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1.
Nitrate contamination of groundwater in an agroecosystem in Zhangye Oasis,Northwest China 总被引:5,自引:2,他引:3
In order to assess the extent of groundwater contamination by nitrate (NO3
−–N) and to provide information about the deterioration of the groundwater quality in Zhangye Oasis, Northwest China, a study
was conducted in this area. The mean value of NO3
−–N concentrations in groundwater samples was 10.66 ± 0.19 mg l−1. NO3
−–N concentrations exceeding 10 mg l−1 (the threshold for drinking water set by the World Health Organization) were found in 32.4% of 71 wells, and were 13, 33.3,
52.4 and 50.0% in the groundwater samples from drinking wells, irrigation wells, hand-pumping wells and groundwater table
observation wells, respectively. The result showed that the groundwater samples that had NO3
−–N concentrations exceeding the threshold for drinking water were mostly collected from a depth of less than 20 m. Groundwater
NO3
−–N concentrations in areas used for the cultivation of vegetables, seed maize and intercropped maize were significantly higher
than those in urban or paddy areas. NO3
−–N contamination of groundwater in areas with sandy soil was more severe than in those with loam soil. 相似文献
2.
The Kingston Basin in Jamaica is an important hydrologic basin in terms of both domestic and industrial sector. The Kingston
hydrologic basin covers an area of approximately 258 km2 of which 111 km2 underlain by an alluvium aquifer, 34 km2 by a limestone aquifer and the remainder underlain by low permeability rocks with insignificant groundwater resources. Rapid
development in recent years has led to an increased demand for water, which is increasingly being fulfilled by groundwater
abstraction. A detailed knowledge of the water quality can enhance understanding of the hydrochemical system, promoting sustainable
development and effective management of groundwater resources. To achieve this, a hydrochemical investigation was carried
out in the Kingston Basin. Results showed that the water is Na–Ca–Cl–HCO3 and Na–Ca–HCO3 type with higher concentrations of nitrate, sodium and chloride as the leading causes of contamination in most of the wells.
High concentrations of nitrate correlate with wells from areas of high population density and could be attributed to anthropogenic
causes, mainly involving improper sewage treatment methodologies or leaking sewer lines. Jamaica, owing to its island nature,
has the continuous problem of saline water intrusion, and this is reflected in the higher levels of chloride, sodium and conductivity
in the water samples collected from the wells. The wells studied show higher concentrations of chloride ranging from around
10.2 mg/l in wells located approximately (4931.45 m) from the coast to around 234 mg/l in the well located near to the coast.
The conductivity values also closely correlate with the chloride levels found in the wells. 相似文献
3.
Influence of hydrogeochemical processes on temporal changes in groundwater quality in a part of Nalgonda district, Andhra Pradesh, India 总被引:4,自引:3,他引:1
Geochemical processes that take place in the aquifer have played a major role in spatial and temporal variations of groundwater
quality. This study was carried out with an objective of identifying the hydrogeochemical processes that controls the groundwater
quality in a weathered hard rock aquifer in a part of Nalgonda district, Andhra Pradesh, India. Groundwater samples were collected
from 45 wells once every 2 months from March 2008 to September 2009. Chemical parameters of groundwater such as groundwater
level, EC and pH were measured insitu. The major ion concentrations such as Ca2+, Mg2+, Na+, K+, Cl−, and SO4
2− were analyzed using ion chromatograph. CO3
− and HCO3
− concentration was determined by acid–base titration. The abundance of major cation concentration in groundwater is as Na+ > Ca2+ > Mg2+ > K+ while that of anions is HCO3
− > SO4
2− > Cl− > CO3
−. Ca–HCO3, Na–Cl, Ca–Na–HCO3 and Ca–Mg–Cl are the dominant groundwater types in this area. Relation between temporal variation in groundwater level and
saturation index of minerals reveals the evaporation process. The ion-exchange process controls the concentration of ions
such as calcium, magnesium and sodium. The ionic ratio of Ca/Mg explains the contribution of calcite and dolomite to groundwater.
