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21.
M. Aziz Hasan Prosun Bhattacharya Ondra Sracek Kazi Matin Ahmed Mattias von Brmssen Gunnar Jacks 《Journal of Hydrology》2009,378(1-2):105-118
Hydrogeochemical investigations along an E–W transect in the middle Meghna basin show groundwater chemistry and redox condition vary considerably with the change in geology. Groundwater in the Holocene shallow (<150 m bgl) alluvial aquifer in western part of the transect is affected by high arsenic concentration (As > 10 μg/l) and salinity. On the other hand, groundwater from the Pliocene Dupi Tila sandy aquifer in the eastern part is fresh and low in As (<10 μg/l). The Holocene shallow aquifers are high in dissolved As, , Fe and dissolved organic carbon (DOC), but generally low in and . High concentrations (250–716 mg/l) together with high DOC concentrations (1.4–21.7 mg/l) in these aquifers reflect active sources of degradable natural organic matter that drives the biogeochemical process. There is generally de-coupling of As from other redox-sensitive elements. In contrast, the Pliocene aquifers are low in As, and DOC. Molar ratio of /H4SiO4 suggests that silicate weathering is dominant in the deeper Holocene aquifers and in the Pliocene aquifers. Molar ratios of Cl−/ and Na+/Cl− suggest mixing of relict seawater with the fresh water as the origin of groundwater salinity. Speciation calculations show that saturation indices for siderite and rhodochrosite vary significantly between the Holocene and Pliocene aquifers. Stable isotopes (δ2H and δ18O) in groundwater indicate rapid infiltration without significant effects of evaporation. The isotopic data also indicates groundwater recharge from monsoonal precipitation with some impact of altitude effect at the base of the Tripura Hills in the east. The results of the study clearly indicate geological control (i.e. change in lithofacies) on groundwater chemistry and distribution of redox-sensitive elements such as As along the transect. 相似文献
22.
Dynamics of arsenic adsorption in the targeted arsenic-safe aquifers in Matlab, south-eastern Bangladesh: Insight from experimental studies 总被引：1，自引：0，他引：1
Clare Robinson Mattias von Brömssen Prosun BhattacharyaSara Häller Annelie BivénMohammed Hossain Gunnar JacksKazi Matin Ahmed M. Aziz HasanRoger Thunvik 《Applied Geochemistry》2011,26(4):624-635
Targeting shallow low-As aquifers based on sediment colour may be a viable solution for supplying As-safe drinking water to rural communities in some regions of Bangladesh and West Bengal in India. The sustainability of this solution with regard to the long-term risk of As-safe oxidized aquifers becoming enriched with As needs to be assessed. This study focuses on the adsorption behaviour of shallow oxidized sediments from Matlab Region, Bangladesh, and their capacity to attenuate As if cross-contamination of the oxidized aquifers occurs. Water quality analyses of samples collected from 20 tube-wells in the region indicate that while there may be some seasonal variability, the groundwater chemistry in the reduced and oxidized aquifers was relatively stable from 2004 to 2009. Although sediment extractions indicate a relatively low amount of As in the oxidized sediments, below 2.5 mg kg−1, batch isotherm experiments show that the sediments have a high capacity to adsorb As. Simulations using a surface complexation model that considers adsorption to amorphous Fe(III) oxide minerals only, under-predict the experimental isotherms. This suggests that a large proportion of the adsorption sites in the oxidized sediments may be associated with crystalline Fe(III) oxides, Mn(IV) and Al(III) oxides, and clay minerals. Replicate breakthrough column experiments conducted with lactose added to the influent solution demonstrate that the high adsorption capacity of the oxidized sediments may be reduced if water drawn down into the oxidized aquifers contains high levels of electron donors such as reactive dissolved organic C. 相似文献
23.
Eight ophiuroid species, six from the northern Kattegat-eastern Skagerrak and three from the northern Adriatic Sea, were examined for regeneration of arms. The species were separated into groups based upon mode of feeding and habitat. Comparison between groups collected in the northern Kattegat-eastern Skagerrak showed that infaunal suspension- and deposit-feeding species (Amphiura filiformis and A. chiajei) had significantly more scars per arm (mean number 0.78) than epibenthic suspension feeders (Ophiothrix fragilis and Ophiocomina nigra, 0.29) or epibenthic carnivores and deposit feeders (Ophiura ophiura and O. albida, 0.13). Spatial variation in arm regeneration incidence was found between sampling sites in the northern Kattegat-eastern Skagerrak for Amphiura filiformis and in the northern Adriatic Sea for Ophiothrix quinquemaculata. The ash-free dry weight (AFDW) and nitrogen (N) contents were measured in arms of six species of brittle-stars from the northern Kattegat-eastern Skagerrak. Differences between species were found, with highest concentrations of AFDW and N in Amphiura filiformis, intermediate in A. chiajei, Ophiocomina nigra and Ophiothrix fragilis, and lowest in Ophiura ophiura and O. albida. As the infaunal suspension- and deposit-feeding brittle-stars (Amphiura spp.) had the highest proportions of damaged arms and highest AFDW and N contents in their arms in this comparison, it is suggested that selective cropping of arms by demersal fish is the main cause of arm damage on Amphiura spp. in this area. 相似文献
24.
