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  • 1
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    Springer
    In:  Karst Water Environment : Advances in Research, Management and Policy | The Handbook of Environmental Chemistry
    Publication Date: 2018-09-11
    Description: Examination of microbial communities within karst aquifers is an important aspect of determining the quality of the drinking water obtained from groundwater. While past work has been based on culture-based assays, a more complete view of the microbial community within karst aquifers can be achieved using molecular approaches based on DNA sequencing. Due to a reduced cell number when compared to surface environments, collecting sufficient microbial cells for analysis in karst aquifers can be problematic. In addition to issues of cell density, particulates due to the geologic location, technological limitations of equipment that can be hand-carried and work for extended periods underground, and even the physical access to some of these subsurface sites, all contribute to making examination of the microbiology in karst aquifers a challenge. This chapter highlights some of the approaches we have used to successfully isolate microbial cells for DNA extraction from an aquifer accessed in a remote cave location. The methods we developed can aid other researchers to evaluate the microbiology of similar isolated karst aquifers.
    Language: English
    Type: http://purl.org/eprint/type/BookItem
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  • 2
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    In:  Natural Gas Engines: For Transportation and Power Generation | Energy, Environment, and Sustainability
    Publication Date: 2018-11-29
    Description: Lean-burn natural gas engines can be used to reduce exhaust emissions significantly. However, as the mixture is leaned out, the occurrence of extinction and incomplete combustion increases, resulting in poor performance and stability, as well as elevated levels of unburned hydrocarbon (UHC) and nitrogen oxides (NOx) emissions. The partially stratified charge (PSC) method can be used to mitigate these issues, while extending the lean misfire limit (LML) beyond its equivalent, homogeneous level. In this chapter, the PSC ignition and combustion processes are examined following a comprehensive experimental and numerical approach. Experiments are conducted in an idealized PSC configuration, using a constant volume combustion chamber (CVCC), to identify the principle enabling mechanisms of the PSC methodology. Engine tests conducted in a single-cylinder research engine (SCRE) demonstrate the feasibility of various PSC implementations in improving performance and emission characteristics in real-world settings. Complementary numerical analyses for the CVCC are obtained through large eddy simulations (LES), while Reynolds-averaged Navier–Stokes (RANS) simulations are conducted for SCRE with reduced chemical kinetics. The corresponding simulated results provide additional insights in characterizing the effect of fuel stratification on flame kernel maturation and flame propagation, the interplay between chemistry and turbulence at different overall air–fuel ratios, as well as formation of major pollutant species.
    Language: English
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  • 3
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    In:  In: Oceanographic and Biological Aspects of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer Oceanography Series . Springer, Cham, pp. 185-194.
    Publication Date: 2018-12-11
    Description: The deep-sea brines of the Red Sea are unusual extreme environments and form characteristically steep gradients across the brine-seawater interfaces. Due to their unusual nature and unique combination of physical-chemical conditions these interfaces provide an interesting source of new findings in the fields of geochemistry, geology, microbiology, biotechnology, virology, and general biology. The current chapter summarizes recent and new results in the study of geochemistry and life at the interfaces of brine-filled deeps of the Red Sea.
    Type: Book chapter , NonPeerReviewed
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  • 4
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    In:  In: Geological Setting, Palaeoenvironment and Archaeology of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer, Cham, pp. 37-52.
    Publication Date: 2018-12-14
    Description: Continental rifting and ocean basin formation can be observed at the present day in the Red Sea, which is used as the modern analogue for the formation of mid-ocean ridges. Competing theories for how spreading begins—either by quasi-instantaneous formation of a whole spreading segment or by initiation of spreading at multiple discrete “nodes” separated by thinned continental lithosphere—have been put forward based, until recently, on the observations that many seafloor features and geophysical anomalies (gravity, magnetics) along the axis of the Red Sea appeared anomalous compared to ancient and modern examples of ocean basins in other parts of the world. The latest research shows, however, that most of the differences between the Red Sea Rift (RSR) and other (ultra)slow-spreading mid-ocean ridges can be related to its relatively young age and the presence and movement of giant submarine salt flows that blanket large portions of the rift valley. In addition, the geophysical data that was previously used to support the presence of continental crust between the axial basins with outcropping oceanic crust (formerly named “spreading nodes”) can be equally well explained by processes related to the sedimentary blanketing and hydrothermal alteration. The observed spreading nodes are not separated from one another by tectonic boundaries but rather represent “windows” onto a continuous spreading axis which is locally inundated and masked by massive slumping of sediments or evaporites from the rift flanks. Volcanic and tectonic morphologies are comparable to those observed along slow and ultra-slow spreading ridges elsewhere and regional systematics of volcanic occurrences are related to variations in volcanic activity and mantle heat flow. Melt-salt interaction due to salt flows, that locally cover the active spreading segments, and the absence of large detachment faults as a result of the nearby Afar plume are unique features of the RSR. The differences and anomalies seen in the Red Sea still may be applicable to all young oceanic rifts, associated with plumes and/or evaporites, which makes the Red Sea a unique but highly relevant type example for the initiation of slow rifting and seafloor spreading and one of the most interesting targets for future ocean research.
    Type: Book chapter , NonPeerReviewed
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  • 5
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    In:  In: Geological Setting, Palaeoenvironment and Archaeology of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer, Cham, pp. 221-232.
    Publication Date: 2018-12-14
    Description: Hydrothermal circulation at mid-ocean ridges and assimilation of hydrothermally altered crust or hydrothermal fluids by rising magma can be traced by measuring chlorine (Cl) excess in erupted lavas. The Red Sea Rift provides a unique opportunity to study assimilation of hydrothermally altered crust at an ultra-slow spreading ridge (maximum 1.6 cm yr−1 full spreading rate) by Cl, due to its saline seawater (40–42‰, cf. 35‰ in open ocean water), the presence of (hot) brine pools (up to 270‰ salinity and 68 °C) and the thick evaporite sequences that flank the young rift. Absolute chlorine concentrations (up to 1300 ppm) and Cl concentrations relative to minor or trace elements of similar mantle incompatibility (e.g., K, Nb) are much higher in Red Sea basalts than in basalts from average slow spreading ridges. Mantle Cl/Nb concentrations can be used to calculate the Cl-excess, above the magmatic Cl, that is present in the samples. Homogeneous within-sample Cl concentrations, high Cl/H2O, the decoupling of Cl-excess from other trace elements and its independence of the presence of highly saline seafloor brines at the site of eruption indicate that Cl is not enriched at the seafloor. Instead we find basaltic Cl-excess to be spatially closely correlated with evidence of hydrothermal activity, suggesting that deeper assimilation of hydrothermal Cl is the dominant Cl-enrichment process. A proximity of samples to both evaporite outcrops and bathymetric signs of volcanism on the seafloor enhance Cl-excess in basalts. The basaltic Cl-excess can be used as a tracer together with new bathymetric maps as well as indications of hydrothermal venting (hot brine pools, metalliferous Hydrothermal circulation at mid-ocean ridges and assimilation of hydrothermally altered crust or hydrothermal fluids by rising magma can be traced by measuring chlorine (Cl) excess in erupted lavas. The Red Sea Rift provides a unique opportunity to study assimilation of hydrothermally altered crust at an ultra-slow spreading ridge (maximum 1.6 cm yr−1 full spreading rate) by Cl, due to its saline seawater (40–42‰, cf. 35‰ in open ocean water), the presence of (hot) brine pools (up to 270‰ salinity and 68 °C) and the thick evaporite sequences that flank the young rift. Absolute chlorine concentrations (up to 1300 ppm) and Cl concentrations relative to minor or trace elements of similar mantle incompatibility (e.g., K, Nb) are much higher in Red Sea basalts than in basalts from average slow spreading ridges. Mantle Cl/Nb concentrations can be used to calculate the Cl-excess, above the magmatic Cl, that is present in the samples. Homogeneous within-sample Cl concentrations, high Cl/H2O, the decoupling of Cl-excess from other trace elements and its independence of the presence of highly saline seafloor brines at the site of eruption indicate that Cl is not enriched at the seafloor. Instead we find basaltic Cl-excess to be spatially closely correlated with evidence of hydrothermal activity, suggesting that deeper assimilation of hydrothermal Cl is the dominant Cl-enrichment process. A proximity of samples to both evaporite outcrops and bathymetric signs of volcanism on the seafloor enhance Cl-excess in basalts. The basaltic Cl-excess can be used as a tracer together with new bathymetric maps as well as indications of hydrothermal venting (hot brine pools, metalliferous sediments) to predict where hydrothermal venting or now inactive hydrothermal vent fields can be expected. Sites of particular interest for future hydrothermal research are the Mabahiss Deep, the Thetis-HadarbaHatiba Deeps and Shagara-Aswad-Erba Deeps (especially their large axial domes), and Poseidon Deep. Older hydrothermal vent fields may be present at the Nereus and Suakin Deeps. These sites significantly increase the potential of hydrothermal vent field prospection in the Red Sea.
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  • 6
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    In:  In: Oceanographic and Biological Aspects of the Red Sea. , ed. by Rasul, N. M. A. and Stewart, I. C. F. Springer, Cham, Switzerland, pp. 401-418. ISBN 978-3-319-99416-1
    Publication Date: 2018-12-14
    Description: Coral reefs in the Red Sea belong to the most diverse and productive reef ecosystems worldwide, although they are exposed to strong seasonal variability, high temperature, and high salinity. These factors are considered stressful for coral reef biota and challenge reef growth in other oceans, but coral reefs in the Red Sea thrive despite these challenges. In the central Red Sea high temperatures, high salinities, and low dissolved oxygen on the one hand reflect conditions that are predicted for ‘future oceans’ under global warming. On the other hand, alkalinity and other carbonate chemistry parameters are considered favourable for coral growth. In coral reefs of the central Red Sea, temperature and salinity follow a seasonal cycle, while chlorophyll and inorganic nutrients mostly vary spatially, and dissolved oxygen and pH fluctuate on the scale of hours to days. Within these strong environmental gradients micro- and macroscopic reef communities are dynamic and demonstrate plasticity and acclimatisation potential. Epilithic biofilm communities of bacteria and algae, crucial for the recruitment of reef-builders, undergo seasonal community shifts that are mainly driven by changes in temperature, salinity, and dissolved oxygen. These variables are predicted to change with the progression of global environmental change and suggest an immediate effect of climate change on the microbial community composition of biofilms. Corals are so-called holobionts and associate with a variety of microbial organisms that fulfill important functions in coral health and productivity. For instance, coral-associated bacterial communities are more specific and less diverse than those of marine biofilms, and in many coral species in the central Red Sea they are dominated by bacteria from the genus Endozoicomonas. Generally, coral microbiomes align with ecological differences between reef sites. They are similar at sites where these corals are abundant and successful. Coral microbiomes reveal a measurable footprint of anthropogenic influence at polluted sites. Coral-associated communities of endosymbiotic dinoflagellates in central Red Sea corals are dominated by Symbiodinium from clade C. Some corals harbour the same specific symbiont with a high physiological plasticity throughout their distribution range, while others maintain a more flexible association with varying symbionts of high physiological specificity over depths, seasons, or reef locations. The coral-Symbiodinium endosymbiosis drives calcification of the coral skeleton, which is a key process that provides maintenance and formation of the reef framework. Calcification rates and reef growth are not higher than in other coral reef regions, despite the beneficial carbonate chemistry in the central Red Sea. This may be related to the comparatively high temperatures, as indicated by reduced summer calcification and long-term slowing of growth rates that correlate with ocean warming trends. Indeed, thermal limits of abundant coral species in the central Red Sea may have been exceeded, as evidenced by repeated mass bleaching events during previous years. Recent comprehensive baseline data from central Red Sea reefs allow for insight into coral reef functioning and for quantification of the impacts of environmental change in the region.