In general, the geochemical processes and temporal variation of groundwater in this area are influenced by evaporation processes,
ion exchange and dissolution of minerals. 相似文献
4.
M. A. Halim R. K. Majumder S. A. Nessa K. Oda Y. Hiroshiro B. B. Saha S. M. Hassain Sk. A. Latif M. A. Islam K. Jinno 《Environmental Geology》2009,58(1):73-84
An integrated study has been carried out to elucidate the distribution and occurrence of arsenic in selected groundwater samples
in the area of Sherajdikhan, Bangladesh. Arsenic and other parameters (T, pH, EC, Na+, K+, Ca2+, Mg2+, Cl−, NO3
−, SO4
2−, HCO3
−, PO4
3−, Fe, Mn and DOC) have been measured in groundwater samples collected from shallow/deep tube wells at different depths. Hydrogeochemical
data suggest that the groundwaters are generally Ca–Mg–HCO3 and Mg–Ca–HCO3 types with bicarbonate (HCO3
−) as the dominant anion, though the other type of water has also been observed. Dissolved arsenic in groundwater ranged from
0.006 to 0.461 mg/l, with 69% groundwater samples exceeded the Bangladesh limit for safe drinking water (0.05 mg/l). Correlation
and principal component analysis have been performed to find out possible relationships among the examined parameters in groundwater.
Low concentrations of NO3
− and SO4
2−, and high concentrations of DOC, HCO3
− and PO4
3− indicate the reducing condition of subsurface aquifer where sediments are deposited with abundant organic matter. Distinct
relationship of As with Fe and Mn, and strong correlation with DOC suggests that the biodegradation of organic matter along
with reductive dissolution of Fe–Mn oxyhydroxides has being considered the dominant process to release As in the aquifers
studied herein. 相似文献
5.
Hydrochemical characteristics of groundwater in the Zhangye Basin, Northwestern China 总被引:3,自引:0,他引:3
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
6.
Ibticem Chamtouri Habib Abida Hafedh Khanfir Salem Bouri 《Environmental Geology》2008,55(5):1123-1133
Groundwater in Sfax City (Tunisia) has been known since the beginning of the century for its deterioration in quality, as
a result of wastewater recharge into the aquifer. An average value of 12 × 106 m3 of untreated wastewater reaches the groundwater aquifer each year. This would result not only in a chemical and biological
contamination of the groundwater, but also in an increase of the aquifer piezometric level. Quantitative impacts were evaluated
by examining the groundwater piezometric level at 57 surface wells and piezometers. The survey showed that, during the last
two decades, the groundwater level was ever increasing in the urban area with values reaching 7 m in part; and decreasing
in Sidi Abid (agricultural area) with values exceeding −3 m. Groundwater samples for chemical and microbial analysis were
collected from 41 wells spread throughout the study area. Results showed significantly elevated levels of sodium, chlorides,
nitrates and coliform bacteria all over the urban area. High levels (NO3: 56–254 mg/l; Na >1,500 mg/l; Coliforms >30/100 ml) can be related to more densely populated areas with a higher density
of pit latrine and recharge wells. Alternatively results showed a very variable chemical composition of groundwater, e.g.
electrical conductivity ranges from 4,040 to19,620 μs/cm and the dry residual varies between 1.4 and 14 g/l with concentrations
increasing downstream. Furthermore a softening of groundwater in Set Ezzit (highly populated sector) was observed. 相似文献
7.
