La lagune de Ghar El Melh : Diagnostic écologique et perspectives d'aménagement hydraulique

La lagune de Ghar El Melh, située au Nord de la Tunisie (dans le Golfe de Tunis), est caractérisée par une superficie de 28,5 km2, une faible profondeur et une faible communication avec la mer. Actuellement, sous l'effet des actions anthropiques (les rejets terrestres), elle connaît une dégradation progressive de la qualité de ses eaux et sédiments dont les conséquences sont la chute de la richesse biologique et la réduction des ressources halieutiques de la lagune.Dans ce travail, nous présentons les résultats de l'analyse des caractéristiques physico-chimiques et biologiques des eaux de la lagune. Ces analyses montent bien l'hyper-eutrophisation du milieu caractérisé par de fortes concentrations des eaux en azote total et en phosphore total. Les résultats de simulation du fonctionnement hydrodynamique, que nous avons réalisée à l'aide d'un modèle à 2 dimensions intégré sur la hauteur, montrent une stagnation des eaux dans environ 80% de surface de la lagune qui a fortement amplifié la dégradation de la qualité de l'écosystème. Parmi plusieurs scénarios d'aménagements simulés, nous proposons la création d'une nouvelle communication avec la mer dont la simulation hydrodynamique montre une nette augmentation des échanges d'eau mer-lagune. Nous présentons ensuite un modèle écologique homogène de la lagune de Ghar El Melh qui a été mis au point et calibré en s'appuyant sur les mesures de terrain. Les simulations, avec ce modèle, montrent que l'arrêt total des rejets terrestres et la création d'un nouveau grau réduisent considérablement l'eutrophisation du milieu ce qui conduiraient certainement à une nette amélioration de la production halieutique dans la lagune.The Ghar El Melh lagoon is a Mediterranean water body, situated in Northeastern Tunisia, on the Northwestern side of the Gulf of Tunis. The Ghar El Melh lagoon is a vestigial part of the Utique Sea, and this lagoon was largely open at the time of the Roman invasion. Due to a combination of the shape of the coastline and alluvium deposits from the Medjerda River, this small gulf has become progressively closed from the Utique Sea, causing the lagoon to become progressively shaped to its present morphology. The coastal barrier separating the lagoon from the Mediterranean Sea was interrupted, allowing a permanent hydraulic communication across a local opening. The lagoon has an elliptical shape of approximately 28.5 km2 and an average depth of 0.8 m. Due to human activities within the lagoon itself and in the surrounding area, the lagoon ecosystem has suffered a progressive deterioration. This deterioration has led to a reduction in biodiversity resulting mainly in a decrease in fish resources and production.In order to improve the water quality of the lagoon for ecological and economical purposes, a diagnostic survey was carried out to characterize the present site conditions and to provide data for calibration of hydrodynamic and ecological models. The main results of the annual survey of biotic and non-biotic parameters demonstrated the existence of zones within the lagoon, with some seasonal variation. Thus, a decreasing biotic and non-biotic gradient was measured from the area of the lagoon under marine influence towards the bottom of the lagoon, under the continental and anthropogenic influence of the west side. The lagoon could be considered hypereutrophic with an annual average concentration of total phosphorus of 350 mg/m3. In order to conceptualize and optimise hydraulic structures for water quality improvement in the lagoon, a numerical model of the velocity fields (depth averaged) and water depth was used. The hydrodynamic model used was bi-dimensional, adapted for use in shallow lagoons. After model calibration using in-situ measurements, simulations were carried out to analyse the present hydrodynamic condition of the lagoon. Several stagnation zones were detected, which contributed to the altered water quality that was observed. Several management practices were proposed and simulated, aiming to control and improve the internal circulation and water exchange between the lagoon and the Mediterranean Sea. The main goal of these simulations was to improve water mobility inside the lagoon, and thus improve the water quality. The proposed hydraulic development measures consisted mainly of the creation of a new hydraulic communication in the south-eastern area of the lagoon, by dredging the south part of the lake or by channel creation in front of the new communication, reaching the stagnation zones of the lagoon. The impact assessment of the proposed development was verified with simulations using the bi-dimensional hydrodynamic model.An ecological model based on nitrogen and phosphorus cycling, was also developed for Ghar El Melh lagoon. It took into account one ecological compartment, the macro algae, that included Cladophora sp., Ulva sp. and Enteromorpha sp. Algae (A), inorganic nitrogen (NA), inorganic phosphorus (PA), organic nitrogen (NEorg) and organic phosphorus (PEorg), were the main variables of this model. After calibration of the model, a 10-yr simulation showed that all variables demonstrated a steady behaviour and that the lagoon eutrophication level remained. Model sensitivity analysis allowed the choice of some restoration scenarios and the prediction of their impacts on the ecological behaviour of the ecosystem. The simulations showed that wastewater load deviation combined with an increase in the sea-lagoon water exchange, instead of a decrease of nutrient diffusion from the sediments, led to a substantial decrease in the eutrophication level of the lagoon. Indeed, the annual average nutrient concentrations decreased from 270 to 60 mg/m3 for total nitrogen and from 350 to 20 mg/m3 for total phosphorus in the Ghar El Melh lagoon

