Geographic information system (GIS) and remote sensing for multi-temporal analysis of sand encroachment at Oglet Merteba (South Tunisia)

Sand encroachment in South Tunisia is one of the most serious environmental problems. Close to six decades, several irrational human activities are responsible for the increase in the magnitude of sand encroachment. They include overgrazing, denudation of vegetation cover and many other disturbances of the fragile arid ecosystem. Mapping this phenomenon is now essential for a better understanding of the general evolution of this process to setup and implement efficient protection techniques. The study done in the “Oglet Merteba” area was performed using the geographic information system (GIS) and remote sensing techniques particularly those referring to change detection. This kind of approach integrates direct and calculated environmental parameters in a geo-referenced data base, allowing the spatial and temporal analysis of the evolution of this phenomenon. The results show that despite the multiple efforts put together to control wind erosion, areas prone to wind erosion increased from 5 % in 1975 to 6.7% in 2006. The most important progression rate is noticed between 1987 and 2000.Key words: South Tunisia, sand encroachment, geographic information system (GIS), remote sensing, change detection, progression rate

Transfer and accumulation of lead, zinc, cadmium and copper in plants growing in abandoned mining-district area

The analysis of the Jebel Hallouf-Sidi Bouaouane mining-district soil has shown that the surface horizons are strongly contaminated by heavy metals, especially during floods or in lee-side areas. The contents of metallic-trace elements (MTE), in the soil and two cultivated plant species, have been determined by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). The results show that the concentration of metals in the soil are up to 39 g. kg-1, 6.3 g. kg-1, 56 mg. kg-1 and 131 mg. kg-1, for lead (Pb), zinc (Zn), cadmium (Cd) and copper (Cu), respectively. The chemical analysis of plants: broad beans [Vicia faba (L.)] and barley [Hordeum vulgare (L.)], sampled inside the mining district, show that the roots and the upper part (leaves and stem) are enriched for Pb (up to 508 and 220 mg.kg-1, respectively), Cd (up to 8 and 5 mg.kg-1, respectively), and Zn (up to 491 and 468 mg.kg-1, respectively) when compared with similar species collected far from the contaminated site (up to 9.6 and 0.8 mg.kg-1 for Pb, up to 0.04 and 0.04 mg.kg-1 for Cd, up to 44 and 15 mg.kg-1 for Zn, respectively). Statistically, the concentration of MTE in the soils and plants of the mining area is significantly different from the concentrations of the same elements in the soils and plants of the control ones (p < 0.01). This is expressed by a strong Enrichment Coefficient (EC), which is given by the ratio between the concentration of the metal in the contaminated plant and the concentration of the same element in the similar control one. The results (up to 405, 342 and 32, respectively), indicate that the contamination has reached the first link of the food chain. However, the calculation of the translocation factor (TF), deduced from the ratio between the concentration of the metal in the outer part of the plant and the concentration of the same element in the roots, shows that, the broad beans accumulates metals in the roots (TF < 1); whereas for barley, metals are fairly distributed between the roots and the outer part (TF ≈ 1). These results suggest that the cultivated areas inside the mining district constitute a serious source of contamination of the food chain. Therefore, actions have to be taken in order to remedy this problem.Key words: MTE, contamination, transfer, soil, plant

Fusion of Face and Speech Data for person identity authentication

Multi-modal person identity authentication is gaining more and more attention in the biometrics area. Combining different modalities increases the performance and robustness of identity authentication systems. The authentication problem is a binary classification problem. The fusion of different modalities can be therefore performed by binary classifiers. We propose to evaluate different binary classification schemes (SVM, MLP, C4.5, Fisher's linear discriminant, Bayesian classifier) on a large database (295 subjects) containing audio and video data. The identity authentication is based on two modalities: face and speech

Metal origin and Pb isotopes in water of the mine-draining Mejerda river system, north Tunisia

International audienceWater samples (< 0.45 µm) from the Mejerda hydrographic system were analysed for trace metals and Pb isotopes, together with Pb isotope measurements of galena from the mines of the system. Water was collected (i) within the mines, (ii) in tributaries lying as close as possible to the mines, (iii) along the tributaries, (iv) along the main Mejerda River, and (v) in dammed lakes. All metal concentrations measured in the waters are below the limits given for health purposes of surface water, though some of them are close. Metals such as Al, V, Ni, Cu, Pb, and U are slightly enriched in the uppermost part of the system but they do not exceed 20 ppb (µg l–1), with the exception of Al reaching 120 ppb. In the lower Mejerda sector, a few high Zn concentrations of up to 550 ppb are observed, and up to 80 ppb for Ba. Lead isotopic compositions of 41 water samples show large variations, yielding ratios at 17.736–18.884 for 206Pb/204Pb, 15.504–15.977 for 207Pb/204Pb, and 37.135–39.992 for 208Pb/204Pb. In contrast, Pb isotopic compositions of 11 galena samples from different mines define a surprisingly narrow field, being systematically more radiogenic in 206Pb than water. Compared to water and galena, Pb in Tunisian gasoline has a very different and much less radiogenic Pb isotopic composition at 16.351, 15.493, and 36.135, respectively. No significant contribution of such gasoline Pb can be detected either in the main Mejerda River or the numerous tributaries. The same observation is made for galena Pb, with the particularity that water lying closest to the isotopic compositions of galena was sampled in the lower part of the system where mines are absent. For the upper part of the system, minor contributions from the mines cannot be ruled out. The full set of Pb isotopic data substantiates the ultimate sources of Pb to have evolved with large variations in time-integrated U/Th/Pb ratios, including differences in mantle extraction ages. Simple mixing between two end-members can be ruled out for most of the water Pb data. It is therefore suggested that Pb and other metals of Mejerda water originate from local soils, from where they can be leached from alteration phases. In contrast to water showing a wide variation of ultimate source lithologies, the particularly narrow field of galena Pb isotopic compositions requires Pb extraction from a surprisingly homogenous and strongly U- and Th-depleted reservoir. This reservoir is most likely the Triassic evaporites, essentially gypsum, forming in a well mixed water volume devoid of significant detrital input

Évaluation de la vulnérabilité à la pollution potentielle par les pesticides, de la nappe côtière alluvionnaire de la plaine de Metline-Ras Jebel-Raf Raf, Nord-Est tunisien, selon la méthode DRASTIC appliquée par les systèmes d’information géographique

L’exploitation des ressources en eau de la nappe de Metline-Ras Jebel-Raf Raf est un impératif économique jugé prioritaire étant donné que cette région est une région agricole par excellence puisqu’une grande partie de la population s’active dans le domaine agricole. L’utilisation des pesticides dans le domaine de l’agriculture ne cesse de s’accentuer, de ce fait une étude de la vulnérabilité à la pollution de la nappe par les pesticides paraissait nécessaire. L’étude de la vulnérabilité à la pollution par les pesticides de la nappe de la plaine côtière de Metline-Ras Jebel-Raf Raf a été effectuée en appliquant la méthode DRASTIC pesticides, par les logiciels des systèmes d’information géographique (SIG) : ARC/Info et Idrisi. La carte de vulnérabilité obtenue, montre des zones à vulnérabilité élevée, moyenne, et faible. Les zones à vulnérabilité élevée occupent 33 % de la superficie totale de la plaine, celles à vulnérabilité moyenne occupent 53 %, et celles à vulnérabilité faible occupent 14 %. Ces résultats montrent que la nappe étudiée est une nappe assez vulnérable à la pollution par les pesticides, de plus, les zones à vulnérabilité élevée se concentrent dans des région agricoles, là où les pesticides sont fréquemment utilisés, ce qui augmente le risque de pollution