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  • 7
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    In:  Springer Oceanography Book series . Springer, Cham, Switzerland, 550 pp. ISBN 978-3-319-99417-8
    Publication Date: 2018-12-14
    Description: This book includes invited contributions presenting the latest research on the oceanography and environment of the Red Sea. In addition to covering topics relevant to research in the region and providing insights into marine science for non-experts, it is also of interest to those involved in the management of coastal zones and encourages further research on the Red Sea
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  • 8
    Publication Date: 2019-02-06
    Description: Diseases increasingly threaten aquaculture of kelps and other seaweeds. At the same time, protection concepts that are based upon application of biocides are usually not applicable, as such compounds would be rapidly diluted in the sea, causing ecological damage. An alternative concept could be the application of immune stimulants to prevent and control diseases in farmed seaweeds. We here present a pilot study that investigated the effects of oligoalginate elicitation on juvenile and adult sporophytes of Saccharina japonica cultivated in China and on adult sporophytes of Saccharina latissima cultivated in Germany. In two consecutive years, treatment with oligoalginate clearly reduced the detachment of S. japonica juveniles from their substrate curtains during the nursery stage in greenhouse ponds. Oligoalginate elicitation also decreased the density of endobionts and the number of bacterial cells on sporophytes of S. latissima that were cultivated on sea-based rafts. However, the treatment increased the susceptibility of kelp adults to settlement of epibionts (barnacles in Germany and filamentous algal epiphytes in China). In addition, oligoalginate elicitation accelerated the aging of S. japonica adults. Based upon these findings, oligoalginate elicitation could be a feasible way to provide “environmentally friendly” protection of kelp juveniles in nurseries. The same treatment causes not only beneficial, but also unwanted effects in adult kelp sporophytes. Therefore, it is not recommended as a treatment after the juvenile stage is completed. Future tests with other elicitors and other cultivated seaweed species may allow for the development of more feasible applications of targeted defense elicitation in seaweed aquaculture.
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  • 9
    Publication Date: 2019-02-11
    Description: The present study details the effects of basin-scale hydrographic characteristics of the Red Sea on the macroecology of Chaetognatha, a major plankton component in the pelagic realm. The hydrographic attributes and circulation of the Red Sea as a result of its limited connection with the northern Indian Ocean make it a unique ecohydrographic region in the world ocean. Here, we aimed to identify the prime determinants governing the community structure and vertical distribution of the Cheatognatha in this ecologically significant world ocean basin. The intrusion of Gulf of Aden Water influenced the Chaetognatha community composition in the south, whereas the overturning circulation altered their vertical distribution in the north. The existence of hypoxic waters (〈 100 µmol kg−1) at mid-depth also influenced their vertical distribution. The detailed evaluation of the responses of the different life stages of Chaetognatha revealed an increased susceptibility of adult individuals to hypoxic waters compared to immature stages. Higher oxygen demands of the adults for the egg and sperm production might have prevented them from inhabiting the oxygen-deficient mid-depth zones. The carbon and nitrogen content of the Copepoda and Chaetognatha communities and the quantification of the predation impact of Chaetognatha on Copepoda based on the feeding rate helped in corroborating the significant trophic link between these two prey–predator taxa. The observed influences of physical and chemical attributes on the distribution of Chaetognatha can be used as a model example for the role of the hydrography on the zooplankton community of the Red Sea.
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  • 10
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉In many important coastal habitats, a combination of increasing soil salinization due to sea level rise, reduced precipitation and storm surges may induce regime shift from salinity-intolerant glycophytic vegetation to salinity-tolerant halophytic species. Early detection of regime shift due to salinity stress in vegetation may facilitate conservation efforts. It has been shown that the 〈sup〉18〈/sup〉O value of water in the xylem of trees can be used as a surrogate for salinity in the rooting zone of plants. Coupling measured δ〈sup〉18〈/sup〉O values in the tree xylem with simulated δ〈sup〉18〈/sup〉O values in trees and salinity in the vadose zone can be used to investigate competitive responses of glycophytic versus halophytic trees. MANTRA-O18 simulations suggest that the impacts of salinization on diminishing the resilience of salinity-intolerant trees can be detected up to 25 years before the glycophytic trees are threatened with regime shift to halophytic species. This early detection provides critical lead time and valuable information and insights useful for planning adaptation strategy to mitigate against the adverse impacts of sea level rise and climate change.〈/p〉
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    Topics: Geosciences
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  • 11
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The advection-dispersion equation, ADE, has commonly been used to describe solute transport in fractured rock. However, there is one key question that must be addressed before the mathematical form of the so-called Fickian dispersion that underlies the ADE takes on physical meaning in fractures. 〈em〉What is the required travel distance, or travel time, before the Fickian condition is met and the ADE becomes physically reasonable?〈/em〉 A simple theory is presented to address this question in tapered channels. It is shown that spreading of solute under forced-gradient flow conditions is mostly dominated by advective mechanisms. Nevertheless, the ADE might be valid under natural flow conditions. Furthermore, several concerns are raised in this paper with regard to using the concept of a field-scale matrix diffusion coefficient in fractured rocks. The concerns are mainly directed toward uncertainties and potential bias involved in finding the continuum model parameters. It is illustrated that good curve fitting does not ensure the physical reasonability of the model parameters. It is suggested that it is feasible and adequate to describe flow and transport in fractured rocks as taking place in three-dimensional networks of channels, as embodied in the channel network concept. It is argued that this conceptualization provides a convenient framework to capture the impacts of spatial heterogeneities in fractured rocks and can accommodate the physical mechanisms underlying the behavior of solute transport in fractures. All these issues are discussed in relation to analyzing and predicting actual tracer tests in fractured crystalline rocks.〈/p〉
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  • 12
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Urban groundwater in Sub-Saharan Africa provides vital freshwater to rapidly growing cities. In the Thiaroye aquifer of Dakar (Senegal), groundwater within Quaternary unconsolidated sands provided nearly half of the city’s water supply into the 1980s. Rising nitrate concentrations traced to faecal contamination sharply curtailed groundwater withdrawals, which now contribute just 5% to Dakar’s water supply. To understand the attenuation capacity of this urban aquifer under a monsoonal semi-arid climate, stable-isotope ratios of O and H and radioactive tritium (〈sup〉3〈/sup〉H), compiled over several studies, are used together with piezometric data to trace the origin of groundwater recharge and groundwater flowpaths. Shallow groundwaters derive predominantly from modern rainfall (tritium 〉2 TU in 85% of sampled wells). δ〈sup〉18〈/sup〉O and δ〈sup〉2〈/sup〉H values in groundwater vary by 〉4 and 20‰, respectively, reflecting substantial variability in evaporative enrichment prior to recharge. These signatures in groundwater regress to a value on the local meteoric water line that is depleted in heavy isotopes relative to the weighted-mean average composition of local rainfall, a bias that suggests recharge derives preferentially from isotopically depleted rainfall observed during the latter part of the monsoon (September). The distribution of tritium in groundwater is consistent with groundwater flowpaths to seasonal lakes and wetlands, defined by piezometric records. Piezometric data further confirm the diffuse nature and seasonality of rain-fed recharge. The conceptual understanding of groundwater recharge and flow provides a context to evaluate attenuation of anthropogenic recharge that is effectively diffuse and constant from the vast network of sanitation facilities that drain to this aquifer.〈/p〉
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  • 13
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Water scarcity in urban areas is a common problem in many cities of India, and Visakhapatnam, a fast growing industrial city on the east coast of India, is no exception. Increasing urban population, industrial expansion and shrinking surface-water sources have widened the gap between the demand and supply, resulting in groundwater depletion and saline water intrusion along the coastal region. MODFLOW is a widely used numerical groundwater flow model but requires realistic estimation of field inputs in order to contribute effectively to recommendations for proper management actions. The present study focuses on computing the spatial and temporal variations of model inputs such as pumping and recharge rates using the field data collected from various organizations. The developed PMWIN MODFLOW model provides insight into the present and future trends in the variation of groundwater levels. Observation wells data are used in the model calibration to fix the aquifer parameters through the parameter estimation algorithm PEST. Models are performed for four projected scenarios with different rates of pumping and recharge values. Results indicate the importance of improving the recharge capability of potential areas, to sustain the aquifer’s capacity to cope with stresses on groundwater resources. The model results are useful to fix optimum pumping limits in the study area for sustainable groundwater management and will help to prevent disastrous impacts on groundwater potential in the future.〈/p〉
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  • 14
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Limited scientific information has been published on the application of tools in the geographic information system (GIS) environment to understand factors that influence groundwater recharge. The objectives of the research reported here were to understand the spatial variability of factors that influence groundwater recharge using GIS, and to estimate the amount of groundwater recharge and its spatial distribution in Illala catchment, northern Ethiopia. Reconnaissance surveys coupled with satellite imagery were used to collect data related to water, dry-deposition and hydrogeology from the study catchment. The data analysis involved geo-statistics. The chloride mass balance (CMB) method was applied to estimate mean groundwater recharge. The study catchment is distinguished by a semi-arid climate (average aridity index value of 0.35) and it is dominated by limestone-shale-marl intercalation. Mean chloride concentration in rainwater ranges from 0.4 to 1.28 mg/L, while values in dry deposition vary from 1.78 to 1.82 mg/m〈sup〉2〈/sup〉. Groundwater and runoff chloride concentration ranges are 1.4–31.96 mg/L and 0.60–1.56 mg/L, respectively. Mean annual groundwater recharge estimated by the CMB method varies from 6.1 to 288.3 mm, and the mean groundwater recharge represents 11.7% of the 548 mm mean annual rainfall. The CMB-derived groundwater recharge estimation showed a nearly comparable value with the recharge estimated by other approaches. More effort should be made to boost groundwater recharge using various recharge enhancing techniques such as constructing artificial recharge wells and water harvesting structures, targeting areas with the lowest recharge.〈/p〉
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  • 15
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Several methodologies exist for the design of optimal groundwater monitoring networks. Those that employ geostatistical techniques are usually dependent on a variogram. In practice, different variograms for an environmental variable can be fitted depending on the number of available data, their spatial distribution, and their variability. For this reason, in most cases, it is difficult to get an adequate variogram. This report evaluates the influence of the groundwater level data available in the construction of a product-sum spatiotemporal variogram model and its consequences on a geostatistical-based methodology that uses the Kalman filter for the design of optimal spatiotemporal monitoring networks. Additionally, a sensitivity analysis is carried out to determine the variations in the optimal number of wells and monitoring frequency for the monitoring network, depending on the selected spatiotemporal variogram model. The results show the importance of getting a good quality spatiotemporal variogram when designing optimal groundwater-level monitoring networks using geostatistical-based methodologies.〈/p〉
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  • 16
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉A procedure is presented for valuation of information analysis (VOIA) to determine the need for additional information when assessing the effect of several design alternatives to manage future disturbances in hydrogeological systems. When planning for groundwater extraction and drawdown in areas where risks—such as land subsidence, wells running dry and drainage of streams and wetlands—are present, the need for risk-reducing safety measures must be carefully evaluated and managed. The heterogeneity of the subsurface calls for an assessment of trade-offs between the benefits of additional information to reduce the risk of erroneous decisions and the cost of collecting this information. A method is suggested that combines existing procedures for inverse probabilistic groundwater modelling with a novel method for VOIA. The method results in (1) a prior analysis where uncertainties regarding the efficiency of safety measures are estimated, and (2) a pre-posterior analysis, where the benefits of expected uncertainty reduction deriving from additional information are compared with the costs for obtaining this information. In comparison with existing approaches for VOIA, the method can assess multiple design alternatives, use hydrogeological parameters as proxies for failure, and produce spatially distributed VOIA maps. The method is demonstrated for a case study of a planned tunnel in Stockholm, Sweden, where additional investigations produce a low number of benefits as a result of low failure rates for the studied alternatives and a cause-effect chain where the resulting failure probability is more dependent on interactions within the whole system rather than on specific features.〈/p〉
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  • 17