Hydrochemical appraisal of groundwater and its suitability in the intensive agricultural area of Muzaffarnagar district,Uttar Pradesh,India 总被引:1,自引:0,他引:1
Muzaffarnagar is an economically rich district situated in the most fertile plains of two great rivers Ganga and Yamuna in
the Indo-gangetic plains, with agricultural land irrigated by both surface water as well as groundwater. An investigation
has been carried out to understand the hydrochemistry of the groundwater and its suitability for irrigation uses. Groundwater
in the study area is neutral to moderately alkaline in nature. Chemistry of groundwater suggests that alkaline earths (Ca + Mg)
significantly exceed the alkalis (Na + K) and weak acids exceed the strong acids (Cl + SO4), suggesting the dominance of carbonate weathering followed by silicate weathering. Majority of the groundwater samples (62%)
posses Ca–Mg–HCO3 type of hydrochemical species, followed by Ca–Na–Mg–HCO3, Na–Ca–Mg–HCO3, Ca–Mg–Na–HCO3–Cl and Na–Ca–HCO3–SO4 types. A positive high correlation (r
2 = 0.928) between Na and Cl suggests that the salinity of groundwater is due to intermixing of two or more groundwater bodies
with different hydrochemical compositions. Barring a few locations, most of the groundwater samples are suitable for irrigation
uses. Chemical fertilizers, sugar factories and anthropogenic activities are contributing to the sulphate and chloride concentrations
in the groundwater of the study area. Overexploitation of aquifers induced multi componential mixing of groundwater with agricultural
return flow waters is responsible for generating groundwater of various compositions in its lateral extent. 相似文献
8.
Fluoride,nitrate and water hardness in groundwater supplied to the rural communities of Ensenada County,Baja California,Mexico 总被引:1,自引:0,他引:1
L. W. Daesslé L. Ruiz-Montoya H. J. Tobschall R. Chandrajith V. F. Camacho-Ibar L. G. Mendoza-Espinosa A. L. Quintanilla-Montoya K. C. Lugo-Ibarra 《Environmental Geology》2009,58(2):419-429
The hydrogeochemistry of 26 wells belonging to ten different aquifers in the county of Ensenada, Baja California, is studied.
These wells are all used to supply the rural communities in the region, which comprise ~37,000 inhabitants, excluding the
city of Ensenada. High total dissolved solids (TDS) concentrations (maximum 7.35 g l−1) indicate that salt is a ubiquitous contaminant in the aquifers due to seawater intrusion. The aquifers that support extensive
agriculture activities (Maneadero, San Quintín, San Simón and El Rosario) are characterized by higher N–NO3 concentrations (maximum 20 mg l−1) derived from fertilizers. Fluoride concentrations exceed the 1.5 mg l−1 Mexican official limit in only four wells. The enrichments of F− in the southern aquifers are thought to be associated to water–rock interactions controlled mainly by Na–Ca equilibrium reactions
with fluorite, as suggested from high dissolved Na concentrations in these waters. In the northern aquifer of Maneadero, no
enrichment of Na is found and a geothermal source for F− is likely. Water is hard to moderately hard, with Ca/Mg ratios >1. Although drinking water directly from the tap is not a
common practice in these localities, most sources have concentrations of major ions and TDS that exceed the Mexican official
limits. 相似文献
9.
Assessment of groundwater quality and contamination problems ascribed to an abandoned uranium mine (Cunha Baixa region,Central Portugal) 总被引:2,自引:0,他引:2
The assessment of groundwater quality and its environmental implications in the region of the abandoned Cunha Baixa uranium
mine (Central Portugal) was carried out from 1995 to 2004. Shallow groundwater is the major water supply source for irrigation
in the neighbourhood of Cunha Baixa village. Water samples from the mine site as well as from private wells were collected
in order to identify the mining impact on water composition, the extent of contamination and the seasonal and temporal groundwater
quality variations. Some of the sampled private wells contain waters having low pH (<4.5–5) and high values of EC, TDS, SO4, F, Ca, Mg, Al, Mn, Ni, U, Zn and 226Ra. The wells located through the ESE–WSE groundwater flow path (1 km down gradient of the mining site) display the most contaminated
water. In the summer season, the levels of SO4, Al, Mn, and U were 50–120 times higher than those registered for uncontaminated waters and exceeded the quality limits for
irrigation purposes, presenting soil degradation risks. Nevertheless, this study indicates that groundwater contamination
suffered a small decrease from 1999 to 2004. The bioaccumulation of toxic metals such as Al, Mn, and U within the food chain
may cause a serious health hazard to the Cunha Baixa village inhabitants. 相似文献
10.
