Évaluation de la vulnérabilité à la pollution potentielle de la nappe côtière alluvionnaire de Meltine-Ras Jebel-Raf Raf (Nord-Est tunisien) selon les méthodes paramétriques DRASTIC, SINTACS et SI

La nappe alluvionnaire de Metline-Ras Jebel-Raf Raf (gouvernorat de Bizerte, côte Nord Est de la Tunisie), qui occupe une superficie de 35 km2, représente une ressource économique jugée prioritaire du fait qu’elle est utilisée dans les domaines d’irrigation et de consommation domestique. L’aire de la nappe est occupée essentiellement par des zones agricoles caractérisées par une utilisation de plus en plus importante des engrais chimiques qui représentent, en plus des rejets des zones industrielles, un risque permanent pour la qualité des eaux souterraines. L’étude de la vulnérabilité à la pollution par les polluants inorganiques de cette nappe a été effectuée en appliquant les méthodes DRASTIC standard (Aller et al., 1987; Engel et al., 1996), SINTACS (Civita, 1994) et SI (Ribeiro, 2000), avec l’aide des logiciels des systèmes d’information géographique, ARC/Info et Idrisi. Une comparaison statistique des cartes de vulnérabilité obtenues a été effectuée. Cette comparaison a montré une certaine ressemblance entre les résultats obtenus en utilisant les méthodes SINTACS et SI. En revanche, la carte DRASTIC standard s’avère différente par rapport aux autres.The alluvial aquifer of Metline-Ras Jebel-Raf Raf (prefecture of Bizerta, northeast coast of Tunisia), which occupies a surface of 35 km2, is of great economic importance because it is used for irrigation and domestic consumption. The area of the aquifer is essentially occupied by agricultural zones characterised by an increasing use of chemical fertilizers. These chemical fertilizers, together with discharges from the industrial zones that have appeared during the last 25 years, threaten the quality of the ground waters. The vulnerability of the aquifer to pollution by generic pollutants has been studied by applying the following methods: the generic DRASTIC method, the SINTACS method and the SI method. For the application of these methods GIS techniques were used. A statistical comparison among the vulnerability maps generated by each method has been carried out. On the one hand, this comparison shows a certain similarity between the results obtained using the SI and SINTACS methods. On the other hand, the DRASTIC map classification shows different results

A GIS-Based DRASTIC Model for Assessing Phreatic Aquifere of Bekalta (Tunisian Sahel)

"La situación actual en el país en cuanto a las universidades acreditadas ante la Entidad Mexicana de Acreditación A.C. (ema, A.C.), es uno de los temas de mayor importancia para las instituciones educativas. En el país solo se cuenta con cuatro universidades acreditadas en laboratorios de ensayo en la industria de la construcción. Las universidades que ya cuentan con esta acreditación son: la Universidad Autónoma de Guadalajara A.C., la Universidad Autónoma de Nuevo León, la Universidad Autónoma del Estado de México, la Universidad de Guadalajara; estas instituciones educativas se diferencian de las demás por tener un prestigio a nivel nacional ante dicha entidad (ema, A.C.).

Oxygen consumption and nutrient fluxes in coastal marine sediments off the Mejerda River delta (Gulf of Tunis)

International audienceThe authors studied the benthic flux of oxygen, dissolved iron and manganese, and nutrients in-situ at three points in the Mejerda River Delta, at depths of 10 m, 20 m, and 40 m, in March and August 2012. Three sedimentary cores were simultaneously drilled, at the same locations, to determine the diffusive flux of Fe2+, Mn2+, NO3-, NH4+, and PO43- and to estimate the diagenetic mechanisms occurring below the sediment–water interface. Photosynthesis was not sufficiently high during the day and the oxygen consumption at the sediment-water interface was about 1.7 to 10 mmol/m²/day, essentially controlled by the degradation of organic matter and oxidation of reduced elements. Nitrate contents were relatively high in the sediment (above 140 μM for NO3-) and their production was not always in conformity with the general scheme of early diagenesis, moreover, the benthic flux between the water and sediment was not clearly established. The diffusive flux of NH4+ and PO43- was always directed to the water column, at averages of 1.27 μmol/m²/day for PO43- and 96.5 μmol/m²/day for NH4+, complying with those measured by the benthic chambers, but representing less than 30% of the benthic fluxes for NH4+ and less than 5% for PO43

Bioavailability and assessment of heavy metal pollution in sediment cores off the Mejerda River Delta (Gulf of Tunis): How useful is a multiproxy approach ?

