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1.
M. Shamsudduha L. J. Marzen A. Uddin M.-K. Lee J. A. Saunders 《Environmental Geology》2009,57(7):1521-1535
The present study has examined the relationship of groundwater arsenic (As) levels in alluvial aquifers with topographic elevation,
slope, and groundwater level on a large basinal-scale using high-resolution (90 m × 90 m) Shuttle Radar Topography Mission
(SRTM) digital elevation model and water-table data in Bangladesh. Results show that high As (>50 μg/l) tubewells are located
in low-lying areas, where mean surface elevation is approximately 10 m. Similarly, high As concentrations are found within
extremely low slopes (<0.7°) in the country. Groundwater elevation (weekly measured by Bangladesh Water Development Board)
was mapped using water-table data from 950 shallow (depth <100 m) piezometers distributed over the entire country. The minimum,
maximum and mean groundwater elevation maps for 2003 were generated using Universal Kriging interpolation method. High As
tubewells are located mainly in the Ganges–Brahmaputra–Meghna delta, Sylhet Trough, and recent floodplains, where groundwater
elevation in shallow aquifers is low with a mean value of 4.5 m above the Public Works Datum (PWD) level. Extremely low groundwater
gradients (0.01–0.001 m/km) within the GBM delta complex hinder groundwater flow and cause slow flushing of aquifers. Low
elevation and gentle slope favor accumulation of finer sediments, As-carrying iron-oxyhydroxide minerals, and abundant organic
matter within floodplains and alluvial deposits. At low horizontal hydraulic gradients and under reducing conditions, As is
released in groundwater by microbial activity, causing widespread contamination in the low-lying deltaic and floodplain areas,
where As is being recycled with time due to complex biogeochemical processes. 相似文献
2.
Groundwater vulnerability is a cornerstone in evaluating the risk of groundwater contamination and developing management options
to preserve the quality of groundwater. Based on the professional model (DRASTIC model) and geographical information system
(GIS) techniques, this paper carries out the shallow groundwater vulnerability assessment in the Zhangye Basin. The DRASTIC
model uses seven environmental parameters (depth to water, net recharge, aquifer media, soil media, topography, impact of
vadose zone, and hydraulic conductivity) to characterize the hydrogeological setting and evaluate aquifer vulnerability. According
to the results of the shallow groundwater vulnerability assessment, the Zhangye Basin can be divided into three zones: low
groundwater vulnerability risk zone (risk index <120); middle groundwater vulnerability risk zone (risk indexes 120–140) and
high risk zone (risk index >140). Under the natural conditions, the middle and high groundwater vulnerability risk zones of
the Zhangye Basin are mainly located in the groundwater recharge zones and the important cities. The high, middle and low
groundwater vulnerability risk zones of the Zhangye Basin cover around 17, 21 and 62% of study area, respectively. 相似文献
3.
Alternative water resources in granitic rock: a case study from Kinmen Island,Taiwan 总被引:1,自引:1,他引:0
Tai-Sheng Liou Yuan-Hsi Lee Li-Wei Chiang Wayne Lin Tai-Rong Guo Wen-Shan Chen Jeng-Ming Chien 《Environmental Earth Sciences》2010,59(5):1033-1046
Kinmen Island is a small, tectonically stable, granitic island that has been suffering from a scarcity of fresh water resources
due to excessive annual evapotranspiration over annual precipitation. Recent studies further indicate that shallow (0–70 m)
sedimentary aquifers, the major sources of groundwater supply, have already been over-exploited. Therefore, this preliminary
study is to investigate the existence of exploitable water resources that can balance the shortage of fresh water on this
island. Site characterization data are obtained from island-wide geophysical surveys as well as small-scale tests performed
in a study area formed by three deep (maximum depth to 560 m) vertical boreholes installed in mid-east Kinmen northeast to
Taiwu Mountain. Vertical fracture frequency data indicate that the rock body is fractured with a spatially correlated pattern,
from which three major fracture zones (depths 0–70, 330–360, and below 450 m) can be identified. Geologic investigations indicate
that the deepest fracture zone is caused by the large-scale, steeply dipping Taiwushan fault. This fault may have caused a
laterally extensive low-resistivity zone, a potential fractured aquifer, near Taiwu Mountain. The middle fracture zone is
induced by the Taiwushan fault and intersects the fault approximately 21 m southeast of the study area below a depth of 350 m.
