Assessing groundwater vulnerability using GIS-based DRASTIC model for Ahmedabad district,India     

Mona Khakhar  Jayesh P. Ruparelia  Anjana Vyas 《Environmental Earth Sciences》2017,76(12):440

The present research aims to derive the intrinsic vulnerability of groundwater against contamination using the GIS platform. The study applies DRASTIC model for Ahmedabad district in Gujarat, India. The model uses parameters like depth, recharge, aquifer, soil, topography, vadose zone and hydraulic conductivity, which depict the hydrogeology of the area. The research demonstrates that northern part of district with 46.4% of area is under low vulnerability, the central and southern parts with 48.4% of the area are under moderate vulnerability, while 5.2% of area in the south-east of district is under high vulnerability. It is observed from the study that lower vulnerability in northern part may be mostly due to the greater depth of vadose zone, deeper water tables and alluvial aquifer system with minor clay lenses. The moderate and high vulnerability in central and southern parts of study area may be due to lesser depth to water tables, smaller vadose zone depths, unconfined to semi-confined alluvial aquifer system and greater amount of recharge due to irrigation practices. Further, the map removal and single-parameter sensitivity analysis indicate that groundwater vulnerability index has higher influence of vadose zone, recharge, depth and aquifer parameters for the given study area. The research also contributes to validating the existence of higher concentrations of contaminants/indicators like electrical conductivity, chloride, total dissolved solids, sulphate, nitrate, calcium, sodium and magnesium with respect to groundwater vulnerability status in the study area. The contaminants/indicators exceeding the prescribed limits for drinking water as per Indian Standard 10500 (1991) were mostly found in areas under moderate and high vulnerability. Finally, the research successfully delineates the groundwater vulnerability in the region which can aid land-use policies and norms for activities related to recharge and seepage with respect to existing status of groundwater vulnerability and its quality.  相似文献   

Advection-Dispersion Analysis of Solute Transport in Undisturbed Soil Monoliths     

Karsten Høgh Jensen  Georgia Destouni  Mona Sassner 《Ground water》1996,34(6):1090-1097

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New firm formation in old industrial regions – a study of entrepreneurial in-migrants in Bergslagen,Sweden     

Mona Hedfeldt  Mats Lundmark 《Norsk geografisk tidsskrift. Norwegian journal of geography》2015,69(2):90-101

The article examines new firm formation in the old industrial region (OIR) of Bergslagen in Sweden, and in particular the role of in-migrants. The study is based on longitudinal georeferenced microdata (1993–2008) compiled by Statistics Sweden and providing information on individuals' attachments to the Swedish labour market, as well as workplaces and firms, education, income, and family composition. This specially commissioned database enabled the characterization and analysis of emerging forms of entrepreneurship and self-employment, as well as the socio-economics of the labour market. The longitudinal data allowed the authors to trace actions taken by individuals over time. The results indicate that new firm formation is related to private services, rather than to the traditional manufacturing sector and public services that currently dominate the regional labour market. Self-employed in-migrants are active in other sectors than non-migrants, and show some distinct features in terms of their lower age, better education, and more often non-Nordic background. The study showed that both in-migration and return migration had a positive, significant, and substantial effect on migrants' decision to start a business when a number of other individual characteristics had been controlled for.  相似文献   

Crustal structure of northern Egypt from joint inversion of receiver functions and surface wave dispersion velocities     

Ahmed Badawy  Mona Hegazi  Hanan Gaber  Ibrahim Korrat 《Journal of Seismology》2018,22(3):697-719

In this study, we used a combined inversion of body wave receiver functions and surface wave dispersion measurements to provide constraints on the crustal structure of northern Egypt. The two techniques are complementary to each other: receiver functions (RFs) are sensitive to shear-wave velocity contrasts, while surface wave dispersion (SWD) measurements are sensitive to finite variations of shear-wave velocity with depth. A database of 122 teleseismic events digitally recorded by the Egyptian National Seismological Network (ENSN) stations has been used as well. To enhance the resulting RFs at each ENSN station, the H-k stacking method was applied. A joint inversion process between the resulting receiver functions and the surface wave dispersion curves was applied as well. We have produced three averaged velocity structure models for distinct geographic and tectonic provinces namely Sinai, eastern desert, and western desert from east to the west respectively. These models will deeply help in estimation the epicenter distance of earthquake, focal mechanism solutions, and earthquake hazard analysis in northern Egypt. An obvious image of the subsurface structure has been determined which shows that generally the crustal structure of northern Egypt consists of three layers covered with a sequence of sediments that differs in thickness from across the region except in the Sharm area where the sedimentary cover is absent. The obtained results indicate that crustal thickness differs from east to west and reaches its maximum value of about 36 km at Siwa station (SWA) in the western desert and its minimum value of about 28 km at Sharm station (SHR) of the southern tip of the Sinai Peninsula. The Vp/Vs ratio varies between 1.71 and 2.07 in northern Egypt. Generally, the high values (1.93) of (Vp/Vs) at SWA station may reflect the well-known rich aquifer with fully saturated sediments of the Swia Oasis in the Western Desert. Moreover, the highest value (2.07) of (Vp/Vs) at BNS station may be attributed to the widespread recently discovered hydrocarbon fields at the Beni-Suef Basin along the Eastern Desert. Finally, an integrated geophysical and hydrological study of the dimensions and physical properties of the aquifer and hydrocarbon fields at SWA and BNS stations to confirm if they are sufficient to produce the elevated Vp/Vs ratios or not become essential and highly recommended.  相似文献   