Nakka vagu, a tributary of the River Manjira in the Medak district of Andhra Pradesh, has a catchment area of ∼500 km2. Patancheru is an industrial development area (IDA) near the vagu. There are about 350 industries of varied nature (pulp,
plastic, bulk drugs, pharmaceuticals, paints and steel rolling mills) that are engaged in the manufacture/processing of their
respective products and that use water extensively. The hydrogeological setup has a bearing on the widespread contamination
in the area because of discharge of industrial effluents into open land and streams. Several dug wells and boreholes situated
in the study area have been monitored for water level fluctuations and quality variations. Pumping tests have been conducted
to evaluate aquifer parameters. The geology, drainage, chemistry and other related anthropogenic factors play a major role
in the spread of pollution in the area. Hence, it is very important to determine the degree of vulnerability to pollution
based on hydrogeological factors. Amidst the granite terrain, the Nakka vagu has been identified as a paleo-channel (composed
of clay–silt–sand facies); its presence in the area has immensely increased the spread of groundwater contamination. The transmissivity
of the alluvial aquifer varies from 750 to 1315 m2/day. The adjoining granite has a transmissivity that varies from 30–430 m2/day. The thickness of the valley fill in the discharge region is about 10–12 m, with a lateral spread of 500–700 m, east
of Nakka vagu.
Received: 17 November 1999 · Accepted: 14 March 2000 相似文献
11.
Evaluation of hydrogeochemical processes in arsenic-contaminated alluvial aquifers in parts of Mid-Ganga Basin,Bihar, Eastern India 总被引:1,自引:1,他引:0
Dipankar Saha Sreehari S. Sarangam Shailendra N. Dwivedi Kuldeep G. Bhartariya 《Environmental Earth Sciences》2010,61(4):799-811
The study region covers 1,650 km2 of the Mid-Ganga Basin in Bihar, experiencing intensive groundwater draft. The area forms a part of the Gangetic alluvial
plain where high incidence of arsenic groundwater contamination (>50 μg/l) has recently been detected. Seventy-seven groundwater
samples have been collected and analysed for major ions, iron and arsenic. Arsenic contamination (max 620 μg/l) is confined
in hand pump zones (15–35 m) within the newer alluvium deposited during Middle Holocene to Recent age. The older alluvial
aquifers are arsenic-safe and recorded maximum concentration as 9 μg/l. Out of 12 hydrochemical facies identified, four have
been found arsenic-affected: Ca–HCO3, Mg–HCO3, Ca–Mg–HCO3 and Mg–Ca–HCO3. The geochemical evolution of groundwater, as investigated by graphical interpretation and statistical techniques (correlation,
principal component analysis) revealed that dissolution of detrital calcite, dolomite and infiltration of rainwater are the
major processes shaping the groundwater chemistry in the newer alluvium. Arsenic and iron showed strong positive correlation.
Rainfall infiltration, carrying organic matter from recently accumulated biomass from this flood-prone belt, plays a critical
role in releasing arsenic and iron present in the sediments. Geochemical evolution of groundwater in older alluvium follows
a different path, where cation-exchange has been identified as a significant process. 相似文献
12.
Water samples collected from dug wells and tube wells from the Kurunegala District of Sri Lanka have been studied for their
major hydrogeochemical parameters to understand the chemical quality of water in the terrain. The region is composed of Precambrian
metamorphic rocks where groundwater is only available in the regolith and along weak structural discontinuities. The study
of the major chemical constituents of groundwater revealed several relationships with the aquifer lithology. Groundwater from
mafic rocks have high dissolved solids, while quartzose metaclastic rocks yield water with low dissolved solids. The study
area displays very low SO4
2− contents of the groundwater. The chloride content is higher in the dry regions and in terrains underlain by pink granite
and marble/calc gneiss while areas with marble, as expected, show high concentrations of Ca and Mg ions. The waters in the
region can be classified into non-dominant cations to Na + K dominant and Cl− and HCO3
− dominant types. Water from charnockite-bearing areas tends to have non-dominant cations and more CO3
2− + HCO3
− types. Effects such as soluble salts in the regolith, fracture intensity and climatic variations play a significant role
in the behavior of the hydrogeochemistry in the area. 相似文献
13.
