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1.
The Zhangye Basin, located in arid northwest China, is an important agricultural and industrial center. In recent years rapid development has created an increased demand for water, which is increasingly being fulfilled by groundwater abstraction. Detailed knowledge of the geochemical evolution of groundwater and water quality can enhance understanding of the hydrochemical system, promoting sustainable development and effective management of groundwater resources. To this end, a hydrochemical investigation was conducted in the Zhangye Basin. Types of shallow groundwater in the Zhangye Basin were found to be HCO3 −, HCO3 −–SO4 2−, SO4 2−–HCO3 −, SO4 2−–Cl−, Cl−–SO4 2− and Cl− . The deep aquifer groundwater type was found to be HCO3−–SO42− throughout the entire area. Ionic ratio and saturation index calculations suggest that silicate rock weathering and evaporation deposition are the main processes that determine the ionic composition in the study area. The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification and the Wilcox diagram. In the study area, the compositions of the stable isotopes δ18O and δD in groundwater samples were found to range from −4.00 to −9.28‰ and from −34.0 to −65.0‰, respectively. These values indicate that precipitation is the main recharge source for the groundwater system; some local values indicate high levels of evaporation. Tritium analysis was used to estimate the ages of the different groundwaters; the tritium values of the groundwater samples varied from 3.13 to 36.62 TU. The age of the groundwater at depths of less than 30 m is about 5–10 years. The age of the groundwater at depths of 30–50 m is about 10–23 years. The age of the groundwater at depths of 50–100 m is about 12–29 years. For groundwater samples at depths of greater than 100 m, the renewal time is about 40 years.  相似文献   

2.
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3.
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   

4.
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   

5.
The scarcity of surface water resources in arid and semi-arid regions from North African countries contributes to the considerable increase of groundwater exploitation, which leads to the development of hydrogeological studies. However, due to the lack of hydrodynamic data in these regions, these studies focus more and more on the geochemical and environmental isotope techniques to insure a better understanding of the hydrodynamic functioning of subsurface systems. In this study, which interests an important unconfined aquifer in central Tunisia, tritium data and chloride mass balance (CMB) method were applied in order to (1) understand the mode of recharge of this aquifer and (2) obtain a reliable estimation of its recharge amount as well as (3) estimate its annual renewal rate. It has been demonstrated that the shallow groundwaters are classified into two groups according to their tritium contents. The first group includes wells located mainly downstream and highlights the significant role of the post-nuclear lineal recharge through Wadis courses. The second group encloses wells located practically overall the rest of the basin and refers to relatively modern waters originated from areal recharge of present-day rainfall. Based on the CMB method, the recharge to this unconfined aquifer is estimated to 31.7 mm year−1, which corresponds to 10.5% of the total rainfall. The annual renewal rate of groundwater, evaluated based on the tritium contents, is up to 16%.  相似文献   

6.
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   

7.
Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr2+/Ca2+ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ 18O = −2.66‰, δD −7.60‰) similar to rainfall (δ 18O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ 18O = −0.46‰, δD = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr2+/Ca2+ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr2+/Ca2+ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the total fresh and saline water input.  相似文献   

8.
Groundwater is the major source of water supply for most uses in the rural settlements in Ghana. A groundwater flow model was calibrated for some aquifers of the southern Voltaian sedimentary system under steady-state conditions. The objective was to determine estimates of the hydraulic conductivities of the different hydrostratigraphic units of the southern Voltaian, and the distribution of recharge from precipitation. Data on the stable isotopes of oxygen and hydrogen from the study area suggest that groundwater recharge in the area is from rainfall. The calibrated steady-state model suggests that aquifer hydraulic conductivities in the study area range from 1.19 to 6.3 m/day. Hydrostratigraphic unit specific hydraulic conductivities are discussed. The calibrated recharge ranges from 3.81e−05 m/day to 6.0e−04 m/day, which represents 0.9–6% of the precipitation in the form of rainfall. Six distinct flowpaths have been defined using particle tracking. The particle tracking simulation suggests travel times in the range of 380 to 5,199 years from recharge areas to discharge areas along the flowpaths identified. A contaminant dropped at the recharge areas in the central sections of the model area would travel at these rates along the flowpaths, assuming that advection is the dominant transport process. Inverse geochemical modeling indicates the dissolution of albite, K-feldspars and anorthite, respectively, along flowpaths I and IV. The inverse modeling along flowpaths I and IV suggest the dissolution of albite, K-feldspar and anorthite, respectively, at 1.085e−06, 3.16e−08 and 3.168e−07 mmol/year.  相似文献   

