Bilans hydrologiques de la lagune de Bizerte (nord-est de la Tunisie)

Les flux liquides et solides (écoulés à partir des principaux tributaires de la lagune de Bizerte), corrélés positivement, sont influencés par les conditions environnementales et par les aménagements hydrauliques en amont. C’est dans ce contexte que nous présentons cette étude qui consiste à présenter un bilan d’évolution mensuel des flux liquides, solides et en composants azotés et phosphatés dissous dans les eaux des principaux affluents de la lagune de Bizerte au cours de l’année hydrologique (octobre 2004 - septembre 2005). L’utilisation fréquente et intensive par les agriculteurs d’engrais chimiques azotés et phosphatés, d’une part, et le déversement d’eaux usées domestiques et industrielles dans les principaux tributaires de la lagune, d’autre part, participent activement à la pollution des eaux de la lagune. Cette dernière est liée à la garaet Ichkeul par l’intermédiaire de l’oued Tinja. En hiver, les eaux circulent de la garaet Ichkeul vers la lagune de Bizerte, avec des flux liquides et solides respectivement estimés à 418 (± 28) Mm3 et (28 ± 5) x 103 (t). Ainsi, l’oued Tinja représente la principale source d’apports en éléments nutritifs à la lagune de Bizerte (74 (± 15), 954 (± 76), 92 (± 11) et 70 (± 11) (t) respectivement de nitrite, nitrate, ammonium et phosphate), alors que durant la période sèche, cet oued permet aux eaux marines (8  (± 2) Mm3) de pénétrer dans la garaet Ichkeul à travers la lagune de Bizerte.The water and solid fluxes (drained from the principal tributaries of the Bizerte Lagoon) were positively correlated and were influenced by the environmental conditions and by the upstream hydraulic installations. It is within this context that we present this study on the monthly variation of water, solid and dissolved nutrient fluxes associated with the principal tributaries of the Bizerte Lagoon during the October 2004 – September 2005 hydrologic year. The frequent and intensive use of chemical nitrogenous and phosphate fertilizer by farmers, on one hand, and the discharge of domestic sewage and industrial wastewater to the principal tributaries of this lagoon, on the other hand, actively contribute to the pollution of the lagoon waters. The Bizerte Lagoon is linked to the garaet Ichkeul by the Tinja wadi. In winter, waters flow from garaet Ichkeul towards the Bizerte Lagoon, and the water and solid fluxes are estimated to be 418 ± 29 Mm3 and (28 ± 5) x 103 (t), respectively. Thus, the Tinja wadi represents the main nutrient supply to the Bizerte Lagoon: 75 ± 15; 954 ± 76; 92 ± 11; and 70 ± 11 (t) for nitrite, nitrate, ammonium and phosphate, respectively. In contrast, during the dry period, this wadi allows marine waters (84 ± 2.5 Mm3) to penetrate in the garaet Ichkeul through the Bizerte Lagoon

Evaluación del riesgo de contaminación por metales pesados en sedimentos superficiales de la Laguna Sur de Túnez mediante un procedimiento de extracción secuencial

