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1.
We evaluated sources and pathways of groundwater recharge for a heterogeneous alluvial aquifer beneath an agricultural field, based on multi‐level monitoring of hydrochemistry and environmental isotopes of a riverside groundwater system at Buyeo, Korea. Two distinct groundwater zones were identified with depth: (1) a shallow oxic groundwater zone, characterized by elevated concentrations of NO3? and (2) a deeper (>10–14 m from the ground surface) sub‐oxic groundwater zone with high concentrations of dissolved Fe, silica, and HCO3?, but little nitrate. The change of redox zones occurred at a depth where the aquifer sediments change from an upper sandy stratum to a silty stratum with mud caps. The δ18O and δ2H values of groundwater were also different between the two zones. Hydrochemical and δ18O? δ2H data of oxic groundwater are similar to those of soil water. This illustrates that recharge of oxic groundwater mainly occurs through direct infiltration of rain and irrigation water in the sandy soil area where vegetable cropping with abundant fertilizer use is predominant. Oxic groundwater is therefore severely contaminated by agrochemical pollutants such as nitrate. In contrast, deeper sub‐oxic groundwater contains only small amounts of dissolved oxygen (DO) and NO3?. The 3H contents and elevated silica concentrations in sub‐oxic groundwater indicate a somewhat longer mean residence time of groundwater within this part of the aquifer. Sub‐oxic groundwater was also characterized by higher δ18O and δ2H values and lower d‐excess values, indicating significant evaporation during recharge. We suggest that recharge of sub‐oxic groundwater occurs in the areas of paddy rice fields where standing irrigation and rain water are affected by strong evaporation, and that reducing conditions develop during subsequent sub‐surface infiltration. This study illustrates the existence of two groundwater bodies with different recharge processes within an alluvial aquifer. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

2.
Geochemical evaluation of the sources and movement of saline groundwater in coastal aquifers can aid in the initial mapping of the subsurface when geological information is unavailable. Chloride concentrations of groundwater in a coastal aquifer near San Diego, California, range from about 57 to 39,400 mg/L. On the basis of relative proportions of major‐ions, the chemical composition is classified as Na‐Ca‐Cl‐SO4, Na‐Cl, or Na‐Ca‐Cl type water. δ2H and δ18O values range from ?47.7‰ to ?12.8‰ and from ?7.0‰ to ?1.2‰, respectively. The isotopically depleted groundwater occurs in the deeper part of the coastal aquifer, and the isotopically enriched groundwater occurs in zones of sea water intrusion. 87Sr/86Sr ratios range from about 0.7050 to 0.7090, and differ between shallower and deeper flow paths in the coastal aquifer. 3H and 14C analyses indicate that most of the groundwater was recharged many thousands of years ago. The analysis of multiple chemical and isotopic tracers indicates that the sources and movement of saline groundwater in the San Diego coastal aquifer are dominated by: (1) recharge of local precipitation in relatively shallow parts of the flow system; (2) regional flow of recharge of higher‐elevation precipitation along deep flow paths that freshen a previously saline aquifer; and (3) intrusion of sea water that entered the aquifer primarily during premodern times. Two northwest‐to‐southeast trending sections show the spatial distribution of the different geochemical groups and suggest the subsurface in the coastal aquifer can be separated into two predominant hydrostratigraphic layers.  相似文献   

3.
Abstract

Chemical and isotopic data of groundwater of the Upper Cretaceous aquifer in the Orontes basin, Syria, have been used to assess the groundwater geochemistry, the origin of groundwater recharge and groundwater residence time. The chemical data indicate that dissolution of evaporite minerals is the main process controlling groundwater mineralization. The composition of stable isotopes δ18O and δ2H, together with 14C activity, reflect the existence of three different groups: (a) groundwater in the Coastal Mountains with δ18O of –6.65‰, quite similar to modern-day precipitation, and high 14C (>50 pmC); (b) groundwater in the unconfined aquifer of the Hama Uplift, which has δ18O of –5.52‰ and 14C near 20 pmC, and is recharged locally; and (c) groundwater from the confined aquifer of the Homs Depression, which is characterized by more depleted δ18O,, –8.01‰, and low 14C (<7 pmC), and might be recharged in the northern piedmont of the Anti-Lebanon Mountains. The distinctive isotope signatures of the latter two groups indicate different recharge elevations and palaeoclimatic effects. The low recharge rate of the groundwater in the Hama Uplift aquifer, and the even slower recharge rate in the Homs Depression aquifer, are reflected by groundwater 14C residence times of 5 and over 22 Ka BP, respectively.