9.
The groundwater in headwater region is an important recharge source for the adjacent mountain-front plain. In order to reveal the relationship among precipitation, soil water and groundwater, from June to September in 2004, stable isotopes (deuterium and oxygen-18) in precipitation and soil waters at the depths of 10, 20, 30, 50, 70, 90, and 110 cm were analyzed at two sites covered by black locust (Robinia Pseudoacia L.) (Site A) and grass predominated by Themeda triandra (T. japonica (Willd.) Tanaka) and Bothriochloa ischaemum (B. ischaemum (L.) Keng) (Site B) in an experimental catchment at Taihang Mt., North China, respectively. The δ18O of precipitation in daily rain events shows large variations (−13.3 to −4.3‰) with a mean of 8.1‰. The δ18O and δ D of soil waters along profiles in two sites suggest that the influence of canopy cover was just up to 10 cm in top soil water. The soil water moved over the zero flux plane at 70 cm in-depth is expected to escape the evaporative effect at the end of September in both sites. The results show that the stable isotope, instead of tritium as tradition, can be used to trace the soil water behaviors based on the movement of isotopic peak along the vertical profiles in this semi-arid and semi-humid mountainous region. The infiltration depths of soil water in Taihang Mt. are 12 and 10 mm/day from June to September in 2004 in Site A and Site B, respectively. Tracing by stable isotope, recharge fluxes of soil water to local groundwater are of 3.8 and 3.2 mm/day in Site A and Site B, respectively. The results provide desirable information for assessment of local groundwater resources. An erratum to this article can be found at  相似文献   

10.
Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population, quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater was recharged by precipitation and was characterized by Ca–HCO3 type water with depleted δ18O and δD (mean value of −8.8‰ δ18O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex (Ca–Na–Mg–HCO3–Cl–SO4 type), and heavier δ18O and δD were observed (around −8‰ δ18O). Before the surface water with mean δ18O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ18O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal end of the fan. The groundwater underwent chemical evolution from Ca–HCO3, Na–HCO3, to Na–SO4. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical evolution, and groundwater flow paths in the complex alluvial fan aquifer system.  相似文献   

11.
The Qinghai-Xizang Plateau is an area where a large number of salt lakes are distributed. We have collected several hundred samples of natural waters over the Plateau since 1976 and carried out researches on their hydrogen and oxygen isotopes. The results indicate that theδD and δ18O values of the salt lake waters over the Plateau range from −64.1 to +12.4‰ and from −11.19 to +8.62‰, respectively. From the different types of surfaces, ground and lake waters of various salinities it is inferred that the compositions of H and O isotopes in the initial water of Qinghai Lake areδD=−55.0‰ and {ie336-1}; and those in the original water from the lakes in northern Xizang, areδD=−116.0‰ and {ie336-2}. Brines in the salt lakes are derived from rain water through prolonged circulation. Oilfield water also makes some contribution to the salt lakes in the Qaidam Basin. Similar slopes of evaporation lines of water isotopes are noticed for the Qinghai Lake area and northern Xizang. This is attributed to the evolution of the isotopes in these water bodies in an environment of middle latitude and high elevation.  相似文献   