In this study, the total concentrations and chemical forms of heavy metals (Fe, Zn, Pb, Cu, Cr, Cd, and Ni) in surface sediments of the South Lagoon of Tunis located in northeast Tunisia were investigated. Multiple geochemical indices were applied to assess the potential environmental risks. The South Lagoon is a valuable regional resource for fisheries, tourism and aquaculture. Total metal concentrations exhibited significant spatial variation attributed to the principal water circulation direction (east to west). The chemical speciation of Fe, Cr and Ni shows that they were mostly related to the residual fraction (Fe 34.8%, Cr 37.4% and Ni 37.9%), while Pb, Zn, Cu, and Cd were mostly related to the non-residual fraction (labile fraction Pb 89.4%, Zn 26.1%, Cu 71.8% and Cd 84.3%). Pb, Zn, Cu and Cr are of high potential bioavailability. The highest pollution was found on the west side of the lagoon according to the calculated global contamination factors. Besides, individual contamination factors, Pb followed by Zn and Cu, posed the highest risk of contamination. This study shows that, even after dredging, the persistence of low concentrations of some contaminants may cause environmental problems in certain physico-chemical conditions.En este estudio, se investigaron las concentraciones totales y las formas químicas de los metales pesados (Fe, Zn, Pb, Cu, Cr, Cd y Ni) en los sedimentos superficiales de la Laguna Sur de Túnez, ubicada en el noreste de Túnez. Se aplicaron múltiples índices geoquímicos para evaluar los riesgos ambientales potenciales. La Laguna Sur es un valioso recurso regional para la pesca, el turismo y la acuicultura. Las concentraciones totales de metales exhibieron una variación espacial significativa, atribuida a la dirección principal de circulación del agua (Este a Oeste). La especiación química de Fe, Cr y Ni muestra que están esencialmente relacionados con la fracción residual (Fe: 34,8%, Cr: 37,4% y Ni: 37,9%), mientras que Pb, Zn, Cu y Cd se encontraron mayoritariamente en la fracción no residual. -fracción residual (fracción lábil Pb: 89,4%, Zn: 26,1%, Cu: 71,8% y Cd: 84,3%). Estos elementos (Pb, Zn, Cu y Cr) tienen un alto potencial de biodisponibilidad. La mayor contaminación se encontró en el lado oeste de la laguna, según los factores de contaminación global calculados. Además, los factores de contaminación individuales, Pb seguido de Zn y Cu, presentaron el mayor riesgo de contaminación. Este estudio muestra que, incluso después de la operación de dragado, la persistencia de bajas concentraciones de algunos contaminantes puede causar problemas ambientales en determinadas condiciones físico-químicas

Évolution biosédimentaire du dépôt quaternaire de la lagune de l'Ariana, Tunisie (une zone humide du Maghreb Nord)

La sebkha de l’Ariana est une lagune fermée qui fait partie des zones humides du Maghreb. Elle a une superficie de 30 à 35 km2et est située sur la bordure nord-ouest du golfe de Tunis, au sud de l’oued Medjerda. Vers 190 000 ans BP, elle a été occupée par la mer Méditerranée. Actuellement, elle en est séparée par un cordon littoral. Ce dernier s’est mis en place lors du comblement d’un golfe peu profond sous l’impulsion d’importantes quantités d’alluvions déposées par le fleuve de la Medjerda sur sa plaine deltaïque dont elle fait partie. Cette étude de l’évolution et de la dynamique de la sebkha de l’Ariana, ainsi que des changements environnementaux récents qui gouvernent la sédimentation, est basée sur une approche sédimentologique, paléontologique et isotopique. Six carottes longues de 20 m à 50 m, prélevées dans les dépôts alluviaux de la sebkha, ont fait l’objet d’une étude détaillée qui a permis de suivre la répartition spatio-temporelle du stock sédimentaire – formé essentiellement de silts argileux vaseux à la base, surmontés de sables – et de mettre en évidence des associations faunistiques particulières traduisant des modifications environnementales : environnement marin (Pléistocène moyen), lagune ouverte (Holocène) et sebkha (Actuel). Cette évolution d’un milieu marin franc vers un environnement typiquement évaporitique (sebkha) pratiquement azoïque, est probablement en rapport avec le changement climatique quaternaire.The Sebkha of Ariana, covering 30 to 35 km2is a closed lagoon, located south of the Medjerda and considered to be part of the Maghreb humid zones. It belongs to the Mediterranean coast and is positioned on the N-W margin of the Gulf of Tunis. The Sebkha is situated on Quaternary lowland resulting from the filling-up of a shallow gulf by alluvial deposits sourced from the Medjerda delta. Historically at - 190 ka, the lagoon was related to the sea but at the present time, being bunged up from the seaside by a beach barrier, is shaped to the sediments of the Madjerda low valley. The study of the evolution and the dynamics of the Ariana Sebkha as well as the recent environmental changes which have governed sedimentation are based on a sedimentological, palaeontological and isotopic approach. For that, six cores (from 20 to 50 m) were realised from four sites of the Sebkha respectively. Furthermore, correlations between the different cores throughout the lagoon have allowed the reconstruction of the spatial‑temporal distribution of sediments. The granulometric analyses revealed an alluvial sedimentation mainly composed of argillaceous silts at the base, becoming sandy towards the top. On the other hand, the benthonic fauna determinations of the six cores show a distinct evolution from an open-marine environment to a typically lagoonal environment where fauna are rare to absent. Moreover, the palaeontological study yielded particular benthonic foraminifera associations suggesting important palaeonvironmental changes which in turn are related to Quaternary climatic changes

