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1.
Water source and lake landscape position can strongly influence the physico‐chemical characteristics of flowing waters over space and time. We examined the physico‐chemical heterogeneity in surface waters of an alpine stream‐lake network (>2600 m a.s.l.) in Switzerland. The catchment comprises two basins interspersed with 26 cirque lakes. The larger lakes in each basin are interconnected by streams that converge in a lowermost lake with an outlet stream. The north basin is primarily fed by precipitation and groundwater, whereas the south basin is fed mostly by glacial melt from rock glaciers. Surface flow of the entire channel network contracted by ～60% in early autumn, when snowmelt runoff ceased and cold temperatures reduced glacial outputs, particularly in the south basin. Average water temperatures were ～4 °C cooler in the south basin, and temperatures increased by about 4–6 °C along the longitudinal gradient within each basin. Although overall water conductivity was low (<27 µS cm?1) because of bedrock geology (ortho‐gneiss), the south basin had two times higher conductivity values than the north basin. Phosphate‐phosphorus levels were below analytical detection limits, but particulate phosphorus was about four times higher in the north basin (seasonal average: 9 µg l?1) than in the south basin (seasonal average: 2 µg l?1). Dissolved nitrogen constituents were around two times higher in the south basin than in the north basin, with highest values averaging > 300 µg l?1 (nitrite + nitrate‐nitrogen), whereas particulate nitrogen was approximately nine times greater in the north basin (seasonal average: 97 µg l?1) than in the south basin (seasonal average: 12 µg l?1). Total inorganic carbon was low (usually <0·8 mg l?1), silica was sufficient for algal growth, and particulate organic carbon was 4·5 times higher in the north basin (average: 0·9 mg l?1) than in the south basin (average: 0·2 mg l?1). North‐basin streams showed strong seasonality in turbidity, particulate‐nitrogen and ‐phosphorus, and particulate organic carbon, whereas strong seasonality in south‐basin streams was observed in conductivity and dissolved nitrogen. Lake position influenced the seasonal dynamics in stream temperatures and nutrients, particularly in the groundwater/precipitation‐fed north‐basin network. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
2.
Chloride is a major anion in soil water and its concentration rises essentially as a function of evapotranspiration. Compared to herbaceous vegetation, high transpiration rates are measured for isolated trees, shelterbelts or hedgerows. This article deals with the influence of a tree hedge on the soil and groundwater Cl? concentrations and the possibility of using Cl? as an indicator of transpiration and water movements near the tree rows. Cl? concentrations were measured over 1 year at different depths in the unsaturated zone and in the groundwater along a transect intersecting a bottomland oak hedge. We observed a strong spatial heterogeneity of Cl? concentrations, with very high values up to 2 g l?1 in the unsaturated zone and 1·2 g l?1 in the upper part of the groundwater. This contrasts with the low and homogeneous concentrations (60–70 mg l?1) in the deeper part of the groundwater. Cl? accumulation in the unsaturated zone at the end of the vegetation season allows us to identify the active root zone extension of trees. In winter, upslope of the tree row, downwards leaching partly renews the soil solution in the root zone, while the slow water movement under the trees or farther downslope results in Cl? accumulation and leads to a salinization of the soil and groundwater. This salinization is of the same order as experimental conditions produce negative effects on oak seedlings. The measurement of Cl? concentrations in the unsaturated zone under tree rows at the end of the vegetation season would indicate whether certain topographic, pedological or climatic conditions are likely to favour a strong salinization of the soil, as observed in the present study. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
3.
