had been undertaken over a 2-years period in order to investigate the origin of waters pumped from the CT aquifer with an emphasis on its hydraulic relationships with the underlying and the overlying CI and PQ aquifers. Geochemistry indicates that groundwater samples collected from different wells show an evolution of the water types from Na-Cl to Ca-SO4-Cl. Dissolution of halite, gypsum and anhydrite-bearing rocks is the main mechanism that leads to the salinization of the groundwater. Isotopic data indicate the old origin of all groundwater in the aquifer system. Mixing and evaporation effects characterizing the CT and the PQ aquifers were identified using δ2H and δ18O relationship and confirmed by the conjunction of δ2H with chloride concentration.  相似文献   

14.
Figeh watershed spring is one of the important groundwater aquifer, which is considered a major source for drinking waters of Damascus city and countryside. The origin identification and recharge estimates of groundwater are significant components of sustainable groundwater development in this Mountain karst aquifer of Figeh spring. During the period 2001–2009, monthly groundwater and precipitation samples were taken and the isotopic compositions of δ18O, δ2H, and chloride contents were analyzed to identify groundwater origins and to estimate recharge rates. The δ18O, δ2H of the groundwater show that the groundwater recharge is of meteoric origin. The chloride mass balance (CMB) method was used to quantify recharge rates of groundwater in the Mountain karst aquifer of Figeh spring. The recharge rate varies from 192 to 826 mm/year, which corresponds to 43 and 67% of the total annual rainfall. Recharge rates estimated by CMB were compared with values obtained from other methods and were found to be in good agreement. This study can be used to develop effective programs for groundwater management and development.  相似文献   

15.
Groundwater is of utmost significance to socio-economic development and ecological recovery for the Loess Plateau. However, studies regarding the mechanism governing groundwater recharge over this area appear to be inadequate. This study is to examine the spatio-temporal variations of δ2H and δ18O in precipitation and shallow groundwater. On the basis of this, the mechanisms governing shallow groundwater recharge were explored. Precipitation and groundwater were sampled monthly from May to October during the period 2004–2006 at 13 sites in the Chabagou Catchment (187 km2). In the Caopingxigou Experimental Watershed (0.1 km2), meteorological variables were observed and rainfall larger than 5 mm was sampled immediately after each rain event. Across the area, 90% of the precipitation occurred from May to September primarily in the form of heavy rains or rainstorms with great spatial variability. There were about 30 localized rains in each year. It was indicated that there existed notable seasonality and pronounced spatial variability in precipitation isotopic compositions. Contributing factors and indications of isotopic compositions, as well as their climatic indications such as monsoon intensities and mixing processes of water vapor, were investigated. The δ2H–δ18O relation of groundwater was found to be δ2H = 3.22 × δ18O − 38.1, deviating from the local meteoric water line δ2H = 7.57 × δ18O + 3.9. The range of δ values in groundwater is shrunken to be 15–21% of that in individual precipitations, and groundwater in the middle reaches shows a wider range of δ values. Isotopic results showed that groundwater originates from precipitation with hydrogen and oxygen isotopic compositions being −69 and −9.7‰, respectively, and most groundwater experiences serious evaporation and adequate mixing with old water during infiltration or percolation in the aerated zone. It was also founded that obvious fluctuations of isotopic compositions in groundwater mainly appear in the middle reaches especially at sites that are close to valleys, suggesting varying sources of groundwater from precipitation, precipitation runoff, isotopically enriched surface water and/or lateral recharge of adjacent groundwater.  相似文献   

16.
The groundwaters from Zhongxiang City, Hubei Province of central China, have high fluoride concentration up to 3.67 mg/L, and cases of dental fluorosis have been found in this region. To delineate the nature and extent of high fluoride groundwaters and to assess the major geochemical factors controlling the fluoride enrichment in groundwater, 14 groundwater samples and 5 Quaternary sediment samples were collected and their chemistry were determined in this study. Some water samples from fissured hard rock aquifers and Quaternary aquifers have high fluoride concentrations, whereas all karst water samples contain fluoride less than 1.5 mg/L due to their high Ca/Na ratios. For the high fluoride groundwaters in the fissured hard rocks, high HCO3 − concentration and alkaline condition favor dissolution of fluorite and anion exchange between OH− in groundwater and exchangeable F− in some fluoride-bearing minerals. For fluoride enrichment in groundwaters of Quaternary aquifers, high contents of fluoride in the aquifer sediments and evapotranspiration are important controls.  相似文献   

