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1.
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   

2.
A hydrochemical investigation was conducted in the Ejina Basin to identify the hydrochemical characteristics and the salinity of groundwater. The results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area. The ionic ration plot and saturation index (SI) calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area. Most of the stable isotope δ18O and δD compositions in the groundwater is a meteoric water feature, indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation. Based on radioactive isotope tritium (3H) analysis, the groundwater ages were approximately estimated in different aquifers. The groundwater age ranges from less than 5 years, between 5 years and 50 years, and more than 50 years. Within 1 km of the river water influence zone, the groundwater recharges from recent Heihe river water and the groundwater age is about less than 5 years in shallow aquifer. From 1 km to 10 km of the river water influence zone, the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer. The groundwater age is more than 50 years in deep confined aquifer.  相似文献   

3.
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   

4.
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   

5.
The characteristics of δD and δ18O in precipitation, groundwater and surface water have been used to understand the groundwater flow system in the Ordos Plateau, north-central China. The slope of the local meteoric water line (LMWL) is smaller than that of the global meteoric water line (GMWL), which signifies secondary evaporation during rainfall. The distribution of stable isotopes of precipitation is influenced by temperature and the amount of precipitation. The lake water is enriched isotopically due to evaporation and its isotopic composition is closely related to the source of recharge and location in the groundwater flow systems. River water is enriched isotopically, indicating that it suffers evaporation. The deep groundwater (more than 150?m) is depleted in heavy isotopes relative to the shallow groundwater (less than 150?m), suggesting that deep groundwater may have been recharged during the late Pleistocene and early Holocene, when the climate was wetter and colder than at present. All groundwater samples plot around the LMWL, implying groundwater is of meteoric origin. Shallow groundwater has undergone evaporation and the average evaporation loss is 53%. There are two recharge mechanisms: preferential flow, and the mixture of evaporated soil moisture and subsequent rain.  相似文献   

6.
Evolution of the shallow groundwater quality under saline intrusion in porous aquifer system has been studied with environmental isotopes and geochemistry in the Laizhou Bay area, China. Two campaigns of water sampling from various sources were carried out in spring and winter for environmental isotopic and chemical analyses. The origin of groundwater salinity from intrusion of both modern seawater and deep brine water was identified by analysing the correlations between 18O, D, T, Cl−, SO42− and electrical conductivity. The results indicate that the brine is originated from evaporating and concentrating of intruded seawater and its δD and δ18O are different from modern seawater but similar to those of mixture of seawater with fresh groundwater. It is hard to distinguish the salinity origin in this area by the δD–δ18O relationship alone. The relations between δ18O and conductivity, Cl− and SO42− have been used to identify the salinity origin due to the distinct difference in salinity between the brine and seawater, conjunctively with use of T. A threshold of T = 12 TU was adopted to identify the origin of saline groundwater.  相似文献   

7.
The Agadir-Essaouira area in the occidental High Atlas Mountains of Morocco is characterized by a semi-arid climate. The scarcity and quality of water resources, exacerbated by long drought periods, constitute a major problem for a sustainable development of this region. Groundwater resources of carbonate units within Jurassic and Cretaceous aquifers are requested for drinking and irrigation purposes. In this study, we collected 84 samples from wells, boreholes, springs, and rivers. Hydrochemical and isotopic data were used to examine the mineralization and origin of water, which control groundwater quality. The chemical composition of water seems to be controlled by water-rock interactions, such as dissolution of carbonates (calcite and dolomite), weathering of gypsum, as well as ion exchange processes, which explain the observed variability. Stable isotopes results show that groundwater from the mainly marly Cretaceous aquifer are submitted to an evaporation effect, while samples from the chiefly calcareous Jurassic aquifer indicate a meteoric origin, due to a rapid infiltration of recharge runoff through the karstic outcrops. The low values of δ18O and δ2H suggest a local recharge from areas with elevations ranging from 400 to 1200 m for the Cretaceous aquifer and from 800 to 1500 m for the Jurassic units.  相似文献   

8.
Assessing the seasonal variation of groundwater recharge is important for effective management of groundwater resources. Stable isotopes of oxygen and hydrogen were used to estimate the sources of groundwater and seasonal contributions of precipitation to groundwater recharge in Chih-Pen Creek basin of eastern Taiwan. Based on the isotopes of precipitation (n = 177), two different local meteoric water regression lines (LMWL) can be obtained for the different seasons: δD = 8.0618O + 10.08 for wet season precipitation (May through October) and δD = 8.65δ18O + 17.09 for dry season precipitation (November through April). The slope and intercept of regression line for wet season precipitation are virtually identical to the global meteoric water line (GMWL) of Craig (1961). In contrast to during dry season precipitation due to evaporation effect the intercept of 17.09 is much higher than of the GMWL of 10. The results show the stable isotopes compositions of precipitation decrease with increasing rainfall amount and air temperature, due to the amount effect of precipitation is pronounced. The amount effect is clearly but do not show the temperature effect from January to December 2007. Using a mass-balance equation, a comparison of deuterium excess or d values of precipitation and groundwater indicates the groundwater consist of 76% wet season precipitation and 24% dry season precipitation, representing a distinct seasonal variation of groundwater recharge in study area. About 79% of the groundwater is recharged from the river water of the mountain watershed and 21% is from the rain that falls on the basin.  相似文献   

