Lake Of Tunis Research Articles

Évolution des environnements de la Lagune de Tunis du Pléistocène moyen à l’Holocène

The lake of Tunis, located in northern Tunisia, is part of the coastal wetlands sensitive to climatic and anthropic variations. This fragile ecosystem was an open bay 190 ka BP ago. Today, it is separated from the Mediterranean by a sandy barrier fed mainly by the Madjerda wadi. This study, based on a multidisciplinary geological approach, examines the evolution of the dynamics of the Tunis Lake, as well as the recent environmental changes that control the sedimentation. Two cores LN1 (55m) and LS1 (40m) were collected in the alluvial deposits, respectively in the North-East and South-East of the Lake. These cores have been studied in detail to determine the spatio-temporal distribution of the sedimentary stock. The data from this study complemented by those from previous work allowed us to refine and establish spatio-temporal correlation scenarios of the sediments filling the Tunis lagoon. These correlations are established between the LN1 core and the core taken at the SE (LS1). Spatial and temporal monitoring of sediment deposition in these cores has revealed a general regressive evolutionary trend, from a frankly marine environment to a lagoon environment more or less communicating with the sea, from the Middle Pleistocene (an age between 159 and 205 ka) to the present Holocene. The identification of ostracod associations typical of open marine or lagoon environments and of benthic foraminifera associations of lagoon environments has allowed us to trace the history of the Tunis Lake over the last two millennia. It begins with an open marine environment (around 2030 years BP) followed by an open lagoon environment around 1700 years BP.

Spatial distribution, contamination assessment and potential ecological risk of some trace metals in the surface sediments of the Gulf of Tunis, North Tunisia

To evaluate the trace metals contamination status in the Gulf of Tunis, forty one sediment samples were analyzed using different approaches. According to certain contamination and ecological risk indices (Contamination Factor, Geoaccumulation index and Ecological risk index), Hg has the highest contamination level while pollution by Ni, Pb, Cd and Cr was absent. The highest concentrations of trace metals were found in sediments collected from the offshore and coastal areas located opposite the main exchange points with the gulf particularly, the Mejerda and Meliane Rivers, the Khalij Channel, Ghar El Melh and El Malah lagoons, Tunis Lake and Sebkhat Ariana. However, further ecological indices (Potential ecological risk index, Toxic unit and Mean effect-range median quotient) and comparison with sediment quality guidelines suggest that in addition to Mercury, Cr, Pb and Ni concentrations are detrimental to biota in both the offshore and areas near to the exchange points with the gulf. Moreover, in these areas the results from sequential extraction and individual contamination factor calculation pointed to the mobility and bioavailability of Cr, Pb and Ni.

Acute toxicity and biomarker responses in Gammarus locusta amphipods exposed to copper, cadmium, and the organochlorine insecticide dieldrin.

The toxicity of copper, cadmium, and dieldrin in adult Gammarus locusta (a marine amphipod) is currently unclear. Thus, G. locusta from the North Lake of Tunis were subjected to acute toxicity tests to assess LC50s at 48-96 h and to biomarker response tests through the assessment of catalase and acetylcholinesterase activities and malondialdehyde levels. The present study demonstrated the abilities of a chlorinated hydrocarbon pesticide (dieldrin) induce to oxidative stress and neurotoxicity. The comparison of metal toxicity showed that G. locusta was more sensitive to cadmium than copper. The three stressors caused significant inductions of all three biomarkers in a concentration-dependent manner. Catalase induction was dependent on exposure duration for all pollutants, while only copper led to increased malondialdehyde with longer exposure times. Catalase induction and malondialdehyde increase appeared to be sex dependent for all three pollutants. The neurotoxic effects of the pollutants were concentration dependent according to inhibition of acetylcholinesterase activity. In conclusion, catalase, malondialdehyde, and acetylcholinesterase are efficient biomarkers of copper, cadmium, and dieldrin in G. locusta.

