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1.
Investigations in the Jiaozuo coal-mining district (China) aim to link water-inrush aquifers with the sources of groundwater recharge. Concentrations of TDS, HCO 3 – , Cl– and Na+ in the groundwater samples gradually decrease with increasing depth; in contrast, the factor 1 value of the Q-mode analysis gradually increases, which indicates that the deep groundwater may upflow, recharging the aquifers near the faulted zone. Some groundwater samples (above the local meteoric water line and ‘evaporation line 1’) may originate from recharge by infiltrating local rainfall. Spring and river samples are symmetrically distributed on the regression line of the Ordovician and Carboniferous limestone aquifer groundwater (δ2H?=?3.76?×?δ18O?–?31.77) and may, therefore, originate from groundwater recharge in the northern Taihang mountains. This mechanism is supported by the observation that groundwater levels change with rainfall. According to radiocarbon residence-time estimates, two groundwater sample sites may have been recharged during the late glacial stage.  相似文献   

2.
Groundwater recharge is a key factor in water-balance studies, especially in (semi-)arid areas. In this study, multiple methods were used to estimate groundwater recharge in the Ordos Plateau (China), including reference to water-table fluctuation, Darcy’s law and the water budget. The mean annual recharge rates found were: water-table-fluctuation method (46??09?mm/yr); saturated-zone Darcian method (17??4?mm/yr); and water-budget method (21??09?mm/yr). Generally, groundwater-recharge rates are higher in the eastern part of the plateau where the land surface is covered by permeable sand that is favorable for infiltration. Along with results from previous studies using the empirical method, the chloride-mass-balance method, the unsaturated-zone Darcian method and the hydrograph-separation method, groundwater recharge rates were compared. There is no one method that would consistently produce the largest or smallest estimate of annual recharge for all groundwater systems. The largest recharge estimates were usually determined using the unsaturated-zone Darcian method and the smallest estimates were usually determined using the chloride-mass-balance method. Comparison of multiple methods is found to be valuable for determining the range of plausible recharge rates and for highlighting the uncertainty of the estimates.  相似文献   

3.
Priebe  E. H.  Hamilton  S. M.  Lemieux  A.  Rowan  D. J.  Clark  I. D. 《Hydrogeology Journal》2023,31(3):641-659

Modern, ambient tritium concentrations in precipitation are lower and more temporally consistent now that they have recovered from the historic thermonuclear bomb peak of the mid-1960s. With the bomb peak no longer the overriding influence on atmospheric tritium concentrations, anthropogenic point sources, such as nuclear-generating stations (NGS), have the largest influence, though the extent and temporal variability of this influence remains uncharacterized. The lack of precipitation monitoring locations means that spatial trends in tritium concentrations in precipitation are unknown. To address this data gap, tritium concentrations in shallow modern groundwater are interpolated throughout southern Ontario (Canada), at the center of the Great Lakes Basin, and the interpolation is tested as a precipitation proxy with a statistical comparison that shows good agreement between the shallow groundwater and precipitation datasets. The shallow groundwater tritium interpolation is used to delineate the extent of NGS influence as representing 66% of the study area. Recharge timings in the subcropping bedrock aquifers of the study area are interpreted qualitatively in areas outside of NGS influence to be primarily a mix of pre-bomb and modern recharge, with no indication of peak recharge levels remaining. The influence of drift thickness on the proportion of tritium-dead versus tritium-live samples is observed spatially and confirmed by comparing data distributions. The oldest waters (pre-1953) tend to occur in subcropping bedrock aquifers underlying the thickest sediment packages.

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4.

The travel time of groundwater plays a major role in the understanding of hydrogeological systems; however, large data sets necessary for regional studies of groundwater age are rare. In this study, a unique large data set of groundwater samples analysed for tritium and helium isotopes collected over the last 20 years from Cenozoic aquifers of the North German Plain is explored. Hereby, the variety of natural and technical influences on the tritium-helium age, including screen depth and length, groundwater recharge rate and climatic effects, are investigated. To a sampling depth of ~40 m below ground level, the median tritium-helium age increases almost linearly with depth, reaching a maximum of 40 years. Below, the portion of older, tritium-free water rises. The tritium-helium ages of the tritium-bearing portion increase only slightly to a maximum of about 46 years. The depth distribution of the tritium-helium age shows a dependency on groundwater recharge rates. Considering the same depth level, younger ages are related to higher groundwater recharge rates as compared to groundwater that infiltrated in areas with lower recharge rates. This is especially observed for shallow depths. Tritium-helium ages younger than 40 years are reflected well in the atmospheric tritium input curves, while deviations from it can be related to anthropogenic influences such as input from nuclear power plants and irrigation with deep, tritium-poor groundwater. The regional distribution for shallow wells indicates increasing tritium-helium ages from west to east, corresponding to decreasing groundwater recharge rates due to the more continental climate in the east.