9.
Isotopes of deuterium and oxygen-18 in thermal groundwater in China   总被引：1，自引：0，他引：1  
Compositions of deuterium and 18O isotopes of 90 representative samples indicate that thermal groundwater in most parts of China is meteoric in origin. Latitude, altitude, and continent effects have significant bearing on the values of δD and δ18O of the hot water samples. Oxygen-18 shift is not significant in most of the thermal groundwater, especially the hot water of low-to-moderate temperature. Slight oxygen-18 shift is only found in some hot springs of high temperature in Tibet and western Yunnan and in thermal groundwater of low-to-moderate temperature in the deep-seated carbonate aquifers in the northern North China Plain (including the Tianjin area). Near-surface boiling may causes the shift of the former and the latter may be attributed to exchange of oxygen-18 between water and carbonates in the geothermal systems of taphrogenic basin-type. Hot springs in Tibet and western Sichuan have very low contents of δD and δ18O, possibly due to recharge of precipitation and snow-melting water of extremely depleted δD and δ18O values at high latitudes of several thousands of meters.  相似文献   

10.
Chemical compositions and stable isotope ratios of water and sulphate were used to characterise sources and processes responsible for elevated concentrations of sulphate and other constituents in groundwater from aquifers at Colima State along Mexico’s Pacific Coast. The δ18O and δ2H values of the groundwater were similar to those of precipitation indicating a meteoric origin, and recharge processes are relatively uniform in large parts of the study area with only slight local evaporation effects. δ34Ssulphate and δ18Osulphate analyses indicated that high sulphate concentrations of up to 1,480 mg/l are mainly due to dissolution of evaporites and volcanic exhalations. Chloride is largely related to sources other than seawater. The Marabasco sub basin is affected by anthropogenic contamination through manganese and iron ore mining activities. The obtained knowledge regarding sources and areas of contamination will be essential for the development and design of a water quality monitoring program in the study area.  相似文献   

11.
High water demand for domestic use in Douala with over 3 million inhabitants is met mainly by shallow groundwater. Field measurements and water sampling in January 2015 were carried out to examine the major controls on the groundwater composition and spatial view of ions in the water, timing of recharge and link between the recharge process and quality of the water. Fifty-two water samples were analysed for major ions and stable hydrogen and oxygen isotopes. Low pH values (3.61–6.92) in the groundwater indicated an acidic aquifer; thus, prone to acidification. The dominant water type was Na–Cl. Nitrate, which exceeded the WHO guide value of 50 mg/l in 22% of the groundwater, poses a health problem. Mass ratios of Cl?/Br? in the water ranged from 54 to 3249 and scattered mostly along the mixing lines between dilute waters, septic-tank effluent and domestic sewage. A majority of the samples, especially the high NO3 ? shallow wells, clustered around the septic-tank effluent-end-member indicating high contamination by seepage from pit latrines; hence, vulnerable to pollution. Stable isotopes in the groundwater indicated its meteoric origin and rapid infiltration after rainfall. The δ18O values showed narrow ranges and overlaps in rivers, springs, open wells and boreholes. These observations depict hydraulic connectivity, good water mixing and a homogeneous aquifer system mainly receiving local direct uniform areal recharge from rainfall. The rapid and diffused recharge favours the leaching of effluent from the pit toilets into the aquifer; hence, the high NO3 ? and Cl? in shallow wells. Silicate weathering, ion exchange and leaching of waste from pit toilets are the dominant controls on the groundwater chemistry. Drilling of deep boreholes is highly recommended for good-quality water supply. However, due the hydraulic connection to the shallow aquifer, geochemical modelling of future effects of such an exploitation of the deeper aquifer should support groundwater management and be ahead of the field actions.  相似文献   