Hydrogeochemical processes in the groundwater environment of Heihe River Basin,northwest China 总被引:5,自引:0,他引:5
Zhu Gaofeng Su Yonghong Huang Chunlin Feng Qi Liu Zhiguang 《Environmental Earth Sciences》2010,60(1):139-153
The Heihe River Basin is a typical arid inland river basin for examining stress on groundwater resources in northwest China.
The basin is composed of large volumes of unconsolidated Quaternary sediments of widely differing grain size, and during the
past half century, rapid socio-economic development has created an increased demand for groundwater resources. Understanding
the hydrogeochemical processes of groundwater and water quality is important for sustainable development and effective management
of groundwater resources in the Heihe River basin. To this end, a total of 30 representative groundwater samples were collected
from different wells to monitor the water chemistry of various ions and its quality for irrigation. Chemical analysis shows
that water presents a large spatial variability of chemical facies (SO4
2−–HCO3−, SO4
2−–Cl−, and Cl−–SO4
2−) as groundwater flow from recharge area to discharge area. The ionic ratio indicates positive correlation between the flowing
pairs of parameters: Cl− and Na+(r = 0.95), SO4
2− and Na+ (r = 0.84), HCO3
− and Mg2+(r = 0.86), and SO4
2− and Ca2+ (r = 0.91). Dissolution of minerals, such as halite, gypsum, dolomite, silicate, and Mirabilite (Na2SO4·10H2O) in the sediments results in the Cl−, SO4
2−, HCO3
−, Na+, Ca2+ and Mg2+ content in the groundwater. Other reactions, such as evaporation, ion exchange, and deposition also influence the water composition.
The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification
and the Wilcox diagram. The results show that most of the groundwater samples are suitable for irrigation uses barring a few
locations in the dessert region in the northern sub-basin. 相似文献
14.
Water samples were collected from the Yellow River and from wells for chemical and isotopic measurement in the counties of
Yucheng and Qihe, to which 6–9×108 m3 of water is diverted annually from the Yellow River. A zone of high electrical conductivity (EC) in groundwater corresponds
well on the regional scale with a ridge in groundwater level, which is the main flow path through the region, but has a low
gradient. The zone of highest EC along this ridge occurs at a position with the lowest ground altitude in the study area.
The unique characteristic of the groundwater is the linear relationship among the principal anions as the result of mixing.
The mixing effect is confirmed by its isotopic signature, which was then used to calculate the contributions from three sources:
rainfall, old water, and diverted water with an average mixing rate of 18, 17, and 65%, respectively. As an indicator of water
movement, Cl– content varies across a wide range in the profile from 30–10 m with a maximum concentration at about 1.2 m depth. Concentrations
are relatively stable at about 2 m, which is the average boundary of the saturated and unsaturated zone. The water from the
Yellow River has proved to be dominant in mixing in the aquifer in terms of groundwater flow and geochemistry.
Electronic Publication 相似文献
15.
The source of fluoride toxicity in Muteh area,Isfahan, Iran 总被引:1,自引:0,他引:1
Behnam Keshavarzi Farid Moore Ali Esmaeili Fatemeh Rastmanesh 《Environmental Earth Sciences》2010,61(4):777-786
Endemic dental fluorosis has been observed in most inhabitants of three villages of Muteh area, located in northwest of Isfahan
province, with mottled enamel related to high levels of fluoride in drinking water (1.8–2.2 ppm). Forty-seven groundwater
samples from six villages were collected and fluoride concentrations along with physico-chemical parameters were analyzed.