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5.
Noble gas recharge temperatures (NGTs) and radiocarbon ages were determined for 43 groundwater samples collected in the eastern Espa?ola Basin, New Mexico (USA), to identify mountain-block recharge in waters <10 thousand years (ka) old and to evaluate possible changes in mountain-block recharge over the past ??35?ka. For Holocene samples from the southeastern area, NGTs are dominantly 2?C4° cooler than the measured water-table temperature near the mountain front. Computed minimum mountain-block recharge fractions are dominantly 0.2?C0.5, consistent with previous large mountain-block recharge estimates. NGTs do not display the distinct low during the last glacial maximum observed in other paleorecharge studies; samples recharged 15?C25?ka ago are on average only 1.3° cooler than Holocene samples. Instead, samples with the coldest NGTs were recharged 25?C35?ka ago. A proposed explanation is that higher precipitation rates during the last glacial maximum resulted in a lower mean recharge elevation for the basin, essentially buffering the effect of the lower mean annual air temperature and producing NGTs similar to the Holocene. In the period preceding the last glacial maximum, precipitation rates more like today??s resulted in Holocene-like mountain-block recharge fractions, producing a mean NGT ??5° cooler than the Holocene, as expected.  相似文献   

6.
Hydrochemical and isotopic study of Miocene and Mio-Plio-Quaternary (M-P-Q) aquifers in Wadi El Hechim?CGaraa Hamra basin, Central Tunisia was undertaken in order to investigate recharge mode and processes leading to mineralization of groundwater as well as interaction between both systems. The results revealed striking differences between the two aquifer systems. While the Miocene aquifer contains recently recharged waters with generally low mineralization (around 0.5?g?L?1), stemming mainly from dissolution of carbonate minerals, the M-P-Q aquifer reveals TDS values reaching 3?g?L?1, controlled mainly by dissolution of evaporitic minerals. Isotopic data indicate that the Miocene aquifer contains water recharged in past several decades (bomb tritium and bomb radiocarbon detected). The M-P-Q system appears to be much slower, with time scales of groundwater flow possibly reaching some thousands of years. Sharp discontinuity of hydrochemical and isotope characteristic of groundwater observed across the major tectonic fault separating the Miocene and M-P-Q aquifers supports the idea of very limited (if any) hydraulic interconnection between both studied systems. This in turn calls for revision of existing conceptual models of groundwater flow in the region postulating significant groundwater fluxes crossing the fault in the direction of M-P-Q aquifer and adjacent aquifers in the Wadi al Fakka plain.  相似文献   

7.
Groundwater is the major source of water and a critical resource for socioeconomic development in semi-arid environments like the Johannesburg area. Environmental isotopes are employed in this study to characterise groundwater recharge and flow mechanisms in the bedrock aquifers of Johannesburg, which is known for polluted surface water. With the exception of boreholes near the Hartbeespoort Dam, groundwater in the study area was derived from meteoric water that has undergone some degree of evaporation before recharge, possibly via diffuse mechanisms. Boreholes that tap groundwater from the Transvaal Supergroup Formation show depletion in δ18O and δ2H values. This is attributed to diffuse recharge through weathering fractures at high elevation that are undergoing deep circulation or recharge from depleted rainfall from the high-latitude moisture sources. The influence of focused recharge from the Hartbeespoort Dam was observed in the boreholes north of the dam, possibly as a result of the north–south trending fault lines and the north-dipping fractures in the bedding planes of quartzites. This is also supported by a reservoir water budget method which indicated a mean annual net flux of 2,084,131 m3 from Hartbeespoort Dam recharging groundwater per annum. Using tritium in the dam and boreholes located at 750 m and 5400 m downstream, average groundwater flow velocity was estimated as 202 m/year. An open system was observed in shale, andesite and granitic-gneiss aquifers indicating soil CO2 as a dominant source of carbon (δ13C) in groundwater. A closed system was also observed in dolomitic aquifers indicating carbonate dissolution as the predominant source of carbon.  相似文献   