12.
Groundwater is a valuable resource in the semiarid Ordos Plateau region where abundant mineral resources, such as coal, natural gas, and halite, are present. With resources development, groundwater demand will increase dramatically. The origin identification and recharge estimates of groundwater are significant components of sustainable groundwater development in the Ordos Plateau. Groundwater and precipitation samples were taken and the isotopic compositions δ2H, δ18O, and chloride were analyzed to identify groundwater origins and to estimate recharge rates. The δ2H and δ18O 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 Ordos Plateau, which varies from 2.93 to 22.11% of the effective 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   

13.
The aim of the paper is to understand the geological control of groundwater, the recharge sources, the relative age of groundwater and the interaction between surface water and groundwater of the southwestern part of North Bengal Plain in the alluvium filled gap between the Rajmahal hills on the west and the Garo hills on the east. The area is covered by Quaternary alluvia of two different ages, viz. the Older Alluvium and the Newer Alluvium. The Older Alluvium of Pleistocene age is made up of argillaceous bed reddish brown in color and interspread with ‘kankar’ and laterite debris and the Newer Alluvium is dark, loosely compacted and has a high moisture content. A hydrostarigraphic model of the top 120 m geological column has been built by direct field observation, constructing Fence diagram, lithofacies and isotope analyses. The model indicates an oscillating environment of deposition of sediments from bottom to top with oxidizing at the bottom followed by reducing and then oxidizing environment at the top. The hydrogeochemistry of groundwater also suggests a predominantly reducing condition of the aquifer with high HCO3 −, low SO4 2− and NO3 − concentrations. The shallow groundwater at places contains heavy metals such as copper, cadmium, manganese, iron, chromium and arsenic. The δ18O and tritium values of groundwater are within the range of monsoon precipitation composition which indicates that groundwater is probably recharged primarily from precipitation. The plots of δ18O and δD show slight deviation from the Local Mean Water Lines suggesting that some evaporation of rainfall occurs prior to or during infiltration. Therefore groundwater occurs under unconfined condition. Lithofacies analysis indicates that the sediments below the depth of 40 m are the potential water bearing formation. Depletion or enrichment of δ18O and δD with depth was not observed and tritium content is also similar at various depths indicating possibility of mixing of groundwater from various depths due to pumping which may lead to contamination of the deeper aquifer by heavy metals and arsenic.  相似文献   

14.
The Guadalupe Valley aquifer is the only water source for one of the most important wine industries in Mexico, and also the main public water supply for the nearby city of Ensenada. This groundwater is monitored for major ion, N-NO3, P-PO4, Fe, As, Se, Mo, Cd, Cu, Pb, Zn and Sb concentrations, as well as TDS, pH, dissolved oxygen and temperature. High concentrations of N-NO3 (26 mg l−1), Se (70 μg l−1), Mo (18 μg l−1) and Cu (4.3 μg l−1) suggest that groundwater is being polluted by the use of fertilizers only in the western section of the aquifer, known as El Porvenir graben. Unlike the sites located near the main recharge area to the East of the aquifer, the water in El Porvenir graben has low tritium concentrations (<1.9 TU), indicating a pre-modern age, and thus longer water residence time. No significant variations in water quality (generally <10%) were detected throughout 2001–2002 in the aquifer, suggesting that reduced rainfall and recharge during this dry period did not significantly affect water quality. However, the wells nearest to the main recharge area in the Eastern aquifer show a slight but constant increase in TDS with time, probably as a result of the high (∼200 L S−1) uninterrupted extraction of water at this specific recharge site. Relatively high As concentrations for the aquifer (10.5 μg l−1) are only found near the northern limit of the basin associated with a geological fault.  相似文献   