Application of the SBAS-DInSAR technique for deformation monitoring in Tunis City and Mornag plain

The ground deformation phenomena are the result of the application of natural stress (tectonic) or anthropogenic stress (overexploitation of groundwater, embankment) on the soil. The land deformation may cause several impacts on the environment and human life. A good understanding of the deformation behaviour of the soil is essential to mitigate risks on the infrastructure and environment. In this study, a radar interferometry is carried out to analyse the mobility of an urban and suburban area of Greater Tunis region. The interferometric synthetic aperture radar (SAR) technique has been proven to be an effective methodology for detecting and monitoring soil displacement with millimetre accuracy and also, improving our understanding of the current deformations in the study area. Indeed, the application of differential SAR interferometry made it possible to determine the origin of the surface deformations related to natural or anthropic phenomena. In this paper, the interferometric method of small baseline subset (SBAS) developed by Berardino et al. 2002has been chosen, in order to monitor the spatial and temporal pattern of the deformation phenomena in Greater Tunis region. The analysis of Envisat ASAR (2003–2007, descending satellite orbit) and Sentinel 1B (2016–2018, ascending satellite orbit) SAR data allowed us to create deformation velocity maps associated with line of sight displacement time series. The results obtained by this method showed the existence of subsidence phenomenon in the urban areas (Tunis City) as well as in the rural areas (Mornag plain). In the first site (Tunis City), the subsidence rate reaches up to 13.98 mm/year and 19 mm/year during 2003–2007 and 2016–2018, respectively. The ground deformation that is detected around the region of Tunis Lake and Sebkhet Essijoumi, is probably due to the nature of the highly compressible and thickness alluvial deposits and whose substratum depth sometimes reaches more than 60 m. In the second studied site, ground subsidence was identified in the whole plain of Mornag. Indeed, the comparison between piezometric data and time series deformations shows that the trend of soil subsidence is coherent with the dynamic change in groundwater levels. Furthermore, the analysis of velocity deformation, geological data and hydrogeological information allows us to associate all the detected settlement patterns to groundwater overexploitation and compressible alluvium all over the plain. This overexploitation of groundwater in Mornag plain is mainly caused by the expansion of agricultural and industrial activities and the decrease in annual rainfall in recent years (from 2003 to 2018).

How useful are geochemical and mineralogical indicators in assessing trace metal contamination and bioavailability in a post-restoration Mediterranean lagoon?

Tunis's Lake North (LNT), located on the Mediterranean Sea, and Tunisia's most important lagoon due to its economic value and its strategic position within the city, has recently undergone a vast sanitation project. To study the lagoon's level of metal pollution, three sediment cores were taken and the sediments were analyzed for trace and major elements, acid volatile sulfides (AVS), total organic carbon (TOC), and minerals. Results showed that TOC concentrations (0.2-3.1%) decreased following the lagoon's restoration. In addition, in comparison to historical data, concentrations of Cu (16-69.5μgg-1), Zn (60.6-191.4μgg-1), and Pb (13-100.9μgg-1) also decreased. Enrichment factor calculation with respect to the crust and local background showed that the sediment had long been contaminated by human pollution and especially by Pb, Zn, and Cu. The AVS to simultaneously extracted metal (SEM) ratio revealed values generally less than 1 indicating no sediment toxicity risks. Statistics revealed a detrital origin for certain metals and a diagenetic origin for FeS2 and carbonate minerals.

Book Review: Sven Björk. Limnological Methods for Environmental Rehabilitation. The Fine Art of Restoring Aquatic Ecosystems