Probabilistic failure analysis of riprap as riverbank protection under flood uncertainties     

Mona?JafarnejadEmail authorView author&#;s OrcID profile  Michael?Pfister  Eugen?Brühwiler  Anton?J.?Schleiss 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(7):1839-1851

Existing riverbank riprap could face the risk of failure if the flood regime changes in future. Additionally, changed sediment transport in rivers, as a possible result of climate change, impacts the failure risk of flood protection measures. Evaluation of this potential failure is the primary issue of riprap stability and safety assessment. The consequences of the bank failure are probably uncontrolled erosion and flooding with disastrous consequences in residential areas or damage to infrastructures. Thus, a probabilistic analysis of riprap failure considering different mechanisms due to the flood and sediment transport uncertainties is required to assess embankment stability. In this article, the concept of a probabilistic assessment model based on Monte Carlo simulation method, moment analysis methods, and Rosenblueth point estimation method are presented to define the failure risk of riprap as the river bank protection. The probability of failure in different modes, namely direct block erosion, toe scouring and overtopping, has been defined by taking into account the river bed level variation based on bedload transport described with a probabilistic function of the peak discharge. The result of three models comparison revealed a good agreement (the average deviation of less than 2%) in estimation of riprap failure probability. This model is a strategical tool to search the critical river reaches and helps to evaluate the risk maps. So that, the model could cover the engineering aspect of environmental stability in the rivers with riprap as the bank protections.  相似文献   

Chemical variations of sulfides and metal in enstatite chondrites—Introduction of a new classification scheme          下载免费PDF全文

Mona Weyrauch  Marian Horstmann  Addi Bischoff 《Meteoritics & planetary science》2018,53(3):394-415

In this study, the metal and sulfide compositions of 45 enstatite chondrites were analyzed to determine possible mineral-chemical trends correlated with the petrologic type. Data for 35 additional samples were taken from the literature. Considering the data from this huge number of different E chondrite samples (80 in total), none of the trends previously described in the literature could be clearly confirmed. Also, among the opaque phases of enstatite chondrites, no other “new” correlations between mineral chemistry and the petrologic type were found. However, major differences in the sulfide and metal chemistry became obvious. Specifically, a certain number of chondrites in the EH and the EL groups have Cr in troilite above 2 wt%, Fe in niningerite or alabandite above 20 wt%, and lack abundant daubréelite. Differences were also found for Ni concentrations in kamacite. Thus, we propose a system for classifying E chondrites by defining four major subgroups: EH_a, EL_a, EH_b, and EL_b. All subgroups show full petrologic sequences that are similar to each other. This observation, in combination with the differences in sulfide and metal chemistry, suggests an origin of the samples from different parent bodies. Considering the anomalous E chondrite samples that neither fit in the previous classification scheme nor in the new one described here, the samples investigated in this study require at least eight different parent bodies.  相似文献   

Si‐bearing metal and niningerite in Almahata Sitta fine‐grained ureilites and insights into the diversity of metal on the ureilite parent body     

Marian Horstmann  Munir Humayun  Mario Fischer‐Gödde  Addi Bischoff  Mona Weyrauch 《Meteoritics & planetary science》2014,49(10):1948-1977

A detailed mineralogical and chemical study of Almahata Sitta fine‐grained ureilites (MS‐20, MS‐165, MS‐168) was performed to shed light on the origin of these lithologies and their sulfide and metal. The Almahata Sitta fine‐grained ureilites (silicates <30 μm grain size) show textural and chemical evidence for severe impact smelting as described for other fine‐grained ureilites. Highly reduced areas in Almahata Sitta fine‐grained ureilites show large (up to ～1 mm) Si‐bearing metal grains (up to ～4.5 wt% Si) and niningerite [Mg_>0.5,(Mn,Fe)_<0.5S] with some similarities to the mineralogy of enstatite (E) chondrites. Overall, metal grains show a large compositional variability in Ni and Si concentrations. Niningerite grains probably formed as a by‐product of smelting via sulfidation. The large Si‐Ni variation in fine‐grained ureilite metal could be the result of variable degrees of reduction during impact smelting, inherited from coarse‐grained ureilite precursors, or a combination of both. Large Si‐bearing metal grains probably formed via coalescence of existing and newly formed metal during impact smelting. Bulk and in situ siderophile trace element abundances indicate three distinct populations of (1) metal crystallized from partial melts in MS‐20, (2) metal resembling bulk chondritic compositions in MS‐165, and (3) residual metal in MS‐168. Almahata Sitta fine‐grained ureilites developed their distinctive mineralogy due to severe reduction during smelting. Despite the presence of E chondrite and ureilite stones in the Almahata Sitta fall, a mixing relation of E chondrites or their constituents and ureilite material in Almahata Sitta can be ruled out based on isotopic, textural, and mineral‐chemical reasons.  相似文献   