Editor D. Koutsoyiannis

Citation Al-Charideh, A., 2013. Recharge and mineralization of groundwater of the Upper Cretaceous aquifer in Orontes basin (Syria). Hydrological Sciences Journal, 58 (2), 452–467.  相似文献   

4.
Traditional aquifer vulnerability techniques primarily rely on spatial property data for a region and are limited by their ability to directly or indirectly assess flow and transport processes occurring from the surface to depth within an aquifer system. The main objective of this study was to investigate groundwater vulnerability in terms of aquifer interconnectivity and flow dynamics. A combination of stable isotopes, groundwater age‐dating (radiocarbon), and geomorphic/geogenic spatial analyses was applied to a regional, highly developed coastal aquifer to explain the presence of nitrate at depth. The average δ13C value (?17.3 ± 2‰ VPDB, n = 27) is characteristic of groundwater originating from locally infiltrated precipitation through extensively cultivated soils. The average δ18O and δD values (?4.0 ± 0.1‰ VSMOW, n = 27; δD: ?19.3 ± 1‰ VSMOW, n = 27, respectively) are similar to precipitation water derived from maritime sources feeding the region's surface water and groundwater. Stable and radioactive isotopes reveal significant mixing between shallow and deep aquifers due to high velocities, hydraulic connection, and input of local recharge water to depths. Groundwater overdevelopment enhances deeper and faster modern water downward flux, amplifying aquifer vulnerability. Therefore, aquifer vulnerability is a variable, dependent on the type and degree of stress conditions experienced by a groundwater system as well as the geospatial properties at the near surface.  相似文献   

5.
Recharge areas of the Guarani Aquifer System (GAS) are particularly sensitive and vulnerable to climate variability; therefore, the understanding of infiltration mechanisms for aquifer recharge and surface run‐off generation represent a relevant issue for water resources management in the southeastern portion of the Brazilian territory, particularly in the Jacaré‐Pepira River watershed. The main purpose of this study is to understand the interactions between precipitation, surface water, and groundwater using stable isotopes during the strong 2014–2016 El Niño Southern Oscillation event. The large variation in the isotopic composition of precipitation (from ?9.26‰ to +0.02‰ for δ18O and from ?63.3‰ to +17.6‰ for δ2H), mainly associated with regional climatic features, was not reflected in the isotopic composition of surface water (from ?7.84‰ to ?5.83‰ for δ18O and from ?49.7‰ to +33.6‰ for δ2H), mainly due to the monthly sampling frequency, and groundwater (from ?7.04‰ to ?7.76‰ for δ18O and from ?49.5‰ to ?44.7‰ for δ2H), which exhibited less variation throughout the year. However, variations in deuterium excess (d‐excess) in groundwater and surface water suggest the occurrence of strong secondary evaporation during the infiltration process, corresponding with groundwater level recovery. Similar isotopic composition in groundwater and surface water, as well as the same temporal variations in d‐excess and line‐conditioned excess denote the strong connectivity between these two reservoirs during baseflow recession periods. Isotopic mass balance modelling and hydrograph separation estimate that the groundwater contribution varied between 70% and 80%, however, during peak flows, the isotopic mass balance tends to overestimate the groundwater contribution when compared with the other hydrograph separation methods. Our findings indicate that the application of isotopic mass balance methods for ungauged rivers draining large groundwater reservoirs, such as the GAS outcrop, could provide a powerful tool for hydrological studies in the future, helping in the identification of flow contributions to river discharge draining these areas.  相似文献   