Biologically mediated redox processes in the riparian zone, like denitrification, can have substantially beneficial impacts on stream water quality. The extent of these effects, however, depends greatly on the hydrological boundary conditions. The impact of hydrological processes on a wetland's nitrogen sink capacity was investigated in a forested riparian fen which is drained by a first‐order perennial stream. Here, we analysed the frequency distributions and time‐series of pH and nitrogen, silica, organic carbon and oxygen concentrations in throughfall, soil solution, groundwater and stream water, and the groundwater levels and stream discharges from a 3‐year period. During baseflow conditions, the stream was fed by discharging shallow, anoxic groundwater and by deep, oxic groundwater. Whereas the latter delivered considerable amounts of nitrogen (～0·37 mg l?1) to the stream, the former was almost entirely depleted of nitrogen. During stormflow, near‐surface runoff in the upper 30 cm soil layer bypassed the denitrifying zone and added significant amounts to the nitrogen load of the stream. Nitrate‐nitrogen was close to 100% of deep groundwater and stream‐water nitrogen concentration. Stream‐water baseflow concentrations of nitrate, dissolved carbon and silica were about 1·6 mg l?1, 4 mg l?1 and 7·5 mg l?1 respectively, and >3 mg l?1, >10 mg l?1 and <4 mg l?1 respectively during discharge peaks. In addition to that macroscale bypassing effect, there was evidence for a corresponding microscale effect: Shallow groundwater sampled by soil suction cups indicated complete denitrification and lacked any seasonal signal of solute concentration, which was in contrast to piezometer samples from the same depth. Moreover, mean solute concentration in the piezometer samples resembled more that of suction‐cup samples from shallower depth than that of the same depth. We conclude that the soil solution cups sampled to a large extent the immobile soil‐water fraction. In contrast, the mobile fraction that was sampled by the piezometers exhibited substantially shorter residence time, thus being less exposed to denitrification, but predominating discharge of that layer to the stream. Consequently, assessing the nitrogen budget based on suction‐cup data tended to overestimate the nitrogen consumption in the riparian wetland. These effects are likely to become more important with the increased frequency and intensity of rainstorms that are expected due to climate change. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
Located at southern coast of China, the Pearl River Delta (PRD) is facing serious water problems in both quantity and quality after its rapid urbanization in the last decade. Most remarkably, the local groundwater, that was used to be the source of drinking water before the urbanization was polluted due to poor management of the septic tanks. In order to study the effects of suburban development on local groundwater flow and water quality in the PRD region, Fengcun of Guangzhou has been chosen as the study area. In Fengcun, drinking water was groundwater before the 1990s, but now piped reservoir water is used by each family because the groundwater has been polluted. This study clarifies the source and process of the groundwater pollution from septic tanks using isotopic and geochemical characteristics, especially nitrate (NO3?) concentrations. Water samples were collected from the wells and ponds in Fengcun in March and July 2005 and in July 2006. Based on the pe–pH diagram, NO3? and ammonium of groundwater are from the effect of human activities, rather than from nitrification and ammonification of N2. NO3? pollution of groundwater is from point sources, and NO3? concentrations decrease from northeast to southwest. Groundwater is polluted rapidly by the leakage of septic tanks. NO3? concentrations of pollution sources were lower than 20 mg l?1 in March 2005, but had increased to about 120 mg l?1 in July 2006. This implies that groundwater protection should be strengthened in rural areas of the PRD. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
5.
Hydrograph separation to improve understanding of Dissolved Organic Carbon Dynamics in Headwater catchments 
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下载免费PDF全文 Dissolved organic carbon (DOC) is a key component of the global carbon cycle, but, to date, large uncertainties still exist on its source and fate in first‐order streams. In a 23 ha rangeland and steep‐slope headwater of South Africa, our aim was to quantify the contribution of overland flow (OF), soil water (SW) and ground water (GW) to DOC fluxes (DOCF), and to interpret the results in terms of DOC sources and fate. The average 2010–2011 DOC concentration (DOCC) at the catchment outlet was 4.7 mg C l?1 with a standard error of ±2.5 mg C l?1, which was significantly lower than in SW (15.2 ± 1.6 mg C l?1) and OF (11.9 ± 0.8 mg C l?1), but higher than in GW (2.3 ± 0.6 mg C l?1). Based on end‐member mixing using Si and Na concentration in the water compartments, the average SW contribution to DOCF was 66.4%, followed by OF (30.0%) and GW (3.6%). The resulting estimated DOCF at the catchment outlet was 8.05 g C m2 y?1. This was much higher than the observed value of 2.80 g C m2 y?1, meaning that 5.25 g C m2 y?1 or 65% of the DOC is lost during its downslope and/or downstream transport to the catchment outlet. Complementary investigations revealed that the DOCC in SW dropped from 15.2 ± 1.6 to 2.6 ± 0.3 mg C l?1 during its downslope transport to the river system, which corresponded to a net loss of 5.10 g C m2 y?1, or 97% of the catchment DOC losses. These results on DOC sources and potential fate in headwaters are expected to improve our understanding of the impact of hydrology on the global C‐cycle. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
6.