Response of free-living Nematodes to the quality of water and sediment at Bou Chrara Lagoon (Tunisia) during winter 2000

The Bou Ghrara lagoon, a stretch of water in southeastern Tunisia, has shown an alarming reduction of its fishery resources since 1993. In order to study the response of free-living nematodes to the water and sediment quality of this area, thirteen stations have been sampled. According to this study, the heavy metal, organic carbon and hydrocarbon content of sediments are key factors negatively influencing the density, biomass and diversity of the nematofauna

Analyse de sensibilité du système oasien et mesures de sauvegarde de l’oasis de Métouia (Tunisie)

L’oasis de Métouia, située au sud‑est de la Tunisie, est caractérisée par un climat aride où les précipitations sont rares et irrégulières. L’oasis doit donc son existence aux eaux souterraines qui, autrefois, provenaient de sources artésiennes actuellement taries suite à une surexploitation de la nappe profonde. La pédogenèse actuelle est dominée par l’évolution des processus de salinisation et d’hydromorphie affectant en totalité ou en partie le profil pédologique. Cette salinisation est la résultante des effets cumulés de la salinité des eaux d’irrigation et celle de la nappe phréatique proche de la surface dont la remontée capillaire génère des efflorescences salines. Ce facteur est accentué par l’absence de lessivage des sols et le dysfonctionnement du réseau de drainage. Le suivi des paramètres abiotiques de l’oasis durant quatre années successives (2001 – 2004), a révélé une interdépendance étroite entre la qualité des eaux précédemment décrite et les processus géochimiques qui en résultent, d’une part, et la dégradation de la zone non saturée, siège des accumulations gypseuses, d’autre part. Par ailleurs, aux facteurs précédemment signalés, viennent s’ajouter la mauvaise exploitation des parcelles et l’absence de règles de gestion du système oasien dans sa globalité. Afin de contrecarrer ces phénomènes qui affectent profondément la sensibilité du système oasien, on a élaboré des recommandations visant l’optimisation des besoins dynamiques en eau, du mode de distribution, ainsi que du réseau de drainage freinant la remontée de la nappe et améliorant l’aération et le lessivage de la zone non saturée.The Métouia oasis is situated in south-eastern Tunisia near the coast of Gabès City. The climate is arid with rare and irregular precipitation events. The oasis originated from a confined subsurface that was hydraulically connected to surface springs that had already been exhausted by human activities. The soil features are presently dominated by the evolution of salinization and water-saturation processes either partially or totally affecting the soil profile. The visible salt deposits and soil salinization processes are generated by the salinity of irrigation water and the shallow water table as well as the rising capillarity head. These processes are strongly influenced by the weak soil leaching mechanisms, on the one hand, and the poor drainage schemes, on the other hand. The four-year monitoring programme (2001 – 2004) focussed on important abiotic water and soil parameters and showed a close relationship between water quality and the generated geochemical processes parallel to the degradation of the non-saturated zone, in which gypsum accumulation processes are taking place. In addition to the above mentioned factors, the poor land exploitation system and the lack of integrated management of the oasis system are also important. Due to the high sensitivity of the oasis and in order to overcome the problems, several recommendations were proposed concerning the optimization of the irrigation scheme, the water supply network and drainage schemes. The recommended hydraulic infrastructure, combined with the proposed management rules for the oasis, would lead to better control of ground-water fluctuations and improvement of leaching and aeration processes in the unsaturated zone