6.
Groundwater supplies a significant proportion of water use in the United States and is critical to the maintenance of healthy ecosystems and environmental processes, thus characterizing aquifer hydrology is important to managing and preserving these resources. While groundwater isotopes provide insight into hydrologic and ecologic processes, their application is limited to where measurements exist. To help overcome this limitation, we used the random forest algorithm to develop a predictive model for shallow groundwater isotopes in the conterminous United States. Our model uses environmental variables (e.g. temperature, elevation, precipitation isotopes) as predictors. We used our model to develop the first shallow groundwater isoscape of δ2H and δ18O for the conterminous United States. We describe the patterns in groundwater isotopes using both observations and our modelled isoscape. We find that throughout much of the Eastern United States, groundwater isotopes are close to annual amount weighted precipitation, while groundwater isotopes are significantly depleted relative precipitation across much of the High Plains and Western United States. Furthermore, we compare the observations compiled for this study to isotopes of precipitation, which allows us to determine the relative recharge efficiency (i.e. ratio of groundwater recharge to precipitation) between seasons and the proportion of annual recharge that occurs in a given season. Our findings suggest that winter recharge is generally more efficient than summer recharge; however, the dominant recharge season is more varied as it is the product of both seasonal recharge efficiency and the seasonal timing of precipitation. Parts of the central United States have summer dominant recharge, which is likely the result of heavy summer precipitation/nocturnal summer precipitation. Interestingly, parts of coastal California appear to have summer dominant recharge, which we suggest could be due to recharge from fog-drip. Our results summarize spatial patterns in groundwater isotopes across the conterminous United States, provide insight into the hydrologic processes affecting shallow groundwater, and are valuable information for future ecologic and hydrologic studies.  相似文献   

7.
Characterization of stable isotope compositions (δ2H and δ18O) of surface water and groundwater in a catchment is critical for refining moisture sources and establishing modern isotope–elevation relationships for paleoelevation reconstructions. There is no consensus on the moisture sources of precipitation in the Yellow River source region during summer season. This study presents δ2H and δ18O data from 111 water samples collected from tributaries, mainstream, lakes, and groundwater across the Yellow River source region during summertime. Measured δ18O values of the tributaries range from ?13.5‰ to ?5.8‰ with an average of ?11.0‰. Measured δ18O values of the groundwater samples range from ?12.7‰ to ?10.5‰ with an average of ?11.9‰. The δ18O data of tributary waters display a northward increase of 1.66‰ per degree latitude. The δ18O data and d‐excess values imply that moisture sources of the Yellow River source region during summertime are mainly from the mixing of the Indian Summer Monsoon and the Westerlies, local water recycling, and subcloud evaporation. Analysis of tributary δ18O data from the Yellow River source region and streamwater and precipitation δ18O data from its surrounding areas leads to a best‐fit second‐order polynomial relationship between δ18O and elevation over a 4,600 m elevation range. A δ18O elevation gradient of ?1.6‰/km is also established using these data, and the gradient is in consistence with the δ18O elevation gradient of north and eastern plateau. Such relationships can be used for paleoelevation reconstructions in the Yellow River source region.  相似文献   

8.
Water resources are the most critical factors to ecology and society in arid basins, such as Kaidu River basin. Isotope technique was convenient to trace this process and reveal the influence from the environment. In this paper, we try to investigate the temporal and spatial characteristics in stable isotope (18O and 2H) of surface water and groundwater in Kaidu River. Through the water stable isotope composition measurement, spatial and temporal characteristics of deuterium (δ2H) and oxygen 18 (δ18O) were analysed. It is revealed that (1) comparing the stream water line with the groundwater line and local meteorological water line of Urumqi City, it is found that the contribution of precipitation to surface water in stream runoff is the main source, whereas the surface water is the main source of groundwater. Groundwater is mainly drainage of surface runoff in the river; (2) in the main stream of Kaidu River, the spatial variability of river water showed a ‘heavier‐lighter‐heavier’ change along with the main stream for δ18O, and temporal variability showed higher in summer and lower in winter; (3) the δ18O and δ2H values of groundwater samples ranged from ?11.36 to ?7.97‰ and ?73.45 to ?60.05‰, respectively. There is an increasing trend of isotopic values along the groundwater flow path. The seasonal fluctuation of δ18O is not clear in most samples. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