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The karst aquifer of Jinfoshan Karst (JFK) in UNESCO’s South China Karst World Heritage Site was investigated. An artificial tracer test, geochemistry, and oxygen and hydrogen isotopes were employed to assess the impacts of effluent from the Jinfoshan Holiday Hotel (JHH), Chongqing, on the karst aquifer and its outlet, Shuifang spring (SFS). Most of the fluorescent dye (uranine) flushed into a JHH toilet was recovered at SFS, suggesting a strong hydraulic connection between JHH and SFS. The waters of SFS were of HCO〈sub〉3〈/sub〉–Ca type, whereas the effluent had more complex hydrochemical characteristics. The effluent was characterized by higher mean δD and δ〈sup〉18〈/sup〉O values. The slope of the δD–δ〈sup〉18〈/sup〉O evaporation line for effluent was significantly lower than that of the local meteoric water line, indicating evaporation. Concentrations of major elements at SFS were below the threshold values of the Chinese Standard for Groundwater Quality. However, hydrogen and oxygen isotopic compositions of SFS waters were influenced by the effluent and mixing with water from diffuse sources within the aquifer. Low values of d-excess at SFS corresponded well to periods of high tourism activity (weekends and holidays), suggesting that declining d-excess probably signifies an increased release of contaminants from the hotel. The contribution of effluent to the discharge of the SFS was ~18%. Because of tourism activities and their production of wastewater, the results of this study may be relevant to other karst environments and World Heritage Sites throughout the world.〈/p〉
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  • 18
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Sustainable yield is defined as the amount of groundwater abstraction that can be maintained for an indefinite time without causing unacceptable environmental, economic and social consequences. It is usually determined by monitoring the water-table depth, without the need for costly pumping exercises and subsequent deterioration of the groundwater and ecological environment. Groundwater numerical modelling provides an effective way to determine the yield by analysing the responding water levels to various pumping scenarios. In this study, the natural flow system and flow with pumping scenarios were simulated using FEFLOW for the fractured-rock aquifer in Table Mountain Group, South Africa. Results for different pumping rates show the distinct impact of groundwater abstraction on hydraulic head, which indicates that long-term abstraction slowly increases the well drawdown, but it would stabilize at a level that is dependent on pumping rate and induced recharge. To estimate the aquifer sustainable yield, a relationship between simulated drawdown and pumping rate was established, namely an exponential function with parameters that may change value between sites. This empirical relation, derived from this site-specific study, provides an option for informed decision-making. The issue of how to sustainably abstract groundwater might rely on a compromise between the groundwater user and the governmental authority.〈/p〉
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  • 19
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Human-induced landscape salinization, including the effects of dryland salinity, is negatively impacting many catchments in southern Australia. Salinization occurs due to increased recharge and water-table rise following land clearing of deep-rooted native vegetation. In low-lying areas with poor drainage, groundwater-level rise can lead to increased evapotranspiration, mobilization of vadose zone salt, and salt scalding. Alternatively, these same processes of increased recharge and groundwater rise can lead to decreased salinization as accumulated salts are flushed into surface waters. This study in a high-rainfall area of the Mount Lofty Ranges of South Australia documents catchment desalinization. A 28-year record (1989–2016) of flow and salinity in Scott Creek was analysed based on monthly data. Analysis of catchment-scale chloride deposition and export determined that approximately three times more chloride is exported than is input to the catchment from atmospheric sources. Over the time period investigated, salt load exported to surface water decreased by, on average, 6.4 t annually due to catchment freshening. Analysis of monthly salinity balance of a sub-catchment drained by an intermittent stream demonstrates that accumulation of chloride, rather than export, occurs during drought years. In the catchment, as a whole, salts are being flushed via groundwater flow into the permanent stream in all years of the record. Deep groundwater is input to the permanent stream, with mixing of deeper more saline and fresher shallow groundwater. Thus, a complex interaction of landscape hydrologic parameters such as relief, precipitation, chloride deposition and land-use history, determine whether a catchment undergoes salinization or desalinization.〈/p〉
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  • 20
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Complex hydrogeological systems require detailed knowledge of aquifer dynamics to ensure appropriate and sustainable management of the groundwater resource. The Riardo Plain aquifer, southern Italy, is a strategic resource for conjunctive uses; nevertheless, the conceptual model still suffers some uncertainties due to the presence of a deep lateral inflow through the carbonate basement. Therefore, the realisation of a 3D numerical model at catchment scale needs preliminary tests to constrain the possible additional inflow rate, which is at the moment only estimated through the results of the groundwater budget calculation. A 2D section of the mixing area was modelled using FEFLOW in order to test the hypothesis of a combined recharge. Seven versions of the same model were calibrated over an increasing number of adjustable parameters according to their sensitivity. The most efficient model version was identified according to the calculated information criteria and the sum of squared-weighted residuals. In the second phase of the work, nine model scenarios characterised by different deep inflow rates were calibrated and validated according to the same procedure of the first model, in order to identify the range of possible acceptable solutions. The most likely deep inflow rate is 34 ± 4% of the total recharge, corresponding to an estimated deep inflow of 415 ± 50 L/s in the Riardo Plain aquifer through the carbonate basement. This methodological approach will be the basis of following numerical 3D numerical models of the Riardo Plain and can be a valuable tool in conceptualising similar mineral water areas.〈/p〉
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  • 21
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Groundwater quantity and quality may be affected by climate change through intricate direct and indirect mechanisms. At the same time, population growth and rapid urbanization have made groundwater an increasingly important source of water for multiple uses around the world, including southern Africa. The present study investigates the coupled human and natural system (CHANS) linking climate, sanitation, and groundwater quality in Ramotswa, a rapidly growing peri-urban area in the semi-arid southeastern Botswana, which relies on the transboundary Ramotswa aquifer for water supply. Analysis of long-term rainfall records indicated that droughts like the one in 2013–2016 are increasing in likelihood in the area due to climate change. Key informant interviews showed that due to the drought, people increasingly used pit latrines rather than flush toilets. Nitrate, fecal coliforms, and caffeine analyses of Ramotswa groundwater revealed that human waste leaching from pit latrines is the likely source of nitrate pollution. The results in conjunction indicate critical indirect linkages between climate change, sanitation, groundwater quality, and water security in the area. Improved sanitation, groundwater protection and remediation, and local water treatment would enhance reliable access to water, de-couple the community from reliance on surface water and associated water shortage risks, and help prevent transboundary tension over the shared aquifer.〈/p〉
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  • 22
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The groundwater recharge produced by discrete precipitation events in unconfined aquifers is often estimated from water-table fluctuations (WTFs) recorded in shallow wells. This recharge estimate is prone to uncertainties when recharge is not instantaneous, when there is groundwater drainage, and when there are other processes producing WTFs. A numerical analysis of these uncertainties is presented, which accounts for noninstantaneous recharge and the changes in the stage of a river connected to the unconfined aquifer. This analysis is performed for idealized synthetic unconfined aquifers with one-dimensional (1-D) and 2-D numerical flow models which account for the anisotropy and the spatial heterogeneity of the hydraulic conductivity (〈em〉K〈/em〉). The logarithm of 〈em〉K〈/em〉 is assumed to be a Gaussian random field with a spherical semivariogram. Groundwater recharge may be grossly underestimated with the WTF data when the recharge is not instantaneous. Estimation errors are especially important near the river. On the other hand, the recharge may be largely overestimated when the river stage rises simultaneously during the recharge episode. The errors increase with the variance of the Ln 〈em〉K〈/em〉 value and depend on the main direction of anisotropy and the spatial connectivity of the most permeable areas near the river. The errors are large along the most permeable zones connected to the river in the main direction of anisotropy. The recharge estimation errors are largest when the main direction of anisotropy is perpendicular to the river and are smallest when the main direction of anisotropy is parallel to the river.〈/p〉
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  • 23
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Prediction of subsurface flow (SF) in hillslopes is more complicated than prediction of surface flow; hence, a simple and practical SF model would interest hydrogeologists. For the first time, the time-area method is employed to estimate the SF of hillslopes. The locations of the isochrone curves for complex hillslopes were determined using SF travel-time equations. Some equations were developed to delineate the isochrones and the subsurface time area (STA). The analytic equations suggested by the characteristics method of solving a hillslope-storage kinematic wave were used for validation of the STA method results in complex hillslopes. The average values of the coefficient of efficiency (CE), correlation coefficient (〈em〉R〈/em〉), error of peak flow (EPF) and root-mean-square error (RMSE) of the STA method for the nine defined hillslopes are, respectively, 0.96, 0.96, 1.35, and 0.076. To further verify the results, a laboratory rainfall simulator with sandy loam soil was employed, which was conditioned under artificial rainfall intensities of 31.7, 4.6 and 63.46 mm/hr, and slopes of 3°, 6° and 9°. The STA model results were compared with those of a laboratory model of subsurface flow. The average values of CE, 〈em〉R〈/em〉, EPF and RMSE of the STA method for the nine events are, respectively, 0.81, 0.85, 0.98, and 0.017, which are regarded as good values. For the final evaluation of the STA model, the subsurface flow rates obtained from the Richards’ equation using HYDRUS were also used. The proposed STA model has good agreement with the results of the laboratory and HYDRUS models.〈/p〉
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  • 24
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The presented study explores the salt dissolution potential of fluids around a salt diapir in the Transylvanian town of Ocna Mures, Romania, which is facing land-collapse hazards related to salt mining activities. A structural three-dimensional (3D) model of the salt diapir, the adjacent basin sediments, and the mining galleries was developed based on existing maps, borehole data, own field observations, and geological publications of the Transylvanian Basin. The salt dissolution potential was estimated from 2D vertical thermohaline flow and transport model scenarios along the southeastern flank of the diapir. Results showed that the following factors increase the salt dissolution capacity along the upper 180 m of the diapir: (1) the presence of more permeable Quaternary alluvial sediments in connection with a fault zone of higher permeability along the diapir, and (2) the presence of more permeable sandstone units within the Miocene sediments in the east of the diapir, which provide freshwater access to the upper parts of the diapir. Thermohaline simulation with viscosity variation of the fluid, instead of a constant viscosity, influences the resulting salt fluxes by up to 50% within studied temperature ranges of 10–60 °C in the model domain. The range of theoretical dissolution rates along the upper 180 m of the diapir supports the hypothesis that cavern collapse is more likely to occur where cavern side walls have already been mined to almost no remaining side walls of rock salt, which is the case in the southeastern part of the diapir.〈/p〉
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  • 25
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Sustainable utilization of groundwater in parts of hyper-arid Sub-Saharan Africa, like the Namib Desert, is always a challenge due to lack of resources and data. For the Omdel Aquifer in the Omaruru catchment, Namibia, issues to investigate include the lack of information on the geology and hydrogeological setting, the hydraulic properties and geometry of the aquifer at the inflow and outflow sections, groundwater recharge conditions upstream of the aquifer, and the impact of artificial recharge. In this desert environment, the methods applied are hydrogeological surveys and site visits, together with interpretation of geological, hydrological and geomorphological data from investigations carried out to define the hydrogeological characteristics of the Omdel Aquifer. The bedrock geometry of the aquifer indicates that the Main channel (one of four palaeochannels) is the largest reservoir of stored fresh groundwater, estimated at 133 Mm〈sup〉3〈/sup〉, and it is deeper than the other three channels, with an average sediment thickness of 80 m. All groundwater chemistry facies of the selected boreholes tapping the Omdel Aquifer reveal a NaCl character, indicating a coastal environment. The yield of the Omdel Aquifer is estimated to have increased from 2.8 Mm〈sup〉3〈/sup〉/year before construction of a recharge enhancement dam to 4.6 Mm〈sup〉3〈/sup〉/year after the construction. This paper focuses on the understanding of hydrogeological characteristics of the Omaruru Delta Aquifer System in terms of groundwater recharge and discharge, groundwater dynamics within the aquifer and groundwater chemistry, in order to assess whether the current abstractions are operating within the hydrogeological limits of sustainability.〈/p〉
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  • 26