Study of the movement of water and solute within soil profiles is important for a number of reasons. Accumulation of prominent contaminants from agricultural chemicals in the unsaturated zone over the years is a major concern in many parts of the world. As a result, the unsaturated zone has been a subject of great research interest during the past decade. Hence, an intensive field study was conducted in a part of Palar and Cheyyar river basins to understand the variation of major ions and nutrients in the soil zone during paddy cultivation. The chloride and nitrate data were used to model the movement of these chemicals in the unsaturated zone using the HYDRUS‐2D model. The field study shows that fertilizer application and irrigation return flow increases the major ions and nutrients concentration in the unsaturated zone. Further, the nutrient concentrations are regulated by plant uptake, fertilizer application and infiltration rate. Additionally, denitrification and soil mineralization processes also regulate the nitrogen concentration in the unsaturated zone. The solute transport modelling study concluded that the simulated results match reasonably with the observed trends. Simulated concentrations of chloride and nitrate for a 5‐year period indicate that the concentrations of these ions fluctuate in a cyclic manner (from 60 to 68 mg l?1 and from 3·4 to 3·5 mg l?1 respectively in groundwater) with no upward and downward trend. The influence of excessive fertilizer application on groundwater was also modelled. The model predicts an increase of about 17 mg l?1 of chloride and 2·3 mg l?1 of nitrogen in the groundwater of this area when the application of fertilizers is doubled. The model indicates that the present level of use of agrochemicals is no threat to the groundwater quality. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
7.
《水文科学杂志》2013,58(6):1230-1240
Abstract This study aims to identify the hydrogeochemical processes influencing the high fluoride concentrations in groundwater of the Nairobi area, Kenya. For this purpose 16 groundwater samples were collected and analysed. Fluoride concentrations above the WHO standard are found in the downstream areas. The high F? concentrations are correlated with high sodium and pH and low Ca2+ concentrations. Weathering of sodium-rich alkaline igneous rocks causes a pH increase resulting in an increase in HCO3 ? and CO3 2- by dissolution of CO2. Groundwater becomes oversaturated compared to calcite and calcite precipitation occurs, leading to a decrease in Ca2+. This causes a sub-saturation with respect to fluorite and dissolution of fluorite increases the F? concentration. These reactions were modelled using the PHREEQC model and the results showed a good agreement with the measured groundwater quality, indicating that the proposed reactions are plausible for explaining the observed concentrations in groundwater. 相似文献
8.
Abstract Large-scale agricultural activities cause deterioration of groundwater resources throughout the world. This study focuses on the irrigated agricultural district of Jinghuiqu in Shaanxi, China. The objectives are to identify the main sources and processes that control nitrate transport, and to assess the impact of long-term irrigation practices on nitrate leaching. The hydrogeochemistry of major solute constituents and stable isotope ratios of NO3 ? in groundwater were used to identify historical sources of contamination and transformation processes occurring in the shallow groundwater of the Jinghuiqu irrigation district. The N-NO3 ? concentrations in groundwater ranged from 0.0 to more than 100 mg L?1 in April 1990, and from 0.47 to 42.0 mg L?1 in December 2009. Our measurements of N-NO3 ? show that the main reasons for this dramatic decline in N-NO3 ? concentrations from 1990 to 2009 are denitrification, which controls nitrogen types, together with the sharp decline of the groundwater table. The isotope ratios in collected samples showed that the source of nitrate was mainly manure, a result that corresponds with historical data showing that manure was the main nitrate source before the 1980s, and that fertilizers became dominant thereafter. A numerical model was then used to evaluate future impacts of current irrigation practices on groundwater sources. The HYDRUS-1D model was employed first to evaluate the water movement and the N-NO3 ? solute transport for a single irrigation pulse experiment carried out under field conditions, and then in evaluating the long-term impact of irrigation on N-NO3 ? leaching. Simulations showed that, after introducing irrigation, the downward drainage fluxes of N-NO3 ?, and the N-NO3 ? and N-tot concentrations increased at all depths within the 2-m soil profile. This indicates that N concentrations below 1-m depth and in the groundwater could become even more elevated with increased future irrigation. Editor D. Koutsoyiannis Citation Liu, X.-H., Sun, S.-J., Ji, P., and ?im?nek, J., 2013. Evaluation of historical nitrate sources in groundwater and impact of current irrigation practices on groundwater quality. Hydrological Sciences Journal, 58 (1), 1–15. 相似文献
9.