9.
A detailed study using environmental tracers such as chloride (Cl?) and tritium (3H), deuterium (2H) and oxygen (18O) isotopes was performed in an alluvial coastal aquifer in two contrasting environments (urban and agricultural). These environmental tracers combined with a high‐resolution multi‐level sampling approach were used to estimate groundwater residence time and recharge patterns and to validate the hydrogeochemical conceptual model already proposed in previous studies. δ18O and δ2H combined with Cl? data proved that the hypersaline groundwater present in the deepest part of the aquifer was sourced from the underlying hypersaline aquitard via an upward flux. Both chemical and isotopic data were employed to calibrate a density‐dependent numerical model based on SEAWAT 4.0, where 3H and Cl? were helped quantifying solutes transport within the modelled aquifer. Model results highlighted the differences on estimated recharge in the two contrasting environments, with the urban one exhibiting concentrated recharge because of preferential infiltration associated to the storm water drains network, while scarce local recharge characterized the agriculture setting. In the urban field site, is still possible to recognize at 9 m b.g.l. the input of the atmospheric anthropogenic 3H generated by testing of thermonuclear weapons, while in the agricultural field site, the 3H peak has been washed out at 6 m b.g.l. because the groundwater circulation is restricted only to the upper fresh part of the aquifer, drained by the reclamation system. The presented approach that combined high‐resolution field monitoring, environmental tracers and numerical modelling, resulted effective in validating the conceptual model of the aquifer salinization. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

10.
Abstract

The Complex Terminal (CT) and Plio-Quaternary (P-Q) aquifers in the Chott Gharsa plain in southwestern Tunisia have been investigated with the aid of chemical and isotopic tools. It has been demonstrated that groundwater from the CT is mainly of palaeo-origin, especially in the western and central parts of the plain where the most negative values of δ18O and δ2H were observed (between??8.1 and??7.6‰ for δ18O, and??60 to??57‰ for δ2H), combined with low concentrations of radiocarbon (6.8–7.5 pmc) and absence of tritium. Modern recharge of the aquifer occurs only in the eastern part of the system where younger waters were observed, as indicated by their stable isotope composition, relatively high radiocarbon content and presence of tritium. Groundwater from the P-Q multi-layer aquifer represents mixtures of ascending deep CT waters and modern water recharging the P-Q aquifer system. Isotope mass balance was used to quantify mixing proportions. The calculations showed that the contribution of deep CT groundwater to the P-Q aquifer system reaches about 75% in the western and central parts of the plain where the CT aquifer remains strongly artesian. This contribution decreases to about 15% towards the eastern part of the plain, as a consequence of significant reduction of artesian pressure in this area of the CT aquifer. Chemical data suggest that mineralization of the studied groundwater systems is controlled mainly by dissolution of evaporative minerals (halite, anhydrite and gypsum) and cation exchange reactions with the matrix, possibly enhanced by recent anthropogenic disturbance of the system caused by lowering of the water table due to heavy exploitation and return flow of saline irrigation water into the P-Q aquifer.

Editor D. Koutsoyiannis; Associate editor E. Custodio

Citation Yangui, H., Abidi, I., Zouari, K., and Rozanski, K., 2012. Deciphering groundwater flow between the Complex Terminal and Plio-Quaternary aquifers in Chott Gharsa plain (southwestern Tunisia) using isotopic and chemical tools. Hydrological Sciences Journal, 57 (5), 967–984.  相似文献   