Géochimie et thermodynamique des évaporites continentales. Etude du lac Natron en Tanzanie et du Chott El Jerid en Tunisie

Gueddari Moncef. Géochimie et thermodynamique des évaporites continentales. Etude du lac Natron en Tanzanie et du Chott El Jerid en Tunisie. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1984. 164 p. (Sciences Géologiques. Mémoire, 76

Impact Assessment of Phosphogypsum Leachate on Groundwater of Sfax-Agareb (Southeast of Tunisia): Using Geochemical and Isotopic Investigation

The production of phosphoric acid by the Tunisian Chemical Group, in Sfax, Tunisia, led to the degradation of the groundwater quality of the Sfax-Agareb aquifer mainly by the phosphogypsum leachates infiltration. Spatiotemporal monitoring of the quality of groundwater was carried out by performing bimonthly sampling between October 2013 and October 2014. Samples culled in the current study were subject to physicochemical parameters measurements and analysis of the major elements, orthophosphates, fluorine, trace metals, and stable isotopes (18O, 2H). The obtained results show that the phosphogypsum leachates infiltration has a major effect on the downstream part of the aquifer, where the highest values of conductivity, SO42-, Ortho-P, and F-, and the lowest pH were recorded. In addition, these results indicated that phosphogypsum leachates contained much higher amount of Cr, Cd, Zn, Cu, Fe, and Al compared to the groundwater. Spatiotemporal variation of the conductivity and concentrations of major elements is linked to the phosphogypsum leachates infiltration as well as to a wide range of factors such as the natural conditions of feeding and the water residence time. Contents of O18 and 2H showed that the water of the Sfax-Agareb aquifer undergoes a large scale evaporation process originated from recent rainfall

Removal of phosphorus from secondary effluents using infiltration–percolation process

Abstract Intermittent infiltration–percolation is an extensively used treatment process which is capable of oxidizing and decontaminating wastewater. The main purpose of this study was to evaluate the efficiency of this treatment process regarding particularly the removal of phosphorus from urban wastewater effluents. The phosphorus removal mechanisms that may occur in sand filters were investigated. Results confirmed that infiltration–percolation is performed as an advanced treatment technique for suspended solids, organic matter and nitrogen. However, it is less efficient concerning the reduction of orthophosphate. The experimental study has shown the influence of the filter depth, the hydraulic load and its fractionation on phosphorus removal. Analyses of the percolating water sampled at 50, 100 and 150 cm bed depths showed that efficiency of phosphorus removal increased significantly with the depth of the filtering medium. Results indicated that providing more and smaller sequences improves the efficiency of orthophosphate retention. During the experimentation period, phosphorus removal rates do not seem to be affected by the variation of temperature. The scatter plots and the Pearson’s correlation coefficient indicate that there is no apparent linear pattern between orthophosphate retention rates and temperature. This finding confirms that phosphorus removal is not attributed to microbial uptake but it is mainly governed by physical–chemical mechanisms such as adsorption and precipitation

Géochimie de la silice dans les milieux évaporitiques sulfato-chlorurés. Etude des saumures du Chott El Jerid en Tunisie

Waters and brines of the Chott El Jerid in Tunisia are of sulfate, chloride, sodium and magnesium type. The silica molality in solution decreases as a function of the brine concentration. A new calculation method of ion and water activities (Pitzer's model) and silica activity in brines (Marshall's equations) allows the discussion of the precipitation conditions of silica and silicates in evaporitic environments.Les eaux et les saumures du Chott El Jerid en Tunisie sont sulfatées, chlorurées, sodiques et magnésiennes. La teneur en silice des solutions diminue au fur et à mesure que la concentration croît. Une nouvelle méthode de calcul des activités des ions, de l'eau (modèle de pitzer) et de la silice (modèle de Marshall), permet de discuter des conditions de précipitation de silice amorphe et de silicates magnésiens dans les milieux évaporitiques.Gueddari Moncef, Fritz Bertrand, Tardy Yves. Géochimie de la silice dans les milieux évaporitiques sulfato-chlorurés. Etude des saumures du Chott El Jerid en Tunisie. In: Sciences Géologiques. Bulletin, tome 35, n°1-2, 1982. Géochimie de la silice. pp. 41-54