Slug testing results yield fracture transmissivity varying from 4.8 × 10−7 to 2.2 × 10−4 m2/s. Cross-hole tests have confirmed that hydraulic connectivity of the deeper rock body is controlled by the Taiwushan fault
and the middle fracture zone. This connectivity may extend vertically to the sedimentary aquifers through high-angle joint
sets. Despite the presence of a flow barrier formed by doleritic dike at about 300 m depth, the existence of fresh as well
as meteoric water in the deeper rock body manifests that certain flow paths must exist through which the deeper fractured
aquifers can be connected to the upper rock body. Therefore, groundwater stored within the Taiwushan fault and the associated
low-resistivity zone can be considered as additional fresh water resources for future exploitation. 相似文献
4.
J. Jiménez-Martínez K. Tamoh L. Candela F. J. Elorza D. Hunkeler 《Mathematical Geosciences》2012,44(2):187-208
Tritium is a short-lived radioactive isotope (T
1/2=12.33 yr) produced naturally in the atmosphere by cosmic radiation but also released into the atmosphere and hydrosphere
by nuclear activities (nuclear power stations, radioactive waste disposal). Tritium of natural or anthropogenic origin may
end up in soils through tritiated rain, and may eventually appear in groundwater. Tritium in groundwater can be re-emitted
to the atmosphere through the vadose zone. The tritium concentration in soil varies sharply close to the ground surface and
is very sensitive to many interrelated factors like rainfall amount, evapotranspiration rate, rooting depth and water table
position, rendering the modeling a rather complex task. Among many existing codes, SOLVEG is a one-dimensional numerical model
to simulate multiphase transport through the unsaturated zone. Processes include tritium diffusion in both, gas and liquid
phase, advection and dispersion for tritium in liquid phase, radioactive decay and equilibrium partitioning between liquid
and gas phase. For its application with bare or vegetated (perennial vegetation or crops) soil surfaces and shallow or deep
groundwater levels (contaminated or non-contaminated aquifer) the model has been adapted in order to include ground cover,
root growth and root water uptake. The current work describes the approach and results of the modeling of a tracer test with
tritiated water (7.3×108 Bq m−3) in a cultivated soil with an underlying 14 m deep unsaturated zone (non-contaminated). According to the simulation results,
the soil’s natural attenuation process is governed by evapotranspiration and tritium re-emission. The latter process is due
to a tritium concentration gradient between soil air and an atmospheric boundary layer at the soil surface. Re-emission generally
occurs during night time, since at day time it is coupled with the evaporation process. Evapotranspiration and re-emission
removed considerable quantities of tritium and limited penetration of surface-applied tritiated water in the vadose zone to
no more than ∼1–2 m. After a period of 15 months tritium background concentration in soil was attained. 相似文献
5.
In this study, we tried to model the processes of moisture and heat transfers in the soil–vegetation–atmosphere system in
an integrated comprehensive way. The purpose of the study is to simulate profiles of soil water content and temperature at
root active zone (i.e., 0–50 cm), taking the root water uptake, soil evaporation, and canopy transpiration into account. The
water and heat transfer equations are solved by an iterative Newton–Raphson technique and a finite difference method is used
to solve the governing equations. Soil water content and soil temperature dynamics could be simulated rather accurately in
a cropped field on Loess Plateau area. The water and heat transfer flux predicted by the classical theory of Philip and de
Vries (Tans Am Geophys Union 38:222–232, 1957) slightly overestimated near the surface and underestimated at the deeper depths, as a result of the overestimated soil evaporation
at the top soil layer (0–10 cm) and underestimated crop canopy transpiration at the deeper depths (10–50 cm). Water content
tended to be underestimated for the entire profile at the soil surface (from 0 to 50 cm). Soil temperatures during the simulated
period was slightly overestimated in the nighttimes and underestimated in the daytimes, as a result of the underestimated
soil water content at the top soil layer (0–10 cm) and overestimated at the deeper depths (10–50 cm). Soil temperatures tended
to be underestimated for the entire profile at the soil surface (from 0 to 50 cm). While the sum of the water and heat regimes
yielded a much better match with the soil water content and soil temperature obtained from the field observations. The results
obtained show that the model coupled water and heat transfer is able to capture the dynamics of soil water content. 相似文献
6.