11.
This paper reports the first results on δ18O and δ2H analysis of precipitations, cave drip waters, and groundwaters from sites in Mallorca (Balearic Islands, western Mediterranean), a key region for paleoclimate studies. Understanding the isotopic variability and the sources of moisture in modern climate systems is required to develop speleothem isotope‐based climate reconstructions. The stable isotopic composition of precipitation was analysed in samples collected between March 2012 and March 2013. The values are in the range reported by GNIP Palma station. Based on these results, the local meteoric water line (LMWL) δ2H = 7.9 (±0.3) δ18O + 10.8 (±2.5) was derived, with slightly lower slope than Global Meteoric Water Line. The results help tracking two main sources of air masses affecting the study sites: rain events with the highest δ18O values (> ?5‰) originate over the Mediterranean Sea, whereas the more depleted samples (< ?8‰) are sourced in the North Atlantic region. The back trajectory analysis and deuterium excess values, ranging from 0.4 to 18.4‰, further support our findings. To assess the isotopic variation across the island, water samples from eight caves were collected. The δ18O values range between ?6.9 and ?1.6‰. With one exception (Artà), the isotopic composition of waters in caves located along the coast (Drac, Vallgornera, Cala Varques, Tancada, and Son Sant Martí) indicates Mediterranean‐sourced moisture masses. By contrast, the drip water δ18O values for inland caves (Campanet, ses Rates Pinyades) or developed under a thick (>50 m) limestone cap (Artà) exhibit more negative values. A well‐homogenized aquifer supplied by rainwaters of both origins is clearly indicated by groundwater δ18O values, which show to be within 2.4‰ of the unweighted arithmetic mean of ?7.4‰. Although limited, the isotopic data presented here constitute the baseline for future studies using speleothem δ18O records for western Mediterranean paleoclimate reconstructions. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

12.
The deeply buried river‐connected Xishan karst aquifer (XKA) in western Beijing, China, has been suffering from diminishing recharge for several decades, which in turn leads to the disappearing of spring water outflows and continuously lowering of groundwater level in the area. Thus, it is important to correctly recognize the groundwater recharge and flow paths for the sustainable development of the XKA. To investigate these issues, the hydrochemical and isotopic compositions are analysed for both surface water and groundwater samples collected over an area of about 280 km2. Results show that (a) the river water is characterized by high Na contents; (b) the δ2H and δ18O values in the river water are distinctively higher than those of groundwater samples, after experiencing the long‐time evaporative enrichment in the upstream reservoir; (c) the Sr concentrations and 87Sr/86Sr ratios of groundwater clearly indicated the interaction between water and carbonate minerals but excluded the water–silicate interaction; and (d) the groundwater samples in the direct recharge area of the XKA have the lowest Na concentrations and the δ2H and δ18O values. Based on the large differences in the Na contents and 18O values of groundwater and surface water, a simple two‐component mixing model is developed for the study area and the fractions of the river water are estimated for groundwater samples. We find that the distribution pattern of the river water fractions in the XKA clearly shows a change of directions in the preferential flow path of the groundwater from its source zone to the discharge area. Overall, our results suggest that the recharged surface water can be a useful evidence for delineating the groundwater flow path in river‐connected karst aquifer. This study improves our understanding of the heterogeneity in karst groundwater systems.  相似文献   

