Rivers In Tunisia Research Articles

Determination of organochlorine pesticides in the surface water from Medjerda river, Tunisia

ABSTRACT In recent years there have been growing environmental concern, especially regarding the utilisation and discharge of toxic substances. Many organic pollutants are detected in aquatic ecosystems such as pesticides. Because they are large-scale production and usage, toxicity, bioaccumulation, and persistence in the environment, they cause harmful effects to organisms and human health. The Medjerda River is one among the main rivers in Tunisia and a number of other studies addressed the importance of this river regarding ecology, geochemistry, and sociology. The organochlorine pesticides (OCPs) were investigated in surface water samples from eight sampling sites in the Medjerda River. The extraction of water samples was performed by liquid-liquid extraction with hexane. Gas chromatography coupled to the mass spectrum (GC-MS) was used to perform qualitative and quantitative determinations. The levels of OCPs in water varied between 4.41 ng g−1 and 29.04 ng g−1. The Hexachlorobenzene (HCB) and ∑DDT are the most dominant compounds in different sampling sites. Distribution of HCB, ∑DDT, and other OCPs are different indicating different sources of contamination. The concentrations of OCPs in the water pose no threat to human and aquatic living species.

Ecotoxicity profile of heavily contaminated surface water of two rivers in Tunisia

Persistent organic and inorganic contaminants generated by industrial effluent wastes poses a threat to the maintenance of aquatic ecosystems and public health. The Khniss and Hamdoun rivers, located in the central-east of Tunisia, receive regularly domestic and textile wastewater load. The present study aimed to survey the water quality of these rivers using physicochemical, analytical and toxicological approaches. In the physicochemical analysis, the recorded levels of COD and TSS in both samples exceed the Tunisian standards. Using the analytical approach, several metals and some textile dyes were detected. Indeed, 17 metals were detected in both samples in varying concentrations, which do not exceed the Tunisian standards. The sources of metals pollution can be of natural and anthropogenic origin. Three textile disperse dyes were detected with high levels compared to other studies: the disperse orange 37 was detected in the Khniss river with a concentration of 6.438 μg/L and the disperse red 1 and the disperse yellow 3 were detected in the Hamdoun river with concentrations of 3.873 μg/L and 1895 μg/L, respectively. Textile activities were the major sources of disperse dyes. For both samples, acute and chronic ecotoxicity was observed in all the studied organisms, however, no genotoxic activity was detected. The presence of metals and textile disperse dyes could be associated with the ecotoxicological effects observed in the river waters, in particular due to the industrial activity, a fact that could deteriorate the ecosystem and therefore threaten the human health of the population living in the study areas. Combining chemical and biological approaches, allowed the detection of water ecotoxicity in testing organisms and the identification of possible contributors to the toxicity observed in these multi-stressed water reservoirs.

In situ genotoxicity assessment in freshwater zooplankton and sediments from different dams, ponds, and temporary rivers in Tunisia.

Tunisia water resources are limited. The country currently has 29 large dams, more than 1000 hill lakes, and 220 small dams which are essential for economic and social development given their contribution to irrigation, drinking water consumption, flooding protection, production of electrical energy, groundwater recharge, and industrial uses. Given the scarcity of these resources, it is crucial to be able to ensure the quality of freshwater environments, particularly those intended for human consumption. In this study, we meant to assess the health status of various freshwater ecosystems in different regions of Tunisia (north and center west) in order to detect genotoxic components in sediments and their potential effect on zooplankton (cladocerans). Sediment and cladoceran species were collected from dams, ponds, and temporary rivers in Tunisia. For each collection site, micronucleus (MN) assay was performed, in triplicates, using a pool of ten specimens of the same cladoceran species. MN occurrence in cladocerans varied from one site to another and MN frequencies varied between 0.67 and 22‰, suggesting the presence of genotoxic substances in certain sites. Sediment genotoxicity and mutagenicity were assessed using the SOS Chromotest and the Ames test. Sediment results showed that genotoxicity varies from one site to another displaying a quantitative and a qualitative variation of pollutant among the sites. These results suggest an urgent need for continuous monitoring of freshwater environments in Tunisia, particularly those intended for drinking water.