This book relates the long experience of its author S. Bjork and colleagues, presenting numerous cases of restoration of shallow lakes and wetlands in Sweden and all over the globe. The historical conditions that led to the degraded state of ecosystems are well described. In Sweden, the lake levels were lowered to gain fertile arable land. Agricultural activities and concentrations of populations in these areas have resulted in nutrient inputs that favored the colonization of these shallow lakes by macrophytes. Water surfaces were reduced, and even disappeared. Local authorities wanted to find clean lakes and open water favorable to present human activities, but also create biodiversity. Lake Trummen is a good example of the successful restoration of a shallow and small lake (depth < 3 m; 1 km2) started in the 70s. Substantial resources were needed (dredging). It is interesting to compare the cost of this restoration after decades of pollution, that is less than the annual cost of phosphorus removal from effluents in the wastewater treatment plant that discharges its treated water into the lake. The example of Lake Hornborga shows the limitations of the methods when the lake area is larger and invasion by macrophytes such that there is no more open water. The photographic illustration, which is on the book’s cover, shows the landscape changes throughout the 45 years of restoration work. In terms of biodiversity, especially birds, the lake was returned to a good condition at the end of the 90s (Hertzman & Larsson, 1999). However, today, the lake is still in “unsustainable development”. These two lakes are excellent examples of restoration of shallow lakes where the removal of the internal load is obviously essential. The reduction or even elimination of the external load from the entire watershed would not suffice. The book then addresses other examples which include the same concepts of restoration: lagoons (Lake of Tunis, Lagoa Rodrigo de Freitas in Brazil) and lakes (Lake Paranoia in Brazil, Lake Hangzhou in China). The question is different in the Hongyuan wetlands : how to exploit peat, keeping the option to restore the ecosystem by the end of the operation? This example is treated in a very interesting way. This book focuses on the long experience of its author and his team. It deals mainly with shallow ecosystems where it is necessary to extract or exploit the internal load. It is well illustrated, with old Swedish maps that highlight the history of these environments and ancient human impact. Limnologists, scientists and engineers, as well as wetland historians will read this book with interest.

Using a Three-Isotope Bayesian Mixing Model to Assess The Contribution of Refuse Dumps in The Diet of Yellow-Legged GullLarus michahellis

Summary. The yellow-legged gull Larus michahellis is usually considered as an opportunistic species that depends on food derived from anthropogenic activity, such as garbage and fishery discards. However, although it has become a problematic species in many Mediterranean countries, there is still no information about its status in Tunisia. The aim of this work was to assess the differential use of marine and terrestrial resources by the yellow-legged gulls breeding in an urban area on Chikly Island. Dietary reconstructions were performed through the analysis of regurgitates and δ13C, δ34S and δ15N of fledgling's feathers. Contrary to most Mediterranean breeding colonies, and to our expectations, the mixing model showed that yellow-legged gulls from Chikly are above all marine foragers. Whereas the Lake of Tunis was the principal source of food in 2005 and 2007, chicks from 2006 were fed mainly with prey from the Gulf of Tunis. Although the Gulf is located further from the breeding colony and has less fish...

First assessment of Perkinsosis and brown ring disease co-infection in Ruditapes decussatus in the North Lake of Tunis (southern Mediterranean Sea)

Carpet shell clam populations on the Tunisian coastline are susceptible to several microbial pathogen challenges. In this study we report the results of five years' surveillance, conducted from January 2004 till June 2009, for detection of Perkinsosis and brown ring disease (BRD). The survey covered three sites of natural populations of Ruditapes decussatus in a Tunisian lagoon, the North Lake of Tunis. Perkinsosis was detected preferentially in winter periods from the external and marine site, BRD was detected more frequently in the summer periods in a more proximal collection site (in the lake) and was positively correlated with concentrations of heterotrophic Vibrio sp. Our results suggest that several factors other than temperature and salinity might explain spatial distribution variability and natural intensities for these infections in carpet shell clam populations.

The genus Leptoplana (Leptoplanidae, Polycladida) in the Mediterranean basin. Redescription of the species Leptoplana mediterranea (Bock, 1913) comb. nov.

A revision of the genus Leptoplana Ehrenberg, 1831 in the Mediterranean basin is undertaken. This revision deals withthe distribution and validity of the species of Leptoplana known for the area. The Mediterranean sub-species polyclad,Leptoplana tremellaris forma mediterranea Bock, 1913 is elevated to the specific level. Leptoplana mediterranea comb.nov. is redescribed from the Lake of Tunis, Tunisia. This flatworm is distinguished from Leptoplana tremellaris mainlyby having a prostatic vesicle provided with a long diverticulum attached ventrally to the seminal vesicle, a genital pit clos-er to the male pore than to the female one and a twelve-eyed hatching juvenile instead of the four-eyed juvenile of L. tremellaris. The direct development in L. mediterranea is described at 15 °C.

