Integration of multi-parametric fuzzy analytic hierarchy process and GIS along the UNESCO World Heritage: a flood hazard index,Mombasa County,Kenya

Natural Hazards - Flood is a natural hazard affecting human life and ecosystem globally causing catastrophic disasters. Most flood-induced socioeconomic losses are exacerbated by unabated urban...     

Hydromechanical Heterogeneities of a Mature Fault Zone: Impacts on Fluid Flow

In this paper, fluid flow is examined for a mature strike‐slip fault zone with anisotropic permeability and internal heterogeneity. The hydraulic properties of the fault zone were first characterized in situ by microgeophysical (V_P and σ_c) and rock‐quality measurements (Q‐value) performed along a 50‐m long profile perpendicular to the fault zone. Then, the local hydrogeological context of the fault was modified to conduct a water‐injection test. The resulting fluid pressures and flow rates through the different fault‐zone compartments were then analyzed with a two‐phase fluid‐flow numerical simulation. Fault hydraulic properties estimated from the injection test signals were compared to the properties estimated from the multiscale geological approach. We found that (1) the microgeophysical measurements that we made yield valuable information on the porosity and the specific storage coefficient within the fault zone and (2) the Q‐value method highlights significant contrasts in permeability. Fault hydrodynamic behavior can be modeled by a permeability tensor rotation across the fault zone and by a storativity increase. The permeability tensor rotation is linked to the modification of the preexisting fracture properties and to the development of new fractures during the faulting process, whereas the storativity increase results from the development of micro‐ and macrofractures that lower the fault‐zone stiffness and allows an increased extension of the pore space within the fault damage zone. Finally, heterogeneities internal to the fault zones create complex patterns of fluid flow that reflect the connections of paths with contrasting properties.     

A mineralogical and geochemical study of polymict eucrite discovered in Sahara of southwest Algeria

NWA2268 is a polymict eucrite discovered in the Sahara, at southwest Algeria, close to the region of Tindouf. This meteorite weighs 65 g and presents a thin black fusion crust. The rock is fine- to medium-grained breccia and contains mineral fragments of plagioclases, pyroxenes, spinel, olivine and silica. The rock contains some basaltic fragments with sub-ophitic or cumulative textures, constituted by plagioclases and exsolved pigeonite. Pyroxferroite grains are present and locally destabilised in an association of hedenbergite, fayalite and silica. It also presents unequilibrated eucritic clast with heterogeneous pyroxenes and plagioclases compositions. Pyroxenes in the all of the other clasts have equilibrated composition, with exolved pigeonites with augite lamellaes. This polymict eucrite contains also partially devitrified glass that represents impact melts linked to impact event. None recrystallization of this glass confirms a lack of post-brecciation metamorphism. Diogenitic fragments are less abundant than 10 %. The oxygen isotopic composition of NWA2268 is Δ¹⁷O (?0.43). This meteorite is interpreted as belonging to the HED group attributed to the 4-Vesta asteroid.     

A preliminary methods comparison for measurement of dissolved organic nitrogen in seawater

Routine determination of dissolved organic nitrogen (DON) is performed in numerous laboratories around the world using one of three families of methods: UV oxidation (UV), persulfate oxidation (PO), or high temperature combustion (HTC). Essentially all routine methods measure total dissolved nitrogen (TDN) and calculate DON by subtracting the dissolved inorganic nitrogen (DIN). While there is currently no strong suggestion that any of these methods is inadequate, there are continuing suspicions of slight inaccuracy by UV methods.This is a report of a broad community methods comparison where 29 sets (7 UV, 13 PO, and 9 HTC) of TDN analyses were performed on five samples with varying TDN and DIN concentrations. Analyses were done in a “blind” procedure with results sent to the first author. With editing out one set of extreme outliers (representing 5 out of 145 ampoules analyzed), the community comparability for analyzing the TDN samples was in the 8–28% range (coefficient of variation representing one standard deviation for the five individual samples by 28 analyses). When DIN concentrations were subtracted uniformly (single DIN value for each sample), the comparability was obviously worse (19–46% cv). This comparison represents a larger and more diverse set of analyses, but the overall comparability is only marginally better than that of the Seattle workshop of a decade ago. Grouping methods, little difference was seen other than inconclusive evidence that the UV methods gave TDN values for several of the samples higher than HTC methods. Since there was much scatter for each of the groups of methods and for all analyses when grouped, it is thought that more uniformity in procedures is probably needed. An important unplanned observation is that variability in DIN analyses (used in determining the final analyte in most UV and PO methods) is essentially as large as the variability in the TDN analyses.This exercise should not be viewed as a qualification exercise for the analysts, but should instead be considered a broad preliminary test of the comparison of the families of methods being used in various laboratories around the world. Based on many independent analyses here, none of the routinely used methods appears to be grossly inaccurate, thus, most routine TDN analyses being reported in the literature are apparently accurate. However, it is not reassuring that the ability of the international community to determine DON in deep oceanic waters continues to be poor. It is suggested that as an outgrowth of this paper, analysts using UV and PO methods experiment and look more carefully at the completeness of DIN conversion to the final analyte and also at the accuracy of their analysis of the final analyte. HTC methods appear to be relatively easy and convenient and have potential for routine adoption. Several of the authors of this paper are currently working together on an interlaboratory comparison on HTC methodology.     