8.
The continuous abstraction of groundwater from Arusha aquifers in northern Tanzania has resulted in a decline in water levels and subsequent yield reduction in most production wells. The situation is threatening sustainability of the aquifers and concise knowledge on the existing groundwater challenge is of utmost importance. To gain such knowledge, stable isotopes of hydrogen and oxygen, and radiocarbon dating on dissolved inorganic carbon (DIC), were employed to establish groundwater mean residence time and recharge mechanism.14C activity of DIC was measured in groundwater samples and corrected using a δ13C mixing method prior to groundwater age dating. The results indicated that groundwater ranging from 1,400 years BP to modern is being abstracted from deeper aquifers that are under intensive development. This implies that the groundwater system is continuously depleted due to over-pumping, as most of the sampled wells and springs revealed recently recharged groundwater. High 14C activities observed in spring water (98.1?±?7.9 pMC) correspond with modern groundwater in the study area. The presence of modern groundwater suggests that shallow aquifers are actively recharged and respond positively to seasonal variations.  相似文献   

9.
An approach combining the use of water dissolved chemical species and isotopic fingerprints has been used to understand the behavior of a phreatic aquifer and to determine the origin of its different water components. This aquifer is located in the large sedimentary basin of the Great Oriental Erg (Algeria) and overlies two deeper aquifers: the Complexe Terminal (CT) and the Continental Intercalaire (CI). Besides the deterioration of its groundwater quality, its water table has risen during the last 20 years. A water budget surplus between 950 and 2500 l s?1 was estimated. Down-gradient groundwater evolution (south-north) has shown that the mineralisation increases from 1.23 to 5.20 g l?1 due to evaporite minerals dissolution. Chemical and isotopic data demonstrated that in addition to rainfall there is a contribution from the CT and CI aquifers. The latter are tritium-free and less mineralized than the phreatic aquifer. Their radiocarbon contents are very low (<10 pmC, percent modern Carbon) (Pleistocene recharge) whereas quite the contrary is observed for the superficial aquifer which exhibits fairly high and variable C-14 activities (50–100 pmC), evidence of recent recharge. On the basis of tritium contents, two groundwater groups were identified for the phreatic aquifer.  相似文献   

10.
The common recommendation that recharge should be estimated from multiple methods is sound, but the inherent differences of the methods make it difficult to assess the accuracy of differing results. In this study, four methods for estimating groundwater recharge and two methods for estimating base flow (as a proxy for recharge) are compared at two hydrologic research sites in east-central Pennsylvania, USA. Results from the multiple methods all provided reasonable estimates of groundwater recharge that differed considerably. The estimates of mean annual recharge for the period 1994-2001 ranged from 22.9 to 35.7 cm—about 45% of the mean of all estimates. For individual years, recharge estimates from the multiple methods ranged from 30 to 42% of the mean value during the dry years and 64 to 76% of the mean value during wet years. Comparison of multiple methods was found to be useful for determining the range of plausible recharge rates and highlighting the uncertainty of the estimates.  相似文献   

11.
This study demonstrates the importance of the conceptual hydrogeological model for the estimation of groundwater recharge rates in an alluvial system interconnected with an ephemeral or intermittent stream in south-east Queensland, Australia. The losing/gaining condition of these streams is typically subject to temporal and spatial variability, and knowledge of these hydrological processes is critical for the interpretation of recharge estimates. Recharge rate estimates of 76–182 mm/year were determined using the water budget method. The water budget method provides useful broad approximations of recharge and discharge fluxes. The chloride mass balance (CMB) method and the tritium method were used on 17 and 13 sites respectively, yielding recharge rates of 1–43 mm/year (CMB) and 4–553 mm/year (tritium method). However, the conceptual hydrogeological model confirms that the results from the CMB method at some sites are not applicable in this setting because of overland flow and channel leakage. The tritium method was appropriate here and could be applied to other alluvial systems, provided that channel leakage and diffuse infiltration of rainfall can be accurately estimated. The water-table fluctuation (WTF) method was also applied to data from 16 bores; recharge estimates ranged from 0 to 721 mm/year. The WTF method was not suitable where bank storage processes occurred.  相似文献   