Impact of dams and climate on the evolution of the sediment loads to the sea by the Mejerda River (Golf of Tunis) using a paleo-hydrological approach

Abstract: The Mejerda River is the one of the major rivers in Tunisia and several studies dealt with the importance of this river in terms of ecology, geochemistry and sociology. However, the sedimentary contributions to the coastal zone from the Mejerda River were poorly observed, and we did not find any continuous monitoring. The main objective of this work is to assess the impact of reduction on sediment transport from the upper basins to the coastal area, after the construction of large dams which may have strong and long-lasting effects on coastal geomorphology and ecosystems. In this paper, a paleo-hydrological approach was applied through the study of sediment cores sampled in the low valley meander on alluvial terrace. We attempt to emphasize, through this approach, the reduction in sediment loads to the sea (Gulf of Tunis) due to the construction of dams on the Mejerda River and to changes in climate conditions. Three cores (C1, C3, C5) were sampled in the lower part of the Mejerda near the hydrometric station of Jdaida with different depths (0.9 m, 1.2 m and 3.0 m) and in different dates (2014–2015). Visible successions of sedimentary layers corresponding to the deposits of successive flood events were identified and the history of the sedimentary contributions to the Mejerda was reconstructed. The thickest layers of sedimentary deposits were related to the exceptional events. They are mainly concentrated on the lower part of the core and are predominantly composed of sands. Since the construction of the Sidi Salem dam in 1981, all of the cores C1, C3 and specially C5 presented mostly a succession of small layers of fine material (silt or clay) without any sand deposits in the downstream River bed. In C5, 18 individual slackwater flood units were identified. A strong decrease in the accumulation rate of sediment was observed based on the length of the flood units and the number of years between flood events. A lower sedimentation rate is observed between 1982 and 2015 of about 2.3 cm/year, while it was much more important between 1963 and 1981 of about 4.75 cm/year, and around 10 cm/year between 1950 and 1962. The statistical study of precipitation indicated three climatic successive periods between 1951 and 2009 characterized as wet, dry and intermediate. Thus, the sediment rate was higher before 1974 reaching about 8.47 cm/year for the wet condition, of about 4 cm/year for the dry period between 1974 and 1989, and about 1.6 cm/year in the intermediate period afterward to 2009 that also witnessed the construction of the major dams.

Bioavailability of Pb, Zn, Cu, Cd, Ni and Cr in the sediments of the Tessa River: A mining area in the North-West Tunisia

Tessa River is seen as one of the important rivers in Tunisia. Its catchment is known for its agricultural and mining activities, especially the Bougrine and Fedj Lahdhoum mines. Eighteen (18) surface sediments and five (5) water samples were collected from the Tessa River, near these two mining sites. Sediments are essentially sandy (>80%), the most important mineral is quartz (20–73%), then calcite (41%) and dolomites (4%). Heavy metal contents are relatively high near the mining sites, 356 μg g−1 for Pb, 3000 μg g−1 for Zn, and 5 μg g−1 for Cd. These values are lower downstream due to watercourse dilution effects. Other heavy metals: Cu, Ni and Cr, are low, and values are relatively constant in all the studied samples, even near the mining sites. The metals originate from natural sources and not from mining activities. This trend is confirmed by the enrichment factor (EF) where EFNi, EFCu and EFCr are lower or equal to 1, unlike EFPb, EFZn or EFCd where values are much higher (>20). Chemical speciation of these metals does not show any spatial variation. Except for cadmium which is bound to the residual fraction and in the carbonates; all other heavy metals are bound to the five sediment chemical fractions: the residual fraction (>52%), followed by the oxyhydroxides fraction (21%) and carbonates (16%), and finally bound to the organic matter and to the exchangeable fraction (<10%). The bioavailable fraction of the studied heavy metals exceeds 45%, which present risk of toxicity.

Ecological and genetic differentiation of Barbus callensis populations in Tunisia

Enzyme electrophoresis on horizontal starch gel was carried out on 356 barbel individuals. The sampling comprised 278 individuals of the species Barbus callensis from 10 rivers in Tunisia. The other individuals belonged to reference species (outgroups) from France and Morocco. An ecological study was also carried out on Tunisian rivers. The results show a clear differentiation of the two samples from northwestern Tunisia, which was only partly correlated with ecological characteristics of the rivers they inhabit. There is no genetic cline, but rather a discontinuity between populations in the northwestern‐most watershed and all the other Tunisian populations. This differentiation probably has a paleohistoric origin not only related to adaptation to ecological conditions but also to difficulties in colonizing the watersheds. The results do not indicate clearly a colonization direction for the genus Barbus in North Africa. Analysis of the Algerian populations would appear to be indispensable. Lastly, in contrast with the usual taxonomy, Morocco and Tunisia are populated by two closely related species, but B. callensis should remain the name of the Tunisian species, which was the first to be described in the small El Kebir basin, a river that flows from Tunisia to Algeria.