Fluoride concentration in this area varies from 0.2 to 9.2 mg/l with highest fluoride level at Muteh gold mine (Chahkhatun
mine). Fluoride concentration positively correlates with pH and HCO3
− indicating that alkaline pH provides a suitable condition for leaching of fluoride from surrounding rocks. The district is
mainly covered by three lithological units, namely, metamorphic and granite rocks, alluvial sediments, and carbonate rocks.
Factor analysis shows that parameters can be classified into four components: electrical conductivity (EC), total dissolved
solids (TDS), Cl−, Na+ and K+, pH and F−, SO4
2−and Mg2+, HCO3
− and Ca2
+. The groundwaters from the three geological units were compared using Mann–Whitney U test. The order of median fluoride concentration is: metamorphic and granite rocks > alluvial sediments > carbonate rocks.
Hence, the fluoride content is most probably related to fluoride-bearing minerals such as amphibole and mica group minerals
in metamorphic and granitic rocks. The concentration of fluoride in drinking water wells located near the metamorphic complex
in Muteh area is above 2 ppm. 相似文献
16.
Nitrate pollution of groundwater in Toyserkan,western Iran 总被引:5,自引:2,他引:3
Mohsen Jalali 《Environmental Earth Sciences》2011,62(5):907-913
A total of 95 groundwater samples were collected from Toyserkan, western Iran to assess the chemical composition and nitrate
(NO3
−) status of groundwater. The most prevalent water type is Ca–HCO3 followed by water types Ca–Mg–HCO3. In comparison with the World Health Organization (WHO) drinking water guideline of 50 mg l−1 for NO3
−, a total of nine wells (9.5%) showed higher concentrations. In 36% of samples (34) NO3
− concentration was low (<20 mg l−1), and in 53.7% of samples (51), in the range of 20–50 mg l−1. The samples were classified into four groups based on NO3
− and chloride (Cl−) concentrations. Of the samples, 40% were classified as group 4 and were relatively high in Cl− and NO3
− (Cl− > 47 mg l−1, NO3
− > 27 mg l−1). The high correlation between NO3
− and Cl− (r = 0.86, p < 0.01) is consistent with a manure source, resulting from the practice of adding salt to animal feed. Pollution of groundwaters
appeared to be affected by the application of inorganic fertilizer at greater than agronomic rates, Cl-salt inputs, and irrigation
practice. 相似文献
17.
Water fluxes were estimated and a water budget developed for the land surface and a surficial 10-m-deep section of the coastal
sabkhas that extend from the city of Abu Dhabi, United Arab Emirates, west to the border with Saudi Arabia. The fluxes were
estimated on the basis of water levels and hydraulic conductivities measured in wells and evaporation rates measured with
a humidity chamber. In contrast with conceptual models proposed in earlier studies, groundwater inflow is estimated to be
small, whereas the largest components of the water budget are recharge from rainfall and evaporation from the water table.
Estimates within a rectilinear volume of sabkha, defined as 1 m wide by 10 km long by 10 m deep, indicate that about 1 m3/year of water enters and exits by lateral groundwater flow; 40–50 m3/year enters by upward leakage; and 640 m3/year enters by recharge from rainfall. Based on the water and solute fluxes estimated for the upward leakage into the sabkha,
7–8 pore volumes of brine have entered the sabkha from below since the time the sabkha became saturated (7,000 years ago)
as a result of the last global sea-level rise.
相似文献
Ward E. SanfordEmail: |
18.