Deformation mechanisms and hydraulic properties of fault zones in unconsolidated sediments; the Roer Valley Rift System,The Netherlands 总被引:1,自引:0,他引:1
In general, faults cutting through the unconsolidated sediments of the Roer Valley Rift System (RVRS), The Netherlands, form
strong barriers to horizontal groundwater flow. The relationships between deformation mechanisms along fault zones and their
impact on the hydrogeological structure of the fault zone are analyzed in a shallow (0–5 m below land surface) trench over
one of the faults in the study area. Recently developed digital-image-analysis techniques are used to estimate the spatial
distribution of hydraulic conductivity at the millimeter-scale and to describe the micromorphologic characteristics of the
fault zone. In addition, laboratory measurements of hydraulic conductivity on core-plug samples show the larger-scale distribution
of hydraulic conductivity in the damage zone flanking the main fault plane. Particulate flow is the deformation mechanism
at shallow depths, which causes the damage zone around the fault, in the sand-rich parts, to have a relatively enhanced hydraulic
conductivity. The fault core is characterized by reduced hydraulic conductivity due to clay smearing, grain-scale mixing,
and iron-oxide precipitation.
Electronic Publication 相似文献
7.
Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula,Lagos, Nigeria 总被引:2,自引:0,他引:2
A. A. Adepelumi B. D. Ako T. R. Ajayi O. Afolabi E. J. Omotoso 《Environmental Geology》2009,56(5):927-933
Recently, the deterioration of water quality in the coastal zones of Lekki Peninsula area of Lagos due to saltwater infiltration
into the freshwater aquifer has become a major concern. With the aim of providing valuable information on the hydrogeologic
system of the aquifers, the subsurface lithology and delineating the groundwater salinity, vertical electrical resistivity
(VES) sounding survey was carried out utilizing surface Schlumberger electrode arrays, and electrode spacing varying between
1 and 150 m. The DC resistivity surveys revealed significant variations in subsurface resistivity. Also, the VES resistivity
curves showed a dominant trend of decreasing resistivity with depth (thus increasing salinity). In general, the presence of
four distinct resistivity zones were delineated viz.: the unconsolidated dry sand (A) having resistivity values ranging between
125 and 1,028 Ωm represent the first layer; the fresh water-saturated soil (zone B) having resistivity values which correspond
to 32–256 Ωm is the second layer; the third layer (zone C) is interpreted as the mixing (transition) zone of fresh with brackish
groundwater. The resistivity of this layer ranges from 4 to 32 Ωm; while layer four (zone D) is characterized with resistivities
values generally below 4 Ωm reflecting an aquifer possibly containing brine. The rock matrix, salinity and water saturation
are the major factors controlling the resistivity of the formation. Moreover, this investigation shows that saline water intrusion
into the aquifers can be accurately mapped using surface DC resistivity method. 相似文献
8.
J. W. Peterson E. M. Johnson J. L. Cencer C. J. Thomason 《Environmental Geology》2006,49(8):1125-1138
An insect, Folsomia candida, was found in a shallow aquifer along the southwestern coast of Michigan. F. candida is a standard organism for soil toxicity testing but its occurrence in groundwater is uncommon to rare, or has been under-reported
in the literature. Attempts to correlate the presence of F. candida to water and soil parameters yielded: (1) F. candida is present in the upper 15–25 cm of topsoil, but absent in the underlying vadose zone except directly above the water table,
regardless of the presence in groundwater; (2) F. candida is most abundant in groundwater 4.3–5.0 m below land surface; (3) Most F. candida occur in wells with dissolved oxygen ranging from 4 to 5 ppm; (4) F. candida is most abundant in water between about 14 and 18°C; (5) F. candida is abundant in groundwater with high concentrations of Cl−, Na+, and K+; and, (6) Small differences in pore space volume determine the feasibility of F. candida occupancy, but not the presence of F. candida in the study area. 相似文献
9.
Eva Pacioni Marco Petitta Ezio Burri Maria Fanelli Piero Mazzeo Fabrizio Ruggieri 《Environmental Earth Sciences》2010,61(1):201-216
This paper analyses flow and transport of pesticides from the unsaturated zone to groundwater so as to predict concentration
of those contaminants in the Fucino Plain’s groundwater, by site investigations and numerical simulations. Pesticides were
detected in surface water (peaks of 13 μg L−1) and groundwater (peaks of 0.37 μg L−1). Modelling tools made it possible to identify that pattern of precipitation, organic matter content, and root thickness
are the key factors involved in vertical seepage of pesticides. Numerical simulations indicated that a significant fraction
of contaminants is leached from the most surficial soil layers through runoff, while only a secondary fraction is mobilised
towards groundwater. Likelihood of contaminating deep groundwater is fairly low, whereas surface waters show higher susceptibility.
