Organisation hydrochimique,biologique et sédimentologique d’un lac intracontinental à peuplements lagunaires : la Birket Karoun (Fayoum,Egypte)

Résumé

La Birket Karoun a été étudiée d’un point de vue biogéologique sur une période de 12 mois. Les données ainsi obtenues, ajoutées à celles de la littérature disponible, permettent de présenter les caractéristiques biogéologiques essentielles de ce bassin original.

Le lac n’est alimenté actuellement que par des eaux continentales issues du système nilotique ce qui entraîne des propriétés hydrochimiques assez différentes des corps d’eau paraliques influencés par la mer. Cependant, les caractéristiques hydrologiques, biologiques et sédimen-taires de la Birket Karoun la classent parmi les écosystèmes de type lagunaire. Il est même possible d’y reconnaître une organisation biogéologique zonale très semblable à celle des lagunes, la partie la plus « marine » (ou la moins confinée) se situant à l’opposé de la zone des apports d’eau douce. Une connexion entre le lac et la mer, actuelle ou passée, étant à peu près exclues, il faut admettre que les eaux continentales concentrées peuvent présenter, dans certains cas, des caractéristiques chimiques et biochimiques presque marines vis-à-vis des êtres vivants.

Dans cette optique, la Birket Karoun apparaît comme un modèle actuel susceptible de fournir une alternative à l’hypothèse d’une « Mer Saharienne » pour rendre compte de l’existence des lacs sahariens pleistocènes à faunes fossiles lagunaires.     

Comparison of NATM and umbrella arch method in terms of cost,completion time,and deformation

In all kinds of tunnel excavations, especially those excavated in cities, it is important to control surface settlements and prevent damage to the surface and subsurface structures. For this purpose, in weak rocks and soils, the umbrella arch method (UAM) has been used in addition to the new Austrian tunneling method (NATM). NATM and UAM are the best-known classical methods used in tunnel excavation. In classical tunneling, NATM is usually preferred in normal rocks. However, in some cases, NATM may be insufficient. UAM is a very effective alternative especially in soils and weak rocks. In soil and weak rocks, UAM is especially necessary to prevent excessive deformations. Selection of UAM or NATM is based on the following factors: cost comparison of NATM and UAM, allowable deformations, quality of rock or soil, application time of NATM and UAM, availability of skilled workers, and qualification level of the workers. Therefore, selecting the excavation method in these kinds of grounds is vital in terms of achieving the project goals in time, managing the project costs effectively, and controlling the probable deformations on nearby structures. A critical issue in successful tunneling application is the ability to evaluate and predict the deformations, costs, and project time. In this paper, application times, costs, and deformation effects are compared between NATM and UAM in sensitive regions at the Uskudar-Umraniye-Cekmekoy metro project (UUCMP). Also, efficiency of the deformation control of UAM is demonstrated by using the 2D numerical analysis method. UUCMP is part of the Istanbul metro network. The tunnels have a cross section of 75.60 m² for NATM and 83.42 m² for UAM. Geology in this section is composed of weak sandstone. Diabase and andesite dykes are also rarely observed. This study shows that the construction cost of UAM are 1.7 times more expensive than NATM. Although application time of UAM is 2.5 times longer than NATM, it is 2.5 times more efficient in controlling the deformations. This efficiency in controlling the deformations is confirmed via two-dimensional numerical analyses.     

Some phenomenological aspects of carbonate geochemistry. The control effect of transition metals

The dualism in carbonate geochemistry — organic or inorganic production — leads to an erroneous definition of the carbonate system. A different formulation of the chemical mechanism is proposed where traces of transition metals together with organic matter in natural environments play a central role in carbonate production. This approach is verified in a series of experiments using natural and artificial sea water and as chelating agents citric, tartaric, malonic, and oxalic acids with five transition metals: Ni, Co, Fe, Mn and Zn. The final product of carbonate precipitation depends on the type of metal acting as a central atom. In the series Ni, Co, Fe, Mn, Zn the potential for calcium uptake increases from Ni to Zn, while magnesium uptake increases in the opposit direction from Zn to Ni. Dolomite can precipitate from Mg-rich natural waters by the catalytic effect of Fe(II)-chelates. If the waters containing Fe(II)-chelates are exhausted with respect to magnesium carbonate, they will attack dolomite to form calcite.