International audienceThree core samples were taken from zones offshore from the Mejerda River Delta (Tunisia) and analyzed formajor and trace elements to assess their relationships with organic matter, monosulfides and carbonates, aswell as for pollution and bioavailability. Chemical speciation,ΣSEM/AVS, the enrichment factor (EF) and thegeo-accumulation index (I-geo) were used. Iron, cadmium, lead and zinc – the most frequently mined metalsin the Mejerda catchment – were found as contaminants in the offshore areas. Estimations of trace elementaccumulation using the EF and the I-geo index show that lead, and to a lesser extent zinc, are the most pollutingmetals off the Mejerda outlet. According to their bioavailability, these metals are also the most toxic. Only cadmiumis heavily present in delta sediment (EF N 100) though deeply sequestrated (100% bound to the residualfraction) and thus presents no toxicity

Chemical speciation of Fe, Mn, Pb, Zn, Cd, Cu, Co, Ni and Cr in the suspended particulate matter off the Mejerda River Delta (Gulf of Tunis, Tunisia)

International audienceFluxes of suspended particulate matter (SPM) and their associated metals were performed off the Mejerda River Delta during both the wet (March) and the dry (July) seasons in 2012, using sediment traps at study stations at depths of 10, 20 and 40 m. Fluxes nearest to the Mejerda outlet were more significant, especially during winter (36 g m−2 day−1), but dissipated further offshore, 24.5–6 g m−2 day−1 at the 20 m and 21.8–4.8 g m−2 day−1 at the 40 m stations. Many variations observed in seasonal and spatial metal fluxes are similar to those of SPM, in particular Pb and Zn, probably because they are associated with the mining activity characteristic of the Mejerda catchment. Chemical speciation reveals that most of the metals (20–100%) are bound to the residual fraction. The most toxic metals (Pb, Zn) are bound in part to the exchangeable fraction (20–50% for Pb and 5–15% for Zn) making them relatively bioavailable and therefore potentially toxic. While Cu and Cd fluxes are not always clearly established according to season, both metals are apparently sequestered deep in the sediment, bound especially to clays (40–80% for Cd and up to 100% for Cu)

Diagenetic processes and sediment-water exchanges of heavy metals in the Mejerda River Delta (Gulf of Tunis)

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Suspended particulate matter fluxes along with their associated metals, organic matter and carbonates in a coastal Mediterranean area affected by mining activities

International audienceA study of suspended particulate matter (SPM) fluxes along with their associated metals, organic matter and carbonates, was conducted off the Mejerda River outlet in May 2011 and in March and July 2012 at depths of 10, 20 and 40 m using sediment traps. SPM fluxes are more significant near the Mejerda outlet, especially in winter, but dissipate further offshore. Normalization reveals that the Mejerda is a major source of Pb, Zn, Cd, Cu, Ni, and Co, all of which are the result of human activities. In contrast, Fe, Mn and N are of authigenic origin. The enrichment factor shows that Pb, Zn and especially Cd are the most highly polluting metals off the Mejerda outlet. This confirms the trend observed on the shores of the Mejerda prodelta and is consistent with the type of mining activities conducted in the Mejerda catchment

Metal transfer budgets in a Mediterranean marine environment subjected to natural and anthropogenic inputs: case of the Mejerda River Delta (Gulf of Tunis, northern Tunisia)

International audienceDeltaic sediments are important for biogeochemical metal cycling since they are hotspots for metal inputs. In addition, they are potential sites for diagenetic processes leading to either the burial of inorganic contaminants or their release. Diffusive fluxes of certain metals (Fe, Mn, Pb, Zn, Cu and Cd) in the sediments of the Mejerda River Delta (MRD) (Gulf of Tunis, Tunisia) were quantified by modeling the available concentration profiles in the pore water. The metals’ burial and sedimentation fluxes were also calculated using both the asymptotic concentrations of available metal profiles and sediment trap results. These fluxes were assembled with the exchange fluxes at the sedimentwater interface in order to develop complete metal transfer budgets. The results showed that budgets of Cu and Zn are almost neutral. The sediment appears tobe a good trap for iron since its average burial flux at the three studied stations is about 332.6 g m−2 year−1. Organic matter degradation, carbonate dissolution, and oxyhydroxide reduction are the main mechanisms which accelerate the release of metals associated with the suspended particle matter once they reach the pore water in the seabed

Nutrient exchange and oxygen demand at the sediment–water interface during dry and wet seasons off the Medjerda River Delta (Tunis Gulf, Tunisia)

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