Results of the proposed conceptual hydrogeological model show that pesticides are more likely to be entrained by mixing of
stream water with shallow groundwater in periods of high water exploitation from shallow wells. 相似文献
10.
The natural (electrical) potential (NP) method – also known as self-potential, spontaneous potential and streaming potential
(SP) – has been used to locate areas of groundwater flow in karst terrane. NP is the naturally occurring voltage at the ground
surface resulting from ambient electrical currents within the earth. The measurement of NP can be used to characterize groundwater
flow in karst terrane because electrical potential gradients are generated by the horizontal flow of water along fractures
or conduits and the vertical infiltration of water into fractures or shafts. NP data from a site on the Mitchell Plain of
southern Indiana, USA, revealed that NP data can be decomposed into three components: topographic effect, residual NP and
noise. At this site, NP was inversely proportional to elevation, but the correlation varied with time. The topographic correction
factor varied from –2.5 to –1.2 mV/m (NP change per unit elevation increase), with an average linear correlation coefficient
(R) of 0.95. Because the site slopes toward an adjacent creek that is the local groundwater discharge zone, one possible explanation
for this effect is a streaming-potential mechanism generated by groundwater movement toward the creek. The residual NP data
revealed three negative anomalies at the survey area. Two of them coincide with sinkholes. A part of the third anomaly is
coincident with a small valley, and concentrated infiltration does occur at this elevation in other valleys at the site, as
evidenced by the existence of sinkholes. However, the dispersed, low-magnitude nature of the third anomaly does not prove
the existence of concentrated groundwater recharge activity.
Received: 18 March 1998 · Accepted: 27 April 1998 相似文献
11.
John Rapaglia 《Estuaries and Coasts》2005,28(5):705-713
Venice Lagoon, Italy, rests on a series of aquifers that are 1,000 m thick. Measurements of submarine groundwater discharge
(SGD) were made in Venice Lagoon using benthic chambers vented to a plastic collection bag. Two hundred measurements taken
in a pristine northern lagoon site (Isola la Cura) revealed flow rates as high as 200 cm d−1 with an average of 30 cm d−1. Over 100 measurements taken adjacent to a bulkhead shoreline in the Porto Marghera industrial zone (Fusina) showed flow
rates as high as 30 cm d−1 and averaging 6 cm d−1. These flow rates, if representative of even a fraction of the lagoon floor, are easily able to account for the 15% deficit
previously calculated between precipitation and runoff for the entire Venice Lagoon drainage basin. Land elevation surrounding
the Venice Lagoon is < 10 m within 20 km of the shoreline and is unable to support any substantial onshore water table. Submarine
groundwater discharge most likely represents upward artesian discharge from deeper partially confined aquifers. Over 60 samples
were collected in total from both sites for nutrient analysis. Ammonium concentration was found to be 2–8 fold higher in the
device water than in the lagoon water at the northern site depending on season, and 10–30 times higher at the industrial zone
site. These numbers suggest that SGD may be the primary pathway for nutrients and perhaps other contaminants to enter Venice
Lagoon. 相似文献
12.
Few hydrology studies have investigated glacial till older than Illinoian time (> 300,000 BP) despite these older tills overlying a large portion of North America. An 8- and 6-well monitoring well nest installed into a 31 m thick pre-Illinoian till sequence near Cedar Rapids, Iowa was characterized using traditional hydrologic methods and chemical tracers. The aquitard system consists of about 9 m of fine-grained oxidized pre-Illinoian till overlying 22 m of unoxidized till and Devonian dolomite bedrock. Hydraulic conductivity ranged from 10−7 m/s in oxidized till and 10−10 m/s in unoxidized till. Hydraulic head relations indicated downward groundwater flow through the till profile with hydraulic gradients steepest near the unoxidized till/bedrock interface. Tritium and nitrate concentrations indicated recent (< 50 years old) recharge to a depth of 9–12 m below land surface. 18O and 2H results ranged between −6.2 to −7.9% and −38.0 to −50.9%, respectively, and plotted near the local Meteoric Water Line. A 1 per mil shift toward less negative 18O values with depth may suggest a climate change signal contained in the till water but more data are needed to verify this trend. Vertical groundwater velocity through the unoxidized till was estimated to range from 0.4 to 5.7 cm/year. The thickness of unoxidized pre-Illinoian till in Linn County was estimated from available records and contoured against vertical travel times to evaluate the effectiveness of pre-Illinoian till in preventing nitrate migration to underlying bedrock aquifers. 相似文献
13.