---

Zusammenfassung Die Gegensätzlichkeit der Geochemie der Karbonate — organische oder anorganische Produktion — führte zu einer widersprüchlichen Definition des Karbonatsystems. Es wird hier eine abweichende Formulierung der chemischen Mechanismen vorgeschlagen, wobei Spuren von Ubergangsmetallen zusammen mit organischen Substanzen in natürlicher Umgebung eine zentrale Rolle bei der Karbonatproduktion spielen. Dieser Ansatz läßt sich in Experimenten nachweisen, wobei in natürlichem und künstlichem Meereswasser chelatbildende Substanzen wie Zitronensäure, Weinsäure, Apfelsäure und Oxalsäure mit 5 Übergangsmetallen Ni, Co, Fe, Mn und Zn zusammengebracht werden. Das Endprodukt einer Karbonatfällung hängt von dem Metall ab, das als zentrales Atom in den Komplexen wirkt. In der Serie Ni, Co, Fe, Mn und Zn nimmt das Potential zur Kalziumaufnahme von Ni nach Zn zu, während die Magnesiumaufnahme in entgegengesetzter Richtung, nämlich von Zn nach Ni zunimmt. Dolomit kann man aus natürlichen Wässern unter Zuhilfenahme des katalytischen Effekts von Fe(II)-chelaten fällen, während man in eisenchelathaltigen Wässern mit einem Unterschuß an Magnesiumkarbonat den Dolomit in Kalzit umwandeln kann.

---

Résumé En géochimie des carbonates, la dualité — production organique ou inorganique — conduit à une définition erronée du système carbonate. Les auteurs proposent un modèle différent du mécanisme chimique, dans lequel des métaux de transition en traces, ainsi que des substances organiques de l'environnement naturel jouent un rôle prépondérant dans la genèse des carbonates. Cette approche est vérifiée par une série d'expériences dans lesquelles on ajoute à de l'eau de mer naturelle ou artificielle: d'une part 5 métaux de transition: Ni, Co, Fe, Mn, Zn; d'autre part des agents chélatants tels que: acide citrique, tartrique, malonique ou oxalique. Le produit final d'une précipitation carbonatée dépend du métal qui constitue l'atome central du complexe. Dans la série Ni, Co, Fe, Mn, Zn, le potentiel de fixation du Ca augmente du Ni au Zn, tandis que celui du Mg augmente dans l'autre sens, du Zn au Ni. Il est possible de précipiter de la dolomite dans des eaux naturelles, à l'aide de l'effet catalytique de chelates de Fe¹¹, tandis que si du carbonate de Mg est soustrait à des eaux contenant du chélate de F¹¹, on peut transformer la dolomite en calcite.

---

, — , — , . , . , , , .: , , 5 : Ni, , Fe, Mn Zn. , . Ni, , Fe, Mn Zn Ni Zn, — . , .

     

Carbon monoxide levels along roadway

This paper predicts and compares the carbon monoxide (CO) concentration levels along Sembulan Road for years 2004 and 2014 using CAL3QHC air dispersion model at two major locations, i.e., at Sembulan Roundabout and Sutera Harbour Intersection, Kota Kinabalu, Sabah, Malaysia. The CO concentration “hot-spots” were also identified at Sutera Harbour Intersection, and the highest maximum 1-hr average ground level concentrations of CO modeled for Kpg. Air Sembulan located in the northeast of idling road was 9.33 ppm for year 2004. This study showed that there would be no extreme changes in CO concentration trends for year 2014 although a substantial increase in the number of vehicles is assumed to affect the level of CO concentrations. It was also found that the CO levels would be well below the Malaysian Ambient Air Quality Guidelines of 30 ppm for 1-hour Time-Weighted Average (TWA). Comparisons between the modeled and observed outputs using quantitative data analysis technique and statistical methods indicated that the CAL3QHC predicted results correlated well with measured data. It was predicted that receptors located near to the major intersection, in the long-term would be potentially exposed to relatively higher CO levels.     

Iron Isotopic Fractionation and Origin of Chromitites in the Paleo-Moho Transition Zone of the Kop Ophiolite, NE Turkey

The Kop ophiolite in NE Turkey is a fragment of Neo-Tethyan forearc.It can be mainly divided into a paleo-Moho transition zone(MTZ)in the North and a harzburgitic mantle sequence in the South.Dunites are predominant in the MTZ of the Kop ophiolite,and they are locally interlayered with chromitites and enclose minor bodies of harzburgites near the petrological Moho boundary.Large Fe isotopic variations were observed for magnesiochromite(-0.14‰to 0.06‰)and olivine(-0.12‰to 0.14‰)from the MTZ chromitites,dunites and harzburgites.In individual dunite samples,magnesiochromite usually has lighter Fe isotopic compositions than olivine,which was probably caused by subsolidus Mg-Fe exchange between the two mineral phases.Both magnesiochromite and olivine display an increasing trend ofδ56Fe along a profile from chromitite todunite.This trend reflects continuous fractional crystallization in a magma chamber,which resulted in heavier Fe isotopes concentrated in the evolved magmas.In each cumulative cycle of chromitite and dunite,dunite was formed from relatively evolved melts after massive precipitation of magnesiochromite.Mixing of more primitive and evolved melts in the magma chamber was a potential mechanism for triggering the crystallization of magnesiochromite,generating chromitite layers in the cumulate pile.Before mixing happened,the primitive melts had reacted with mantle harzburgites during their ascendance;whereas the evolved melts may lie on the olivine-chromite cotectic near the liquidus field of pyroxene.Variable degrees of magma mixing and differentiation are expected to generate melts with differentδ56Fe values,accounting for the Fe isotopic variations of the Kop MTZ.     