13.
Karst aquifers are well known for their intricate stratigraphy and geologic structures, which make groundwater characterization challenging because flowpaths and recharge sources are complex and difficult to evaluate. Geochemical data, collected from ten closely spaced production wells constructed in two karst aquifers (Bangor Limestone (Mb) and Tuscumbia Limestone/Fort Payne Chert (Mftp)) in Trussville, north‐central Alabama, illustrate two distinctive groundwater end‐members: (1) higher major ion, dissolved inorganic carbon, conductivity, alkalinity concentrations, heavier δ13C ratios (max: −10.2 ± 0.2‰ Vienna Pee Dee Belemnite (PDB)) and lower residence times (mean: 19.5 ± 2 years, n = 2) of groundwater in the Mb aquifer and (2) lower constituent concentrations, lighter δ13C ratios (min: −13.4 ± 0.2‰ PDB) and longer residence times of groundwater (mean: 23.6 ± 2 years, n = 4) in the Mftp aquifer. Summer and fall data and the binary mixing model show aquifer inter‐flow mixing along solution fractures and confirms the distinctive groundwater geochemistry of the two aquifers. Lowering of static water levels over the summer (drawdown from 2 to 5.2 m) leads to more reducing groundwater conditions (lower Eh values) and slightly enriched δ18O and δD ratios during the fall [δ18O: −4.8 ± 0.1 to −5.4 ± 0.1‰ Vienna Standard Mean Oceanic Water (VSMOW), n = 9; δD: −25.4 ± 1 to −27.4 ± 1‰ VSMOW, n = 9] when compared with summer season samples (δ18O: −5.1 ± 0.1 to −5.7 ± 0.1‰ VSMOW, n = 11; δD: −25.0 ± 1 to −30.6 ± 1‰ VSMOW, n = 11). GIS analyses confirm the localized origin of recharge to the investigated aquifers. The combination of GIS, field parameters and geochemistry analyses can be successfully used to identify recharge sources, evaluate groundwater flow and transport pathways and to improve understanding of how groundwater withdrawals impact the sustainability and susceptibility to contamination of karst aquifers. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
Clay aquitards are semipermeable membranes that allow groundwater flow while retarding solute migration has been researched extensively but also subjected to much debate. At present, there is no evidence of whether the physical and chemical properties of clay soil and the isotopic composition of pore water affect the semipermeable membrane effect. In this study, we collected clay samples from drilling cores (30–90 m) in the Hengshui area located in the North China Plain (NCP), then extracted pore water using a high-pressure squeezing device. Vertical hydrochemical and isotopic profile variation trends for the pore water were revealed using hydrochemical (Cl−, Na+, Ca2+, K+, Mg2+, and SO42−) and stable isotopic measurements of H, O and Cl. The results showed that the hydrochemical clay interlayer pore water of the saline aquifer is Cl/SO4-Na/Mg type and the average total dissolved solids (TDS) are 10.17 g/L. However, the hydrochemical clay aquitard pore water is of the Cl/SO4-Na/Ca type with an average TDS of 1.90 g/L. The hydrochemical clay interlayer pore water of aquifer II is of Cl-Na/Ca type with an average TDS of 1.10 g/L. Our results showed that the water quality of the aquifer II is not affected by the upper part of the saline aquifer, thus the clay aquitard acts as a significant barrier to salt movement. A polarization layer concentrated in ions was formed between the upper part of the saline aquifer and the clay aquitard. The concentration polarization layer increases the salt-inhibition effect. H, O and Cl isotopic composition results showed significant fractionation. The pore water of aquifer II lacked heavy isotopes (2H, 18O, 37Cl), but had significant heavy isotope enrichment in the concentrated polarized layer (the δ2H value was −76‰, the δ18O value was −8.4‰, and the δ37Cl value was 1.59‰). Hyperfiltration thus played a significant role in isotope fractionation.  相似文献   

15.
We characterize the precipitation and groundwater in a mountainous (peaks slightly above 3000 m a.s.l.), semi‐arid river basin in SE Spain in terms of the isotopes 18O and 2H. This basin, with an extension of about 7000 km2, is an ideal site for such a study because fronts from the Atlantic and the Mediterranean converge here. Much of the land is farmed and irrigated both by groundwater and runoff water collected in reservoirs. A total of approximately 100 water samples from precipitation and 300 from groundwater have been analysed. To sample precipitation we set up a network of 39 stations at different altitudes (800–1700 m a.s.l.), with which we were able to collect the rain and snowfall from 29 separate events between July 2005 and April 2007 and take monthly samples during the periods of maximum recharge of the aquifers. To characterize the groundwater we set up a control network of 43 points (23 springs and 20 wells) to sample every 3 months the main aquifers and both the thermal and non‐thermal groundwater. We also sampled two shallow‐water sites (a reservoir and a river). The isotope composition of the precipitation forms a local meteoric water line (LMWL) characterized by the equation δD = 7·72δ18O + 9·90, with mean values for δ18O and δD of − 10·28‰ and − 69·33‰, respectively, and 12·9‰ for the d‐excess value. To correlate the isotope composition of the rainfall water with groundwater we calculated the weighted local meteoric water line (WLMWL), characterized by the equation δD = 7·40δ18O + 7·24, which takes into account the quantity of water precipitated during each event. These values of (dδD/dδ18O)< 8 and d‐excess (δD–8δ18O)< 10 in each curve bear witness to the ‘amount effect’, an effect which is more manifest between May and September, when the ground temperature is higher. Other effects noted in the basin were those of altitude and the continental influence. The isotopic compositions of the groundwater are represented by the equation δD = 4·79δ18O − 18·64. The groundwater is richer in heavy isotopes than the rainfall, with mean values of − 8·48‰ for δ18O and − 59·27‰ for δD. The isotope enrichment processes detected include a higher rate of evaporation from detrital aquifers than from carbonate ones, the effects of recharging aquifers from irrigation return flow and/or from reservoirs' leakage and enrichment in δ18O from thermal water. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