Hydrogeologic data of 455 water wells comprising geologic logs, water qualities, and aquifer test results are analyzed to
determine hydrogeological characteristics, water quality, and sustainable yield of the groundwater resources of Cheju volcanic
island. The groundwater of the island occurs in unconsolidated pyroclastic deposits and clinkers interbedded in highly jointed
basaltic and andesitic rocks as high-level, basal, and parabasal groundwater under unconfined conditions. The total storage
of groundwater is estimated at about 44 billion m3. The average transmissivity and specific yield of the aquifer are at about 0.34 m2 s–1(29300 m2 day–1) and 0.12, respectively. The average annual precipitation is about 3.39 billion m3, of which 1.49 billion m3– equivalent to 44.0% of the total annual precipitation – is recharged into aquifers, with 0.638 billion m3 year–1 of runoff and 1.26 billion m3 year–1 of evapotranspiration. Based on a groundwater budget analysis, the sustainable yield is estimated at about 0.62 billion m3 year–1, equivalent to 41.6% of annual recharge. A low-permeability marine sedimentary formation (Sehwari formation), composed of
loosely cemented sandy silt, was recently found to be situated at 120±68 m below mean sea level. If the said marine sediment
is distributed as a basal formation of the freshwater zone of the island, most of its groundwater will be of parabasal type.
So the marine sediment is one of the most important hydrogeological boundaries and groundwater occurrences in the area.
Received: 16 January 1997 / Accepted: 16 June 1997 相似文献
19.
Geochemical study of arsenic and other trace elements in groundwater and sediments of the Old Brahmaputra River Plain,Bangladesh 总被引:1,自引:1,他引:0
Faruque Ahmed M. Hawa Bibi Hiroaki Ishiga Takehiko Fukushima Teruyuki Maruoka 《Environmental Earth Sciences》2010,60(6):1303-1316
The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate
the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved
oxygen (DO) of 0.8–1.8 mg/l, Ca contents of 5–50 mg/l, and Fe contents of 0.2–12.9 mg/l. Arsenic concentrations ranged from
8 to 251 μg/l, with an average value of 63 μg/l. A strong positive correlation exists between As and Fe (r
2 = 0.802; p = 0.001) concentrations in groundwater. The stratigraphic sequences in the cores consist of yellowish silty clays at top,
passing downward into grayish to yellowish clays and sands. The uppermost 3 m and lower parts (from 13 to 31 m) of the core
sediments are oxidized (average oxidation reduction potential (ORP) +170 and +220 mV, respectively), and the ORP values gradually
become negative from 3 to 13 m depths (−35 to −180 mV), indicating that anoxic conditions prevail in the shallow aquifers
of the Brahmaputra plain. Age determinations suggest that clay horizons at ~10 m depth were deposited at around 2,000 and
5,000 years BP (14C ages) during the transgressive phase of sea-level change. Elevated concentrations of As, Pb, Zn, Cu, Ni, Cr, and V are present
in the silts and clays, probably due to adsorption onto clay particles. Significant concentrations of As occur in black peat
and peaty sediments at depths between 9 and 13 m. A strong positive correlation between As and Fe was found in the sediments,
indicating As may be adsorbed onto Fe oxides in aquifer sediments. 相似文献
20.
S. J. Appleyard 《Environmental Geology》1996,28(2):106-110
Drilling of 15 boreholes at a disused liquid waste disposal site near Perth, Western Australia, has indicated that a contamination
plume extends about 1000 m in a southerly direction from the site in the direction of groundwater flow. The plume is up to
600 m wide and 5–40 m thick. Chemical and microbiological analyses have indicated that contaminated groundwater contains high
concentrations of ammonia, iron, and bacteria at levels that commonly exceed national drinking water guidelines. It is likely
that a proposed water supply production well in the path of the contamination plume will have to be abandoned, and additional
wells may have to be abandoned if the plume continues to extend in the direction of groundwater flow. There is currently insufficient
information to indicate whether the plume is continuing to expand, but studies on similar plumes in the Perth metropolitan
area have indicated that contaminated groundwater can move at rates up to 100 m yr–1. Several other liquid waste disposal sites are now located in residential areas of Perth where wells are used for garden
irrigation. Further work is required to ensure that there is no potential impact of groundwater contamination on public health
in these areas.
Received: 31 July 1995 · Accepted: 18 September 1995 相似文献