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Novel findings about the general properties of an aquifer were obtained by applying the pumping approach introduced by Summa (2010). The approach of keeping the pump’s rotation speed constant was chosen over the well-known and widely used constant discharge method. The present analysis was performed on a set of unpublished data acquired during the same field test that was described in Summa (2010). The values of the instantaneous discharge and instantaneous drawdown were obtained. The contribution of the water already stored in the well to the overall capacitance of the aquifer was cancelled out for the field data that were processed. It was then possible to obtain a discharge-time function depending only upon the aquifer discharge. The discharge-time curve that was obtained showed a behaviour practically indistinguishable from the discharge-time curve for a resistor-inductor-capacitor (RLC) circuit with a direct current. By fully exploiting that circuit analogy, it was possible to evaluate the resistance, capacitance and inductance (inertia) of the aquifer. These parameters were estimated from the RLC solution that best fit the discharge-time curve. The value of the hydraulic resistance that was obtained was of the same order of magnitude as the inverse value of the transmissivity, already calculated for the same aquifer in previous work. This matching suggests that this model, as a future development of the present study, can be tested against the standard models regarding the determination of the traditional hydrogeological parameters. Summa G (2010) A new approach to the step-drawdown test, Water SA, 36(3):279–286.〈/p〉
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  • 27
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Little attention has been paid to non-Darcy fluid flow through rough-walled rock joints under high hydraulic gradient. Water fluid flow through splitting granite joints was tested beyond the range of previously tested conditions by using an experimental apparatus designed for this study. This apparatus facilitated the quantification of the effects of joint surface roughness and aperture on fluid flow properties. Experimental results showed that Forchheimer’s law could provide an excellent description of the nonlinear relationship between hydraulic gradient and flow velocity, and the variations of Forchheimer coefficients with joint surface roughness and aperture were further explored. In this work, the Reynolds numbers varied between 2,881 and 290,338, and greatly exceeded the critical value of 2,300. Moreover, the fluid flow entered the turbulent flow regime. In accordance with the discriminant factor 〈em〉α〈/em〉 = 0.9 on the basis of Forchheimer’s law, the fluid flow regimes were further divided into two categories: weak turbulence and fully developed turbulence. The corresponding critical Reynolds numbers were obtained and ranged from 17,169 to 94,385. Finally, a new seepage calculation formula for fluid flow through open rough-walled rock joints was established and verified by experimental observations and other formulae. Through a comprehensive consideration of the joint surface roughness and the uneven aperture distribution, the proposed formula could reflect the real fluid flow situation. The findings may prove beneficial for improving understanding of the nonlinear fluid flow in jointed rocks.〈/p〉
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  • 28
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉VDFST-CFP (variable-density flow and solute transport–conduit flow process) is a density-dependent discrete-continuum numerical model for simulating seawater intrusion in a dual-permeability coastal karst aquifer. A previous study (Xu and Hu 2017) simulates variable-density flow only in a single conduit, and studies the parameter sensitivities only in the horizontal case (2D domain as horizontal section) by the VDFST-CFP model. This paper focuses on the density-dependent vertical case (2D domain as vertical section) with two major improvements: 1) when implementing double-conduit networks in the domain, simulated intruded plumes in the porous medium are extended in the double-conduit scenario, compared to the single-conduit system; 2) by quantifying micro-textures on the conduit wall by the Goudar-Sonnad equation and considering macro-structures as local head loss. Sensitivity analysis shows that medium hydraulic conductivity, conduit diameter and effective porosity are important parameters for simulating seawater intrusion in the discrete-continuum system. On the other hand, rougher micro-structures and additional macro-structure components on the conduit wall would reduce the distance of seawater intrusion to the conduit system, but, rarely affect salinity distribution in the matrix. Compared to the equivalent mean roughness height, the new method (with more detailed description of structure) simulates seawater intrusion slightly landward in the conduit system. The macro-structure measured by local head loss is more reasonable but needs further study on conduit flow. Xu and Hu (2017) Development of a discrete-continuum VDFST-CFP numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system. Water Resources Research: 53, 688-711.〈/p〉
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  • 29
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Gol-Gohar iron ore mines, with a reserve of about 1.1 billion tons, constitute the largest iron ore mine complex in Iran. Pit number 3 (Gohar-Zamin mine) has the largest reserve of ore among the others. Pit advancement toward deeper parts of the aquifer has increased groundwater inflow into the pit. During exploratory drillings in Gohar-Zamin mine, some of the boreholes became artesian. The water outflow from these boreholes has high salinity (classified as brine) and high pressure of a gas with an unknown origin. A conceptual model of groundwater flow was established using the available evidence and information. The prepared model revealed that there is a minimum of three aquifers, two alluvial aquifers (with electrical conductivity (EC) of 4,000–37,000 μS/cm) and one hard-rock aquifer (EC of 91,800–169,000 μS/cm) in the study area, with different lithological and hydrochemical characteristics. The brine outflow from the artesian boreholes originated from the hard-rock aquifer, which is a confined and high-pressure system without active recharge, i.e. an unsustainable resource. There is no hydraulic connection between the pit mine and the playa, located 13 km north of the mine, through the hard-rock aquifer, and the brine in the hard-rock aquifer is fossil water or has a metamorphic origin. The present study shows that the groundwater in the hard-rock aquifer is entrapped between fault planes without any hydraulic connection with overlying aquifers. Further, the results suggest that numerical groundwater flow models can only be successfully applied to the alluvial aquifer.〈/p〉
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  • 30
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Mandalay is a major city in central Myanmar with a high urban population and which lacks a central wastewater management system, a solid waste disposal process, and access to treated drinking water. The purpose of this study is to investigate the groundwater quality of local dug wells and tube wells, determine quantitative data on characteristics of the Amarapura Aquifer, and compare seasonal variations in groundwater flow and quality. Water samples were collected during the dry and wet seasons, then analyzed for major ion chemistry using ion chromatography to identify indicators of wastewater contamination transport to the shallow aquifer and to compare seasonal variations in groundwater chemistry. An open-source analytic element model, GFLOW, was used to describe the physical hydrogeology and to determine groundwater flow characteristics in the aquifer. Hydrogeochemistry data and numerical groundwater flow models provide evidence that the Amarapura Aquifer is susceptible to contamination from anthropogenic sources. The dominant water types in most dug wells and tube wells is Na-Cl, but there is no known geologic source of NaCl near Mandalay. Many of these wells also contain water with high electrical conductivity, chloride, nitrate, ammonium, and 〈em〉E. coli〈/em〉. Physical measurements and GFLOW characterize groundwater flow directions predominantly towards the Irrawaddy River and with average linear velocities ranging from 1.76 × 10〈sup〉−2〈/sup〉 m/day (2.04 × 10〈sup〉−7〈/sup〉 m/s) to 9.25 m/day (1.07 × 10〈sup〉−4〈/sup〉 m/s). This is the first hydrogeological characterization conducted in Myanmar.〈/p〉
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  • 31
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Many environmental dilemmas such as water scarcity originate from human behavior. This study aimed to analyze Iranian farmers’ water conservation behavior using Bandura’s social-cognitive theory. To this end, a cross-sectional survey was conducted to collect the required data. The research instrument was a questionnaire. A sample of 380 farmers was selected using a multistage stratified random sampling method. The results indicated that variables of social-cognitive theory could predict about 73% of farmers’ water conservation behavior variance. Investigation of direct effects of factors on farmers’ water conservation behavior revealed that the major determinants are as follows: intention of water conservation, social-structural factors, perception of others’ behavior, outcome expectancy, self-efficacy, and water conservation co-regulation. Findings showed that factors that have been mentioned in social-cognitive theory could be considered for enhancing farmers’ water conservation behaviors since the theory provides a more realistic insight into farmers’ behaviors with an emphasis on farmers’ social and structural contexts.〈/p〉
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  • 32
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The use of snowmelt as an inexpensive multi-component tracer solution for active aquifer characterization is investigated, creating a valid alternative to existing artificial water isotope labelling using enriched deuterium oxide (〈sup〉2〈/sup〉H〈sub〉2〈/sub〉O) and water-〈sup〉18〈/sup〉O (H〈sub〉2〈/sub〉〈sup〉18〈/sup〉O). The approach directly takes advantage of natural differences between groundwater and precipitation. It is shown, at laboratory-scale and small field-scale, that a direct injection of snowmelt into a porous medium allows for the tracing of water flow and, therefore, for the determination of transport parameters based on the stable isotope signatures (δ〈sup〉2〈/sup〉H and δ〈sup〉18〈/sup〉O) and on the sum parameter electrical conductivity (EC). The differences in the isotope signature between the snowmelt and groundwater applied in this study were significant, with ∆(δ〈sup〉2〈/sup〉H) = 61.0‰ and ∆(δ〈sup〉18〈/sup〉O) = 8.2‰, while the EC difference was ~0.5 mS/cm. Stable isotope breakthrough was observed to be almost congruent to sodium chloride (laboratory tracer experiment) and to uranine (field-scale push-drift-pull test), clearly supporting the assumption of conservative transport. A crosscheck of the isotope data in δ〈sup〉2〈/sup〉H-δ〈sup〉18〈/sup〉O plots revealed no significant biases in the tests. On the other hand, the snowmelt’s EC breakthrough suffered from a slight retardation due to ion exchange and mineral reactions.〈/p〉
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  • 33
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Assessment of the groundwater potential of crystalline basement aquifers is challenging. These systems can be highly spatially variable, as indicated by the drilling of numerous dry boreholes and seasonal variation in discharge rates. This paper reviews methodologies applied for the evaluation of groundwater occurrence and yield estimation in the crystalline basement aquifers of Zimbabwe. These aquifers underlie much of the country and are described in terms of low yield owing to low recharge potential in the semiarid climate. In such regions, exploitable groundwater forms a strategic supply of potable water used to meet the socio-economic needs of the local population. Case studies are used to show how remote sensing and geophysical methods are integrated to improve borehole success rates in the basement aquifers of Zimbabwe. Potential threats to groundwater resources and quality within crystalline basement aquifers are discussed. It can be concluded that major issues remain to be addressed if sustainable use of the water resources of crystalline basement aquifers in Zimbabwe is to be achieved, especially with respect to borehole-siting approaches and prevention of groundwater contamination. The key recommendation is to address the paucity of primary groundwater monitoring data within the crystalline basement aquifers at the national level, thereby creating a technical groundwater management framework.〈/p〉
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  • 34
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The main factors that cause land subsidence are groundwater withdrawal and the load of high-rise buildings. Previous studies on land subsidence caused by high-rise buildings have focused on small areas. Few scholars have proposed land subsidence models that combine the effects of groundwater withdrawal and high-rise building load at a regional scale. This work was based on Biot’s consolidation theory and the nonlinear rheology theory. The soil parameters were varied in accordance with the Kozeny-Carman equation and Duncan-Zhang nonlinear model, and applied to a site in eastern China. A three-dimensional finite element method (FEM) program, fully coupling varying soil parameter values and fluid-solid characteristics of land subsidence, was coded using FORTRAN. The program was used to simulate and predict regional land subsidence and to study the coupling effects of groundwater withdrawal and high-rise building load. The results showed that the soil parameters varied in reasonable range and the trend of variation was consistent with the characteristics of soil deformation. The sum of the land subsidence under high-rise building load alone and groundwater withdrawal alone differed from land subsidence under the combined effects of groundwater withdrawal and high-rise building load. The coupling effect of land subsidence caused by high-rise building load and groundwater withdrawal was shown to be nonlinear.〈/p〉
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  • 35
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    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The last 60 years has seen unprecedented groundwater extraction and overdraft as well as development of new technologies for water treatment that together drive the advance in intentional groundwater replenishment known as managed aquifer recharge (MAR). This paper is the first known attempt to quantify the volume of MAR at global scale, and to illustrate the advancement of all the major types of MAR and relate these to research and regulatory advancements. Faced with changing climate and rising intensity of climate extremes, MAR is an increasingly important water management strategy, alongside demand management, to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. During this time, scientific research—on hydraulic design of facilities, tracer studies, managing clogging, recovery efficiency and water quality changes in aquifers—has underpinned practical improvements in MAR and has had broader benefits in hydrogeology. Recharge wells have greatly accelerated recharge, particularly in urban areas and for mine water management. In recent years, research into governance, operating practices, reliability, economics, risk assessment and public acceptance of MAR has been undertaken. Since the 1960s, implementation of MAR has accelerated at a rate of 5%/year, but is not keeping pace with increasing groundwater extraction. Currently, MAR has reached an estimated 10 km〈sup〉3〈/sup〉/year, ~2.4% of groundwater extraction in countries reporting MAR (or ~1.0% of global groundwater extraction). MAR is likely to exceed 10% of global extraction, based on experience where MAR is more advanced, to sustain quantity, reliability and quality of water supplies.〈/p〉
