Caractérisation géochimique et bactériologique des nappes d’une région à climat tropical sec au centre Sud de Madagascar

Résumé

Le district de Betroka, soumis à un climat tropical sec, connaît d’importants problèmes de ressource en eau. Cette situation se traduit pour de nombreux habitants par la consommation d’eau de très mauvaise qualité tant sur le plan physico-chimique, que sur le plan bactériologique. Pour tenter d’améliorer cette situation, le gouvernement malgache a entrepris un programme d’alimentation en eau potable et assainissement en milieu rural (projet 350 forages), cadre du présent travail, afin d’assurer à l’eau destinée à l’alimentation humaine une qualité suffisante en termes bactériologique et minéral. L’étude microbiologique de l’eau souterraine du district de Betroka a confirmé l’absence de bactéries d’origine fécale. L’étude hydrochimique a révélé différents processus conduisant à la minéralisation des eaux souterraines en relation avec : (a) la remontée d’eau saline d’origine profonde à partir des fractures transversales du cisaillement majeur de Betroka, et à partir des failles normales à l’origine du graben de Mangoky et du domaine du massif en dôme et bassin du complexe intrusif d’Ianakafy ; (b) la dissolution des aérosols et embruns marins déposés, dissous par la pluie et entraînés jusqu’aux aquifères ; et (c) l’interaction des eaux météoriques et souterraines avec les minéraux des roches encaissantes (scapolite, phlogopite, biotite, hornblende, pyroxène…) qui pourrait également contribuer à la forte minéralisation observée.     

Hisslers observed during daytime in a low latitude ground station

The observation of hisslers during daytime at low latitude station Jammu, India, is reported. The hissler elements are quasi-periodic falling tones observed during the period of hiss activity and appear in minutelong sequences with average spacing between individual elements of the order of 0.15 s. Hissler elements exhibit almost no dispersion and no complex internal structure in slope and intensity, and successive hissler elements do not overlap in time. It seems that the reported hisslers might have propagated in prolongitudinal mode.     

Modelling of Riparian-Imitated Constructed Wetland for Fish Habitat

This paper presents a hydrodynamic-based investigation of constructed wetland suitability for fish habitat. A constructed wetland adjacent to river is manoeuvred to imitate riparian fish habitat by means of computer modelling. Flow-velocity conditions, water depths and effects of macrophytes to resistance of flow in constructed wetland are modelled and steered towards creating a favourable ground for natural substrate spawning of native fish species. The model suggests combination of two zones, which are a macrophyte zone for typical functions of a wetland and an open water zone with gravel bed to support fish reproductive cycles.     

The role of hydrologic information in reservoir operation – Learning from historical releases

Closing the gap between theoretical reservoir operation and the real-world implementation remains a challenge in contemporary reservoir operations. Past research has focused on optimization algorithms and establishing optimal policies for reservoir operations. In this study, we attempt to understand operators’ release decisions by investigating historical release data from 79 reservoirs in California and the Great Plains, using a data-mining approach. The 79 reservoirs are classified by hydrological regions, intra-annual seasons, average annual precipitation (climate), ratio of maximum reservoir capacity to average annual inflow (size ratio), hydrologic uncertainty associated with inflows, and reservoirs’ main usage. We use information theory – specifically, mutual information – to measure the quality of inference between a set of classic indicators and observed releases at the monthly and weekly timescales. Several general trends are found to explain which sources of hydrologic information dictate reservoir release decisions under different conditions. Current inflow is the most important indicator during wet seasons, while previous releases are more relevant during dry seasons and in weekly data (as compared with monthly data). Inflow forecasting is the least important indicator in release decision making, but its importance increases linearly with hydrologic uncertainty and decreases logarithmically with reservoir size. No single hydrologic indicator is dominant across all reservoirs in either of the two regions.     