A new systematic approach using the Modified Gaussian Model: Insight for the characterization of chemical composition of olivines, pyroxenes and olivine-pyroxene mixtures

An automatic procedure has been implemented on the original MGM approach (Sunshine et al., 1990) in order to deal with an a priori unknown mafic mineralogy observed in the visible-near infrared by reflectance spectroscopy in the case of laboratory or natural rock spectra. We consider all the mixture possibilities involving orthopyroxene, clinopyroxene and olivine, and use accordingly for each configuration different numbers of Gaussians, depending on the potential complexity of the mixture. A key issue is to initialize the MGM procedure with a proper setting for the Gaussians parameters. An automatic analysis of the shape of the spectrum is first performed. The continuum is handled with a second order polynomial adjusted on the local maxima along the spectrum and Gaussians parameters initial settings are made on the basis of laboratory results available in the literature in the case of simple mixtures of mafic minerals. The returned MGM solutions are then assessed on spectroscopic grounds and either validated or discarded, on the basis of a mineralogical sorting.The results presented in this paper are a first quantitative step to characterize both modal and chemical compositions of pyroxenes and olivines. A demonstration of the methodology on specific examples of binary and ternary olivine-pyroxenes mixtures has been made, which shows that the different non-linear effects which affect the Gaussian parameters (center and strength) can be successfully handled. Of note is the fact that the band center positions associated with the different mafic minerals are not set here in the inverse problem, and thus the MGM outputs are truly informative of the chemical composition of pyroxenes and olivines. With the consideration of some limits on the detection thresholds, these results are quite promising for increasing the operational use of the Modified Gaussian Model with large hyperspectral data sets in view of establishing detailed mineralogical mappings of magmatic units.     

Monitoring the evolution of irrigated areas with Landsat images using backward and forward change detection analysis in the Kou watershed,Burkina Faso

The Kou watershed is characterized by important water resources used for drinking, agriculture (especially in the irrigated areas), industry and the preservation of aquatic fauna and flora. For several decades, there has been increasing pressure on the Kou's water resources, partly because of the expansion of the irrigated agricultural areas. This study was conducted to examine this issue, focusing on one specific irrigated area. In order to monitor the expansion of irrigated areas in developing countries, a low-cost remote sensing method based on Landsat images and aerial photographs was developed. The method is based on maximum-likelihood classification, followed by backward and forward change detection analysis requiring agronomic expertise. Using pixel trajectory analysis, the method connects all pixels to their consecutive states in order to correct their current states. The study showed that the irrigated area has expanded by almost 70% over 20 years, with most of this expansion occurring in the past 10 years. The method, if validated, could be used to obtain better information on past occupation in the rural irrigated areas for which there is currently no archived data, making temporal analyses impossible.     

Magnetotellurics applied to the study of the crustal structures in Senegal (West Africa)

Abstract

In Senegal, magnetotellurie (MT) method has been used in an attempt to resolve the principal structural features by their electrical response. On the basis of numerical modelling of data, an unified model of possible crustal structure is presented for the West african margin. The results are in agreement with other independent geophysical and geological information.     