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  • 36
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉This work numerically simulates fracture flow in natural fractures, specifically in a joint with plumose pattern. A natural fracture surface, previously measured in the field using LiDAR scanning, was used to rebuild an open fracture geometry, assuming mode 1 fracture opening. Three-dimensional fracture flow was modeled by solving Stokes equation in a stationary regime using the finite element method. Three different pressure gradients and apertures were numerically investigated to better understand the impact of plumose patterns with different degrees of roughness. Resulting fracture flow fields were characterized by hydraulic aperture and by statistics on the directional components of the three-dimensional velocity vector. The results show that the hydraulic aperture and the longitudinal component of the velocity vector decrease with increasing roughness. Beyond this classical finding, the study shows that the variance of the longitudinal component of the flow velocity vector also decreases with increasing roughness. This behavior can be predicted based on variance estimates connected to the parabolic profile. The results further revealed that the variances of the transverse components of the velocity vector increase with fracture surface roughness. These findings suggest that the roughness-induced reduction in the mean and the variance of the longitudinal component of the velocity vector in joints with rough surfaces is accompanied with a simultaneous increase of the transverse components of the three-dimensional velocity vector.〈/p〉
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  • 37
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Groundwater sampled at the outlets of uncased flowing wells in a thick unconfined aquifer, which has undergone mixing, has been found to have hydrochemistry similar to deep groundwater in discharge areas. To identify the hydrodynamic causes, transient models of groundwater flow and age in a three-dimensional homogeneous unit basin with flowing wells are constructed to obtain flow rates in wells and groundwater mean age around wells. Inflow of groundwater to the well in the deep part leads to mixing of groundwater from different sources, and the finally mixed groundwater is found to have the same age as groundwater in the aquifer at a specific depth, termed the equivalent position (EP). EP is always found in the lower half of the flowing well, indicating that a mixed sample at the outlet could represent deep groundwater. Outflow from the well to the unconfined aquifer in the shallow part results in aging of groundwater around the well. For fully penetrating flowing wells in confined aquifers, EP is found in the upper half of the aquifer. The different relative depths of EP to the screen interval in the two types of flowing wells are mainly due to the profiles of horizontal velocity in the inflow segment, which is basically uniform in a confined aquifer but increases from zero to a maximum value in unconfined aquifers. Thus, groundwater at the outlets of topography-controlled flowing wells is a window of the deep part of a basin, and existing long-screen wells could have the potential for groundwater sampling.〈/p〉
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  • 38
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    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Freshwater scarcity is an ever-increasing problem throughout the arid and semi-arid countries, and it often results in poverty. Thus, it is necessary to enhance understanding of freshwater resources availability, particularly for groundwater, and to be able to implement functional water resources plans. This study introduces a novel statistical approach combined with a data-mining ensemble model, through implementing evidential belief function and boosted regression tree (EBF-BRT) algorithms for groundwater potential mapping of the Lordegan aquifer in central Iran. To do so, spring locations are determined and partitioned into two groups for training and validating the individual and ensemble methods. In the next step, 12 groundwater-conditioning factors (GCFs), including topographical and hydrogeological factors, are prepared for the modeling process. The mentioned factors are employed in the application of the EBF model. Then, the EBF values of the GCFs are implemented as input to the BRT algorithm. The results of the modeling process are plotted to produce spring (groundwater) potential maps. To verify the results, the receiver operating characteristics (ROC) test is applied to the model’s output. The findings of the test indicated that the areas under the ROC curves are 75 and 82% for the EBF and EBF-BRT models, respectively. Therefore, it can be inferred that the combination of the two techniques could increase the efficacy of these methods in groundwater potential mapping.〈/p〉
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  • 39
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Nitrate is necessary for agricultural productivity, but it is also one of the most common water contaminants in developed countries. The riverbank filtration (RBF) systems in Káraný (Czechia), with nearly 500 wells regularly distributed along 22 km of the alluvium aquifer/river interface, presents a unique field laboratory where the adverse effects of intensive agriculture on groundwater can be traced from 〉50 years of nitrate concentration records. The largest control over nitrate concentrations in the RBF systems has been the mixing of the river-water component (low in nitrate) with the local recharge, which has a nitrate content of 100–250 mg/L. The mixing is mainly controlled by the intensity of the effective precipitation. Increases in nitrate concentration are caused by rapid hydraulic pulse propagation during the high-recharge periods to the discharge areas. In contrast, during dry periods, the river-water fraction dilutes nitrate in wells. The lowest nitrate content occurs above the weirs on the river, as well as in those areas where the alluvial aquifer is partly fed by older and/or denitrified groundwater from deeper zones of the underlying sandstone aquifer. High nitrate concentrations occur in wells where the low saturated thickness of the alluvial aquifer limits the inflow of river water. This study shows that factors affecting nitrate concentrations in the alluvium are numerous, and that long-term sampling is necessary to distinguish the oscillations caused by variability in the recharge intensity from decade-long trends controlled by the fertilizer load and nitrate lag time in the aquifer.〈/p〉
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  • 40
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Surface-water/groundwater exchange through the evaluation of riparian-zone temperature data has attracted increasing attention in recent years. The Fox Ditch Canal, Nevada, USA, was chosen for this study on seasonal variations of riparian-zone water exchange. Groundwater temperature and hydraulic head real-time monitoring data were collected from March to November 2012. A calibrated hydro-thermal coupling model was used to characterize the riparian-zone temporal and spatial temperature distribution, thereby providing a standard against which the performances of four analytical solution models for calculated riparian-zone vertical seepage velocity could be assessed. The results indicated that the proposed model provided a simulation that was able to represent dynamic changes in riparian-zone soil temperature. Although small variations in patterns and magnitudes of riparian-zone water exchange were evident at a daily scale, they varied significantly over a seasonal scale. Comparison of the results of the four analytical solutions and numerical computation found that the Hatch solution by the amplitude method provided the highest accuracy for calculating groundwater velocity in this area (2.47 × 10〈sup〉−6〈/sup〉 to 3.15 × 10〈sup〉−6〈/sup〉 m/s). Global sensitivity analysis of hydro-thermal coupling model parameters showed that porosity had the most significant impact on temperature in the model.〈/p〉
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  • 41
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Evaluating the patterns of NO〈sub〉3〈/sub〉-N concentrations at karst springs can be used to infer hydrologic processes and nutrient dynamics in karst aquifers. In this study, NO〈sub〉3〈/sub〉-N concentrations observed at two karst springs in northeast Iowa (USA) were evaluated for a 2-year period using high-frequency sensors. Despite similar watershed land use dominated by intense row cropping of corn and soybean production (〉70%), NO〈sub〉3〈/sub〉-N concentrations and temporal patterns were very different between the two springs. At the Manchester spring, NO〈sub〉3〈/sub〉-N stored in overburden materials above the karst-enhanced Silurian-age bedrock provides a continuing source of NO〈sub〉3〈/sub〉-N to the spring. Rainfall events mobilize the stored NO〈sub〉3〈/sub〉-N and concentrations increase. At Big Spring, the karst system is overlain by a thin layer of sediments and the bedrock is dominated by sinkholes and losing streams. Rainfall events dilute the spring NO〈sub〉3〈/sub〉-N concentrations which rapidly decreased during events before rebounding to previous levels. Spectral analyses revealed that concentrations at both springs were a fractal process, with the scaling exponent at Manchester (2.0) considerably larger than that measured at Big Spring (1.4), indicating a higher degree of autocorrelation in NO〈sub〉3〈/sub〉-N concentrations at Manchester, consistent with the conceptual model. Overall, results argue for greater use of high-frequency NO〈sub〉3〈/sub〉-N monitoring at karst springs to better assess short- and long-term variations in NO〈sub〉3〈/sub〉-N concentrations and to unravel karst processes.〈/p〉
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  • 42
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The Azraq basin, Jordan, is characterized by high variability and a heterogeneous spatial distribution of groundwater recharge. Most of the recharge occurs in the north of the basin. The central part of the basin is covered by wetland (Azraq Oasis), characterized by a unique ecosystem and biodiversity. Groundwater abstraction for agricultural and domestic purposes occurs mainly near the oasis and results in a considerable decline of the water table. A groundwater model was developed for the Azraq basin to analyze and predict the groundwater level response to different pumping strategies. The model also enables determination of the safe yield. The extent to which the safe yield and specific pumping strategies are socially and economically acceptable was analyzed. Multi-criteria analysis using an analytic hierarchy process was applied to obtain the abstraction rate that achieves the most suitable trade-off between environmental and socio-economic criteria under two scenarios of future socio-economic development. Based on the calibrated groundwater model the response of the groundwater level until 2045 was simulated, resulting in a 15–25 m decline if current pumping strategies continue. At present, the safe yield of the groundwater resource equals 30% of the overall actual pumping rate, indicating that the aquifer is highly exploited. Results of the multi-criteria analysis show that the ‘safe yield alternative’ is the most suitable for the basin under a scenario of future economic prosperity. For circumstances of poor economy and low social awareness, keeping the current pumping rate was found to be the scenario with the highest priority.〈/p〉
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  • 43
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉The Kasserine Aquifer System (KAS) is a transboundary aquifer, located in an arid region in central Tunisia and extending into northeastern Algeria. The system consists of four compartments: Oum Ali-Thelepte, Feriana-Skhirat, and the Plateau and the Plaine of Kasserine. The challenge of this study was to evaluate the influence of regional faults on groundwater flow in the different compartments of the KAS and to estimate the regional impact of current and future groundwater use. A three-dimensional saturated regional groundwater flow model for the steady state and transient conditions (1980–2015) was created and calibrated. This work was achieved using numerical flow modelling, coupled with geological modelling, using FEFLOW and GeoModeller software. The significance of regional faults as potential barriers or conduits to groundwater flow in the different aquifer compartments was evaluated by considering the different recharge rates. Two connectivity hypotheses were proposed at each major fault, and the general hydraulic relationship of units that are juxtaposed by each fault were considered. This study contributes rigorous estimates for the diffuse and concentrated recharge in the arid study region, and evaluates the groundwater behavior that shows a gradual decline in the water table over time, using a regional model. Different predicted outcomes for the KAS based on variable potential groundwater extraction scenarios for the period 2015–2050 have been developed. The results of numerical simulation provide useful information regarding the behavior of the KAS aquifers, and contribute significant knowledge to guide sustainable practice for present and future groundwater management.〈/p〉
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  • 44
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉A case study is presented that implements two numerical models for simulating a 30-year pump-and-treat (PAT) operation conducted at a large contaminated site for which high-resolution data sets are available. A Markov chain based stochastic method is used to conditionally generate the realizations with random distribution of heterogeneity for the Tucson International Airport Area (TIAA) federal Superfund site in the USA. The fields were conditioned to data collected for 245 boreholes drilled at the site. Both MT3DMS and the advanced random-walk particle method (RWhet) were used to simulate the PAT-based mass removal process. The results show that both MT3DMS and RWhet represent the measured data reasonably, with root mean square error (RMSE) less than 0.03. The use of fine grids and the total-variation-diminishing method (TVD) limited the effects of numerical dispersion for MT3DMS. However, the effects of numerical dispersion were observed when compared to the simulations produced with RWhet using a larger number of particles, which provided more accurate results with RMSE diminishing from 0.027 to 0.024 to 0.020 for simulations with 1, 20, and 50 particles, respectively. The computational time increased with more particles used in the model, but was still much less than the time required for MT3DMS, which is an advantage of RWhet. By showing the results using both methods, this study provides guidance for simulating long-term PAT systems. This work will improve understanding of contaminant transport and plume persistence, and in turn will enhance site characterization and site management for contaminated sites with large plumes.〈/p〉
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  • 45