Xi Wang Zhang Bing Fang Wu Xiao Song Li Shan Long Lu 《Environmental Earth Sciences》2012,65(1):221-229
The spatial pattern of soil erosion can provide valuable insights into the soil erosion processes that require a rapid assessment
in practical applications. Generally, quantitative technique is expensive and time-consuming. The objective of this paper
is to reveal the spatial pattern of erosion with a rapid assessment method. The affecting factors such as land cover, vegetation
fraction and slope gradient are integrated into this method using a qualitative means. Beijing-1 images in 2006 were used
to produce land-cover and vegetation fraction, and 1:50,000 topographic maps were used to calculate slope gradient. The study
area was classified into six grades. Results show that the upstream area of Guanting Reservoir, in general, is exposed to
a moderate risk; there are 17,740.33 km2 of land that suffered from water soil erosion in 2006, occupied 40.69% of the total area, and most of the soil erosion area
is on the light and moderate risk, which occupied 25.05 and 62.83% of the eroded area, respectively. Eight elevation zones
and six slope gradient zones were overlaid with the assessed risk. The analyzed results show that: (1) the areas above 2,000 m
have the lowest erosion risk, which is only 0.75% of the eroded area; 1,250–1,500 m elevation zone has the highest erosion
risk, which is 34.72% of the eroded area. (2) The slope gradient zone less than 5 degrees and greater than 35 degrees have
the lowest erosion risk, which is 0.02 and 0.75% of the eroded area, respectively; the slope gradient zone with 8–15 degrees
has the highest erosion risk, which is 36.40% of the eroded area. These results will be useful for water and soil conservation
management and the planning of mitigation measures. 相似文献
14.
This study evaluated remedial alternatives for a petroleum-contaminated site where an unconfined aquifer composed of a sandy layer of about 3–3.5 m thickness is covered by alluvial deposits and reclaimed soil of about 1.5 m thickness. Precambrian gneiss, of low permeability, lies below the sandy layer. The shallow water table is about 3 m below the surface, but shows high fluctuations of up to 1.5 m in response to precipitation events. The unsaturated soil near the water table and the groundwater are highly contaminated with petroleum hydrocarbons, especially toluene, which have apparently leaked from storage tanks. Selection of the remedial alternatives required consideration of the relevant laws on soil and groundwater conservation in Korea, the results of risk analysis and the hydrogeological conditions. The contaminated area has been divided into zones in which different remediation goals are set based on risk analysis and the degree of natural attenuation. It is estimated that the clean-up goal can be achieved in two years by the combined use of a trench drain and well point pumping to collect the contaminated groundwater for treatment, and a dual air injection system for the contaminated soil. 相似文献
15.
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
16.
The shear wave velocity (VS) profile based on the dispersive characteristics of fundamental mode of Rayleigh type surface waves indicate underground
stiffness change with depth as well as near surface stiffness. The most important utility of shear wave velocity (VS) is to estimate the liquefaction hazard potential of an area particularly in seismically active region. Rayleigh type surface
waves were utilized to estimate the velocity (VS) of shallow subsurface covering a depth range of 30–50 m employing multichannel analysis of surface waves. The liquefaction
hazard map predicts an approximate percentage of an area that will have surface manifestation of liquefaction during an earth
quake. The surface wave data acquired in an earth quake prone region of Jabalpur (Seismic zone III), India, yields a velocity
(VS) range of 200–750 m/s corresponding to the subsurface depth of 30–35 m. The results were analyzed for possible liquefaction
hazard in the study area and presented here besides the N values. 相似文献
17.
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
18.