16.
Previous studies of the Dakota Aquifer in South Dakota attributed elevated groundwater sulfate concentrations to Madison Aquifer recharge in the Black Hills with subsequent chemical evolution prior to upward migration into the Dakota Aquifer. This study examines the plausibility of a Madison Aquifer origin for groundwater in northeastern Nebraska. Dakota Aquifer water samples were collected for major ion chemistry and isotopic analysis (18O, 2H, 3H, 14C, 13C, 34S, 18O-SO4, 87Sr, 37Cl). Results show that groundwater beneath the eastern, unconfined portion of the study area is distinctly different from groundwater sampled beneath the western, confined portion. In the east, groundwater is calcium-bicarbonate type, with δ18O values (−9.6 to −12.4) similar to local, modern precipitation (−7.4 to −10), and tritium values reflecting modern recharge. In the west, groundwater is calcium-sulfate type, having depleted δ18O values (−16 to −18) relative to local, modern precipitation, and 14C ages 32,000 to more than 47,000 years before present. Sulfate, δ18O, δ2H, δ34S, and δ18O-SO4 concentrations are similar to those found in Madison Aquifer groundwater in South Dakota. Thus, it is proposed that Madison Aquifer source water is also present within the Dakota Aquifer beneath northeastern Nebraska. A simple Darcy equation estimate of groundwater velocities and travel times using reported physical parameters from the Madison and Dakota Aquifers suggests such a migration is plausible. However, discrepancies between 14C and Darcy age estimates indicate that 14C ages may not accurately reflect aquifer residence time, due to mixtures of varying aged water.  相似文献   

17.
《水文科学杂志》2013,58(3):526-537
Abstract

The study of the Continental Intercalaire aquifer system of southern Tunisia, based on the interpretation of geochemical (major elements) and isotopic (18O, 2H, 13C and 14C) data, has aided the understanding of the hydrodynamics of this multi-layer aquifer system, which is greatly influenced by tectonics. The determination of the origin of groundwater salinization and the understanding of the hydrogeological and geochemical behaviour of this aquifer were achieved by studying the correlation between the major elements and total mineralization (TDS). By using isotopic tools, it was shown that the water of this aquifer has been recharged under cooler, palaeoclimatic conditions. The technique also made it possible to better understand the hydrodynamic functioning of the aquifer system: it showed that the relatively recent recharge of the aquifer has been by direct infiltration from carbonate and sandy outcrops of the Cretaceous and Miocene, respectively, located in the eastern and northeastern parts of the aquifer. The 18O content was used to calculate the altitude of recharge basins. The isotopic gradient defined in this study is ?0.5 δ18O ‰/100 m.  相似文献   