Protozoan and myxozoan infections in wild gilthead seabream (Sparus aurata L.) from North Lake of Tunis, Tunisia

A total of 150 gilthead seabream Sparus aurata L., from North Lake of Tunis, Tunisia, were studied for protozoan and myxozoan parasites. The parasitological survey revealed the presence of ectoparasites (Amyloodinium ocellatum Brown, 1931, Trichodina lepsii Lom, 1962 on the gills) and endoparasites (Ceratomyxa sparusaurati Sitjà-Bobadilla, Palenzuela et Alvarez-Pellitero, 1995 infecting the gallbladder, and Eimeria sparis Sitjà-Bobadilla, Palenzuela et Alvarez-Pellitero, 1996 parasitizing the intestine). This is the first record of Amyloodinium ocellatum, Trichodina lepsii, Ceratomyxa sparusaurati, and Eimeria sparis in S. aurata from Tunisian waters. Data on prevalence and intensity of infection are provided. A comparison of the present species with previously described species in cultured gilthead seabream from other Mediterranean countries is also presented. In this study Trichodina lepsii is identified for the first time in Sparus aurata. A taxonomic description of this species based on silver nitrate method is provided.

Alexandrium catenella and Alexandrium tamarense in the North Lake of Tunis: bloom characteristics and the occurrence of paralytic shellfish toxin

The dinoflagellate Alexandrium is thought to be the main species responsible for paralytic shellfish poisoning (PSP) throughout the world. The genus Alexandrium is present in unusually high diversity in the North Lake of Tunis, a productive Mediterranean fishing and shellfish collecting area. High abundances of Alexandrium tamarense (7 × 103 cells l–1) were recorded here in August 2007, and of A. catenella (5.5 × 04 cells l–1) in January 2008 for the first time. High densities of A. tamarense were associated with high surface temperature (29.3 °C) and high salinity (40.6), while A. catenella blooms occurred at lower temperature (15.9 °C) and salinity (36.7). Alexandrium tamarense cell densities correlated positively with NH4 + (47.10 μmol l–1), but negatively with NO3 − (0.55 μmol l–1). In contrast, A. catenella proliferated when NO3 − was high (2.15 μmol l–1) and NH4 + was relatively low (8.38 μmol l–1). To study the toxicity of A. catenella and A. tamarense, extracts from clams Ruditapes decussatus were analysed by mouse bioassay and Jellett rapid PSP test from July 2007 to April 2008. The December 2007 and January 2008 samples were positive, corresponding to blooms of Alexandrium catenella, but the PSP concentrations were below 80 μg STX equivalent 100 g–1 of shellfish meat.

Determination of P, Ca, Zn, Cd and Pb concentrations in muscle, gills, liver, gonads and skeletons of two natural populations of Atherina lagunae in North Tunis Lake, Tunisia

In this study, zinc (Zn), cadmium (Cd), lead (Pb), phosphorus (P) and calcium (Ca) concentrations in mus-cles, gills, liver, gonads and skeletons of two natural populations of sand smelt Atherina lagunae (Teleostean, Atherinidae) normal and deformed, as well as bioaccumulation of these elements from the water and the sediment in the North Tunis Lake were investigated. The analysis of Ca was performed with flame atomic absorption spectrometry. The average concentrations of Ca in the different tissues analyzed show higher val-ues in healthy atherines except in gonads where the average concentration of Ca in deformed atherines sig-nificantly exceeds that in normal atherines (p < 0.05) and the spine Ca concentrations were similar in the two populations. Zinc, cadmium, lead and phosphorus were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The Zn concentrations of Atherina lagunae in North Tunis Lake were very high compared to other studies in other lagoons. The highest concentrations were found in deformed atherines. The differences are significant for all tissues studied (p < 0.05). The average concentration of P in different tissues analyzed shows that the highest values were detected in the normal population of Atherina lagunae. The potential rate of Cd was below the detection limit in the different organs analyzed, in water and sediment.