12.
In order to mine lignite from the Neyveli opencast mines, about 200 km south of Madras, India, the Neyveli aquifer has been undergoing depressurisation continuously for almost three decades. To gain insight into the aquifer hydrodynamics, environmental-isotope and chloride measurements on selected groundwater samples were initiated two decades ago, and detailed studies were undertaken during 1985–91. This article demonstrates the effect of large-scale groundwater withdrawals on the hydrologic regime and the effects on environmental chloride and isotopic distributions. A feature common to both the radiocarbon and chloride data of 1991 is their marked variation in a small area between the recharge zone and the mine area where pumping is concentrated. Furthermore, an excellent correlation exists between the temporal increase in the apparent radiocarbon ages of groundwater sampled in 1991 and 1985 and the corresponding lowering of potentiometric levels. Isochlors based on 1991 and 1985 data also indicate a changed hydrologic regime. In certain areas, heavy withdrawals have resulted in increased groundwater salinity.  相似文献   

13.
In evaluating potential impacts of climate change on water resources, water managers seek to understand how future conditions may differ from the recent past. Studies of climate impacts on groundwater recharge often compare simulated recharge from future and historical time periods on an average monthly or overall average annual basis, or compare average recharge from future decades to that from a single recent decade. Baseline historical recharge estimates, which are compared with future conditions, are often from simulations using observed historical climate data. Comparison of average monthly results, average annual results, or even averaging over selected historical decades, may mask the true variability in historical results and lead to misinterpretation of future conditions. Comparison of future recharge results simulated using general circulation model (GCM) climate data to recharge results simulated using actual historical climate data may also result in an incomplete understanding of the likelihood of future changes. In this study, groundwater recharge is estimated in the upper Colorado River basin, USA, using a distributed-parameter soil-water balance groundwater recharge model for the period 1951–2010. Recharge simulations are performed using precipitation, maximum temperature, and minimum temperature data from observed climate data and from 97 CMIP5 (Coupled Model Intercomparison Project, phase 5) projections. Results indicate that average monthly and average annual simulated recharge are similar using observed and GCM climate data. However, 10-year moving-average recharge results show substantial differences between observed and simulated climate data, particularly during period 1970–2000, with much greater variability seen for results using observed climate data.  相似文献   

14.
Gafsa region is one of the most productive artesian basins in Southern Tunisia. It is located in the southwestern part of the country, and its groundwater resources are developed for water supply and irrigation. Proper understanding of the geochemical evolution of groundwater is important for sustainable development of water resources in this region. A hydrogeochemical survey was conducted on the Plio-Quaternary shallow and on the Complex Terminal aquifers system using major (Ca, Mg, Na, SO4, Cl, NO3 and HCO3) and minor (Sr) elements, in order to evaluate the groundwater chemistry patterns and the main mineralization processes occurring in this system. Hydrochemical and isotopic data were used in conjunction with hydrogeological characteristics to investigate the groundwater composition in these aquifers. It has been demonstrated that groundwaters acquire their mineralization principally by water–rock interaction, i.e. dissolution of evaporites (halite/gypsum, pyrite, etc.) and return flow of irrigation waters, and by anthropogenic activities due to the use of nitrogen (N) fertilizers–pesticides in agriculture. The isotopic study of “stable isotopes, radiocarbon and tritium” (Yermani 2002) shows that a paleoclimatic recharge is corroborated by the relatively low carbon-14 activities (5–25.3%) of the referred groundwater group samples, which were interpreted as recharge occurring during the late Pleistocene and the early Holocene periods. The water feedings of these aquifers are mainly provided by infiltration of precipitations, infiltration of irrigation water, lateral feeding from Cretaceous relieves from the South and the North and along recent and fossil drainage networks that constitute major freshwater sources in groundwater tables (Hamed et al., J Environ Protect 1:466–474, 2010a).  相似文献   

15.
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16.
华北平原地下水年龄校正   总被引：4，自引：0，他引：4  
郭娇  石建省  王伟 《地球学报》2007,28(4):396-404
地下水14C年龄一般指地下水和土壤CO2隔绝至今的年代.地下水测年在地下水水文学中占有特殊的位置,地下水测年可以用来确定补给区,估算地下水流速度、流量、补给速率、水力传导系数和有效孔L隙度,而且年龄数据还可以用来完善地下水流模型.本研究选择华北平原为重点研究区,利用地下水中的同位素和化学组分的测试结果,应用水文地球化学及同位素水文学等相关知识,通过六种传统模型和反向质量平衡模型(NETPATH)对华北平原地下水年龄进行校正.根据年龄校正结果,分析了深层地下水的年龄变化特点,确定了水流路径上发生的水文地球化  相似文献   