A two‐dimensional variable‐density groundwater flow and transport model was developed to provide a conceptual understanding of past and future conditions of nitrate (NO3) transport and estimate groundwater nitrate flux to the Gulf of Mexico. Simulation results show that contaminant discharge to the coast decreases as the extent of saltwater intrusion increases. Other natural and/or artificial surface waters such as navigation channels may serve as major sinks for contaminant loading and act to alter expected transport pathways discharging contaminants to other areas. Concentrations of NO3 in the saturated zone were estimated to range between 30 and 160 mg?L?1 as NO3. Relatively high hydraulic vertical gradients and mixing likely play a significant role in the transport processes, enhancing dilution and contaminant migration to depth. Residence times of NO3 in the deeper aquifers vary from 100 (locally) to about 300 years through the investigated aquifer system. NO3 mass fluxes from the shallow aquifers (0 to 5.7 × 104 mg?m?2?day?1) were primarily directed towards the navigation channel, which intersects and captures a portion of the shallow groundwater flow/discharge. Direct NO3 discharge to the sea (i.e. Gulf of Mexico) from the shallow aquifer was very low (0 to 9.0 × 101 mg · m?2?day?1) compared with discharge from the deeper aquifer system (0 to 8.2 × 103 mg?m?2?day?1). Both model‐calibrated and radiocarbon tracer‐determined contaminant flux estimates reveal similar discharge trends, validating the use of the model for density‐dependent flow conditions. The modelling approach shows promise to evaluate contaminant and nutrient loading for similar coastal regions worldwide. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
10.
The hydrology and nitrogen biogeochemistry of a riparian zone were compared before and after the construction of beaver dams along an agricultural stream in southern Ontario, Canada. The beaver dams increased surface flooding and raised the riparian water table by up to 1·0 m. Increased hydraulic gradients inland from the stream limited the entry of oxic nitrate‐rich subsurface water from adjacent cropland. Permeable riparian sediments overlying dense till remained saturated during the summer and autumn months, whereas before dam construction a large area of the riparian zone was unsaturated in these seasons each year. Beaver dam construction produced significant changes in riparian groundwater chemistry. Median dissolved oxygen concentrations were lower in riparian groundwater after dam construction (0·9–2·1 mg L?1) than in the pre‐dam period (2·3–3·9 mg L?1). Median NO3‐N concentrations in autumn and spring were also lower in the post‐dam (0·03–0·07 mg L?1) versus the pre‐dam period (0·1–0·3 mg L?1). In contrast, median NH4‐N concentrations in autumn and spring months were higher after dam construction (0·3–0·4 mg L?1) than before construction (0·13–0·14 mg L?1). Results suggest that beaver dams can increase stream inflow to riparian areas that limit water table declines and increase depths of saturated riparian soils which become more anaerobic. These changes in subsurface hydrology and chemistry have the potential to affect the transport and transformation of nitrate fluxes from adjacent cropland in agricultural landscapes. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
11.
ABSTRACTThe aim of the study was to locate and describe groundwater outflows in a selected lake basin and measure the spring output of water and the physical characteristics of the studied waters (temperature and conductivity). The final aim was to gauge the effects of the spring output on the lake hydrology. The time scope of the work included the period from January 2011 to September 2012. The spatial scope of the work included the area of Lake Raduńskie Górne and its direct catchment located in the Kashubian Lake District in northern Poland. Four groundwater outflows were located in the course of the study. Their total output was 4.6 L s?1 and ranged between 0.5 and 2.5 L s?1. This produces an annual yield of about 145 000 m3 year?1. These results confirm that one of the forms of supply to the lakes are the under-lake springs. For lakes located in the area of young glacial accumulation this can be decisive.
Editor D. Koutsoyiannis Associate editor D. Gerten 相似文献
12.