Little Egret (Egretta garzetta) as a bioindicator of trace element pollution in Tunisian aquatic ecosystems

The Little Egret, Egretta garzetta, has breeding colonies in the island of Chikly (in the lake of Tunis) and in Thyna saltpans (in the gulf of Gabès), two important Tunisian wetlands that are strongly affected by anthropogenic activity. Here, we used E. garzetta chick feathers for environmental monitoring of breeding grounds of this species. Since trophic ecology is fundamental when interpreting contamination levels, our approach combined both trace-element (Hg, Pb, Cd, and Se) and stable-isotope analysis of δ13C, δ15N, and δ34S. Hg, Se, and δ15N levels were higher in specimens collected on Chikly than in Thyna. These observations highlight the degree of eutrophication of the lake of Tunis. Yellow-legged gulls (Larus michahellis) breeding in the same areas also feeds in the lake and attains similar concentrations of Hg and Se. In Thyna, egrets and gulls exploit distinct foraging habitats, as demonstrated by stable isotope analysis. The highest Hg and Se concentrations were found in Thyna. This result is consistent with greater exploitation of marine resources from the gulf of Gabès.

Présence de trois espèces de grégarines (Apicomplexa : Eugregarinorida) chez l’Annélide PolycheteMarphysa sanguinea(Montagu, 1815) dans le lac de Tunis

Three species of gregarines were found in specimens of the annelid polychaete Marphysa sanguinea collected in the Lake of Tunis: Bhatiella marphysae Setna, 1931, described from Marphysa sanguinea (India); Ferraria cornucephala iwamusi H. Hoshide, 1956, found in Marphysa iwamusi (Japan); and Viviera sp. a species sharing characteristics with Viviera marphysae Schrével, 1963, described in France from Marphysa sanguinea. These gregarines are reported for the first time from this host in Tunisia. Bhatiella marphysae and Viviera sp. belong to the family Lecudinidae (Aseptatorina). Our observations confirm the occurrence of a true septum in Ferraria cornucephala which must be maintained in Polyrhabdinae (Septatorina).

Biomonitoring of coastal areas in Tunisia: Stable isotope and trace element analysis in the Yellow-legged Gull

We used Yellow-legged Gull (YLG) chicks to monitor trace elements in Tunisian areas subject to different pollution stresses: urban contamination (Chikly), industrial pollution (Thyna) and an unpolluted area (Kneis).We measured trace element concentrations (Hg, Se and Pb) in chick feathers. We also assessed their feeding ecology by analyzing both regurgitates and stable isotopes (SIA) in chick feathers and in their prey, to determine the main entry route of pollutants. SIA revealed that YLG feed mainly on aquatic resources from the Lake of Tunis (Chikly colony) and the Gulf of Gabès (Thyna and Kneis colonies). Moreover, the enriched δ15N found in feathers from Chikly are attributed to the eutrophication of the Lake of Tunis. Hg and Se were higher in Kneis and Thyna colonies, in agreement with the higher consumption of marine resources and the greater availability of these elements resulting from the impact of the industrial activity in the area. Pb concentrations were higher in Chikly, related to the heavier traffic around the Lake of Tunis and the use of leaded gasoline.