A new approach for developing comprehensive agricultural drought index using satellite-derived biophysical parameters and factor analysis method

The accurate assessment of drought and its monitoring is highly depending on the selection of appropriate indices. Despite the availability of countless drought indices, due to variability in environmental properties, a single universally drought index has not been presented yet. In this study, a new approach for developing comprehensive agricultural drought index from satellite-derived biophysical parameters is presented. Therefore, the potential of satellite-derived biophysical parameters for improved understanding of the water status of pistachio (Pistachio vera L.) crop grown in a semiarid area is evaluated. Exploratory factor analysis with principal component extraction method is performed to select the most influential parameters from seven biophysical parameters including surface temperature (T _s), surface albedo (α), leaf area index (LAI), soil heat flux (G _o), soil-adjusted vegetation index (SAVI), normalized difference vegetation index (NDVI), and net radiation (R _n). T _s and G _o were found as the most effective parameters by this method. However, T _s, LAI, α, and SAVI that accounts for 99.6 % of the total variance of seven inputs were selected to model a new biophysical water stress index (BPWSI). The values of BPWSI were stretched independently and compared with the range of actual evapotranspiration estimated through well-known METRIC (mapping evapotranspiration at high resolution with internal calibration) energy balance model. The results showed that BPWSI can be efficiently used for the prediction of the pistachio water status (RMSE of 0.52, 0.31, and 0.48 mm/day on three image dates of April 28, July 17, and August 2, 2010). The study confirmed that crop water status is accounted by several satellite-based biophysical parameters rather than single parameter.     

Dependence of radon exhalation on grain size of sedimentary waste

Tailings resulted from sulphuric acid leaching process of uranium from sedimentary rocks contain high concentrations of ²²⁶Ra and its daughters, the most important of which is ²²²Rn. Movement of radon gas out of the tailings is strongly influenced by the physicochemical characteristics of these tailings especially their radium content and the grain size. So, the tailing samples were size fractionated into four sizes (>?250, 250–125, 125–74 and <?74 µm). The natural radioactivity was investigated using hyper-pure germanium detector and solid-state nuclear track detectors (CR-39) for bulk size and after size fractionation. The activity concentrations of different radionuclides in size-fractionated tailing samples have been shown to be strongly dependent on the size of the particles. In the range of >?250 and <?74 µm, the activity concentrations of ²³⁰Th, ²²⁶Ra, ²¹⁴Pb, ²¹⁴Bi, ²¹⁰Pb, ²³²Th and ⁴⁰K increased throughout with decreasing particle size, while that of ²³⁸U, ²³⁴U and ²³⁵U have an opposite effect. The results revealed an inverse relationship between the radon exhalation rate and size fractionation. Also, the results showed a good correlation between radium activity concentration and radon mass exhalation rate.     

Interaction of longitudinal surface settlements for twin tunnels in shallow and soft soils: the case of Istanbul Metro

Increasing demands on infrastructures increases the attention on shallow soft ground tunneling methods in urbanized areas. Especially, in metro tunnel excavations, it is important to control the surface settlements observed before and after excavation, which may cause damage to surface structures. To solve this problem, earth pressure balance machines (EPBMs) have widely been used throughout the world. This study focuses on surface settlement measurements, the interaction of twin tunnel surface settlement, and the relationship between shield parameters and surface settlement for parallel tunnels using EPBM shields in clay and sand soils. In this study, the tunnels were excavated using two EPBMs. The tunnels were 6.5 m in diameter, as twin tubes with a 14 m distance from center to center. The EPBM in the first tube followed about 100 m behind the other tube. Segmental lining with 1.4 m of length was employed as a final support. The results from this study showed that (1) the most important parameters for the maximum surface settlements are the face pressure and backfill; (2) in twin tunnel excavation with EPBM for longitudinal profile, the settlement rate reached its peak value when the shield came to the monitoring section and this peak value continued until the shield passed the monitoring section; (3) every shield affected the other tunnel’s longitudinal surface settlement profile by approximately 35–36.8 %; (4) S _A, S _B and S _C values were found to be 38.0, 35.8 and 26.2 %, respectively for an EPBM, and (5) ensuring good construction quality is a very effective way to control face stability and minimize surface settlement.