Interactions of uranium with bacteria and kaolinite clay

We assessed the accumulation of uranium (VI) by a bacterium, Bacillus subtilis, suspended in a slurry of kaolinite clay, to elucidate the role of microbes on the mobility of U(VI). Various mixtures of bacteria and the koalinite were exposed to solutions of 8 × 10^− 6 M- and 4 × 10^− 4 M-U(VI) in 0.01 M NaCl at pH 4.7. After 48 h, the mixtures were separated from the solutions by centrifugation, and treated with a 1 M CH₃COOK for 24 h to determine the associations of U within the mixture. The mixture exposed to 4 × 10^− 4 M U was analyzed by transmission electron microscope (TEM) equipped with EDS. The accumulation of U by the mixture increased with an increase in the amount of B. subtilis cells present at both U concentrations. Treatment of kaolinite with CH₃COOK, removed approximately 80% of the associated uranium. However, in the presence of B. subtilis the amount of U removed was much less. TEM–EDS analysis confirmed that most of the U removed from solution was associated with B. subtilis. XANES analysis of the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both revealed that it was present as U(VI). These results suggest that the bacteria have a higher affinity for U than the kaolinite clay mineral under the experimental conditions tested, and that they can immobilize significant amount of uranium.     

Neoproterozoic Tectonic Events of Egypt

The Egyptian Nubian Shield(ENS) represents the northwestern part of the Arabian-Nubian Shield and the northern extension of the East African Orogen. The ENS is regarded as being formed due to northward-directed escape tectonics. It is characterized by mild accretion and suture zones dominated by major strike-slip zones with a commonly sinistral sense of movement; some shear zones display a dextral sense of shear. It is dominated by gneisses and migmatites in the south, arc volcaniclastic metasediments and highly dismembered ophiolites in the central parts, whereas its northern part is dominated by late-to post-tectonic granitoids. In southern Sinai, the Neoproterozoic rocks are grouped into four complexes, namely Feiran–Solaf, Sa'al–Zaghra, Kid and Taba. The ENS ophiolites were formed between 730–750 Ma, mainly in a supra-subduction zone setting. The ENS has undergone a Neoproterozoic deformation history involving three successive phases:(1) Early N–S shortening phase(D1),(2) Syn-accretionary phase(D2) and(3) Post-accretionary phase(D3). The initial island-arc stage(780–730 Ma) is a N–S shortening phase initiated by collision between the Eastern Desert tectonic terrane to the north with both the Gebeit and Gabgaba terranes to the south(830–720 Ma). During the arc-splitting and back-arc spreading stage(730–620), voluminous syn-tectonic granitoids intruded into the ENS(750–610 Ma). The E–W-directed compressional/transpressional phase(620–450 Ma) led to the overall uplift of the central part of the ENS and consequently the development and exhumation of the core complexes in oblique convergent zones. The E–W intense shortening deformation resulted also in the formation of NW-and NE-striking sinistral and dextral strike-slip shear zones, respectively. The latest periods of the E–W-directed compressional/transpressional regime were characterized by deposition of the molasse-type Hammamat Sediments unconformably over the Dokhan Volcanics, or interbedded with them. The combined thrusting, folding and sinistral-reverse shearing structures have been interpreted to resulted from the E–Wdirected compressional/transpressional phase in response to the oblique shortening of the Arabian-Nubian Shield between East and West Gondwana.     

Architects and planners approaches to urban form and design in the Toronto region: A comparative analysis

This study compares architectural and planning approaches to urban form and design within a North American context. It presents a critical assessment of the results of semi-structured, in-depth interviews with a group of highly experienced architects, landscape architects, and planners from the Greater Toronto Region. Dialogues with practitioners revealed a growing intellectual divide in regard to understanding urban form and design issues. Planners portrayed the urban form as a product of social and economic forces or a backdrop for civic institutions, private development initiatives, and public action. Architects and landscape architects, on the other hand, emphasized the importance of built configurations and spatial relations in shaping economic, social, and cultural patterns. With such a polarized perspective of urban development processes, each group of practitioners proposed different and somewhat contradictory visions for the future of North American built forms. This study develops an understanding of theoretical and pragmatic concerns within design professions (architecture/landscape architecture) and social science professions (planning at large) that hamper the development of integrative urban design visions. It extends an interdisciplinary understanding of built environments and the forces that shape them and paves the way for more in-depth studies aimed at creating more integrative urban design theories and development strategies.     

Erratum to: Transpressional regime in southern Arabian Shield: Insights from Wadi Yiba Area,Saudi Arabia

Mineralogy and Petrology -