Change, stress and sustainability: aquatic ecosystem resilience in North Africa

Summary report of a workshop held at the Institute Scientifique, University Mohammed V, Rabat, Morocco, 2-5th December 1998. Cassarina report no. 4

A multiple spacecraft detection of the 2 April 2022 M-class flare and filament eruption during the first close Solar Orbiter perihelion

CONTEXT: The Solar Orbiter mission completed its first remote-sensing observation windows in the spring of 2022. On 2 April 2022, an M-class flare followed by a filament eruption was seen both by the instruments on board the mission and from several observatories in Earth’s orbit, providing an unprecedented view of a flaring region with a large range of observations. AIMS: We aim to understand the nature of the flaring and filament eruption events via the analysis of the available dataset. The complexity of the observed features is compared with the predictions given by the standard flare model in 3D. METHOD: In this paper, we use the observations from a multi-view dataset, which includes extreme ultraviolet (EUV) imaging to spectroscopy and magnetic field measurements. These data come from the Interface Region Imaging Spectrograph, the Solar Dynamics Observatory, Hinode, as well as several instruments on Solar Orbiter. RESULTS: The large temporal coverage of the region allows us to analyse the whole sequence of the filament eruption starting with its pre-eruptive state. Information given by spectropolarimetry from SDO/HMI and Solar Orbiter PHI/HRT shows that a parasitic polarity emerging underneath the filament is responsible for bringing the flux rope to an unstable state. As the flux rope erupts, Hinode EIS captures blue-shifted emission in the transition region and coronal lines in the northern leg of the flux rope prior to the flare peak. This may be revealing the unwinding of one of the flux rope legs. At the same time, Solar Orbiter SPICE captures the whole region, complementing the Doppler diagnostics of the filament eruption. Analyses of the formation and evolution of a complex set of flare ribbons and loops, of the hard and soft X-ray emissions with STIX, show that the parasitic emerging bipole plays an important role in the evolution of the flaring region. CONCLUSIONS: The extensive dataset covering this M-class flare event demonstrates how important multiple viewpoints and varied observations are in order to understand the complexity of flaring regions. While the analysed data are overall consistent with the standard flare model, the present particular magnetic configuration shows that surrounding magnetic activity such as nearby emergence needs to be taken into account to fully understand the processes at work. This filament eruption is the first to be covered from different angles by spectroscopic instruments, and provides an unprecedented diagnostic of the multi-thermal structures present before and during the flare. This complete dataset of an eruptive event showcases the capabilities of coordinated observations with the Solar Orbiter mission

Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone : Insights from the Otway Basin, SE Australia