In many agricultural areas, hedgerows give rise to strong expectations of reducing the inputs of excess nitrate to the groundwater and rivers. This study aims to analyse the spatial and seasonal influences of a hedgerow on nitrate dynamics in the soil and groundwater. Nitrate (NO3?) and chloride (Cl?) concentrations were measured with spatially dense sampling in the unsaturated soil and in the groundwater along a transect intersecting a bottomland oak (Quercus rubor) hedgerow after the growing season and during the dormant season. We explain NO3? dynamics by using Cl? as an index of tree‐root extension and water transfer. At the end of the growing season, NO3? is entirely absorbed by the trees over a large and deep volume corresponding to the rooting zone, where, in contrast Cl? is highly concentrated due to root exclusion. However, these observed patterns in the soil have no influence on the deep groundwater composition at this season. During the dormant season, water transfer processes feeding the shallow groundwater layer are different upslope and downslope from the hedgerow in relation to the thickness of the unsaturated zone. Upslope, the shallow groundwater is fed by rainwater infiltration through the soil which favours Cl? dilution. Right under the hedge and downslope, the rapid ascent of the groundwater near the ground surface prevents rainwater input and Cl? dilution. Under the hedgerow the highest concentrations of Cl? coincide with the absence of NO3? in the shallow groundwater layer and with high concentrations of dissolved organic carbon. The absence of NO3? during the dormant season seems to be due to denitrification in the hedgerow rooting zone when it is rapidly saturated by groundwater. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
The concentration levels of Cd (25 ng l?1), Cu (0.45 μg l?1), Ni (0.48 μg l?1), Fe (0.2–7.0 μg l?1), Pb (40 ng l?1) and Zn (0.80 μg l?1) have been determined in the Danish Sounds and in the Kattegat. Different sampling techniques have been used and analyses have been carried out separately by two different investigators, both using freon-extraction followed by determination by atomic absorption spectrometry (a.a.s.). Except for iron, found mainly in the particulate phase, the metals are found predominantly in a dissolved and labile (extractable) form. The results are compared with trace metal levels found in the two main water masses entering the Kattegat—the North Sea and the Baltic Sea. 相似文献
14.
Solute concentrations and fluxes in rainfall, throughfall and stemflow in two forest types, and stream flow in a 90 ha catchment in southern Chile (39°44′S, 73°10′W) were measured. Bulk precipitation pH was 6·1 and conductivity was low. Cation concentrations in rainfall were low (0·58 mg Ca2+ l?1, 0·13 mg K+ l?1, 0·11 mg Mg2+ l?1 and <0·08 mg NH4–N l?1), except for sodium (1·10 mg l?1). Unexpected high levels of nitrate deposition in rainfall (mean concentration 0·38 mg NO3–N l?1, total flux 6·3 kg NO3–N ha?1) were measured. Concentrations of soluble phosphorous in bulk precipitation and stream flow were below detection limits (<0·09 mg l?1) for all events. Stream‐flow pH was 6·3 and conductivity was 28·3 μs. Stream‐water chemistry was also dominated by sodium (2·70 mg l?1) followed by Ca, Mg and K (1·31, 0·70 and 0·36 mg l?1). The solute budget indicated a net loss of 3·8 kg Na+ ha?1 year?1, 5·4 kg Mg2+ ha?1 year?1, 1·5 kg Ca2+ ha?1 year?1 and 0·9 kg K+ ha?1 year?1, while 4·9 kg NO3–N ha?1 year?1 was retained by the ecosystem. Stream water is not suitable for domestic use owing to high manganese and, especially, iron concentrations. Throughfall and stemflow chemistry at a pine stand (Pinus radiata D. Don) and a native forest site (Siempreverde type), both located within the catchment, were compared. Nitrate fluxes within both forest sites were similar (1·3 kg NO3–N ha?1 year?1 as throughfall). Cation fluxes in net rainfall (throughfall plus stemflow) at the pine stand generally were higher (34·8 kg Na+ ha?1 year?1, 21·5 kg K+ ha?1 year?1, 5·1 kg Mg2+ ha?1 year?1) compared with the secondary native forest site (24·7 kg Na+ ha?1 year?1, 18·9 kg K+ ha?1 year?1 and 4·4 kg Mg2+ ha?1 year?1). However, calcium deposition beneath the native forest stand was higher (15·9 kg Ca2+ ha?1 year?1) compared with the pine stand (12·6 kg Ca2+ ha?1 year?1). Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
15.