La couverture océanique des ultrabasites de Lanzo (Alpes occidentales) : arguments lithostratigraphiques et pétrologiques

Résumé

De nombreuses analogies entre les évolutions pétro-logiques et métamorphiques des ultrabasites de Lanzo et des ophiohtes liguro-piémontaises ont été soulignées récemment. Ces analogies concernent: la nature des ultrabasites (Iherzolites à plagioclase peu appauvries), la présence de gabbros et de filons basaltiques superficiels intrusifs dans les péridotites, l’existence de reliques de paragenèses métamorphiques de haute température attribuables à un épisode océanique, l’empreinte du métamorphisme alpin de haute pression. Ces faits ont conduit certains auteurs à proposer que les péridotites de Lanzo représentent un fragment du plancher océanique téthysien.

Nous avons tenté de vérifier cette hypothèse en recherchant la couverture océanique (volcanique et/ou sédimentaire) des péridotites de Lanzo, dans la partie occidentale du massif où des pincées de métabasites et de schistes lustrés s.l. sont visibles associées aux serpentinites.

Aux environs du village de Richiaglio, à l’Est de la cicatrice de Viù, les successions lithostratigraphiques reconstituées comprennent schémati-quement : les ultrabasites serpentinisées du corps de Lanzo, des métabasites, des quartzites manganésifères (comparables à celles du Mont Viso par exemple), et des calcschistes. Ces successions s’apparentent à celles décrites dans les couvertures d’autres ophiolites piémontaises, ce qui conduit à proposer que ces ensembles métavolcaniques et Dimetaires dimentaires représentent des résidus de la couverture océanique originelle des péridotites. L’analyse des paragenèses éclogitiques des métasédiments et des métabasites permet de montrer que l’évolution P,T alpine de ces lambeaux est compatible avec celle du corps de Lanzo. Cette interprétation et ses implications sont discutées.     

Karst et évolution des rivières : le cas de l’Ardenne

Résumé

Dans les régions karstiques comprenant des vallées épigénétiques, les phénomènes tectoniques ont deux influences majeures : a) la surrection donne de l’énergie potentielle en créant des différences d’altitude, générant à la fois le creusement des vallées et celui du karst ; b) une tectonique est nécessaire pour que le processus de karstification débute. L’opposition entre le développement privilégié soit des vallées, soit des réseaux karstiques dépend ainsi du type dissipée. Les réseaux karstiques de l’Ardenne se situent surtout entre 5 et 15 m au-dessus de la surface piézométrique pour les réseaux secs, et dans la zone saturée pour les parties actives. La structuration de ces réseaux karstiques est favorisée par un ralentissement de la surrection et une activité tectonique. Cette période se situe dans le Pléistocène moyen et récent, d apres les datations U/Th de spéléothèmes. © Elsevier, Paris     

Sedimentary diatoms along a temporal and spatial gradient of metal contamination

We examined changes at the community and population level of sedimentary diatoms over a wide temporal and spatial gradient of metal pollution encountered in cores from three lakes in the Abitibi mining region (Québec, Canada). Diatom communities on the whole appeared to be very tolerant of metal contamination, as shown by diatom cell accumulation rates decreasing only under the most severe conditions of contamination, which were found from the 1930s to the 1980s in Lac Dufault (cadmium, up to 94 μg/g dry sediment; Cu, up to 8600 μg/g; Zn, up to 9000 μg/g). Under the moderate conditions of contamination observed in the other two lakes and in the most recent sediment of Lac Dufault, diatom cell accumulation rates tended to increase over values typical of the pre-mining period. However, there were increasing rearrangements of the community composition along the contamination gradient. Under moderate metal enrichment, the diatom community of Lac Vaudray experienced only subtle changes, with Cyclotella stelligera, albeit decreasing, remaining the dominant taxon. In the intermediately contaminated Lac Caron, several benthic taxa, noticeably Cymbella silesiaca and several Fragilaria species, rose in taxonomic importance. The most extreme contamination observed in Lac Dufault led to a severely impoverished community almost entirely represented by Achnanthes minutissima and Brachysira vitrea. With increasing levels of contamination, there was a shift from planktonic to benthic taxa and morphotypes and a consistent decrease in the siliceous stomatocysts/diatom frustules ratio. These trends suggest that littoral zones may represent an important refugium under conditions of high contamination. Responses to metal stress were in general more evident at the population than at the community level. Cyclotella stelligera and B. vitrea had a consistent negative and positive response, respectively, along the gradient and are the most promising indicators of metal pollution for this region.