Showing papers by "Lotfi Aleya published in 2012"

Water masses exchanged through the Channel of Sicily : evidence for the presence of new water masses on the Tunisian side of the Channel

Abstract: Studies of water masses present in the Channel of Sicily are relevant to understanding not only the overall Mediterranean circulation but also the Tunisian coastal shelf circulation. This study attempts to clarify the dynamics of water masses exchanged through the channel and its variability using data collected during six hydrographic cruises in the western half of the Cap Bon – Mazara del Vallo section during 2003. Hydrographic measurements clearly show the signature of the Atlantic Tunisian Current along the Tunisian coast characterized by important mesoscale variability. Computation of a normalized temperature and salinity standard deviation makes it possible to distinguish areas of high temporal variability located in the transitional layer between the Atlantic Water and the Levantine Intermediate Water. This transitional layer is created by the presence of both Western Intermediate Water and Ionian Water. In addition to highlighting the relevance of the mesoscale activity, a comparison between direct current measurements and adjusted geostrophic currents produced a more confident estimate of the surface and deep transports through the western part of the channel. Our conclusions on seasonal and mesoscale variability are confirmed by a high resolution numerical simulation.

Factors determining the dynamics of toxic blooms of Alexandrium minutum during a 10-year study along the shallow southwestern Mediterranean coasts

Abstract: Many blooms of the toxic dinoflagellate Alexandrium minutum have been recorded since 1990 in the Gulf of Gabes (southwestern Mediterranean Sea). To understand the determining factors of bloom formation, we studied the distribution of A. minutum in relation to environmental factors in samples taken at shallow sandy (<1 m) beach stations and a lagoon between 1997 and 2006. This was accompanied by laboratory experiments to identify A. minutum. The species forms harmful algal blooms (HABs) in stations subjected to anthropogenic eutrophication and in confined lagoons, living under conditions of varying salinity which gives it a unique opportunity to broaden its physiological tolerance and increase its colonisation potential. Increases in phosphorus appear to be more important than nitrogen or temperature in the control of A. minutum. The stations sampled all along the coast present specific hydrographic properties (shallowness, turbulence) suggesting that factors other than temperature and nutrients influence Alexandrium distribution, the exception being Boughrara Lagoon where the species developed in accordance with published data. Our findings and their interpretations indicate that the mechanism of the sudden A. minutum blooms along the nearshore of the Gulf of Gabes was complex and differed from that of true coastal ecosystems.

The Bioaccumulation Performance of Reeds and Cattails in a Constructed Treatment Wetland for Removal of Heavy Metals in Landfill Leachate Treatment (Etueffont, France)

Abstract: The aim of this study was to evaluate and compare the capacities of cattail (Typha latifolia L.) and reed (Phragmites australis L.) for heavy metal storage in the phytomass. Samples were studied in the fourth of the four interconnected natural lagooning basins of a constructed treatment wetland, developed as an integrated pilot system for the treatment of leachates in a domestic landfill site at Etueffont (Territoire de Belfort, France). The efficiency of the lagooning system was evaluated through physical and chemical parameter measurements over a period of three seasons. Anion/cation and heavy metal concentrations were sampled and analyzed in water flowing into and out of the lagooning basin. Simultaneously, reed and cattail biomass samples (roots/rhizomes, shoots) were collected at both inflow and outflow, and the biomass characteristics were determined. The average above-ground biomass of T. latifolia and P. australis varied, respectively, from 0.41 to 1.81 kg DW m−2 in the fall, 0.31 to 1.34 kg DW m−2 in winter, and 0.38 to 1.68 kg DW m−2 in spring, with significant seasonal variations. The greatest mean concentrations of heavy metals were found in the below-ground plant parts of the two species during the spring season. The average standing stock of heavy metals was higher in the below-ground than in the above-ground phytomass, whatever the season. With the exception of nickel, heavy metal concentrations in the inflow were correlated to the plant content of both species.

Effects of irrigation on soil physico‐chemistry: a case study of the triffa plain (morocco)

Abstract: The Triffa Plain is the most productive irrigated agricultural zone in north-eastern Morocco. Irrigated agriculture in (semi-)arid regions may exert different pressures on soil resources, but in northern Africa these are often poorly documented. A field survey conducted in 2005 to assess soil quality in the region focuses on the soil’s physico-chemical parameters and analyses their spatial dependency on a regional scale. As most of the soils are light-textured, with poor organic matter content and slightly basic pH, they are vulnerable to soil nutrient depletion. Multivariate analysis shows that organic matter content is well correlated to the soil’s P and K content, while the total and active lime correlate well with the alkalinity and pH, which in turn correlate negatively with nitrate content and soil electrical conductivity. The spatial structure of the soil parameters can be modelled using Gaussian semi-variograms, suggesting consistent spatial structuring of the parameters. The low nutritional status of the soils is compensated by important fertiliser supplements, leading to nutrient imbalances and further environmental deterioration.

Seasonal dynamics of plankton communities coupled with environmental factors in a semi arid area: Sidi Saâd reservoir (Center of Tunisia)

Abstract: In this study, we studied the influence of the physical-chemical and biological factors (bacterioplankton and phytoplankton abundances) for zooplankton dynamics in a Sidi Saâd reservoir in Centre of Tunisia. The samplings were carried out in spring, summer, autumn and winter (2005 to 2006) in the deepest station (surface, 5, 10 and 15 m). In this reservoir, the highest density of zooplankton abundance was recorded in summer (92.2 ind L -1 ; 0.43 × 10 3 μg L -1 ) and autumn (86.9 ind L -1 ; 0.23 × 10 3 μg L -1 ) at a depth of 10 m. The copepods (56% of total zooplankton abundance) and cladocera (42% of total zooplankton abundance) were the most abundant groups. The physico-chemical factors, especially the water temperature (r = 0.53, p = 0.027, n = 16) and dissolved oxygen (r = -0.59, p = 0.03, n = 16), influence directly the zooplankton community. It was suggested that in Sidi Saâd reservoir, both the top-down and bottom-up regulations account for the regulation of zooplankton. The phytoplankton was the factor responsible for the structure and seasonal dynamics of the zooplankton community, which are well related to changes in algae diversity and abundance, noting that cyanobacteria have major impacts. The “top-down” effect of planktivorous fish on the zooplankton is a significant factor affecting the plankton community’s dynamics in this reservoir. Key words : Sidi Saâd reservoir, water temperature, bacterioplankton, phytoplankton, zooplankton, top-down and bottom-up regulations.

The Kelvin probe technique for assessing efficiency of stearic acid removal from gold surfaces using atmospheric-pressure plasma

Abstract: Plasma removal is an alternative cleaning method used to avoid effluents and volatile organic compounds resulting from the use of detergents and solvents. An innovative method to estimate residual stearic acid (C18H36O2) after the atmospheric-pressure plasma cleaning process of a gold surface is presented. This method, based on surface potential measurement by a Kelvin probe, enables monitoring of treated samples. The Quartz Crystal Microbalance (QCM) technique is used as a reference technique to specify with precision both initial and residual stearic acid masses. Stearic acid remaining on gold surfaces is proportional to the time of exposure to plasma and initial contamination. Moreover, the results reveal that surface potential evolution post-plasma exposure is a function of residual stearic acid, whatever the degree of initial contamination.