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Shenzhen is the major financial and high-tech center in southern China. The megacity has grown rapidly in the last 40 years with the population increasing from about 30,000 in 1979 to 20 million in 2016. The study area (2,015 km〈sup〉2〈/sup〉) is about 42% urban and 58% undeveloped land. The rapid development of the megacity has resulted in severe degradation of the groundwater and surface-water resources and has created a nearly insatiable demand for water, with an average consumption of 2000 × 10〈sup〉6〈/sup〉 m〈sup〉3〈/sup〉/year. Groundwater is an important component of the baseflow of the many streams in the area and is used for potable water supply and irrigation in some of the rural parts of the municipality. This study develops a conceptual model and quantitative framework for assessing the groundwater resources of Shenzhen. The groundwater system consists of shallow aquifers of alluvium and weathered bedrock overlying low permeability igneous and sedimentary rocks. The complex geologic setting was conceptualized as a block structure with blocks bounded by high-angle faults. The water budget in Shenzhen was quantified. The estimated average groundwater discharge is about 12% of annual precipitation. The study provides a starting point to investigate how a megacity such as Shenzhen should manage and protect its groundwater as a strategic resource and environmental asset. It is also a basic management tool for analyzing and contributing to urban drainage concepts such as the “sponge city”.〈/p〉
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  • 46
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    Springer
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Water and salt migration properties are important in many disciplines, including engineering construction, natural disaster prevention, agricultural irrigation and wastewater disposal. Relevant research into unsaturated loess caters to the development needs of the cities located on it. The objective of this study is to identify the water flow dynamics and consequent salt migration and redistribution (as well as their influence on microstructure alteration of the soil) during long-term seepage in unsaturated loess. In this experimental study, a long-term and one-dimensional seepage simulation test is conducted in a loess column. Probes are buried at different depths along the vertical profile to monitor and record the variations of volume water content and electrical conductivity. After the seepage test, soils at different depths are analyzed with different methods to make further investigation, including use of a pressure-plate apparatus to obtain soil-water characteristic curves, ion chromatography to determine the soluble salt components, and scanning electron microscopy to observe the microstructure changes. Good consistency between the different tests is obtained. Based on those results, the water and salt migration patterns and their influence on loess are analyzed and concluded.〈/p〉
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  • 47
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉Extensive dissolution of evaporites has occurred in the Williston Basin, Canada, but it is unclear what effect this has had on bulk permeability. The bulk of this dissolution has occurred from the Prairie Evaporite Formation, which is predominantly halite and potash. However, minor evaporite beds and porosity infilling have also been removed from the overlying Dawson Bay and Souris River formations, which are predominantly carbonates. This study examines whether permeability values in the Dawson Bay and Souris River formations have been affected by dissolution, by analyzing 142 drillstem tests from those formations. For both the Dawson Bay and Souris River formations, the highest permeabilities were found in areas where halite dissolution had occurred. However, the mean permeabilities were not statistically different in areas of halite dissolution compared to those containing connate water. Subsequent precipitation of anhydrite is known to have clogged pore spaces and fractures in some instances. Geochemical relationships found here support this idea but there is no statistically significant relationship between anhydrite saturation and permeability. Geomechanical effects, notably closure of fractures due to collapse, could be a mitigating factor. The results indicate that coupling dissolution and precipitation to changes in permeability in regional flow models remains a significant challenge.〈/p〉
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  • 48
    Publication Date: 2019
    Description: 〈h3〉Abstract〈/h3〉 〈p〉A new semi-analytical solution to study groundwater flow fields associated with pumping or injection wells in confined isotropic aquifers with uniform regional flow is proposed and tested against steady-state and transient-state numerical simulations on MODFLOW-MODPATH. The solution is based on the complex potential theory and can be used for large numbers of arbitrarily positioned wells operated with different rates. The solution can be used to follow the movement of water particles in space (within pores or within the equivalent continuous media) and in time with two tracking modes: forward (from origin to target) and backward (from target to origin). The proposed solution is a useful tool that can be used for establishing groundwater resources management practices like designing groundwater remediation solutions, delineating capture zones, defining safeguard perimeters and mapping groundwater vulnerability. Moreover, the paper gives a comparative numerical study of flow fields near pumping wells, showing that, in terms of their shape and position, delineating capture zones using either steady-state or transient-state simulations would lead to practically similar results for long pumping periods. It is also shown that in such cases, the main differences between steady-state and transient-state simulation are present in the computed water particles’ transport time.〈/p〉
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  • 49
    Publication Date: 2018-06-11
    Description: Sea surface salinity (SSS) derived from the multi-satellite missions, NASA’s Aquarius/SAC–D and Soil Moisture Active and Passive (SMAP), and ESA’s Soil Moisture and Ocean Salinity (SMOS) are compared and used to estimate horizontal advective salt fluxes in the Southern Ocean (SO). In comparison with an Argo product, all three satellites estimate similar SSS in the Southern Hemisphere mid-latitudes (30° S–45° S) with low variability among the products. At high latitudes, there are temporal patterns of bias (relative to Argo) in Aquarius during Austral summer and in SMOS during Austral winter. Differences in the satellite products and Argo exist along coastal boundaries, low temperatures, and strong currents. Satellite-derived salinity indicates low temporal–mean standard deviations with Aquarius (0.215) and moderate standard deviations with SMOS (0.294) and SMAP (0.325) against Argo in the SO. Differences in satellite-derived zonal and meridional SSS gradients are large; standard deviation values are 2.52 and 1.49 × 10 −6  psu m −1 , respectively, and similarly located within the sub-tropical salinity maxima, Antarctic Circumpolar Current, and coastal zones. Differences in the horizontal advective fluxes are on average small, but large variability greater than 275 mm month −1 indicates errors of similar magnitude to the estimated Argo flux. Based on these results, the use of satellite-derived salinity may prove to be a useful resource for observing salinity and horizontal salt fluxes, outside the inaccuracies associated with the high latitudes and coastal currents between the various remotely sensed products, and could significantly influence the results depending on the product.
    Print ISSN: 2520-8195
    Electronic ISSN: 2520-8209
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  • 50
    Publication Date: 2018-03-09
    Description: Main conclusion TpRNAMP5 is mainly expressed in the plasma membrane of roots and basal stems. It functions as a metal transporter for Cd, Mn and Co accumulation. Numerous natural resistance-associated macrophage proteins (NRAMPs) have been functionally identified in various plant species, including Arabidopsis , rice, soybean and tobacco, but no information is available on NRAMP genes in wheat. In this study, we isolated a TpNRAMP5 from dwarf Polish wheat (DPW, Triticum polonicum L.), a species with high tolerance to Cd and Zn. Expression pattern analysis revealed that TpNRAMP5 is mainly expressed in roots and basal stems of DPW. TpNRAMP5 was localized at the plasma membrane of Arabidopsis leaf protoplast. Expression of TpNRAMP5 in yeast significantly increased yeast sensitivity to Cd and Co, but not Zn, and enhanced Cd and Co concentrations. Expression of TpNRAMP5 in Arabidopsis significantly increased Cd, Co and Mn concentrations in roots, shoots and whole plants, but had no effect on Fe and Zn concentrations. These results indicate that TpNRAMP5 is a metal transporter enhancing the accumulation of Cd, Co and Mn, but not Zn and Fe. Genetic manipulation of TpNRAMP5 can be applied in the future to limit the transfer of Cd from soil to wheat grains, thereby protecting human health.
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  • 51
    Publication Date: 2018-03-09
    Description: Main conclusion Constitutive expression of AchGLK from A. chinensis in transgenic tomato ( S. lycopersicum ) confers fruits an elevated plastid biogenesis with intensified granule thylakoid stacks and increased content of nutritional compounds. Plastid development is regulated by multiple environmental and genetic factors. Golden2-like (GLK) genes, members from GARP subfamily of the MYB transcription factors, have been shown to regulate plastid biogenesis and development in several species. In tomato ( S. lycopersicum ), SlGLK2 gene is expressed in the fruit in a manner of latitudinal gradient and determines the green shoulder phenotype. Here, we report the isolation and characterization of a kiwifruit ( A. chinensis ) GLK homolog (AchGLK). Transcription analysis showed that AchGLK is highly expressed in mature leaves and in fruits 60-day post-anthesis. Overexpression of AchGLK in transgenic tomato resulted in dark green immature fruit with higher concentration of chlorophyll and overall increased chloroplast compartment, both number and size. The ripened fruit had higher levels of carotenoids and sugars as well. Nevertheless, no phenotypic changes were observed in the transgenic leaves, similar to the previously described overexpression of SlGLK2 in tomato. Our study suggests that AchGLK is functionally homologous to tomato GLK2 with a potential in regulating plastid level in fruit that could contribute to improvement of fruit quality.
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  • 52
    Publication Date: 2018-03-09
    Description: Main conclusion A powerful acquired thermotolerance response in potato was demonstrated and characterised in detail, showing the time course required for tolerance, the reversibility of the process and requirement for light. Potato is particularly vulnerable to increased temperature, considered to be the most important uncontrollable factor affecting growth and yield of this globally significant crop. Here, we describe an acquired thermotolerance response in potato, whereby treatment at a mildly elevated temperature primes the plant for more severe heat stress. We define the time course for acquiring thermotolerance and demonstrate that light is essential for the process. In all four commercial tetraploid cultivars that were tested, acquisition of thermotolerance by priming was required for tolerance at elevated temperature. Accessions from several wild-type species and diploid genotypes did not require priming for heat tolerance under the test conditions employed, suggesting that useful variation for this trait exists. Physiological, transcriptomic and metabolomic approaches were employed to elucidate potential mechanisms that underpin the acquisition of heat tolerance. This analysis indicated a role for cell wall modification, auxin and ethylene signalling, and chromatin remodelling in acclimatory priming resulting in reduced metabolic perturbation and delayed stress responses in acclimated plants following transfer to 40 °C.
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  • 53
    Publication Date: 2018-03-09
    Description: Main conclusion The inducible vectors pER8–Gateway–3Flag and pER8–Gateway–3Flag–SRDX have been subjected to considerable research in terms of the function of transcription factors (TFs) via transcription activity and repression, respectively. Approximately 1500 TFs have been identified in Arabidopsis thaliana genome. To identify their functions, loss-of-function and gain-of-function mutants were generated to analyze the phenotype. However, many loss-of-function mutants did not show any evident phenotype because of the functional redundancy within the TF family. The constitutive misexpression of some TFs may result in lethality or sterility. To overcome these problems, we produced a Gateway-compatible inducible binary vector system that facilitates fast and reliable DNA cloning and biological function identification. The vector can be used for the inducible expression of protein fusions to a polypeptide protein tag named 3xFLAG tag. This vector system can also be used to generate an inducible transcription inhibition of protein fusion to an Ethylene-Responsive Factor-associated amphiphilic repression (EAR) motif. The EAR motif makes it possible to get rid of redundancy within a TF family, thereby facilitating studies on loss of function. With these Gateway vectors, conventional subcloning technology that depends on restriction digestion and ligation is avoided. Thus, these Gateway vectors should be useful not only for the rapid analysis of the functions of redundant plant TFs, but also for the manipulation of TF overexpression, resulting in plant lethality or sterility, via an inducible promoter.
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  • 54
    Publication Date: 2018-03-09
    Description: Porifera dominate vast areas of the Antarctic shelves and are successfully colonized by bacteria. Quorum sensing (QS) is a cell-to-cell communication system based on bacterial population density that, enabling the coordination of group-based behaviour, plays a critical role in the successful colonization of higher organisms, also driving the formation of biofilm for adhesion to surfaces. In this study, the production of N -Acyl homoserine lactones (AHLs), signal molecules involved in the QS mechanism, was examined for 211 Antarctic sponge-associated Gram-negative bacteria. AHL production was screened by using three different AHL biodetection systems, i.e. Agrobacterium tumefaciens pZLR4, Chromobacterium violaceum CV026 and Pseudomonas putida pKR-C12 with optimal sensitivity to moderate-chain (C8–C12), short-chain (C4–C8) and long-chain (≥ C14) AHLs, respectively. 57.8% of tested isolates activated at least one of the monitor systems used and belonged mainly to bacterial genera that are known to be involved in surface colonization by biofilm production. A thin-layer chromatographic assay based on the A. tumefaciens reporter system was utilized to determine the AHL profiles of five selected positive isolates. Visible spots on thin-layer chromatography (TLC) plates were produced by Roseobacter sp. TB60 and Psychrobacter sp. TB67 (both from the sponge, Anoxycalyx joubini ). The former probably produced N -(3-oxohexanoyl)-L-homoserine lactone (similar to the standard 3-oxo-C6-HSL), whereas the isolate TB67 produced molecules that were similar to the standard N -butanoyl-homoserine lactone (C4-HSL). The obtained results demonstrated that AHL-based signalling may play a key role in sponge–bacteria interactions also in the Antarctic environment.