Iron environment in a montmorillonite from Gola del Furlo (Marche,Italy). A synchrotron radiation XANES and a Mössbauer study 总被引：1，自引：0，他引：1
Summary The iron environment and oxidation state has been determined by XANES spectroscopy in a montmorillonite sample from Gola del Furlo (Marche, Italy). A comparison with the XANES spectra of Fe2– in a natural hematite from Elba (Italy) and of Fe 21 in a synthetic Fe[C03] (the fine structures in the spectra of which have also been clarified in detail on the basis of the known crystal structures) permits recognizing that in this sheet silicate Fe is mostly in the trivalent oxidation state and in a distorted octahedral coordination. Mössbauer spectroscopy confirms the XANES assignment, but it also shows that minor octahedral Fee+ is present besides the predominant octahedral Fe3—.
Zusammenfassung Synchroton Radiation XANES und Mössbauer-Studien zur Vertielung des Eisens im Montmorillonit aus Gola del Furlo(Marche, Italien) Die Verteilung und die Oxidationsstufe des Eisens eines Montmorillonites aus Gola del Furlo (Marche, Italien) wurden untersucht. Ein Vergleich der XANES Spektren dieses Schichtsilikates mit denen von FeFe3+ eines natürlichen Hämatites von Elba (Italien) und von Fe2+ eines synthetischen Fe[C03], wobei die Details der Spektren auf Grund der Kenntnis der bekannten Kristallstruktur geklärt werden konnten, zeigt, daß Eisen großteils in dreiwertiger Form und in verzerrter oktaedrischer Koordination vorliegt. Mössbauer-Studien bestätigen die Ergebnisse der XANES Untersuchungen, zeigen aber auch, daß untergeordnet Fe e+ an Stelle von Fe3+ in der oktaedrischen Position eingebaut wird.相似文献
25.
The influence of foliation on the fragility of granitic rocks, image analysis and quantitative microscopy 总被引：6，自引：0，他引：6
Urban kesson Jimmy Stigh Jan Erik Lindqvist Mattias G ransson 《Engineering Geology》2003,68(3-4):275-288
Fabric-dependent anisotropy is important in understanding the mechanical behaviour of foliated rocks because the foliation creates mechanically weak discontinuities. Using optical microscopy, a foliation index (FIX) was calculated for a group of granitic rocks in southern Sweden that displays a range of textures from foliated to nonfoliated. Image analysis from scanning electron microscope with backscattered detector (SEM/BSE) images was used in order to measure the rock texture of these samples. The analyses were compared with the Los Angeles (LA) test, which measures resistance of rock aggregate to fragmentation. The results demonstrate that the measured grain size, shape and spatial arrangement are important parameters controlling the fragility of the rock. Both the texture and foliation must be taken into account to obtain a significant relationship with the mechanical analyses. We suggest that this alternative method could be a helpful tool for predicting a rock's suitability as an aggregate as it gives a better understanding of the material properties compared to mechanical testing. 相似文献
26.
Kristin Jonsdottir Mattias Lindman Roland Roberts Bjrn Lund Reynir Bdvarsson 《Tectonophysics》2006,424(3-4):195
The distribution of waiting times between time-neighbouring events for a time series obeying the Omori law is examined theoretically and numerically with the aim of understanding the characteristics of these distributions, how these characteristics change (e.g. scale) with the parameters of the Omori series, and thus how empirical waiting time data may be correctly interpreted. It is found that the waiting time distribution, for a single Omori aftershock sequence, consists in general of two power law segments followed by a rapid decay at larger waiting times. The analyses are illustrated using real data from the SIL network on Iceland. This data often shows characteristics predominantly consistent with the Omori law, but there are significant exceptions. We conclude that waiting time distributions and related statistical analysis has meaningful potential for the analysis of earthquake data sets, as a step towards developing physical models of the earthquake process. 相似文献
27.
Climate change is a fundamental challenge for which agriculture is sensitive and vulnerable. The Intergovernmental Panel on Climate Change has identified relevant information as key to enabling appropriate climate adaptation and mitigation action. Information specifically directed to farmers can be found, for example, in specialized farming magazines. While recent studies examine how national news media frame climate change, less—if any—studies have addressed climate framings and coverage in specialized media. Media framings are storylines that provide meaning by communicating how and why an issue should be seen as a problem, how it should be handled, and who is responsible for it. This paper analyses the framings and coverage of climate change in two Swedish specialized farming magazines from 2000 to 2009. It examines the extent of the climate change coverage, the content of the media items, and the dominant framings underlying their climate change coverage. The study identifies: increased coverage of climate change starting in 2007; frequent coverage of agriculture’s contribution to climate change, climate change impacts on agriculture, and consequences of climate politics for agriculture; and four prominent frames: conflict, scientific certainty, economic burden, and action. The paper concludes that climate change communicators addressing farmers and agricultural extension officers should pay attention to how these frames may be interpreted by different target audiences. Research is needed on how specialized media reports on climate-related issues and how science-based climate information is understood by different groups of farmers and which other factors influence farmers’ engagement in climate mitigation and adaptation. 相似文献