12.
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   

13.
The present work was conducted in the Sinai Peninsula (1) to identify the recharge and flow characteristics and to evaluate the continuity of the Lower Cretaceous Nubian Sandstone aquifer; and (2) to provide information for the aquifer's rational appraisal. Isotopic and hydrochemical compositions combined with the geological and hydrogeological settings were used for this purpose. A considerable depletion in isotopic content (oxygen-18 and deuterium) and low d-excess values exist in the studied groundwater, reflecting the contribution of old meteoric water that recharged the aquifer in pluvial times. Modern recharge also occurs from precipitation that falls on the aquifer outcrops. The wide scatter of the data points around the two meteoric lines, the global meteoric water line (GMWL) and Mediterranean meteoric water line (MMWL), in the δ18O–δD diagram indicates considerable variation in recharge conditions (amount, altitude, temperature, air masses, distances from catchment, overland flow, etc.). The isotopic composition in the El-Bruk area is minimum (18O=–9.53‰), very close to the average value of the Western Desert Nubian Sandstone (18O=–10‰), where the local structural and lithologic conditions retard groundwater flow and the main bulk of water becomes noncyclic. The continuity of the aquifer in northern and central Sinai is evidenced by the isotopic similarity between samples taken from above and below the central Sinai Ragabet El-Naam fault, the distribution of potentiometric head, and hydrogeological cross sections. The combination of isotopic composition in terms of 18O and chemical composition in terms of TDS and salt contents is the basis for separating the studied groundwater into groups that reflect the recharge sources and isotopic and chemical modifications during flow. Electronic Publication  相似文献   

14.
We investigated major ions, stable isotopes, and radiocarbon dates in a Quaternary aquifer in semi-arid northwestern China to gain insights into groundwater recharge and evolution. Most deep and shallow groundwater in the Helan Mountains was fresh, with total dissolved solids <1,000 mg L?1 and Cl? <250 mg L?1. The relationships of major ions with Cl? suggest strong dissolution of evaporites. However, dissolution of carbonates, albite weathering, and ion exchange are also the major groundwater process in Jilantai basin. The shallow desert groundwater is enriched in δ18O and intercepts the local meteoric water line at δ18O = ?13.4 ‰, indicating that direct infiltration is a minor recharge source. The isotope compositions in intermediate confined aquifers resemble those of shallow unconfined groundwater, revealing that upward recharge from intermediate formations is a major source of shallow groundwater in the plains and desert. The estimated residence time of 10.0 kyr at one desert site, indicating that some replenishment of desert aquifers occurred in the late Pleistocene and early Holocene with a wetter and colder climate than at present.  相似文献   

15.
The hydrodynamic groundwater data and stable isotopes of water have been used jointly for better understanding of upward leakage and mixing processes in the Djerid aquifer system (southwestern Tunisia). The aquifer system is composed of the upper unconfined Plio-Quaternary (PQ) aquifer, the intermediate (semi-)confined Complex Terminal (CT) aquifer and the deeper confined Continental Intercalaire (CI) aquifer. A total of 41 groundwater samples from the CT and PQ aquifers were collected during June 2001. The stable isotope composition of waters establishes that the CT deep groundwater (depleted as compared to present Nefta local rainfall) is ancient water recharged during late Quaternary time. The relatively recent water in the shallow PQ aquifer is composed of mixed water resulting from upward leakage and sporadic meteoric recharge. In order to characterize the meteoric input signal for PQ in the study area, rainfall water samples were collected during 4 years (2000–2003) at the Nefta meteorological station. Weighted mean values of isotopic contents with respect to rainfall amounts have been computed. Despite the short collection period in the study area, results agree with those found in Beni Abbes (southwestern Algerian Sahara) by Fontes on 9 years of rainfall surveillance. Stable isotopic relationships provide clear evidence of shallow PQ aquifer replenishment by deep CT groundwater. The 18O/upward leakage rate allowed the identification of distinctive PQ waters related to CT aquifer configuration (confined in the western part of the study area, semi-permeable in the eastern part). These trends were confirmed by the relation 18O/TDS. The isotope balance model indicated a contribution of up to 75% of the deep CT groundwater to the upper PQ aquifer in the western study area, between Nefta and Hazoua.  相似文献   

16.
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   

17.
The negative correlation between values δD and δ18O and concentrations of dissolved silicon in nitrogen hot springs is ascertained, which attests to the directed alteration of their hydroisotopic composition towards being depleted in heavy isotopes during interaction in the water-rock system. This fact can be allowed for the cases of the lighter isotopic composition of the hot springs of meteogenic origin relative to that of local atmospheric precipitation. The shifts in points of isotopic composition of hot springs from the global meteoric water line can be caused by alterations in either oxygen or hydrogen composition.  相似文献   

18.
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19.
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.  相似文献   

20.
Stable isotopes (C, O, S) and mineralogical studies of the world-class amethyst-geode deposits of the Los Catalanes gemological district, Uruguay, constrain processes operative during mineral deposition. The mineralized basaltic andesites from the Cretaceous Paraná volcanic province are intensely altered to zeolites (clinoptilolite) and clay minerals. Variations in the δ18O values of silica minerals in geodes (chalcedony, quartz, and amethyst) are much larger and the values generally somewhat lower (21.2–31.5‰) in the Uruguayan deposits than in the Ametista do Sul area of southern Brazil. The range of δ34S values (−15.0 to −0.3‰) of altered basaltic rocks requires (in addition to sulfur of magmatic origin) the involvement of 34S-depleted sedimentary sulfur from bacterial sulfate reduction. The results delimit the mineralizing processes to a post-eruption environment characterized by low temperature and strong interaction of the lava flows with meteoric water.  相似文献   

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