    Print ISSN: 0722-4060
    Electronic ISSN: 1432-2056
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  • 55
    Publication Date: 2018-03-09
    Description: Atmospheric turbulence is a major hazard in the aviation industry and can cause injuries to passengers and crew. Understanding the physical and dynamical generation mechanisms of turbulence aids with the development of new forecasting algorithms and, therefore, reduces the impact that it has on the aviation industry. The scope of this paper is to review the dynamics of aviation turbulence, its response to climate change, and current forecasting methods at the cruising altitude of aircraft. Aviation-affecting turbulence comes from three main sources: vertical wind shear instabilities, convection, and mountain waves. Understanding these features helps researchers to develop better turbulence diagnostics. Recent research suggests that turbulence will increase in frequency and strength with climate change, and therefore, turbulence forecasting may become more important in the future. The current methods of forecasting are unable to predict every turbulence event, and research is ongoing to find the best solution to this problem by combining turbulence predictors and using ensemble forecasts to increase skill. The skill of operational turbulence forecasts has increased steadily over recent decades, mirroring improvements in our understanding. However, more work is needed—ideally in collaboration with the aviation industry—to improve observations and increase forecast skill, to help maintain and enhance aviation safety standards in the future.
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    Electronic ISSN: 1420-9136
    Topics: Geosciences , Physics
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  • 56
    Publication Date: 2018-03-09
    Description: A series of thermoset/clay nanocomposites are prepared by thiol-epoxy click reaction using commercially available starting compounds at ambient conditions in very good yields. The incorporation and exfoliation of clay nanolayers in the thermoset matrix are confirmed by FT-IR, XRD and TEM analyses. The influence of clay loadings on the thermal and mechanical analyses is investigated and all nanocomposites exhibit improved properties than that of the pristine thermoset. The nanocomposite containing 1% montmorillonite by weight has the most improved mechanical properties due to its highly exfoliated structure resulting in efficient interactions between clay and polymer matrix. A further increase of the clay loading results in the aggregation of clay plates to form intercalated structures leading to deteriorated thermal and mechanical properties of nanocomposites.
    Print ISSN: 0170-0839
    Electronic ISSN: 1436-2449
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 57
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    Publication Date: 2018-03-09
    Description: Weather is by far the most important factor in air traffic delays in the United States’ National Airspace System (NAS) according to the Federal Aviation Administration (FAA). Geostationary satellites have been an effective tool for the monitoring of meteorological conditions that affect aviation operations since the launch of the first Synchronous Meteorological Satellite (SMS) in the United States in 1974. This paper will review the global use of geostationary satellites in support of aviation weather since their inception, with an emphasis on the latest generation of satellites, such as Geostationary Operational Environmental Satellite (GOES)-R (16) with its Advanced Baseline Imager (ABI) and Geostationary Lightning Mapper (GLM). Specific applications discussed in this paper include monitoring of convective storms and their associated hazards, fog and low stratus, turbulence, volcanic hazards, and aircraft icing.
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  • 58
    Publication Date: 2018-03-09
    Description: The phylum Nemertea is an important component of the benthic ecosystems of the Southern Ocean, but its biodiversity is still relatively poorly known in Antarctic waters. There are few common and well-known nemertean species occurring in the shallow Antarctic waters, and these include the congeneric Antarctonemertes valida (Bürger, 1893) and Antarctonemertes riesgoae Taboada et al., 2013, two relatively small brooding hoplonemerteans whose females lay eggs inside cocoons. A third Antarctic member of the genus, Antarctonemertes belgica (Bürger, 1904), was reported only in the original description. Here we document the existence of a fourth Antarctic member of the genus Antarctonemertes originally described as Tetrastemma unilineatum Joubin, 1910. Our phylogenetic analysis resulted into the placement of the new Antarctonemertes in a robustly supported clade –Antarctic Antarctonemertes – containing the other two congeneric Antarctic species ( A.   valida and A.   riesgoae ), and pairwise COI molecular distances between the three species ranged from 5.2 to 6.2% ( p distance). The analysis of 104 COI sequences of the three species showed star-like haplotype networks, as in other studies on Antarctic invertebrates. Antarctonemertes unilineata comb. nov. is similar in shape to its Antarctic congeneric relatives and its most prominent morphological character is a dorsal mid-longitudinal band present along the body. We also document the presence of a cocoon built by females of A.   unilineata comb. nov., a character shared with its Antarctic congeners analysed here. Although the four Antarctic Antarctonemertes species appear to overlap their distribution, A.   riesgoae , A.   valida and A. belgica appear in sympatry in the West Antarctic shores while A.   unilineata comb. nov. has been mainly found in the East Antarctic shores and sub-Antarctic Islands.
    Print ISSN: 0722-4060
    Electronic ISSN: 1432-2056
    Topics: Biology
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  • 59
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    Springer
    Publication Date: 2018-03-09
    Description: Coordination of Np(III–VII) atoms in the crystal structures of all the oxygen-containing compounds characterized with the R -factor lower than 0.1 was analyzed with the aid of Voronoi–Dirichlet polyhedra (VDPs). Nine types of NpO n coordination polyhedra (6 ≤ n ≤ 12) are realized. The most characteristic of them are trigonal dodecahedra [Np(IV)], penta- and hexagonal bipyramids [Np(V) and Np(VI)], and octahedra [Np(VII)] based on square NpO 4 – cores. For Np atoms of a fixed oxidation state, the volume of their VDPs in the NpO n complexes is virtually independent of the coordination number n . The VDP parameters can be used for determining the valence state of the Np atoms, finding compounds with the maximal nonlinearity of the NpO 2 + and NpO 2 2+ dioxocations, and revealing errors in the crystal structure data. Anion–anion interactions involving NpO 4 – and OH – ions are an important structure-forming factor in Np(VII) compounds. In sublattices consisting of Np atoms only (Np sublattices), the rule of 14 neighbors is fulfilled. Compounds in which binding Np···Np 5f interactions in crystal structures are possible were revealed by analysis of the VDPs of the atoms in the Np sublattices. In such compounds, the metal atoms form bent Np=O–Np bridging fragments and the Np V O 7 bipyramids are combined in dimers sharing a common axial edge, with the Np atoms of the dimers being also bound via two carboxylate bridges.
    Print ISSN: 1066-3622
    Electronic ISSN: 1608-3288
    Topics: Chemistry and Pharmacology
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  • 60
    Publication Date: 2018-03-09
    Description: A natural polymineral compound in which the major uranium-containing mineral is polycrase (Ti- Ta-niobate) described by the formula АВ 2 О 6 was chosen as a model for studying the behavior of recoil atoms produced by α-decay of actinides. Polycrase, despite its metamict structure, is characterized by the following features distinguishing it from Ti-Ta-niobates of the formula А 2 В 2 О 7 (pyrochlore and betafite): (1) 1/3 of uranium atoms preserve the initial valence state, U(IV); (2) the U(IV) fraction is characterized by the isotope activity ratio AR( 234 U/ 238 U) close to that at secular equilibrium; (3) the uranium atoms that underwent oxidation “memorize” their radiogenic origin; as a result, the AR( 234 U/ 238 U) ratio in the U(VI) fraction is 0.90, and in the most altered part of the mineral it decreases to 0.77; (4) the parent uranium is relatively stable in the metamict structure of polycrase: The half-leaching time for 238 U atoms is 2 times longer than that in betafite, zircon, or sphene.
    Print ISSN: 1066-3622
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    Topics: Chemistry and Pharmacology
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  • 61
    Publication Date: 2018-03-09
    Description: Oxiracetam was labeled with 99 m Tc using sodium dithionite (Na 2 S 2 O 4 ) as a reducing agent. The influence exerted on the labeling yield by the amounts of the reducing agent and substrate, pH, temperature, and reaction time was studied to optimize the labeling process. Biodistribution studies show that the 99 m Tcoxiracetam complex is suitable as a highly selective tracer for brain imaging.
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    Topics: Chemistry and Pharmacology
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  • 62
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    Springer
    Publication Date: 2018-03-09
    Description: Uridine, a pyrimidine nucleoside essential for the synthesis of RNA and biomembranes, was radiolabeled with 99 m Tc to obtain a potential tumor imaging agent. The maximal radiochemical yield of about 96.5%, as determined by paper chromatography and instant thin-layer chromatography, was reached under the following optimum conditions: 1 mg of uridine, 20 μg of SnCl 2 ·2H 2 O as reducing agent, 20 mg of mannitol as a stabilizer, and pH 8. 99 m Tc-uridine is stable in vitro at room temperature for up to 6 h post labeling. The biodistrbution study in tumor-bearing mice shows high target-to-nontarget ratio. These results match with the high docking score of the complex on uridine phosphorylase enzyme. 99 m Tc-uridine shows promise as a tumor imaging agent.
    Print ISSN: 1066-3622
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    Topics: Chemistry and Pharmacology
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  • 63
    Publication Date: 2018-03-09
    Description: Two procedures for preparing the compounds M(NpO 4 ) 2 · n H 2 O (M = Mg, Ca, Sr, Ba) using boric acid were suggested. In the first procedure, samples of freshly prepared salts M 3 (NpO 5 ) 2 · n H 2 O (M = Ca, Sr, Ba) are treated with excess 0.5 M H 3 BO 3 with vigorous stirring. In the process, the initially light green salts rapidly transform into black products of the general composition M(NpO 4 ) 2 · n H 2 O. In the second procedure, a measured volume of a Np(VII) solution with a known LiOH concentration was added to excess 0.5 M H3BO3 solution containing a calculated amount of Mg, Ca, Sr, or Ba nitrate. The reaction yields black precipitates of the same compounds as in the previous case. After washing with water and drying in an oxygen stream, the final products contain a small impurity of Np(VI). The IR spectra suggest that the compounds obtained are structurally related to the previously studied salts MNpO 4 (M = K–Cs), i.e., in their lattices there are neptunium–oxygen layers built of NpO 2 3+ cations and bridging O atoms. New data on the properties of the compounds M 3 (NpO 5 ) 2 · n H 2 O with M = Ca, Sr, and Ba were also obtained.
    Print ISSN: 1066-3622
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  • 64
    Publication Date: 2018-03-09
    Print ISSN: 0723-2632
    Electronic ISSN: 1434-453X
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
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  • 65
    Publication Date: 2018-03-09
    Description: The motion of aerosol particles in open cell foam material is studied. The porous medium is investigated for a three-dimensional case with detailed simulation of cellular structures within an ordered geometry. Numerical calculations of the motion of particles and their deposition due to inertial and gravitational mechanisms are performed. Deposition efficiency curves for a broad range of particle sizes are constructed. The effect deposition mechanisms have on the efficiency of the porous material as a filter is analyzed.
    Print ISSN: 0036-0244
    Electronic ISSN: 1531-863X
    Topics: Chemistry and Pharmacology , Physics
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  • 66
    Publication Date: 2018-03-09
    Description: The phase transition temperatures of chromates and molybdates of certain alkali metals, and the melting temperature and enthalpy of polymorphic transformations for tungstates, are determined by means of thermal analysis. Enthalpies of dissolution of rubidium and cesium chromates in water and enthalpies of dissolution of alkali metal tungstates in a melt at 923 K are measured via calorimetry. Standard enthalpies of formation of sought chromates are calculated. The linear correlations between the enthalpies of formation of sulfates, selenates, chromates, tungstates, and molybdates are established, and a linear correlation within − (Δ G o ox ) -1 -(Δ MV ) ox ) −1 coordinates is found for isopolymolybdates.
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    Topics: Chemistry and Pharmacology , Physics
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  • 67
    Publication Date: 2018-03-09
    Description: Field and laboratory observation data on aerosol particles in the lower stratosphere are considered. The microphysics of their formation, mechanisms of heterogeneous chemical reactions involving reservoir gases (e.g., HCl, ClONO 2 , etc.) and their kinetic characteristics are analyzed. A new model of global transport of gaseous and aerosol admixtures in the lower stratosphere is described. The preliminary results from a numerical simulation of the formation of sulfate particles of the Junge layer and particles of polar stratospheric clouds (PSCs, types Ia, Ib, and II) are presented, and their effect on the gas and aerosol composition is analyzed.