Biosorption of Cu 2+ and Zn 2+ from aqueous solutions by dried marine green macroalga Chaetomorpha linum

The biosorption of the heavy metals Cu 2+ and Zn 2+ by dried marine green macroalga ( Chaetomorpha linum) was investigated. The biosorption capacities of the dried alga for copper and zinc were studied at different solution pH values (2–6), different algal particle sizes (100–800 μm) and different initial metal solution concentrations (0.5–10 mM). An optimum pH value of 5 was found suitable for both metal ions biosorption for both metal ions. At the optimum particle size (100–315 μm), biosorbent dosage (20 g/l) and initial solution pH (pH 5), the dried alga produced maximum copper and zinc uptakes values ( q max) of 1.46 and 1.97 mmol/g respectively (according to the Langmuir model). The kinetic data obtained at different initial metal concentrations indicated that the biosorption rate was fast and most of the process was completed within 120 min. This study illustrated an alternative technique for the management of unwanted biological materials using processed algal material. C. linum is one of the fast-growing marine algae in the lake of Tunis and could be utilized as a biosorbent for the treatment of Cu 2+ and Zn 2+ contaminated wastewater streams.

First recorded proliferation of Coolia monotis (Meunier, 1919) in the North Lake of Tunis (Tunisia) correlation with environmental factors

Coolia monotis is a potentially toxic epiphytic dinoflagellate widespread along the Mediterranean coasts, where it is frequently detected year round at low concentrations. However, it only proliferates recurrently in some localities. The North Lake of Tunis is one of the affected areas in the southwestern part of the Mediterranean Sea. This site is one of the most productive aquatic Tunisian areas (Recreational Fisheries and shellfish collecting). In the south part of this area of study, recurrent C. monotis proliferation (5 x10(5) cells per liter) took place in late spring and early summer of 2006. During this proliferation, the spatial distribution of C. monotis species, phytoplankton community, and abiotic factors were studied. The composition of the phytoplankton community exhibited a clear dominance of dinoflagellates over other genera. We suggest that proliferation development of C. monotis was linked to climatic conditions, water temperature (r = 0.24, p < 0.05) and high concentrations of nitrogenous nutrients, essentially NH(4)(+) (r = 0.18, p < 0.05) and NO(3)(-) (r = 0.21, p < 0.05).

Imposex expression in Hexaplex trunculus from the North Tunis Lake transplanted to Bizerta channel (Tunisia)

Abstract Adult specimens of the muricid gastropod Hexaplex trunculus were collected from their natural habitat: the Lake Club station located in the North Tunis Lake, a sampling site characterized by the absence of shipping activity and an imposex incidence of 12.9%. These specimens were transplanted to a sampling site with intense shipping traffic: the Bizerta channel, where a preliminary survey detected an imposex incidence of 100%. The transplanted specimens were tagged prior to release and periodical recaptures were made every 60 days during a study period of 8 months (from July 2004 to March 2005) in order to compare the imposex development between both sampling sites. After 5 months of exposure in the Bizerta channel, all transplanted females were affected by imposex (with the development of an incomplete male genital tract). Microscopic examinations showed that imposex begun by the development of a small portion of vas deferens located halfway between the expected position of the future penis and the vagina. The imposex indices used in this study were the imposex frequency (I (%)), the vas deferens sequence index (VDSI), the relative penis length index (RPL), the average female penis length index (FPL) and the average female vas deferens length (VDL). All these indices increased in the transplanted population as compared to the population from the original sampling site, but VDSI and VDL were considered the best indices to assess the environmental pollution by tributyltin (TBT) and its deleterious effects in H. trunculus.

Seasonal dynamics of macro-algae in the South Lake of Tunis

Seasonal dynamics of macro-algae in the South Lake of Tunis

Seasonal dynamics of macro-algae in the South Lake of Tunis

The macro-algae communities observed in the south lake of Tunis are characterized by the predominance of nitrophilous algae which are in the order of biomass importance:Ulva, Cladophora andEnteromorpha. We have noted seasonal changes of alga distribution. The wind appears to be one of the most important factors influencing this distribution. The total biomass reaches a maximum in the spring. Rapid decomposition of the biomass leads to a severe ecological imbalance, resulting in crises of anoxia and fish death. A restoration project has already started. It aims at removal of contaminated muds and the introduction of a new circulation system. The main objectives of this work were to collect information on the distribution and biomass of the phytobenthic communities as a first step in the constitution of a database for further comparison.