15.
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   

16.
Geographical information system (GIS) technology was used to investigate NO3 − concentration of groundwater in the Zhangye Basin, Northwest China. Thematic information and NO3 − data of groundwater from the Zhangye Basin were analyzed in a GIS environment to study the extent and variation of NO3 − concentration and to establish spatial relationships with corresponding land use types. About 38.8% of groundwater samples showed NO3 − concentration above the human affected value (13 mg/l NO3 −), while more than 10.2% exceeded the maximum acceptable level (50 mg/l NO3 −) according to WHO regulations. The spatial distribution of NO3 − of groundwater in the Zhangye Basin showed an obvious character of zonation; the high NO3 − concentration was mainly located in the city seat areas, and Zhangye City was the high-value center. The probability of over 90% for NO3 − concentration exceeding 13 mg/l was found in urban seat areas. The spatial analyses indicated that groundwater contamination by NO3 − was closely related to one specific land use class, the urban. The NO3 − concentration of groundwater under urban was significantly higher than that under irrigation land or sand dune. Most of the unacceptable NO3 − levels were found in groundwater samples assigned to urban area, but a few were also found allotted to irrigation land class. Therefore, urban source was considered the principal source of NO3 − contamination of groundwater in the Zhangye Basin, while irrigation land source was still a possible source of NO3 − contamination.  相似文献   

17.
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   

18.
Despite its extreme aridity, the Ordos Basin in northern China is rich in groundwater. Many artesian wells or springs with large fluxes are utilized for drinking, irrigation and industrial production. In a search for the origin of the groundwater, a detailed investigation of the stable isotopes of oxygen and hydrogen in the local precipitation, the river water, the springs, the well water, as well as the soil water extracted from six soil profiles in the Ordos Basin, was carried out. The data show that δD, δ18O and TDS values of the river water are similar to those of groundwater, while the TDS values of the soil water are about ten times greater than those of groundwater. Furthermore, the mean isotopic compositions of the local precipitation are significantly higher than those of river water and groundwater. Based on the chloride mass balance method, the estimated recharge rates range from 5.2 to 17.2 mm/year, with a mean value of 10.5 mm/year. The results show that the main source of recharge of the groundwater in the Ordos Basin is not the local precipitation, but must come from a region where the precipitation is characterized by much lower δD and δ18O values. In addition, the groundwater in the Ordos Basin contains a component of mantle-derived 3He and crust-derived 4He suggesting that the groundwater may partly derive from flows through basement faults beneath the Ordos Basin.  相似文献   

19.
Sources of deep groundwater salinity in the southwestern zone of Bangladesh   总被引：2，自引：2，他引：0  
Twenty groundwater samples were collected from two different areas in Satkhira Sadar Upazila to identify the source of salinity in deep groundwater aquifer. Most of the analyzed groundwater is of Na–Cl–HCO3 type water. The trends of anion and cation are Cl− > HCO3 − > NO3 − > SO4 2− and Na+ > Ca2+ > Mg2+ > K+, respectively. Groundwater chemistry in the study area is mainly governed by rock dissolution and ion exchange. The dissolved minerals in groundwater mainly come from silicate weathering. The salinity of groundwater samples varies from ~1 to ~5%, and its source is possibly the paleo-brackish water which may be entrapped during past geologic periods.  相似文献   

20.
Quantification of groundwater recharge is important for water resources management. Different methods can be used to estimate groundwater recharge. The most suitable approach depends on site characteristics. Water balance model was used in this study to quantify groundwater recharge from rainfall in Ruataniwha Basin, Hawke’s Bay, New Zealand. Because it is a closed basin, this method was determined to be more suitable than any other method. The basin is fed by surface water flow and rainfall, without any lateral groundwater flow. Records of surface water inflow and outflow are available with a certain degree of reliability. To cope with uncertainty in different components of water balance, different sampling methods were used. The Mean Value Latin Hypercube Sampling (MVLHS) was used and compared with Latin Hypercube Sampling (LHS), and Monte Carlo Simulation (MCS). It was found the groundwater recharge from rainfall is about 415 million m3/year. Results of this study have revealed that MVLHS converges faster and with lower variance than LHS and MCS.  相似文献   

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