Seawater intrusion causes many problems for groundwater quality, whereas natural remediation is time consuming. However, in cases where groundwater replenishment is feasible, groundwater quality remediation is possible and rapid. The alluvial aquifer in the lowland of the Glafkos River basin, which extends south of Patras city, was for over 30 years the major water source supplying the broader area. Groundwater quality has been degraded due to seawater intrusion, caused by overpumping and generally by inappropriate groundwater management. During the last decade, groundwater quality has been remedied due to diminished groundwater abstractions. The remediation rate was further higher because of rapid discharge of the brackish groundwater, through wells with freely flowing water in the coastal area, where, however, groundwater quality remains low. This paper deals with the hydrogeochemical processes that take place in the area. It is ascertained that ion exchange and mineral dilution processes are dominant. The ion relations between chloride, bromide and iodide, as well as the distribution maps of their concentrations, were used to determine the spatial distribution of the seawater intrusion front. In the lower part of the area in a distance from 1000 and 1500 m from the coast, the rBr?/rCl? ratio showed low values (<2·5 × 10?3) similar to those of seawater. The rI?/rCl? ratio also presented low values (<7 × 10?5), with the lowest one (2·7 × 10?5) detected along the coastline. In the upper part of the area, a gradual change of those ratios was observed upstream, until they receive values similar to those of the surface waters of Glafkos River. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
16.
Studies on the hydrogeological conditions of the Mesogea basin in east Attica reveal that the aquifers developed on the post‐alpine formations at the inner part of the coastal brackish zone exhibit positive hydraulic head. These Neogene and Quaternary deposits present high salt concentrations. Selected points were sampled (total 85: 51 wells and 34 boreholes) in order to obtain hydrogeological and hydrochemical data for a better understanding of the structure, operation and dynamics of the aquifer of the area. Statistical methods, R‐mode factor analysis and scatter‐plot diagrams were used for the hydrochemical analysis and presentation of the data. The groundwater resources are relatively weak and there is significant quality degradation due to the geological structure of the greater area, as well as the bad management of the aquifer and anthropogenic activities. Groundwater is characterized by high salt concentrations. Electrical conductivity values range between 260 and 6970 µS cm?1. High salt concentrations at the coastal aquifers are due to sea intrusion, whereas they are attributed to the dissolution of minerals of the geological environment in the inland area. The groundwaters of the study area can be classified into five water types: Ca–HCO3, Mg–HCO3, Na–HCO3, Na–Cl and Mg–Cl. They are saturated in dolomite and calcite, whereas they are unsaturated in anhydrite. High ion concentrations, e.g. ] (0‐221 mg l?1), ] (0·01‐1·88 mg l?1), ] (0·01‐6·75 mg l?1), as well as high heavy metals concentrations are attributed to anthropogenic impacts. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
17.
Factors contributing to nitrate contamination in a groundwater recharge area of the North China Plain 总被引：4，自引：0，他引：4 下载免费PDF全文
下载免费PDF全文 Shiqin Wang Changyuan Tang Xianfang Song Ruiqiang Yuan Zhiwei Han Yun Pan 《水文研究》2016,30(13):2271-2285
Nitrate contamination is a common problem in groundwater of the North China Plain (NCP) owing to overuse of fertilizers and discharge of wastewater. Accordingly, it is important to investigate nitrate contamination in recharge areas to understand the fate of nitrate in the plains area. In this study, the spatial and temporal distribution characteristics of nitrate and factors contributing to its sources and transformation in shallow groundwater of the Beiyishui River watershed, NCP, were analysed by a combination of multiple regression and multi‐tracer methods. The nitrate concentration of 79% of the samples exceeded the natural environmental standard of 13.3 mg l?1, while that of 23% of the samples exceeded the World Health Organization (WHO) drinking water standard of 50 mg l?1. Groundwater age estimation of the hill regions based on chlorofluorocarbons (CFCs) revealed a mix of young water from 1982 to 1990 and old, low CFC water. The analysis based on the variations in land use in past years revealed that part of the grassland was converted into woodland between 1980 and 1995; therefore, the land use at the recharge time was used to determine which surface conditions influence groundwater nitrate concentrations. Multiple regression analysis showed that point source pollution contributed to the high concentration of nitrate in the hill region. Fertilizer application associated with land use change from grassland to woodland was also related to the present nitrate concentration. In the plains area, the contribution of fresh water from fault fractures and denitrification led to 31 to 72% and 6 to 51% reductions in nitrate concentrations, respectively. Our results suggested that controlling point source contamination and fertilizer input to hilly regions of the study will prevent groundwater of the plains area from deterioration in future years by mixing fresh water into the aquifers and decreasing denitrification, and therefore nitrate concentrations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
18.