Géochimie de la silice dans les milieux évaporitiques sulfato-chlorurés. Etude des saumures du Chott El Jerid en Tunisie

Waters and brines of the Chott El Jerid in Tunisia are of sulfate, chloride, sodium and magnesium type. The silica molality in solution decreases as a function of the brine concentration. A new calculation method of ion and water activities (Pitzer's model) and silica activity in brines (Marshall's equations) allows the discussion of the precipitation conditions of silica and silicates in evaporitic environments.Les eaux et les saumures du Chott El Jerid en Tunisie sont sulfatées, chlorurées, sodiques et magnésiennes. La teneur en silice des solutions diminue au fur et à mesure que la concentration croît. Une nouvelle méthode de calcul des activités des ions, de l'eau (modèle de pitzer) et de la silice (modèle de Marshall), permet de discuter des conditions de précipitation de silice amorphe et de silicates magnésiens dans les milieux évaporitiques.Gueddari Moncef, Fritz Bertrand, Tardy Yves. Géochimie de la silice dans les milieux évaporitiques sulfato-chlorurés. Etude des saumures du Chott El Jerid en Tunisie. In: Sciences Géologiques. Bulletin, tome 35, n°1-2, 1982. Géochimie de la silice. pp. 41-54

Spatial and Temporal Variations of Water Quality of Mateur Aquifer (Northeastern Tunisia): Suitability for Irrigation and Drinking Purposes

The present study aims to assess the spatial and temporal variations of the hydrochemical characteristics of Mateur aquifer groundwaters, a crucial water resource in the northeast of Tunisia. The aquifer was subject to water quality deterioration due to salinization and nitrate contamination, and a new assessment of water quality was needed. For this purpose, 40 groundwater samples were collected during wet and dry seasons and analyzed for salinity, pH, T, O2, major cations and anions, and nutrient elements using standard methods and Water Quality Index (WQI). The results showed that most of the groundwater parameters were not within the permissible limits set by the World Health Organization in both seasons. The geochemical data were interpreted using WQI for drinking water. The spatial distribution maps of Water Quality Index showed that the highest quality was found, during both seasons, in the northwest and the southeast part of the aquifer, corresponding to the recharge zone, whereas the poor and very poor water quality was found in the outflow part of the aquifer. According to sodium adsorption ratio (SAR) and Na% values, most of the groundwater samples were not suitable for irrigation purposes and characterizing the eastern part of the aquifer and the outflow part of the aquifer, around the Ichkeul marshes

Assessment of the Trophic Status of the South Lagoon of Tunis (Tunisia, Mediterranean Sea): Geochemical and Statistical Approaches

The trophic status assessment of the South Lagoon of Tunis, a shallow Mediterranean coastal area after its restoration, is addressed herein with respect to its various environmental settings which are taken as indicators of water quality. The lagoon had, in the past, witnessed severe environmental quality issues. To resolve these problems, a large restoration project of the lagoon was undertaken which consisted of dredging the bottom sediments removing areas of water stagnation and improving water circulation. After this restoration work, the lagoon morphology has radically changed. In this paper, we attempt to evaluate the lagoon water’s trophic state to analyze the eutrophication risk after almost 16 years. In order to achieve these purposes, two water quality monitoring campaigns were conducted (July 2013 and February 2014). Natural and anthropogenic factors controlling the nutrient content of the lagoon water have been assessed through both geochemical methods and multivariate statistical tools. The results show that the nutrients are from external sources due to the discharge of municipal and industrial wastewater from the surrounding city of the catchment in the lagoon’s south side. According to the TRIX index, the lagoon remains eutrophic presenting a “poor” water quality, notwithstanding the engineering project due to the high level of nutrients