17.
In this paper, the long-term mean annual groundwater recharge of Taiwan is estimated with the help of a water-balance approach coupled with the base-flow-record estimation and stable-base-flow analysis. Long-term mean annual groundwater recharge was derived by determining the product of estimated long-term mean annual runoff (the difference between precipitation and evapotranspiration) and the base-flow index (BFI). The BFI was calculated from daily streamflow data obtained from streamflow gauging stations in Taiwan. Mapping was achieved by using geographic information systems (GIS) and geostatistics. The presented approach does not require complex hydrogeologic modeling or detailed knowledge of soil characteristics, vegetation cover, or land-use practices. Contours of the resulting long-term mean annual P, BFI, runoff, groundwater recharge, and recharge rates fields are well matched with the topographical distribution of Taiwan, which extends from mountain range toward the alluvial plains of the island. The total groundwater recharge of Taiwan obtained by the employed method is about 18 billion tons per year.An erratum to this article can be found at  相似文献   

18.
The recharge sources and groundwater age in the Songnen Plain, Northeast China, were confirmed using environmental isotopes. The isotopic signatures of the unconfined aquifers in the southeast elevated plain and the north and west piedmont, cluster along local meteoric water lines (LMWLs) with a slope of about 5. The signature of source water was obtained by the intersection of these LMWLs with the regional meteoric water line (RMWL). This finding provides evidence that the recharge water for these areas originate from the Changbai Mountains and the Low and High Hingan Mountains, respectively. Groundwater in the unconfined aquifer in the low plain yields a LMWL with a slope of 4.4; its nitrate concentration indicates the admixture of irrigation return flow. The δ-values of the unconfined aquifer in the east elevated plain plot along the RMWL, reflecting recharge by local precipitation. The mean residence time of groundwater in these aquifers is less than 50?years. However, the 14C age of the groundwater in the confined Quaternary aquifer ranges from modern to 19,500?years, and in the Tertiary confined aquifer from 3,100 to 24,900?years. Modern groundwater is mainly recharged to the Quaternary confined aquifer on the piedmont by local precipitation and lateral subsurface flow.  相似文献   

19.
环境同位素方法在平凉市岩溶地下水研究中的应用   总被引：4，自引：2，他引：2  
马致远 《地质论评》2004,50(4):433-439
应用环境同位素方法对平凉隐伏岩溶水的研究结果表明 ,研究区隐伏岩溶水形成较早 ,且有大量现代水的混入 ,平均混入量为 5 4 %。说明研究区隐伏岩溶水的补给和更新能力较好。环境同位素分析结果还显示 ,大岔河隐伏岩溶水为一相对独立、半开放的水文地质单元。其补给来源部分为流域内大气降水、地表水的补给 ,部分为东南部三道沟岩溶地下水的补给。根据环境同位素 EPM与 EM两种模型计算 ,地下水的滞留时间为 36 a。地下水储存量为 1.314× 10 8m3;储水系数为 7.2 9× 10 - 3。这一结果与传统勘探方法的计算结果基本吻合 ,说明环境同位素方法的实用性 ,可在地下水资源调查中作为传统方法的补充和对比。  相似文献   

20.
北京市平原区地下水更新能力变化的动态均衡证据   总被引：1，自引：0，他引：1  
对北京市地下水更新能力的时空变化进行分析,为地下水资源管理提供依据。用地下水动态均衡法对北京市平原区地下水,尤其是开采层地下水的补给量、更新周期、更新速率和补给速率等参数做了计算,进而对地下水更新能力及其时空变化做评价和分析。研究结果表明：在自然状态下,地下水更新能力总体上自山前至平原区腹地由强变弱,但总体上更新能力较强;含水层接受外来水源补给的边界条件和赋水条件良好,降水量的多寡是影响地下水更新能力的瓶颈因素;2001－2008年的地下水平均补给速率（0.28 m/a）比1981－2000年减少了35.6%,更新能力明显减弱;近些年地下水开采强度连年大于其更新能力,导致与自然状态下相比地下水位埋深平均下降幅度已达19.73 m,含水层中地下水减少量达101×108 m3。以上证据表明,在气候变化和人类活动的双重影响下,北京市未来的地下水资源可持续供水问题十分严峻。  相似文献   

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