    Print ISSN: 0036-0244
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    Topics: Chemistry and Pharmacology , Physics
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  • 68
    Publication Date: 2018-03-09
    Description: An approach is formulated that theoretically describes the structure of a rough surface of small aerosol particles obtained from a liquid droplet upon its rapid cooling. The problem consists of two stages. In the first stage, a concentration profile of the droplet–vapor transition region is calculated. In the second stage, local fractions of vacant sites and their pairs are found on the basis of this profile, and the rough structure of a frozen droplet surface transitioning to the solid state is calculated. Model parameters are the temperature of the initial droplet and those of the lateral interaction between droplet atoms. Information on vacant sites inside the region of transition allows us to identify adsorption centers and estimate the monolayer capacity, compared to that of the total space of the region of transition. The approach is oriented toward calculating adsorption isotherms on real surfaces.
    Print ISSN: 0036-0244
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    Topics: Chemistry and Pharmacology , Physics
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  • 69
    Publication Date: 2018-03-09
    Description: Values of the contact angle of wetting of a surface of glassy carbon by molten chlorides of lithium, sodium, potassium, and cesium are measured by the meniscus weight method to determine the common factors of wettability of solid surfaces by ionic melts upon a change in the salt phase composition and a jump in electric potential. It is found that with a potential shift in the positive direction the shape of the curve of the contact angle’s dependence on the potential varies upon substitution of one salt by another: the angle of wetting shrinks monotonously in lithium chloride but remains constant in molten cesium chloride. This phenomenon is explained by the hypothesis that the nature of the halide anion adsorption on the positively charged surface of an electrode is chemical and not electrostatic. It is shown that the adsorption process is accompanied by charge transfer through the interface, with covalent bonding between the adsorbent and adsorbate.
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    Topics: Chemistry and Pharmacology , Physics
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  • 70
    Publication Date: 2018-03-09
    Description: The optimal conditions (40°С, 16 MPa, process duration of 30 min) for the extraction of Pelargonium graveolens L’Her essential oil using supercritical (SC) carbon dioxide are determined. GC-MS analysis shows higher concentrations of the target components (e.g., citronellol, geraniol) in the product in comparison to the oil obtained using a traditional method (steam distillation). Additional components, such as camphene, sabinene, and others are also present in the product obtained by the extraction with SC-CO 2 .
    Print ISSN: 1990-7931
    Electronic ISSN: 1990-7923
    Topics: Chemistry and Pharmacology , Physics
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  • 71
    Publication Date: 2018-03-09
    Description: Supercritical phase equilibria in the ternary system K 2 SO 4 –KOH–H 2 O at 420–500°C and up to 130 MPa pressure with binary boundary subsystems of different types are studied. The binary subsystem of type 1 features no critical phenomena in saturated (l = g) aqueous solution and no phase separation (l1–l2) (KOH–H 2 O); the binary subsystem of type 2 is characterized by immiscibility of the liquid phase and has two critical end-points \(p(g = l-_{S_{K_{2}SO_{4}}})\) and \(Q(l_{1} = l_{2}-_{S_{K_{2}SO_{4}}})\) in saturated aqueous solution (K 2 SO 4 –H 2 O). The ternary system has two three-phase equilibria (g–l–s) and (l1–l2–s), separated by a two-phase supercritical fluid region \((fl-_{S_{K_{2}SO_{4}}})\) , and two types of monovariant critical curves \((g=l-_{S_{K_{2}SO_{4}}})\) and \((l_{1}=l_{2}-_{S_{K_{2}SO_{4}}})\) . The three-phase regions approach each other upon temperature increase up to the point where the two-phase supercritical equilibrium disappears, and the two mentioned monovariant critical curves are joined into a double homogeneous critical point \((g=l-_{S_{K_{2}SO_{4}}} \leftrightarrow l_{1} = l_{2}-_{S_{K_{2}SO_{4}}})\) at maximum temperature ~445°C and 51–52 MPa.
    Print ISSN: 1990-7931
    Electronic ISSN: 1990-7923
    Topics: Chemistry and Pharmacology , Physics
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  • 72
    Publication Date: 2018-03-09
    Description: The process of carbon dioxide supercritical fluid extraction (SFE) of secondary metabolites from the lichen of Cladonia genus is studied. The yield of solid extract during SFE with carbon dioxide is significantly higher than during the extraction with acetone, ethanol, and petroleum ether on the Soxhlet apparatus. The maximum content of the target component—usnic acid (UA)—in the extract (91%, yield—2.5% of absolutely dry raw material) is obtained under pressure of 35 MPa, temperature 40°C, and duration of the process of 40 min. Introduction of cosolvents (acetone, ethanol, methylene chloride) to carbon dioxide increases the yield of the target product to 3%.
    Print ISSN: 1990-7931
    Electronic ISSN: 1990-7923
    Topics: Chemistry and Pharmacology , Physics
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  • 73
    Publication Date: 2018-03-09
    Description: Rainfall and temperature are the most important environmental factors influencing crop growth, development, and yield. The northwestern (NW) part of India is one of the main regions of food grain production of the country. It comprises of six meteorological subdivisions (Haryana, Punjab, West Rajasthan, East Rajasthan, Gujarat and Saurashtra, Kutch and Diu). In this study, attempts were made to study variability and trends in rainfall and temperature during 30-year climate normal periods (CN) and 10-year decadal excess or deficit rainfall frequency during the historical period from 1871 to 2016. The Mann-Kendall and Spearman’s rank correlation (Spearman’s rho) tests were used to determine significance of trends. Least square linear fitting method was adopted to find out the slopes of the trend lines. The long-term mean annual rainfall over North West India is 587.7 mm (standard deviation of 153.0 mm and coefficient of variation 26.0). There was increasing trend in minimum and maximum temperatures during post monsoon season in entire study period and current climate normal period (1991–2016) due to which the sowing of rabi season crops may be delayed and there may be germination problem too. There was a non-significant decreasing trend in rainfall during monsoon season and an increasing trend in rainfall during post monsoon over North West India during entire study period. During current CN5 (1991–2016), all the subdivision (except the Saurashtra region) showed a decreasing trend in rainfall during monsoon season which is a matter of concern for kharif crops and those rabi crops which are grown as rainfed on conserved soil moisture. The decadal annual and seasonal frequencies of excess and deficit years results revealed that the annual total deficit rainfall years (24) exceeded total excess rainfall years (22) in North West India during the entire study period. While during the current decadal period (2011 to 2016), single year was the excess year and 2 years were deficit rainfall years in all subdivisions (except East Rajasthan) on annual basis.
    Print ISSN: 0177-798X
    Electronic ISSN: 1434-4483
    Topics: Geosciences , Physics
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  • 74
    Publication Date: 2018-03-09
    Description: Stress and water injection induce deformations and changes in pore pressure in the soil. The interaction between the mechanical deformations and the flow of water induces a change in porosity and permeability, which results in nonlinearity. To investigate this interaction and the impact of mechanical vibrations and pressure pulses on the flow rate through the pores of a porous medium under a pressure gradient, a poroelastic model is proposed. In this paper, a Galerkin finite element method is applied for solving the quasi-static Biot’s consolidation problem for poroelasticity, considering nonlinear permeability. Space discretisation using Taylor–Hood elements is considered, and the implicit Euler scheme for time stepping is used. Furthermore, Monte Carlo simulations are performed to quantify the impact of variation in the parameters on the model output. Numerical results show that pressure pulses and soil vibrations in the direction of the flow increase the amount of water that can be injected into a deformable fluid-saturated porous medium.
    Print ISSN: 0169-3913
    Topics: Geosciences , Technology
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  • 75
    Publication Date: 2018-03-09
    Description: We investigated immiscible displacement in a channel considering regular surface roughness at walls. A color-fluid LBM code is developed and validated against the Hagen–Poiseuille flow before it is employed for simulating the displacement process. The dimensionless roughness height and roughness spacing ratio are defined to characterize the surface roughness. The simulation results show that the presence of surface roughness obviously impels a finger formation in a channel. The impelling effect is more significant at larger roughness heights and medium roughness spacing ratios. The critical capillary number and viscosity ratio of a finger formation is reduced with increasing roughness height. The obvious effect of wettability on the finger development in a smooth channel is attenuated in rough channels. The attenuation magnitude increases with increasing roughness height.
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    Topics: Geosciences , Technology
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  • 76
    Publication Date: 2018-03-09
    Description: Genetically engineered pigs are often created with a targeting vector that contains a loxP flanked selectable marker like neomycin. The Cre–loxP recombinase system can be used to remove the selectable marker gene from the resulting offspring or cell line. Here is described a new method to remove a loxP flanked neomycin cassette by direct zygote injection of an mRNA encoding Cre recombinase. The optimal concentration of mRNA was determined to be 10 ng/μL when compared to 2 and 100 ng/μL ( P  〈 0.0001). Development to the blastocyst stage was 14.1% after zygote injection with 10 ng/μL. This method successfully removed the neomycin cassette in 81.9% of injected in vitro derived embryos; which was significantly higher than the control ( P  〈 0.0001). Embryo transfer resulted in the birth of one live piglet with a Cre deleted neomycin cassette. The new method described can be used to efficiently remove selectable markers in genetically engineered animals without the need for long term cell culture and subsequent somatic cell nuclear transfer.
    Print ISSN: 0962-8819
    Electronic ISSN: 1573-9368
    Topics: Biology
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  • 77
    Publication Date: 2018-03-09
    Description: This paper evaluates the simulation performance of the 37 coupled models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) with respect to the East Asian summer monsoon (EASM) and the Indo-Pacific warm pool and North Pacific Ocean dipole (IPOD) and also the interrelationships between them. The results show that the majority of the models are unable to accurately simulate the interannual variability and long-term trends of the EASM, and their simulations of the temporal and spatial variations of the IPOD are also limited. Further analysis showed that the correlation coefficients between the simulated and observed EASM index (EASMI) is proportional to those between the simulated and observed IPOD index (IPODI); that is, if the models have skills to simulate one of them then they will likely generate good simulations of another. Based on the above relationship, this paper proposes a conditional multi-model ensemble method (CMME) that eliminates those models without capability to simulate the IPOD and EASM when calculating the multi-model ensemble (MME). The analysis shows that, compared with the MME, this CMME method can significantly improve the simulations of the spatial and temporal variations of both the IPOD and EASM as well as their interrelationship, suggesting the potential for the CMME approach to be used in place of the MME method.
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  • 78
    Publication Date: 2018-03-09
    Description: Steady, 2-,3-D Darcian flows generated by a dipole (a pair of horizontal or vertical injection–abstraction wells closely placed one above another), with circulation of fresh water inside an interface confined lens or “bubble” underneath an impermeable caprock, surrounded by a static saline groundwater, are analytically studied. For 2-D dipole, the complex potential domain is a plane with a horizontal cut. This domain is conformally mapped onto a reference half-plane where the Keldysh–Sedov formula is used to obtain the complex physical coordinates. Explicit closed-form expressions for the vase-shaped interface, flow net, isohypses, magnitudes of the Darcian velocity and Riesenkampf’s resultant force are obtained, depending on the dipole moment, its position with respect to the caprock, and the ratio of densities of the two fluids. It is shown that for sufficiently small injection-pumping rates the fresh water “vase” separates from the caprock and becomes a circle, inside which streamlines are Newtons’ loops of monodiametral degenerate hyperbolae (cubics). Two numerical codes, MT3DMS and SEAWAT, are also used for delineation of isoconcentric lines, which qualitatively corroborate the analytical solutions in delineation of the “bubble” in the part where the sharp interface model predicts stable free boundaries and evidencing “dimples” on the boundary of the “bubble” where the saline water overlies the fresh one. For 3-D dipole not bounded by the caprock, the analytical fresh water “bubble” is a sphere and solution follows, mutatis mutandis , from the textbook formulae for flow of an ideal fluid past an impermeable sphere. The Stokes streamlines inside the sphere are sixtics; isotachs are plotted in an axial section. Stability of the soil matrix near the wells is also discussed.
    Print ISSN: 0169-3913