This research forms part of a PhD project supported by the Australian Research Council [Discovery Project DP160101158] and through an Australian Government Research Training Program Scholarship. Dave Healy acknowledges the support of the Natural Environment Research Council (NERC, UK) through the award NE/N003063/1 ‘Quantifying the Anisotropy of Permeability in Stressed Rock’. This study was also funded by scholarships from the Petroleum Exploration Society of Australia and the Australian Petroleum Production and Exploration Association. We thank Gordon Holm for preparing thin sections and Colin Taylor for carrying out particle size measurements and mercury injection capillary pressure analyses. Aoife McFadden and David Kelsey from Adelaide Microscopy, Braden Morgan, and Sophie Harland are acknowledged for their assistance with laboratory work. Field assistants James Hall, Rowan Hansberry, and Lachlan Furness are also gratefully acknowledged for their assistance with sample collection. Discussions with Ian Duddy on the mineralogy of the Eumeralla Formation are also greatly appreciated. This forms TRaX record 416.Peer reviewedPublisher PD

Acoustic emission signal processing framework to identify fracture in aluminum alloys

Acoustic emission (AE) is a common nondestructive evaluation tool that has been used to monitor fracture in materials and structures. The direct connection between AE events and their source, however, is difficult because of material, geometry and sensor contributions to the recorded signals. Moreover, the recorded AE activity is affected by several noise sources which further complicate the identification process. This article uses a combination of in situ experiments inside the scanning electron microscope to observe fracture in an aluminum alloy at the time and scale it occurs and a novel AE signal processing framework to identify characteristics that correlate with fracture events. Specifically, a signal processing method is designed to cluster AE activity based on the selection of a subset of features objectively identified by examining their correlation and variance. The identified clusters are then compared to both mechanical and in situ observed microstructural damage. Results from a set of nanoindentation tests as well as a carefully designed computational model are also presented to validate the conclusions drawn from signal processing

High resolution human leukocyte antigen (HLA) class I and class II allele typing in Mexican mestizo women with sporadic breast cancer: case-control study

<p>Abstract</p> <p>Background</p> <p>The development of breast cancer is multifactorial. Hormonal, environmental factors and genetic predisposition, among others, could interact in the presentation of breast carcinoma. Human leukocyte antigen (HLA) alleles play an important role in immunity (cellular immunity) and may be important genetic traits. HLAAllele-specific interaction has not been well established. Recently, several studies had been conducted in order to do so, but the results are controversial and in some instances contradictory.</p> <p>Methods</p> <p>We designed a case-control study to quantify the association of HLA class I and II genes and breast cancer. HLA typing was performed by high resolution sequence-specific oligotyping after DNA amplification (PCR-SSOP) of 100 breast cancer Mexican mestizo patients and 99 matched healthy controls.</p> <p>Results</p> <p>HLA-A frequencies that we were able to observe that there was no difference between both groups from the statistical viewpoint. HLA-B*1501 was found three times more common in the case group (OR, 3.714; <it>p </it>= 0.031). HLA-Cw is not a marker neither for risk, nor protection for the disease, because we did not find significant statistical differences between the two groups. DRB1*1301, which is expressed in seven cases and in only one control, observing an risk increase of up to seven times and DRB1*1602, which behaves similarly in being present solely in the cases (OR, 16.701; 95% CI, 0.947 – 294.670). DQ*0301-allele expression, which is much more common in the control group and could be protective for the presentation of the disease (OR, 0.078; 95% CI, 0.027–0.223, <it>p </it>= 0.00001).</p> <p>Conclusion</p> <p>Our results reveal the role of the MHC genes in the pathophysiology of breast cancer, suggesting that in the development of breast cancer exists a disorder of immune regulation. The triggering factor seems to be restricted to certain ethnic groups and certain geographical regions since the relevant MHC alleles are highly diverse. This is the first study in Mexican population where high resolutions HLA typing has been performed in order to try to establish an association with malignancy.</p

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P &lt; 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Inversion formulas for Riemann-Liouville transform and its dual associated with singular partial differential operators

We define Riemann-Liouville transform ℛα and its dual tℛα associated with two singular partial differential operators. We establish some results of harmonic analysis for the Fourier transform connected with ℛα. Next, we prove inversion formulas for the operators ℛα, tℛα and a Plancherel theorem for tℛα