ABSTRACTIntegrated two-dimensional electrical resistivity imaging (ERI) and hydrochemical surveys were used to investigate the groundwater alluvial aquifer in Kuala Langat, Malaysia. The study in the Langat basin considered the thickness of the aquifer, the depth of the bedrock, the regions influenced by seawater intrusion, and the monitoring of water levels. The resistivity imaging results show that the upper layer consists of clay, while the second layer is an aquifer whose thickness varies mostly in the range of 10–30 m, and in some cases extends to 40 m. The bedrock depth varies from 30 to 65 m. The chemical analyses were carried out on groundwater samples from nine boreholes collected between 2008 and 2012. The analyses indicate that the total dissolved solids (TDS) exceed 1000 mg L-1 near the coastal area and are often less than 500 mg L-1 further inland. The ERI and hydrochemical analyses reveal that groundwater in the study area, especially towards the coast, is a mixture of brackish and fresh waters.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR M.D. Fidelibus 相似文献
19.
Abstract Groundwater development potential in northern Ghana (108 671 km2) has been assessed by combining spatial layers for five critical factors—recharge rate, regolith thickness, transmissivity, borehole success rate and static water level—through a multi-criteria analysis approach to rank development potential from the viewpoint of groundwater availability and accessibility at a resolution of 1 km2. The results indicate a high potential for development in the study area, as about 70% of the area was found to have high to moderate groundwater availability, while 83% has high to medium groundwater accessibility. Comparing the two main hydrogeological environments, the Precambrian Basement rocks (PCB) area was found to generally have a higher groundwater development potential than the Voltaian Sedimentary rocks (VSB). More detailed investigation revealed that the VSB can produce a small proportion of exceptionally high-yielding boreholes that can support large-scale irrigation. A test of the reliability of results showed that generally, the majority of high- and low-yielding boreholes fall in areas predicted by the model as having high and low groundwater availability, respectively. Editor D. Koutsoyiannis; Associate editor D. Hughes Citation Forkuor, G., Pavelic, P., Asare, E., and Obuobie, E., 2013. Modelling potential areas of groundwater development for agriculture in northern Ghana using GIS/RS. Hydrological Sciences Journal, 58 (2), 437–451. 相似文献
20.
Abstract An investigation on the groundwater potentials of the Egbe-Mopa area in central Nigeria, underlain by the Basement Complex, is presented. The investigation involved mapping of the subsurface by use of vertical electrical soundings; measurement of depth to groundwater; and evaluation of hydraulic conductivity, transmissivity and yield by means of pumping test interpretation. The results indicate subsurface units that range from three to five resistivity layers; depth to groundwater of 0–10 m; overburden thickness of 3–16 m; hydraulic conductivity of 6.2?×?10?6 to 3.4?×?10?4 m/s; transmissivity of 4.3?×?10?7 to 2?×?10?3 m2/s; and groundwater yield of 0.2–2.5 L/s. The hydraulic head assessments revealed a general northward groundwater flow direction. The study identified three aquifer potential types, of high, medium and low productivity, respectively. Based on the longitudinal conductance of the overburden units, four distinct Aquifer Protective Capacity zones were delineated, namely, poor, weak, moderate and good. Citation Okogbue, C.O. and Omonona, O.V., 2013. Groundwater potential of Egbe-Mopa basement area, central Nigeria. Hydrological Sciences Journal, 58 (4), 826–840. 相似文献