B. J. M. Goes 《Hydrogeology Journal》1999,7(3):294-304
The Hadejia–Nguru Wetlands are annually inundated flood plains in semi-arid northeastern Nigeria. The area has a unique ecosystem
that forms a natural barrier against the encroachment of the Sahara desert. Both the rich wetland vegetation and local farmers
using shallow tube wells depend on a groundwater mound (with a water table less than 6 m below the surface) that is present
in the unconfined aquifer under the flood-plain area. Using well records (1991–97) and a hydrogeologic profile based on piezometers
that were monitored for two years, it is shown that recharge through the annually inundated flood plains is the source of
the groundwater mound. Maintenance of the groundwater-recharge function of the flood plains depends on wet-season releases
from two large upstream dams. On the basis of a water-budget method, the mean (1991–97) wet-season unconfined groundwater
recharge in the flood-plain area between Hadejia and Nguru and in the immediate vicinity (1250 km2) is estimated to be 132 mm (range, 73–197 mm). Outflow from the unconfined flood-plain aquifer to the unconfined upland aquifer
is approximately 10% of the wet-season flood-plain recharge. The unconfined groundwater outflow from the flood-plain area
can provide a significant contribution to the present-day rural water supply in the surrounding uplands, but it does not offer
much potential for additional groundwater abstraction. In addition to outflow to the upland aquifer (∼14 mm), the distribution
of the annually recharged water volume of the shallow flood-plain aquifer is (1) domestic uses (3 mm), (2) small-scale irrigation
(∼15 mm), and (3) evapotranspiration ( 1 100 mm). Along the hydrogeologic profile, the recharge in the upland (i.e., outflow
from the unconfined flood-plain aquifer and possibly diffuse rain-fed recharge) is in balance with the water uses (i.e., domestic
uses, groundwater outflow, and evapotranspiration). The absence of a seasonal water-level trend in the two piezometers in
the upland indicates that no rain-fed recharge occurs through preferential path-way (macropore) flow.
Received, June 1998 / Revised, November 1998, January 1999 / Accepted, January 1999 相似文献
19.
Kelly Addy Arthur Gold Barbara Nowicki James McKenna Mark Stolt Peter Groffman 《Estuaries and Coasts》2005,28(6):896-908
Coastal waters are severely threatened by nitrogen (N) loading from direct groundwater discharge. The subterranean estuary,
the mixing zone of fresh groundwater and sea water in a coastal aquifer, has a high potential to remove substantial N. A network
of piezometers was used to characterize the denitrification capacity and groundwater flow paths in the subterranean estuary
below a Rhode Island fringing salt marsh.15N-enriched nitrate was injected into the subterranean estuary (in situ push-pull method) to evaluate the denitrification capacity
of the saturated zone at multiple depths (125–300 cm) below different zones (upland-marsh transition zone, high marsh, and
low marsh). From the upland to low marsh, the water table became shallower, groundwater dissolved oxygen decreased, and groundwater
pH, soil organic carbon, and total root biomass increased. As groundwater approached the high and low marsh, the hydraulic
gradient increased and deep groundwater upwelled. In the warm season (groundwater temperature >12 °C), elevated groundwater
denitrification capacity within each zone was observed. The warm season low marsh groundwater denitrification capacity was
significantly higher than all other zones and depths. In the cool season (groundwater temperature <10.5 °C), elevated groundwater
denitrification capacity was only found in the low marsh. Additions of dissolved organic carbon did not alter groundwater
denitrification capacity suggesting that an alternative electron donor, possibly transported by tidal inundation from the
root zone, may be limiting. Combining flow paths with denitrification capacity and saturated porewater residence time, we
estimated that as much as 29–60 mg N could be removed from 11 of water flowing through the subterranean estuary below the
low marsh, arguing for the significance of subterranean estuaries in annual watershed scale N budgets. 相似文献
20.
An experiment was carried out in two soils of oasis farmland and the surrounding desert at the southern periphery of the Gurbantonggut
Desert, in central Asia, to test the effects of land use on soil organic carbon (SOC) stock and carbon efflux in deep soil.
The result showed that although SOC content in the topsoil (0–0.2 m) decreased by 27% after desert soil was cultivated, total
carbon stock within the soil profile (0–2.5 m) increased by 57% due to the significant increase in carbon stock at 0.2- to
2.5-m depth, and carbon efflux also markedly increased at 0- to 0.6-m depth. In the topsoil, the carbon process of the oasis
was mainly dominated by consumption; in the subsoil (0.2–0.6 m) it was likely to be co-dominated by storage and consumption,
and the greatest difference in SOC stock between the two soils also lay in this layer; while in the deep layer (0.6–2.5 m)
of the oasis, with a more stable carbon stock, there was carbon storage dominated. Moreover, carbon stocks in the deep layer
of the two soils contributed about 65% of the total carbon stocks, and correspondingly, microbial activities contributed 71%
to the total microbial activity in the entire soil profile, confirming the importance of carbon cycling in the deep layer.
Desert cultivation in this area may produce unexpectedly high carbon stocks from the whole profile despite carbon loss in
the topsoil. 相似文献