Lake stratigraphy implies an 80 000 yr delayed melting of buried dead ice in northern Russia     

Mona Henriksen  Jan Mangerud  Alexei Matiouchkov  Aage Paus  John Inge Svendsen 《第四纪科学杂志》2003,18(7):663-679

Sediment cores from lakes Kormovoye and Oshkoty in the glaciated region of the Pechora Lowland, northern Russia, reveal sediment gravity flow deposits overlain by lacustrine mud and gyttja. The sediments were deposited mainly during melting of buried glacier ice beneath the lakes. In Lake Kormovoye, differential melting of dead ice caused the lake bottom to subside at different places at different times, resulting in sedimentation and erosion occurring only some few metres apart and at shifting locations, as further melting caused inversion of the lake bottom. Basal radiocarbon dates from the two lakes, ranging between 13 and 9 ka, match with basal dates from other lakes in the Pechora Lowland as well as melting of ice‐wedges. This indicates that buried glacier ice has survived for ca. 80 000 years from the last glaciation of this area at 90 ka until about 13 ka when a warmer climate caused melting of permafrost and buried glacier ice, forming numerous lakes and a fresh‐looking glacial landscape. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Why did some larger benthic foraminifera become so large and flat?     

Pamela Hallock  Mona Seddighi 《Sedimentology》2022,69(1):74-87

Biostromes and low-relief bioherms, some of which are characterized by exceptionally large, flat specimens of larger benthic foraminifera, are common in Palaeogene and Miocene carbonates, most notably those deposited along the Neotethys Seaway and tropical Pacific islands. By incorporating insights from palaeoceanographic research and the biology of living larger benthic foraminifera, a scenario is proposed that can account for palaeontological and sedimentological features while augmenting previous interpretations. Sexual reproduction by gamete broadcasting is common in foraminiferal taxa, including extant Nummulitidae and Amphisteginidae. Resultant zygotes can develop into tiny, resistant, easily dispersed propagules that recruit in suitable benthic-environmental conditions. The role of algal symbiosis in the biology of larger benthic foraminifera is well-documented. Palaeoceanographically, such taxa proliferated during times of reduced thermal stratification of the oceans. In regions with exceptionally clear, nutrient-depleted waters, ‘twilight-zone’ light penetration was sufficient, at least intermittently, to support some photosynthesis. On outer-shelf or promontory sites at depths of ca 100 to 200 m, the tiny propagules of larger benthic foraminiferal species, incorporating algal symbionts with the lowest light requirements, could have settled and recruited, growing very slowly, nourished by feeding on bacteria and the limited photosynthate produced by their algal symbionts. Under such conditions, thin microspheric individuals of one or two larger benthic foraminiferal taxa could have survived and grown slowly over several years to very large shell diameters, seldom reproducing asexually. Resulting carbonate accumulation rates would have been very slow, such that even rare disturbances by currents, major storms or internal waves could have produced evidence of winnowing and sedimentary structures. The fossil evidence of such habitats should include biostromes or possibly low-relief bioherms of low diversity assemblages characterized by abundant, exceptionally large, flat, microspheric larger benthic foraminifera.  相似文献   

Macrochondrules in chondrites—Formation by melting of mega‐sized dust aggregates and/or by rapid collisions at high temperatures?     

Mona WEYRAUCH  Addi BISCHOFF 《Meteoritics & planetary science》2012,47(12):2237-2250

Abstract– Seventy‐four macrochondrules with sizes >3 mm were studied. Considering the extraordinary size of the chondrules (occasionally achieving a mass of 1000 times (and more) the mass of a normal‐sized chondrule), the conditions in the formation process must have been somewhat different compared with the conditions for the formation of the common chondrules. Macrochondrules are typically rich in olivine and texturally similar to specific chondrule types (barred, radial, porphyritic, and cryptocrystalline) of normal‐sized chondrules. However, our studies show that most of the macrochondrules are fine‐grained or have elongated crystals (mostly BO, RP, and C), which lead to the assumption that they were once totally molten and cooled quite rapidly. Porphyritic chondrules belong to the least abundant types of macrochondrules. This distribution of chondrule types is highly unusual and just a reverse of the distribution of chondrule types among the typical‐sized chondrules in most chondrite groups except for the CH and CB chondrites. New chondrule subtypes (like radial‐olivine [RO] or multi‐radial [MR] chondrules) are defined to better describe the textures of certain large chondrules. Macrochondrules may have formed due to melting of huge precursor dust aggregates or due to rapid collisions of superheated melt droplets, which led to the growth of large molten spherules in regions with high dust densities and high electrostatic attraction.  相似文献