18.
A portable Wavelength Scanned‐Cavity Ring‐Down Spectrometer (Picarro L2120) fitted with a diffusion sampler (DS‐CRDS) was used for the first time to continuously measure δ18O and δ2H of stream water. The experiment took place during a storm event in a wet tropical agricultural catchment in north‐eastern Australia. At a temporal resolution of one minute, the DS‐CRDS measured 2160 δ18O and δ2H values continuously over a period of 36 h with a precision of ±0.08 and 0.5‰ for δ18O and δ2H, respectively. Four main advantages in using high temporal resolution stream δ18O and δ2H data during a storm event are highlighted from this study. First, they enabled us to separate components of the hydrograph, which was not possible using high temporal resolution electrical conductivity data that represented changes in solute transfers during the storm event rather than physical hydrological processes. The results from the hydrograph separation confirm fast groundwater contribution to the stream, with the first 5 h of increases in stream discharge comprising over 70% pre‐event water. Second, the high temporal resolution stream δ18O and δ2H data allowed us to detect a short‐lived reversal in stream isotopic values (δ18O increase by 0.4‰ over 9 min), which was observed immediately after the heavy rainfall period. Third, δ18O values were used to calculate a time lag of 20 min between the physical and chemical stream responses during the storm event. Finally, the hydrograph separation highlights the role of event waters in the runoff transfers of herbicides and nutrients from this heavily cultivated catchment to the Great Barrier Reef. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

19.
Graeme L. Scott 《Island Arc》2004,13(2):370-386
Abstract The influence of major active faults on rock alteration and stable isotope geochemistry is described for the Tongonan geothermal field, Leyte, the Philippines. In the Pliocene, acid alteration with characteristic iron enrichment (3 g/100 g) and calcium depletion (2 g/100 g) occurred along a Riedel shear fault in the Malitbog sector, and initial minor acid alteration also occurred along a similar shear in the Mahiao sector. Later, sodium metasomatism (5 g/100 g) coincided with the highest aquifer chloride (10 000 mg/kg) as a result of dissociation of saline magmatic fluids discharging through the reservoir rocks in the Upper Mahiao. The incursion of magmatic fluids (possibly δD 35‰, δ18O +7‰) set up a vigorous convection cell of meteoric water, which focused around low‐angle (L) shears centered in the Sambaloran sector. Meteoric water (δD ?35 to ?40‰, δ18O ?6 ± 1‰) depleted the reservoir in silica (6 g/100 g) and potassium (1–2 g/100 g). It also completely exchanged oxygen isotopes rapidly (within months) at high temperatures (300–400°C), and now does so continuously with fractured isotopically fresh or incompletely altered rock at small scales (centimeters or less) exposed by a 2 cm/year creep around the L shears to form a new component called geothermal water. Geothermal water mixes with meteoric water at lower temperatures (<300°C) to create the characteristic shift in δ18O of 6‰ at near constant δD (?35 ± 5‰). The 10‰ variation in δD is due to groundwater recharge derived from rain falling on steep terrain (5‰) and to enrichment of deuterium in boiling saline solutions (5‰); it is not due to two‐component mixing of meteoric with magmatic water. The low (～1) isotopic water/rock (W/R) ratios calculated from oxygen isotopes in previously published reports are meaningless, because the water contains four components (predominantly geothermal and meteoric water; <10% magmatic and rock water). W/R ratios of up to 1500 calculated from spring and rock chemistry are more realistic and, with a flow rate of approximately 50 L/s through a 30 km3 reservoir, can account for the estimated 3 My age of the system.  相似文献   

20.
ABSTRACT

This study aims to differentiate the potential recharge areas and flow mechanisms in the North-eastern Basin, Palestine. The results differentiate the recharge into three main groups. The first is related to springs and some of the deep wells close to the Anabta Anticline, through the Upper Aquifer (Turonian) formation, with depleted δ18O and δ2H. The second is through the Upper Cenomanian formation surrounding the Rujeib Monocline in the southeast, where the lineament of the Faria Fault plays an important role, with relatively enriched δ13CDIC values of about ?4‰ (VPDB). The third is the Jenin Sub-series, which shows higher δ13CDIC values, with enriched δ18O and δ2H and more saline content. The deep wells from the Nablus area in the south of the basin indicate low δ13CDIC values due to their proximity to freshwater infiltrating faults. The deep wells located to the northwest of the basin have δ13CDIC values from ?8 to ?9‰ (VPDB), with enriched δ18O signatures, indicating slow recharge through thick soil.  相似文献   

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