17.
Conjoint consideration of distribution of major, rare earth elements (REE) and Y (combined to REY) and of H, O, C, S, Sr isotopes reveals that four types of groundwater are distinguishable by their chemical composition presented by spider patterns. REY patterns indicate thermo-saline deep water and two types of shallow saline groundwaters. Presence of connate waters is not detectable. Sr isotope ratios distinguish three sources of Sr: fast and slow weathering of biotite and K-feldspar in Pleistocene sediments, respectively, and dissolution of limestones. δ13C(DIC) indicate dissolution of limestone under closed and open system conditions. Numerous samples show δ13C(DIC) > 13‰ which is probably caused by incongruent dissolution of calcite and dolomite. The brines from below 1,000 m represent mixtures of pre-Pleistocene seawater or its evaporation brines and infiltrated post-Pleistocene precipitation. The shallow waters represent mixtures of Pleistocene and Recent precipitation salinized by dissolution of evaporites or by mixing with ascending brines. The distribution of water types is independent on geologic units and lithologies. Even the Tertiary Rupelian aquiclude does not prevent salinization of the upper aquifer.  相似文献   

18.
An investigation was conducted in Beijing to identify the groundwater evolution and recharge in the quaternary aquifers. Water samples were collected from precipitation, rivers, wells, and springs for hydrochemical and isotopic measurements. The recharge and the origin of groundwater and its residence time were further studied. The groundwater in the upper aquifer is characterized by Ca-Mg-HCO3 type in the upstream area and Na-HCO3 type in the downstream area of the groundwater flow field. The groundwater in the lower aquifer is mainly characterized by Ca-Mg-HCO3 type in the upstream area and Ca-Na-Mg-HCO3 and Na-Ca-Mg-HCO3 type in the downstream area. The δD and δ18O in precipitation are linearly correlated, which is similar to WMWL. The δD and δ18O values of river, well and spring water are within the same ranges as those found in the alluvial fan zone, and lay slightly above or below LMWL. The δD and δ18O values have a decreasing trend generally following the precipitation → surface water → shallow groundwater → spring water → deep groundwater direction. There is evidence of enrichment of heavy isotopes in groundwater due to evaporation. Tritium values of unconfined groundwater give evidence for ongoing recharge in modern times with mean residence times <50 a. It shows a clear renewal evolution along the groundwater flow paths and represents modern recharge locally from precipitation and surface water to the shallow aquifers (<150 m). In contrast, according to 14C ages in the confined aquifers and residence time of groundwater flow lines, the deep groundwater is approximately or older than 10 ka, and was recharged during a period when the climate was wetter and colder mainly from the piedmont surrounding the plain. The groundwater exploitation is considered to be “mined unsustainably” because more water is withdrawn than it is replenished.  相似文献   

19.
Major element concentrations, stable (δ18O and δ2H) and radiogenic (3H, 14C) isotopes determined in groundwater provided useful initial tracers for understanding the processes that control groundwater mineralization and identifying recharge sources in semi-arid Cherichira basin (central Tunisia).Chemical data based on the chemistry of several major ions has revealed that the main sources of salinity in the groundwaters are related to the water–rock interaction such as the dissolution of evaporitic and carbonate minerals and some reactions with silicate and feldspar minerals.The stable isotope compositions provide evidence that groundwaters are derived from recent recharge. The δ18O and δ2H relationships implied rapid infiltration during recharge to both the Oligocene and Quaternary aquifers, with only limited evaporation occurring in the Quaternary aquifer.Chemical and isotopic signatures of the reservoir waters show large seasonal evolution and differ clearly from those of groundwaters.Tritium data support the existence of recent recharge in Quaternary groundwaters. But, the low tritium values in Oligocene groundwaters are justified by the existence of clay lenses which limit the infiltration of meteoric water in the unsaturated zone and prolong the groundwater residence time.Carbon-14 activities confirm that groundwaters are recharged from the surface runoff coming from precipitation.  相似文献   

20.
A comprehensive set of measurements of oxygen and hydrogen isotopic ratios in groundwaters as well as waters from rivers, lakes, hot springs etc. taken from a variety of locations in India has been carried out for the first time. Isotopically the most depleted samples occur in the high altitude precipitations in the Himalayas e.g. in the lakes of Bhutan and the source water of the Ganga. The shallow groundwater data display a continental effect where the heavy isotope content decreases with distance from the coast (about 4 to 6 per mil decrease in δ18O per 1000 km). The δ D and δ18O of these fresh waters are linearly related and an analysis of this relation vis-a-vis the meteoric water line shows the unambiguous effect of enrichment due to evaporation from soils.  相似文献   

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